| Titanium has superior performance, it is known as ‘the metal of the 21 st century’ for its wide application field. The demand of spherical titanium powder is on the increase for its excellent performance with the development of net shaping and thermal spraying technology.Plasma technology has advantages and good prospects over other methods of preparing spherical powder, meanwhile, as a frontier subject, its reaction mechanisms is more complicated, the study of which is meaningful to both academic and engineering. Aiming at inductively coupled plasma(hereinafter referred to as ICP) and titanium powder, the main contents of this research were summarized as follows:(1) Laminar plasma is a ideal object to reveal the spatial distribution of the plasma jet.Owing to the dielectric constant of ICP is akin to the vacuum, which can be treated as Magnetic fluid. Equations of electromagnetic field and MHD(Magnetohydrodynamics) under3-D cylindrical coordinate system were proposed based on Maxwell’s equations and some reasonable assumptions. The 3-D model of the reactor and meshing was established via pre-processing software. New scalar equations to calculate magnetic vector A and potential ?were introduced by meas of the UDS(User-Defined Scalar) and Complex-Vector technology,source terms of heat, Lorentz Force, A and ? were added in different zones by the corresponding UDF(User-defined Function)program based on the secondary development of FLUENT.(2) Files of grid, UDF and properties of argon were imported into FLUENT to conduct the 3-D numerical simulation, spatial distribution of temperature field, velocity field, Lorentz force can be achieved after the simulation. The result showed that the high temperature concentrated where the coil covered, this is because the gas were fully ionized while the movement of the massive charged particles would produce more joule heat herein. Moreover,the max temperature is near the inner wall of the quartz tube for the existence of Conductor Skin Effect. Distribution of the velocity is much more complicated, back-flow region appeared at the end of the gas filling pipe. Owing to the effect of the Lorentz force, plasma jet presents a layered movement, the inner plasma presents inside-out tumbling movement while the outside presents spin movement, the max velocity located in the lower part of the torch.Finally, simulation of different parameters on the distribution of the flow field have been carried out. The results showed that coil current has greater influence on the flow field due to the strongly dependency between magnetic vector A, potential ?, Lorentz force and joule heat.Temperature of the plasma raised with the increasing of current, then more thermal energywould converted into kinetic energy, which leads the augment of the peak velocity. The completion of the simulation would provide theoretical basis for the debugging of the spheroidizing experiment.(3) DPM(Discrete Phase Model) module provided by the FLUENT was available to conduct the coupling calculation between discrete and continuous phase. Particle motion model was established, moreover, the Lagrange method of bidirectional coupling method was used to track particle trajectory and heat process with different particle size. The simulation results showed that particle with different size has different trajectory and heat process, the smaller of the particle size, the bigger of the back-flow’s influence. Furthermore, the injection of particle has certain influence on the flow field, so it is vital to choose appropriate parameters according to particle size in practical application. Simple titanium powder spheroidizing experiment were carried out with RF(Radio Frequency) plasma equipment to verify the superiority of ICP in titanium powder spheroidizing. Changes of particle’s surface morphology before and after the spheroidization can be observed by means of Scanning Electron Microscope, particles with uniform size distribution, smooth surface, better liquidity and dispersion after spheroidization. |
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