Air quality in buildings is often controlled by various Heating, Ventilation, and Air Conditioning (HVAC) systems. These systems are equipped with air filters to reduce dust and aerosol load in the air. Ambient aerosol particles may contain different organic matter such as pollen, bacteria, and fungi. In warm and humid indoor air conditions, the presence of such air particles may result in the growth and transmission of infectious bacteria, fungi, and mold spores.

During the impact and solidification of thermal spray droplets on a substrate, the density increases when the droplet solidifies. Depending on the material, the changes in density could be significant. For example, aluminum oxide's density changes by 66%, while the changes are 12% and 19% for nickel and copper, respectively. For zirconia, this change is 24%. The effect of such densification on the dynamic of the droplet impact and the formation of porosity could be dramatic. In this study, the effect of shrinkage of a molten droplet during solidification on droplet impact is numerically investigated for several materials. Results for the impact of molten alumina, nickel, copper, and zirconia droplets on both smooth and rough surfaces are presented. The results of variable density cases are compared with those assuming constant density. The effect of thermal shrinkage is particularly vital in the interaction of two impacting droplets. The shrinkage promotes the formation of additional pores.

Viruses and microbial pathogens can survive for hours on fabrics. This paper reports that copper-doping of natural and synthetic fabrics inactivates, within minutes, a human COVID surrogate pathogen. The fabric is embedded with copper particles by twin-wire arc thermal spray. The long-lasting fabric surface simultaneously provides good breathability, it is scalable and cost-effective. Virucidal activity is not affected by repeated washing of the fabric. Importantly, copper-embedded material will provide effective protection against all classes of pathogens, regardless of their mutation rates and infection strategies. It also can provide protection against all classes of pathogens, regardless of their mutation rates in industrial and residential filters.

In this work, numerical models are developed and used to simulate magneto-hydrodynamic fields inside a dc plasma torch during suspension plasma spraying and their influence on arc attachment. A Reynolds stress model is used to simulate turbulent plasma flow and a discrete phase model simulates the effects of arc fluctuation on suspension droplets in the plasma jet. Submicron yttria-stabilized zirconia particles, suspended in ethanol, are modeled as multicomponent droplets and the KHRT model is used to simulate their breakup. The results show that particles are significantly affected by plasma arc fluctuations and that fine particles near the centerline of the torch are hotter and experience better penetration into the plasma jet.

This study was focused on the biocidal efficacy on spores of copper alloy sheet and copper alloy coating at two different surface topographies. Endospores can remain viable in a dormant state for centuries. Our work compares the effectiveness of copper alloy coating and copper sheet metal in killing endospores. A twin-wire arc spray system was used for coating of stainless steel coupons. The feedstock was CuNiZn wire, the coating thickness was 400 µm. The copper alloy sheet metal had the same composition and is registered as antimicrobial by Environmental Protection Agency (US). Uncoated stainless steel coupons were used as controls in all experiments. The surface was polished to two roughness levels: Ra=3.5 µm and Ra=0.1 µm. The surface topography was analyzed by a stylus profilometer and 3D image analysis. EDS and FIB were used to characterize the elemental composition and structure of flower-like nanostructures and endospores. The results obtained in this study indicated that changes in Ra values of 0.1 and 3.5 µm had no significant impact on the biocidal activity of sheet metal and the coating on E. coli , S. epidermidis and B. subtilis . The coating was as effective as the EPA-certified sheet metal in the destruction of vegetative cells within 5 minutes. This study indicates that degradation of B. subtilis endospore begins within 2 hours after exposure to the coating. By day seven, only extensively degraded endospores and nanostructures were visible on both surfaces. Our results show that thermal spray copper alloy coatings were as effective as certified antimicrobial sheet metal in the destruction of endospores within hours; however, the coating was more effective in killing the endospores after one week of exposure.

Wire arc is an effective and affordable type of coating process. Detailed understanding of it helps improving design and optimization of currently available guns. In wire arc process, an arc forming between two charged wires generates enough heat to melt the metallic wires. Blow of air at high velocity over this bath of molten metal leads to atomization. The formed droplets are then accelerated towards the substrate where they impact and solidify during the coating process. The current work is a follow up to our earlier numerical study where numerical simulation of wire arc spraying using ANSYS FLUENT revealed flow circulations inside the gun can affect flow pattern and contribute to energy dissipation. In this study, an attempt has been made to validate and measure this matter using experimental procedures and to seek potential ways of improvement.

The authors performed a time-dependent, three-dimensional numerical simulation of a non-transferred DC plasma spray with externally applied magnetic fields. Compressible Navier-Stokes equations with MHD source terms and Maxwell's equations were used as the governing equations for plasma flows. In the simulation, two operating conditions, electric currents and strength of externally applied magnetic fields, were parametrically varied in a range of 300 A to 500 A and 0.2 T to 0.8 T, respectively. Numerical results show that the application of strong magnetic fields such as 0.4 T and 0.8 T is recommended for an anode arc rotation leading to elongating an anode lifetime. A voltage variation due to the anode arc rotation shows periodic behavior with a small amplitude, which is expected to be good for plasma spraying processes. Lagrangian approach was used to track injected particles in the plasma jet and the particle temperature and position distributions on a cross section normal to the central axis of spray were studied. Swirl flows induced by the arc rotation hinder the particles from reaching the hot plasma jet. Our numerical results demonstrated that injecting particles in the opposite direction to the swirl flow is an effective way to heat the particles.

In this work, a numerical model is developed and used to investigate changes that occur to ceramic suspensions in a plasma jet. The model accounts for atomization processes, evaporation of the fluid phase, and melting of the solid phase. Attention is also given to changes in the physical properties of the suspension mixture as the liquid phase evaporates. The findings clearly show that inclusion of a valid viscosity model is essential to understanding particle trajectories and breakup patterns. The validity of the model is evaluated for tests cases involving YSZ suspensions sprayed at different velocities, injection angles, and injector configurations. Particles for each test case are captured on substrates placed 8 cm away from the nozzle and particle counts and spatial distributions are compared.

In the present work, hollow sphere YSZ powders were deposited by dc plasma spraying using a mixture of CO 2 and CH 4 gases. The plasma plume was monitored with an IR camera and in-flight particle velocity and temperature distributions were recorded at impact. Single splats were collected on mirror polished stainless steel and, along with coating samples, were characterized and compared to splats and coatings deposited by conventional argon spraying. In the case of CO 2 -CH 4 spraying, particle temperatures were at least 100 °C higher than the YSZ melting point and almost all splats were completely melted. Coating surfaces were also found to be smoother, indicating less unmelted or partially melted splats.

In this study, zirconia coatings were fabricated by vacuum plasma spraying using hollow spherical and fused and crushed YSZ powders. Relationships between spray parameters and in-flight particle velocities and temperatures were investigated in real time and correlated with coating microstructure and density obtained under vacuum as well as atmospheric spraying conditions. The results indicate that plasma sprayed particles reach higher velocities under vacuum and slightly higher temperatures in atmospheric conditions. Powder morphology and structure play a major role in determining coating microstructure and porosity, especially in vacuum spraying. The fused and crushed powder yielded the densest coatings under the vacuum process conditions employed.

The aim of this study is to evaluate the antimicrobial properties of wire-arc-sprayed Cu-Ni-Zn alloy coatings. The biocidal efficacy of the coatings is compared to that of stainless steel and sheet metal using Escherichia Coli as a contaminant. The influence of surface roughness on biocidal activity is investigated as well.

In this study, porous and dense layers of alloy 625 are deposited on nickel foam sheets using a modified twin wire arc spraying process. Sandwich panels with arc-sprayed alloy 625 skins on nickel foam cores were fabricated then subjected to four-point bend testing. The effects of skin porosity on flexural rigidity and overall mechanical behavior are investigated. The ductility of porous alloy 625 skins was improved after heat treatment at 1100 °C for 3 h.

In this work, tunnel plasma spraying is used to produce Cu 36 Zr 48 Al 8 Ag 8 metallic glass coatings on stainless steel. The results show that cooling gas flow rates play a vital role in oxidation and the formation of intermetallic phases in coating microstructures. Phase formation and microstructural features were evaluated by XRD and SEM-EDX analysis. Coating properties including hardness, sliding wear, and corrosion resistance were measured and the results are compared with the presence of secondary phases. It is shown that an increase in secondary phases improves sliding wear resistance but reduces resistance to corrosion.

In this study, twin wire arc spraying is used to bond wire mesh to the outside surfaces of stainless steel pipes in order to increase heat transfer surface area. At the optimum spray distance, the oxide content, porosity, and adhesion strength of the coatings are shown to be 6.6%, 2.1%, and 24 MPa, respectively. Pipes with different wire mesh configurations were placed in an oven and heated to temperatures from 300 °C to 900 °C. Water temperatures were measured at the inlet and outlet of the pipe for flow rates between 0.2 and 0.5 gpm. A maximum water temperature rise of 13 °C was achieved, corresponding to a total heat flux of 57 kW/m2. Heat transfer efficiency is shown to depend strongly on the quality of the bonds between the wire mesh and pipe and the spacing of wires in the mesh.

In this study, twin wire arc spraying is used to deposit dense Inconel skins on 40 PPI nickel foam sheets. A design-of-experiments approach is used to investigate the effects of grit blasting on the surface characteristics of paste-filled foam. In-flight behavior of molten droplets and its effect on coating properties is assessed at three spray distances. The Inconel coatings are evaluated based on SEM and EDS analysis, roughness measurements, and adhesion testing. The results indicate that acceptable adhesion, porosity, and oxide content can be achieved over a small range of grit blasting parameters.

This study investigates isothermal transformation kinetics in Ti-6Al-4V alloys structures produced by vacuum plasma spray forming. As-sprayed samples were homogenized in the β phase followed by fast cooling to the two-phase temperature region, then quenching to suppress further transformation. The microstructure of heat-treated specimens was examined by optical microscopy and equilibrium phases were measured using image analysis. The kinetics of the β → α+β phase transformation are revealed by plotting the amount of α-phase obtained over a 10 to 60 s interval at isothermal temperatures of 800, 850, 900, and 950 °C. Corresponding phase transformation rates are also calculated based on Johnson-Mehl-Avrami (JMA) theory. At temperatures below 900 °C, the main phase transformation mechanism is homogeneous nucleation and growth of α-phase. At higher temperatures, phase transformations are driven by two mechanisms: the formation of α-phase in grain boundaries and α-plate nucleation and growth.

A numerical investigation of fluid flow and heat transfer through thermal spray formed metal foam heat exchangers is presented. Experimentally obtained fluid flow and heat transfer parameters are used in the simulations. Analytically obtained values of effective thermal conductivity are used to model heat transfer. A 3D CFD model was created for a metal foam heat exchanger with a square cross-section. The external walls were deposited on the foam using a wire-arc process. The channel walls of the foam were exposed to a constant temperature of 400 K and an air flow with an inlet velocity of 2 m/s. The model was verified by comparing sample results to experiments. The effect of the foam on heat transfer was then studied by varying thermal conductivity values.

This work deals with the selection and deposition of wear-resistant coatings for ball valves used in coal slurry pipelines. Several NiCrBSi and WC-CoCr powders were deposited on stainless steel substrates by various methods, including atmospheric plasma spraying (APS) with and without post-process fusion, plasma transferred arc (PTA) spraying, and high-velocity oxyfuel (HVOF). The HVOF deposits had very low porosity and uniform carbide distribution in the metallic matrix. WC-CoCr coatings obtained by HVOF spraying were dense and well-adhered and experienced the least amount of mass loss in wear testing. As a result, they were recommended for testing in coal-water slurry pipelines and continue to perform well after more than two years.

Infection of medical devices and treatment rooms can cause significant morbidity and mortality. Having antibacterial surfaces such as silver and copper coated areas reduces the risk of bacteria growth considerably. In the current study, wire arc spraying technique has been utilized to produce an ultra fine microstructure Antibacterial copper coating on stainless steel substrate. The chemical composition, microstructure, and surface morphology of copper coatings were characterized with X-ray diffraction (XRD) and scanning electron microscope. Determination of thickness and adhesion of the coating were investigated. The antibacterial property of copper coatings was analyzed by both gram negative Escherichia coli NCTC 10418 and gram positive Staphylococcus aureus NCTC 11047. The antibacterial performance of coatings was compared to stainless steel 316 and a micro grain structure of the commercially available copper. Results indicated that as-sprayed copper coatings have an excellent antibacterial behavior compared to stainless steel and micro grain copper which can be contributed to the fine grain size and existing of defects and micro pores in the microstructure.

Yttrium oxide (Y 2 O 3 ) can be used in different applications such as corrosion resistance, high temperature applications and semi-conductor production equipment due to its very high thermal and chemical stability. In the current research, yttria coatings were processed using a new type of DC plasma gun consisted of molecular gases CO 2 +CH 4 . Physical and structural properties were compared with the coating made by SG-100 plasma torch. Gas mixture of CO 2 +CH 4 improves the torch efficiency due to its high thermal enthalpy and conductivity which leads to increased particle temperature and complete fusion of the sprayed particles during the process of coating. SEM study of the structure revealed that the coating has higher density and lower porosity compared to the coating produced by SG-100 torch. No unmelted particles can be observed in the coating. XRD analysis of the coating showed that the coating contains no amount of harmful metastable monoclinic phases. This all proves the better quality of the coatings deposited by CO 2 +CH 4 gas mixture in comparison to the conventional coatings.