Abstract
Sintering characteristics of three kinds of iron and FeCo alloy ultrafine powders (UFPs) in vacuum and a hydrogen atmosphere were examined by continuously measuring their dimensions, and observing their structural changes. The UFPs exposed to air contain mixtures of oxide and hydroxide phases. The oxide phase increased during heating in vacuum. The compacts of the UFPs shrunk slightly at temperatures between 450 and 700 K, where the surface oxides sintered, and then densified rapidly above 700 K. The shrinkage in a stream of hydrogen occurred at much lower temperatures than that in vacuum. The reduction reaction is ratecontrolled by an interface reaction and the reduction rate of the UFPs depends on the oxidation level, where the more highly oxidized UFPs tend to the lower reduction rate. Activation energies of the reduction rate constants of the iron UFPs and FeCo UFPs lie in the range 48–59 kJ mol−1.
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Sakka, Y., Uchikoshi, T. & Ozawa, E. Sintering characteristics of Fe and FeCo alloy ultrafine powders. JOURNAL OF MATERIALS SCIENCE 28, 203–217 (1993). https://doi.org/10.1007/BF00349053
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DOI: https://doi.org/10.1007/BF00349053