Method of making glass with reduced Se burnoff

Details Method of making glass with reduced Se burnoff Method of making glass with reduced Se burnoff

2001-04-26

2004-01-06

Vincent, Sean (Department: 1731)

Glass manufacturing

Processes

Fining or homogenizing molten glass

C065S134100

Reexamination Certificate

active

06672108

ABSTRACT:

This invention relates to a method of making glass (e.g., grey or dark in color) using a technique where selenium (Se) burnoff is reduced during the process of manufacture so as to reduce pollution. The resulting glass compositions are thus useful, for example, in vehicle windows and/or architectural applications.
BACKGROUND OF THE INVENTION
Privacy windows for use in automobiles and/or architectural applications are becoming more popular, as is demand for grey glass in general. These glasses are typically based upon a standard soda-lime-silica glass composition (used to make float glass) to which is added various colorants to attain the desired coloring and spectral properties. Iron, typically including both ferric (Fe
3+
) and ferrous (Fe
2+
) iron, is often used in such glasses. Ferric iron is a strong ultraviolet (UV) absorber and yellow/green colorant while ferrous iron is a known infrared (IR) absorber and blue colorant. Other colorants which are often used in such glasses include Se, Co, Cr, Mn, V, Ce, Ti, Mo, and the like.
Commonly owned U.S. Pat. No. 5,932,502 (hereby incorporated herein by reference) discloses a dark grey privacy glass composition including a colorant portion of Fe
2
O
3
(total iron), Co
3
O
4
, Se, and Cr
2
O
3
. The resulting glass of the '502 patent has good coloring and spectral characteristics.
Unfortunately, when making the glass of the '502 patent a large percentage of the Se originally added to the batch burns off during the process of glass manufacture (i.e., a high rate of Se burnoff is experienced). Se is a known pollutant, and high rates of Se burnoff are thus undesirable for environmental reasons. For example, when making glass according to the '502 patent commercially, about 0.1000% (wt. %) metallic Se is originally provided in the batch along with about 1.0% salt cake which is used as a refining agent. After the batch is melted and processed, the resulting glass has only about 0.0026-0.0028% Se left therein (the rest of the Se has burned off). This translates into a Se retention of less than 10% (i.e., at least about 90% of the Se originally present in the batch burns off during the process of manufacture). This high rate/percentage of Se burnoff is undesirable.
U.S. Pat. No. 5,346,867 discusses the problem of Se vaporization. In response to the problem, the '867 patent uses manganese oxide in order to decrease Se burnoff. Unfortunately, the MnO
2
technique used in the '867 patent only enables up to 22.3% of the originally presented Se to be retained (see Table III in the '867 patent).
In view of the above, it will be apparent to those skilled in the art that there exists a need in the art for a method of making Se-inclusive glass wherein the rate and/or percentage of Se burnoff during the process of glass manufacture can be reduced and/or minimized.
SUMMARY OF THE INVENTION
An object of this invention is to provide a method of making a selenium (Se) inclusive glass in a manner such that Se burnoff during the process of manufacture is reduced. This method may be applied to grey colored glass in certain embodiments of this invention, as well as to other colored glasses in other embodiments of this invention.
Another object of this invention is to reduce Se burnoff in a process of glass manufacture by using Epsom salt(s) (e.g., MgSO
4
×7H
2
O) as a refining agent and/or melting aide. Surprisingly, it has been found that the use of Epsom salt(s) (e.g., instead of and/or in addition to salt cake or the like) as a batch component enables more Se to be retained (i.e., less Se burnoff).
Another object is to fulfill one or more of the above-listed objects and/or needs.
Generally speaking, this invention fulfills one or more of the above-listed objects or needs by providing a method of making glass, the method comprising:
processing a molten glass batch including Se in order to form a resulting glass product comprising SiO2 and Se, in a manner so that the resulting glass product retains at least 30% of the Se originally present prior to melting.
In other embodiments of this invention, one or more of the above-listed needs and/or objects is/are fulfilled by providing a method of making glass, the method comprising:
providing a glass batch including SiO2, Fe2O3, Epsom salt, and an original amount of Se; and
forming a resulting glass product from the glass batch in a manner such that the resulting glass product includes at least 30% of the original amount of Se due at least to the presence of a sufficient quantity of the Epsom salt in the batch.
In certain other embodiments of this invention, one or more of the above-listed needs or objects is fulfilled by providing a method of making a grey colored glass, the method comprising:
providing a molten glass batch comprising SiO2, Se, and Epsom salt;
processing the glass batch in order to make a resulting grey colored glass product, the grey colored glass product including a base glass portion comprising:
Ingredient
wt. %
SiO
2
67-75%
Na
2
O
10-20%
CaO
 5-15%
MgO
0-5%
Al
2
O
3
0-5%
K
2
O
0-5%
BaO
0-1%
and a colorant portion comprising:
Ingredient
Amount
Total iron (expressed as Fe
2
O
3
):
1.0 to 2.2% (wt. %)
selenium (Se):
10 to 50 ppm
cobalt oxide:
0.015 to 0.040%
titanium oxide:
0 to 3.5%
chromium oxide:
0 to 0.03%; and
wherein the Epsom salt is provided in the glass batch in sufficient quantity so that the resulting glass product retains at least 30% of the Se originally present in the batch.
Certain other embodiments of this invention fulfill a desired need by providing a grey colored glass comprising:
a base portion and a colorant portion;
said base portion of the glass comprising:
Ingredient
wt. %
SiO
2
67-75%
Na
2
O
10-20%
CaO
 5-15%
MgO
0-5%
Al
2
O
3
0-5%
K
2
O
0-5%
BaO
0-1%
and said colorant portion consisting essentially of:
Ingredient
Amount
Total iron (expressed as Fe
2
O
3
):
1.4 to 1.8% (wt. %)
selenium (Se):
10 to 50 ppm
cobalt oxide:
0.015 to 0.040%
titanium oxide:
0.2 to 3.5%
chromium oxide:
0 to 0.03%; and
wherein the glass is grey in color and has a dominant wavelength in the range of from 435 nm to 570 nm, is substantially free of manganese dioxide, and is substantially free of nickel.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THIS INVENTION
Glasses (e.g., colored grey or any other suitable color) according to different embodiments of this invention may be used, for example, in the automotive industry (e.g., windshields, backlites, side windows, etc.), in architectural applications, and/or in other suitable applications. Resulting glass products herein may be from about 1-12 mm thick in different embodiments.
Certain glasses according to this invention utilize soda-lime-silica flat glass as their base composition/glass, to which is added certain ingredients making up a colorant portion. An exemplary soda-lime-silica base glass according to certain embodiments of this invention, on a weight percentage (wt. %) basis, includes the following basic ingredients:
TABLE 1
EXEMPLARY BASE GLASS
Ingredient
Wt. %
SiO
2
67-75%
Na
2
O
10-20%
CaO
 5-15%
MgO
0-5%
Al
2
O
3
0-5%
K
2
O
0-5%
BaO
0-1%
B
2
O
3
0-5%
In certain embodiments, for example, glass herein may be made from batch raw materials silica sand, soda ash, dolomite, limestone, with the use of at least Epsom salt(s) as refining agent and/or melting aide. Other minor ingredients, including various conventional refining aids may also be included in the base glass. Additionally, in certain embodiments a spectral modifier such as sodium phosphate (Na
2
HPO
4
) in an amount of from 0 to 2.0%, more preferably from 0 to 1.5%, may be added to the batch for color adjustment purposes. Sodium phosphate, while a color modifier, is not defined as a “colorant” herein.
As explained in more detail below, the use of Epsom salts (e.g., MgSO
4
×7H
2
O) in the process of glass manufacture has surprisingly been found to reduce Se burnoff during the manufacturing process (e.g., conventional melt and float processing). This reduction in selenium (Se) burnoff is significant in that it bo

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