Spray Process Research Articles

Numerical Study of Powder Particle Flight Behavior during Gas Detonation Spraying Process

Numerical Study of Powder Particle Flight Behavior during Gas Detonation Spraying Process

3D printing austenitic stainless steel 316L by cold spray process: optimum post-spraying heat treatment conditions

3D printing austenitic stainless steel 316L by cold spray process: optimum post-spraying heat treatment conditions

Coupling APS/SPS Techniques for Cu-TiO2 Antibacterial Coating Deposition: Application to Water Treatment

Since the COVID-19 pandemic, efforts in the field of surface decontamination have been redoubled. Finding innovative self-cleaning devices has become a challenge, and several solutions have been proposed in the market in recent years. In this work, an optimized powder/suspension plasma spray process at atmospheric pressure, using a Triplex Pro 210TM torch, is implemented to produce Cu-TiO2 surface coatings on stainless steel. The purpose is to investigate the potential improvement of antibacterial efficacy by the reactive surface species generated from TiO2 photoactivity under irradiation. A water-based suspension, prepared with AnalaR NORMAPURTM TiO2, is used as a precursor to incorporate the photocatalyst into an antibacterial copper matrix. Surface antibacterial tests according to ASTM 2180 standards were performed, and experiments were performed in treated contaminated water. Sub-stoichiometric blue TiO2 coatings showed complete bacterial elimination after 90 min of visible light irradiation, and Cu-TiO2 surface coatings were even able to disinfect the surfaces under white light, making the application interesting for bacterial destruction under natural illumination. These materials are also intended for application in water treatment, including both pathogens and chemical micropollutants, which is a pressing issue facing many countries today.

Rapid preparation and mechanism investigation of covalent organic framework membranes by 3D printing based on electrostatic spraying

Covalent organic framework (COF) has great advantages in the field of membrane separation, but the efficient and convenient preparation of COF membranes is still a challenge. Herein, we propose a novel method with green solvent for the preparation of COF membranes based on electrostatic spraying, which can be successfully prepared within 10 min, forming the TpPa COF with a pore size of 1.8 nm. Molecular dynamics simulations demonstrate that electrostatic spraying enhances the reaction rate by lowering the energy barrier and increasing the movement of reacting monomers. Atomization of the solvent in electrostatic spraying causes the rapid volatilization of the solvent, resulting in supersaturation of the generated TpPa, precipitation and crystallization, and promotes the formation of TpPa COF structure. The optimal COF membrane for the separation of Congo red wastewater is prepared by adjusting the voltage, concentration, and spraying time, with selectivity of Na2SO4 for Congo Red attaining 118 and water permeance reaching 70.2 L m-2 h-1 bar-1. This work not only elaborates the membrane preparation mechanism in the electrostatic spraying process, but also greatly shortens the time of COF membrane preparation compared to the traditional method (2–3 days), which contributes to the possibility for practical application of COF membranes.

Development of New Spray Dust Suppression Materials in Metal Mines and Prediction of Algorithm Simulation Effect

PROBLEM: Dust contamination in metal mining poses substantial dangers to environmental quality and human health. Modern mining operations cannot use traditional spray dust suppression methods because they are poorly adapted to changing climate conditions, low efficient, and detrimental to the environment. INTRODUCTION: Dust pollution seriously impacts the environment and human health in metal mine operations. Traditional spray dust suppression technology has many problems, such as limited effect, environmental impact, and poor climate adaptability. OBJECTIVES: The purpose of this article is to develop a new type of spray dust suppression material and predict its dust suppression effect through algorithm simulation. Firstly, efficient and environmentally friendly dust-reducing materials were screened, and after evaluating the dust-reducing effect under laboratory conditions, the optimal material combination was determined. METHODS: Using computational fluid dynamics (CFD), a numerical model of the spray process was constructed to simulate the dust suppression effect of different materials under different climatic conditions. RESULTS: The results show that the highest dust reduction efficiency of the new spray dust reduction material is more than 4.3% higher than that of the traditional material, and it shows good stability. CONCLUSION: The new spray dust control material and its effect prediction method studied in this article provide an effective solution for dust control in metal mines, which has important theoretical value and practical application prospects.

A means of destroying sites of perennial root shoot weeds with pests and diseases in them

BACKGROUND: The subject of the study is the technological process of protective spraying of agricultural crops using a combined method against perennial weeds in sites in the field using two pneumohydraulic devices with slot atomizers as part of an improved small-sized boom sprayer. AIM: Development of a technical mean for exterminating sites of perennial root shoot weeds with pests and diseases in them. METHODS: The developed pneumohydraulic devices were used for an improved mounted boom sprayer of plants to treat sites of perennial weeds in the field. Chemical spraying with combined use of the traditional method and the developed pneumohydraulic devices with axial fans and 12 V electric motors, ensuring the distribution of droplet liquid on the treatment surface with two sprayers over 4 meters, is able to reduce the amount of the applied chemicals compared to the conventional technology and to reduce the pesticide load on crop plants by local destruction of sites of weeds, pests and diseases. Based on the developed methods, the results of spraying the surface with a drop liquid with a known dispersion using slot sprayers and controlled liquid pressures with a dial gauge during experiments were obtained. SCIENTIFIC NOVELTY: For the first time, a combined method and technical mean of achieving the research aim have been proposed for the destruction of sites of perennial weeds in the field and the diseases and pests of agricultural crops spread in them. RESULTS: When using a mounted sprayer with two containers for working fluids of combined herbicide solutions or for an insecticide solution in one of the containers and installation of the improved pneumohydraulic devices on the edges of the boom with a conventional arrangement of slot atomizers, it is possible to meet agrotechnical requirements for the use of herbicides, insecticides and fungicides. The simultaneous impact of large drops of herbicides on weeds and the penetration of small drops into plants will destroy sites of rhizome and root weeds with pests and diseases to ensure favorable conditions for the production of agricultural crops. CONCLUSION: A combined method and the technical mean of chemical treatment of perennial weeds with pests and diseases to create favorable conditions for the production of cultivated plants has been experimentally substantiated. Compliance with the conditions is ensured by equipping the mounted sprayer with two containers, pumps for supplying liquid through hoses to slot atomizers, and installing pneumohydraulic liquid nozzles at the edges of the boom. Working liquid sprayers ensure spraying width of more than 4 m, taking into account the size of a site, as well as spraying inaccessible areas using conventional technical means. The efficiency of the developed combined protective spraying of agricultural crops against perennial weeds and pests by the technical mean of its implementation lies in the savings of expensive herbicides and insecticides up to 70% in the later stages of their growing season (as they grow over the field area) compared to the forced continuous application of the herbicide over the entire field area.

Probing trade-off between critical size and velocity in cold-pray: An atomistic simulation

The detailed mechanism of bonding in the cold spray process has remained elusive for both experimental and theoretical parties. Adiabatic shear instability and hydrodynamic plasticity models have been so far the most popular explanations. Here, using molecular dynamics simulation, we investigate their validity at the nanoscale. The present study has potential applications in the fabrication of ultrathin layers in the electronics industry. For this aim, we considered Ti nanoparticles of different diameters and Si substrates of different orientations. It is shown that very high spray velocities are required for a jet to be observed at the nanoscale. We propose a method for thermostating the substrate that enables utilizing high spray velocities. For the first time, we demonstrate an oscillatory behavior in both the normal and radial stress components within the substrate that can propagate into the particle. We have shown that neither the adiabatic shear instability model nor the hydrodynamic plasticity model can be ignored at the nanoscale. In addition, the formation of a low-resistance titanium silicide proper for electronic application is illustrated.

Influence of Detonation Spraying Parameters on the Microstructure and Mechanical Properties of Hydroxyapatite Coatings.

The process of osteointegration depends significantly on the surface roughness, structure, chemical composition, and mechanical characteristics of the coating. In this regard, an important direction in the development of medical materials is the development of new techniques of surface modification and the creation of bioactive ceramic coatings. Calcium-phosphate materials based on hydroxyapatite have been proposed as bioactive ceramic coatings on titanium implants for the effective acceleration of bone tissue healing. To obtain bioactive ceramic coatings, pulse power sources are best suited, namely detonation spraying, in which the energy of the explosion of gas mixtures is used as a source of pulse action. The pulse mode of operation in the detonation spraying method is preferable for the formation of bioactive ceramic coatings. It provides a high velocity of hydroxyapatite particles, which promotes their effective fixation on the titanium substrate, while minimizing the heating of the material. This approach preserves the substrate structure and improves the coating adhesion. Four different types of coatings with varying O2/C2H2 molar ratios, ranging from 2.6 to 3.7, were obtained using detonation spraying. Powders and obtained coatings of hydroxyapatite were studied by Raman spectroscopy and XRD structural analysis. The results of XRD phase analysis showed the partial conversion of the hydroxyapatite phase to the α-tricalcium phosphate (α-TCP) phase during the detonation spraying process. The results obtained by Raman spectroscopy indicate that hydroxyapatite is the main phase in coatings. All hydroxyapatite-based coatings exhibited hydrophobic properties, which was confirmed by contact-angle values above 90° in wettability tests, characteristic of hydrophobic surfaces. The adhesive strength of the coatings was measured by the scratch test method. Tribological tests were conducted using the ball-on-disk method under both dry conditions and in Ringer's solution. This approach enabled the evaluation of wear resistance and friction coefficient of the coatings in different environments, simulating both lubrication-free conditions and those resembling physiological environments.

Failure Evaluation of Thermal Spray Coating Using High-Velocity Oxy-Fuel (HVOF) on Steam Turbine Shaft 940-PT 2 A/B

The repair of worn steel shaft surfaces in power transmission systems is made possible by thermal spray procedures, which have become an essential technology in many sectors. With this novel approach, worn shaft components may be recycled effectively since an API 687-compliant wear-resistant coating designed for specialty rotating equipment repairs is applied. The process's efficacy stems from its capacity to extend the functional life of essential mechanical components, therefore decreasing replacement expenses and downtime. The variety of factors that affect the result highlights the intricacy of thermal spray techniques. Finding the ideal mix of these crucial process variables becomes essential to provide the required degree of wear resistance. The coated shafts perform better as a result of this careful tuning, which also guarantees dependability under challenging working conditions. The coated shafts' surface hardness data in this investigation showed that the initial coating hardness value was below the predetermined goals. Several parts that interact with the shaft were redesigned strategically in response to these discoveries. These adjustments were mainly motivated by economic considerations, to optimize effectiveness while resolving the noted hardness deficiencies. Furthermore, a thorough analysis of failure data showed important correlations between different operational parameters and how they interacted, offering a further understanding of how these factors affected wear resistance. This research allowed for the identification of crucial parameters that required change and emphasized the precise balance essential for optimum thermal spray application. All things considered, this study emphasizes how critical it is to use a methodical approach to improve thermal spray processes, guarantee successful shaft component restoration, and ultimately increase the operational longevity of such components in challenging applications.

Surface modification of WE43 Mg alloy via combination of cold spray and micro-arc oxidation for wear related applications at high temperatures

This study investigates the high temperature wear behaviour of a WE43 Mg alloy after covering it with single and dual layer coatings. For this purpose, cold spray and micro-arc oxidation processes were employed individually and sequentially. Single-layer coatings fabricated by cold spray and micro-arc oxidation processes were Al/Al2O3 composite and MgO-based ceramic, respectively. Sequential application of cold spray and micro arc oxidation processes induced dual layer coating upon synthesizing an external Al2O3–based layer over the Al/Al2O3 composite layer. Results of the wear tests conducted under the load of 2 N revealed the superior resistance of the dual layer coated sample against the rubbing action of the counterface compared to single layer coatings. Thus, the presence of a relatively hard and tough external Al2O3-based layer over the Al/Al2O3 composite layer sustained protection up to the temperature of 320 °C, where the dominant wear mechanism was fatigue wear. However, the increase in the test temperature to 350 °C caused detachment of the external Al2O3-based layer. Reduction of the wear test load from 2 to 1 N resulted in the remaining of external Al2O3-based layer intact with the underlying Al/Al2O3 composite layer even at a test temperature of 350 °C. It is therefore concluded that the combination of cold spray and micro-arc oxidation processes is promising to broaden the reliable use of WE43 and other Mg alloys in wear related applications at high service temperatures.

Study on the water and mold resistance of ZnO/polyurethane superhydrophobic coating on circuit boards

In this work, superhydrophobic coatings were prepared on circuit boards based on the susceptibility of circuit boards to harsh environments such as humidity and mold adhesion, leading to reduced service life. Firstly, cetyltrimethoxysilane and γaminopropyltriethoxysilane were used to modify zinc oxide nanoparticles with different particle sizes. Then polyurethane and modified nanoparticles were successively sprayed on the circuit boards with a spraying process, and the superhydrophobic coatings were finally produced. The impact of the zinc oxide mass ratio with different particle sizes, silane coupling agent content, and surface modifier content on the hydrophobicity of the coatings were investigated. The results show that when the mass ratio of zinc oxide (30nm) to zinc oxide (90nm) is 1:1, the silane coupling agent content is 12‰. The surface modifier content is 12‰, the hydrophobicity of the coating is the best, and its CA can be up to 169.5°, and its SA can be up to 2.8°. It exhibits good protection of circuit boards in the tests of adhesion, acid, and alkali corrosion resistance, self-cleaning performance, and anti-mold performance. Performance, so that the coating is in the future field of electronic equipment applications.

High speed impact induced dehydrogenation of titanium hydride and formation of cellular structure via cold spray

In this study, it is revealed for the first time that ultra-high-speed impact can trigger in-situ dehydrogenation at the impact interface of titanium hydride (TiH). This phenomenon leads to a phase transformation from brittle TiH to ductile Ti, causing a shift in the ductile-to-brittle transition from the impact interface to the particle interior. Inspired by this unique behavior, and considering the mechanical interactions between particles during the spray process, TiH powders were used as feedstock to successfully produce a large-scale random cellular structure through cold spray. A systematic investigation of the deposition process revealed that unbroken TiH particles interact with dehydrogenated ones, resulting in only the ductile portion of the TiH particle being deposited, while the brittle interior is spalled off, consequently forming the “walls” of the cellular structures. This work highlights the potential of TiH powders to advance cold spray technology, particularly in the creation of complex cellular structures.

Optimizing concrete rheology to mitigate aerosol pollutants in wet-mix shotcrete processes

Studies focusing on optimizing the pumpability and sprayability of concrete exist; however, research addressing the control of aerosol pollutants during the spraying process is limited. This study investigated the intricate relationships among additive formulations, rheology properties of fresh mixes, and aerosol pollutant emissions using a Box–Behnken design, combined with response surface methodology and gray correlation coefficient analysis. The developed high-accuracy regression model offers valuable insights into the impact of water-reducing agents (WRA), air-entraining agents (AEA), thickening agents (TA), and defoaming agents (DA) on the zeta potential, slump, surface tension of fresh mix concrete, and spread angle during wet-mix shotcrete (WMS), with R2 values of 0.94, 0.95, 0.95, and 0.95, respectively. Additionally, by considering both sprayability and a low spread angle, this approach facilitated the development of an optimal composite incorporating 1.36% WRA, 1.50% AEA, 0.20% TA, and 1.00% DA, yielding desired properties, including a slump of 200mm, spread angle of 20°, and aerosol pollutant concentration of 21mg/m3. This study provides a model to aid the formulation of shotcrete that mitigates aerosol pollutant generation during the WMS process, thereby contributing to the broader objectives of environmental sustainability and workplace safety.

Influence of FeSiAl Content on the Morphological Evolution and Electromagnetic Properties of FeSiAl/CaO–B2O3–SiO2 Microwave-Absorbing Coatings

CaO–B2O3–SiO2 (CBS) is a promising lightweight, low-dielectric matrix material for high-temperature microwave-absorbing coatings. However, the comprehensive study of absorbent morphology evolution within such coatings and its influence on electromagnetic (EM) performance has not been conducted. In this work, a series of FeSiAl (FSA)/CBS composite coatings with various FSA contents were fabricated using atmospheric plasma spraying. The morphological evolution of the FSA phase and the resulting EM properties of the coatings were systematically analyzed. Experimental findings show that during the spraying process, when the size of FSA clusters in the composite powder exceeds the thickness of CBS splats, FSA clusters form a rigid contact with the underlying solidified coating, leading to the development of a lamellar structure. This lamellar FSA phase creates local conductive networks, which significantly increase the complex permittivity of the coating. These results provide valuable guidance for controlling absorbent morphology and optimizing the EM properties of CBS-based coatings.

Enhancing corrosion resistance of Al alloy sheets with potential gradient by arc-sprayed Zn coatings

To improve the corrosion resistance and wide the application of Al alloy sheet in the engineering production, a corrosion potential gradient along the thickness of the Al alloy sheet was fabricated using the sprayed Zn layer. The process of arc spraying was employed to obtain the Zn coating with optimizing the parameters. Electrochemical testing was conducted on the surface of Al alloy sprayed with Zn layers at different depths. As the depth in the thickness direction increases, the content of Zn alloy elements gradually decreases and the potential gradually increases. This exhibits a gradual decrease in corrosion tendency. The results of electrochemical impedance spectra (EIS) revealed the existence of pitting corrosion on the surface of the Al alloy. This even extended to the underlying substrate material. In contrast, the Zn coating, when exposed to a corrosive environment, demonstrated the beneficial cathodic effect as a sacrificial anode and the protective function of a passivating film, thus mitigating corrosion. The gradual increase in charge transfer resistance in the impedance spectrum suggested that the corrosion resistance of the sample is increasingly improved. Therefore, it exhibited remarkable resistance to corrosion. Additionally, the SEM surface morphology and XRD pattern were utilized to further explain the corrosion mechanism of the arc-sprayed Zn coating. The Zn coating can provide sacrificial protection to the Al layer due to its higher negative potential and localized corrosion reactivity. This is attributed to the micro-galvanic couples formed between the Zn and Al layer, thus increasing the corrosion resistance of the sheets.

Structure and Properties of the Electroexplosive Coating of the TiB2-Ag System after Electron Beam Treatment

A coating of the TiB2-Ag system was formed through the use of sequential operations of electroexplosive spraying and electron beam processing. The values of electrical conductivity (62.0 MS/m), Vickers microhardness (0.251-0.265 GPa at the point of measurement on a silver matrix and 25-32 GPa at the point of measurement at inclusions of boride phases), nanohardness (4.48 ± 0.76 GPa) were determined), Young’s modulus (116±29 GPa), wear parameter under dry friction-sliding conditions (1.2 mm3/N • m) and friction coefficient (0.5). Switching wear resistance during accelerated tests was 7000 on and off cycles with an electrical resistance of 10.01 - 11.76 LiOhm. The thickness of the coatings is 100 microns. The coatings are formed by a silver matrix with inclusions of titanium borides located in it with three types of sizes: nanocrystalline, submicrocrystalline and microcrystalline. Quantitatively, in the structural composition among titanium borides, titanium diboride and silver (56 wt. %) are formed predominantly (41 wt. %), while other titanium borides account for 3 wt. %. Structural transformations are described using complementary methods of X-ray phase analysis, scanning and transmission electron microscopy.

Effect of injection strategy on spray and combustion processes in 2-stroke rod-less opposed piston engine (2S-ROPE)

The 2-stroke Rod-less Opposed Piston Engine (2S-ROPE) is a novel engine design that has garnered attention owing to its high power and low fuel consumption. This study investigated the effects of different fuel injection strategies on the in-cylinder working process of a 2S-ROPE engine, which features a smaller combustion space and lateral injection than conventional diesel engines. A high-precision three-dimensional simulation model was developed to examine the fuel atomization and in-cylinder combustion processes under four distinct injection strategies (S1, S2, S3, and S4). The results demonstrated that the injection strategy significantly influenced the number of oil droplets, particularly for small particles. The number of small droplets in S4 was approximately 6 times that in S1. The double-layer injection strategies (S3 and S4) exhibited a better atomization breakup and oil-air mixing, leading to a faster combustion rate and higher lift power than the single-layer injection strategies (S1 and S2). These findings suggest that the double-layer injection strategy is more suitable for a 2S-ROPE engine, increasing the lift power by up to 23 %. The results can guide the improvement of combustion parameters in most opposed piston engines.

Thick and dense nitrogen-doped hafnium carbide ultra-high temperature thermal protection coating for outstanding ablation resistance up to 2600 ℃

Transition metal carbon-nitrides, typically represented by HfCN, have become the latest progress among the ultra-high temperature ceramics. In this study, single-phase solid solution HfCN coating was successfully synthesized from spray granulated HfC-HfN composite powder followed by employing the dual solid solution effects of radio frequency inductively coupled plasma spheroidization and supersonic atmospheric plasma spraying processes. The coating was nearly dense (only 2.3% in porosity) with a high thickness of ~ 270 μm. Compared with HfC coating, the HfCN coating exhibited higher hardness and elastic modulus. After plasma ablation at a high heat flux of 8.2MW/m2 for 200s, the HfCN coating exhibited a surface temperature of up to 2600 ℃ and can firmly protect the refractory tungsten substrate from oxidation failure. This outstanding performance illustrates that doping N element in HfC crystal can effectively improve the energy barrier for oxidation reaction and oxygen adsorption compared with typical HfC coating.

Corrosion mechanisms of plasma sprayed porous coatings of Ni80Cr20 and alloy C-276 investigated by numerical and experimental method

Abstract: In this study, the corrosion performance of Ni80Cr20 and alloy C-276 (UNS N10276) coatings on 7075 aluminum alloy substrates was evaluated using a variety of performance characterization tests. Significant amounts of nickel oxide were found in the corrosion products of the two coatings that were stripped, with molybdenum in the two coatings that were not stripped effectively slowing down the corrosion rate. Both coatings selectively corrode Cr, where it is worth noting that the preferential corrosion of W elements in alloy C-276 has a positive effect on its surface protection. It is not only the amount of molybdenum content, but also the influence of the W element that leads to better corrosion resistance of alloy C-276 coating than Ni80Cr20 alloy coating. The coating spraying process due to process parameters and its own nature, etc. has caused different sizes of pores, while these pores in the corrosion process will have a certain degree of influence on the corrosion process. The size of the pore defects for the coating transverse corrosion effect was more significant, and small pore defects accelerated the corrosion process. The number of pore defects had a more significant effect on the longitudinal corrosion of the coating, and multiple pore defects slowed the corrosion process.

Study of coatings of the Ni–Ti–(SiC, WC, B4C) system applied to the surface of titanium alloy plates using cold gas dynamic spraying and laser processing

The technology of applying composite intermetallic coatings of the Ni–Ti system reinforced with carbides based on powders (SiC, WC, B4C) on the surface of titanium alloy plates with the sequential use of the CGDN method and laser processing is considered. The technological parameters of the laser-thermal processing, ensuring the production of composite coatings of the Ni–Ti–(SiC, WC, B4C) system of high hardness, are determined.