The cascaded-anode plasma torch makes it possible to get a longer and more stable plasma jet with higher specific enthalpy than conventional plasma torches. It is now used widely, but there are still ...few models of the cascaded-anode plasma torch. This study developed a 3-D time-dependent model that couples the gas phase and electrodes by encompassing the electromagnetic and heat equations both in the electrodes and gas phase. The model was applied to a commercial plasma spray gun equipped with a single cathode, single cylindrical anode and an inter-electrode insert to fix the average arc length. This paper examines the effect of the boundary conditions for the magnetic vector potential and electric current density on the electromagnetic, velocity and temperature fields of the plasma jet. The model predictions showed that, for such plasma torches where the arc is close to walls, the Biot and Savart formalism is required at the domain boundaries for the magnetic vector potential. They also showed that similar plasma fields could be obtained by imposing an electric current density profile at the cathode tip or by including the electrodes in the computational domain. However, this profile has to be chosen according to the specific design of the cathode, which is not obvious when the cathode has a design different from that of conventional plasma torches with sharp conical tip or rounded tip.
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Currently, an extensive effort is ongoing in academia and industry to design cost-effective coatings that can protect the surfaces against microorganisms, by limiting their ...transmission and growth. Thermal spray can be used to improve the functionality of thermoplastic surfaces by combining an innovative design with the antimicrobial properties of metallic materials. This systematic review deals with copper coatings deposited on thermoplastics by thermal spray techniques. Its aim is to understand the role that surface roughness, material microstructure and surface chemistry plays on the inactivation rate of microorganisms, especially viruses. In addition, a general view of the interaction mechanisms between metallic surface and microorganisms is emphasized. The antimicrobial coatings should be engineered to control the release of metal ions which is directly linked with the lifespan of the microorganism. They must also comply with the ISO 21702:2019 that stipulates suitable methods for antiviral activity measurement on plastics and other non-porous surfaces of antiviral-treated products. The designed coatings should provide long-lasting virus protection and prevent the degradation of the surface. Finally, an outline of the effect of the copper deposition method onto thermoplastic surfaces, coating microstructure, and surface specific oxygen species is presented in correlation with antimicrobial properties.
Nano-structured coatings should exhibit better properties than micro-structured coatings because of a high volume fraction of internal interfaces. Since the mid-nineties a large body of works have ...been devoted to suspension and solution plasma spraying for the deposition of finely and even nanometer-structured coatings. The aim of this paper is to take stock of our present knowledge in the field of suspension plasma spraying that is, at the moment, essentially used for oxide ceramic coatings. It will first tackle the injection of the suspension in the plasma jet and the behavior of nano or sub-micro-meter particles processed in the plasma jet core involving the liquid breakup and vaporization that releases the solid particles from the solvent droplets. It will, then, deal with the plasma torches and liquid feeding systems available to suspension spraying. It will finally discuss the key characteristics of suspensions (solvent, dispersant, and particle morphologies), designing of coating microstructure, and potential industrial applications, with the developments requested to cope with these applications.
In DC plasma spray torches, anode erosion is a common concern. It mainly depends on the heat flux brought by the arc and on the dimensions and residence time of the arc attachment to a given location ...on the anode wall. The latter depend, to a great extent, on the attachment mode of the arc on the anode wall. This paper compares the anode arc attachment modes predicted by an LTE (Local Thermodynamic Equilibrium) and 2-T (two-temperature) arc models that include the electrodes in the computational domain. It deals with a commercial cascaded-anode plasma torch operated at high current (500 A) and low gas flow rate (60 NLPM of argon). It shows that the LTE model predicted a constricted anode arc attachment that moves on the anode ring, while the 2-T model predicted a diffuse and steady arc attachment. The comparison between the predicted and measured arc voltage showed that the 2-T prediction is closer to the actual voltage. Also, the post-mortem observation of a new anode ring of the actual plasma torch operated under the same conditions for a short time confirmed a diffuse arc attachment on a new anode.
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