Heat resistive phosphate sintered bodies and a process for producing the

Abstract

A heat resistive phosphate sintered body including a solid solution of R.sub.y Zr.sub.4 Si.sub.x P.sub.6-x O.sub.24 in which O.ltoreq.x.ltoreq.2, 2/3.ltoreq.y.ltoreq.2, R is a combination of one or more of cations having 2-3 valences, and x and y meet an electrically neutral condition, wherein a thermal expansion hysteresis loss is not more than 0.3%, and a dimensional change after a heat cycling in which heating and cooling are repeated between 100.degree. C. and 1,200.degree. C. at 100 times is not more than 1%. A process for producing such a heat resistive phosphate is also disclosed. The process includes the steps of preparing a batch mixture, as a starting material, of (ZrO).sub.2 P.sub.2 O.sub.7, ZrP.sub.2 O.sub.7, RO and/or a phosphate of R in which R is a combination of one or more of cations having two or three valences, and if necessary further SiO.sub.2, calcining, milling and shaping the thus prepared mixture, and firing the thus shaped body, wherein a calcining temperature is not less than 1,400.degree. C. and equal to or higher than a firing temperature, the starting material is a powder milled to an average particle diameter of not more than 7 .mu.m, and the firing temperature is not less than 1,300.degree. C.