INFLUENCE OF CHARACTERISTICS OF ADDITIVE AL2O3 POWDERS ON THE SINTERING BEHAVIOR OF (NI,CO)O CERAMICS

Sintering behavior of (Ni, Co)O ceramics with 2 mass% Al2O3 having var ious characteristics was investigated. Characteristics of Al2O3 powder was changed by heating of a raw Al2O3 powder consisting of ru and gam ma phases from 200 to 1200 degrees C for 5h. The fraction of gamma pha se in the Al2O3 powder decreased remarkably at temperatures between 90 0 and 1100 degrees C, the specific surface area of the Al2O3 powder de creased, and the particle size increased remarkably at temperatures be tween 1000 and 1100 degrees C, The shrinking behavior of (Ni, Co)O dop ed with these Al2O3 powders was measured from 800 to 1400 degrees C by TMA, In the temperature region 800 to 1100 degrees C, the shrinkage o f CN I, which was defined as (Ni, Co)O with Al2O3 treated below 1000 d egrees C, was smaller than that of CN II, which was defined as (Ni, Co )O with Al2O3 treated above 1100 degrees C. The CN I, however, shrank drastically above 1120 degrees C, and more extensively than CN II: abo ve 1200 degrees C. The relative density of CN I sintered at 1300 degre es C for 10h was more than 98%, while that of CN II was less than 95%.