RECRYSTALLIZATION AND SINTERING OF OXIDES. Progress Report, September 1, 1960 to August 31, 1960
Progress was made toward understanding the effect of imparities on the properties of alumina and magnesia previously proposed for investigation. Systematic investigation of variables thought to influence the rate of shrinkage of powder compacts was carried out. Geometry of powder particles as well as experimental factors associated with shrirkage measurements were investigated. The activation energy for diffusion for several different types of alumina powders was determined to be 135 Kcal/mole. Measurement of the electrical conductivity of sapphire showed it to be ohmic and history dependent below about 1300 deg C and non-ohmic above that temperature. Preliminary expeniments indicated conductivity through the air surrounding the sample is larger than through the sample itself at temperature above 1300 deg C. Exaggerated grain growth in sintered alumina is impurity dependent. At least one of perhaps several impurities that can influence exaggerated grain growth is sodium oxide, a common constituent of all commercial alumina powders. The chemical nature of sodium oxide and its volatility at high temperatures makes quantitative measarements extremely difficult; however, qualitative results amply demonstrate the effect of sodium oxide in stimulating exaggerated grain growth. Normal grain growth proceeds in sintered magnesia and calcia with little regard to changes in porosity. Self consistent data were obtained with reagent grade oxides; however, recent work gives evidence of a large dependence of grain growth on impurities. The diffusion of iron oxide (FeO) into magnesium oxide single crystals can be followed readily by observing movement of a colored interface. The rate of movement is dependent uPon the vacancy concentration as determined by the Fe/sup +3//Fe/sup +2/ ratio in the FeO. The diffusion profile also confirms the idea that the diffusion constant is concentration dependent. This result is to be expected on the basis that cation vacancies accompany the diffusion of trivalent iron ions into the magnesia lattice. (auth)
- Research Organization:
- Utah. Univ., Salt Lake City. Inst. for the Study of Rate Processes
- DOE Contract Number:
- AT(11-1)-82
- NSA Number:
- NSA-15-029670
- OSTI ID:
- 4842752
- Report Number(s):
- TId-13592
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-61
- Country of Publication:
- United States
- Language:
- English
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RECRYSTALLIZATION AND SINTERING OF OXIDES. Progress Report for September 1, 1959 to August 31, 1960
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Related Subjects
AIR
ALUMINUM OXIDES
CALCIUM OXIDES
CONFIGURATION
CRYSTALS
DEFECTS
DEFORMATION
DIFFUSION
DISTRIBUTION
ELECTRIC CONDUCTIVITY
GRAIN SIZE
HIGH TEMPERATURE
IMPURITIES
IONS
IRON
IRON OXIDES
LATTICES
MAGNESIUM OXIDES
MEASURED VALUES
PARTICLES
POROSITY
POWDERS
RECRYSTALLIZATION
SAPPHIRE
SINTERED MATERIALS
SINTERING
SODIUM OXIDES
VACANCIES
VOLATILITY