EFFECT OF IMPURITIES FROM BALL MILL ON DENSIFICATION BEHAVIOR OF ALPHA-FE2O3 POWDERS

Alpha-Fe2O3 powder was ground by ball-mill with alumina and zirconia b alls. Densification behavior with respect to both specific surface are a and the amount of impurities from the balls was investigated. The on set temperature of shrinkage for the powders milled with alumina balls decreased with increasing specific surface area and decreasing impuri ty contents. On the other hand, the onset temperatures for the powder milled with zirconia balls increased, although the specific surface ar ea of the powder was increased by milling. Density and microstructure of the samples sintered at 1100 degrees C for 10h were evaluated. Rela tive densities of sintered samples by the powders with 3.5 mol% and 1. 1 mol% Al2O3 were 99.4% and 99.3%, respectively. Average grain sizes o f these samples were 5.4 mu m and 10.1 mu m, respectively. The relativ e density of sintered sample by the powder with 0.7 mol% ZrO2 was 97.8 %. This value was lower than those by the powders milled with alumina balls, although there was no difference in specific surface area in th ese powders. This result indicates that Al2O3 does not influence the d ensification of alpha-Fe2O3, however ZrO2 inhibits densification. The cause of densification inhibition by ZrO2 was considered that the diff usion rate of oxigen ion is decreased by the decrease of oxigen ion va cancies, which is caused by the dissolution of ZrO2 in alpha-Fe2O3.