U.S. patent application number 13/660683 was filed with the patent office on 2013-04-25 for glass articles with improved chemical and mechanical durability.
This patent application is currently assigned to CORNING INCORPORATED. The applicant listed for this patent is Corning Incorporated. Invention is credited to Paul Steven Danielson, I, Steven Edward DeMartino, Robert Michael Morena, John S. Peanasky, Robert Anthony Schaut.
Application Number | 20130101764 13/660683 |
Document ID | / |
Family ID | 47116521 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130101764 |
Kind Code |
A1 |
Schaut; Robert Anthony ; et
al. |
April 25, 2013 |
Glass Articles with Improved Chemical and Mechanical Durability
Abstract
A glass article may formed from a glass composition that may
include from about 70 mol. % to about 78 mol. % SiO.sub.2, from
about 3 mol. % to about 13 mol. % alkaline earth oxide, X mol. %
Al.sub.2O.sub.3, and Y mol. % alkali oxide. The alkali oxide may
include Na.sub.2O in an amount greater than or equal to about 9
mol. % and less than or equal to about 15 mol. %. The ratio of Y:X
may be greater than 1. The glass article may be free of boron and
compounds of boron. The glass article may have a compressive stress
layer with a compressive stress greater than or equal to about 250
MPa and depth of layer greater than or equal to about 25 .mu.m. The
glass article may have at least a type HGA2 hydrolytic resistance
according to the ISO 720 standard.
Inventors: |
Schaut; Robert Anthony;
(Painted Post, NY) ; Morena; Robert Michael;
(Lindley, NY) ; Danielson, I; Paul Steven;
(Dundee, NY) ; DeMartino; Steven Edward; (Painted
Post, NY) ; Peanasky; John S.; (Big Flats,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated; |
Painted Post |
NY |
US |
|
|
Assignee: |
CORNING INCORPORATED
Painted Post
NY
|
Family ID: |
47116521 |
Appl. No.: |
13/660683 |
Filed: |
October 25, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61551163 |
Oct 25, 2011 |
|
|
|
Current U.S.
Class: |
428/34.4 ;
428/410 |
Current CPC
Class: |
A61J 1/00 20130101; C03C
2204/00 20130101; C03C 3/087 20130101; C03C 3/091 20130101; C03C
21/002 20130101; Y10T 428/26 20150115; Y10T 428/1317 20150115; C03C
4/20 20130101; Y10T 428/315 20150115; C03C 4/18 20130101; Y10T
428/131 20150115 |
Class at
Publication: |
428/34.4 ;
428/410 |
International
Class: |
C03C 4/00 20060101
C03C004/00; C03C 3/083 20060101 C03C003/083 |
Claims
1. A glass article formed from a glass composition comprising: from
about 70 mol. % to about 78 mol. % SiO.sub.2; from about 3 mol. %
to about 13 mol. % alkaline earth oxide; X mol. % Al.sub.2O.sub.3;
Y mol. % alkali oxide, wherein the alkali oxide comprises Na.sub.2O
in an amount greater than or equal to about 9 mol. % and less than
or equal to about 15 mol. %, and wherein: a ratio of Y:X is greater
than 1; the glass article is free of boron and compounds of boron;
the glass article comprises a compressive stress layer with a
compressive stress greater than or equal to about 250 MPa and depth
of layer greater than or equal to about 25 .mu.m; and the glass
article has at least a type HGA2 hydrolytic resistance according to
ISO 720.
2. The glass article of claim 1, wherein the glass article is a
beverage package.
3. The glass article of claim 2, wherein the beverage package is a
container for storing alcoholic beverages.
4. The glass article of claim 1, wherein the glass article is a
food package.
5. The glass article of claim 1, wherein the glass article is
household glassware.
6. The glass article of claim 1, wherein the glass article is
laboratory glassware.
7. The glass article of claim 1, wherein the glass article is a
cosmetics package.
8. The glass article of claim 1, wherein the glass article is
structural glazing or vehicle glazing.
9. The glass article of claim 1, wherein the glass article is
cookware.
10. The glass article of claim 1, wherein the glass article is a
lighting product.
11. The glass article of claim 1, wherein the glass article is an
ornamental item.
12. The glass article of claim 1, wherein the glass article is
display glass.
13. The glass article of claim 1, wherein the glass article is
industrial tubing.
14. The glass article of claim 1, wherein the glass article is a
scientific instrument.
15. A glass article formed from a glass composition comprising:
from about 70 mol. % to about 78 mol. % SiO.sub.2; from about 3
mol. % to about 13 mol. % alkaline earth oxide, wherein the
alkaline earth oxide comprises from about 0.1 mol. % to about 1.0
mol. % CaO; X mol. % Al.sub.2O.sub.3; Y mol. % alkali oxide,
wherein the alkali oxide comprises Na.sub.2O in an amount greater
than or equal to about 9 mol. % and less than or equal to about 15
mol. %, and wherein: a ratio of Y:X is from about 1 to about 2; the
glass article is free of boron and compounds of boron; the glass
article comprises a compressive stress layer with a compressive
stress greater than or equal to about 250 MPa and depth of layer
greater than or equal to about 25 .mu.m; the glass article has at
least a type HGA2 hydrolytic resistance according to ISO 720; and
the glass article is a beverage package, a food package, household
glassware, laboratory glassware, a cosmetics package, structural
glazing, automobile glazing, cookware, a lighting product, an
ornamental item, display glass, industrial tubing, or a scientific
instrument.
16. The glass article of claim 15, wherein the glass article is
free of phosphorous and compounds of phosphorous.
17. The glass article of claim 15, wherein the glass composition
comprises from about 72 mol. % to about 78 mol. % SiO.sub.2.
18. The glass article of claim 15, wherein the glass composition
comprises from about 4 mol. % to about 8 mol. % alkaline earth
oxide.
19. The glass article of claim 15, wherein the ratio of Y:X is from
about 1.3 to 2.
20. The glass article of claim 15, wherein the alkaline earth oxide
comprises MgO and CaO and a ratio (CaO (mol. %)/(CaO (mol. %)+MgO
(mol. %))) is less than or equal to 0.5.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Patent Application Ser. No. 61/551,163, filed Oct. 25, 2011
(Attorney Docket No. SP11-240P) and entitled "Glass Compositions
With Improved Chemical and Mechanical Durability," the entirety of
which is incorporated by reference herein.
BACKGROUND
Field
[0002] The present specification generally relates to glass
articles and, more specifically, to chemically and mechanically
durable glass articles.
Technical Background
[0003] Historically, glass has been used as a preferred material
for many applications, including food and beverage packaging,
kitchen and laboratory glassware, and windows or other
architectural features, because of its hermeticity, optical clarity
and excellent chemical durability relative to other materials. For
various applications, glass articles must have acceptable chemical
durability, which often depends on the context in which the glass
article is used. For example, the glass used in beverage packaging
applications must have adequate chemical durability so as not to
contaminate the beverage contained therein.
[0004] However, use of glass for many applications is limited by
the mechanical performance of the glass. A strong glass is
desirable in many applications, such as windshield or windows.
Additionally, in the food and beverage packaging industry, glass
breakage is a safety concern for the end user as the broken package
and/or the contents of the package may injure the end user.
Breakage can be costly to many food or beverage packaging
industries because, for example, breakage within a filling line may
require that neighboring unbroken containers be discarded as the
containers may contain fragments from the broken container.
Breakage may also require that the filling line be slowed or
stopped, lowering production yields. Further, non-catastrophic
breakage (i.e., when the glass cracks but does not break) may cause
the contents to lose their sterility which, in turn, may result in
costly product recalls.
[0005] One approach to improving the mechanical durability of the
glass article is to thermally temper the glass article. Thermal
tempering strengthens glass by inducing a surface compressive
stress during rapid cooling after forming. This technique works
well for glass articles with flat geometries (such as windows),
glass articles with thicknesses>2 mm, and glass compositions
with high thermal expansion. However, for many glass article
applications it is desirable or required to have complex
geometries, thin walls (.about.1-1.5 mm), and are produced from low
expansion glasses (30-55.times.10.sup.-7K.sup.-1) making many glass
articles unsuitable for strengthening by thermal tempering.
[0006] Chemical tempering also strengthens glass by the
introduction of surface compressive stress. The stress is
introduced by submerging the article in a molten salt bath. As ions
from the glass are replaced by larger ions from the molten salt, a
compressive stress is induced in the surface of the glass. The
advantage of chemical tempering is that it can be used on complex
geometries, thin samples, and is relatively insensitive to the
thermal expansion characteristics of the glass substrate. However,
glass compositions which exhibit a moderate susceptibility to
chemical tempering generally exhibit poor chemical durability and
vice-versa.
[0007] Accordingly, a need exists for glass articles formed from
glass compositions which are chemically durable and susceptible to
chemical strengthening by ion exchange.
SUMMARY
[0008] According to one embodiment, a glass article may be formed
from a glass composition comprising from about 70 mol. % to about
78 mol. % SiO.sub.2, from about 3 mol. % to about 13 mol. %
alkaline earth oxide, X mol. % Al.sub.2O.sub.3, and Y mol. % alkali
oxide. The alkali oxide may comprise Na.sub.2O in an amount greater
than or equal to about 9 mol. % and less than or equal to about 15
mol. %. The ratio of Y:X may be greater than 1. The glass article
may be free of boron and compounds of boron. The glass article may
comprise a compressive stress layer with a compressive stress
greater than or equal to about 250 MPa and depth of layer greater
than or equal to about 25 .mu.m. The glass article may have at
least a type HGA2 hydrolytic resistance according to ISO 720.
[0009] According to another embodiment, a glass article may be
formed from a glass composition comprising from about 70 mol. % to
about 78 mol. % SiO.sub.2, from about 3 mol. % to about 13 mol. %
alkaline earth oxide, X mol. % Al.sub.2O.sub.3, and Y mol. % alkali
oxide. The alkaline earth oxide may comprise from about 0.1 mol. %
to about 1.0 mol. % CaO. The alkali oxide may comprise Na.sub.2O in
an amount greater than or equal to about 9 mol. % and less than or
equal to about 15 mol. %. A ratio of Y:X may be from about 1 to
about 2. The glass article may be free of boron and compounds of
boron. The glass article may comprise a compressive stress layer
with a compressive stress greater than or equal to about 250 MPa
and depth of layer greater than or equal to about 25 .mu.m. The
glass article may have at least a type HGA2 hydrolytic resistance
according to ISO 720. The glass article may be a beverage package,
a food package, household glassware, laboratory glassware, a
cosmetics package, structural glazing, automobile glazing,
cookware, a lighting product, an ornamental item, display glass,
industrial tubing, or a scientific instrument.
[0010] Additional features and advantages will be set forth in the
detailed description which follows, and in part will be readily
apparent to those skilled in the art from that description or
recognized by practicing the embodiments described herein,
including the detailed description which follows, the claims, as
well as the appended drawings.
[0011] It is to be understood that both the foregoing general
description and the following detailed description describe various
embodiments and are intended to provide an overview or framework
for understanding the nature and character of the claimed subject
matter. The accompanying drawings are included to provide a further
understanding of the various embodiments, and are incorporated into
and constitute a part of this specification. The drawings
illustrate the various embodiments described herein, and together
with the description serve to explain the principles and operations
of the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 graphically depicts the relationship between the
ratio of alkali oxides to alumina (x-axis) and the strain point,
annealing point, and softening point (y-axes) of inventive and
comparative glass compositions;
[0013] FIG. 2 graphically depicts the relationship between the
ratio of alkali oxides to alumina (x-axis) and the maximum
compressive stress and stress change (y-axes) of inventive and
comparative glass compositions;
[0014] FIG. 3 graphically depicts the relationship between the
ratio of alkali oxides to alumina (x-axis) and hydrolytic
resistance as determined from the ISO 720 standard (y-axis) of
inventive and comparative glass compositions;
[0015] FIG. 4 graphically depicts diffusivity D (y-axis) as a
function of the ratio (CaO/(CaO+MgO)) (x-axis) for inventive and
comparative glass compositions;
[0016] FIG. 5 graphically depicts the maximum compressive stress
(y-axis) as a function of the ratio (CaO/(CaO+MgO)) (x-axis) for
inventive and comparative glass compositions;
[0017] FIG. 6 graphically depicts diffusivity D (y-axis) as a
function of the ratio (B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3))
(x-axis) for inventive and comparative glass compositions; and
[0018] FIG. 7 graphically depicts the hydrolytic resistance as
determined from the ISO 720 standard (y-axis) as a function of the
ratio (B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3)) (x-axis) for
inventive and comparative glass compositions.
DETAILED DESCRIPTION
[0019] Reference will now be made in detail to various embodiments
of glass articles comprising glass compositions which exhibit
improved chemical and mechanical durability. Such glass
compositions are suitable for use in a wide variety of
applications. The glass compositions may also be chemically
strengthened thereby imparting increased mechanical durability to
the glass. The glass compositions described herein generally
comprise silica (SiO.sub.2), alumina (Al.sub.2O.sub.3), alkaline
earth oxides (such as MgO and/or CaO), and alkali oxides (such as
Na.sub.2O and/or K.sub.2O) in amounts which impart chemical
durability to the glass composition. Moreover, the alkali oxides
present in the glass compositions facilitate chemically
strengthening the glass compositions by ion exchange. Various
embodiments of the glass compositions will be described herein and
further illustrated with reference to specific examples.
[0020] The term "softening point," as used herein, refers to the
temperature at which the viscosity of the glass composition is
1.times.10.sup.7.6 poise.
[0021] The term "annealing point," as used herein, refers to the
temperature at which the viscosity of the glass composition is
1.times.10.sup.13 poise.
[0022] The terms "strain point" and "T.sub.strain" as used herein,
refers to the temperature at which the viscosity of the glass
composition is 3.times.10.sup.14 poise.
[0023] The term "CTE," as used herein, refers to the coefficient of
thermal expansion of the glass composition over a temperature range
from about room temperature (RT) to about 300.degree. C.
[0024] In the embodiments of the glass compositions described
herein, the concentrations of constituent components (e.g.,
SiO.sub.2, Al.sub.2O.sub.3, and the like) are specified in mole
percent (mol. %) on an oxide basis, unless otherwise specified.
[0025] The terms "free" and "substantially free," when used to
describe the concentration and/or absence of a particular
constituent component in a glass composition, means that the
constituent component is not intentionally added to the glass
composition. However, the glass composition may contain traces of
the constituent component as a contaminant or tramp in amounts of
less than 0.01 mol. %.
[0026] The term "chemical durability," as used herein, refers to
the ability of the glass composition to resist degradation upon
exposure to specified chemical conditions. Specifically, the
chemical durability of the glass compositions described herein was
assessed according to three established material testing standards:
DIN 12116 dated March 2001 and entitled "Testing of
glass--Resistance to attack by a boiling aqueous solution of
hydrochloric acid--Method of test and classification"; ISO 695:1991
entitled "Glass--Resistance to attack by a boiling aqueous solution
of mixed alkali--Method of test and classification"; and ISO
720:1985 entitled "Glass--Hydrolytic resistance of glass grains at
121 degrees C.--Method of test and classification." The chemical
durability of the glass may also be assessed according to ISO
719:1985 "Glass--Hydrolytic resistance of glass grains at 98
degrees C.--Method of test and classification," in addition to the
above referenced standards. The ISO 719 standard is a less rigorous
version of the ISO 720 standard and, as such, it is believed that a
glass which meets a specified classification of the ISO 720
standard will also meet the corresponding classification of the ISO
719 standard. The classifications associated with each standard are
described in further detail herein.
[0027] The glass compositions described herein are alkali
aluminosilicate glass compositions which generally include a
combination of SiO.sub.2, Al.sub.2O.sub.3, at least one alkaline
earth oxide, and one or more alkali oxides, such as Na.sub.2O
and/or K.sub.2O. In some embodiments, the glass compositions may be
free from boron and compounds containing boron. The combination of
these components enables a glass composition which is resistant to
chemical degradation and is also suitable for chemical
strengthening by ion exchange. In some embodiments the glass
compositions may further comprise minor amounts of one or more
additional oxides such as, for example, SnO.sub.2, ZrO.sub.2, ZnO,
TiO.sub.2, As.sub.2O.sub.3 or the like. These components may be
added as fining agents and/or to further enhance the chemical
durability of the glass composition.
[0028] In the embodiments of the glass compositions described
herein SiO.sub.2 is the largest constituent of the composition and,
as such, is the primary constituent of the resulting glass network.
SiO.sub.2 enhances the chemical durability of the glass and, in
particular, the resistance of the glass composition to
decomposition in acid and the resistance of the glass composition
to decomposition in water. Accordingly, a high SiO.sub.2
concentration is generally desired. However, if the content of
SiO.sub.2 is too high, the formability of the glass may be
diminished as higher concentrations of SiO.sub.2 increase the
difficulty of melting the glass which, in turn, adversely impacts
the formability of the glass. In the embodiments described herein,
the glass composition generally comprises SiO.sub.2 in an amount
greater than or equal to 67 mol. % and less than or equal to about
80 mol. % or even less than or equal to 78 mol. %. In some
embodiments, the amount of SiO.sub.2 in the glass composition may
be greater than about 68 mol. %, greater than about 69 mol. % or
even greater than about 70 mol. %. In some other embodiments, the
amount of SiO.sub.2 in the glass composition may be greater than 72
mol. %, greater than 73 mol. % or even greater than 74 mol. %. For
example, in some embodiments, the glass composition may include
from about 68 mol. % to about 80 mol. % or even to about 78 mol. %
SiO.sub.2. In some other embodiments the glass composition may
include from about 69 mol. % to about 80 mol. % or even to about 78
mol. % SiO.sub.2. In some other embodiments the glass composition
may include from about 70 mol. % to about 80 mol. % or even to
about 78 mol. % SiO.sub.2. In still other embodiments, the glass
composition comprises SiO.sub.2 in an amount greater than or equal
to 70 mol. % and less than or equal to 78 mol. %. In some
embodiments, SiO.sub.2 may be present in the glass composition in
an amount from about 72 mol. % to about 78 mol. %. In some other
embodiments, SiO.sub.2 may be present in the glass composition in
an amount from about 73 mol. % to about 78 mol. %. In other
embodiments, SiO.sub.2 may be present in the glass composition in
an amount from about 74 mol. % to about 78 mol. %. In still other
embodiments, SiO.sub.2 may be present in the glass composition in
an amount from about 70 mol. % to about 76 mol. %.
[0029] The glass compositions described herein further include
Al.sub.2O.sub.3. Al.sub.2O.sub.3, in conjunction with alkali oxides
present in the glass compositions such as Na.sub.2O or the like,
improves the susceptibility of the glass to ion exchange
strengthening. In the embodiments described herein, Al.sub.2O.sub.3
is present in the glass compositions in X mol. % while the alkali
oxides are present in the glass composition in Y mol. %. The ratio
Y:X in the glass compositions described herein is greater than 1 in
order to facilitate the aforementioned susceptibility to ion
exchange strengthening. Specifically, the diffusion coefficient or
diffusivity D of the glass composition relates to the rate at which
alkali ions penetrate into the glass surface during ion exchange.
Glasses which have a ratio Y:X greater than about 0.9 or even
greater than about 1 have a greater diffusivity than glasses which
have a ratio Y:X less than 0.9. Glasses in which the alkali ions
have a greater diffusivity can obtain a greater depth of layer for
a given ion exchange time and ion exchange temperature than glasses
in which the alkali ions have a lower diffusivity. Moreover, as the
ratio of Y:X increases, the strain point, anneal point, and
softening point of the glass decrease, such that the glass is more
readily formable. In addition, for a given ion exchange time and
ion exchange temperature, it has been found that compressive
stresses induced in glasses which have a ratio Y:X greater than
about 0.9 and less than or equal to 2 are generally greater than
those generated in glasses in which the ratio Y:X is less than 0.9
or greater than 2. Accordingly, in some embodiments, the ratio of
Y:X is greater than 0.9 or even greater than 1. In some
embodiments, the ratio of Y:X is greater than 0.9, or even greater
than 1, and less than or equal to about 2. In still other
embodiments, the ratio of Y:X may be greater than or equal to about
1.3 and less than or equal to about 2.0 in order to maximize the
amount of compressive stress induced in the glass for a specified
ion exchange time and a specified ion exchange temperature.
[0030] However, if the amount of Al.sub.2O.sub.3 in the glass
composition is too high, the resistance of the glass composition to
acid attack is diminished. Accordingly, the glass compositions
described herein generally include Al.sub.2O.sub.3 in an amount
greater than or equal to about 2 mol. % and less than or equal to
about 10 mol. %. In some embodiments, the amount of Al.sub.2O.sub.3
in the glass composition is greater than or equal to about 4 mol. %
and less than or equal to about 8 mol. %. In some other
embodiments, the amount of Al.sub.2O.sub.3 in the glass composition
is greater than or equal to about 5 mol. % to less than or equal to
about 7 mol. %. In some other embodiments, the amount of
Al.sub.2O.sub.3 in the glass composition is greater than or equal
to about 6 mol. % to less than or equal to about 8 mol. %. In still
other embodiments, the amount of Al.sub.2O.sub.3 in the glass
composition is greater than or equal to about 5 mol. % to less than
or equal to about 6 mol. %.
[0031] The glass compositions also include one or more alkali
oxides such as Na.sub.2O and/or K.sub.2O. The alkali oxides
facilitate the ion exchangeability of the glass composition and, as
such, facilitate chemically strengthening the glass. The alkali
oxide may include one or more of Na.sub.2O and K.sub.2O. The alkali
oxides are generally present in the glass composition in a total
concentration of Y mol. %. In some embodiments described herein, Y
may be greater than about 2 mol. % and less than or equal to about
18 mol. %. In some other embodiments, Y may be greater than about 8
mol. %, greater than about 9 mol. %, greater than about 10 mol. %
or even greater than about 11 mol. %. For example, in some
embodiments described herein Y is greater than or equal to about 8
mol. % and less than or equal to about 18 mol. %. In still other
embodiments, Y may be greater than or equal to about 9 mol. % and
less than or equal to about 14 mol. %.
[0032] The ion exchangeability of the glass composition is
primarily imparted to the glass composition by the amount of the
alkali oxide Na.sub.2O initially present in the glass composition
prior to ion exchange. Accordingly, in the embodiments of the glass
compositions described herein, the alkali oxide present in the
glass composition includes at least Na.sub.2O. Specifically, in
order to achieve the desired compressive strength and depth of
layer in the glass composition upon ion exchange strengthening, the
glass compositions include Na.sub.2O in an amount from about 2 mol.
% to about 15 mol. % based on the molecular weight of the glass
composition. In some embodiments the glass composition includes at
least about 8 mol. % of Na.sub.2O based on the molecular weight of
the glass composition. For example, the concentration of Na.sub.2O
may be greater than 9 mol. %, greater than 10 mol. % or even
greater than 11 mol. %. In some embodiments, the concentration of
Na.sub.2O may be greater than or equal to 9 mol. % or even greater
than or equal to 10 mol. %. For example, in some embodiments the
glass composition may include Na.sub.2O in an amount greater than
or equal to about 9 mol. % and less than or equal to about 15 mol.
% or even greater than or equal to about 9 mol. % and less than or
equal to 13 mol. %.
[0033] As noted above, the alkali oxide in the glass composition
may further include K.sub.2O. The amount of K.sub.2O present in the
glass composition also relates to the ion exchangeability of the
glass composition. Specifically, as the amount of K.sub.2O present
in the glass composition increases, the compressive stress
obtainable through ion exchange decreases as a result of the
exchange of potassium and sodium ions. Accordingly, it is desirable
to limit the amount of K.sub.2O present in the glass composition.
In some embodiments, the amount of K.sub.2O is greater than or
equal to 0 mol. % and less than or equal to 3 mol. %. In some
embodiments, the amount of K.sub.2O is less or equal to 2 mol. % or
even less than or equal to 1.0 mol. %. In embodiments where the
glass composition includes K.sub.2O, the K.sub.2O may be present in
a concentration greater than or equal to about 0.01 mol. % and less
than or equal to about 3.0 mol. % or even greater than or equal to
about 0.01 mol. % and less than or equal to about 2.0 mol. %. In
some embodiments, the amount of K.sub.2O present in the glass
composition is greater than or equal to about 0.01 mol. % and less
than or equal to about 1.0 mol. %. Accordingly, it should be
understood that K.sub.2O need not be present in the glass
composition. However, when K.sub.2O is included in the glass
composition, the amount of K.sub.2O is generally less than about 3
mol. % based on the molecular weight of the glass composition.
[0034] The alkaline earth oxides present in the composition improve
the meltability of the glass batch materials and increase the
chemical durability of the glass composition. In the glass
compositions described herein, the total mol. % of alkaline earth
oxides present in the glass compositions is generally less than the
total mol. % of alkali oxides present in the glass compositions in
order to improve the ion exchangeability of the glass composition.
In the embodiments described herein, the glass compositions
generally include from about 3 mol. % to about 13 mol. % of
alkaline earth oxide. In some of these embodiments, the amount of
alkaline earth oxide in the glass composition may be from about 4
mol. % to about 8 mol. % or even from about 4 mol. % to about 7
mol. %.
[0035] The alkaline earth oxide in the glass composition may
include MgO, CaO, SrO, BaO or combinations thereof. In some
embodiments, the alkaline earth oxide includes MgO, CaO or
combinations thereof. For example, in the embodiments described
herein the alkaline earth oxide includes MgO. MgO is present in the
glass composition in an amount which is greater than or equal to
about 3 mol. % and less than or equal to about 8 mol. % MgO. In
some embodiments, MgO may be present in the glass composition in an
amount which is greater than or equal to about 3 mol. % and less
than or equal to about 7 mol. % or even greater than or equal to 4
mol. % and less than or equal to about 7 mol. % by molecular weight
of the glass composition.
[0036] In some embodiments, the alkaline earth oxide may further
include CaO. In these embodiments CaO is present in the glass
composition in an amount from about 0 mol. % to less than or equal
to 6 mol. % by molecular weight of the glass composition. For
example, the amount of CaO present in the glass composition may be
less than or equal to 5 mol. %, less than or equal to 4 mol. %,
less than or equal to 3 mol. %, or even less than or equal to 2
mol. %. In some of these embodiments, CaO may be present in the
glass composition in an amount greater than or equal to about 0.1
mol. % and less than or equal to about 1.0 mol. %. For example, CaO
may be present in the glass composition in an amount greater than
or equal to about 0.2 mol. % and less than or equal to about 0.7
mol. % or even in an amount greater than or equal to about 0.3 mol.
% and less than or equal to about 0.6 mol. %.
[0037] In the embodiments described herein, the glass compositions
are generally rich in MgO, (i.e., the concentration of MgO in the
glass composition is greater than the concentration of the other
alkaline earth oxides in the glass composition including, without
limitation, CaO). Forming the glass composition such that the glass
composition is MgO-rich improves the hydrolytic resistance of the
resultant glass, particularly following ion exchange strengthening.
Moreover, glass compositions which are MgO-rich generally exhibit
improved ion exchange performance relative to glass compositions
which are rich in other alkaline earth oxides. Specifically,
glasses formed from MgO-rich glass compositions generally have a
greater diffusivity than glass compositions which are rich in other
alkaline earth oxides, such as CaO. The greater diffusivity enables
the formation of a deeper depth of layer in the glass. MgO-rich
glass compositions also enable a higher compressive stress to be
achieved in the surface of the glass compared to glass compositions
which are rich in other alkaline earth oxides such as CaO. In
addition, it is generally understood that as the ion exchange
process proceeds and alkali ions penetrate more deeply into the
glass, the maximum compressive stress achieved at the surface of
the glass may decrease with time. However, glasses formed from
glass compositions which are MgO-rich exhibit a lower reduction in
compressive stress than glasses formed from glass compositions that
are CaO-rich or rich in other alkaline earth oxides (i.e., glasses
which are MgO-poor). Thus, MgO-rich glass compositions enable
glasses which have higher compressive stress at the surface and
greater depths of layer than glasses which are rich in other
alkaline earth oxides.
[0038] In order to fully realize the benefits of MgO in the glass
compositions described herein, it has been determined that the
ratio of the concentration of CaO to the sum of the concentration
of CaO and the concentration of MgO in mol. % (i.e.,
(CaO/(CaO+MgO)) should be minimized. Specifically, it has been
determined that (CaO/(CaO+MgO)) should be less than or equal to
0.5. In some embodiments (CaO/(CaO+MgO)) is less than or equal to
0.3 or even less than or equal to 0.2. In some other embodiments
(CaO/(CaO+MgO)) may even be less than or equal to 0.1.
[0039] Boron oxide (B.sub.2O.sub.3) is a flux which may be added to
glass compositions to reduce the viscosity at a given temperature
(e.g., the strain, anneal and softening temperatures) thereby
improving the formability of the glass. However, it has been found
that additions of boron significantly decrease the diffusivity of
sodium and potassium ions in the glass composition which, in turn,
adversely impacts the ion exchange performance of the resultant
glass. In particular, it has been found that additions of boron
significantly increase the time required to achieve a given depth
of layer relative to glass compositions which are boron free.
Accordingly, in some embodiments described herein, the amount of
boron added to the glass composition is minimized in order to
improve the ion exchange performance of the glass composition.
[0040] For example, it has been determined that the impact of boron
on the ion exchange performance of a glass composition can be
mitigated by controlling the ratio of the concentration of
B.sub.2O.sub.3 to the difference between the total concentration of
the alkali oxides (i.e., R.sub.2O, where R is the alkali metals)
and alumina (i.e., B.sub.2O.sub.3 (mol. %)/(R.sub.2O (mol.
%)-Al.sub.2O.sub.3 (mol. %)). In particular, it has been determined
that when the ratio of B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3)
is greater than or equal to about 0 and less than about 0.3 or even
less than about 0.2, the diffusivities of alkali oxides in the
glass compositions are not diminished and, as such, the ion
exchange performance of the glass composition is maintained.
Accordingly, in some embodiments, the ratio of
B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) is greater than 0 and
less than or equal to 0.3. In some of these embodiments, the ratio
of B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) is greater than 0 and
less than or equal to 0.2. In some embodiments, the ratio of
B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) is greater than 0 and
less than or equal to 0.15 or even less than or equal to 0.1. In
some other embodiments, the ratio of
B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) may be greater than 0
and less than or equal to 0.05. Maintaining the ratio
B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) to be less than or equal
to 0.3 or even less than or equal to 0.2 permits the inclusion of
B.sub.2O.sub.3 to lower the strain point, anneal point and
softening point of the glass composition without the B.sub.2O.sub.3
adversely impacting the ion exchange performance of the glass.
[0041] In the embodiments described herein, the concentration of
B.sub.2O.sub.3 in the glass composition is generally less than or
equal to about 4 mol. %, less than or equal to about 3 mol. %, less
than or equal to about 2 mol. %, or even less than or equal to 1
mol. %. For example, in embodiments where B.sub.2O.sub.3 is present
in the glass composition, the concentration of B.sub.2O.sub.3 may
be greater than about 0.01 mol. % and less than or equal to 4 mol.
%. In some of these embodiments, the concentration of
B.sub.2O.sub.3 may be greater than about 0.01 mol. % and less than
or equal to 3 mol. % In some embodiments, the B.sub.2O.sub.3 may be
present in an amount greater than or equal to about 0.01 mol. % and
less than or equal to 2 mol. %, or even less than or equal to 1.5
mol. %. Alternatively, the B.sub.2O.sub.3 may be present in an
amount greater than or equal to about 1 mol. % and less than or
equal to 4 mol. %, greater than or equal to about 1 mol. % and less
than or equal to 3 mol. % or even greater than or equal to about 1
mol. % and less than or equal to 2 mol. %. In some of these
embodiments, the concentration of B.sub.2O.sub.3 may be greater
than or equal to about 0.1 mol. % and less than or equal to 1.0
mol. %.
[0042] While in some embodiments the concentration of
B.sub.2O.sub.3 in the glass composition is minimized to improve the
forming properties of the glass without detracting from the ion
exchange performance of the glass, in some other embodiments the
glass compositions are free from boron and compounds of boron such
as B.sub.2O.sub.3. Specifically, it has been determined that
forming the glass composition without boron or compounds of boron
improves the ion exchangeability of the glass compositions by
reducing the process time and/or temperature required to achieve a
specific value of compressive stress and/or depth of layer.
[0043] In some embodiments of the glass compositions described
herein, the glass compositions are free from phosphorous and
compounds containing phosphorous including, without limitation,
P.sub.2O.sub.5. Specifically, it has been determined that
formulating the glass composition without phosphorous or compounds
of phosphorous increases the chemical durability of the glass
composition.
[0044] In addition to the SiO.sub.2, Al.sub.2O.sub.3, alkali oxides
and alkaline earth oxides, the glass compositions described herein
may optionally further comprise one or more fining agents such as,
for example, SnO.sub.2, As.sub.2O.sub.3, and/or Cl.sup.- (from NaCl
or the like). When a fining agent is present in the glass
composition, the fining agent may be present in an amount less than
or equal to about 1 mol. % or even less than or equal to about 0.4
mol. %. For example, in some embodiments the glass composition may
include SnO.sub.2 as a fining agent. In these embodiments SnO.sub.2
may be present in the glass composition in an amount greater than
about 0 mol. % and less than or equal to about 1 mol. % or even an
amount greater than or equal to about 0.01 mol. % and less than or
equal to about 0.30 mol. %.
[0045] Moreover, the glass compositions described herein may
comprise one or more additional metal oxides to further improve the
chemical durability of the glass composition. For example, the
glass composition may further include ZnO, TiO.sub.2, or ZrO.sub.2,
each of which further improves the resistance of the glass
composition to chemical attack. In these embodiments, the
additional metal oxide may be present in an amount which is greater
than or equal to about 0 mol. % and less than or equal to about 2
mol. %. For example, when the additional metal oxide is ZnO, the
ZnO may be present in an amount greater than or equal to 1 mol. %
and less than or equal to about 2 mol. %. When the additional metal
oxide is ZrO.sub.2 or TiO.sub.2, the ZrO.sub.2 or TiO.sub.2 may be
present in an amount less than or equal to about 1 mol. %.
[0046] Based on the foregoing, it should be understood that, in a
first exemplary embodiment, a glass composition may include:
SiO.sub.2 in a concentration greater than about 70 mol. % and Y
mol. % alkali oxide. The alkali oxide may include Na.sub.2O in an
amount greater than about 8 mol. %. The glass composition may be
free of boron and compounds of boron. The concentration of
SiO.sub.2 in this glass composition may be greater than or equal to
about 72 mol. %, greater than 73 mol. % or even greater than 74
mol. %. The glass composition of this first exemplary embodiment
may be free from phosphorous and compounds of phosphorous. The
glass composition may also include X mol. % Al.sub.2O.sub.3. When
Al.sub.2O.sub.3 is included, the ratio of Y:X may be greater than
1. The concentration of Al.sub.2O.sub.3 may be greater than or
equal to about 2 mol. % and less than or equal to about 10 mol.
%.
[0047] The glass composition of this first exemplary embodiment may
also include alkaline earth oxide in an amount from about 3 mol. %
to about 13 mol. %. The alkaline earth oxide may include MgO and
CaO. The CaO may be present in an amount greater than or equal to
about 0.1 mol. % and less than or equal to about 1.0 mol. %. A
ratio (CaO (mol. %)/(CaO (mol. %)+MgO (mol. %))) may be less than
or equal to 0.5.
[0048] In a second exemplary embodiment, a glass composition may
include: greater than about 68 mol. % SiO.sub.2; X mol. %
Al.sub.2O.sub.3; Y mol. % alkali oxide; and B.sub.2O.sub.3. The
alkali oxide may include Na.sub.2O in an amount greater than about
8 mol %. A ratio (B.sub.2O.sub.3 (mol. %)/(Y mol. %-X mol. %) may
be greater than 0 and less than 0.3. The concentration of SiO.sub.2
in this glass composition may be greater than or equal to about 72
mol. %, greater than 73 mol. % or even greater than 74 mol. %. The
concentration of Al.sub.2O.sub.3 may be greater than or equal to
about 2 mol. % and less than or equal to about 10 mol. %. In this
second exemplary embodiment, the ratio of Y:X may be greater than
1. When the ratio of Y:X is greater than 1, an upper bound of the
ratio of Y:X may be less than or equal to 2. The glass composition
of this first exemplary embodiment may be free from phosphorous and
compounds of phosphorous.
[0049] The glass composition of this second exemplary embodiment
may also include alkaline earth oxide. The alkaline earth oxide may
include MgO and CaO. The CaO may be present in an amount greater
than or equal to about 0.1 mol. % and less than or equal to about
1.0 mol. %. A ratio (CaO (mol. %)/(CaO (mol. %)+MgO (mol. %))) may
be less than or equal to 0.5.
[0050] The concentration of B.sub.2O.sub.3 in this second exemplary
embodiment may be greater than or equal to about 0.01 mol. % and
less than or equal to about 4 mol. %.
[0051] In a third exemplary embodiment, a glass article may have a
type HgB1 hydrolytic resistance according to ISO 719. The glass
article may include greater than about 8 mol. % Na.sub.2O and less
than about 4 mol. % B.sub.2O.sub.3. The glass article may further
comprise X mol. % Al.sub.2O.sub.3 and Y mol. % alkali oxide. The
ratio (B.sub.2O.sub.3 (mol. %)/(Y mol. %-X mol. %) may be greater
than 0 and less than 0.3. The glass article of this third exemplary
embodiment may further include a compressive stress layer having a
surface compressive stress greater than or equal to about 250 MPa.
The glass article may also have at least a class S3 acid resistance
according to DIN 12116; at least a class A2 base resistance
according to ISO 695; and a type HGA1 hydrolytic resistance
according to ISO 720.
[0052] In a fourth exemplary embodiment, a glass article may
include SiO.sub.2 in an amount greater than about 70 mol. %; X mol.
% Al.sub.2O.sub.3; and Y mol. % alkali oxide. The alkali oxide may
include Na.sub.2O in an amount greater than about 8 mol. %. A ratio
of a concentration of B.sub.2O.sub.3 (mol. %) in the glass article
to (Y mol. %-X mol. %) may be less than 0.3. The glass article may
also have a type HGB1 hydrolytic resistance according to ISO 719.
The concentration of SiO.sub.2 in the glass article of this fourth
exemplary embodiment may be greater than or equal to 72 mol. % and
less than or equal to about 78 mol. % or even greater than 74 mol.
% and less than or equal to about 78 mol. %. The concentration of
Al.sub.2O.sub.3 in the glass article may be greater than or equal
to about 4 mol. % and less than or equal to about 8 mol. %. A ratio
of Y:X may be greater than 1 and less than 2.
[0053] The glass article of this fourth exemplary embodiment may
also include alkaline earth oxide in an amount from about 4 mol. %
to about 8 mol. %. The alkaline earth oxide may include MgO and
CaO. The CaO may be present in an amount greater than or equal to
about 0.2 mol. % and less than or equal to about 0.7 mol. %. A
ratio (CaO (mol. %)/(CaO (mol. %)+MgO (mol. %))) may be less than
or equal to 0.5. The glass article of this fourth exemplary
embodiment may have a type HGA1 hydrolytic resistance according to
ISO 720.
[0054] In a fifth exemplary embodiment, a glass composition may
include from about 70 mol. % to about 80 mol. % SiO.sub.2; from
about 3 mol. % to about 13 mol. % alkaline earth oxide; X mol. %
Al.sub.2O.sub.3; and Y mol. % alkali oxide. The alkali oxide may
include Na.sub.2O in an amount greater than about 8 mol. %. A ratio
of Y:X may be greater than 1. The glass composition may be free of
boron and compounds of boron.
[0055] In a sixth exemplary embodiment, a glass composition may
include from about 68 mol. % to about 80 mol. % SiO.sub.2; from
about 3 mol. % to about 13 mol. % alkaline earth oxide; X mol. %
Al.sub.2O.sub.3; and Y mol. % alkali oxide. The alkali oxide may
include Na.sub.2O in an amount greater than about 8 mol. %. The
glass composition of this sixth exemplary embodiment may also
include B.sub.2O.sub.3. A ratio (B.sub.2O.sub.3 (mol. %)/(Y mol.
%-X mol. %) may be greater than 0 and less than 0.3. A ratio of Y:X
may be greater than 1.
[0056] In a seventh exemplary embodiment, a glass composition may
include from about 70 mol. % to about 80 mol. % SiO.sub.2; from
about 3 mol. % to about 13 mol. % alkaline earth oxide; X mol. %
Al.sub.2O.sub.3; and Y mol. % alkali oxide. The amount of
Al.sub.2O.sub.3 in the glass composition may be greater than or
equal to about 2 mol. % and less than or equal to about 10 mol. %.
The alkaline earth oxide may include CaO in an amount greater than
or equal to about 0.1 mol. % and less than or equal to about 1.0
mol. %. The alkali oxide may include from about 0.01 mol. % to
about 1.0 mol. % K.sub.2O. A ratio of Y:X may be greater than 1.
The glass composition may be free of boron and compounds of boron.
The glass composition may be amenable to strengthening by ion
exchange.
[0057] In a seventh exemplary embodiment, a glass composition may
include SiO.sub.2 in an amount greater than about 70 mol. % and
less than or equal to about 80 mol. %; X mol. % Al.sub.2O.sub.3;
and Y mol. % alkali oxide. The alkali oxide may include Na.sub.2O
in an amount greater than about 8 mol. %. A ratio of a
concentration of B.sub.2O.sub.3 (mol. %) in the glass article to (Y
mol. %-X mol. %) may be less than 0.3. A ratio of Y:X may be
greater than 1.
[0058] In an eighth exemplary embodiment, a glass composition may
include from about 72 mol. % to about 78 mol. % SiO.sub.2; from
about 4 mol. % to about 8 mol. % alkaline earth oxide; X mol. %
Al.sub.2O.sub.3, wherein X is greater than or equal to about 4 mol.
% and less than or equal to about 8 mol. %; and Y mol. % alkali
oxide, wherein the alkali oxide comprises Na.sub.2O in an amount
greater than or equal to about 9 mol. % and less than or equal to
about 15 mol. %. A ratio of a concentration of B.sub.2O.sub.3 (mol.
%) in the glass article to (Y mol. %-X mol. %) is less than 0.3. A
ratio of Y:X may be greater than 1.
[0059] In a ninth exemplary embodiment, a glass article may include
from about 70 mol. % to about 78 mol. % SiO.sub.2; from about 3
mol. % to about 13 mol. % alkaline earth oxide; X mol. %
Al.sub.2O.sub.3, wherein X is greater than or equal to 2 mol. % and
less than or equal to about 10 mol. %; and Y mol. % alkali oxide,
wherein the alkali oxide comprises Na.sub.2O in an amount greater
than about 8 mol. %. The alkaline earth oxide may include CaO in an
amount less than or equal to about 6.0 mol. %. A ratio of Y:X may
be greater than about 1. The glass article may be free of boron and
compounds of boron and may include a compressive stress layer with
a compressive stress greater than or equal to about 250 MPa and a
depth of layer greater than or equal to about 10 .mu.m.
[0060] In a tenth exemplary embodiment, a glass article may be
formed from a glass composition comprising from about 70 mol. % to
about 78 mol. % SiO.sub.2; alkaline earth oxide, wherein the
alkaline earth oxide comprises MgO and CaO and a ratio (CaO (mol.
%)/(CaO (mol. %)+MgO (mol. %))) is less than or equal to 0.5; X
mol. % Al.sub.2O.sub.3, wherein X is from about 2 mol. % to about
10 mol. %; and Y mol. % alkali oxide, wherein the alkali oxide
comprises Na.sub.2O in an amount greater than about 8 mol. % and a
ratio of Y:X is greater than 1. The glass article may be ion
exchange strengthened with a compressive stress greater than or
equal to 250 MPa and a depth of layer greater than or equal to 10
.mu.m. The glass article may have a type HGA1 hydrolytic resistance
according to ISO 720.
[0061] As noted above, the presence of alkali oxides in the glass
composition facilitates chemically strengthening the glass by ion
exchange. Specifically, alkali ions, such as potassium ions, sodium
ions and the like, are sufficiently mobile in the glass to
facilitate ion exchange. In some embodiments, the glass composition
is ion exchangeable to form a compressive stress layer having a
depth of layer greater than or equal to 10 .mu.m. In some
embodiments, the depth of layer may be greater than or equal to
about 25 .mu.m or even greater than or equal to about 50 .mu.m. In
some other embodiments, the depth of the layer may be greater than
or equal to 75 .mu.m or even greater than or equal to 100 .mu.m. In
still other embodiments, the depth of layer may be greater than or
equal to 10 .mu.m and less than or equal to about 100 .mu.m. The
associated surface compressive stress may be greater than or equal
to about 250 MPa, greater than or equal to 300 MPa or even greater
than or equal to about 350 MPa after the glass composition is
treated in a salt bath of 100% molten KNO.sub.3 at a temperature of
350.degree. C. to 500.degree. C. for a time period of less than
about 30 hours or even about less than 20 hours.
[0062] The glass articles formed from the glass compositions
described herein may have a hydrolytic resistance of HGB2 or even
HGB1 under ISO 719 and/or a hydrolytic resistance of HGA2 or even
HGA1 under ISO 720 (as described further herein) in addition to
having improved mechanical characteristics due to ion exchange
strengthening. In some embodiments described herein the glass
articles may have compressive stress layers which extend from the
surface into the glass article to a depth of layer greater than or
equal to 25 .mu.m or even greater than or equal to 35 .mu.m. In
some embodiments, the depth of layer may be greater than or equal
to 40 .mu.m or even greater than or equal to 50 .mu.m. The surface
compressive stress of the glass article may be greater than or
equal to 250 MPa, greater than or equal to 350 MPa, or even greater
than or equal to 400 MPa. The glass compositions described herein
facilitate achieving the aforementioned depths of layer and surface
compressive stresses more rapidly and/or at lower temperatures than
conventional glass compositions due to the enhanced alkali ion
diffusivity of the glass compositions as described hereinabove. For
example, the depths of layer (i.e., greater than or equal to 25
.mu.m) and the compressive stresses (i.e., greater than or equal to
250 MPa) may be achieved by ion exchanging the glass article in a
molten salt bath of 100% KNO.sub.3 (or a mixed salt bath of
KNO.sub.3 and NaNO.sub.3) for a time period of less than or equal
to 5 hours, or even less than or equal to 4.5 hours, at a
temperature less than or equal to 500.degree. C. or even less than
or equal to 450.degree. C. In some embodiments, the time period for
achieving these depths of layer and compressive stresses may be
less than or equal to 4 hours or even less than or equal to 3.5
hours. The temperature for achieving these depths of layers and
compressive stresses may be less than or equal to 400.degree. C. or
even less than or equal to 350.degree. C.
[0063] These improved ion exchange characteristics can be achieved
when the glass composition has a threshold diffusivity of greater
than about 16 .mu.m.sup.2/hr at a temperature less than or equal to
450.degree. C. or even greater than or equal to 20 .mu.m.sup.2/hr
at a temperature less than or equal to 450.degree. C. In some
embodiments, the threshold diffusivity may be greater than or equal
to about 25 .mu.m.sup.2/hr at a temperature less than or equal to
450.degree. C. or even 30 .mu.m.sup.2/hr at a temperature less than
or equal to 450.degree. C. In some other embodiments, the threshold
diffusivity may be greater than or equal to about 35 .mu.m.sup.2/hr
at a temperature less than or equal to 450.degree. C. or even 40
.mu.m.sup.2/hr at a temperature less than or equal to 450.degree.
C. In still other embodiments, the threshold diffusivity may be
greater than or equal to about 45 .mu.m.sup.2/hr at a temperature
less than or equal to 450.degree. C. or even 50 .mu.m.sup.2/hr at a
temperature less than or equal to 450.degree. C.
[0064] The glass compositions described herein may generally have a
strain point greater than or equal to about 525.degree. C. and less
than or equal to about 650.degree. C. The glasses may also have an
anneal point greater than or equal to about 560.degree. C. and less
than or equal to about 725.degree. C. and a softening point greater
than or equal to about 750.degree. C. and less than or equal to
about 960.degree. C.
[0065] In the embodiments described herein the glass compositions
have a CTE of less than about 70.times.10.sup.-7K.sup.-1 or even
less than about 60.times.10.sup.-7K.sup.-1. These lower CTE values
improve the survivability of the glass to thermal cycling or
thermal stress conditions relative to glass compositions with
higher CTEs.
[0066] Further, as noted hereinabove, the glass compositions are
chemically durable and resistant to degradation as determined by
the DIN 12116 standard, the ISO 695 standard, and the ISO 720
standard.
[0067] Specifically, the DIN 12116 standard is a measure of the
resistance of the glass to decomposition when placed in an acidic
solution. In brief, the DIN 12116 standard utilizes a polished
glass sample of a known surface area which is weighed and then
positioned in contact with a proportional amount of boiling 6M
hydrochloric acid for 6 hours. The sample is then removed from the
solution, dried and weighed again. The glass mass lost during
exposure to the acidic solution is a measure of the acid durability
of the sample with smaller numbers indicative of greater
durability. The results of the test are reported in units of
half-mass per surface area, specifically mg/dm.sup.2. The DIN 12116
standard is broken into individual classes. Class S1 indicates
weight losses of up to 0.7 mg/dm.sup.2; Class S2 indicates weight
losses from 0.7 mg/dm.sup.2 up to 1.5 mg/dm.sup.2; Class S3
indicates weight losses from 1.5 mg/dm.sup.2 up to 15 mg/dm.sup.2;
and Class S4 indicates weight losses of more than 15
mg/dm.sup.2.
[0068] The ISO 695 standard is a measure of the resistance of the
glass to decomposition when placed in a basic solution. In brief,
the ISO 695 standard utilizes a polished glass sample which is
weighed and then placed in a solution of boiling 1M NaOH+0.5M
Na.sub.2CO.sub.3 for 3 hours. The sample is then removed from the
solution, dried and weighed again. The glass mass lost during
exposure to the basic solution is a measure of the base durability
of the sample with smaller numbers indicative of greater
durability. As with the DIN 12116 standard, the results of the ISO
695 standard are reported in units of mass per surface area,
specifically mg/dm.sup.2. The ISO 695 standard is broken into
individual classes. Class A1 indicates weight losses of up to 75
mg/dm.sup.2; Class A2 indicates weight losses from 75 mg/dm.sup.2
up to 175 mg/dm.sup.2; and Class A3 indicates weight losses of more
than 175 mg/dm.sup.2.
[0069] The ISO 720 standard is a measure of the resistance of the
glass to degradation in purified, CO.sub.2-free water. In brief,
the ISO 720 standard protocol utilizes crushed glass grains which
are placed in contact with the purified, CO.sub.2-free water under
autoclave conditions (121.degree. C., 2 atm) for 30 minutes. The
solution is then titrated colorimetrically with dilute HCl to
neutral pH. The amount of HCl required to titrate to a neutral
solution is then converted to an equivalent of Na.sub.2O extracted
from the glass and reported in .mu.g Na.sub.2O per weight of glass
with smaller values indicative of greater durability. The ISO 720
standard is broken into individual types. Type HGA1 is indicative
of up to 62 .mu.g extracted equivalent of Na.sub.2O per gram of
glass tested; Type HGA2 is indicative of more than 62 .mu.g and up
to 527 .mu.g extracted equivalent of Na.sub.2O per gram of glass
tested; and Type HGA3 is indicative of more than 527 .mu.g and up
to 930 .mu.g extracted equivalent of Na.sub.2O per gram of glass
tested.
[0070] The ISO 719 standard is a measure of the resistance of the
glass to degradation in purified, CO.sub.2-free water. In brief,
the ISO 719 standard protocol utilizes crushed glass grains which
are placed in contact with the purified, CO.sub.2-free water at a
temperature of 98.degree. C. at 1 atmosphere for 30 minutes. The
solution is then titrated colorimetrically with dilute HCl to
neutral pH. The amount of HCl required to titrate to a neutral
solution is then converted to an equivalent of Na.sub.2O extracted
from the glass and reported in .mu.g Na.sub.2O per weight of glass
with smaller values indicative of greater durability. The ISO 719
standard is broken into individual types. The ISO 719 standard is
broken into individual types. Type HGB1 is indicative of up to 31
.mu.g extracted equivalent of Na.sub.2O; Type HGB2 is indicative of
more than 31 .mu.g and up to 62 .mu.g extracted equivalent of
Na.sub.2O; Type HGB3 is indicative of more than 62 .mu.g and up to
264 .mu.g extracted equivalent of Na.sub.2O; Type HGB4 is
indicative of more than 264 .mu.g and up to 620 .mu.g extracted
equivalent of Na.sub.2O; and Type HGB5 is indicative of more than
620 .mu.g and up to 1085 .mu.g extracted equivalent of Na.sub.2O.
The glass compositions described herein have an ISO 719 hydrolytic
resistance of type HGB2 or better with some embodiments having a
type HGB1 hydrolytic resistance.
[0071] The glass compositions described herein have an acid
resistance of at least class S3 according to DIN 12116 both before
and after ion exchange strengthening with some embodiments having
an acid resistance of at least class S2 or even class S1 following
ion exchange strengthening. In some other embodiments, the glass
compositions may have an acid resistance of at least class S2 both
before and after ion exchange strengthening with some embodiments
having an acid resistance of class S1 following ion exchange
strengthening. Further, the glass compositions described herein
have a base resistance according to ISO 695 of at least class A2
before and after ion exchange strengthening with some embodiments
having a class A1 base resistance at least after ion exchange
strengthening. The glass compositions described herein also have an
ISO 720 type HGA2 hydrolytic resistance both before and after ion
exchange strengthening with some embodiments having a type HGA1
hydrolytic resistance after ion exchange strengthening and some
other embodiments having a type HGA1 hydrolytic resistance both
before and after ion exchange strengthening. The glass compositions
described herein have an ISO 719 hydrolytic resistance of type HGB2
or better with some embodiments having a type HGB1 hydrolytic
resistance. It should be understood that, when referring to the
above referenced classifications according to DIN 12116, ISO 695,
ISO 720 and ISO 719, a glass composition or glass article which has
"at least" a specified classification means that the performance of
the glass composition is as good as or better than the specified
classification. For example, a glass article which has a DIN 12116
acid resistance of "at least class S2" may have a DIN 12116
classification of either S1 or S2.
[0072] The glass compositions described herein are formed by mixing
a batch of glass raw materials (e.g., powders of SiO.sub.2,
Al.sub.2O.sub.3, alkali oxides, alkaline earth oxides and the like)
such that the batch of glass raw materials has the desired
composition. Thereafter, the batch of glass raw materials is heated
to form a molten glass composition which is subsequently cooled and
solidified to form the glass composition. During solidification
(i.e., when the glass composition is plastically deformable) the
glass composition may be shaped using standard forming techniques
to shape the glass composition into a desired final form.
Alternatively, the glass article may be shaped into a stock form,
such as a sheet, tube or the like, and subsequently reheated and
formed into the desired final form.
[0073] The enhanced strength and chemical durability of the glass
compositions described herein is desirable to many glass article
applications. The glass articles formed from the glass compositions
described herein may have a variety of shapes, such as, for
example, sheets, tubes or non-symmetric shapes, a variety of sizes,
and other geometric features for various applications. Such glass
articles may be suitable for use in a wide variety of applications
including, without limitation, beverage packaging, food packaging,
household glassware, laboratory glassware, cosmetics packaging,
structural glazing, automobile glazing, cookware, lighting
products, ornamental items, display glass, industrial tubing, or
scientific instruments.
[0074] In one embodiment, the glass article may be a beverage
package. Without limitation, examples of beverage packages include
single serving beverage bottles (e.g., beer bottles, soda bottles,
juice bottles, water bottles), wine bottles, liquor bottles, and
any other container that may store a beverage. The glass articles
disclosed herein may be particularly well suited as beverage
containers for beverages which contain aqueous solutions, including
but not limited to acidic, basic, or alcohol containing solutions.
For example, the glass articles described herein may serve as a
packaging container for an alcoholic beverage such as a beverage
comprising about 5, about 10, about 20, about 40, about 60 or about
80 proof alcohol content. Some beverage packages may be capable of
being sealed to prevent contamination of the beverage within and/or
to prevent spoilage or other chemical degradation of the beverage
within.
[0075] In another embodiment, the glass article may be a food
package. Without limitation, examples of food packages include
canning jars and any other jar or other container suitable for
containing food. For example, foods commonly packaged in glass
articles include, without limitation, baby food, condiments, salad
dressings, and pickled foods.
[0076] In yet another embodiment, the glass article may be
household glassware. Without limitation, examples of household
glassware include wine glasses, pub glasses, mugs, goblets, jugs,
pitchers, flasks, decanters, and any other household glassware item
designed for drinking or storing beverages.
[0077] In yet another embodiment, the glass article may be
laboratory glassware. Without limitation, examples of laboratory
glassware include beakers, standard flasks, round bottom flasks,
test tubes, petri dishes, and any other like storage container
suitable for use in a laboratory.
[0078] In yet another embodiment, the glass article may be a
cosmetics package. Without limitation, examples of cosmetics
packages include perfume containers, cologne containers, and
containers which store other scented products, for human use or
otherwise, foundation containers, mascara containers, eyeshadow
containers, lip gloss containers, lipstick containers, and other
like cosmetic products containers.
[0079] In yet another embodiment, the glass article may be
structural glazing. Without limitation, examples of structural
glazing include glass for framed or unframed windows in any
structure (including residential structures and commercial
structures), glass for doors, such as storm doors or shower doors,
or glass for any other architectural element of a structure.
[0080] In yet another embodiment, the glass article may be vehicle
glazing. Without limitation, examples of vehicle glazing include
glazings for automobiles, such as automobile windows (including
windshields), and windows on other vehicles such as boats and
airplanes. For example, the glass article may be a window that may
be submerged in water (including sea water) such as windows on a
nautical vessel.
[0081] In yet another embodiment, the glass article may be
cookware. Without limitation, examples of cookware include any
dishware such as bowls, casserole dishes, dip containers, plates,
baking sheets, any other bakeware, and any other items suitable for
food preparation or for serving food in or upon.
[0082] In yet another embodiment, the glass article may be a
lighting product. Without limitation, examples of lighting products
include fluorescent lighting tubes, light bulbs, and LED
lighting.
[0083] In yet another embodiment, the glass article may an
ornamental item. Without limitation, examples of ornamental items
include glass tiles, glass figurines, and holiday tree ornaments.
It should be understood that as used herein the term "ornamental"
does not mean that the item must completely lack functionality.
[0084] In yet another embodiment, the glass article may be display
glass. Without limitation, display glass includes any glass that is
used in a display device, such as a television, a computer monitor,
a mobile device (e.g., a mobile phone with touch screen) or any
other electronic visual display. The display device may employ an
LCD screen, LED backlight screen, plasma screen, a touchscreen,
etc.
[0085] In yet another embodiment, the glass article may industrial
tubing. Such tubing may be useful for the storage and/or transport
of chemicals, especially chemicals with corrosive properties or for
chemicals that must not be contaminated.
[0086] In yet another embodiment, the glass article may be glass
for scientific instrument. For example, the glass article may be a
thermometer, lens, etc.
[0087] The glass articles described herein may have varying
transparency, translucency, and color (or lack thereof). For
example, additional additives to the glass composition can change
the optical properties of the glass. The glass without
compositional additives may be substantially clear and colorless,
such as at least as clear in appearance as traditional soda lime
glass, and may be desired for a number of types of glass articles
contemplated herein. For example, windows are often desired to be
clear and colorless. However, colored glass may be desirable in
other applications, such as a brown color for beer bottles or
decorative colors for ornamental glassware.
[0088] The glass compositions described herein may be particularly
useful for applications where they are in direct contact with a
material that should not be contaminated by the glass of the glass
article. For example, some glass compositions will degrade by
flaking, sometimes known as delamination, on their outer surface
that is in contact with a material. The flaking may be more likely
existent or more severe in cases where the glass is contacted
directly by, for example and without limitation, a material that
contains water, an acidic material, a basic material, or an organic
material. Glass flaking may particularly be a problem in the
context of a glass article in contact with a material that will be
consumed by humans, such as food or beverages.
EXAMPLES
[0089] The embodiments of the glass articles formed from glass
compositions described herein will be further clarified by the
following examples.
Example 1
[0090] Six exemplary inventive glass compositions (compositions
A-F) were prepared. The specific compositions of each exemplary
glass composition are reported below in Table 1. Multiple samples
of each exemplary glass composition were produced. One set of
samples of each composition was ion exchanged in a molten salt bath
of 100% KNO.sub.3 at a temperature of 450.degree. C. for at least 5
hours to induce a compressive layer in the surface of the sample.
The compressive layer had a surface compressive stress of at least
500 MPa and a depth of layer of at least 45 .mu.m.
[0091] The chemical durability of each exemplary glass composition
was then determined utilizing the DIN 12116 standard, the ISO 695
standard, and the ISO 720 standard described above. Specifically,
non-ion exchanged test samples of each exemplary glass composition
were subjected to testing according to one of the DIN 12116
standard, the ISO 695 standard, or the ISO 720 standard to
determine the acid resistance, the base resistance or the
hydrolytic resistance of the test sample, respectively. The
hydrolytic resistance of the ion exchanged samples of each
exemplary composition was determined according to the ISO 720
standard. To determine the hydrolytic resistance of the ion
exchanged samples, the glass was crushed to the grain size required
in the ISO 720 standard, ion exchanged ion exchanged in a molten
salt bath of 100% KNO.sub.3 at a temperature of 450.degree. C. for
at least 5 hours to induce a compressive stress layer in the
individual grains of glass, and then tested according to the ISO
720 standard. The average results of all samples tested are
reported below in Table 1.
[0092] As shown in Table 1, exemplary glass compositions A-F all
demonstrated a glass mass loss of less than 5 mg/dm.sup.2 and
greater than 1 mg/dm.sup.2 following testing according to the DIN
12116 standard with exemplary glass composition E having the lowest
glass mass loss at 1.2 mg/dm.sup.2. Accordingly, each of the
exemplary glass compositions were classified in at least class S3
of the DIN 12116 standard, with exemplary glass composition E
classified in class S2. Based on these test results, it is believed
that the acid resistance of the glass samples improves with
increased SiO.sub.2 content.
[0093] Further, exemplary glass compositions A-F all demonstrated a
glass mass loss of less than 80 mg/dm.sup.2 following testing
according to the ISO 695 standard with exemplary glass composition
A having the lowest glass mass loss at 60 mg/dm.sup.2. Accordingly,
each of the exemplary glass compositions were classified in at
least class A2 of the ISO 695 standard, with exemplary glass
compositions A, B, D and F classified in class A1. In general,
compositions with higher silica content exhibited lower base
resistance and compositions with higher alkali/alkaline earth
content exhibited greater base resistance.
[0094] Table 1 also shows that the non-ion exchanged test samples
of exemplary glass compositions A-F all demonstrated a hydrolytic
resistance of at least Type HGA2 following testing according to the
ISO 720 standard with exemplary glass compositions C--F having a
hydrolytic resistance of Type HGA1. The hydrolytic resistance of
exemplary glass compositions C-F is believed to be due to higher
amounts of SiO.sub.2 and the lower amounts of Na.sub.2O in the
glass compositions relative to exemplary glass compositions A and
B.
[0095] Moreover, the ion exchanged test samples of exemplary glass
compositions B-F demonstrated lower amounts of extracted Na.sub.2O
per gram of glass than the non-ion exchanged test samples of the
same exemplary glass compositions following testing according to
the ISO 720 standard.
TABLE-US-00001 TABLE 1 Composition and Properties of Exemplary
Glass Compositions Composition in mole % A B C D E F SiO.sub.2 70.8
72.8 74.8 76.8 76.8 77.4 Al.sub.2O.sub.3 7.5 7 6.5 6 6 7 Na.sub.2O
13.7 12.7 11.7 10.7 11.6 10 K.sub.2O 1 1 1 1 0.1 0.1 MgO 6.3 5.8
5.3 4.8 4.8 4.8 CaO 0.5 0.5 0.5 0.5 0.5 0.5 SnO.sub.2 0.2 0.2 0.2
0.2 0.2 0.2 DIN 12116 3.2 2.0 1.7 1.6 1.2 1.7 (mg/dm.sup.2)
classification S3 S3 S3 S3 S2 S3 ISO 695 60.7 65.4 77.9 71.5 76.5
62.4 (mg/dm.sup.2) classification A1 A1 A2 A1 A2 A1 ISO 720 100.7
87.0 54.8 57.5 50.7 37.7 (ug Na.sub.2O/ g glass) classification
HGA2 HGA2 HGA1 HGA1 HGA1 HGA1 ISO 720 60.3 51.9 39.0 30.1 32.9 23.3
(with IX) (ug Na.sub.2O/ g glass) classification HGA1 HGA1 HGA1
HGA1 HGA1 HGA1
Example 2
[0096] Three exemplary inventive glass compositions (compositions
G-I) and three comparative glass compositions (compositions 1-3)
were prepared. The ratio of alkali oxides to alumina (i.e., Y:X)
was varied in each of the compositions in order to assess the
effect of this ratio on various properties of the resultant glass
melt and glass. The specific compositions of each of the exemplary
inventive glass compositions and the comparative glass compositions
are reported in Table 2. The strain point, anneal point, and
softening point of melts formed from each of the glass compositions
were determined and are reported in Table 2. In addition, the
coefficient of thermal expansion (CTE), density, and stress optic
coefficient (SOC) of the resultant glasses were also determined and
are reported in Table 2. The hydrolytic resistance of glass samples
formed from each exemplary inventive glass composition and each
comparative glass composition was determined according to the ISO
720 Standard both before ion exchange and after ion exchange in a
molten salt bath of 100% KNO.sub.3 at 450.degree. C. for 5 hours.
For those samples that were ion exchanged, the compressive stress
was determined with a fundamental stress meter (FSM) instrument,
with the compressive stress value based on the measured stress
optical coefficient (SOC). The FSM instrument couples light into
and out of the birefringent glass surface. The measured
birefringence is then related to stress through a material
constant, the stress-optic or photoelastic coefficient (SOC or PEC)
and two parameters are obtained: the maximum surface compressive
stress (CS) and the exchanged depth of layer (DOL). The diffusivity
of the alkali ions in the glass and the change in stress per square
root of time were also determined. The diffusivity (D) of the glass
is calculated from the measured depth of layer (DOL) and the ion
exchange time (t) according to the relationship:
DOL=.about.1.4*sqrt(4*D*t). Diffusivity increases with temperature
according to an Arrhenius relationship, and, as such, it is
reported at a specific temperature.
TABLE-US-00002 TABLE 2 Glass properties as a function of alkali to
alumina ratio Composition Mole % G H I 1 2 3 SiO.sub.2 76.965
76.852 76.962 76.919 76.960 77.156 Al.sub.2O.sub.3 5.943 6.974
7.958 8.950 4.977 3.997 Na.sub.2O 11.427 10.473 9.451 8.468 12.393
13.277 K.sub.2O 0.101 0.100 0.102 0.105 0.100 0.100 MgO 4.842 4.878
4.802 4.836 4.852 4.757 CaO 0.474 0.478 0.481 0.480 0.468 0.462
SnO.sub.2 0.198 0.195 0.197 0.197 0.196 0.196 Strain (.degree. C.)
578 616 654 683 548 518 Anneal (.degree. C.) 633 674 716 745 600
567 Softening (.degree. C.) 892 946 1003 1042 846 798 Expansion
(10.sup.-7 K.sup.-1) 67.3 64.3 59.3 55.1 71.8 74.6 Density
(g/cm.sup.3) 2.388 2.384 2.381 2.382 2.392 2.396 SOC (nm/mm/Mpa)
3.127 3.181 3.195 3.232 3.066 3.038 ISO720 (non-IX) 88.4 60.9 47.3
38.4 117.1 208.1 ISO720 (IX450.degree. C.-5 hr) 25.3 26 20.5 17.8
57.5 102.5 R.sub.2O/Al.sub.2O.sub.3 1.940 1.516 1.200 0.958 2.510
3.347 CS@t = 0 (MPa) 708 743 738 655 623 502 CS/ t (MPa/hr.sup.1/2)
-35 -24 -14 -7 -44 -37 D (.mu.m.sup.2/hr) 52.0 53.2 50.3 45.1 51.1
52.4
[0097] The data in Table 2 indicates that the alkali to alumina
ratio Y:X influences the melting behavior, hydrolytic resistance,
and the compressive stress obtainable through ion exchange
strengthening. In particular, FIG. 1 graphically depicts the strain
point, anneal point, and softening point as a function of Y:X ratio
for the glass compositions of Table 2. FIG. 1 demonstrates that, as
the ratio of Y:X decreases below 0.9, the strain point, anneal
point, and softening point of the glass rapidly increase.
Accordingly, to obtain a glass which is readily meltable and
formable, the ratio Y:X should be greater than or equal to 0.9 or
even greater than or equal to 1.
[0098] Further, the data in Table 2 indicates that the diffusivity
of the glass compositions generally decreases with the ratio of
Y:X. Accordingly, to achieve glasses that can be rapidly ion
exchanged in order to reduce process times (and costs) the ratio of
Y:X should be greater than or equal to 0.9 or even greater than or
equal to 1.
[0099] Moreover, FIG. 2 indicates that for a given ion exchange
time and ion exchange temperature, the maximum compressive stresses
are obtained when the ratio of Y:X is greater than or equal to
about 0.9, or even greater than or equal to about 1, and less than
or equal to about 2, specifically greater than or equal to about
1.3 and less than or equal to about 2.0. Accordingly, the maximum
improvement in the load bearing strength of the glass can be
obtained when the ratio of Y:X is greater than about 1 and less
than or equal to about 2. It is generally understood that the
maximum stress achievable by ion exchange will decay with
increasing ion-exchange duration as indicated by the stress change
rate (i.e., the measured compressive stress divided by the square
root of the ion exchange time). FIG. 2 generally shows that the
stress change rate decreases as the ratio Y:X decreases.
[0100] FIG. 3 graphically depicts the hydrolytic resistance
(y-axis) as a function of the ratio Y:X (x-axis). As shown in FIG.
3, the hydrolytic resistance of the glasses generally improves as
the ratio Y:X decreases.
[0101] Based on the foregoing it should be understood that glasses
with good melt behavior, superior ion exchange performance, and
superior hydrolytic resistance can be achieved by maintaining the
ratio Y:X in the glass from greater than or equal to about 0.9, or
even greater than or equal to about 1, and less than or equal to
about 2.
Example 3
[0102] Three exemplary inventive glass compositions (compositions
J-L) and three comparative glass compositions (compositions 4-6)
were prepared. The concentration of MgO and CaO in the glass
compositions was varied to produce both MgO-rich compositions
(i.e., compositions J-L and 4) and CaO-rich compositions (i.e.,
compositions 5-6). The relative amounts of MgO and CaO were also
varied such that the glass compositions had different values for
the ratio (CaO/(CaO+MgO)). The specific compositions of each of the
exemplary inventive glass compositions and the comparative glass
compositions are reported below in Table 3. The properties of each
composition were determined as described above with respect to
Example 2.
TABLE-US-00003 TABLE 3 Glass properties as function of CaO content
Composition Mole % J K L 4 5 6 SiO.sub.2 76.99 77.10 77.10 77.01
76.97 77.12 Al.sub.2O.sub.3 5.98 5.97 5.96 5.96 5.97 5.98 Na.sub.2O
11.38 11.33 11.37 11.38 11.40 11.34 K.sub.2O 0.10 0.10 0.10 0.10
0.10 0.10 MgO 5.23 4.79 3.78 2.83 1.84 0.09 CaO 0.07 0.45 1.45 2.46
3.47 5.12 SnO.sub.2 0.20 0.19 0.19 0.19 0.19 0.19 Strain (.degree.
C.) 585 579 568 562 566 561 Anneal (.degree. C.) 641 634 620 612
611 610 Softening (.degree. C.) 902 895 872 859 847 834 Expansion
(10.sup.-7 K.sup.-1) 67.9 67.1 68.1 68.8 69.4 70.1 Density
(g/cm.sup.3) 2.384 2.387 2.394 2.402 2.41 2.42 SOC nm/mm/Mpa 3.12
3.08 3.04 3.06 3.04 3.01 ISO720 (non-IX) 83.2 83.9 86 86 88.7 96.9
ISO720 (IX450.degree. C.-5 hr) 29.1 28.4 33.2 37.3 40.1 Fraction of
RO as CaO 0.014 0.086 0.277 0.465 0.654 0.982 CS@t = 0 (MPa) 707
717 713 689 693 676 CS/ t (MPa/hr.sup.1/2) -36 -37 -39 -38 -43 -44
D (.mu.m.sup.2/hr) 57.2 50.8 40.2 31.4 26.4 20.7
[0103] FIG. 4 graphically depicts the diffusivity D of the
compositions listed in Table 3 as a function of the ratio
(CaO/(CaO+MgO)). Specifically, FIG. 4 indicates that as the ratio
(CaO/(CaO+MgO)) increases, the diffusivity of alkali ions in the
resultant glass decreases thereby diminishing the ion exchange
performance of the glass. This trend is supported by the data in
Table 3 and FIG. 5. FIG. 5 graphically depicts the maximum
compressive stress and stress change rate (y-axes) as a function of
the ratio (CaO/(CaO+MgO)). FIG. 5 indicates that as the ratio
(CaO/(CaO+MgO)) increases, the maximum obtainable compressive
stress decreases for a given ion exchange temperature and ion
exchange time. FIG. 5 also indicates that as the ratio
(CaO/(CaO+MgO)) increases, the stress change rate increases (i.e.,
becomes more negative and less desirable).
[0104] Accordingly, based on the data in Table 3 and FIGS. 4 and 5,
it should be understood that glasses with higher diffusivities can
be produced by minimizing the ratio (CaO/(CaO+MgO)). It has been
determined that glasses with suitable diffusivities can be produced
when the (CaO/(CaO+MgO)) ratio is less than about 0.5. The
diffusivity values of the glass when the (CaO/(CaO+MgO)) ratio is
less than about 0.5 decreases the ion exchange process times needed
to achieve a given compressive stress and depth of layer.
Alternatively, glasses with higher diffusivities due to the ratio
(CaO/(CaO+MgO)) may be used to achieve a higher compressive stress
and depth of layer for a given ion exchange temperature and ion
exchange time.
[0105] Moreover, the data in Table 3 also indicates that decreasing
the ratio (CaO/(CaO+MgO)) by increasing the MgO concentration
generally improves the resistance of the glass to hydrolytic
degradation as measured by the ISO 720 standard.
Example 4
[0106] Three exemplary inventive glass compositions (compositions
M-O) and three comparative glass compositions (compositions 7-9)
were prepared. The concentration of B.sub.2O.sub.3 in the glass
compositions was varied from 0 mol. % to about 4.6 mol. % such that
the resultant glasses had different values for the ratio
B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3). The specific
compositions of each of the exemplary inventive glass compositions
and the comparative glass compositions are reported below in Table
4. The properties of each glass composition were determined as
described above with respect to Examples 2 and 3.
TABLE-US-00004 TABLE 4 Glass properties as a function of
B.sub.2O.sub.3 content Composition Mole % M N O 7 8 9 SiO.sub.2
76.860 76.778 76.396 74.780 73.843 72.782 Al.sub.2O.sub.3 5.964
5.948 5.919 5.793 5.720 5.867 B.sub.2O.sub.3 0.000 0.214 0.777
2.840 4.443 4.636 Na.sub.2O 11.486 11.408 11.294 11.036 10.580
11.099 K.sub.2O 0.101 0.100 0.100 0.098 0.088 0.098 MgO 4.849 4.827
4.801 4.754 4.645 4.817 CaO 0.492 0.480 0.475 0.463 0.453 0.465
SnO.sub.2 0.197 0.192 0.192 0.188 0.183 0.189 Strain (.degree. C.)
579 575 572 560 552 548 Anneal (.degree. C.) 632 626 622 606 597
590 Softening (.degree. C.) 889 880 873 836 816 801 Expansion
(10.sup.-7 K.sup.-1) 68.3 67.4 67.4 65.8 64.1 67.3 Density
(g/cm.sup.3) 2.388 2.389 2.390 2.394 2.392 2.403 SOC (nm/mm/MPa)
3.13 3.12 3.13 3.17 3.21 3.18 ISO720 (non-IX) 86.3 78.8 68.5 64.4
52.7 54.1 ISO720 (IX450.degree. C.-5 hr) 32.2 30.1 26 24.7 22.6
26.7 B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) 0.000 0.038 0.142
0.532 0.898 0.870 CS@t = 0 (MPa) 703 714 722 701 686 734 CS/ t
(MPa/hr.sup.1/2) -38 -38 -38 -33 -32 -39 D (.mu.m.sup.2/hr) 51.7
43.8 38.6 22.9 16.6 15.6
[0107] FIG. 6 graphically depicts the diffusivity D (y-axis) of the
glass compositions in Table 4 as a function of the ratio
B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) (x-axis) for the glass
compositions of Table 4. As shown in FIG. 6, the diffusivity of
alkali ions in the glass generally decreases as the ratio
B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) increases.
[0108] FIG. 7 graphically depicts the hydrolytic resistance
according to the ISO 720 standard (y-axis) as a function of the
ratio B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) (x-axis) for the
glass compositions of Table 4. As shown in FIG. 6, the hydrolytic
resistance of the glass compositions generally improves as the
ratio B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) increases.
[0109] Based on FIGS. 6 and 7, it should be understood that
minimizing the ratio B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3)
improves the diffusivity of alkali ions in the glass thereby
improving the ion exchange characteristics of the glass. Further,
increasing the ratio B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3)
also generally improves the resistance of the glass to hydrolytic
degradation. In addition, it has been found that the resistance of
the glass to degradation in acidic solutions (as measured by the
DIN 12116 standard) generally improves with decreasing
concentrations of B.sub.2O.sub.3. Accordingly, it has been
determined that maintaining the ratio
B.sub.2O.sub.3/(R.sub.2O--Al.sub.2O.sub.3) to less than or equal to
about 0.3 provides the glass with improved hydrolytic and acid
resistances as well as providing for improved ion exchange
characteristics.
[0110] Based on the foregoing, it should now be understood that
various aspects of glass compositions that may form glass articles
are disclosed. According to a first aspect, a glass composition may
include: SiO.sub.2 in a concentration greater than about 70 mol. %
and Y mol. % alkali oxide. The alkali oxide may include Na.sub.2O
in an amount greater than about 8 mol. %. The glass composition may
be free of boron and compounds of boron.
[0111] In a second aspect, the glass composition of the first
aspect includes SiO.sub.2 in an amount greater than or equal to
about 72 mol. %.
[0112] In a third aspect, the glass composition of the first or
second aspects is free from phosphorous and compounds of
phosphorous.
[0113] In a fourth aspect, the glass composition of any of the
first through third aspects further includes X mol. %
Al.sub.2O.sub.3, wherein a ratio of Y:X is greater than 1.
[0114] In a fifth aspect, the glass composition of the ratio of Y:X
in the fourth aspect is less than or equal to 2.
[0115] In a sixth aspect, the glass composition of the amount of
Al.sub.2O.sub.3 in the fourth or fifth aspects is greater than or
equal to about 2 mol. % and less than or equal to about 10 mol.
%.
[0116] In a seventh aspect, the glass composition of any of the
first through fifth aspects further includes from about 3 mol. % to
about 13 mol. % alkaline earth oxide.
[0117] In an eighth aspect, the alkaline earth oxide of the seventh
aspect includes MgO and CaO, the CaO is present in an amount
greater than or equal to about 0.1 mol. % and less than or equal to
about 1.0 mol. %, and a ratio (CaO (mol. %)/(CaO (mol. %)+MgO (mol.
%))) is less than or equal to 0.5.
[0118] In a ninth aspect, a glass composition may include greater
than about 68 mol. % SiO.sub.2; X mol. % Al.sub.2O.sub.3 and Y mol.
% alkali oxide; and B.sub.2O.sub.3. The alkali oxide may include
Na.sub.2O in an amount greater than about 8 mol %. A ratio
(B.sub.2O.sub.3 (mol. %)/(Y mol. %-X mol. %) may be greater than 0
and less than 0.3.
[0119] In a tenth aspect, the glass composition of the ninth aspect
includes SiO.sub.2 in an amount greater than or equal to about 72
mol. %.
[0120] In an eleventh aspect, the glass composition of the ninth
aspect or the tenth aspect includes B.sub.2O.sub.3 in an amount
greater than or equal to about 0.01 mol. % and less than or equal
to about 4 mol. %.
[0121] In a twelfth aspect, the glass composition of any of the
ninth through eleventh aspects, wherein the glass composition has a
ratio of Y:X is greater than 1.
[0122] In a thirteenth aspect, the ratio of Y:X of the twelfth
aspect is less than or equal to 2.
[0123] A fourteenth aspect includes the glass composition of any of
the ninth through thirteenth aspects wherein X is greater than or
equal to about 2 mol. % and less than or equal to about 10 mol.
%.
[0124] A fifteenth aspect includes the glass composition of any of
the ninth through fourteenth aspects wherein the glass composition
is free from phosphorous and compounds of phosphorous.
[0125] A sixteenth aspect includes the glass composition of any of
the ninth through fifteenth aspects, wherein the glass composition
further comprises MgO and CaO, the CaO is present in an amount
greater than or equal to about 0.1 mol. % and less than or equal to
about 1.0 mol. %, and a ratio (CaO (mol. %)/(CaO (mol. %)+MgO (mol.
%))) is less than or equal to 0.5.
[0126] In a seventeenth aspect, a glass article may have a type
HGB1 hydrolytic resistance according to ISO 719. The glass article
may include greater than about 8 mol. % Na.sub.2O and less than
about 4 mol. % B.sub.2O.sub.3.
[0127] In an eighteenth aspect, the glass article of the
seventeenth aspect further comprises X mol. % Al.sub.2O.sub.3 and Y
mol. % alkali oxide, wherein a ratio (B.sub.2O.sub.3 (mol. %)/(Y
mol. %-X mol. %) is greater than 0 and less than 0.3.
[0128] In a nineteenth aspect, the glass article of any of the
seventeenth through eighteenth aspects further comprises a
compressive stress layer having a surface compressive stress
greater than or equal to about 250 MPa.
[0129] A twentieth aspect includes the glass article of any of the
seventeenth through nineteenth aspects, wherein the glass article
has at least a class S3 acid resistance according to DIN 12116.
[0130] A twenty-first aspect includes the glass article of any of
the seventeenth through twentieth aspect in which the glass article
has at least a class A2 base resistance according to ISO 695.
[0131] A twenty-second aspect includes the glass article of any of
the seventeenth through twenty-first aspects wherein the glass
article has a type HGA1 hydrolytic resistance according to ISO
720.
[0132] In a twenty-third aspect, a glass article may include: SiO2
in an amount greater than about 70 mol. %; X mol. %
Al.sub.2O.sub.3; and Y mol. % alkali oxide. The alkali oxide may
include Na.sub.2O in an amount greater than about 8 mol. %. A ratio
of a concentration of B.sub.2O.sub.3 (mol. %) in the glass article
to (Y mol. %-X mol. %) may be less than 0.3. The glass article may
also have a type HGB1 hydrolytic resistance according to ISO
719.
[0133] A twenty-fourth aspect includes the glass article of the
twenty-third aspect wherein the amount of SiO.sub.2 is greater than
or equal to 72 mol. % and less than or equal to about 78 mol.
%.
[0134] A twenty-fifth aspect includes the glass article of the
twenty-third through twenty-fourth aspects wherein X is greater
than or equal to about 4 mol. % and less than or equal to about 8
mol. %.
[0135] A twenty-sixth aspect includes the glass article of the
twenty-third through twenty-fifth aspects wherein a ratio of Y:X is
greater than 1.
[0136] A twenty-seventh aspect includes the glass article of the
twenty-third through twenty-sixth aspects, wherein a ratio of Y:X
is less than 2.
[0137] A twenty-eighth aspect includes the glass article of the
twenty-third through twenty-seventh aspects which further comprises
from about 4 mol. % to about 8 mol. % alkaline earth oxide.
[0138] A twenty-ninth aspect includes the glass article of the
twenty-third through twenty-eighth aspects which the further
comprises MgO and CaO, CaO is present in an amount greater than or
equal to about 0.2 mol. % and less than or equal to about 0.7 mol.
% and a ratio (CaO (mol. %)/(CaO (mol. %)+MgO (mol. %))) is less
than or equal to 0.5.
[0139] A thirtieth aspect includes the glass article of the
twenty-third through twenty-ninth aspects, wherein the glass
article has a type HGA1 hydrolytic resistance according to ISO
720.
[0140] In a thirty-first aspect, a glass composition may include
from about 70 mol. % to about 80 mol. % SiO.sub.2; from about 3
mol. % to about 13 mol. % alkaline earth oxide; X mol. %
Al.sub.2O.sub.3; and Y mol. % alkali oxide. The alkali oxide may
include Na.sub.2O in an amount greater than about 8 mol. %. A ratio
of Y:X may be greater than 1 and the glass composition may be free
of boron and compounds of boron.
[0141] In a thirty-second aspect, a glass composition may include:
from about 72 mol. % to about 78 mol. % SiO.sub.2; from about 4
mol. % to about 8 mol. % alkaline earth oxide; X mol. %
Al.sub.2O.sub.3; and Y mol. % alkali oxide. The amount of alkaline
earth oxide may be greater than or equal to about 4 mol. % and less
than or equal to about 8 mol. %. The alkali oxide may include Na2O
in an amount greater than or equal to about 9 mol. % and less than
or equal to about 15 mol. %. A ratio of Y:X may be greater than 1.
The glass composition may be free of boron and compounds of
boron.
[0142] In a thirty-third aspect, a glass composition may include:
from about 68 mol. % to about 80 mol. % SiO.sub.2; from about 3
mol. % to about 13 mol. % alkaline earth oxide; X mol. %
Al.sub.2O.sub.3; and Y mol. % alkali oxide. The alkali oxide may
include Na.sub.2O in an amount greater than about 8 mol. %. The
glass composition may also include B.sub.2O.sub.3. A ratio
(B.sub.2O.sub.3 (mol. %)/(Y mol. %-X mol. %) may be greater than 0
and less than 0.3, and a ratio of Y:X may be greater than 1.
[0143] In a thirty-fourth aspect, a glass composition may include
from about 70 mol. % to about 80 mol. % SiO.sub.2; from about 3
mol. % to about 13 mol. % alkaline earth oxide; X mol. %
Al.sub.2O.sub.3; and Y mol. % alkali oxide. The alkaline earth
oxide may include CaO in an amount greater than or equal to about
0.1 mol. % and less than or equal to about 1.0 mol. %. X may be
greater than or equal to about 2 mol. % and less than or equal to
about 10 mol. %. The alkali oxide may include from about 0.01 mol.
% to about 1.0 mol. % K.sub.2O. A ratio of Y:X may be greater than
1. The glass composition may be free of boron and compounds of
boron.
[0144] In a thirty-fifth aspect, a glass composition may include
SiO.sub.2 in an amount greater than about 70 mol. % and less than
or equal to about 80 mol. %; from about 3 mol. % to about 13 mol. %
alkaline earth oxide; X mol. % Al.sub.2O.sub.3; and Y mol. % alkali
oxide. The alkali oxide may include Na.sub.2O in an amount greater
than about 8 mol. %. A ratio of a concentration of B.sub.2O.sub.3
(mol. %) in the glass composition to (Y mol. %-X mol. %) may be
less than 0.3. A ratio of Y:X may be greater than 1.
[0145] In a thirty-sixth aspect, the glass composition of any of
the thirty-first through thirty-fifth aspects wherein the SiO.sub.2
is present in an amount less than or equal to 78 mol. %.
[0146] A thirty-seventh aspect includes the glass composition of
any of thirty-first through thirty-sixth aspects, wherein an amount
of the alkaline earth oxide is greater than or equal to about 4
mol. % and less than or equal to about 8 mol. %.
[0147] A thirty-eighth aspect includes the glass composition of any
of the thirty-first through thirty-seventh aspects wherein the
alkaline earth oxide comprises MgO and CaO and a ratio (CaO (mol.
%)/(CaO (mol. %)+MgO (mol. %))) is less than or equal to 0.5.
[0148] A thirty-ninth aspect includes the glass composition of any
of the thirty-first through thirty eighth aspects, wherein the
alkaline earth oxide comprises from about 0.1 mol. % to less than
or equal to about 1.0 mol. % CaO.
[0149] A fortieth aspect includes, the glass composition of any of
the thirty-first through thirty-ninth aspects wherein the alkaline
earth oxide comprises from about 3 mol. % to about 7 mol. %
MgO.
[0150] A forty-first aspect includes the glass composition of any
of the thirty-first, thirty-second, or thirty-fourth aspects,
wherein X is greater than or equal to about 2 mol. % and less than
or equal to about 10 mol. %.
[0151] A forty-second aspect includes the glass composition of any
of the thirty-first through forty-first aspects, wherein the alkali
oxide comprises greater than or equal to about 9 mol. % Na.sub.2O
and less than or equal to about 15 mol. % Na.sub.2O.
[0152] A forty-third aspect includes the glass composition of any
of the thirty-first through forty-second aspects, wherein the ratio
of Y:X is less than or equal to 2.
[0153] A forty-fourth aspect includes the glass composition of any
of the thirty-first through forty-third aspects, wherein the ratio
of Y:X is greater than or equal to 1.3 and less than or equal to
2.0.
[0154] A forty-fifth aspect includes the glass composition of any
of the thirty-first through forty-fourth aspects, wherein the
alkali oxide further comprises K.sub.2O in an amount less than or
equal to about 3 mol. %.
[0155] A forty-sixth aspect includes the glass composition of any
of the thirty-first through forty-fifth aspects, wherein the glass
composition is free of phosphorous and compounds of
phosphorous.
[0156] A forty-seventh includes the glass composition of any of the
thirty-first through forty-sixth aspects, wherein the alkali oxide
comprises K.sub.2O in an amount greater than or equal to about 0.01
mol. % and less than or equal to about 1.0 mol. %.
[0157] A forty-eighth aspect includes the glass composition of any
of the thirty-second or thirty-fourth aspects, wherein an amount of
SiO.sub.2 is greater than or equal to about 70 mol. %.
[0158] A forty-ninth aspect includes the glass composition of any
of the thirty-second or thirty-fourth aspects, wherein the ratio
(B.sub.2O.sub.3 (mol. %)/(Y mol. %-X mol. %) is less than 0.2.
[0159] A fiftieth aspect includes the glass composition of any of
the thirty-second or thirty-fourth aspects, wherein an amount of
B.sub.2O.sub.3 is less than or equal to about 4.0 mol. %.
[0160] A fifty-first aspect includes the glass composition of the
fiftieth aspect, wherein the amount of B.sub.2O.sub.3 is greater
than or equal to about 0.01 mol. %.
[0161] A fifty-second aspect includes the glass composition of the
thirty-fourth aspect, wherein the glass composition is free from
boron and compounds of boron.
[0162] A fifty-third aspect includes the glass composition of any
of the thirty-first through thirty-fourth aspects, wherein the
concentration of SiO.sub.2 is greater than or equal to about 72
mol. %.
[0163] A fifty-fourth aspect includes the glass composition of any
of the thirty-first through fifty-third aspects, wherein the
concentration of SiO.sub.2 is greater than or equal to about 73
mol. %.
[0164] In a fifty-fifth aspects, a glass article is formed from the
glass composition of any of the thirty-first through fifty-fourth
aspects.
[0165] A fifty-sixth aspect includes the glass article of the
fifty-fifth aspect, wherein the glass article has a type HGB1
hydrolytic resistance according to ISO 719.
[0166] A fifty-seventh aspect includes the glass article of any of
the fifty-fifth through fifty-sixth aspects, wherein the glass
article has a type HGA1 hydrolytic resistance according to ISO 720
after ion exchange strengthening.
[0167] A fifty-eighth aspect includes the glass article of any of
the fifty-fifth through fifty-seventh aspects, wherein the glass
article has a type HGA1 hydrolytic resistance according to ISO 720
before and after ion exchange strengthening.
[0168] A fifty-ninth aspect includes the glass article of any of
the fifty-fifth through fifty-eighth aspects, wherein the glass
article has at least a class S3 acid resistance according to DIN
12116.
[0169] A sixtieth aspect includes, the glass article of any of the
fifty-fifth through fifty-ninth aspects, wherein the glass article
has at least a class A2 base resistance according to ISO 695.
[0170] A sixty-first aspect includes the glass article of any of
the fifty-fifth through sixtieth aspects, wherein the glass article
is a beverage package, a food package, household glassware,
laboratory glassware, a cosmetics package, structural glazing,
automobile glazing, cookware, a lighting product, an ornamental
item, display glass, industrial tubing, or a scientific
instrument.
[0171] A sixty-second aspect includes the glass article of any of
the fifty-fifth through sixty-first aspects, wherein the glass
article is ion exchange strengthened.
[0172] A sixty-third aspect includes the glass article of any of
the fifty-fifth through sixty-second aspects in which the glass
article further a compressive stress layer with a depth of layer
greater than or equal to 10 .mu.m and a surface compressive stress
greater than or equal to 250 MPa.
[0173] In a sixty-fourth aspect, a glass article may have a type
HGB1 hydrolytic resistance according to ISO 719. The glass article
may also have a threshold diffusivity of greater than 16 .mu.m2/hr
at a temperature less than or equal to 450.degree. C.
[0174] A sixty-fifth aspect includes the glass article of the
sixty-fourth aspect wherein the threshold diffusivity is greater
than or equal to 20 .mu.m2/hr at a temperature of less than or
equal to 450.degree. C.
[0175] A sixty-sixth aspect includes the glass article of any of
the sixty-third through sixty-fourth aspects wherein the glass
article has a type HGA1 hydrolytic resistance according to ISO 720
after ion exchange strengthening.
[0176] A sixty-seventh aspect includes the glass article of any of
the sixty-fourth through sixty-sixth aspects which further
comprises a compressive stress with a depth of layer greater than
25 .mu.m.
[0177] A sixty-eighth aspect includes the glass article of the
sixty-seventh aspect wherein the depth of layer is greater than 35
.mu.m.
[0178] A sixty-ninth aspect includes the glass article of any of
the sixty-third through sixty-eighth aspects wherein the glass
article is ion exchange strengthened and the ion exchange
strengthening comprises treating the glass article in a molten salt
bath for a time less than or equal to 5 hours at a temperature less
than or equal to 450.degree. C.
[0179] A seventieth aspect includes the glass article of any of the
sixty-third through sixty-ninth aspects which further comprises a
surface compressive stress greater than or equal to 350 MPa.
[0180] A seventy-first aspect includes the glass article of any of
the sixty-third through seventieth aspects wherein the surface
compressive stress is greater than or equal to 400 MPa.
[0181] A seventy-second aspect includes the glass article of any of
the sixty-third through seventy-first aspects, wherein the glass
article is ion exchange strengthened and the ion exchange
strengthening comprises treating the glass article in a molten salt
bath for a time less than or equal to 5 hours at a temperature less
than or equal to 450.degree. C.
[0182] A seventy-second aspect includes the glass article of any of
the sixty-third through seventy-second aspects, wherein the glass
article is a beverage package, a food package, household glassware,
laboratory glassware, a cosmetics package, structural glazing,
automobile glazing, cookware, a lighting product, an ornamental
item, display glass, industrial tubing, or a scientific
instrument.
[0183] In a seventy-third aspect, a glass article may have a type
HGB1 hydrolytic resistance according to ISO 719. The glass article
may also have a compressive stress layer with a depth of layer of
greater than 25 .mu.m and a surface compressive stress of greater
than or equal to 350 MPa. The glass article may be ion exchange
strengthened and the ion exchange strengthening may include
treating the glass article in a molten salt bath for a time less
than or equal to 5 hours at a temperature less than or equal to
450.degree. C.
[0184] A seventy-fourth aspect includes, the glass article of the
seventy-third aspect, wherein the glass article has a type HGA1
hydrolytic resistance according to ISO 720 after ion exchange
strengthening.
[0185] A seventy-fifth aspect includes the glass article of any of
the seventy-third through seventy-fourth aspects, wherein the glass
article has a threshold diffusivity of greater than 16 .mu.m2/hr at
a temperature of less than or equal to 450.degree. C.
[0186] A seventy-sixth aspect includes the glass article of any of
the seventy-third through seventy-fifth aspects, wherein the
threshold diffusivity is greater than or equal to 20 .mu.m2/hr at a
temperature of less than or equal to 450.degree. C.
[0187] A seventy-seventh aspect includes the glass article of any
of the seventy-third through seventy-sixth aspects, wherein the
glass article is a beverage package, a food package, household
glassware, laboratory glassware, a cosmetics package, structural
glazing, automobile glazing, cookware, a lighting product, an
ornamental item, display glass, industrial tubing, or a scientific
instrument.
[0188] It will be apparent to those skilled in the art that various
modifications and variations can be made to the embodiments
described herein without departing from the spirit and scope of the
claimed subject matter. Thus it is intended that the specification
cover the modifications and variations of the various embodiments
described herein provided such modification and variations come
within the scope of the appended claims and their equivalents.
* * * * *