1. Field of the Invention
The present invention relates to Li2Oxe2x80x94Al2O3xe2x80x94SiO2 crystallized glass and Li2Oxe2x80x94Al2O3xe2x80x94SiO2 crystallizable glass therefor.
2. Description of the Related Art
Conventionally, Li2Oxe2x80x94Al2O3xe2x80x94SiO2 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 Li2Oxe2x80x94Al2O3xe2x80x94SiO2 crystallized glass having a xcex2-quartz solid solution represented by the formula Li2Oxe2x80x94Al2O3.nSiO2, in which nxe2x89xa72, or a xcex2-spodumene solid solution represented by the formula Li2Oxe2x80x94Al2O3.nSiO2, in which nxe2x89xa74, both of which are produced in the crystallized glass as a main crystal.
The Li2Oxe2x80x94Al2O3xe2x80x94SiO2 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 Li2Oxe2x80x94Al2O3xe2x80x94SiO2 crystallized glass is alterable by changing heating conditions in a crystallization process, transparent crystallized glass (a xcex2-quartz solid solution (produced) and white and opaque crystallized glass (a xcex2-spodumene solid solution is produced) can be produced from the same composition of raw glass materials. Consequently, in accordance with the application, Li2Oxe2x80x94Al2O3xe2x80x94SiO2 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 1,400xc2x0 C. for melting raw glass materials. Accordingly, as a fining agent added to one batch for glass production, arsenic oxide (As2O3) 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, As2O3 contained in raw glass materials is oxidized at 400 to 500xc2x0 C. so as to form As2O5, and the As2O5 is again reduced at 1,200 to 1,800xc2x0 C. to form As2O3, 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 As2O3 has the fining effect described above, As2O3 has been widely used as a fining agent for glass. In particular, As2O3 is a very effective fining agent for Li2Oxe2x80x94Al2O3xe2x80x94SiO2 crystallized glass that must be subjected to melting at a high temperature.
In addition to the fining effect, As2O3 has an effect of promoting crystallization. Accordingly, it is understood that As2O3 is an essential component in order to obtain desired characteristics of the crystallized glass described above.
However, As2O3 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 As2O3 used. However, when the amount of As2O3 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 As2O3 were not decreased, cannot be obtained.
Accordingly, it is an object of the present invention to provide Li2Oxe2x80x94Al2O3xe2x80x94SiO2 crystallized glass having clarity and glass characteristics equivalent to or superior to those of conventional crystallized glass, even when the amount of As2O3 used is decreased, and to provide Li2Oxe2x80x94Al2O3xe2x80x94SiO2 crystallizable glass as a raw glass material therefor.
According to one aspect of the present invention, there is provided a Li2Oxe2x80x94Al2O3xe2x80x94SiO2 crystallized glass which consists essentially of, by weight, 60 to 75% SiO2, 17 to 27% Al2O3, 3 to 5% Li2O, 0 to 0.9% MgO, 0 to 0.9% ZnO, 0.3 to 5% BaO, 0 to 3% Na2O, 0 to 3% K2O, 0 to 4% TiO2, 1 to 4% ZrO2, 0 to 4% P2O5, 0.05 to 2% Sb2O3, 0 to 0.9% MgO+ZnO, and 0 to 4% Na2O+K2O.
According to another aspect of the present invention, there is provided a Li2Oxe2x80x94Al2O3xe2x80x94SiO2 crystallizable glass which consists essentially of, by weight, 60 to 75% SiO2, 17 to 27% Al2O3, 3 to 5% Li2O, 0 to 0.9% MgO, 0 to 0.9% ZnO, 0.3 to 5% BaO, 0 to 3% Na2O, 0 to 3% K2O, 0 to 4% TiO2, 1 to 4% ZrO2, 0 to 4% P2O5, 0.05 to 2% Sb2O3, 0 to 0.9% MgO+ZnO, and 0 to 4% Na2O+K2O.