**6. Spheroidization of metal powders**

Spherical powders with a particle size of the order of 10 μm are used as starting materials for the manufacture of products from metals and alloys by the additive technologies methods. Processing of powders with irregular particle shape in thermal plasma flows ensures their fusion, leading to the formation of spherical particles [31].

Titanium powders (fractions of 40–70 μm and less than 40 μm) were processed in the flow of thermal argon plasma, generated by an electric arc plasma torch. The hydrogenationdehydrogenation process produced raw titanium powders. After plasma processing, the degree of spheroidization has reached 96%. Average sphericity coefficient was equal to 1.01 (**Figure 7**).

Experimental studies of the production of nonporous spherical powders of multicomponent metal alloys have been performed. Ultrafine powder compositions of alloy components, having a particle size of less than 1 μm, have been used as raw material. Model high-alloy Fe-Ni-Cr alloy particles were used as example, and spherical alloy powders with particle sizes in the range from 25 to 50 μm were produced.

The process consisted of the following stages: microgranulation of ultrafine powder, heat treatment of microgranules (drying at 100°C, removal of organic binder at 300°C, thermochemical treatment in H2 at 1000°C, vacuum treatment at 1200°C), classification of heat-treated microgranules with separation of microgranules fraction in the range 25 to 50 μm, spheroidization of the isolated fraction of microgranules in the thermal plasma flow, separation of

**Figure 7.** Micrographs of spheroidized titan powder.

plasma apparatus, such as reactor diameter and plasma torch nozzle diameter. These parameters determine the dimensions of the high-temperature zone where the nanoparticles formation takes place. The chemical processes, occurring at nanoparticle surface, also could influence the regularities of nanoparticle growth. The results of studies of various nanopowders production in the plasma reactor indicate that the influence of the process parameters on the average particle size is a multifactor problem, where the physicochemical features of the process play significant role. It was found that the average nanoparticle size depends on the synthesis parameters such as the initial precursor concentration, plasma jet enthalpy and velocity. The individual features of the specific process determine the degree of influence of these parameters. Production of nanoparticles of extremely small size in the confined jet reactor can be achieved only if the initial vapor concentration is significantly reduced or the jet velocity is increased. Reducing the initial concentration results in a decrease in the synthesis productivity, and the velocity increase has certain physical and technical limitations. Controlled change of nanoparticles coagulation growth time in the thermal plasma flow manipulates the size of nanoparticles, formed by the VLC mechanism. Additional channel to control the nanoparticle growth time is fast quenching by cold gas injection. Cold gas injection forces cessation of the coagulation

Distributed radial injection of quenching gas was organized at the periphery of the hightemperature flow in the synthesis of alumina nanopowder by oxidation of a metal powder in air plasma flow [25]. Quenching was carried out at the different distances from the reactor inlet, thus varying the particles residence time in the coagulation growth zone. The change of the injection gas flow rate and the injection position allowed the variation of the average particle size in the range of 35 to 75 nm. The obtained results indicate that confined DC plasma jet reactor is capable to produce wide range of individual elements nanopowders as well as

Spherical powders with a particle size of the order of 10 μm are used as starting materials for the manufacture of products from metals and alloys by the additive technologies methods. Processing of powders with irregular particle shape in thermal plasma flows ensures their

Titanium powders (fractions of 40–70 μm and less than 40 μm) were processed in the flow of thermal argon plasma, generated by an electric arc plasma torch. The hydrogenationdehydrogenation process produced raw titanium powders. After plasma processing, the degree of spheroidization has reached 96%. Average sphericity coefficient was equal to 1.01 (**Figure 7**). Experimental studies of the production of nonporous spherical powders of multicomponent metal alloys have been performed. Ultrafine powder compositions of alloy components, having a particle size of less than 1 μm, have been used as raw material. Model high-alloy Fe-Ni-Cr alloy particles were used as example, and spherical alloy powders with particle sizes

growth after completion of vapor–liquid phase transition.

16 Powder Technology

nanopowders of inorganic compounds and composites.

fusion, leading to the formation of spherical particles [31].

**6. Spheroidization of metal powders**

in the range from 25 to 50 μm were produced.

**Figure 8.** Micrographs of granules. (А) – Initial alloy components, (В) – Spheroidized in plasma.

the micron and submicron fraction. Micrographs of the alloy components microgranules and particles, spheroidized in the plasma flow, are shown in **Figure 8**. The presented experimental results indicate the possibility of metallic and alloys powders spheroidization in a confined DC plasma jet apparatus using various initial powder materials.

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Nanopowders Production and Micron-Sized Powders Spheroidization in DC Plasma Reactors

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