U.S. patent number RE46,337 [Application Number 14/955,372] was granted by the patent office on 2017-03-14 for boroalumino silicate glasses.
This patent grant is currently assigned to Corning Incorporated. The grantee listed for this patent is Corning Incorporated. Invention is credited to Adam J. Ellison.
United States Patent |
RE46,337 |
Ellison |
March 14, 2017 |
Boroalumino silicate glasses
Abstract
Disclosed are alkali-free glasses having a liquidus viscosity of
greater than or equal to about 90,000 poises, said glass comprising
SiO.sub.2, Al.sub.2O.sub.3, B.sub.2O.sub.3, MgO, CaO, and SrO such
that, in mole percent on an oxide basis:
64.ltoreq.SiO.sub.2.ltoreq.68.2;
11.ltoreq.Al.sub.2O.sub.3.ltoreq.13.5;
5.ltoreq.B.sub.2O.sub.3.ltoreq.9; 2.ltoreq.MgO.ltoreq.9;
3.ltoreq.CaO.ltoreq.9; and 1.ltoreq.SrO.ltoreq.5. The glasses can
be used to make a display glass substrates, such as thin film
transistor (TFT) display glass substrates for use in active matrix
liquid crystal display devices (AMLCDs) and other flat panel
display devices.
Inventors: |
Ellison; Adam J. (Corning,
NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated |
Corning |
NY |
US |
|
|
Assignee: |
Corning Incorporated (Corning,
NY)
|
Family
ID: |
1000002093361 |
Appl.
No.: |
14/955,372 |
Filed: |
December 1, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
61130474 |
May 30, 2008 |
|
|
|
Reissue of: |
12470968 |
May 22, 2009 |
8598055 |
Dec 3, 2013 |
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03C
3/091 (20130101); C03C 3/091 (20130101); C03C
3/087 (20130101); C03C 3/087 (20130101); Y02E
20/34 (20130101); Y02E 20/344 (20130101) |
Current International
Class: |
C03C
3/091 (20060101); C03C 3/087 (20060101) |
Field of
Search: |
;501/66,56,59,64,67 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1648087 |
|
Aug 2005 |
|
CN |
|
19939789 |
|
Feb 2001 |
|
DE |
|
10000839 |
|
May 2001 |
|
DE |
|
0714862 |
|
Mar 1999 |
|
EP |
|
0576362 |
|
Aug 1999 |
|
EP |
|
1705160 |
|
Sep 2006 |
|
EP |
|
1911725 |
|
Apr 2008 |
|
EP |
|
9-169539 |
|
Jun 1997 |
|
JP |
|
9-263421 |
|
Oct 1997 |
|
JP |
|
10-45422 |
|
Feb 1998 |
|
JP |
|
HEI 10-(1998)45422 |
|
Feb 1998 |
|
JP |
|
10-072237 |
|
Mar 1998 |
|
JP |
|
10-139467 |
|
May 1998 |
|
JP |
|
HEI 10-139467 |
|
May 1998 |
|
JP |
|
10-324526 |
|
Dec 1998 |
|
JP |
|
HEI 10-(1998)324526 |
|
Dec 1998 |
|
JP |
|
2002201040 |
|
Jul 2002 |
|
JP |
|
2004168597 |
|
Jun 2004 |
|
JP |
|
2005-330176 |
|
Dec 2005 |
|
JP |
|
2006-0090175 |
|
Aug 2006 |
|
KR |
|
Primary Examiner: Kugel; Timothy J.
Attorney, Agent or Firm: Klee; Maurice M. Hardee; Ryan
T.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of priority to U.S. provisional
application No. 61/130,474, filed on May 30, 2008 and entitled
"BOROALUMINO SILICATE GLASSES," the content of which is relied upon
and incorporated herein by reference in its entirety.
Claims
The invention claimed is:
1. An alkali-free glass having a liquidus viscosity of greater than
or equal to about 90,000 poises, a melting temperature less than or
equal to about 1620.degree. C.. and an anneal point greater than or
equal to about 725.degree. C., said glass comprising SiO.sub.2,
Al.sub.2O.sub.3, B.sub.2O.sub.3, MgO, CaO, SrO, SnO.sub.2, and
Fe.sub.2O.sub.3, such that, in mole percent on an oxide basis:
64.ltoreq.SiO.sub.2.ltoreq.68.2;
11.ltoreq.Al.sub.2O.sub.3.ltoreq.13.5;
5.ltoreq.B.sub.2O.sub.3.ltoreq.9; 2.ltoreq.MgO.ltoreq.9;
3.ltoreq.CaO.ltoreq.9; 1.ltoreq.SrO.ltoreq.5;
0.02.ltoreq.SnO.sub.2.ltoreq.0.3; and
0.005.ltoreq.Fe.sub.2O.sub.3.ltoreq.0.08; wherein: (i) the glass
comprises less than 0.05% by weight of Sb.sub.2O.sub.3,
As.sub.2O.sub.3, or combinations thereof; (ii) the BaO content of
the glass on an oxide basis is less than 1000 ppm by weight; and
(iii) the glass is in the form of a plate produced by a fusion draw
process.
2. An alkali-free glass according to claim 1 wherein said glass has
a liquidus viscosity of greater than or equal to about 100,000
poises and a liquidus temperature of lower than or equal to about
1200.degree. C.
3. An alkali-free glass according to claim 1 wherein said glass has
a linear coefficient of thermal expansion over the temperature
range of 0.degree. C. to 300.degree. C. of less than or equal to
about 40.times.10.sup.-7/.degree. C.
4. An alkali-free glass according to claim 1, wherein, in mole
percent on an oxide basis:
11.3.ltoreq.Al.sub.2O.sub.3.ltoreq.13.5.
5. An alkali-free glass according to claim 1, wherein, in mole
percent on an oxide basis:
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.45;
0.67.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.92; and
0.45.ltoreq.CaO/(CaO+SrO).ltoreq.0.9; and the glass has a liquidus
temperature of lower than or equal to about 1200.degree. C.
6. An alkali-free glass according to claim 1, wherein, in mole
percent on an oxide basis:
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.3;
0.72.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.9; and
0.55.ltoreq.CaO/(CaO+SrO).ltoreq.0.9.
7. An alkali-free glass according to claim 1, wherein, in mole
percent on an oxide basis:
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.3;
0.72.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.9; and
0.8.ltoreq.CaO/(CaO+SrO).ltoreq.0.9.
8. An alkali-free glass according to claim 1 wherein the glass
contains one or more of CeO.sub.2, and Br.
9. An alkali-free glass according to claim 1, wherein .Iadd.in mole
percent.Iaddend.: F+Cl+Br.ltoreq.0.4.
10. An alkali-free glass according to claim 1, wherein said glass
has a liquidus viscosity of greater than or equal to about 100,000
poises.
11. An alkali-free glass according to claim 1, wherein said glass
has a liquidus viscosity of greater than or equal to about 130,000
poises.
12. An alkali-free glass according to claim 1, wherein said glass
has a liquidus temperature of lower than or equal to about
1200.degree. C.
13. A glass substrate.[., such as a display glass substrate,.].
comprising an alkali-free glass according to claim 1.
14. A glass substrate according to claim 13, wherein the
.[.alkali-free glass is substantially defect-free.]. .Iadd.glass
substrate is a display glass substrate.Iaddend..
15. A flat panel display device comprising a flat, transparent
glass substrate carrying polycrystalline silicon thin film
transistors, wherein said glass substrate comprises an alkali-free
glass according to claim 1.
.Iadd.16. A method of making a glass plate comprising melting,
fining, and forming batch materials so that the glass of the glass
plate is alkali-free and comprises SiO.sub.2, Al.sub.2O.sub.3,
B.sub.2O.sub.3, MgO, CaO, and SrO, wherein the method comprises
using the following relationships to select the batch materials:
1.05.ltoreq.R.sub.o.ltoreq.1.45; 0.67.ltoreq.S.sub.o.ltoreq.0.92;
and 0.45.ltoreq.C.sub.o.ltoreq.0.95; where R.sub.o, S.sub.o, and
C.sub.o are given by: R.sub.o=(MgO+CaO+SrO)/Al.sub.2O.sub.3;
S.sub.o=(CaO+SrO)/Al.sub.2O.sub.3; and C.sub.o=CaO/(CaO+SrO); where
Al.sub.2O.sub.3, MgO, CaO, and SrO are in mole percent on an oxide
basis..Iaddend.
.Iadd.17. The method of claim 16 wherein the glass plate is formed
by a downdraw process..Iaddend.
.Iadd.18. The method of claim 17 wherein the downdraw process is a
fusion downdraw process..Iaddend.
.Iadd.19. The method of claim 16 further comprising using the glass
plate as a substrate for a silicon semiconductor..Iaddend.
.Iadd.20. The method of claim 16 further comprising using the glass
plate as a substrate for a flat panel display device..Iaddend.
.Iadd.21. A method of making a glass plate comprising melting,
fining, and forming batch materials so that the glass of the glass
plate is alkali-free and comprises SiO.sub.2, Al.sub.2O.sub.3,
B.sub.2O.sub.3, MgO, CaO, and SrO; where, in mole percent on an
oxide basis: 64.ltoreq.SiO.sub.2.ltoreq.68.2;
11.ltoreq.Al.sub.2O.sub.3.ltoreq.13.5;
5.ltoreq.B.sub.2O.sub.3.ltoreq.9; 2.ltoreq.MgO.ltoreq.9;
3.ltoreq.CaO.ltoreq.9; and 1.ltoreq.SrO.ltoreq.4.5; and where: (i)
the glass of the glass plate has a liquidus viscosity greater than
or equal to about 90,000 poises; (ii) the glass of the glass plate
has an anneal point greater than or equal to about 725.degree. C.;
and (iii) the BaO content of the glass of the glass plate on an
oxide basis is less than 1000 ppm by weight..Iaddend.
.Iadd.22. The method of claim 21 wherein the glass plate is formed
by a downdraw process..Iaddend.
.Iadd.23. The method of claim 22 wherein the downdraw process is a
fusion downdraw process..Iaddend.
.Iadd.24. The method of claim 21 further comprising using the glass
plate as a substrate for a silicon semiconductor..Iaddend.
.Iadd.25. The method of claim 21 further comprising using the glass
plate as a substrate for a flat panel display device..Iaddend.
Description
TECHNICAL FIELD
The present invention relates, generally, to glasses and, more
particularly, to boroalumino silicate glasses and to methods for
making and using same.
BACKGROUND
Displays may be broadly classified into one of two types: emissive
(e.g., CRTs and plasma display panels (PDPs)) or non-emissive. This
latter family, to which liquid crystal displays (LCDs) belong,
relies upon an external light source, with the display only serving
as a light modulator. In the case of liquid crystal displays, this
external light source may be either ambient light (used in
reflective displays) or a dedicated light source (such as found in
direct view displays).
Liquid crystal displays rely upon three inherent features of liquid
crystal (LC) materials to modulate light. The first is the ability
of LC materials to cause optical rotation of polarized light.
Second is the dependence of such rotation on the mechanical
orientation of the liquid crystal. Third is the ability of the
liquid crystal to undergo mechanical orientation by the application
of an external electric field.
In the construction of a simple, twisted nematic (TN) liquid
crystal display, two substrates surround a layer of liquid crystal
material. In a display type known as Normally White, the
application of alignment layers on the inner surfaces of the
substrates creates a 90.degree. spiral of the liquid crystal
director. This means that the polarization of linearly polarized
light entering one face of the liquid crystal cell will be rotated
90.degree. by the liquid crystal material. Polarization films,
oriented 90.degree. to each other, are placed on the outer surfaces
of the substrates.
Light, upon entering the first polarization film becomes linearly
polarized. Traversing the liquid crystal cell, the polarization of
this light is rotated 90.degree. and is allowed to exit through the
second polarization film. Application of an electric field across
the liquid crystal layer aligns the liquid crystal directors with
the field, interrupting its ability to rotate light. Linearly
polarized light passing through this cell does not have its
polarization rotated and hence is blocked by the second
polarization film. Thus, in the simplest sense, the liquid crystal
material becomes a light valve, whose ability to allow or block
light transmission is controlled by the application of an electric
field.
The above description pertains to the operation of a single pixel
in a liquid crystal display. High information type displays require
the assembly of several million of these pixels, which are referred
to in the art as sub pixels, into a matrix format. Addressing all
of these sub pixels, i.e., applying an electric field to all of
these sub pixels, while maximizing addressing speed and minimizing
cross-talk presents several challenges. One of the preferred ways
to address sub pixels is by controlling the electric field with a
thin film transistor located at each sub pixel, which forms the
basis of active matrix liquid crystal display devices (AMLCDs).
The manufacturing of these displays is extremely complex, and the
properties of the substrate glass can be extremely important when
producing displays having optimal performance. We have described
some suitable substrate glasses in U.S. Pat. No. 6,060,168 to
Kohli, U.S. Pat. No. 6,319,867 to Chacon et al., U.S. Pat. No.
6,831,029 to Chacon et al., and U.S. Pat. No. RE38,959 to Kohli.
However, a need for glasses that can be used as substrates in the
manufacture of active matrix liquid crystal display devices
(AMLCDs) and other flat panel displays continues to exist, and the
present invention is directed, in part, to addressing this
need.
One technical issue facing the glass substrates for LCD displays,
especially those displays made by high-temperature processes such
as polysilicon technology, is the density change (compaction, or
thermal stability) of the glass sheets after they are subjected to
high-temperature treatment steps. The compaction of the glass
sheets can lead to lack of registration of the semiconductor
features created on the surface of the substrates, hence
lower-quality or defective displays. Thermal stability of the glass
sheet is dependent on the glass composition and thermal history
thereof. Whereas a rigorously annealed glass sheet would have less
compaction in down-stream processing, obtaining such
thermodynamically stable glass sheet is difficult and could incur
prohibitive costs to the manufacture process by requiring either a
secondary heat treatment and/or a low production rate. It has been
found that anneal point of the glass material correlates with the
thermal stability of a glass sheet. For glass sheets produced by a
given thermal process, the higher the anneal point of the glass
material, the less the compaction of the glass sheets made
therefrom.
The present invention addresses the various technical issues
discussed supra.
SUMMARY
The present invention relates to an alkali-free glass having a
liquidus viscosity of greater than or equal to about 90,000 poises,
said glass comprising SiO.sub.2, Al.sub.2O.sub.3, B.sub.2O.sub.3,
MgO, CaO, and SrO such that, in mole percent on an oxide basis:
64.ltoreq.SiO.sub.2.ltoreq.68.2;
11.ltoreq.Al.sub.2O.sub.3.ltoreq.13.5;
5.ltoreq.B.sub.2O.sub.3.ltoreq.9; 2.ltoreq.MgO.ltoreq.9;
3.ltoreq.CaO.ltoreq.9; and 1.ltoreq.SrO.ltoreq.5.
These and additional features and embodiments of the present
invention will be more fully illustrated and discussed in the
following drawings and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing compaction after one hour at 450.degree.
C. for glasses with a range of anneal points.
FIG. 2 is a graph of predicted SiO.sub.2 content vs. measured
SiO.sub.2 content for a variety of glasses in accordance with the
present invention.
FIG. 3 is a graph of predicted MgO content vs. measured MgO content
for a variety of glasses in accordance with the present
invention.
FIG. 4 is a graph of melting temperature of various glasses of the
present invention as a function of SiO.sub.2 content.
DETAILED DESCRIPTION
Before the present materials, articles, and/or methods are
disclosed and described, it is to be understood that the aspects
described below are not limited to specific materials, preparative
methods, or uses, but is to be understood to be illustrative of the
invention. It is also to be understood that the terminology used
herein is for the purpose of describing particular aspects only and
is not intended to be limiting.
Throughout this specification and claims, unless the context
requires otherwise, the word "comprise" or variations, such as
"comprises" or "comprising", will be understood to imply the
inclusion of a stated element but not the exclusion of any other
element or group of elements.
It must be noted that, as used in the specification and the
appended claims, the singular forms "a", "an", and "the" include
plural referents unless the context clearly dictates otherwise.
Thus, for example, reference to "a fining agent" is meant to
include mixtures of two or more such fining agents; reference to
"the glass former" is meant to include mixtures of two or more such
glass formers; and the like.
"Optional" or "optionally" means that the subsequently described
event or circumstance can or cannot occur, and that the description
includes instances where the event or circumstance occurs and
instances where it does not.
When values are expressed as approximations, e.g., by use of the
antecedent "about" as in "`about` a particular value", it will be
understood that the particular value forms another aspect of the
invention. Ranges may be expressed herein as "from `about` one
particular value to `about` another particular value", as "less
than `about` a particular value", as "`about` a particular value or
greater", etc. When such ranges are expressed, another aspect of
the invention includes "from the one particular value to the other
particular value", "less than the particular value", and "the
particular value or greater", respectively. It will be further
understood that the endpoints of each of the ranges are significant
both in relation to the other endpoint, and independently of the
other endpoint; and, in cases where no lower endpoint is stated in
a range, the lower endpoint is meant to be and include zero.
A weight percent of a component, unless specifically stated to the
contrary, is based on the total weight of the formulation or
composition in which the component is included. Similarly, a mole
percent of a component, unless specifically stated to the contrary,
is based on the total number of moles of all components in the
formulation or composition in which the component is included.
As discussed above, the present invention relates to an alkali-free
glass that includes SiO.sub.2, Al.sub.2O.sub.3, B.sub.2O.sub.3,
MgO, CaO, and SrO, and the glass can further include a variety of
other components. The SiO.sub.2, Al.sub.2O.sub.3, B.sub.2O.sub.3,
MgO, CaO, SrO, and other components (if any) are chosen such that
the glass includes, as calculated in mole percent on an oxide
basis: 64-68.2SiO.sub.2, 11-13.5Al.sub.2O.sub.3, 5-9B.sub.2O.sub.3,
2-9, MgO, 3-9CaO, and 1-5SrO.
As used herein, "alkali-free" means that the glass (i) is
essentially free of intentionally added alkali metal oxide, for
example, to avoid the possibility of having a negative impact on
thin film transistor (TFT) performance through diffusion of alkali
ions from the glass into the silicon of the TFT; (ii) contains a
total of less than about 0.1 mol % of alkali metal oxides; or (iii)
both.
In certain embodiments, the glass includes, as calculated in mole
percent on an oxide basis, 64-68SiO.sub.2. In certain embodiments,
the glass includes, as calculated in mole percent on an oxide
basis, 11.3-13.5Al.sub.2O.sub.3.
In certain embodiments, the glass satisfies one or more of the
following expressions:
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.45;
0.67.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.92; and
0.45.ltoreq.CaO/(CaO+SrO).ltoreq.0.95.
For example, in certain embodiments, the glass satisfying the above
immediate requirements further has a liquidus temperature of lower
than or equal to about 1200.degree. C., and a melting temperature
of lower than or equal to about 1620.degree. C.
For example, in certain embodiments, the glass satisfies the first
of the aforementioned expressions
(1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.45). In certain
embodiments, the glass satisfies the second of the aforementioned
expressions (0.67.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.92). In
certain embodiments, the glass satisfies the third of the
aforementioned expressions (0.45.ltoreq.CaO/(CaO+SrO).ltoreq.0.95).
In certain embodiments, two or more of the aforementioned
expressions are satisfied. In certain embodiments, all three of the
aforementioned expressions are satisfied. By way of further
illustration, in certain embodiments, the glass satisfies all three
of the following expressions:
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.3;
0.72.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.9; and
0.55.ltoreq.CaO/(CaO+SrO).ltoreq.0.95, such as in the case where
the glass satisfies all three of the following expressions:
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.3;
0.72.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.9; and
0.8.ltoreq.CaO/(CaO+SrO).ltoreq.0.95.
The glasses of the present invention (e.g., any of the glasses
discussed above) can further include a variety of other
components.
For example, the glasses of the present invention can further
include SnO.sub.2, Fe.sub.2O.sub.3, CeO.sub.2, As.sub.2O.sub.3,
Sb.sub.2O.sub.3, Cl, Br, or combinations thereof. These materials
can be added as fining agents (e.g., to facilitate removal of
gaseous inclusions from melted batch materials used to produce the
glass) and/or for other purposes. In certain embodiments, the
glasses of the present invention (e.g., any of the glasses
discussed above) further include SnO.sub.2 (e.g., as calculated in
mole percent on an oxide basis, 0.02-0.3SnO.sub.2, etc.) and
Fe.sub.2O.sub.3 (e.g., as calculated in mole percent on an oxide
basis, 0.005-0.08Fe.sub.2O.sub.3, 0.01-0.08Fe.sub.2O.sub.3, etc.).
By way of illustration, in certain embodiments, the alkali-free
glass of the present invention further includes SnO.sub.2 and
Fe.sub.2O.sub.3, wherein, in mole percent on an oxide basis:
0.02.ltoreq.SnO.sub.2.ltoreq.0.3; and
0.005.ltoreq.Fe.sub.2O.sub.3.ltoreq.0.08.
In certain embodiments, the glasses of the present invention
include less than 0.05% (e.g., less than 0.04%, less than 0.03%,
less than 0.02%, less than 0.01%, etc.) by weight of
Sb.sub.2O.sub.3, As.sub.2O.sub.3, or combinations thereof. In
certain embodiments, the glasses of the present invention further
include SnO.sub.2, Fe.sub.2O.sub.3, CeO.sub.2, Cl, Br, or
combinations thereof and include less than 0.05% (e.g., less than
0.04%, less than 0.03%, less than 0.02%, less than 0.01%, etc.) by
weight of Sb.sub.2O.sub.3, As.sub.2O.sub.3, or combinations
thereof. In certain embodiments, the glasses of the present
invention further include SnO.sub.2 and Fe.sub.2O.sub.3 and include
less than 0.05% (e.g., less than 0.04%, less than 0.03%, less than
0.02%, less than 0.01%, etc.) by weight of Sb.sub.2O.sub.3,
As.sub.2O.sub.3, or combinations thereof. In certain embodiments,
the alkali-free glasses of the present invention further include
SnO.sub.2 and Fe.sub.2O.sub.3, wherein, in mole percent on an oxide
basis: 0.02.ltoreq.SnO.sub.2.ltoreq.0.3; and
0.005.ltoreq.Fe.sub.2O.sub.3.ltoreq.0.08, and include less than
0.05% (e.g., less than 0.04%, less than 0.03%, less than 0.02%,
less than 0.01%, etc.) by weight of Sb.sub.2O.sub.3,
As.sub.2O.sub.3, or combinations thereof.
The glasses of the present invention (e.g., any of the glasses
discussed above) can include F, Cl, or Br, for example, as in the
case where the glasses further include Cl and/or Br as fining
agents. For example, the glass can include fluorine, chlorine,
and/or bromine, wherein, as calculated in mole percent:
F+Cl+Br.ltoreq.0.4, such as where F+Cl+Br.ltoreq.0.3,
F+Cl+Br.ltoreq.0.2, F+Cl+Br.ltoreq.0.1,
0.001.ltoreq.F+Cl+Br.ltoreq.0.4, and/or
0.005.ltoreq.F+Cl+Br.ltoreq.0.4. By way of illustration, in certain
embodiments, the glass further includes SnO.sub.2 and
Fe.sub.2O.sub.3 and, optionally, fluorine, chlorine, and/or
bromine, such that, as calculated in mole percent on an oxide
basis: 0.02.ltoreq.SnO.sub.2.ltoreq.0.3,
0.005.ltoreq.Fe.sub.2O.sub.3.ltoreq.0.08, and F+Cl+Br.ltoreq.0.4;
and, in certain embodiments, the glass further includes SnO.sub.2
and Fe.sub.2O.sub.3 and, optionally, Sb.sub.2O.sub.3,
As.sub.2O.sub.3, fluorine, chlorine, and/or bromine, such that, as
calculated in mole percent on an oxide basis,
0.02.ltoreq.SnO.sub.2.ltoreq.0.3,
0.005.ltoreq.Fe.sub.2O.sub.3.ltoreq.0.08, and F+Cl+Br.ltoreq.0.4,
and such that the glass includes less than 0.05% (e.g., less than
0.04%, less than 0.03%, less than 0.02%, less than 0.01%, etc.) by
weight of Sb.sub.2O.sub.3, As.sub.2O.sub.3, or combinations
thereof.
The use of SnO.sub.2, Fe.sub.2O.sub.3, CeO.sub.2, As.sub.2O.sub.3,
Sb.sub.2O.sub.3, Cl, Br, or combinations thereof as fining can be
especially useful in the manufacture of glasses for certain
applications, such as substrates for flat panel displays. As
mentioned above, fining agents can be added, for example, to
produce glasses that are substantially defect-free by facilitating
removal of gaseous inclusions from melted batch materials used to
produce the glass. Illustratively, iron/tin fining can be used
alone or in combination with other fining techniques if desired.
For example, iron/tin fining can be combined with halide fining,
e.g., bromine fining. However, halide fining presents challenges
from a pollution abatement point of view, and halides can complex
with iron to produce glass with non-optimal transmission
characteristics. Other possible combinations include, but are not
limited to, iron/tin fining plus sulfate, sulfide, cerium oxide,
mechanical bubbling, and/or vacuum fining. However, optimization
may require that the sulfur content of the glass be controlled to
avoid the production of gaseous defects containing SO.sub.2 or
SO.sub.3; and the use of excessive amounts of iron or other
transition metal fining agents may impart undesirable coloration to
the glass.
The glasses of the present invention can further include BaO. In
certain embodiments, the glasses of the present invention include
less than 1000 ppm by weight of BaO.
As noted above, the glasses of the present invention are
"alkali-free". As also noted above, the alkali-free glasses of the
present invention can include alkali oxides (e.g., Li.sub.2O,
Na.sub.2O, K.sub.2O, etc), provided that the glass (i) is
essentially free of intentionally added alkali metal oxide; (ii)
contains a total of less than about 0.1 mol % of alkali metal
oxides; or (iii) both. For example, in those cases where the glass
is to be used as a thin film transistor (TFT) substrate, the
intentional inclusion of alkali oxides is generally viewed as being
undesirable owing to their negative impact on TFT performance. In
certain embodiments, the alkali-free glass of the present invention
includes intentionally added alkali oxides, but in amounts such
that the alkali-free glass contains less than 1000 ppm (e.g., less
than 700 ppm, less than 500 ppm, less than 200 ppm, less than 100
ppm, less than 50 ppm, etc.) by weight of alkali oxides (e.g., in
amounts such that the sum of Li.sub.2O, Na.sub.2O, and K.sub.2O is
less than 1000 ppm by weight). In certain embodiments, the
alkali-free glass of the present invention includes no
intentionally added alkali oxides, and the alkali-free glass
contains a total of less than about 0.1 mol % of alkali metal
oxides.
The glasses of the present invention can further include
contaminants as typically found in commercially prepared glass. In
addition or alternatively, a variety of other oxides (e.g.,
TiO.sub.2, MnO, ZnO, Nb.sub.2O.sub.5, MoO.sub.3, Ta.sub.2O.sub.5,
WO.sub.3, ZrO.sub.2, Y.sub.2O.sub.3, La.sub.2O.sub.3, and the like)
can be added so long as their addition does not push the
composition outside of the ranges described above. In those cases
where the glasses of the present invention further include such
other oxide(s), each of such other oxides are typically present in
an amount not exceeding 1 mole percent, and their total combined
concentration is typically less than or equal to 5 mole percent,
although higher amounts can be used so long as the amounts used do
not place the composition outside of the ranges described above.
The glasses of the invention can also include various contaminants
associated with batch materials and/or introduced into the glass by
the melting, fining, and/or forming equipment used to produce the
glass (e.g., ZrO.sub.2).
As mentioned above, in certain embodiments, the glass satisfies one
or more of the following expressions:
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.45;
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.3;
0.67.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.92;
0.72.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.9;
0.45.ltoreq.CaO/(CaO+SrO).ltoreq.0.95;
0.55.ltoreq.CaO/(CaO+SrO).ltoreq.0.95; and
0.8.ltoreq.CaO/(CaO+SrO).ltoreq.0.95.
Irrespective of whether the glass satisfies none, one, two, or
three, or more of the aforementioned expressions and irrespective
of whether the glass contains none, one, or more of additional
components (e.g., those discussed above), the SiO.sub.2,
Al.sub.2O.sub.3, B.sub.2O.sub.3, MgO, CaO, SrO, and other
components (if any) can be chosen such that, in mole percent on an
oxide basis: -0.3.ltoreq.SiO.sub.2-[SiO.sub.2].sub.pred.ltoreq.0.3
and -0.3.ltoreq.MgO-[MgO].sub.pred.ltoreq.0.3 in which
[SiO.sub.2].sub.pred=[87.57-6.06.times.MgO/B.sub.o+66.54.times.R.sub.o-80-
.61.times.S.sub.o].times.B.sub.o
[MgO].sub.pred=[1.29+12.94.times.R.sub.o-14.4.times.S.sub.o].times.B.sub.-
o and in which R.sub.o=(MgO+CaO+SrO)/Al.sub.2O.sub.3
S.sub.o=(CaO+SrO)/Al.sub.2O.sub.3 B.sub.o=1-B.sub.2O.sub.3/100.
Additionally or alternatively, the SiO.sub.2, Al.sub.2O.sub.3,
B.sub.2O.sub.3, MgO, CaO, SrO, and other components (if any) can be
chosen such that: 0.45.ltoreq.CaO/(CaO+SrO).ltoreq.0.8; such that
64.ltoreq.SiO.sub.2.ltoreq.68; such that
11.3.ltoreq.Al.sub.2O.sub.3.ltoreq.13.5; such that
0.02.ltoreq.SnO.sub.2.ltoreq.0.3; such that
0.005.ltoreq.Fe.sub.2O.sub.3.ltoreq.0.08; such that
F+Cl+Br.ltoreq.0.4; and/or such the glass includes less than 0.05%
(e.g., less than 0.04%, less than 0.03%, less than 0.02%, less than
0.01%, etc.) by weight of Sb.sub.2O.sub.3, As.sub.2O.sub.3, or
combinations thereof.
As mentioned above, the glasses of the present invention include
5-9B.sub.2O.sub.3. Examples of such glasses include those in which
contain, as calculated in mole percent on an oxide basis:
5-8.8B.sub.2O.sub.3, 5-8.5B.sub.2O.sub.3, 5-8.2B.sub.2O.sub.3,
and/or 5-8B.sub.2O.sub.3.
Also as mentioned above, the glasses of the present invention
include 2-9MgO. Examples of such glasses include those which
contain, as calculated in mole percent on an oxide basis: 2-8MgO,
2-7MgO, 2-6MgO, 2.5-9MgO, 2.5-8MgO, 2.5-8MgO, 2.5-7MgO and/or
2.5-6MgO.
Also as mentioned above, the glasses of the present invention
include 1-5SrO. Examples of such glasses include those which
contain, as calculated in mole percent on an oxide basis: 1-4.5SrO,
1-4SrO, 1-3.5SrO, 1.5-5SrO, 1.5-4.5SrO, 1.5-4SrO, 1.5-3.5SrO,
2.5-3.5SrO, and/or 2.5-5SrO.
In certain embodiments, the SiO.sub.2, Al.sub.2O.sub.3,
B.sub.2O.sub.3, MgO, CaO, SrO, and other components (if any) are
chosen such that the glass includes, as calculated in mole percent
on an oxide basis: 64-68.2SiO.sub.2, 11-13.5Al.sub.2O.sub.3,
5-9B.sub.2O.sub.3, 2-9, MgO, 3-9CaO, and 1-3.5SrO.
In certain embodiments, the SiO.sub.2, Al.sub.2O.sub.3,
B.sub.2O.sub.3, MgO, CaO, SrO, and other components (if any) are
chosen such that the glass includes, as calculated in mole percent
on an oxide basis: 64-68.2SiO.sub.2, 11-13.5Al.sub.2O.sub.3,
5-9B.sub.2O.sub.3, 2.5-6, MgO, 3-9CaO, and 1-5SrO.
In certain embodiments, the SiO.sub.2, Al.sub.2O.sub.3,
B.sub.2O.sub.3, MgO, CaO, SrO, and other components (if any) are
chosen such that the glass includes, as calculated in mole percent
on an oxide basis: 64-68.2SiO.sub.2, 11-13.5Al.sub.2O.sub.3,
5-8B.sub.2O.sub.3, 2-9, MgO, 3-9CaO, and 1-5SrO.
In certain embodiments, the SiO.sub.2, Al.sub.2O.sub.3,
B.sub.2O.sub.3, MgO, CaO, SrO, and other components (if any) are
chosen such that the glass includes, as calculated in mole percent
on an oxide basis: 64-68.2SiO.sub.2, 11-13.5Al.sub.2O.sub.3,
5-8B.sub.2O.sub.3, 2.5-6, MgO, 3-9CaO, and 1-3.5SrO.
In certain embodiments, the glasses of the present invention have
densities of less than about 2.6 g/cm.sup.3, such as densities of
less than 2.6 g/cm.sup.3, densities of less than about 2.56
g/cm.sup.3, densities of less than 2.56 g/cm.sup.3, densities of
from about 2.4 g/cm.sup.3 to about 2.6 g/cm.sup.3, densities of
from 2.4 g/cm.sup.3 to 2.6 g/cm.sup.3, densities of from about 2.45
g/cm.sup.3 to about 2.6 g/cm.sup.3, densities of from 2.45
g/cm.sup.3 to 2.6 g/cm.sup.3, etc.
In certain embodiments, the glasses of the present invention have
liquidus temperatures of lower than or equal to about 1200.degree.
C., such as liquidus temperatures lower than or equal to about
1190.degree. C., liquidus temperatures lower than or equal to about
1180.degree. C., liquidus temperatures lower than or equal to about
1170.degree. C., liquidus temperatures lower than or equal to about
1160.degree. C., liquidus temperatures lower than or equal to about
1150.degree. C., liquidus temperatures lower than or equal to about
1140.degree. C., liquidus temperatures lower than or equal to about
1130.degree. C., liquidus temperatures lower than or equal to about
1120.degree. C., liquidus temperatures lower than or equal to about
1110.degree. C., and liquidus temperatures lower than or equal to
about 1100.degree. C.
As mentioned above, the glasses of the present invention have
liquidus viscosities of greater than or equal to about 90,000.
Illustratively, in certain embodiments, the glasses of the present
invention have liquidus viscosities of greater than or equal to
90,000 poises, such as greater than or equal to about 100,000
poises, greater than or equal to 100,000 poises, greater than or
equal to about 110,000 poises, greater than or equal to 110,000
poises, greater than or equal to about 120,000 poises, greater than
or equal to 120,000 poises, greater than or equal to about 130,000
poises, greater than or equal to 130,000 poises, greater than or
equal to about 140,000 poises, greater than or equal to 140,000
poises, greater than or equal to about 150,000 poises, greater than
or equal to 150,000 poises, greater than or equal to about 160,000
poises, greater than or equal to 160,000 poises, greater than or
equal to about 170,000 poises, greater than or equal to 170,000
poises, greater than or equal to about 180,000 poises, greater than
or equal to 180,000 poises, etc.
In certain embodiments, the glasses of the present invention have
linear coefficients of thermal expansion over the temperature range
of 0.degree. C. to 300.degree. C. of less than or equal to about
40.times.10.sup.-7/.degree. C., such as less than or equal to
40.times.10.sup.-7/.degree. C.; less than or equal to about
39.times.10.sup.-7/.degree. C.; less than or equal to
39.times.10.sup.-7/.degree. C.; less than or equal to about
38.times.10.sup.-7/.degree. C.; less than or equal to
38.times.10.sup.-7/.degree. C.; less than or equal to about
37.times.10.sup.-7/.degree. C.; less than or equal to
37.times.10.sup.-7/.degree. C.; less than or equal to about
36.times.10.sup.-7/.degree. C.; less than or equal to
36.times.10.sup.-7/.degree. C.; from about
33.times.10.sup.-7/.degree. C. to about 40.times.10.sup.-7/.degree.
C.; from 33.times.10.sup.-7/.degree. C. to
40.times.10.sup.-7/.degree. C.: from about
33.times.10.sup.-7/.degree. C. to about 36.times.10.sup.-7/.degree.
C.; from 33.times.10.sup.-7/.degree. C. to
36.times.10.sup.-7/.degree. C.; etc.
In certain embodiments, the glasses of the present invention have
strain points of greater than or equal to about 680.degree. C.,
such as greater than or equal to 680.degree. C., greater than or
equal to about 685.degree. C., greater than or equal to 685.degree.
C., greater than or equal to about 690.degree. C., greater than or
equal to 690.degree. C., etc.
In certain embodiments, the glasses of the present invention have
anneal points of greater than or equal to about 725.degree. C.,
such as greater than or equal to 725.degree. C., greater than or
equal to about 730.degree. C., greater than or equal to 730.degree.
C., greater than or equal to about 735.degree. C., greater than or
equal to 735.degree. C., greater than or equal to about 745.degree.
C., greater than or equal to 745.degree. C., from about 725.degree.
C. to about 760.degree. C., from 725.degree. C. 760.degree. C.,
from about 735.degree. C. to about 760.degree. C., from 735.degree.
C. to 760.degree. C., etc.
In certain embodiments, the glasses of the present invention have
melting temperatures of less than or equal to about 1620.degree.
C., such as less than or equal to 1620.degree. C., less than or
equal to about 1615.degree. C., less than or equal to 1615.degree.
C., less than or equal to about 1610.degree. C., less than or equal
to 1610.degree. C., etc.
In certain embodiments, the glasses of the present invention have
specific moduli of greater than or equal to about 30.5 GPacc/g,
such as greater than or equal to 30.5 GPacc/g, greater than or
equal to about 31.5 GPacc/g, greater than or equal to 31.5 GPacc/g,
etc.
The glasses can be produced in a variety of glass shapes, for
example, glass plates (e.g., glass plates having a thickness of
from about 30 .mu.m to about 2 mm, such as from 30 .mu.m to 2 mm,
from about 100 .mu.m to about 1 mm, from 10 .mu.m to 1 mm,
etc.).
The sources of the various oxides contained in glasses of the
present invention are not particularly critical. Batch ingredients
can include fine sand, alumina, boric acid, magnesium oxide,
limestone strontium carbonate, strontium nitrate, tin oxide,
etc.
For example, SiO.sub.2 is typically added as a crushed sand made of
alpha quartz, either from loose sand deposits or mined from
sandstone or quartzite. While these are commercially available at
low cost, other crystalline or amorphous forms of SiO.sub.2 can be
substituted in part or in whole with little impact on melting
behavior. Because molten SiO.sub.2 is very viscous and dissolves
slowly into alkali-free glass, it is generally advantageous that
the sand be crushed so that at least 85% of it passes through a
U.S. mesh size of 100, corresponding to mesh opening sizes of about
150 microns. In production, fines may be lofted by batch transfer
processes or by air-handling equipment, and, to avoid the health
hazards this presents, it may be desirable to remove the smallest
fraction of crushed sand as well.
Alumina is typically used as the source of Al.sub.2O.sub.3.
Boric acid is typically used as the source of B.sub.2O.sub.3.
In addition to the glass formers (SiO.sub.2, Al.sub.2O.sub.3, and
B.sub.2O.sub.3), the glasses of the invention also include MgO,
CaO, and SrO. As known in the art, the alkaline earths are
typically added as oxides (especially MgO), carbonates (CaO and
SrO), nitrates (CaO and SrO), and/or hydroxides (MgO, CaO, and
SrO). In the case of MgO and CaO, naturally-occurring minerals that
can serve as sources include dolomite
(Ca.sub.x,Mg.sub.1-x)CO.sub.3), magnesite (MgCO.sub.3), brucite
(Mg(OH).sub.2), talc (Mg.sub.3Si.sub.4O.sub.10(OH).sub.2), olivine
(Mg.sub.2SiO.sub.4), and limestone (CaCO.sub.3). These natural
sources include iron and so can be used as a way of adding this
component in those cases where iron oxide is to be present in the
glass.
The glasses of the invention can be manufactured using various
techniques known in the art. For example, glass plates can be made
using a downdraw process, such as by a fusion downdraw process.
Compared to other forming processes, such as the float process, the
fusion process may be preferred in certain circumstances for
several reasons. For example, glass substrates made from the fusion
process require less polishing or do not require polishing,
depending, of course, on the desired surface roughness of the final
product. By way of further illustration, glass substrates made from
the fusion process can have reduced average internal stress,
relative to glasses made using other processes.
The glasses of the present invention can be used in a variety of
applications.
Illustratively, they can be used as a substrate for a silicon
semiconductor. For example, the glasses of the present invention
can be used to make display glass substrates, such as display glass
substrates having thicknesses of from about 30 .mu.m to about 2 mm
(e.g., from 30 .mu.m to 2 mm, from about 100 .mu.m to about 1 mm,
from 10 .mu.m to 1 mm, etc.). Examples of display glass substrates
include TFT display glass substrates, such as a TFT display glass
substrates for flat panel display devices.
The present invention also relates to a semiconductor assembly that
includes a semiconductor disposed on a glass substrate, wherein
said glass substrate comprises an alkali-free glass of the present
invention. Examples of semiconductors that can be used in the
aforementioned semiconductor assemblies include transistors,
diodes, silicon transistors, silicon diodes, and other silicon
semiconductors; field effect transistors (FETs), thin-film
transistors (TFTs), organic light-emitting diodes (OLEDs) and other
light-emitting diodes; as well as semiconductors that are useful in
electro-optic (EO) applications, in two photon mixing applications,
in non-linear optical (NLO) applications, in electroluminescent
applications, and in photovoltaic and sensor applications.
The present invention also relates to a flat panel display device
that includes a flat, transparent glass substrate carrying
polycrystalline silicon thin film transistors, wherein said glass
substrate comprises an alkali-free glass of the present invention.
The alkali-free glass includes SiO.sub.2, Al.sub.2O.sub.3,
B.sub.2O.sub.3, MgO, CaO, and SrO such that, in mole percent on an
oxide basis: 64.ltoreq.SiO.sub.2.ltoreq.68.2;
11.ltoreq.Al.sub.2O.sub.3.ltoreq.13.5;
5.ltoreq.B.sub.2O.sub.3.ltoreq.9; 2.ltoreq.MgO.ltoreq.9;
3.ltoreq.CaO.ltoreq.9; and 1.ltoreq.SrO.ltoreq.5. Examples of
suitable glasses from which the glass substrates can be made
include those discussed above, for example, glasses which satisfy
the following expressions:
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.45;
0.67.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.92; and
0.45.ltoreq.CaO/(CaO+SrO).ltoreq.0.95. Typically, in the case of a
flat panel display device, the device includes two plates
(substrate assemblies) that are manufactured separately. One, the
color filter plate, has a series of red, blue, green, and black
organic dyes deposited on it. Each of these primary colors
corresponds precisely with a sub pixel of the companion active
plate. The active plate, so called because it contains the active,
thin film transistors (TFTs), is manufactured using typical
semiconductor type processes. These include sputtering, CVD,
photolithography, and etching.
In certain embodiments, the alkali-free glass used in the
aforementioned substrates (e.g., display glass substrates) can be
substantially defect-free. As discussed above, alkali-free glasses
of the present invention that are substantially defect-free can be
produced, for example, by using one or more fining agents, such as
SnO.sub.2, Fe.sub.2O.sub.3, CeO.sub.2, As.sub.2O.sub.3,
Sb.sub.2O.sub.3, Cl, Br, or combinations thereof. Examples of
suitable combinations are set forth above. Illustratively, the
glass can include, as fining agents, SnO.sub.2 and Fe.sub.2O.sub.3;
0.02-0.3SnO.sub.2 and 0.005-0.08Fe.sub.2O.sub.3; less than 0.05% by
weight of Sb.sub.2O.sub.3 and/or As.sub.2O.sub.3; SnO.sub.2,
Fe.sub.2O.sub.3, CeO.sub.2, Cl, Br, or combinations thereof but
less than 0.05% by weight of Sb.sub.2O.sub.3 and/or
As.sub.2O.sub.3; SnO.sub.2 and Fe.sub.2O.sub.3 but less than 0.05%
by weight of Sb.sub.2O.sub.3 and/or As.sub.2O.sub.3; and/or
0.02-0.3SnO.sub.2 and 0.005-0.08Fe.sub.2O.sub.3 but less than 0.05%
by weight of Sb.sub.2O.sub.3 and/or As.sub.2O.sub.3.
It is believed that the glasses of the present invention are
particularly advantageous in the manufacture of certain substrates
for active matrix liquid crystal display devices (AMLCDs). For
example, AMLCD substrates optimally meet a variety of customer
requirements, several of which are strongly dependent on the fusion
process itself. One of these, a pristine surface, is believed to be
an attribute of fusion, and partially explains why customers are
drawn to substrates made by the fusion process. Another customer
requirement is geometric stability under thermal cycling, and in
this matter the fusion process sometimes comes up short. Because,
in the fusion process, the glass temperature decreases rather
quickly from the forming temperatures (e.g., in excess of
1100.degree. C.) to well below the glass transition temperature
(e.g., about 720.degree. C. for certain products), the glass has a
slightly expanded volume relative to its fully relaxed state, or
the state that would be obtained if the glass were held near
T.sub.g for a considerable length of time. When the glass is
reheated, it naturally relaxes towards its equilibrium volume, and
this three-dimensional contraction or relaxation as sometimes
referred to as "compaction".
Illustratively, for a given draw (and its own specific cooling
profile), and for a particular glass being made into a particular
product (e.g., thickness, area, etc.), the rate of cooling can be
determined almost entirely by the rate (in inches per minute) at
which the sheet comes off the draw. This rate is sometimes referred
to as the "pulling roll speed". From draw to draw, it has been
found that increasing the pulling roll speed can increase
compaction.
If melting takes place at a constant rate (e.g., 900 lbs per hour),
then delivering glass onto a longer isopipe slows down the rate at
which glass is removed, and hence lowers compaction. Thus, as
larger sizes of glass panel substrates are made on a particular
tank, a reprieve (of sorts) is obtained for the compaction problem.
However, to improve efficiency, it is often desirable to make as
many square feet of glass from a given draw as possible. One way to
do this is to increase the melt rate, but this can push the system
toward the compaction limit. This can be especially true of tanks
with smaller isopipes, where high pulling roll rates can result in
glasses close to acceptable limits of compaction (e.g., close to
the compaction resulting from a 450.degree. C. isothermal hold for
one hour).
To pull more glass off of existing assets (i.e., without increasing
the size of tanks and isopipes), pulling roll rates can be
increased, but this may result in glasses having too high
compaction. While it may be possible to revamp the thermal profile
of a draw so as to slow the rate of cooling through the critical
viscosity region, thus reducing compaction, there are practical
limits to how far this can be taken. For example, at some point,
the draw must become higher to allow for slower cooling at a high
pulling roll speed, and this reinvigorates the problem of getting
more glass out of an existing (as opposed to completely redesigned
and rebuilt) asset.
Research shows that isothermal holds of glasses produce less
compaction as the strain or anneal point of a glass increases. FIG.
1 shows compaction after one hour at 450.degree. C. for glasses
with a range of anneal points. Prior to the 450.degree. C. heat
treatment, the glasses were subjected to a thermal cycle intended
to be similar to the cooling profile of a glass coming off of a
fusion draw (e.g., prolonged exposure to high temperature, then
rapid cooling at a rate similar to that used in a fusion draw). As
can be seen from FIG. 1, as anneal point increases, compaction
decreases; however, above an anneal point of about 760.degree. C.,
the additional gain in compaction performance for a given increase
in anneal point diminishes rapidly. The glasses with the highest
anneal point in FIG. 1 are intended for low-temperature polysilicon
("pSi") applications.
By way of further illustration, the compositions of the present
invention can be optimized so as to have liquidus viscosities of 90
kpoise or greater, melting temperatures of 1620.degree. C. or less,
anneal points of 725.degree. C. or greater, and/or specific moduli
of 30.5 GPacc/g or greater. It is believed that compositions of the
present invention having a combination of high modulus and anneal
point can especially desirable for use in certain fusion draw
processes, such as for fusion draw processes at high cooling
rates.
While not intending to be bound or otherwise limited by any theory
by which certain glasses of the present invention may operate, it
is believed that elevated anneal points may provide enhanced
geometric stability during amorphous silicon ("aSi") processing and
may permit higher draw speeds without recourse to annealing or
expensive equipment redesign. It is also believed (again, without
intending to be limited by any theory by which certain glasses of
the present invention may operate) that high level of fluxes and
comparatively low melting temperatures can accelerate melting and,
consequently, may allow for higher melting rates without a
corresponding increase in defects.
Compositions of the glasses of the invention can be determined
using quantitative analysis techniques well known in the art.
Suitable techniques are X-ray fluorescence spectrometry (XRF) for
elements with an atomic number higher than 8, inductively coupled
plasma optical emission spectrometry (ICP-OES), inductively coupled
plasma mass spectrometry (ICP-MS), and electron microprobe
analysis. See, for example, J. Nolte, ICP Emission Spectrometry: A
Practical Guide, Wiley-VCH (2003); H. E. Taylor, Inductively
Coupled Plasma Mass Spectroscopy: Practices and Techniques,
Academic Press (2000); and S. J. B. Reed, Electron Microprobe
Analysis, Cambridge University Press; 2nd edition (1997), which are
hereby incorporated by reference. For an analysis time of about 10
minutes for each element, detection limits of approximately 200 ppm
for F and approximately 20 ppm for Cl, Br, Fe, and Sn can be
readily achieved using electron microprobe analysis. For trace
elements, ICP-MS can be used.
The present invention is further illustrated by the following
non-limiting examples.
EXAMPLES
Example 1
This Example 1 and the following Examples 2 and 3 are meant to
describe how the present invention was made. These Examples are not
meant to, in any way, be limiting; instead, they are provided so
that one skilled in the art might have access to applicant's
thought process and may use this thought process, if appropriate,
to further develop that which is described here to optimize the
glasses of the present invention for use in particular
applications.
Several surprising insights led to this invention.
First was that the glasses with the best combination of liquidus
viscosity, melting temperature, and anneal point tended to have
similar proportions of SiO.sub.2, Al.sub.2O.sub.3, MgO, CaO, and
SrO when projected to B.sub.2O.sub.3-free compositions. To
understand this, it is easiest to consider the example of a single
glass, which will also serve to introduce variables required for
further discussion, the glass
67SiO.sub.2-9B.sub.2O.sub.3-11Al.sub.2O.sub.3-3MgO-7CaO-3SrO. This
can be expressed as a B.sub.2O.sub.3-free glass as follows:
[SiO.sub.2].sub.o=SiO.sub.2/(1-B.sub.2O.sub.3/100)=67/(1-9/100)=73.63
[Al.sub.2O.sub.3].sub.o=Al.sub.2O.sub.3/(1-B.sub.2O.sub.3/100)=11/(1-9/10-
0)=12.09 [MgO].sub.o=MgO/(1-B.sub.2O.sub.3/100)=3/(1-9/100)=3.30
[CaO].sub.o=CaO/(1-B.sub.2O.sub.3/100)=7/(1-9/100)=7.69
[SrO].sub.o=SrO/(1-B.sub.2O.sub.3/100)=3/(1-9/100)=3.30 The
liquidus temperature of this glass is believed to be considerably
higher than that of the glass that contains B.sub.2O.sub.3 because
B.sub.2O.sub.3 dilutes the concentrations of the other oxides and
thus lowers their chemical potentials in the glass. It is further
believed that, as B.sub.2O.sub.3 is added to this composition, the
liquidus temperature will decrease sharply, whereas viscosity will
decrease more gradually. It is estimated that, at about 5 mol %
B.sub.2O.sub.3, the viscosity of the glass at the highest
temperature at which crystals form (the liquidus viscosity) will be
>85 kpoise, and the glass will be compatible with fusion,
perhaps not exactly as generally practiced today, but well within
reach of existing or planned adaptations to the process.
What may be most unexpected is that the B.sub.2O.sub.3-free analogs
of glasses within the ranges of the glasses of the present
invention tend to be very similar to one another, and nearly always
represent advantageous combinations of high liquidus viscosity, low
melting temperature, and high anneal point relative to glasses
outside of these ranges. For example, a B.sub.2O.sub.3 glass
containing no SrO at all would tend to have an unacceptably high
liquidus temperature. B.sub.2O.sub.3 could be added and eventually
a high liquidus viscosity might be obtained, but it would generally
have too low an anneal point to facilitate high pull rates. This
may be because CaO and MgO (particularly MgO) have unfavorable
interactions with SiO.sub.2 and stabilize cristobalite (or
anorthite) relative to a glass containing SrO in the range
2.5.ltoreq.SrO.ltoreq.5. To extend this, consider a glass with no
MgO but in which 1.05.ltoreq.R.sub.o.ltoreq.1.45 (i.e.,
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.45). In such a
glass, S.sub.o (i.e., (SrO+CaO)/Al.sub.2O.sub.3) would be too high
(i.e., outside of the range in which
0.67.ltoreq.S.sub.o.ltoreq.0.92. At fixed B.sub.2O.sub.3
concentration, the SiO.sub.2 concentration of such a glass could be
manipulated so as to increase the liquidus viscosity, perhaps to a
very high value, but the melting temperature would be far higher
than that of a glass in which 0.67.ltoreq.S.sub.o.ltoreq.0.92.
Moreover, other attributes such as, CTE, density, and/or modulus
(which may be of secondary importance, depending on the process by
which the glass is to be formed and the use to which the glass is
to be put) may also suffer relative to an analogous glass in which
0.67.ltoreq.S.sub.o.ltoreq.0.92 and
1.05.ltoreq.R.sub.o.ltoreq.1.45. In other words, it is believed
that many B.sub.2O.sub.3-free compositions having S.sub.o and/or
R.sub.o outside of, but close to, the
0.67.ltoreq.S.sub.o.ltoreq.0.92 and 1.05.ltoreq.R.sub.o.ltoreq.1.45
ranges can be made compatible with fusion, but at a cost of anneal
points that are perhaps too low and/or melt temperatures that are
perhaps too high.
The second surprising insight is that, as R.sub.o increases, the
glass with the best combination of liquidus viscosity, melt
temperature, and anneal point tends to have a higher MgO content
than a glass with the same B.sub.2O.sub.3 content but lower
R.sub.o. Indeed, it is believed that there is a preferred MgO
content determined by R.sub.o and S.sub.o. This preferred MgO
content is referred to as "[MgO].sub.pred". Applicant has
determined [MgO].sub.pred empirically to be approximated by:
[MgO].sub.pred=[1.29+12.94.times.R.sub.o-14.4.times.S.sub.o].times.[1-B.s-
ub.2O.sub.3/100] For a given R.sub.o and S.sub.o, it is believed
that, when the difference between MgO and [MgO].sub.pred is small,
the glass will have at least two of the following: an advantageous
liquidus viscosity, an advantageous melting temperature, an
advantageous anneal point. It is further believed that glasses
having all three advantageous properties (i.e., an advantageous
liquidus viscosity, an advantageous melting temperature, and an
advantageous anneal point) can be obtained when
-0.3.ltoreq.MgO-[MgO].sub.pred.ltoreq.0.3.
The third surprising insight is that glasses with the best
combinations of liquidus viscosity, melting temperature, and anneal
point and 5.ltoreq.B.sub.2O.sub.3.ltoreq.9 tend to have SiO.sub.2
contents that are determined largely by the MgO content, R.sub.o
value, and S.sub.o value of the glass. As is the case with MgO, it
is believed that there is a preferred SiO.sub.2 content determined
by MgO, R.sub.o, and S.sub.o (this preferred SiO.sub.2 content
being referred to as "[SiO.sub.2].sub.pred"), but, for fixed
R.sub.o and S.sub.o, MgO will be determined in part by the level of
B.sub.2O.sub.3 in the glass. Therefore, it is believed that the
preferred value of SiO.sub.2 must be calculated using the MgO
concentration of the B.sub.2O.sub.3-free analog of the composition
in question, e.g., from above.
[MgO].sub.o=MgO/(1-B.sub.2O.sub.3/100). With this, applicant has
determined [SiO.sub.2].sub.pred to be approximated by:
[SiO.sub.2].sub.pred=[87.57-6.06.times.MgO/B.sub.o+66.54.times.R.sub.-
o-80.61.times.S.sub.o].times.B.sub.o in which
B.sub.o=1-B.sub.2O.sub.3/100. It is believed that, when the
difference between SiO.sub.2 and [SiO.sub.2].sub.pred is small, the
glass will have at least two of the following: an advantageous
liquidus viscosity, an advantageous melting temperature, an
advantageous anneal point. It is further believed that glasses
having all three advantageous properties (i.e., an advantageous
liquidus viscosity, an advantageous melting temperature, and an
advantageous anneal point) can be obtained when
-0.3.ltoreq.SiO.sub.2-[SiO.sub.2].sub.pred.ltoreq.0.3.
To see the interplay between these variables, and to see how to use
the relationships set forth in this Example 1 to optimize the
glasses of the present invention for particular applications,
Examples 2 and 3 are provided below.
Example 2
This Example 2 illustrates a procedure for testing a glass
composition to determine whether it is particularly well suited for
use in fusion processes, the use of [MgO].sub.pred and
[SiO.sub.2].sub.pred to optimize the glasses of the present
invention for use in fusion processes.
Consider the glass discussed in Example 1,
67SiO.sub.2-9B.sub.2O.sub.3-11Al.sub.2O.sub.3-3MgO-7CaO-3SrO. As a
preliminary matter, simple inspection reveals that the glass's
oxide components lie within the following ranges:
64.ltoreq.SiO.sub.2.ltoreq.68.2;
11.ltoreq.Al.sub.2O.sub.3.ltoreq.13.5;
5.ltoreq.B.sub.2O.sub.3.ltoreq.9; 2.ltoreq.MgO.ltoreq.9;
3.ltoreq.CaO.ltoreq.9; and 1.ltoreq.SrO.ltoreq.5. Moreover, a
simple calculation shows that the expressions
(MgO+CaO+SrO)/Al.sub.2O.sub.3=(3+7+3)/11=1.18;
(SrO+CaO)/Al.sub.2O.sub.3=(3+7)/11=0.91; and
CaO/(CaO+SrO)=7/(7+3)=0.7 lie within the following ranges:
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.45;
0.67.ltoreq.(SrO+CaO)/Al.sub.2O.sub.3.ltoreq.0.92; and
0.45.ltoreq.CaO/(CaO+SrO).ltoreq.0.95.
Using the expressions given above, R.sub.o, S.sub.o, C.sub.o, and
[MgO].sub.o can be calculated as follows:
R.sub.o=(MgO+CaO+SrO)/Al.sub.2O.sub.3=(3+7+3)/11=1.18
S.sub.o=(CaO+SrO)/Al.sub.2O.sub.3=(7+3)/11=0.91
C.sub.o=CaO/(CaO+SrO)=7/(7+3)=0.7
[MgO].sub.o=MgO/(1-B.sub.2O.sub.3/100)=3/(1-9/100)=3.30 The values
for R.sub.o, S.sub.o, C.sub.o, and [MgO].sub.o can then be used to
calculate the values of [MgO].sub.pred and [SiO.sub.2].sub.pred, as
follows:
[MgO].sub.pred=[1.29+12.94.times.R.sub.o-14.4.times.S.sub.o].times.[1-B.s-
ub.2O.sub.3/100]=[1.29+(12.94)(1.18)-(14.4)(0.91)].times.[1-9/100]=3.18
[SiO].sub.pred=[87.57-6.06.times.MgO/B.sub.o+66.54.times.R.sub.o-80.61.ti-
mes.S.sub.o].times.B.sub.o=[87.57-(6.06)(3.3)+(66.54)(1.18)-(80.61)(0.91)]-
.times.[1-9/100]=66.94 Using these [MgO].sub.pred and
[SiO.sub.2].sub.pred values, the expressions MgO-[MgO].sub.pred and
for SiO.sub.2-[SiO.sub.2].sub.pred can be determined as follows:
MgO-[MgO].sub.pred=3-3.18=-0.18,
SiO.sub.2-[SiO.sub.2].sub.pred=67-66.94=0.06
Thus, the glass composition used in this example (i.e.,
SiO.sub.2-9B.sub.2O.sub.3-11Al.sub.2O.sub.3-3MgO-7CaO-3SrO)
satisfies the expressions:
-0.3.ltoreq.MgO-[MgO].sub.pred.ltoreq.0.3
-0.3.ltoreq.SiO.sub.2-[SiO.sub.2].sub.pred.ltoreq.0.3. It is
believed that, for example, relative to glasses with the same
R.sub.o and S.sub.o values but with MgO or SiO.sub.2 concentrations
outside of the preferred ranges (i.e., those concentrations of MgO
which differ from [MgO].sub.pred by more than 0.3 and those
concentrations of SiO.sub.2 which differ from [SiO.sub.2].sub.pred
by more than 0.3 and, especially, relative to glasses with MgO or
SiO.sub.2 concentrations that lie outside of the ranges
64.ltoreq.SiO.sub.2.ltoreq.68.2 and 2.ltoreq.MgO.ltoreq.9, the
glass in the example
(67SiO.sub.2-9B.sub.2O.sub.3-11Al.sub.2O.sub.3-3MgO-7CaO-3SrO) will
tend to have a better combination of liquidus viscosity, melting
temperature, and anneal point for use in certain processes (such as
in fusion processes).
The process described above in this Example 2 can be repeated for a
variety of candidate glass compositions to determine the glass
compositions' [MgO].sub.pred and [SiO.sub.2].sub.pred values. It is
believed that, by comparing the [MgO].sub.pred and
[SiO.sub.2].sub.pred values with the MgO and SiO.sub.2
concentrations in the candidate glasses, one can obtain glasses
that may have particularly desirable combinations of liquidus
viscosity, melting temperature, and anneal point for use in certain
processes, such as in fusion processes.
Example 3
This Example 3 illustrates a procedure for generating a glass
composition using the relationships described in Example 1.
The procedure involves the following steps: (1) selecting an anneal
point target; (2) selecting trial values for R.sub.o and S.sub.o;
(3) calculating [MgO].sub.o using R.sub.o and S.sub.o; (4)
calculating [SiO.sub.2].sub.o using [MgO].sub.o as the target value
for MgO; (5) calculating [Al.sub.2O.sub.3].sub.o, [CaO].sub.o, and
[SrO].sub.o using R.sub.o, S.sub.o, [MgO].sub.o and
[SiO.sub.2].sub.o; (6) calculating B.sub.2O.sub.3 and using it to
calculate the renormalized concentrations of SiO.sub.2,
B.sub.2O.sub.3, Al.sub.2O.sub.3, MgO and CaO; and (7) comparing the
result with desired density and CTE targets, and if necessary
perform steps 1-6 again with new input parameters.
To perform these steps, we take advantage of three empirical
relationships describing the composition dependence of anneal
point, coefficient of thermal expansion, and density, viz.: Anneal
point=828.3+3.1Al.sub.2O.sub.3-3.9MgO-4.0CaO-4.4SrO-9.4B.sub.2O.sub.3(.de-
gree. C.) CTE=13.6+0.22B.sub.2O.sub.3+0.75MgO+1.58CaO+1.86SrO
(.times.10.sup.-7/.degree. C.)
Density=2.189+0.0088Al.sub.2O.sub.3-0.0046B.sub.2O.sub.3+0.0100MgO+0.0131-
CaO+0.0286SrO (g/cm.sup.3)
The first step is to select an anneal point target. Anneal points
of 740.degree. C. or more afford a substantial increase in pull
rate, but anneal points above 760.degree. C. may offer little
improvement with regard to aSi applications. If the glass were
intended for a larger size sheet, however, it is possible that a
lower anneal point might suffice, as melting rate might be the
limiting factor. In this example, an intermediate target value of
748.degree. C. was selected.
The next step is to select starting values for R.sub.o, S.sub.o and
C.sub.o. The relationship between these variables and the
properties of the final glass are complex, as one may be adjusted
against the other to obtain a range of properties. With this in
mind, and putting aside for the present the question of liquidus
viscosity (and hence compatibility with fusion), it is believed
that, generally: high values of R.sub.o result in low melting
temperatures, low anneal points, high CTEs and high densities
relative to lower R.sub.o values; high values of S.sub.o result in
high melting temperatures, high CTEs, relatively low anneal points,
and high densities relative to lower S.sub.o values; High values of
C.sub.o result in lower melting temperatures, higher CTEs, high
anneal points, and high densities. Given the trends for C.sub.o, it
might seem attractive to make it as high as possible (1.0), but in
fact this tends to drive up liquidus temperatures, and thus
diminish liquidus viscosities.
Since the CTEs and densities of glasses of the present invention
are almost invariably well-suited for AMLCD applications, it is
more usually the case to try to obtain some balance between the
competing attributes of liquidus viscosity, melting temperature,
and anneal point, then adjust a reference composition so as to
improve density or CTE. For this example, the following R.sub.o,
S.sub.o, and C.sub.o values are selected so as to be close to the
mid-points of their respective ranges: R.sub.o=1.23, S.sub.o=0.82,
and C.sub.o=0.65.
With these R.sub.o, S.sub.o, and C.sub.o values in hand, steps (3)
and (4) are performed. More particularly, a target MgO content for
a reference B.sub.2O.sub.3-free glass is calculated as follows:
[MgO].sub.o=1.29+12.94.times.R.sub.o-14.4.times.S.sub.o=5.4 mol %.
Using [MgO].sub.o as input, the idealized SiO.sub.2 content of the
reference B.sub.2O.sub.3-free glass is calculated as follows:
[SiO.sub.2].sub.o=87.57-6.06.times.[MgO].sub.o+66.54.times.R.sub.o-80.61.-
times.S.sub.o=70.59 mol %.
With these values, step (5) can be performed to determine
Al.sub.2O.sub.3, CaO, and SrO contents for the reference
B.sub.2O.sub.3-free glass:
[Al.sub.2O.sub.3].sub.o+[CaO].sub.o+[SrO].sub.o=100-[SiO.sub.2].sub.o-[Mg-
O].sub.o=24 mol % Since
[CaO+SrO].sub.o/[Al.sub.2O.sub.3].sub.o=0.82, combining the
previous two expressions yields: 1.82[Al.sub.2O.sub.3].sub.o=24 mol
% and, solving for [Al.sub.2O.sub.3].sub.o, one obtains
[Al.sub.2O.sub.3].sub.o=13.19 mol %. The combined concentration of
CaO and SrO are determined by difference:
[CaO+SrO].sub.o=24-13.19=10.81 mol %. Since by assumption
[CaO].sub.o/[CaO+SrO].sub.o=0.65, the values of [CaO].sub.o and
[SrO].sub.o are obtained as follows:
[CaO].sub.o=(0.65).times.(10.81)=7.03 mol % [SrO].sub.o=3.78 mol
%
Using these oxide concentrations (which are pertinent to a
B.sub.2O.sub.3-free glass), step (6) can be performed. In step (6),
the anneal point algorithm presented above is used to determine how
much B.sub.2O.sub.3 must be added to produce the desired anneal
point. Substituting the expressions of the form
[M.sub.xO.sub.y].sub.o=M.sub.xO.sub.y.times.(1-B.sub.2O.sub.3/100)
into the anneal point expression, where M.sub.xO.sub.y represents
Al.sub.2O.sub.3, MgO, CaO, and SrO, the following expression is
obtained: Anneal
point=828.3+3.1[Al.sub.2O.sub.3].sub.o.times.(1-B.sub.2O.sub.3/100-
)-3.9[MgO].sub.o.times.(1-B.sub.2O.sub.3/100)-4.0[CaO].sub.o.times.(1-B.su-
b.2O.sub.3/100)-4.4[SrO].sub.o.times.(1-B.sub.2O.sub.3/100)-9.4B.sub.2O.su-
b.3 Defining
K.sub.o=3.1[Al.sub.2O.sub.3].sub.o-3.9[MgO].sub.o-4[CaO].sub.o-4.4[SrO].s-
ub.o the following expression is obtained: Anneal
point=828.3+K.sub.o-B.sub.2O.sub.3.times.K.sub.o/100-9.4[B.sub.2O.sub.3].-
sub.o. With further rearrangement, this expression yields
B.sub.2O.sub.3=(828.3-anneal point+K.sub.o)/(K.sub.o/100+9.4). For
the composition under consideration,
K.sub.o=(3.1).times.(13.19)-(3.9).times.(5.4)-(4).times.(7.03)-(4.4).time-
s.(3.78)=-24.9 Substituting this and the target anneal point of
748.degree. C. into the expression for B.sub.2O.sub.3, the value
for B.sub.2O.sub.3 is calculated:
B.sub.2O.sub.3=(828.3-748-24.923)/(-24.9/100+9.4)=6.05 mol %. The
calculated value for B.sub.2O.sub.3 can now be used to renormalize
the concentrations of the other oxides. For example,
SiO.sub.2=[SiO.sub.2].sub.o.times.(1-6.05/100)=66.32 mol %. The
final composition is SiO.sub.2=66.32 Al.sub.2O.sub.3=12.39
B.sub.2O.sub.3=6.05 MgO=5.07 CaO=6.60 SrO=3.55
Finally, in Step (7), values for CTE and density are calculated to
confirm that they are appropriate for the application in mind:
CTE=13.6+0.22B.sub.2O.sub.3+0.75MgO+1.58CaO+1.86SrO
CTE=35.8.times.10.sup.-7/.degree. C. and
Density=2.189+0.0088Al.sub.2O.sub.3-0.0046B.sub.2O.sub.3+0.0100MgO+0.0131-
CaO+0.0286SrO Density=2.509 g/cm.sup.3.
Both values fall well within the ranges of commercially-available
LCD compositions. If lower CTE or density is required, then lower
values for R.sub.o and/or a higher S.sub.o may drive the properties
in the correct sense, albeit perhaps at the expense of other
attributes, such as melting temperature or liquidus viscosity. The
best balance depends upon the processes envisioned for
manufacturing the glass and limitations on attributes dictated by
customer requirements.
It is believed that glasses in which the SiO.sub.2,
Al.sub.2O.sub.3, B.sub.2O.sub.3, MgO, CaO, SrO, and other
components (if any) are chosen such that the glass includes, as
calculated in mole percent on an oxide basis: 64-68.2SiO.sub.2,
11-13.5Al.sub.2O.sub.3, 5-9B.sub.2O.sub.3, 2-9, MgO, 3-9CaO, and
1-5SrO have one or more (e.g., two or more, three or more, etc.) of
the following advantageous properties: melting temperature less
than or equal to 1620.degree. C. (e.g., less than or equal to
1615.degree. C., less than or equal to 1610.degree. C., etc.);
anneal point greater than or equal to 725.degree. C. (e.g., greater
than or equal to 730.degree. C., greater than or equal to
735.degree. C., greater than or equal to 740.degree. C., greater
than or equal to 745.degree. C., etc.); liquidus viscosities of
greater than or equal to 90 kilopoises (e.g., greater than or equal
to 100 kilopoises, greater than or equal to 110 kilopoises, greater
than or equal to 130 kilopoises. etc.). The data presented in Table
1 below confirm this.
When one migrates outside of the aforementioned ranges (i.e.,
outside of 64-68.2SiO.sub.2, 11-13.5Al.sub.2O.sub.3,
5-9B.sub.2O.sub.3, 2-9, MgO, 3-9CaO, and 1-5SrO), one might be able
to find glasses having one or more of the above-cited advantageous
properties, but, in view of the analysis presented in this Example
3, operating outside these ranges will likely impact one or more of
the above-cited properties in a particularly unfavorable way. For
example, it is believed that having a higher SiO.sub.2 content may
adversely affect the melting point: having a higher B.sub.2O.sub.3
content may adversely affect anneal point; having a lower
B.sub.2O.sub.3 content and/or a lower SiO.sub.2 content may
adversely affect liquidus viscosity; etc.
Moreover, as noted above, in certain embodiments, the glass
components are selected such that the expression
1.05.ltoreq.(MgO+CaO+SrO)/Al.sub.2O.sub.3.ltoreq.1.45 is satisfied.
These glasses are believed to possess particularly good anneal
points and liquidus viscosities, compared to anneal points when
(MgO+CaO+SrO)/Al.sub.2O.sub.3>1.45 and liquidus viscosities when
(MgO+CaO+SrO)/Al.sub.2O.sub.3<1.05.
Examples 4-103
Table 1 lists examples of glasses of the present invention in terms
of mole percents which are either calculated on an oxide basis from
the glass batches. Table 1 also lists various physical properties
for these glasses, the units for these properties being as
follows:
TABLE-US-00001 Strain Point .degree. C. Anneal Point .degree. C.
Softening Point .degree. C. CTE .times.10.sup.-7/.degree. C.
(0-300.degree. C.) Density grams/centimeter.sup.3 Melting Temp.
.degree. C. Liquidus Temp. .degree. C. Liquidus Viscosity
kilopoise
Inasmuch as the sum of the individual constituents totals or very
closely approximates 100, for all practical purposes, the reported
values may be deemed to represent mole percent. The actual batch
ingredients may comprise any materials, either oxides, or other
compounds, which, when melted together with the other batch
components, will be converted into the desired oxide in the proper
proportions. For example, SrCO.sub.3 and CaCO.sub.3 can provide the
source of SrO and CaO, respectively.
The specific batch ingredients used to prepare the glasses of Table
1 were fine sand, alumina, boric acid, magnesium oxide, limestone,
and strontium carbonate or strontium nitrate.
The glasses set forth in Table 1 were prepared by melting 3,000 or
19,000 gram batches of each glass composition at a temperature and
time to result in a relatively homogeneous glass composition, e.g.,
at a temperature of about 1600.degree. C. for a period of about 16
hours in platinum crucibles. In particular, the batch materials
were ball-milled for one hour using ceramic media in a ceramic
mill. The batch was transferred to an 1800 cc platinum crucible and
loaded into a furnace at 1600.degree. C. After 16 hours, the
crucible was removed from the furnace and the glass was poured onto
a cold steel plate. When viscous enough to handle, the glass was
transferred to an annealing oven at 725.degree. C., held for one
hour at this temperature, then cooled at 0.5.degree. C./minute to
room temperature.
The glass properties set forth in Table 1 were determined in
accordance with techniques conventional in the glass art. For
example, the linear coefficient of thermal expansion (CTE) over the
temperature range 0-300.degree. C. is expressed in terms of
.times.10.sup.-7/.degree. C. and the strain point is expressed in
terms of .degree. C. These were determined from fiber elongation
techniques (ASTM references E228-85 and C336, respectively). The
density in terms of grams/cm.sup.3 was measured via the Archimedes
method (ASTM C693). The melting temperature in terms of .degree. C.
(defined as the temperature at which the glass melt demonstrates a
viscosity of 200 poises ("T @ 200 p")) was calculated employing a
Fulcher equation fit to high temperature viscosity data measured
via rotating cylinders viscometry (ASTM C965-81). The liquidus
temperature of the glass in terms of .degree. C. was measured using
the standard gradient boat liquidus method of ASTM C829-81. This
involves placing crushed glass particles in a platinum boat,
placing the boat in a furnace having a region of gradient
temperatures, heating the boat in an appropriate temperature region
for 24 hours, and determining by means of microscopic examination
the highest temperature at which crystals appear in the interior of
the glass. The liquidus viscosity in kilopoises was determined from
the liquidus temperature and the coefficients of the Fulcher
equation.
TABLE-US-00002 TABLE 1 Example 4 5 6 7 8 9 10 11 SiO.sub.2 64.44
66.55 66.31 67.84 66.15 67.32 67.24 67.5 Al.sub.2O.sub.3 11.95 12.5
12.48 12.58 12.5 12.27 12.18 12.63 B.sub.2O.sub.3 6.51 6.45 5.49 6
6.6 5.99 7.09 6.34 MgO 6.47 4.65 5.21 3.29 5 4.23 4.31 3.69 CaO 7.4
6.6 6.16 6.69 6.1 6.52 7.85 5.29 SrO 3.23 3.25 4.23 3.6 3.65 3.51
1.22 4.55 R.sub.o 1.43 1.16 1.25 1.08 1.18 1.16 1.10 1.07 S.sub.o
0.89 0.79 0.83 0.82 0.78 0.82 0.74 0.78 C.sub.o 0.70 0.67 0.59 0.65
0.63 0.65 0.87 0.54 [SiO.sub.2].sub.pred 64.55 66.45 66.30 67.89
66.01 67.39 67.30 67.55 SiO.sub.2 - [SiO.sub.2].sub.pred -0.11 0.09
0.01 -0.05 0.13 -0.07 -0.06 -0.04 [MgO].sub.pred 6.53 4.63 5.17
3.26 4.97 4.27 4.44 3.67 MgO.sub.2 - [MgO].sub.pred -0.06 0.02 0.04
0.03 0.03 -0.04 -0.13 0.02 strain point 685 689 706 700 687 701 698
701 anneal point 735 741 751 755 738 754 749 754 softening point
959 972 981 991 970 986 982 988 CTE 37.5 35 36.5 36.9 35.2 34.5
33.2 35 density 2.520 2.498 2.525 2.495 2.506 2.499 2.448 2.509
melting point 1535 1579 1586 1604 1572 1604 1593 1609 liquidus
temperature 1120 1165 1170 1175 1155 1165 1180 1170 liquidus
viscosity 149 102 109 124 110 152 90 135 Example 12 13 14 15 16 17
18 19 SiO.sub.2 67.41 65.24 68.39 68.09 67.78 67 65.68 65.24
Al.sub.2O.sub.3 12.65 12.36 12.83 12.14 12.19 12.57 12.32 12.28
B.sub.2O.sub.3 5.84 7.58 3.99 6.35 6.2 5.42 7.68 6.99 MgO 4.07 4.77
4.47 3.11 3.58 4.73 4.97 5.12 CaO 6.26 6.31 6.44 6.67 6.6 6.42 5.97
6.07 SrO 3.6 3.74 3.71 3.51 3.52 3.69 3.38 4.18 R.sub.o 1.10 1.20
1.14 1.09 1.12 1.18 1.16 1.25 S.sub.o 0.78 0.81 0.79 0.84 0.83 0.80
0.76 0.83 C.sub.o 0.63 0.63 0.63 0.66 0.65 0.64 0.64 0.59
[SiO.sub.2].sub.pred 67.56 65.12 68.49 68.06 67.79 67.07 65.56
65.23 SiO.sub.2 - [SiO.sub.2].sub.pred -0.14 0.11 -0.1 0.03 -0.01
-0.07 0.11 0.01 [MgO].sub.pred 4.05 4.70 4.45 3.15 3.62 4.71 4.98
5.07 MgO.sub.2 - [MgO].sub.pred 0.02 0.07 0.02 -0.04 -0.04 0.02
-0.01 0.05 strain point 702 685 725 697 698 704 680 685 anneal
point 756 737 777 751 753 758 732 737 softening point 995 971 1009
994 991 988 966 965 CTE 34.1 35.2 35.4 33.8 34.8 35.7 34.9 39.9
density 2.501 2.496 2.521 2.487 2.492 2.512 2.481 2.514 melting
point 1605 1556 1617 1618 1613 1596 1573 1567 liquidus temperature
1160 1140 1195 1160 1165 1160 1150 1150 liquidus viscosity 199 126
115 194 167 174 111 121 Example 20 21 22 23 24 25 26 27 SiO.sub.2
66.84 64.13 63.94 65.17 66.38 67.6 66.42 64.7 Al.sub.2O.sub.3 12.38
12.36 12.23 12.83 12.53 12.2 12.46 12.18 B.sub.2O.sub.3 5.74 7.77
8.19 7.79 5.5 7.05 6.72 7.8 MgO 5.01 5.03 5.66 4.69 5.15 3.55 4.34
5.06 CaO 6.4 6.98 6.83 5.58 7.51 5.85 6.28 6.01 SrO 3.5 3.73 3.15
3.83 2.81 3.75 3.6 4.13 R.sub.o 1.20 1.27 1.28 1.10 1.23 1.08 1.14
1.25 S.sub.o 0.80 0.87 0.82 0.73 0.82 0.79 0.79 0.83 C.sub.o 0.65
0.65 0.68 0.59 0.73 0.61 0.64 0.59 [SiO.sub.2].sub.pred 66.88 63.96
63.74 65.15 66.37 67.54 66.53 64.69 SiO.sub.2 -
[SiO.sub.2].sub.pred -0.04 0.16 0.18 0.02 0.01 0.06 -0.11 0.01
[MgO].sub.pred 5.04 4.87 5.58 4.56 5.10 3.62 4.32 5.02 MgO.sub.2 -
[MgO].sub.pred -0.03 0.16 0.08 0.13 0.05 -0.07 0.02 0.04 strain
point 699 678 677 698 704 686 694 682 anneal point 752 730 728 742
756 741 747 734 softening point 982 958 957 970 984 981 979 964 CTE
35.1 36.9 36 34.6 36.2 33.7 34.5 36.1 density 2.508 2.509 2.492
2.495 2.505 2.485 2.491 2.506 melting point 1589 1535 1540 1573
1587 1607 1588 1566 liquidus temperature 1180 1100 1130 1155 1175
1150 1140 1120 liquidus viscosity 91 254 105 125 96 198 228 234
Example 28 29 30 31 32 33 34 35 SiO.sub.2 67.66 66.85 66.1 67.64
66.89 66.33 66.01 66.83 Al.sub.2O.sub.3 12.7 12.28 12.2 12.46 12.67
12.48 12.32 12.76 B.sub.2O.sub.3 5 5.41 6.2 6.33 5.48 5.49 5.49 5.5
MgO 4.42 5.12 5.7 3.88 5.52 5.79 5.35 4.93 CaO 6.38 6.06 6.05 5.13
5.51 6.3 6.95 8.12 SrO 3.67 4.17 3.75 4.56 3.79 3.49 3.74 1.74
R.sub.o 1.14 1.25 1.27 1.09 1.17 1.25 1.30 1.16 S.sub.o 0.79 0.83
0.80 0.78 0.73 0.78 0.87 0.77 C.sub.o 0.63 0.59 0.62 0.53 0.59 0.64
0.65 0.82 [SiO.sub.2].sub.pred 67.76 66.89 66.06 67.61 66.84 66.32
66.05 66.81 SiO.sub.2 - [SiO.sub.2].sub.pred -0.1 -0.04 0.04 0.02
0.04 0.01 -0.04 0.02 [MgO].sub.pred 4.40 5.16 5.78 3.91 5.54 5.81
5.32 4.87 MgO.sub.2 - [MgO].sub.pred 0.02 -0.04 -0.08 -0.03 -0.02
-0.02 0.03 0.06 strain point 714 712 687 697 705 710 693 705 anneal
point 766 756 739 750 757 754 746 758 softening point 1001 983 966
982 985 983 973 988 CTE 35.2 36.2 34.9 34.6 34 35.9 37.2 34.7
density 2.514 2.522 2.515 2.508 2.513 2.513 2.525 2.471 melting
point 1602 1594 1580 n.d. 1597 1582 1579 1593 liquidus temperature
1180 1175 1160 1160 1175 1165 1150 1180 liquidus viscosity 118 99
102 n.d. 108 114 144 92 Example 36 37 38 39 40 41 42 43 SiO.sub.2
66.58 66.79 66.8 67.01 66.56 66.8 67.24 64.84 Al.sub.2O.sub.3 12.48
12.25 12.5 12.58 12.37 12.5 12.18 12.38 B.sub.2O.sub.3 6.5 5.49 5.4
5.5 5.48 5.4 7.09 7.79 MgO 4.36 5.12 5.73 4.61 5.15 4.59 3.32 4.96
CaO 6.29 7.22 4.97 7.21 7.29 6.12 8.84 4.94 SrO 3.61 2.99 4.59 2.96
3.01 4.59 1.22 4.95 R.sub.o 1.14 1.25 1.22 1.17 1.25 1.22 1.10 1.20
S.sub.o 0.79 0.83 0.76 0.81 0.83 0.86 0.83 0.80 C.sub.o 0.64 0.71
0.52 0.71 0.71 0.57 0.88 0.50 [SiO.sub.2].sub.pred 66.69 66.87
66.68 67.05 66.60 66.69 67.27 64.83 SiO.sub.2 -
[SiO.sub.2].sub.pred -0.1 -0.07 0.11 -0.03 -0.04 0.1 -0.03 0.01
[MgO].sub.pred 4.34 5.17 5.77 4.57 5.15 4.52 3.34 4.89 MgO.sub.2 -
[MgO].sub.pred 0.02 -0.05 -0.04 0.04 0 0.07 -0.02 0.07 strain point
702 700 702 705 700 694 697 679 anneal point 754 753 755 757 753
746 751 731 softening point 984 982 994 987 983 977 987 964 CTE
34.9 35.5 34.4 35.4 36 37.1 33.9 35.8 density 2.502 2.505 2.526
2.503 2.510 2.538 2.448 2.518 melting point 1593 1592 n.d. 1601
1589 n.d. 1595 1558 liquidus temperature 1155 1175 1185 1185 1165
1160 1180 1160 liquidus viscosity 174 101 n.d. 89 123 n.d. 94 87
Example 44 45 46 47 48 49 50 51 SiO.sub.2 67.66 68.03 67.21 66.3
67.32 67.5 65.04 67.73 Al.sub.2O.sub.3 12.08 12.77 12.61 12.47
12.27 12.18 12.48 12.56 B.sub.2O.sub.3 7.13 4.5 5.64 5.49 5.99 7.03
6.89 5.99 MgO 3.42 4.44 4.39 5.7 4.23 3.54 5.13 3.29 CaO 6.47 6.4
6.34 7.02 6.52 5.84 6.89 6.67 SrO 3.24 3.69 3.64 2.89 3.51 3.74
3.57 3.59 R.sub.o 1.09 1.14 1.14 1.25 1.16 1.08 1.25 1.08 S.sub.o
0.80 0.79 0.79 0.79 0.82 0.79 0.84 0.82 C.sub.o 0.67 0.63 0.64 0.71
0.65 0.61 0.66 0.65 [SiO.sub.2].sub.pred 67.55 68.13 67.31 66.30
67.39 67.60 64.87 67.94 SiO.sub.2 - [SiO.sub.2].sub.pred 0.1 -0.1
-0.1 0 -0.07 -0.1 0.16 -0.2 [MgO].sub.pred 3.50 4.42 4.37 5.71 4.27
3.62 5.00 3.26 MgO.sub.2 - [MgO].sub.pred -0.08 0.02 0.02 -0.01
-0.04 -0.08 0.13 0.03 strain point 686 720 706 701 701 700 689 696
anneal point 741 771 759 753 754 753 741 749 softening point 983
1006 988 979 986 986 964 987 CTE 36 34.7 34.7 32.4 34.5 34.6 36.5
34.2 density 2.474 2.517 2.506 2.504 2.499 2.501 2.511 2.487
melting point 1602 1613 1599 1585 1600 1608 1556 n.d. liquidus
temperature 1150 1185 1170 1170 1165 1170 1120 1150 liquidus
viscosity 185 122 151 99 149 131 191 n.d. Example 52 53 54 55 56 57
58 59 SiO.sub.2 67.56 66.84 67.95 66.7 66.59 66.06 66.24 66.6
Al.sub.2O.sub.3 12.06 12.33 11.95 12.5 12.63 12.52 12.41 12.57
B.sub.2O.sub.3 7.12 6.98 6.7 6.15 5.5 6 6.51 5.5 MgO 3.41 3.99 3.4
4.7 5.04 5.17 4.67 5.56 CaO 6.46 5.69 6.15 6.05 7.77 6.66 6.35 6.83
SrO 3.24 3.99 3.85 3.9 2.34 3.59 3.64 2.81 R.sub.o 1.09 1.11 1.12
1.17 1.20 1.23 1.18 1.21 S.sub.o 0.80 0.79 0.84 0.80 0.80 0.82 0.80
0.77 C.sub.o 0.67 0.59 0.62 0.61 0.77 0.65 0.64 0.71
[SiO.sub.2].sub.pred 67.59 66.97 67.75 66.60 66.58 65.91 66.32
66.57 SiO.sub.2 - [SiO.sub.2].sub.pred -0.03 -0.12 0.19 0.09 0.01
0.14 -0.08 0.03 [MgO].sub.pred 3.49 4.02 3.48 4.68 4.99 5.10 4.65
5.57 MgO.sub.2 - [MgO].sub.pred -0.08 -0.03 -0.08 0.02 0.05 0.07
0.02 -0.01 strain point 696 696 687 689 703 692 694 703 anneal
point 750 749 741 742 755 745 746 755 softening point 989 986 981
978 986 977 981 983 CTE 34 33.8 35.7 34.6 36.2 35.9 35.1 34.8
density 2.479 2.488 2.489 2.506 2.495 2.514 2.503 2.501 melting
point 1607 1601 1600 1589 1587 1570 1587 1590 liquidus temperature
1160 1150 1150 1150 1175 1140 1145 1170 liquidus viscosity 188 216
188 156 93 172 177 100 Example 60 61 62 63 64 65 66 67 SiO.sub.2
66.48 66.99 66.01 67.68 65.22 67.45 66.62 66.85 Al.sub.2O.sub.3
12.81 11.71 13.07 11.86 11.42 12.05 12.42 12.31 B.sub.2O.sub.3 6
6.92 6 7.62 8.41 6.65 5.5 5.5 MgO 4.23 5.06 4.23 3.44 4.5 3.75 5.1
5.06 CaO 6.81 4.51 6.95 6.3 6.33 6.2 7.44 7.38 SrO 3.67 4.81 3.74
3.1 4 3.9 2.78 2.76 R.sub.o 1.15 1.23 1.14 1.08 1.30 1.15 1.23 1.23
S.sub.o 0.82 0.80 0.82 0.79 0.90 0.84 0.82 0.82 C.sub.o 0.65 0.48
0.65 0.67 0.61 0.61 0.73 0.73 [SiO.sub.2].sub.pred 66.47 67.10
66.06 67.53 65.26 67.31 66.65 66.91 SiO.sub.2 -
[SiO.sub.2].sub.pred 0.01 -0.1 -0.05 0.14 -0.04 0.13 -0.03 -0.06
[MgO].sub.pred 4.09 5.32 4.01 3.58 4.63 3.81 5.10 5.10 MgO.sub.2 -
[MgO].sub.pred 0.14 -0.26 0.22 -0.14 -0.13 -0.06 0 -0.04 strain
point 698 682 699 683 676 687 704 704 anneal point 751 735 752 736
725 740 755 755 softening point 987 974 985 984 957 980 985 986 CTE
36.1 35.9 38.1 33.5 36.3 34.8 35.7 36.1 density 2.511 2.505 2.514
2.471 2.494 2.496 2.502 2.501 melting point 1583 1586 1578 n.d.
1557 1598 1592 1596 liquidus temperature 1165 1150 1170 1150 1120
1145 1180 1180 liquidus viscosity 116 136 103 n.d. 172 189 88 92
Example 68 69 70 71 72 73 74 75 SiO.sub.2 64.98 65.94 67.55 66.83
67.57 67.4 65.15 67.54 Al.sub.2O.sub.3 12.59 12.42 12.73 12.99 12
12.25 12.34 11.78 B.sub.2O.sub.3 7.8 5.99 6.05 5.55 7.62 6.75 7.56
8.2 MgO 4.83 5.18 3.74 4.24 3.28 3.5 4.77 3.02 CaO 4.84 6.12 6.2
7.44 6.43 5.75 6.29 7.01 SrO 4.83 4.22 3.56 2.95 3.1 4.35 3.73 2.45
R.sub.o 1.15 1.25 1.06 1.13 1.07 1.11 1.20 1.06 S.sub.o 0.77 0.83
0.77 0.80 0.79 0.82 0.81 0.80 C.sub.o 0.50 0.59 0.64 0.72 0.67 0.57
0.63 0.74 [SiO.sub.2].sub.pred 64.96 65.94 67.78 66.84 67.46 67.33
65.19 67.34 SiO.sub.2 - [SiO.sub.2].sub.pred 0.02 0 -0.22 -0.01 0.1
0.07 -0.04 0.18 [MgO].sub.pred 4.73 5.13 3.72 4.09 3.38 3.51 4.71
3.14 MgO.sub.2 - [MgO].sub.pred 0.1 0.05 0.02 0.15 -0.1 -0.01 0.06
-0.12 strain point 685 702 701 706 687 687 688 679 anneal point 735
747 754 759 742 740 739 733 softening point 964 975 990 993 987 979
971 967 CTE 39.9 36 34.4 35.1 33.2 35 35.1 33.3 density 2.541 2.523
2.497 2.503 2.462 2.502 2.497 2.448 melting point 1564 1595 1595
1589 n.d. 1609 1583 n.d. liquidus temperature 1125 1170 1140 1165
1145 1150 1150 1135 liquidus viscosity 219 116 269 137 n.d. 184 142
n.d. Example 76 77 78 79 80 81 82 83 SiO.sub.2 67.16 66.94 65.59
66.58 64.68 65.37 66.32 64.23 Al.sub.2O.sub.3 12.8 12.56 12.34
12.58 12.18 12.03 12.48 11.91 B.sub.2O.sub.3 5.87 5.99 6.49 5.48
7.79 5.49 5.49 8.38 MgO 3.8 4.39 5.15 5.68 6.02 6.09 5.81 5.2 CaO
6.56 6.31 6.1 5.65 4.61 7.09 5.79 7.03 SrO 3.81 3.63 4.2 3.89 4.61
3.82 4 3.25 R.sub.o 1.11 1.14 1.25 1.21 1.25 1.41 1.25 1.30 S.sub.o
0.81 0.79 0.83 0.76 0.76 0.91 0.78 0.86 C.sub.o 0.63 0.63 0.59 0.59
0.50 0.65 0.59 0.68 [SiO.sub.2].sub.pred 67.22 67.05 65.59 66.55
64.65 65.56 66.29 64.15 SiO.sub.2 - [SiO.sub.2].sub.pred -0.06 -0.1
0 0.03 0.03 -0.18 0.02 0.08 [MgO].sub.pred 3.70 4.37 5.11 5.69 6.07
6.15 5.83 5.19 MgO.sub.2 - [MgO].sub.pred 0.1 0.02 0.04 -0.01 -0.05
-0.06 -0.02 0.01
strain point 705 704 688 706 683 690 708 677 anneal point 759 756
740 757 731 741 753 727 softening point 992 987 969 987 960 966 981
954 CTE 35.9 35.1 37.7 35.7 35.9 37.3 35.7 35.8 density 2.506 2.505
2.518 2.513 2.513 2.532 2.521 2.492 melting point 1599 1588 1576
1599 1557 1566 1588 1549 liquidus temperature 1160 1165 1155 1170
1120 1150 1170 1130 liquidus viscosity 170 129 117 114 203 116 110
100 Example 84 85 86 87 88 89 90 91 SiO.sub.2 66.77 67.24 67.76
64.4 64.7 67.15 67.42 67.09 Al.sub.2O.sub.3 12.58 12.18 11.52 11.6
12.18 12.5 12.29 12.26 B.sub.2O.sub.3 7.12 7.09 8.19 7.8 7.8 7.05 6
5.84 MgO 3.71 4.31 3.33 5.4 5.06 3.35 4.23 4.21 CaO 6.13 7.85 6.75
6.4 6.01 5.7 6.54 7.03 SrO 3.52 1.22 2.45 4.4 4.13 4.25 3.52 3.57
R.sub.o 1.06 1.10 1.09 1.40 1.25 1.06 1.16 1.21 S.sub.o 0.77 0.74
0.80 0.93 0.83 0.80 0.82 0.86 C.sub.o 0.64 0.87 0.73 0.59 0.59 0.57
0.65 0.66 [SiO.sub.2].sub.pred 67.00 67.30 67.52 64.45 64.69 67.22
67.33 66.97 SiO.sub.2 - [SiO.sub.2].sub.pred -0.21 -0.06 0.22 -0.05
0.01 -0.07 0.08 0.11 [MgO].sub.pred 3.69 4.44 3.54 5.47 5.02 3.33
4.26 4.19 MgO.sub.2 - [MgO].sub.pred 0.02 -0.13 -0.21 -0.07 0.04
0.02 -0.03 0.02 strain point 697 694 703 677 685 689 697 698 anneal
point 751 748 757 727 732 742 751 751 softening point 985 983 994
950 959 982 992 985 CTE 34.4 33 34.2 38.4 36 34.6 36.2 36.3 density
2.493 2.445 2.492 2.518 2.509 2.496 2.496 2.509 melting point 1597
1601 1607 1549 1566 1597 1602 1587 liquidus temperature 1160 1175
1150 1100 1120 1150 1175 1170 liquidus viscosity 171 96 193 264 226
190 119 99 Example 92 93 94 95 96 97 98 99 SiO.sub.2 64.32 66.95
66.31 66.89 66 66.87 66.62 66.8 Al.sub.2O.sub.3 11.59 12.35 12.47
12.67 11.92 12.5 12.51 12.6 B.sub.2O.sub.3 7.8 7 5.5 5.49 6.26 5.5
6.92 6.7 MgO 5.4 4 7 5.41 5.01 4.34 4.02 4.15 CaO 6.38 5.7 5.59
6.66 6.92 6.93 6.2 6.45 SrO 4.39 4 3.01 2.74 3.89 3.74 3.56 3.3
R.sub.o 1.40 1.11 1.25 1.17 1.33 1.20 1.10 1.10 S.sub.o 0.93 0.79
0.69 0.74 0.91 0.85 0.78 0.77 C.sub.o 0.59 0.59 0.65 0.71 0.64 0.65
0.64 0.66 [SiO.sub.2].sub.pred 64.50 66.91 66.29 66.86 65.94 66.89
66.77 66.78 SiO.sub.2 - [SiO.sub.2].sub.pred -0.16 0.04 0.02 0.03
0.06 -0.02 -0.14 0.02 [MgO].sub.pred 5.48 4.02 7.14 5.42 5.05 4.27
4.00 4.12 MgO.sub.2 - [MgO].sub.pred -0.08 -0.02 -0.14 -0.01 -0.04
0.07 0.02 0.03 strain point 675 685 711 706 689 699 694 689 anneal
point 725 738 756 758 741 752 748 742 softening point 951 980 978
988 969 984 979 977 CTE 37.1 35.2 34.6 34.3 37.6 36.4 34.2 34.7
density 2.516 2.495 2.505 2.498 2.519 2.513 2.491 2.491 melting
point 1551 1592 1581 1591 1565 1595 1592 1594 liquidus temperature
1120 1150 1170 1170 1160 1165 1145 1140 liquidus viscosity 159 159
104 116 87 132 217 223 Example 100 101 102 103 SiO.sub.2 67.3 65.72
66.59 65.14 Al.sub.2O.sub.3 12.63 12.44 12.38 12.83 B.sub.2O.sub.3
5.5 6.74 5.45 7.79 MgO 4.41 5.02 5.16 4.71 CaO 6.35 6.4 6.11 4.7
SrO 3.65 3.68 4.2 4.71 R.sub.o 1.14 1.21 1.25 1.10 S.sub.o 0.79
0.81 0.83 0.73 C.sub.o 0.64 0.63 0.59 0.50 [SiO.sub.2].sub.pred
67.39 65.58 66.60 65.12 SiO.sub.2 - [SiO.sub.2].sub.pred -0.09 0.13
-0.01 0.02 [MgO].sub.pred 4.39 4.96 5.16 4.58 MgO.sub.2 -
[MgO].sub.pred 0.02 0.06 0 0.13 strain point 710 685 707 694 anneal
point 762 737 753 740 softening point 992 968 983 970 CTE 34.9 35.8
35.3 35.2 density 2.507 2.503 2.520 2.512 melting point 1599 1565
1600 1573 liquidus temperature 1170 1160 1180 1150
From Table 1, it can be seen that the compositions that satisfy the
expressions: -0.3.ltoreq.MgO-[MgO].sub.pred.ltoreq.0.3
-0.3.ltoreq.SiO.sub.2-[SiO.sub.2].sub.pred.ltoreq.0.3 have liquidus
viscosities of at least 90 kpoise, and are therefore are compatible
with fusion as practiced today, or can be made compatible with
fusion with minimal adjustment to current processes. For
comparison, the nominal liquidus viscosity of Corning's Eagle XG is
130 kpoise, and devitrification within the quality area has never
been seen for this glass in production. This is because of its
comparatively steep viscosity curve, which permits a smaller
.DELTA.T across the isopipe. Since some glasses set forth in Table
1 have melting temperatures comparable to or lower than Eagle XG
and anneal points higher than Eagle XG, they have still steeper
viscosity curves, and so a slightly lower liquidus viscosity is
believed to be acceptable. Of course, many of the glasses have
liquidus viscosities comparable to or greater than Eagle XG, and,
for these, the risk is much smaller.
FIG. 2 is a plot of SiO.sub.2 concentration for various glasses of
the present invention vs.
[87.46-5.85.times.MgO.times.(1-B.sub.2O.sub.3/100)+63.67.times.M.sub.a-13-
.85.times.S.sub.o].times.[1-B.sub.2O.sub.3/100], the predictive
measure for SiO.sub.2. FIG. 3 is a plot of MgO for various glasses
of the present invention vs.
[1.01+12.77.times.R.sub.o-13.79.times.S.sub.o].times.[1-B.sub.2O.sub.3/10-
0], the predictive measure for MgO. As FIGS. 2 and 3 show, the
actual concentrations of MgO and SiO.sub.2 lie very close to the
predicted values for all compositions.
FIG. 4 is a graph of melting temperature of various glasses of the
present invention as a function of SiO.sub.2 content. As FIG. 4
shows, the melting temperature increases as a relatively steep
function of SiO.sub.2 content for glasses that otherwise satisfy
the expressions: 11.ltoreq.Al.sub.2O.sub.3.ltoreq.13.5;
5.ltoreq.B.sub.2O.sub.3.ltoreq.9; 2.ltoreq.MgO.ltoreq.9;
3.ltoreq.CaO.ltoreq.9; and 1.ltoreq.SrO.ltoreq.5. Accordingly, it
is believed that, when SiO.sub.2 content is above 68.2 mol %,
melting temperatures higher than 1620.degree. C. may result,
particularly in compositions that do not contain arsenic.
Although preferred embodiments have been depicted and described in
detail herein, it will be apparent to those skilled in the relevant
art that various modifications, additions, substitutions and the
like can be made without departing from the spirit of the invention
and these are therefore considered to be within the scope of the
invention, as defined in the claims which follow.
* * * * *