Sinterability of ZrO2 and Al2O3 Powders: The Role of Pore Coordination Number Distribution.
Final rept. 1 Apr 82-31 Mar 83,
ROCKWELL INTERNATIONAL THOUSAND OAKS CA SCIENCE CENTER
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The sinterability of two Zr02 powders containing 2.2 and 6.6 mo Y203, respectively, a Al203 powder, and Al20310 vo Zr02 composite powder was investigated. Shrinkage was measured at a constant heating heating rate. Capillary size distributions were determined by mercury intrusion after heating compacts to various temperatures. Iso-pressing eliminated larger pores with larger coordination numbers which results in greater sinterability. Local densification, i.e., densification of multiple-particle packing units, enlarged pores between these packing units. This phenomenon of local densification initiated prior to bulk shrinkage and stopped when the shrinkage rate reached its maximum. Zr02 inclusions, known to inhibit grain growth, also inhibited sinterability. This observation, coupled with previous work, strongly suggests that grain growth, supported by dense packing units, helps lower the coordination number of pores and therefore is helpful in the sintering process. Large multiple-particle packing units large agglomerates produce unsinterable pores, i.e., pores with high coordination numbers. It was shown that colloidalsedimentation treatments which decrease the size of the soft and hard agglomerates reduced sintering temperatures and increased strength. Author
- Metallurgy and Metallography