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Relation Between Particulate Chemistry and Ceramic Properties
Final technical rept. 1 Jan 1970-31 Dec 1972
AVCO CORP LOWELL MA SYSTEMS DIV
Pagination or Media Count:
In a program designed to inter-relate the chemistry and morphology of initial particulates with microstructure development and mechanical properties of the final product, it was found that the powder precursor may have an important influence on microstructure. Vacuum hot pressed high purity MgO derived from MgOH2 displayed a marked duplex microstructure and a mean grain size thirty times larger than that in bodies fabricated from carbonate-derived material of the same purity and initial particle size. The duplex structure evolved early in the course of consolidation less than 70 density and is attributed to the high degree of mutual orientation of MgO crystallites within relics of the parent brucite plate. Evidence of a partially-penetrating grain boundary phase was found. Grain growth rates at 1526 and 1610C decrease rapidly with time due to transition from boundary-controlled to pore-controlled to abnormal grain growth. Room temperature measurements of delayed fracture in three different environments were determined for high purity vacuum hot pressed MgO derived from the carbonate, and compared with results for less pure materials. The high purity magnesia displayed higher resistance to stress corrosion and a higher static fatigue limit than any other grade of material examined.
APPROVED FOR PUBLIC RELEASE