Spray Process Research Articles

Optimization of High-Velocity Oxygen Fuel Spray Process Parameters to Achieve Maximum Thickness and Minimum Porosity in Vanadium Carbide Coating

Optimization of High-Velocity Oxygen Fuel Spray Process Parameters to Achieve Maximum Thickness and Minimum Porosity in Vanadium Carbide Coating

Visualization study on the ignition and diffusion combustion process of liquid phase ammonia spray ignited by diesel jet in a constant volume vessel

Ammonia fueled engines applying diffusion combustion mode is expected to further improve the thermal and combustion efficiencies with high burning rate and high ammonia energy replacement. However, there is a lack of the fundamental studies about ammonia diffusion combustion characteristics. Therefore, the fundamental optical experiments of liquid phase ammonia spray and combustion, which is ignited by pilot diesel injection, were performed to investigate the ignition and diffusion combustion characteristics of liquid phase ammonia. According to the high-speed photography, interaction processes between the liquid phase ammonia spray and the diesel spray had been described, and the whole ignition and combustion processes were also recorded in detail. The discussion about the effect of diesel jet ignition location on ammonia ignition process shows that the effective ammonia ignition zone by diesel spray is the region of gas entrainment zone except for the liquid phase ammonia volume under evaporated condition, where the interval on ammonia spray axis is about 16 mm ∼ 35 mm away from the ammonia nozzle exit under the current experimental conditions, and the ammonia spray is failed to be ignited at any region out of the effective ignition zone. Moreover, the ammonia diffusion combustion characteristics under various ammonia injection durations reveals that the entrainment, including both the diesel flame and the surrounding ambient gas, into the effective ignition zone of liquid phase ammonia spray, is the effective way to achieve reliable ignition and the subsequent diffusion combustion of ammonia, which can increase the energy ratio (ammonia to pilot diesel) up to at least 2.9. Finally, based on the control of combustion mode of the pilot diesel, utilizing premixed diesel flame to induce the diffusion combustion of ammonia is proved to be an effective regulation scheme to enhance the performance of ammonia combustion under engine-like thermal conditions.

Experimental study on microscopic characteristics of transcritical spray for high density environment

As the power density of diesel engines increases, the in-cylinder spray process appears supercritical phase transition, but the transition boundary and judgment criteria are unclear. This study explores the supercritical phase transition of spray using a constant volume combustion chamber and a high-speed optical system, considering ambient temperatures of 700 K to 1600 K and densities of 12 kg/m3 to 22.8 kg/m3. The results show that under subcritical conditions, the droplets at the end of the spray remain spherical during the evaporation process due to the existence of surface tension, and eventually evaporate. Under supercritical conditions, the droplets begin to be spherical during the evaporation process. As time goes on, the wake appears and falls off, oscillates and deforms, and finally diffuses and disappears, which is regarded as the occurrence of supercritical phase transition. The temperature limit of supercritical phase transition decreases with the increase of ambient density, and the density limit decreases with the increase of ambient temperature. This is because as the ambient density or temperature increases, the heat absorption required to destroy the gas–liquid interface (reducing the surface tension, thickening the interface, and reducing the average free molecular path) decreases. The supercritical phase transition time is shortened with the increase of ambient temperature or ambient density. The reason is that the ambient density and temperature increase under supercritical conditions, the heat and mass transfer is accelerated, and the temperature rise of the droplet surface is accelerated. As the droplet size increases, the supercritical phase transition boundary remains unchanged, and the supercritical transition time is prolonged, which is due to the decrease of the surface volume ratio and the slow heating of the droplet.

Development of a line following autonomous spraying vehicle with Machine vision-based leaf density estimation for cherry tomato greenhouses

Traditional manual spraying systems and even modern automated ones often neglect the critical factors of plant growth stage and coverage density during spraying for plants, which can result in suboptimal yields. To address this issue, this study aims to describe the development of an efficient and affordable autonomous spraying vehicle (ASV) for application in cherry tomato greenhouses. The ASV integrates a visual autonomous spraying system (VASS) and a vehicle control system (VCS). The VASS uses leaf density signalling with machine vision and a vertical spray boom to target leaves for precision spraying application. Leaf density signalling is an algorithm developed to recognise and estimate leaf density by machine, simplifying the real-time determination of leaf density levels in plants. The performance of the algorithm demonstrates an accuracy of 84 % with an average video processing speed of 33.3 ms. The VASS is integrated into VCS to facilitate remote or autonomous navigation. The visual line-following system (VLFS) supports ASV in autonomously navigating between narrow-spaced rows in cherry tomato greenhouses, thereby automating the entire spraying process. The analysis of the comprehensive performance of the ASV and the comparative analysis with knapsack sprayers in field experiments are discussed and presented. Comparative analysis with manually operated sprayers demonstrates the better performance of the ASV. These experiments highlight the potential of the ASV to replace traditional manual spraying methods while enhancing spraying precision.

Cold Spray Process for Co-Deposition of Copper and Aluminum Particles

Mixed-particle spraying has been applied to various aspects of industrial cold spraying for a long time. Due to the complexity of mixed-particle simulations, most studies only consider dozens of particles when considering particle collisions. This paper combines computational fluid dynamics and a discrete element method to analyze the entire trajectories of mixed particles. With simulations involving over one hundred thousand particles, we accurately tracked the three-dimensional positions and velocities of each particle, effectively visualizing their journey from feeder to substrate. By comparing the particles’ velocities to their critical velocities, we could directly assess the deposition efficiency, achieving a comprehensive and accurate simulation of the complete cold spray process. The numerical model was validated using a multi-experimental analysis. The particle distribution and deposition area from the numerical model matched well with the experimental data. It was found that the mutual collision of copper and aluminum particles increased the number of copper particles, surpassing the critical velocity in the mixed powder by 24.2%. When copper particles and aluminum particles collided, the displacement of aluminum particles was more than three times that of copper particles in the direction perpendicular to the jet. This collision caused the aluminum particles to be more dispersed.

Effect of cold spray processing parameters on the microstructure, wear, and corrosion behavior of Cu and Cu–Al2O3 coatings deposited on AZ31 alloy substrate

Cold spray coatings represent a newly emerging and recently implemented approach to enhance the poor wear and corrosion resistance of AZ31 magnesium alloy. In this study, the authors applied pure Cu and Cu-50 wt% Al2O3 composite coatings on an AZ31B substrate using the cold spray deposition method and investigated the effects of gas pressure (1, 2, and 3 MPa) and stand-off distance (1, 2, and 3 cm) on their microstructure characteristics. An increase in gas pressure from 1 MPa to 3 MPa resulted in a decrease in porosity, ranging from 33 % to 38 %, across varying stand-off distances. Increasing the stand-off distance from 1 to 3 cm resulted in a nearly four-fold rise in porosity for 2 and 3 MPa pressures and about 1.5 times for 1 MPa. The porosity increased with higher pressure due to the fragmentation of Al2O3 particles but decreased with greater spraying distance due to reduced Al2O3 retention. Additionally, the incorporation of Al2O3 particles into Cu coatings led to a significant improvement in sliding wear resistance, by up to 50 %, compared to the bare substrate. Abrasive wear and delamination were identified as the dominant wear mechanisms for the composite coatings based on friction coefficient values and micromorphology of wear tracks. Electrochemical results indicated a significant increase in the corrosion resistance of the Cu coating compared to both the bare Mg substrate and Cu–Al2O3 coating, attributed to improved resistance to galvanic corrosion.

Mechanistic Study on the Influence of Hydrogen Fuel in High-Velocity Oxygen-Fuel (HVOF) Thermal Spraying Process

Mechanistic Study on the Influence of Hydrogen Fuel in High-Velocity Oxygen-Fuel (HVOF) Thermal Spraying Process

Effects of Top Ceramic Layers with an Ultrathin Dense Layer on the Thermal–Physical Properties of Thermal Barrier Coatings

Thermal barrier coatings have been used to protect superalloys under extremely harsh conditions. The durability of TBCs with a NiCoCrAlY bond layer prepared via the air plasma spray process and an ultrathin dense layer prepared via magnetron sputtering was investigated under different corrosion conditions. This paper discusses the corrosion resistance improvement mechanism of TBCs with a dense layer produced by magnetron sputtering under corrosion conditions with environmental contaminants such as calcium–magnesium–aluminum–silicon oxide systems (CMAS) at 1300 °C and NaCl-Na2SO4-V2O5 (NV) at 900 °C. The corrosion results show that CMAS will react with the stabilizers of zirconium oxide, which will change the rate of the phase transition, as determined via X-ray diffraction tests. A thermal ablation test verified that TBCs with a dense layer have a better corrosion resistance and better thermal insulation properties. All results show that preparing TBCs with a dense layer via the magnetron sputtering method will be an efficient method to improve TBCs’ properties at high temperatures in the future.

Current status and prospects of flexible solar cells

With the increasing global demand for clean energy, solar cells, as a renewable and pollution-free clean energy source, have attracted much attention. In the past, solar cells have always used rigid materials as substrates. However, this rigid solar panel is not only bulky and limited in layout, but also susceptible to external impact and damage, which is not conducive to its application in various scenarios. Flexible solar cells, developed from rigid solar cells, have the advantages of light weight, small size, high safety, and strong adaptability, gradually becoming the development trend of solar cells. The research and development of flexible solar cells benefit from the rapid development of materials. In recent years, the emergence of various new materials and preparation technologies, such as carbon fibers, polymers, organic materials, and nanostructures, has provided a better foundation for the preparation of flexible batteries. At the same time, flexible batteries can also be processed through printing, spraying and other processing methods, improving manufacturing efficiency. In addition, the demand for wearable devices, smart homes and other emerging scenarios in society has also accelerated the research and application of flexible solar cells, providing broad application prospects for their development. However, its cost is usually higher than that of rigid solar cells, and market regulation under new categories requires time to adapt. The development of flexible solar cells is benign, but it requires the market to test its standardization.

Formation of nanoscale interface in a high-performance TA2/Q235 clad plate

TA2/Q235 clad plates were fabricated using a combination of cold spraying and hot rolling techniques. The cold spraying process involved the high-speed impact that compressed the oxide film present on the surface of both the Ti particle and the steel plate. This compression led to a strong prebonding at the TA2/Q235 interface. Subsequently, a 200 nm-thick interface layer of TiC was formed during the hot rolling process. This TiC layer effectively inhibited the formation of FeTi and Fe2Ti compound layers. As a result, the clad plates exhibited excellent mechanical properties, including an ultimate tensile strength of 560 MPa and an elongation of 32 %.

A photothermal superhydrophobic coating with un-fluorinated modified CNTs for anti-icing applications on concrete

The problem of easy icing and difficult anti-icing on concrete pavement has prompted using superhydrophobic coatings as a potential solution. However, the coatings are prone to wetting failure after repeated icing-deicing cycles. In this study, a superhydrophobic and photothermal coating consisting of unfluorinated modified-carbon nanotubes (M-CNTs) and commercial epoxy is constructed by a simple spray process on concrete for anti-icing. Incorporating M-CNTs imparts the coating with exceptional superhydrophobic and photothermal characteristics, endowing the coating surface with excellent deicing under sunlight irradiation. The contact angle of the coating reaches 151° at −10 °C, and the freezing time extends from 55 s to 680 s. Under one sunlight intensity, the coating temperature rapidly increases from −10 ℃ to 81 ℃, and the ice changes from solid to liquid. It effectively acts as a barrier between water and the concrete surface, making it highly suitable and valuable in practical applications.

Three-Dimensional Structure Measurement for Potted Plant Based on Millimeter-Wave Radar

Potted plant canopy extraction requires a fast, accurate, stable, and affordable detection system for precise pesticide application. In this study, we propose a new method for extracting three-dimensional canopy information of potted plants using millimeter-wave radar and evaluate the system on plants in static, rotating, and rotating-while-spraying states. The position and rotation speed of the rotating platform are used to compute the rotation–translation matrix between point clouds, enabling the multi-view point clouds to be overlaid on the world coordinate system. Point cloud extraction is performed by applying the Density-Based Spatial Clustering of Applications with Noise algorithm (DBSCAN), while an Alpha-shape algorithm is used for three-dimensional reconstruction of the canopy. Our measurement results for the 3D reconstruction of plants at different growth stages showed that the reconstruction model has higher accuracy under the rotation condition than that under the static condition, with average relative errors of 41.61% and 10.21%, respectively. The significant correlation between the sampling data with and without spray reached 0.03, indicating that the effect of the droplets on radar detection during the spray process can be neglected. This study provides guidance for plant canopy detection using millimeter-wave radar for advanced agricultural informatization and automation.

Effect of Cobalt and Chromium Content on Microstructure and Properties of WC-Co-Cr Coatings Prepared by High-Velocity Oxy-Fuel Spraying.

To explore the Co/Cr ratio impact on the high-velocity oxygen fuel (HVOF)-sprayed WC-Co-Cr coatings microstructure and performances, three kinds of WC-Co-Cr coatings, namely WC-4Co-10Cr, WC-7Co-7Cr, and WC-10Co-4Cr, were prepared by using a high-velocity oxygen fuel (HVOF) spraying process. The three coatings' phase composition, microstructure, basic mechanical properties, abrasive wear, and corrosion resistance were investigated. The results show that all three WC-Co-Cr coatings comprise the main phase WC, minor W2C, and amorphous W-Co-Cr phase, besides the WC-4Co-10Cr coating containing a small amount of CrxCy phase. In addition, WC-7Co-7Cr coating exhibited the highest hardness and abrasive wear resistance, followed by WC-10Co-4Cr and WC-4Co-10Cr coatings. The corrosion resistance as a hierarchy was found to be WC-10Co-4Cr > WC-7Co-7Cr > WC-4Co-10Cr.

Film Deposition of Electrochromic Metal Oxides through Spray Coating: A Descriptive Review

Electrochromism induces reversible changes of coloration in specific organic and inorganic materials through electrical charge/discharge reactions. When processed into thin films, electrochromic metal oxides can be integrated into glazing applications such as displays, rearview mirrors, goggles and, most notably, smart windows in energy-efficient buildings. Over the years, the use of spray coating as a liquid-based approach has been acknowledged for its cost-efficient, high-throughput samples production with a low volume consumption. It represents an interesting alternative to vacuum processes and to other wet methods, suitably responding to the current limitations of electrochromic thin films production by offering improved control over deposition parameters and capacities of up-scaling, together with lowered energetic and economic costs. The present review summarizes the main theoretical and practical aspects of spray coating, notably distinguishing room-temperature methodologies from pyrolysis-based, under heating protocols. The main families of functional electrochromic metal oxides are then screened and discussed, establishing how spray processing can challengingly lead to higher levels of optical contrast, commutation kinetics, coloration efficiency and cycling durability, and how low-toxic and environment-friendly precursors can be favored while sustaining large deposition areas.

Investigation of optimized spraying process for directly coated electrode in polymer electrolyte membrane fuel cell

Membrane electrode assembly (MEA) is a core component in polymer electrolyte membrane fuel cells (PEMFCs). A well-constructed catalyst layer is essential for achieving high-performance and reliable fuel cells. Among MEA fabrication processes, direct spray coating has advantages regarding cost-efficiency, processability, and controllability compared to direct sputtering and decal transfer method. In the spray process, the morphology of the catalyst layer depends on conditions in which ink droplets are sprayed and evaporated. Although quantitatively optimizing the spray process is crucial, there is still a lack of well-defined research for optimized spray process. Herein, we propose k-value that can indicate uniform coverage, expressed as a ratio of the area where ink droplets spread compared to the sprayed area. The k-1.0 MEA is fabricated under k-value conditions of one by adjusting nozzle moving speed, which is expected to have the most uniform coverage. Compared to k-0.3 MEA and k-3.0 MEA, the power density improves by 22.3 % and 11.1 %, respectively. This is attributed to the reduced ion transport resistance of the catalyst layer being reduced by 23.7 % and 8.5 % and the increased electrochemical active surface area by 16.1 % and 9.4 %, respectively. Furthermore, the morphology of catalyst layers and substrate temperature effect are investigated.

Solid-state cold spray welding: Evaluation and future direction

Welding is an important manufacturing process for joining complex parts. Despite their widespread use, there exist some drawbacks in the existing liquid-state (e.g., formation of undesirable heat-affected zones around weld area) and solid-state (e.g., high equipment and tooling costs, low production rates, and difficulty in joining intricate geometries) methods. These limitations continually spur the search for new joining processes to improve existing welding methods or develop new ones that circumvent these limitations. To provide a “greener” and low-cost alternative to the traditional welding processes that often produce “soft” heat affected zones (HAZs), we develop and evaluate the expansion of cold spray process—a solid-state high-velocity particle deposition process—to solid-state welding, a process we term cold spray welding (CSW). Using well-defined processing parameters, we cold spray welded (CSWed) AA 6061-T651 plate and compared the results with Tungsten inert gas (TIG) welded counterpart. Although TIG-welded samples exhibit higher tensile properties than CSWed samples (at least based on the CS processing parameters used in this study), our findings show that CSW indeed circumvents major drawbacks in traditional welding processes, including negligible microstructural alterations and the inhibition of deleterious phase transformation and suppression of deleterious HAZ. The examination of CSWed parts reveals low yield strength is connected to ubiquitous microvoids that are formed due to lack of metallurgical bonding; these microvoids act as microcrack initiation sites. We proceed to establish a failure mechanism in the CSWed part to provide direction for future optimization.

Internal Diameter Atmospheric-Plasma-Sprayed High-Performance YSZ-Based Thermal Barrier Coatings

Thermal barrier coatings (TBCs) play a crucial role in enhancing the operating temperature of key equipment. However, when TBCs are sprayed on the internal surface of these components, there are issues related to the imperfect internal diameter atmospheric plasma spray (ID-APS) process and the unsatisfactory performance of TBCs in internal holes. Yttria-stabilized zirconia (YSZ), YSZ + Gadolinium zirconate (GZ) and YSZ + tantalate (RETaO4) TBCs were prepared using the SM F210 ID-APS gun. The thermal shock and particle erosion resistance of the coatings were compared, and the relationship between the structure and properties was investigated. The results show that the hardness, fracture toughness and erosion resistance of the three coatings are the largest in the YSZ coating and the smallest in the GZ coating. YSZ coating also has the best thermal shock resistance. These research findings have important guiding significance for the improvement of the ID-APS process.

Effects of Varying Planting Patterns on Wheat Aphids’ Occurrence and the Control Effect of Pesticide Reduction Spraying Process by Unmanned Aerial Vehicle

A walnut–wheat intercropping pattern is practiced widely in southern Xinjiang to alleviate the contradiction between the lack of cultivated land resources and to increase economic value. Previous studies have confirmed that an alley cropping pattern could change the microclimate by supplying additional ecological functions such as windbreak, light interception, water conservation, etc. Cereal aphids (including Sitobion avenae, Rhopalosiphum padi, Metopolophium dirhodum, etc.) are commonly spread pests that harm wheat plants. But, the difference in population numbers between local patterns is still unknown. Pesticide reduction is the national strategy in China to alleviate the contraction between the demand of grain yield and environment protection. Plant protection-unmanned aerial vehicles (UAV) spraying pesticides are the most efficient method to control pests. However, compared to traditional artificial spraying method, how the UAV spraying method affect the control effect of reduced concentration pesticide is unclear. In order to address this problem, we conducted field investigations at Zepu county in southern Xinjiang to test the difference between walnut–wheat intercropping and wheat monocropping patterns for three consecutive years. And, we employed the field experiments to ensure the effectiveness of the reduced concentration common pesticides through the UAV spraying method. In conclusion, we conducted a comparison of the control effects of two spraying methods under conditions of reduced pesticide usage. Our findings revealed that the population of cereal aphids was larger in the intercropping pattern compared to the monocropping pattern. Although the control effect of the reduced treatment was lower than the regular dosage, some treatments still demonstrated sufficient capability to eliminate aphids, particularly when considering the effect within major varieties. Additionally, the use of the UAV spraying method exhibited a satisfactory effect when compared to the traditional artificial spraying method.

Variable-rate spray system for unmanned aerial applications using lag compensation algorithm and pulse width modulation spray technology

To ensure that a variable-rate spray (VRS) system can perform unmanned aerial spray in accordance with a prescription map at different flight speeds, we examine in this paper such significant factors as the response time of the VRS system and the pressure fluctuation of the nozzle during the variable-rate spraying process. The VRS system uses a lag compensation algorithm (LCA) to counteract the droplet deposition position lag caused by the system response delay. In addition, pulse width modulated (PWM) solenoid valves are used for controlling the flowrates of the nozzles on the variable-rate spray system, and a mathematical model was constructed for the spray rate (L min-1) and the relative proportion of time (duty cycle) each solenoid valve is open. The pressure drop and solenoid valve response time at different duty cycles (50%~90%) were measured by indoor experiments. Meanwhile, the lag distance (LD), spray accuracy, and droplet deposition characteristics of the VRS system were tested by conducting outdoor experiments at different flight speeds (4m s-1, 5m s-1, 6m s-1). The results show that LCA can effectively reduce the lag distance. The lag distance (LD) values of the VRS system with LCA ranged from -0.27 to 0.78m with an average value of 0.32m, while without LCA, the LD values increased to 3.5~4.3m with an average value of 3.87m. The overall spray position accuracy was in the range of 91.56%~97.32%. Furthermore, the spray coverage and deposition density, determined using water sensitive paper (WSP), were used to evaluate the spray application performance taking into account the spray volume applied. The VRS system can provide the most suitable spray volumes for insecticide and fungicide plant protection products. Based on a prescription map, the optimized VRS system can achieve accurate pesticide spraying as well as desirable spray coverage and deposition density.

Influence of Electron Beam Treatment on Structure and Phase Composition of TiB2–Ag Coating Deposited by Electrical Explosion Spraying

Due to many factors, the electrical explosion spraying process is not stable, which directly causes unstable coating quality and structure. Electron beam treatment may be used to improve the surface and modified structure of coatings sprayed by electrical explosions. In this study, a new TiB2–Ag metal matrix composite coating was deposited by electrical explosion spraying and modified by electron beam treatment. The prepared coatings were characterized by surface macro- and microanalysis, XDR, cross-section SEM, and TEM. The composition of the spray-coating phase differs from sample to sample. The electron beam treatment normalized the phase composition. Ag TiB2 B2O became the main phase in the modified coating. Increasing the pulse energy density and duration leads to a reduction in the low-melting Ag phase and the formation of copper contact phases due to heating and melting of the copper substrate by excess electron beam energy. The coating structure consists of a silver matrix and TiB2 inclusions. The electron beam treatment did not affect the structure; however, the microstructure of the coating transformed into a cellular crystallization structure. The silver matrix nanostructure was transformed into a nanocrystalline structure with an average crystal size ranging from tens to hundreds of nanometers.