Technologies for production and treatment of powder materials in thermal plasma of electric arc discharge

Objectives. To summarize the results from studies of plasma processes for the production of specified composition powder materials; to implement plasma processes: plasma-chemical synthesis of nanopowders, granulation of nanopowders, plasma spheroidization of microgranules and micropowders in order to perform nanotechnologies and additive technologies tasks.

Methods. Thermal plasma generation was used at the A.A. Baikov IMET RAS by means of direct-current electric arc plasmatrons with a rated power up to 45 kW with self-adjusting arc length and gas stabilization of discharge, as well as plasmatrons with an interelectrode insert. In order to carry out the processes of nanopowders synthesis and metal powders spheroidization, the plasma reactor design with confined jet flow using thermal plasma of reducing, oxidizing, and inert media was used.

Results. The use of electric arc plasmatron in the processes of plasma chemical synthesis of nanopowders and plasma spheroidization of powders enabled productivity of 0.5 and 10 kg/h, respectively, to be achieved for various metals, alloys, compounds, and their compositions. In the case of the implemented processes of producing nanopowders, where the formation of particles depends on various macro-mechanisms, it was established that the average size of the particles obtained is controlled. This also depends on the synthesis parameters—the initial concentration of the precursor, enthalpy, and flow rate of the plasma jet, cooling rate and vapor condensation. The study shows the results of examining the processes of producing spheroidized powders in thermal plasma flows. These include (Ti, Ta, Fe, Ni, Mo, W), alloys (based on Fe, Ti, Ni, Co, Nb, W, Mg, including stainless, heat-resistant, refractory, hard), compounds (borides, oxides) and compositions (W–Ni–Fe, ZrB₂–SiC, Ni–TiCN, etc.). The possibility of obtaining nonporous spherical powders of various dispersity was also shown: for particles of about 10–100 μm and for granules having a particle size of less than 1 μm. The study described the main process parameters determining the quality of spheroidization, including dispersity of precursor, plasma enthalpy, gas composition, characteristics of plasma flow, and their mixing with initial powders.

Conclusions. The research and development results presented here show the possibilities of plasma processes and apparatuses for producing nanopowders of various metal, inorganic compounds and compositions with given properties. The study also confirmed that powders of metals and alloys, compounds and compositions obtained by a variety of methods can be spheroidized in a plasma reactor with confined jet flow in a wide range of melting points, particle sizes, and morphology. The demonstrated approach using successive stages of plasma-chemical synthesis of nanopowders, their granulation and subsequent plasma spheroidization of microgranules enables tungsten-based composite micropowders with dense spherical particles and submicron structure to be obtained.

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