Toxicol Ind Health

Thermal spray coating is a process that applies a molten metal product under pressure onto a surface. Although thermal spray processes have been used for decades, exposure to aerosols formed during thermal spray coating is an emerging risk. Reports indicate that high concentrations of aerosols composed of toxic metals (e.g. chromium) are generated in the workplace. A knowledge gap exists related to the physicochemical properties of thermal spray coating aerosols as well as any potential associated health effects. The objective of this manuscript was to review thermal spray coating and previous studies that have examined the aerosols produced from this process. A thermal spray coating generator and exposure system is also described that has recently been developed to further evaluate the physical and chemical properties of aerosols formed during thermal spray coating as well as to assess the possible health effects of this process in an effort to mitigate potential occupational health hazards related to the industry.CC999999/ImCDC/Intramural CDC HHS/United States2021-03-24T00:00:00Z33305691PMC7988297940

Heat Transfer Enhancement of Falling Film Evaporation of HFO-1233zd(E) and HFC-134a on a Horizontal Tube by Thermal Spray Coating

A falling film evaporator can reduce the amount of refrigerant compared with a flooded evaporator. Required functions for the heat transfer surface in falling liquid film evaporation are thin liquid film formation without breaking at low heat flux, nucleate boiling promotion in liquid film, and suppression of liquid entrainment at high heat flux. In this study, a porous thermal spray coating using copper as the coating material was made on a copper cylinder. The heat transfer performance of falling film evaporation and pool boiling was evaluated using HFO1233zd(E) as the refrigerant, and the obtained results were compared with those for HFC-134a. The test cylinder was heated by a cartridge heater inserted at the center. Falling film evaporation experiments had been conducted with a film mass flow rate of 3.3×10-2 kg/(m·s), heat flux of 10 to 85 kW/m2, and a saturation temperature at 20 ºC. The effects of the thermal spray coating, heat flux and thermo-physical properties of the refrigerants on heat transfer performance were investigated. The heat transfer coefficient increased with increasing heat flux. For the thermal spray coating, a large hysteresis effect according to the heating procedure with increasing or decreasing heat flux was observed in the characteristics of the heat transfer coefficient. The heat transfer enhancement factor by the thermal spray coating was up to 4.8. The value was higher than that for HFC-134a, especially under high heat flux condition. In the comparison between pool boiling and falling film evaporation heat transfer, falling film produced higher heat transfer coefficients for the thermal spray coating while the heat transfer on the smooth surface deteriorated due to partial dryout. The fine porous structure enhanced liquid spreading by the capillary force and evaporation from the liquid film surface by vapor bubble agitation

MICROSTRUCTURAL STUDIES OF THERMAL SPRAY COATING

Chromium carbide nickel chrome, Cr3C2-NiCr coatings applied on AISI 340 alloy steel through high velocity oxy-fuel (HVOF). In this microstructural studies, steel sample were prepared to differentiate the thickness of the coating based on the hardness value between coating and substrate. The experimental procedures Cr3C2- NiCr thermal spray coating process, testing procedure and equipment involved were being determined through numbers of literature reviews and availability of equipment inside university laboratory. It is to prove that chromium carbide nickel chrome Cr3C2-25NiCr can produce better protection for AISI 340 alloy steel

Sustainable development goals and circularity in thermal spray coating manufacturing and value chain.

Thermally sprayed coating manufacturing utilizes a range of feedstock materials to develop thick layers on high-value solid and conformal structures which provide a wide range of qualities to components or parts. Due to the combination of environmental, economic, social, and regulatory factors, there is compelling need for thermal spray coating manufacturers and those associated with the value chain to embrace the United Nation's Sustainable Development Goals (UN SDGs) and circularity to stay competent in the international market. This could lead to a significant increase in the demand for sustainable and circular manufacturing practices, and potential increase in business opportunities, market size and the economy. There is a need to understand the challenges and identify opportunities for circularity in thermal spray coating manufacturing and value chain

Hot Corrosion Behavior of Thermal Spray Coating

Austenitic stainless steel AISI 304 and Boiler steels (such as P11, P22, P12) find their largest application in the manufacturing industry. These are preferred because of their superior mechanical strength, surface stability, creep and fatigue resistance. However, they are highly susceptible to hot corrosion. Therefore, surface engineering imparts hot corrosion resistance properties in high temperature corrosive environments. In the present study, Cr3C2-25NiCr coating was deposited on the substrate 304SS by High Velocity Oxygen Fuel (HVOF) technique in order to investigate the behavior of the Cr3C2-NiCr thermal spray coating. The bare specimens were boilier steel alloys P11, P12 and P22. Hot corrosion test was conducted on bare and coated specimens in 40%K2SO4 -40%Na2SO4 -10%NaCl -10%KCl environment at 900 °C for 10 cycles. Corrosion kinetics was monitored using weight gain measurements. Characterization of corrosion products was carried out by scanning electron microscope with energy-dispersive x-ray spectroscopy (SEM/EDS) technique. The observed corrosion resistance of the Cr3C2-NiCr coating can be attributed to the formation of protective oxide scale Cr2O3. The corrosion mechanism of the coating is discussed

Hot Corrosion Behaviour of Thermal Spray Coating

Hot corrosion is a phenomenon of corrosion or oxidation that will take place at higher operated temperature such as boiler, furnace and others. The thermal spray coating techniques was invented to overcome and increase the life span of substrate metal from hot corrosion. In this report, the author has stated that, the coating powder ( chromium carbide- nickel chrome) deposited on the substrate metal using HVOF techniques showed a high corrosion resistance in molten salt solution ( sodium sulphate + sodium chloride) at 800 °c for 2 cycles ( 10 hours). This can be prove by observing and analysis the weight gain of the Sample 1(uncoated) and Sample 2(coated). The weight gain is lower at sample 2 is because, the Sample 2 was been protected with oxide layer that prevent the oxidation to occur at the surface of the substrate metal. The SEM, X-ray Map Analysis, and EDAX analysis has been done to observe the surface profile of samples after the hot corrosion test. Based on the analysis, the images, table and graph that were presented by the analysis, the author conclude that, both of the samples shows the precipitation of oxide layer. The Sample 1 that was bare mild steel shows the deposition of iron oxide and at the Sample 2, chromium oxide, nickel oxide and iron oxide were deposited. The iron oxide layer concentration at Sample 1 was much higher compare to metal oxide that were deposited at Sample 2 and this was the reason of higher weight gain at Sample 1

Synthesis of single-component metallic glasses by thermal spray of nanodroplets on amorphous substrates

We show that single component metallic glasses can be synthesized by thermal spray coating of nanodroplets onto an amorphous substrate. We demonstrate this using molecular dynamics simulations of nanodroplets up to 30 nm that the spreading of the nanodroplets during impact on a substrate leads to sufficiently rapid cooling (10^(12)–10^(13) K/s) sustained by the large temperature gradients between the thinned nanodroplets and the bulk substrate. However, even under these conditions, in order to ensure that the glass transition outruns crystal nucleation, it is essential that the substrate be amorphous (eliminating sites for heterogeneous nucleation of crystallization)

Thermal Spray Coating for Corrosion Under Insulation Prevention

orrosion under Insulation (CUI) is one of the predominant mechanical integrity issues affecting the industry. CUI refers to external corrosion, but it is difficult to detect because of the insulation cover that masks the corrosion problem. One of the options to prevent corrosion under insulation is by protective coating systems. Thermal spray coating (TSC) is an advanced coating system and shows promising performance in harsh environment and could be used for preventing CUI. However, the application of TSC is not attractive due to high initial cost. The project focused on evaluation of TSC based on corrosion performance using linear polarization method, salt spray test and evaluation of coating mechanical performance using adhesion test, bend test and microstructure characterization of the coating. For the salt spray test, there was no sign of corrosion products especially at the center (fully coated region). TSC protected the steel satisfactorily, whether by barrier effect and by cathodic protection. Under Scanning Electron Microscope (SEM) TSC did not show any corrosion defects after 336 hours of continuous exposure to salt fog test which means the coating is a perfect barrier from corrosive environment. The LPR test results showed that the TSC yields low corrosion rate of 0.05mm/year compared to the bare steel especially at high temperature 80 oC where usually normal coating fails. In conclusion, TSC was evaluated technically acceptable for long term protection of corrosion under insulation. Further research should be done on corrosion performance and life cycle cost by comparing the TSC with conventional coating

Tribology of Wire Arc Spray Coatings under the Influence of Regenerative Fuels

In order to further optimize the efficiency of today’s internal combustion engines, specific coatings are used on functional surfaces to reduce internal engine friction and wear. In the current research project, oxymethylene ether (OME) is discussed because it is CO2 neutral and has a strong soot-reducing effect as a fuel or fuel additive. In some operational regimes of the internal combustion engine a dilution of engine oil by fuel must be assumed. In this paper, the frictional contact between piston ring and cylinder raceway is modelled using a pin-on-disk tribometer and the friction and wear behavior between a diamond-like carbon coating (DLC) and a thermal spray coating is characterized. The wear of the spray layer could be continuously detected by radionuclide technology (RNT). With the aid of photoelectron spectroscopic measurements (XPS), the steel thermal spray coating was chemically analyzed before and after the tribometer tests and the oxidative influence of OME was investigated. In addition, confocal microscopy was used to assess the topographies of the specimens. The measurements showed that the addition of OME to the lubricant reduced the viscosity and load-bearing capacity of the lubricating film, which led to an increase in the coefficient of friction. While almost no wear on the pin could be detected at 10% OME, the first visible material removal occurs at an OME content of 20% and the layer delaminated at 30% OME. The evaluation of the RNT wear tests showed that both the tests with engine oil and with engine oil plus 20% OME achieved very low wear rates. No corrosion of the thermal spray coating could be detected by XPS. Only the proportion of engine oil additives in the friction track increased with increasing OME concentration

Supersonic particle deposition as potential corrosion treatment method for helicopter part in Malaysia

Aluminium types 7075,2024 and magnesium casting alloys are widely used in aircarft components, example Helicopter because of their inherent weight advantages over other metals but premature failure due to corrosion is one of the main challenges associated with this alloys, which affects the safety and readiness of aircraft. This paper is an outcome of project to address corrosion problem at Helicopter part using supersonic particle deposition as potential corrosion treatment method in Malaysia.Current practise of corrosion treatment by OEMs such as Sikorsky are using DOW-17 process or thermal spray coating. Disadvantage of DOW-17 process,it involve hazard material and Thermal spray coating issue of porosity and fatigue failure.The procedure focusing on particle deposition at supersonic level using material powder that suitable with substrate.Supersonic particle deposition using Aluminium coating will provide total solution for corrosion treatment for Aluminum airframe structure.There is no application yet of this coating technology in Malaysia and on top of that, coating at low temperatue that creates negligible heat affected zone and lead to excellent fatigue properties between deposited material and substrate, this will contribute to a big potential of SPD application in aircraft, automotive and tooling industry