ENSTATITE CERAMICS - A MULTICOMPONENT SYSTEM VIA SOL-GEL

Submicrometre particles with enstatite stoichiometry were prepared by flame-aerosol technique, using a solution of magnesium ethoxide and TEOS in ethylene glycol monomethyl ether. The solution was run through an aerosol generator with a nozzle that delivered the aerosol stream into a highly focused burner. This produced unagglomerated, 300-600 angstrom spherical particles, with a surface area of 108 m2/g. The powder consists of an amorphous (siliceous) phase + forsterite + periclase. Pure enstatite monoliths made by dispersing, casting and gelling these powders were sintered with various atmospheres and thermal histories. A reducing atmosphere results in transient viscous flow, which is the key to effective densification. Samples could be sintered at temperatures as low as 1075-degrees-C without cracking due to volume changes. After processing at 1075-degrees-C, the microstructure consists of interlocking 0.5 mum grains of ortho-, proto-, and clinoenstatite whereas 1100-degrees-C processing gives protoenstatite grains 1-2 mum in size. Fracture toughness for these enstatite monoliths averages 4.2 MPa m1/2.