Effect of powder loading on plasma spheroidization of hydride-dehydride titanium powders

Abstract

Spherical titanium particles have been produced from hydride-dehydride titanium raw powders using an inductively coupled plasma spray system. Taking into account the variously modified particle morphologies with different plasma conditions, the effect of powder loading on spheroidization was quantified and evaluated in terms of the altered particle heating capabilities. The averaged particle heat transfer coefficient was found to vary with powder feeding rate and associated strongly with Ar–H2 gas thermal conductivity. Furthermore, there observed a most efficient particle heating condition for each powder feeding rate, but the efficient heating condition tends to vaporize small raw powders and increase the overall oxygen content unintentionally as a result of the attachment of satellites nanoparticles on spherical particles. It is therefore important that the plasma input power is optimally controlled with particular attention to the altered degree of heat transfer especially for the case of small powder injection.

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“…In a simple thermodynamical model, when the amount of substance N is changed by a factor of λ at a constant gas pressure and temperature, V , energy U , and S in the system have extensivity like: λ U ( S , V , N ) = U (λ S , λ V , λ N ) and λ S ( U , V , N ) = S (λ U , λ V , λ N ) [ 35 ]. We carefully note that this is valid when constituent particles are in equilibrium over the whole volume, and our experiments in which the gas pressure was at several hundreds of Pa are the cases within this criteria; if the pressure increases the level close to the atmospheric pressure [ 37 ], viscous forces in gas flows are dominant over particle diffusions and may break this principle. Within the criteria of homogeneous low pressure throughout the system, the extensivity described here means that, for constant n , change of V is a reversible process without irreversible parts since the extensivity of S is valid due to the reversibility.…”