DEVELOPMENT AND EVALUATION OF TRANSPARENT MAGNESIUM OXIDE
Final rept. 15 Oct 1965-15 Nov 1966
AVCO MISSILES SPACE AND ELECTRONICS GROUP LOWELL MA AVCO SPACE SYSTEMS DIV
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The densification parameters for hot pressing MgO to a theoretically dense polycrystalline body was studied. Two experimental approaches were followed using pure MgO powders, and pressing mixtures of MgO plus small amounts of LiF. In the former case specimens having 60 total transmission adequate for in line observation were obtained by very precise control of the fabrication conditions followed by a long term anneal in hydrogen. The MgO - LiF process yielded thin specimens having 85 total transmission in the visible, and 38 inch thick specimens possessing a maximum transmission of 70. A post hot pressing anneal at temperatures greater than 1200C and heating rates less than 28Chour were required to produce maximum transparency. Evidence obtained by grain growth studies, weight loss experiments and lattice parameter determinations suggest that the densification mechanism for this process was pressure-enhanced diffusion through a solid solution grain boundary layer and a grain boundary phase. At temperatures above the melting point of LiF a pressure-enhanced liquid phase sintering mechanism probably operates.
- Ceramics, Refractories and Glass