In this paper, we review the recent progress in nanofabrication by thermal plasmas, and attempt to define some of the most important issues in the field. For synthesis of nanoparticles, the experimental studies in the past five years are briefly introduced; the theoretical and numerical modelling works of the past 20 years are reviewed with some detailed explanations. Also, the use of thermal plasmas to produce nanostructured films and coatings is described. A wide range of technologies have been developed, ranging from chemical vapour deposition processes to new plasma spraying processes. We present an overview of the different techniques and the important physical phenomena, as well as the requirements for future progress.

This article presents a discussion of the ideas for modelling turbulent thermal plasma flows, reviewing the challenges, efforts, and state-of-the-art simulations. Demonstrative simulations are also performed to present the importance of numerical methods as well as physical models to express turbulent features. A large eddy simulation has been applied to turbulent thermal plasma flows to treat time-dependent and 3D motions of multi-scale eddies. Sub-grid scale models to be used should be able to express not only turbulent but also laminar states because both states co-exist in and around thermal plasmas which have large variations of density as well as transport properties under low Mach-number conditions. Suitable solution algorithms and differencing schemes must be chosen and combined appropriately to capture multi-scale eddies and steep gradients of temperature and chemical species, which are turbulent features of thermal plasma flows with locally variable Reynolds and Mach numbers. Several simulations using different methods under different conditions show commonly that high-temperature plasma regions exhibit less turbulent structures, with only large eddies, whereas low-temperature regions tend to be more turbulent, with numerous small eddies. These numerical results agree with both theoretical insight and photographs that show the characteristics of eddies. Results also show that a turbulence transition of a thermal plasma jet through a generation-breakup process of eddies in a torch is dominated by fluid dynamic instability after ejection rather than non-uniform or unsteady phenomena.

A new model is developed for numerical analysis of the entire growth process of binary alloy nanopowders in thermal plasma synthesis. The model can express any nanopowder profile in the particle size-composition distribution (PSCD). Moreover, its numerical solution algorithm is arithmetic and straightforward so that the model is easy to use. By virtue of these features, the model effectively simulates the collective and simultaneous combined process of binary homogeneous nucleation, binary heterogeneous cocondensation, and coagulation among nanoparticles. The effect of the freezing point depression due to nanoscale particle diameters is also considered in the model. In this study, the metal–silicon systems are particularly chosen as representative binary systems involving cocondensation processes. In consequence, the numerical calculation with the present model reveals the growth mechanisms of the Mo–Si and Ti–Si nanopowders by exhibiting their PSCD evolutions. The difference of the materials’ saturation pressures strongly affects the growth behaviors and mature states of the binary alloy nanopowder.