Forsterite ceramic bodies

Claim 1

A FORSTERITE CERAMIC BODY CONSISTING ESSENTIALLY OF A VITRIFIED MIXTURE OF SIO2 MGO AND AL2O3 HAVING COMPOSITIONAL LIMITS WITHIN THE TRIANGULAR AREA OF THE TERNARY PHASE EQUILIBUM DIAGRAM OF THE SIO2 MGO AND AL2O3 SYSTEM BOUNDED BY STRAIGHT LINES CONNECTING COMPOSITIONS CONSISTING OF ABOUT (1) 42.5 WEIGHT PERCENT SIO2, 56.5 WEIGHT PERCENT SIO2 44 WEIGHT PERCENT AL2O2; (2) 41 WEIGHT PERCENT SIO2 44 WEIGHT PERCENT MGO AND 15 WEIGHT PERCENT AL2O2; AND (3) 34.5 WEIGHT PERCENT AL2O 50.5 WEIGHT PERCENT MGO AND 15 WEIGHT PERCENT AL2O3, SAID BODY BEING VITRIFIED TO THE EXTENT THAT IS VACUUM TIGHT AND FREE FROM CONTINUOUS POROSITY AND NOT TO THE EXTENT THAT SURFACE DEFECTS OR CRACKS ARE PRODUCED, AND SAID BODY CONTAINING CRYSTALLINE FORSTERIE AS THE MAJOR MINERAL CONSTITUENTS AND CONTAINING SPINEL AND GLASS AS MINOR MINERAL CONSTITUENTS AND BEING SUBSTANTIALLY FREE FROM PROTENSTATITE AND FREE MAGNESIUM OXIDE AND HAVING AN AVERAGE COEFFICIENT OF THERMAL EXPANSION BETWEEN 25*C. AND 700*C. OF ABOUT 9.4X10-6 CENTIMETER PER CENTIMER PER *C. TO ABOUT 10.4X10-6 CENTIMETER PER CENTIMETER PER *C. AND MATCHING METALLIC TITANIUM IN THERMAL EXPANSION AND CONTRACTION.