Kinetics of Precipitation and Measurements of Strain in the System MgO-Al2O3-Cr2O3 |
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Authors: | V S STUBICAN C GRESKOVICH H A McKINSTRY |
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Affiliation: | Materials Science Department and Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802 |
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Abstract: | A quantitative X-ray technique for measuring precipitation strains has not been previously applied in metallic or oxide systems. The Warren-Averbach analysis of strain was used to determine the buildup of elastic strain energy in the spinel crystalline solution matrix (gross composition = 60 mol% MgAl2O2+ 40 mol% Cr2O3) during the isothermal (1135°C) precipitation of a metastable (coherent) monoclinic phase. The elastic strain energy of the spinel crystalline solution matrix increased to a maximum of about 3.1 × 107 ergs/cm3 for a reaction time of 8 h. There was a marked decrease in the elastic strain energy during the initial precipitation of the equilibrium corundum crystalline solution with the composition (Al3+0.72 Cr3+0.25)O3. An overall diffusion activation energy for precipitation of the mono-clinic phase was approximately 86 kcal/mol. |
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