Preform core bodies

Claim 1

A preform core body capable of withstanding contact with molten metal at temperatures up to 1,600*C., exhibiting a modulus of rupture of at least 2,000 psi, demonstrating ready leaching when immersed in molten alkali, having a coefficient of thermal expansion ranging between about 30-60 X 10 7/*C., and being relatively inert to nickel and cobalt base superalloys comprising a sintered body consisting essentially, by weight, of 10-80 percent of a highly siliceous material selected from the group consisting of fused quartz, fused silica and silica glass in which there is at least 90 percent silica and 20-90 percent of at least one Cs2O-containing material selected from the group consisting of pollucite mineral, a glass-ceramic consisting essentially, by weight, of >15% but <40% Cs2O, >10% but <55% Al2O3, and >25% but <75% SiO2, wherein the crystal phase thereof consists essentially of pollucite, and a glass-ceramic consisting essentially, by weight, of >4% but <15% Cs2O, >15% but <35% Al2O3, and >35% but <80% SiO2, wherein the crystal phase thereof consists essentially of mullite.