Compositions: ceramic – Ceramic compositions – Devitrified glass-ceramics
Reexamination Certificate
2000-07-27
2002-10-29
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Devitrified glass-ceramics
C501S004000
Reexamination Certificate
active
06472338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to Li
2
O—Al
2
O
3
—SiO
2
crystallized glass and Li
2
O—Al
2
O
3
—SiO
2
crystallizable glass therefor.
2. Description of the Related Art
Conventionally, Li
2
O—Al
2
O
3
—SiO
2
crystallized glass has been used for front glass panels in kerosene heaters, wood stoves, and the like, substrates for high-technology products such as color filters and image sensors, setters for baking electronic devices, shelf boards for microwave ovens, top plates for electromagnetic cooking devices, window glass for fire doors, and the like.
For example, Japanese Examined Patent Publication (JP-B) No. S39-21,049, Japanese Examined Patent Publication (JP-B) No. S40-20,182, and Japanese Unexamined Patent Publication (JP-A) No. H01-308,845 disclose Li
2
O—Al
2
O
3
—SiO
2
crystallized glass having a &bgr;-quartz solid solution represented by the formula Li
2
O—Al
2
O
3
.nSiO
2
, in which n≧2, or a &bgr;-spodumene solid solution represented by the formula Li
2
O—Al
2
O
3
.nSiO
2
, in which n≧4, both of which are produced in the crystallized glass as a main crystal.
The Li
2
O—Al
2
O
3
—SiO
2
crystallized glass mentioned above has high mechanical strength and superior thermal characteristics, such as a low coefficient of thermal expansion. In addition, since the crystal produced in the Li
2
O—Al
2
O
3
—SiO
2
crystallized glass is alterable by changing heating conditions in a crystallization process, transparent crystallized glass (a &bgr;-quartz solid solution (produced) and white and opaque crystallized glass (a &bgr;-spodumene solid solution is produced) can be produced from the same composition of raw glass materials. Consequently, in accordance with the application, Li
2
O—Al
2
O
3
—SiO
2
crystallized glass suitable for the application can be selectively produced.
When this kind of crystallized glass is produced, it is required to heat up to a high temperature above 1,400° C. for melting raw glass materials. Accordingly, as a fining agent added to one batch for glass production, arsenic oxide (As
2
O
3
) is used which is capable of evolving a great deal of gas for fining during melting at a high temperature. In melting in a batch production system, As
2
O
3
contained in raw glass materials is oxidized at 400 to 500° C. so as to form As
2
O
5
, and the As
2
O
5
is again reduced at 1,200 to 1,800° C. to form As
2
O
3
, whereby oxygen gas is evolved. The oxygen gas thus evolved diffuses into bubbles in the glass, and the bubbles enlarge, facilitating rising thereof, whereby the bubbles are removed. Since As
2
O
3
has the fining effect described above, As
2
O
3
has been widely used as a fining agent for glass. In particular, As
2
O
3
is a very effective fining agent for Li
2
O—Al
2
O
3
—SiO
2
crystallized glass that must be subjected to melting at a high temperature.
In addition to the fining effect, As
2
O
3
has an effect of promoting crystallization. Accordingly, it is understood that As
2
O
3
is an essential component in order to obtain desired characteristics of the crystallized glass described above.
However, As
2
O
3
is highly toxic, and hence, environmental pollution may occur during a manufacturing process for glass, disposal of waste glass, and the like. Accordingly, it is desirable to reduce the amount of As
2
O
3
used. However, when the amount of As
2
O
3
is simply decreased, the effects on fining and crystallization are degraded, and as a result, clarity and glass characteristics, which are equivalent to those obtained if the amount of As
2
O
3
were not decreased, cannot be obtained.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide Li
2
O—Al
2
O
3
—SiO
2
crystallized glass having clarity and glass characteristics equivalent to or superior to those of conventional crystallized glass, even when the amount of As
2
O
3
used is decreased, and to provide Li
2
O—Al
2
O
3
—SiO
2
crystallizable glass as a raw glass material therefor.
According to one aspect of the present invention, there is provided a Li
2
O—Al
2
O
3
—SiO
2
crystallized glass which consists essentially of, by weight, 60 to 75% SiO
2
, 17 to 27% Al
2
O
3
, 3 to 5% Li
2
O, 0 to 0.9% MgO, 0 to 0.9% ZnO, 0.3 to 5% BaO, 0 to 3% Na
2
O, 0 to 3% K
2
O, 0 to 4% TiO
2
, 1 to 4% ZrO
2
, 0 to 4% P
2
O
5
, 0.05 to 2% Sb
2
O
3
, 0 to 0.9% MgO+ZnO, and 0 to 4% Na
2
O+K
2
O.
According to another aspect of the present invention, there is provided a Li
2
O—Al
2
O
3
—SiO
2
crystallizable glass which consists essentially of, by weight, 60 to 75% SiO
2
, 17 to 27% Al
2
O
3
, 3 to 5% Li
2
O, 0 to 0.9% MgO, 0 to 0.9% ZnO, 0.3 to 5% BaO, 0 to 3% Na
2
O, 0 to 3% K
2
O, 0 to 4% TiO
2
, 1 to 4% ZrO
2
, 0 to 4% P
2
O
5
, 0.05 to 2% Sb
2
O
3
, 0 to 0.9% MgO+ZnO, and 0 to 4% Na
2
O+K
2
O.
REFERENCES:
patent: 5212122 (1993-05-01), Pannhorst et al.
patent: 5446008 (1995-08-01), Krolla et al.
patent: 43 21 373 (1995-01-01), None
patent: 39-21049 (1939-09-01), None
patent: 40-20182 (1940-09-01), None
patent: 1-308845 (1989-12-01), None
patent: 3120422 (2000-12-01), None
Sakamoto Akihiko
Shimatani Narutoshi
Yamada Hiroyuki
Collard & Roe P.C.
Group Karl
Nippon Electric Glass Co. Ltd.
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