Sinterable ceramic powders from laser heated gas phase reactions and rapidly solidified ceramic materials : annual report.

Abstract

CO[subscript 2] lasers have been employed to heat reactant gases to synthesize Si, Si[subscript 3] N[subscript 4] and SiC powders. The powders are small, uniform in size, nonagglomerated, highly pure and of controlled crystallinity; all parameters considered ideal for fabrication of defect-free ceramic parts. The unique and uniform time-temperature histories achievable with laser heating permit these important characteristics to be realized.

Dispersions of Si powders have been made and characterized extensively. These results have defined an appropriate strategy for making concentrated dispersions and have confirmed earlier preliminary results. Zeta-potential and photon correlation spectrometry have been used to study the effects of water contamination in the alcohol dispersants. Based on current results, we believe that concentrated dispersions will be achieved with steric rather than coulombic stabilization. Coulombic repulsive forces are effective only with dilute dispersions.

Manufacturing cost analysis shows that submicron powders can be made at lower cost with gas phase processes than with comminution proceses. The laser heat source does not contribute significantly to the total costs. Total manufacturing costs are dominated by even lower than present actual feed stock (SiH[subscript 4]) costs. Recent cost reductions indicate that acceptable SIH[subscript 4] costs may be realized soon.

Surface tensions of Al[subscript 2] 0[subscript 3] based melts with MgO, Cr[subscript 2]0[subscript 3], Ti0[subscript 2] and ZrO[subscript 2] additives have been measured In neutral, oxidizing and reducing atmospheres. A new procedure was developed to analyize pendant drops which permits high precisions with the short maximum drop lengths that are characteristic of these materials. A C0[subscript 2] laser heat source was used to melt the polycrystalline feed rods.

Molten oxide drops were splat quenched using a copper piston and anvil quenching apparatus. Approximately 500 samples of 10 oxide materials have been made. These samples are being characterized with respect to crystallinity, grain size, hardness, K[subscript IC] and surface composition. These results will be reported in the future.