Impurity effects on the kinetics of sintering of metal powders. Final report
An analysis of the effect of a surface oxide layer on the sintering kinetics of metal powders has been utilized for the vast majority of metals in the periodic table. Theoretical mathematical models have been applied to numerous metal-oxide systems. Classification of this effect by use of the periodic table has been made. The metal-oxide systems have been divided into four distinct groups. An experimental analysis of the palladium-palladium oxide system has been made. Evaluation of surface area reduction data of pellets sintered in air between 773 and 898 K results in a mechanism characteristic exponent, N, between 6.2 and 6.8 and an activation energy of 14.1 +- 0.4 kcal/mole. Lack of shrinkage and the low vapor pressure of palladium in the solid state lead to the conclusion that surface diffusion is the rate-controlling sintering mechanism. Specimens sintered in the absence of a surface oxide layer in the temperature range between 773 and 1148 K incurred shrinkage with resulting N values between 5.6 and 6.5. Those specimens sintered in vacuum between 773 and 898 K possess an activation energy of 63.9 +- 0.5 kcal/mole. When compared to the literature value for grain boundary diffusion of 31.8 kcal/mole a large discrepancy is noted. The variation is suggested to be due to surface diffusion. Specimens sintered at high temperatures, 1073 to 1148 K, possess an activation energy of 28.8 kcal/mole which is in good agreement with the published value. Specimens sintered in the temperature range between 923 and 1048 K show a coupling between weight loss and shrinkage. The presence of a metastable surface oxide is suggested to account for this phenomenon.
- Research Organization:
- California Univ., Davis (USA). Dept. of Mechanical Engineering
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 6504874
- Report Number(s):
- UCRL-15337
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360101* -- Metals & Alloys-- Preparation & Fabrication
BINARY MIXTURES
CHALCOGENIDES
CLASSIFICATION
DISPERSIONS
ELEMENTS
FABRICATION
KINETICS
METALS
MIXTURES
OXIDES
OXYGEN COMPOUNDS
PALLADIUM
PALLADIUM COMPOUNDS
PALLADIUM OXIDES
PERIODIC SYSTEM
PLATINUM METALS
POWDERS
SINTERING
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS