Method for the production of glass - crystal - mixing bodies based on sio deep 2 - al deep 2 o deep 3 - bao - mgo - tio deep 2, in a similar manner the porcelain appearance and high mechanical and thermal have strengths

摘要

A thermally-crystallizable glass composition consists essentially of 16-19.5% BaO, 7-10% MgO, 16.5-19% Al2O3, 46-49% SiO2 and 6-12% TiO2 by weight, these components in total being at least 95%. A glass-ceramic body may be made by exposing glass of the above composition to 1100-1175 DEG C. Preferably a batch containing the necessary components is melted, then simultaneously shaped and cooled to below the point of transformation to an amorphous solid, then heated to 780-820 DEG C. for 1-6 hours or longer to initiate nucleation, then heated to 1100-1175 DEG C. for 2-24 hours or longer. The transformation point is at about the annealing point, viz. 700-725 DEG C. The articles may after shaping be cooled to room temperature for inspection and decoration before heat treatment. The articles may be heated to the transformation temperature at e.g. 5 DEG C. per minute. The rate of heating after the nucleation step may also be 5 DEG C. per minute. Alternatively, in a one-step heat treatment the body may be heated from the transformation point at not more than 3 DEG C. per minute. The glass-ceramic article may be cooled to room temperature at 5-10 DEG C. per minute or faster. The articles contain hexacelsian (BaO.Al2O3.2SiO2) as primary phase. A minor phase of magnesium dititanate and traces of a phase with 7-2 rA X-ray diffraction peak may be present. Other compatible oxides, e.g. Na2O, K2O, B2O3 as fluxes and ZnO and ZrO2 as chemical stabilizers may be present up to a total of not more than 5%. A fining agent, e.g. As2O3 or Sb2O3 may be present; up to about 1% may be added. The bodies possess modulus of rupture of at least 30,000 p.s.i., linear coefficient of thermal expansion of at most 70 x 10-7 per DEG C., good resistance to food stains, good chemical durability, good compatibility to glazes, and likeness to the appearance and feel of fine china. The articles have crystal content of at least 30%, and the crystals, of diameter less than 30m , are randomly dispersed throughout the glassy matrix. The shaping may be performed by conventional methods. Specifications 829,447 and 975,048 are referred to.