Method for environmentally friendly melting and refining a glass melt for an initial glass of a lithium-aluminium silicate (LAS) glass ceramic

摘要

A lithium aluminum silicate (LAS) batch of glass is prepared with 0.1-0.6 wt% tin oxide as the main clarification agent, omitting arsenic or antimony oxide clarification agents. The quantity of quartz sand providing the SiO 2content, is reduced to preferably below 5 wt%. The glass melt is clarified at 1600[deg] C, preferably at 1650[deg] C or more. A glass batch is prepared with the addition of 0.1 to 0.6 wt% tin oxide and 0.05 to 0.3 wt% of iron oxide for combination clarification. A Li 2O-Al 2O 3-SiO 2combination is used as the main material, forming preferably 70 wt% of the mixture. The main raw material is petalite and/or spodumene. The mixture prepared for the LAS glass system ensures that during clarification the maximum oxygen release obeys the relationship: O 2(mol)/impurity gases(mol) exceeds 0.02. 20-60 wt% of cullet is added to the glass mixture. Infra red absorption of the glass melt is adjusted such that at room temperature, a 4 mm thick glass sheet has a 1600 nm IR transmission of 40-80%. Clarification takes place below 1700[deg] C, avoiding use of additional high temperature equipment. It alternatively takes place at over 1750[deg] C. The throughput or mean residence time is such that a bubble inclusion number of less than 1 bubble/kg of glass is achieved. Specific variant glass compositions are proposed and quantified, based on the foregoing principles. The V 2O 5content is preferably less than 0.03 wt%.