Sintering Alumina: Effect of Atmospheres

Two effects of atmosphere on the sintering of alumina powder compacts were investigated. Changing the oxidizing conditions during early-stage sintering measurements showed that, within the range −70°F dew point oxygen to −70°F hydrogen equilibrated with alumina, there was no observable effect on sintering rate. The effect of trapped atmosphere on closure of pores was determined from apparent density limits obtained at high sintering temperatures and long sintering times. The complete elimination of porosity during sintering of alumina was possible if discontinuous grain growth was controlled and if the ambient atmosphere was hydrogen, oxygen, or vacuum. Porosity could not be completely eliminated when the ambient atmosphere was helium, argon, or nitrogen (or therefore air).