Mullite-beta spodumene composite ceramic

Claim 1

A process for producing a polycrystalline body comprised of from about 50% by weight to about 95% by weight of crystalline mullite phase and from about 5% by weight to about 50% by weight of crystalline beta spodumene phase which comprises providing a mixture comprised of mullite and/or beta spodumene and/or Al 2 O 3 and/or SiO 2 and/or a precursor for Li 2 O, said mixture having a composition required to produce said polycrystalline body, shaping said mixture into a compact, sintering said compact at a temperature ranging from greater than 1423° C. to about 1500° C. at which sufficient liquid phase is generated to liquid phase sinter the compact and produce a densified body having a density greater than about 85% of the theoretical density of said body, said sintering temperature having no significant deleterious effect on said compact or body, said sintered body containing said mullite phase and a glassy phase of beta spodumene, nucleation-annealing said sintered body at a temperature ranging from about 600° C. to about 800° C. to nucleate said glassy beta spodumene phase, crystallization-annealing the resulting nucleated body at a temperature ranging from about 1200° C. to below the temperature at which liquid forms in said body to produce said polycrystalline body, said sintering, said nucleation-annealing and said crystallization-annealing being carried out in an atmosphere or vacuum which has no significant deleterious effect on said compact or body, and said body does not contain a phase of silica.