The influence of gas atmospheres on the first-stage sintering of high-purity niobium powders |
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Authors: | M Krehl K Schulze G Petzow |
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Affiliation: | (1) Institute of Materials Science, Powder Metallurgy Lab, Max-Planck Institute of Metals Research, Stuttgart, West Germany |
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Abstract: | Niobium and tantalum surfaces easily absorb oxygen. With decreasing particle size the content of oxygen increases. The role
of this surface oxygen and oxygen in the sintering atmospheres on the first-stage sintering is not well established. Therefore
the sintering behavior of high-purity niobium powders was studied by annealing cylindrical powder compacts (particle size
<63 μm) in the temperature range from 1000°C to 1600°C in ultra-high vacuum and under low oxygen partial pressures, as well
as in inert gas atrnospheres with low oxygen contents. The specific surface of the samples was determined by metallographic
methods, adsorption, and capacitance measurements. Low oxygen partial pressures (10-3 Pa) lead to a slight enhancement of the surface diffusion which is controlling first-stage sintering. High heating rates
(0T > 3000 min-1) to temperatures above the melting point of Nb2O5 (Tm = 1495 °C) enhances the neck growth due to the formation of a liquid oxide phase on the surface of the powder particles.
This paper is based on a presentation delivered at the symposium “Activated and Liquid Phase Sintering of Refractory Metals
and Their Compounds” held at the annual meeting of the AIME in Atlanta, Georgia on March 9, 1983, under the sponsorship of
the TMS Refractory Metals Committee of AIME |
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