SEMITRANSLUCENT VITREOCERAMIC MATERIAL, METHOD OF OBTAINING SUCH MATERIAL, APPLICATION THEREOF AND PRODUCTS MADE OF SUCH VITREOCERAMIC MATERIAL

摘要

Translucent glass ceramic has a light transmission in the visible region of 0.5 -10 % at a sample thickness of 4 mm, an impact resistance of more than 18 cm tested with a 200 g steel ball in a falling ball test, and a temperature difference strength of more than 650 degrees C. Keatite mixed crystals are present as the predominant crystal phase inside the glass ceramic and high quartz mixed crystals as further mixed crystal phase in the surface layer of the glass ceramic. The thermal expansion of the high quartz mixed crystals is smaller than that of the keatite mixed crystals so that a surface state of the ceramic is produced which counteracts the production of surface damage is avoided. The SiO2 content of the high quartz mixed crystals is less than 80 weight % so that on cooling the ceramic to room temperature conversion of the high quartz mixed crystals to an unwanted deep quartz mixed crystal phase which leads to tears on the surface of the ceramic is avoided. An Independent claim is also included for a process for the production of a plate-like glass ceramic. Preferred Features: The temperature difference strength of the glass ceramic is more than 700 degrees C. The glass ceramic has a composition of (in weight %): 3.0-4.0 Li2O, 0-1.0 Na2O, 0-0.6 K2O, 0.2-1.0 Na2) + K2O, 0-1.5 MgO, 0-0.5 CaO, 0-1.0 SrO, 0-2.5 BaO, 0.2-3.0 CaO + SrO + BaO, 1.0-2.2 ZnO, more than 19.8-23 Al2O3, 66-70 SiO2, 2.0-3.0 TiO2, 0.5-2.0 ZrO2, 0-1.0 P2O5, and optionally a refining agent such as As2O3, Sb2O3, SnO2, CeO2 and/or sulfate and/or chloride compounds in the usual amounts.