Embedding material useful in preparing glass-ceramic products

摘要

The instant invention relates to the development of an embedment material suitable for use in heat treating glass castings to convert them into glass-ceramic articles, whereby the shrinkage customarily experienced resulting from densification of the casting during conversion to a glass-ceramic is minimized and sound glass-ceramic articles of tight dimensional tolerances can be produced. The inventive embedment materials will: (a) contain an inorganic component which is subject to an inversion accompanied with a large change in volume at a temperature below the set point of the glass-ceramic article; (b) demonstrate a coefficient of thermal expansion equal to or no more than about 40x10-7/ DEG C. units greater than that exhibited by the glass-ceramic article; (c) display a refractoriness sufficient to resist thermal deformation and slumping and be resistant to a phase change at the temperature employed to convert the glass casting to a glass-ceramic article; and (d) be inert to the glass and glass-ceramic. One particularly suitable investment consists essentially, by weight, of 5-30% plaster of Paris and 70-95% leucite.