Forming and sintering behaviors of commercial α-Al2O3 powders with different particle size distribution and agglomeration

The Al2O3 structure ceramics have been investigated extensively in previous studies. In order to compare micron- with submicron-scale powder on forming and sintering behaviors, three commercial α-Al2O3 powders were studied: 0.15 μm (denoted S as small in the paper) (granulating), 0.43 μm (denoted M as middle) (granulating), and 1.8 μm (denoted L as large) (granulate-free) at d50 (median size). Although the (M) powder contains hard agglomerates, it forms more easily than the (S) powder. This is principally because the (M)ʹs soft agglomeration strength (0.03 MPa) is weaker than (S) (7 MPa). The (L) bulk formed easily with lower pressure 10 MPa because of wider starting-particle size distribution, 0.2–15 μm. The (S) primary particles rearranged before sintering, so it postponed its sintering onset temperature to about 1200 °C. Additionally, its shrinkage rate becomes maximal and concentrated at the 2nd stage of sintering from 1300 to 1400 °C. (M) bulk revealed the longest shrinkage range from 1000 to 1500 °C because the sintering occurred with its hard agglomerates at first. Although (L) powder formed rather easily, its sintering was impeded by a much wider particle size distribution.