U.S. patent application number 12/385318 was filed with the patent office on 2010-10-07 for low iron high transmission glass with boron oxide for improved optics, durability and refining, and corresponding method.
This patent application is currently assigned to Guardian Industires Corp.. Invention is credited to David Bird, Kevin R. Fulton, Richard Hulme, Abraham W. Michaelis, Mario Resch, Scott V. Thomsen.
Application Number | 20100255980 12/385318 |
Document ID | / |
Family ID | 42370894 |
Filed Date | 2010-10-07 |
United States Patent
Application |
20100255980 |
Kind Code |
A1 |
Fulton; Kevin R. ; et
al. |
October 7, 2010 |
Low iron high transmission glass with boron oxide for improved
optics, durability and refining, and corresponding method
Abstract
This invention relates to a high transmission low iron glass
that includes boron oxide. The boron oxide, added to this low iron
glass, has the effect of improving glass refining, homogeneity and
quality (lower seed count) through its flux action and improves
glass optical parameters of green and clear glass through the
change in refractive index and surface tension. Boron oxide lends
to broader and weaker absorption band of such transition element(s)
as iron which additionally improves the transmittance of low iron
clear glass in certain example embodiments of this invention. In
certain example embodiments, the addition of boron oxide in certain
quantities in advantageous in that it improves the chemical
durability of the glass by decreasing the USPX (or USPXIII) value
of the glass via suppression of the silica, sodium ions in the
glass structure.
Inventors: |
Fulton; Kevin R.; (Howell,
MI) ; Michaelis; Abraham W.; (Haifa, IL) ;
Resch; Mario; (Ramat Ishay, IL) ; Bird; David;
(Superior Township, MI) ; Hulme; Richard;
(Rochester Hills, MI) ; Thomsen; Scott V.; (South
Lyon, MI) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
Guardian Industires Corp.
Auburn Hills
MI
Phoenicia America-Israel (Flat Glass) Ltd.
Nazaret-Ilit
|
Family ID: |
42370894 |
Appl. No.: |
12/385318 |
Filed: |
April 3, 2009 |
Current U.S.
Class: |
501/65 ;
501/64 |
Current CPC
Class: |
C03C 1/00 20130101; C03C
4/0092 20130101; C03C 3/091 20130101; C03C 3/087 20130101 |
Class at
Publication: |
501/65 ;
501/64 |
International
Class: |
C03C 3/089 20060101
C03C003/089; C03C 3/095 20060101 C03C003/095 |
Claims
1. Glass comprising: TABLE-US-00004 Ingredient wt. % SiO.sub.2
69-73% Na.sub.2O 10-20% CaO 5-15% MgO 0-5% K.sub.2O 0-2% total iron
(expressed as Fe.sub.2O.sub.3) 0.005 to 0.04% FeO 0 to 0.0035%
cerium oxide 0 to 0.03% boron oxide 0.1 to 2.5% SO.sub.3 0.1 to
0.6%
wherein the glass has a glass redox of no greater than 0.12, a USPX
value of no greater than 5.8, and a total solar transmission (ISO
9090 1.5 AM, at 3.2 mm reference thickness) of at least 90.8%.
2. The glass of claim 1, wherein the glass comprises:
TABLE-US-00005 total iron (expressed as Fe.sub.2O.sub.3) 0.005 to
0.03% boron oxide 0.5 to 1.5%.
3. The glass of claim 1, wherein the glass has a total solar
(.tau.e) transmission of at least 90.9%.
4. The glass of claim 1, wherein the glass is substantially free or
free of each of erbium oxide, nickel oxide, cerium oxide, cobalt
oxide, zirconium oxide, zinc oxide, neodymium oxide, and
selenium.
5. The glass of claim 1, wherein the glass is substantially free or
free of erbium oxide, cerium oxide, zirconium oxide, zinc oxide,
and nickel oxide.
6. The glass of claim 1, wherein the glass has a positive b* color
value.
7. The glass of claim 1, wherein the glass has a glass redox value
(FeO/Fe.sub.2O.sub.3) no greater than 0.10.
8. The glass of claim 1, wherein the glass comprises from 0 to
0.0020% FeO.
9. The glass of claim 1, wherein the glass substrate is
substantially free of four or more of erbium oxide, nickel oxide,
cobalt oxide, neodymium oxide, chromium oxide, cerium oxide and
selenium.
10. The glass of claim 1, wherein the glass substrate is
substantially free of seven or more of erbium oxide, nickel oxide,
cerium oxide, cobalt oxide, neodymium oxide, zirconium oxide, zinc
oxide and selenium.
11. The glass of claim 1, wherein the glass is substantially free
of erbium oxide, cerium oxide, zirconium oxide, zinc oxide and
nickel oxide.
12. The glass of claim 1, wherein the glass has a transmissive a*
color value of -0.5 to +0.5 and a transmissive b* color value of
from +0.1 to +1.0.
Description
[0001] This invention relates to a high transmission low iron
(total iron no greater than about 0.04%) glass that includes boron
oxide. The boron oxide has the unexpected and surprising effect in
low-iron high transmission glass of improving total solar
transmission. Moreover, the boron oxide also improves glass
refining, homogeneity and quality (lower seed count) through its
flux action and improves glass optical parameters of green and
clear glass through the change in refractive index and surface
tension. Boron oxide lends to broader and weaker absorption band of
such transition element(s) as iron which additionally improves the
transmittance of low iron clear glass in certain example
embodiments of this invention. In certain example embodiments, the
addition of boron oxide in certain quantities in advantageous in
that it improves the chemical durability of the glass by decreasing
the USPX (or USPXIII) value of the glass via suppression of the
silica, sodium ions in the glass structure.
BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION
[0002] This invention relates to glass compositions having improved
total solar transmission, and improved refining and/or melting
characteristics. In a conventional float line process, glass batch
materials are heated in a furnace or melter to form a glass melt.
The glass melt is poured onto a bath of molten tin (tin bath),
where the glass melt is formed and continuously cooled to form a
float glass ribbon. The float glass ribbon is cooled and cut to
form solid glass articles, such as flat glass sheets. For float
glass, the glass batch often includes soda, lime and silica to form
soda-lime-silica based flat glass.
[0003] There is a tradeoff between glass production and the cost of
manufacture. In particular, it is desirable to increase the rate of
glass production but at the same time it is also desirable to
reduce production costs. Certain glass manufacturers are operating
their glass furnaces at higher and higher throughput and
temperatures to meet the increased demand for glass. However, as
more glass batch is processed, more fuel is required to melt the
increased amounts of glass batch thereby increasing production
costs and decreasing thermal efficiency.
[0004] Certain prior art has attempted to solve these problems. For
example, U.S. Pat. No. 6,797,658 (the disclosure of which is hereby
incorporated herein by reference) discloses decreasing the amount
of MgO in the glass composition and increasing the amount of two or
more of CaO, R.sub.2O (Na.sub.2O and K.sub.2O), Al.sub.2O.sub.3,
and SiO.sub.2 by the same amount. The '658 Patent contends that the
melting and/or forming temperature of the glass can be reduced in
such a manner. See also U.S. Pat. No. 6,878,652 (decreasing MgO and
increasing CaO by the same amount), and U.S. Pat. No. 5,071,796,
the disclosures of which are hereby incorporated herein by
reference. However, these compositions are problematic for numerous
reasons and do not provide for the best results.
[0005] Moreover, low iron glasses are known in the art. However,
when low iron glasses are provided, there exists a need in the art
to improve their transmission, including both their visible
transmission and their total solar transmission. Total solar
transmission is discussed herein in the context of ISO 9050, AM
1.5, which is incoporated herein by reference.
[0006] In view of the above, it will be apparent that there exists
a need in the art for a glass having improved total solar
transmission. There is also a need for a method of making a
soda-lime-silica based glass composition which may realize a
reduced refining time and/or increased refining rate. In certain
example instances it would be desirable to provide a glass
composition that is able to realize a lower viscosity so that
refining of the melt occurs faster in the float line manufacturing
process, and./or a method of making such glass.
[0007] Certain embodiments of this invention relate to a method of
making soda-lime-silica based low iron (total iron no greater than
about 0.04%) glass, and/or glass resulting therefrom. In certain
example embodiments, boron oxide (e.g., such as boron trioxide,
B.sub.2O.sub.3) has the unexpected and surprising effect in
low-iron, high transmission, glass of improving total solar
transmission. The boron oxide also is used for improving glass
refining, homogeneity and quality (lower seed count) through its
flux action and improves glass optical parameters of green and
clear glass through the change in refractive index and surface
tension. Boron oxide lends to broader and weaker absorption band of
such transition element(s) as iron which additionally improves the
transmittance of low iron clear glass in certain example
embodiments of this invention. Glass according to certain example
embodiments of this invention may be used in solar cell
applications (where increased total solar transmission is desired),
or in other suitable applications such as in the context of
architectural windows or the like.
[0008] In certain example embodiments, the addition of boron oxide
in certain quantities in advantageous in that it improves the
chemical durability of the glass by decreasing the USPX (or USPX II
or USPXIII) value of the glass via suppression of the silica,
sodium ions in the glass structure. In certain example embodiments,
the USPX value is reduced to no greater than about 6.0, more
preferably no greater than about 5.8, and most preferably no
greater than about 5.75 (conventional glass made by the assignee of
this application has a USPX value of about 6.2).
[0009] The boron oxide may be introduced into the glass batch or
melt in the form of one or more of boric acid (H.sub.3BO.sub.3),
sodium tetraborate decahydrate (Na.sub.2B.sub.4O.sub.7.
10H.sub.2O), sodium tetraborate pentahydrate, sodium pentahydrate
(Na.sub.2B.sub.4O.sub.7.5H.sub.2O), or in any other suitable form.
In certain example embodiments of this invention, the resulting
soda-lime-silica based glass ends up including by weight percentage
from about 0.1 to 3%, more preferably from about 0.1 to 2.5%, and
most preferably from about 0.5 to 1.5% (e.g., about 1%), boron
oxide (e.g., boron trioxide, B.sub.2O.sub.3). It has surprisingly
been found that the use of boron oxide, and/or the form in which
the same is introduced into the glass melt or batch, is
advantageous in that it increases total solar transmission in low
iron glasses, and permits the refining time of the glass to be
substantially reduced (or the refining rate to be increased). Such
glass compositions are useful, for example and without limitation,
in solar cell applications, and in architectural, vehicular and/or
residential glass window applications.
[0010] In certain example embodiments of this invention, there is
provided a method of making soda-lime-silica based low iron glass
comprising a base glass portion that includes: SiO.sub.2 67-75%,
Na.sub.2O 10-20%, CaO 5-15%, Al.sub.2O.sub.3 0-7%, K.sub.2O 0-7%,
the method comprising: providing boron oxide in a glass melt used
in making the glass, the boron oxide acting to increase total solar
transmission of the low iron glass, reduce refining time of the
glass melt; and increasing a pull rate and/or reducing residence
time of the glass melt in a refining zone of a glass manufacturing
apparatus, compared to a situation where no boron oxide is present.
In other example embodiments of this invention, there is provided a
method of making soda-lime-silica based low iron glass, the method
comprising: providing boron oxide in a glass melt used in making
the soda-lime-silica based glass, in order to increase total solar
transmission and reduce refining time of the glass melt.
[0011] In certain example embodiments, there is provided a glass
comprising:
TABLE-US-00001 Ingredient wt. % SiO.sub.2 69-73% Na.sub.2O 10-20%
CaO 5-15% MgO 0-5% K.sub.2O 0-2% total iron (expressed as
Fe.sub.2O.sub.3) 0.005 to 0.04% FeO 0 to 0.0025% cerium oxide 0 to
0.03% boron oxide 0.1 to 2.5% SO.sub.3 0.1 to 0.6%
wherein the glass has a glass redox of no greater than 0.12, a USPX
value of no greater than 5.8, and a total solar transmission (ISO
9090 1.5 AM, at 3.2 mm reference thickness) of at least 90.8%. This
3.2 mm glass thickness is for purposes of reference only for
purposes of total solar transmission measurement, and is not
limiting as to how thick the glass may be according to the claimed
invention.
IN THE DRAWINGS
[0012] FIG. 1 is a table illustrating certain low iron glass made
as described herein, with DOE 1-6, 1-7, 1-8, and 1-9 being
according to example embodiments of this invention and the other
glasses being for purposes of comparison.
[0013] FIG. 2 is a table illustrating measured XRF characteristics
of low iron glasses made as described herein, with DOE 1-6, 1-7,
1-8, and 1-9 being according to example embodiments of this
invention and the other glasses being for purposes of
comparison.
DETAILED DESCRIPTION OF CERTAIN EXAMPLE EMBODIMENTS OF THIS
INVENTION
[0014] This invention relates to low iron glass compositions having
increased total solar transmission and improved refining and/or
melting characteristics. In a conventional float line process,
glass batch materials are heated in a furnace or melter to form a
glass melt. The glass melt is poured onto a bath of molten tin (tin
bath), where the glass melt is formed and continuously cooled to
form a float glass ribbon. The float glass ribbon is cooled and cut
to form solid glass articles, such as flat glass sheets. For float
glass, the glass batch often includes soda, lime and silica to form
soda-lime-silica based flat glass.
[0015] The process by which bubbles are removed from glass melt
when the vigorous reactions of melting are finished is called
refining (or fining). The quality of refining has a significant
effect on the quality of the final glass. The standards for number
and size of seeds (bubbles) depend(s) on the eventual use of the
glass. It is desirable to remove all seeds from the glass during
the refining process; but from a practical point of view this is
hardly possible and those skilled in the art strive to remove as
many seeds as practically possible.
[0016] In making glass, after weighing and mixing the raw materials
(e.g., sand, soda ash, dolomite, limestone, cullet, fluxes,
refining and/or reducing agents), the batch is charged into the
glass melt tank. The heating of the batch results in reactions
between batch components, dissolution of solid grains and forming
the glass melt that may still contain some un-melted batch
particles. The melt is considered batch-free when all, or
substantially all of, such particles are dissolved. After
dissolution of most batch components, the glass melt contains
dissolved gases and bubbles in sizes varying between about 20
micrometers to several millimeters. Some of these gases come from
the breakdown of the raw materials, while some come from air that
is entrapped between the grains of the batch. Examples gases in the
bubbles include nitrogen, carbon dioxide, oxygen, sulfur dioxide,
argon, and water vapor. Example mechanisms governing the refining
of glass beyond batch-free time include (a) the rise of large seeds
to the glass melt surface where they collapse, (b) coalescence of
seeds to make bigger bubbles which rise faster when they collide,
and (c) dissolution of small seeds.
[0017] The typical way of refining or fining is based on the
addition of a certain amount of a compound or a combination of
compounds, which start to decompose after exceeding a certain
fining-onset temperature of the melt. In float glass production,
sodium sulfate, or salt cake, is primarily used as a fining agent.
These compounds release gas at elevated temperatures, thereby
generating numerous large bubbles. As the bubbles quickly rise to
the surface, they sweep the smaller bubbles in the melt along with
them. For faster bubble removal, the temperature may be increased
to decrease the melt viscosity to about 100 dPas. Fining also
depends on the design and operating parameters of a furnace--the
size of the refiner, the pull rate or residence time of the melt in
the fining zone. Moreover, a temperature increase in general tends
to accelerate refining.
[0018] In certain example embodiments of this invention, boron
oxide is used as a refining or fining agent. The boron oxide is
added to the batch in order to decrease seediness of the melt at
the batch-free time and to reduce the time needed for complete
refining. In other words, boron oxide (e.g., B.sub.2O.sub.3) is
used in the glass for reducing the refining time (or increasing the
refining rate) of the soda-lime-silica glass. The boron oxide may
be introduced into the glass batch or melt in the form of one or
more of boric acid (H.sub.3BO.sub.3), sodium tetraborate
decahydrate (Na.sub.2B.sub.4O.sub.7.10H.sub.2O), sodium
pentahydrate (Na.sub.2B.sub.4O.sub.7.5H.sub.2O), sodium tetraborate
pentahydrate, or in any other suitable form. In certain example
embodiments of this invention, the resulting soda-lime-silica based
glass ends up including by weight percentage from about 0.1 to 3%,
more preferably from about 0.1 to 2.5%, and most preferably from
about 0.5 to 2.0% (e.g., about 1%), boron oxide (e.g.,
B.sub.2O.sub.3). In certain example embodiments, the glass-forming
system remains basically that of basic soda-lime-silica matrix
except that the introduction of boron oxide into the batch/melt
suppresses other oxides such as silica, sodium oxide, which may be
subject to adjustments of their amounts.
[0019] It has been found that the use of boron oxide, and/or the
form in which the same is introduced into the glass melt or batch,
is advantageous in that it permits the refining time of the glass
to be substantially reduced (or the refining rate to be increased).
The introduction of the boron oxide improve glass refining,
homogeneity and/or quality (e.g., lower seed count) through its
flux action and improves glass optical parameters of green and
clear glass for example through the change in refractive index and
surface tension thereby decreasing reflection and/or light
scattering. Boron oxide (e.g., B.sub.2O.sub.3) may cause a broader
and weaker absorption band of a transition element(s) such as iron
which may additionally improve the transmittance of low iron clear
glass in certain example embodiments of this invention. In certain
example embodiments, the batch formulation may also rely on sulfate
refining where, in the case of low or no dolomite introduction for
example, part of all of magnesia can be introduced into the batch
as Epsom salt, magnesium sulfate heptahydrate,
MgSO.sub.4.7H.sub.2O.
[0020] The term USPX is derived from Unites States Pharmacopeia
(USP). In this regard, chemical durability (e.g., sodium leaching)
is an area of concern and standards have been defined for measuring
glass performance in this regard. In particular, ASTM C225-85, the
disclosure of which is hereby incorporated herein by reference,
(method P-W) discloses the technique for determining USPX values
for glass. Generally speaking, ASTM C225-85 (Reapproved 1999)
defines a straightforward method to measure the chemical resistance
of glass in terms of USPX. The quantity of ground glass powder is
immersed in 50 ml of DI water, placed in an autoclave and held at a
specified temperature (121 degrees C.) for a specified time
schedule. The resultant solution is titrated to determined the
amount (ml) of 0.020N H.sub.2SO.sub.4 needed to neutralized the
extracted soda. The USPX number/value is the amount of acid added,
reported in fractions milliliters. A lower volume of leached soda
requires a low volume of acid; a low value of USPX is indicative of
greater chemical resistance. Float glass when actually measured
typically has a USPX value of 6.2 to 7.0 or higher. Unfortunately,
over a period of days glass can be susceptible to severe staining
at USPX values of 6.2-7.0 or higher.
[0021] In certain example embodiments, the addition of boron oxide
in certain quantities discussed herein is advantageous in that it
improves the chemical durability of the glass by decreasing the
USPX (or USPX II or USPXIII) value of the glass via suppression of
the silica, sodium ions in the low iron glass structure. In certain
example embodiments, the USPX value is reduced to no greater than
about 6.0, more preferably no greater than about 5.8, and most
preferably no greater than about 5.75 (conventional glass made by
the assignee of this application has a USPX value of about 6.2 or
higher). This improvement resulting from the addition of boron
oxide to low iron float glass is unexpected and advantageous, as it
improves the durability of the glass.
[0022] Certain glasses for patterned substrate 1 according to
example embodiments of this invention utilize soda-lime-silica flat
glass as their base composition/glass. In addition to base
composition/glass, a colorant portion may be provided in order to
achieve a glass that is fairly clear in color and/or has a high
visible transmission.
[0023] An exemplary soda-lime-silica glass according to certain
embodiments of this invention, on a weight percentage basis,
includes the following basic ingredients:
TABLE-US-00002 TABLE 1 EXAMPLE GLASS Ingredient Preferred wt. %
More Preferred % Most Preferred % SiO.sub.2 69-73% 70-72% 70.5-71.5
Na.sub.2O 10-20% 12-15% 12.75-14% CaO 5-15% 7-12% 8-11% MgO 0-5%
1-5% 2-5% K.sub.2O 0-2% 0-1% 0-0.3% Al.sub.2O.sub.3 0-5% 0.5-3%
1-2% MnO 0-1% 0-0.01% 0-0.005% Cr.sub.2O.sub.3 0-1% 0.0001-0.05%
0.0001-0.005% total iron 0.005-0.04% 0.005-0.03% 0.005-0.020% (as
Fe.sub.2O.sub.3) FeO 0-0.0035% 0-0.0020 0-0.0015 cerium oxide
0-0.07% 0-0.03% 0% antimony oxide 0-0.4% 0-0.2% 0-0.01% boron oxide
0.1-3.0% 0.1-2.5% 0.5-1.5% SO.sub.3 0.1-0.6% 0.15-0.5% 0.25-0.47
glass redox <=0.15 <=0.10 <=0.09 (FeO/total iron)
The glass may comprise or consist essentially of the elements
listed above in alternative example embodiments of this invention.
An example glass reference thickness is about 3.2 mm. Other minor
ingredients, including various conventional refining aids, such as
carbon and the like, or titanium oxide, may also be included in the
glass. In certain embodiments, for example, glass herein may be
made from batch raw materials silica sand, soda ash, dolomite,
limestone, with the use of sulfate salts such as salt cake (Na2SO4)
and/or Epsom salt (MgSO4.times.7H2O) and/or gypsum (e.g., about a
1:1 combination of any) as refining agents. In certain embodiments,
the glass may contain from 0.01 to 0.04% total iron, more
preferably from 0.01-0.03% total iron, and sometimes from
0.01-0.02% total iron.
[0024] In certain example embodiments of this invention, the
resulting glass has visible transmission of at least 75%, more
preferably at least 80%, even more preferably of at least 85%, and
most preferably of at least about 90% (sometimes at least 91%) (Lt
D65). In certain example non-limiting instances, such high
transmissions may be achieved at a reference glass thickness of
about 3 to 4 mm (e.g., 3.2 mm). 100211 In certain preferred
embodiments, there is no cerium oxide in the glass. In particular,
the presence of cerium oxide can have a detrimental effect on the
transmission of the glass after exposure to UV and/or sunlight.
This has been seen at 0.01 and 0.02% by weight. Thus, in certain
example embodiments, the glass contains no cerium oxide. In certain
embodiments, the resulting glass may contain from 0 to 0.01% by
weight of cerium oxide. The glass is also free or substantially
free of nickel in certain example embodiments of this invention. In
certain example embodiments, the glass is also free or
substantially free of zirconium oxide and/or zinc oxide. In certain
example embodiments of this invention, the colorant portion is
substantially free of other colorants (other than potentially trace
amounts). However, it should be appreciated that amounts of other
materials (e.g., refining aids, melting aids, colorants and/or
impurities) may be present in the glass in certain other
embodiments of this invention without taking away from the
purpose(s) and/or goal(s) of the instant invention. For instance,
in certain example embodiments of this invention, the glass
composition is substantially free of, or free of, one, two, three,
four, five or all of: erbium oxide, nickel oxide, cobalt oxide,
neodymium oxide, chromium oxide, zinc oxide, zirconium oxide, and
selenium. The phrase "substantially free" means no more than 2 ppm
and possibly as low as 0 ppm of the element or material.
[0025] The total amount of iron present in the glass batch and in
the resulting glass, i.e., in the colorant portion thereof, is
expressed herein in terms of Fe.sub.2O.sub.3 in accordance with
standard practice. This, however, does not imply that all iron is
actually in the form of Fe.sub.2O.sub.3 (see discussion above in
this regard). Likewise, the amount of iron in the ferrous state
(Fe.sup.+2) is reported herein as FeO, even though all ferrous
state iron in the glass batch or glass may not be in the form of
FeO. As mentioned above, iron in the ferrous state (Fe.sup.2+; FeO)
is a blue-green colorant, while iron in the ferric state
(Fe.sup.3+) is a yellow-green colorant; and the blue-green colorant
of ferrous iron is of particular concern, since as a strong
colorant it introduces significant color into the glass which can
sometimes be undesirable when seeking to achieve a neutral or clear
color.
[0026] In view of the above, glasses according to certain example
embodiments of this invention achieve a neutral or substantially
clear color and/or high visible transmission, although there may be
a slight yellow color in certain instances. In certain embodiments,
resulting glasses according to certain example embodiments of this
invention may be characterized by one or more of the following
transmissive optical or color characteristics when measured at a
thickness of from about 1 mm-6 mm (most preferably a thickness of
about 3-4 mm; this is a non-limiting thickness used for purposes of
reference only) (Lta is visible transmission %). It is noted that
in the table below the a* and b* color values are determined per
Ill. D65, 10 degree Obs., and % .tau.e (ISO 9050) [AM 1.5 at 3.2
mm] refers to total solar transmission.
TABLE-US-00003 TABLE 2 GLASS CHARACTERISTICS OF EXAMPLE EMBODIMENTS
Characteristic General More Preferred Most Preferred Lta (Lt D65):
>=85% >=90% >=91% % .tau.e (ISO 9050): >=90.6%
>=90.8% >=90.9% % FeO (wt. %): <=0.004% <=0.003%
<=0.0020% L* (Ill. D65, 10 deg.): 90-99 n/a n/a a* (Ill. D65, 10
deg.): -1.0 to +1.0 -0.5 to +0.5 -0.2 to 0.0 b* (Ill. D65, 10
deg.): 0 to +1.5 +0.1 to +1.0 +0.2 to +0.7
[0027] The aforesaid characteristics of the glass substrate itself.
As can be seen from Table 2 above, glasses for substrate 1 of
certain embodiments of this invention achieve desired features of
fairly clear color and/or high visible and total solar
transmission, with slightly positive b* color in certain
embodiments, while not requiring iron to be eliminated from the
glass composition. This may be achieved through the provision of
the unique material combinations described herein.
EXAMPLES 1-3
[0028] Example glasses were made according to example embodiments
of this invention. Glasses of this invention may be made from batch
ingredients using well known glass melting and refining techniques,
unless otherwise indicated. The compositions of the glasses
according to the examples are set forth in FIGS. 1-2. All amounts
of ingredients are in terms of weight percentage. In particular, in
FIGS. 1-2 the glasses at DOE 1-6, 1-7, 1-8, and 1-9 represent
Examples 1, 2 and 3 of this invention, respectively; whereas the
other glasses in FIGS. 1-2 represent comparative examples.
[0029] FIG. 1 sets forth the glass melt descriptions of the various
glasses including the make-up (constant glass yield=100 g per melt)
of the glass melt and the USPX value of each glass. Meanwhile, FIG.
2 illustrates the measured XRF results matrix for each of the
glasses made in accordance with FIG. 1. Boron oxide was added in
Examples 1-3, but was not present in the comparative examples in
FIGS. 1-2. It can be seen in Examples 1-3 (i.e., DOE 1-6, 1-7, 1-8,
and 1-9) in FIG. 2, that the addition of the boron oxide
surprisingly improves (increases) the total solar transmission (%
.tau.e (ISO 9050)) of the low iron (total iron no greater than
0.04%) glass. Generally speaking, the low iron glasses having boron
oxide had higher total solar transmission than those not having the
boron oxide. Additionally, it can be seen in FIG. 1 that the
addition of the boron oxide to the low iron glasses surpringly
resulted in an improved (lower) USPX value. In the comparative low
iron glasses in which no boron oxide was present (DOE 1-1 through
1-5), the USPX values were from 6.37 to 6.41. Meanwhile, in
Examples 1-3 (i.e., DOE 1-6, 1-7, 1-8, and 1-9) in FIG. 1, the USPX
values were improved (decreased) and ranged from 5.70 to 6.27.
Thus, it can be seen that the addition of the boron oxide to the
low iron glass improved both the USPX values and the total solar
transmission of these particular types of glasses.
[0030] The total amount of iron present in the glass batch and in
the resulting glass, i.e., in the colorant portion thereof, is
expressed herein in terms of Fe.sub.2O.sub.3 in accordance with
standard practice. This, however, does not imply that all iron is
actually in the form of Fe.sub.2O.sub.3 (see discussion above in
this regard). Likewise, the amount of iron in the ferrous state
(Fe.sup.+2) is reported herein as FeO, even though all ferrous
state iron in the glass batch or glass may not be in the form of
FeO. As mentioned above, iron in the ferrous state (Fe.sup.2+; FeO)
is a blue-green colorant, while iron in the ferric state
(Fe.sup.3+) is a yellow-green colorant; and the blue-green colorant
of ferrous iron is of particular concern, since as a strong
colorant it introduces significant color into the glass which can
sometimes be undesirable when seeking to achieve a neutral or clear
color. Deep oxidation in certain example embodiments of this
invention may be achieved by operations adjustments and chemically
by introduction of sulfates in the form of one or more of salt cake
(e.g., Na.sub.2SO.sub.4), Epsom salt (e.g.,
MgSO.sub.4.times.7H.sub.2O) and/or gypsum in significant amounts
and combination of one or more of these with potassium and/or
sodium nitrate. The salt cake may be referred to in the final glass
as SO.sub.3. The high amounts of salt cake used in certain example
embodiments, can be seen from the large amounts of SO.sub.3
mentioned herein with respect to the final glass composition. In
particular, one or more of these oxidizing elements are added to
the glass batch in amount(s) sufficient to cause the glass batch to
realize a batch redox of from about +12 to +30 in certain example
embodiments of this invention, even more preferably from about +15
to +30, and most preferably from about +20 to +30 in certain
example embodiments. It is noted that batch redox is different than
glass redox. Batch redox is known in the art as being generally
based on the following. Each component of the batch is assigned a
redox number, and the batch redox is calculated as the sum total of
the same. The batch redox number is calculated before the glass is
made, from the batch. A detailed discussion of "batch redox" and
how it is determined is provided in The redox number concept and
its use by the glass technologist, W. Simpson and D. D. Myers (1977
or 1978), which is incorporated herein by reference. In contrast
with batch redox, glass redox is calculated after the glass has
been made from spectral data or the like, and is a ratio of % FeO
to total iron in the glass. The high batch redox discussed above
causes iron in the ferrous state (Fe.sup.2+; FeO) to oxidize to the
ferric state (Fe.sup.3+) and thus causes an amount of the strong
blue-green colorant of ferrous iron (Fe.sup.2+; FeO) to oxidize
into the weaker yellow-green ferric iron colorant (Fe.sup.3+)
during the glass melt (note: some ferrous state iron may remain in
the resulting glass). The aforesaid oxidation of the iron tends to
reduce coloration of the glass, reduces % FeO, and causes visible
transmission, % UV and % TS to increase. Any yellowish color caused
by oxidation of iron into ferric state (Fe.sup.3+) iron (i.e.,
positive b*) may be acceptable in solar cell applications and need
not be compensated for by addition of other colorants thereby
saving cost in certain example embodiments of this invention.
[0031] It will be appreciated by those skilled in the art that the
high batch redox results in a glass with a lower "glass redox"
value (i.e., less iron in the ferrous state FeO). In this regard,
the proportion of the total iron in the ferrous state (FeO) is used
to determine the redox state of the glass, and redox is expressed
as the ratio FeO/Fe.sub.2O.sub.3, which is the weight percentage
(%) of iron in the ferrous state (FeO) divided by the weight
percentage (%) of total iron (expressed as Fe.sub.2O.sub.3) in the
resulting glass. Due to at least the presence of the oxidizing
agent(s), the glass redox of glass according to certain example
embodiments of this invention is low as mentioned above, and the
amount of iron in the ferrous state (FeO) will also be low as
discussed above.
[0032] Glass is provided herein which may be used in photovoltaic
(e.g., solar cell) applications. However, the use of the glass
discussed herein is not so limited. Glass described herein may
instead or also be used in applications such as windows, shower
doors, and the like in certain example embodiments of this
invention.
[0033] Once given the above disclosure many other features,
modifications and improvements will become apparent to the skilled
artisan. Such features, modifications and improvements are
therefore considered to be a part of this invention, the scope of
which is to be determined by the following claims:
* * * * *