Spray Conditions Research Articles

Formation of Coatings Containing Cr2AlC MAX Phase During Plasma Spraying of Mixture of Cr3C2+Al Powders

In this article, the structure formation and phase composition of coatings containing Cr2AlC MAX phase under the conditions of plasma spraying were studied. Mechanical mixtures of commercially available Cr3C2 and Al powders were used as a material for spraying. The amount of aluminium in the mixtures was 9 and 18 wt.%. As a result of studying physicochemical processes occurring during plasma spraying of mechanical mixtures of selected compositions, the formation of coatings containing Cr2AlC MAX phase was established, the synthesis of which occurs both at the stage of the particles flight of initial components in the plasma jet as a result of the collision and coagulation, and at the stage of a coating layer formation as a result of layering particles deformed during the collision–splats. It is shown that for the formation of a denser coating with a higher MAX phase content for spraying, it is rational to use a mixture of chromium carbide powders with 9 wt.% of aluminium. A coating with the composition 91Cr3C2-9Al (wt.%) has high corrosion resistance in operation conditions in a chloride-acetate solution, and by its indicators of corrosion resistance, is not inferior to the Cr3C2-NiCr coating, which is widely used in industry to protect parts from corrosion and wear. The obtained results show the possibility and feasibility of using mechanical mixtures of commercially available powders for the formation of coatings containing Cr2AlC MAX phase instead of expensive synthesized MAX-Cr2AlC powders.

Exploring formation path of Cr2AlC phase during plasma spraying Cr/Al/Cr3C2 agglomerates: Water quenching and droplet deposition

In recent years, plasma spraying for the preparation of high-content Cr2AlC coatings has been demonstrated to be feasible. However, the formation mechanism of Cr2AlC during the spraying process remains uncertain. This study intuitively investigated the intermediate phases present during the formation process of Cr2AlC by spraying Cr/Al/Cr3C2 agglomerates. Water-quenching experiments were employed to directly analyze the evolution of agglomerated powders throughout the spraying process. As the quenching distance increased from 200 to 350 mm, a notable growth of molten powders was observed. Additionally, XRD results of agglomerates collected at varying quenching distances revealed the presence of CrC, Al8Cr5 and (Cr, Al)2Cx during the spraying process. To closely emulate the actual spraying conditions, droplets were deposited at different spraying distances. The presence of CrC, Al8Cr5 and (Cr, Al)2Cx in the spray synthesis of Cr2AlC was further substantiated by the observation of the droplets. This study proposed an innovative approach to exploring the formation mechanism of Cr2AlC during the spraying process.

Sex differences in insulin induced hippocampus functional connectivity during visual food cue presentation.

Central insulin has been shown to regulate eating behavior and cognitive processes in a sex-specific manner. Besides memory, the hippocampus is pivotal in the control of appetite. However, how insulin interacts with the hippocampal food cue response and the role of sex hormones in this context remain unclear. Using fMRI, we evaluated task-based functional connectivity (FC) of the hippocampus during food cue presentation in 60 participants (age: 21-69; 30 women) after intranasal insulin or placebo administration, in a randomized within-subject design. In an exploratory analysis, we investigated whether hippocampal FC after intranasal insulin administration is related to estradiol and progesterone levels during the follicular and luteal phase of the menstrual cycle in 13 premenopausal women (age: 20-28). Intranasal insulin increased hippocampal FC with the prefrontal cortex compared to placebo, regardless of sex. This correlated with stronger reduction in subjective feeling of hunger and food craving. Moreover, we observed an interaction between sex and nasal spray condition with higher hippocampal FC to the calcarine gyrus after insulin compared to placebo in men, while women showed a lower response. In premenopausal women, the centrally mediated effect of insulin on hippocampus to calcarine gyrus FC negatively correlated with the estradiol/progesterone ratio in the luteal phase. Central insulin influences hippocampal FC to regions vital for inhibitory control during high-caloric food cue presentation, implying a potential role of the hippocampal network in modulating insulin's anorexic effects. The observed sex differences between the hippocampus and visual cortex might be influenced by sex hormone action.

Justification and implementation of the layer thickness control method in ultrasonic spraying

Relevance. The need for the development and widespread use of the ultrasonic spraying method, which has unique advantages, to solve the most pressing problems of modern industry. In particular: minimal, of all known methods, energy consumption for the implementation of the process, the possibility of forming fine droplets without the use of gas under pressure, regulating the dispersion of the formed aerosol by the parameters of the emitter, etc. However, for widespread practical use of the ultrasonic spraying method, it is necessary to ensure spraying conditions with a specified dispersion and productivity. In this regard, there is a need to develop a method for controlling and maintaining the necessary and sufficient thickness of the liquid layer on the surface of the piezoelectric transducer of the atomizer, the spraying of which will ensure, at a given spraying performance, the formation of an aerosol with the smallest deviation in the size of the formed droplets relative to the average value. It is proposed to control the thickness of the liquid layer by identifying the dependence of the resonant frequency of the piezoelectric transducer of the atomizer on the thickness of the liquid film on the oscillating surface of the atomizer. Aim. To develop a method and means for controlling the thickness of the layer of sprayed liquid by changing the resonant frequency of the ultrasonic oscillatory system and maintaining the optimal value of the layer thickness by changing the amplitude of vibrations of the surface of the ultrasonic sprayer. Objects. Liquid atomizing with ultrasonic high-amplitude vibrations. Methods. Obtaining the frequency characteristics of ultrasonic oscillatory systems, analyzing changes in the amplitude-frequency characteristics of oscillating systems and identifying criteria that allow monitoring and managing the ultrasonic spraying. Results. The authors have proposed and developed the method for indirectly monitoring the thickness of a sprayed liquid layer on the oscillating surface of an ultrasonic atomizer, based on measuring the resonant frequency of an ultrasonic oscillating system. The possibility of implementing the method and its practical application is caused by the fact that in the working range of layer thicknesses of the sprayed liquid, the change in the resonant frequency can reach 100 Hz, and with a frequency measurement accuracy of 1 Hz, the accuracy of determining the layer thickness will be no more than 2% of the working layer thickness. The identified dependencies and certain values of possible ranges of changes in the controlled parameter made it possible for the first time to develop a method for automatically controlling ultrasonic spraying, ensuring the maintenance of optimal modes of ultrasonic influence (amplitude of vibrations of the spray surface) and the thickness of the layer of sprayed liquid.

Experimental study of twin-fluid flow differences and Sauter mean diameter prediction according to Y-jet nozzle mixing-tube design

In this study, we experimentally investigate the effect of internal flow variation on the design characteristics of a Y-jet twin-fluid nozzle and its utilization for spray droplet size prediction. For this study, a laboratory-scale twin-fluid nozzle spray test system was constructed. Sauter mean diameter (SMD) measurements were made by a droplet measurement system using the laser diffraction principle, and spray images were obtained using a high-speed camera. The mass flow rate of the twin fluids under different spray conditions was expressed in terms of the gas-to-liquid mass flow rate ratio (GLR) and turn-down ratio. The GLR tended to decrease when the nozzle orifice diameter increased because the pressure of the supplied twin-fluid was the same. By contrast, increasing the nozzle mixing-tube length resulted in a negligible increase in GLR. This is because the nozzle design characteristics affect the internal pressure of the nozzle, which changes its spray characteristics. In general, the spray characteristics of Y-jet nozzles are most affected by GLR. However, in this study, a generalised GLR was devised to consider not only GLR but also the difference in the flow rate of the twin-fluid due to nozzle design factors. The generalised GLR has the advantage that it is constant under changes in twin-fluid pressure, unlike the GLR expressed by considering only the mass flow rate of the twin-fluid. Therefore, to estimate the SMD more accurately under different spray pressures for a constant GLR, we investigated the SMD estimation using the internal pressure ratio and generalised GLR.

Determination of Binding Constants and Gas Phase Stabilities of Artificial Carbohydrate Receptor Complexes Using Electrospray Mass Spectrometry.

In recent years, binding studies to determine complex stabilities and selectivities of artificial carbohydrate receptors with glycosides have been mainly performed using 1H NMR, isothermal titration calorimetry (ITC), and other spectroscopic titration techniques. Native electrospray ionization (ESI) mass spectrometry is used only to verify the complex stoichiometries, although determination of dissociation constants is also possible. Herein, the binding of a 1,3,5-substituted 2,4,6-triethylbenzene-based receptor (CHR) to four alkyl-β-d-glucosides with varying alkyl side chain lengths (methyl (MGP), hexyl (HGP), octyl (OGP), and dodecyl (DGP)-β-d-glucosides), which was analyzed by ESI Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) under optimized spray conditions in both ion modes, is reported. The complexes of the receptor with different sugars could be detected in 1:1 and 2:1 stoichiometries. Dissociation constants calculated for the 1:1 complexes showed a stability trend depending on the length of the alkyl side chain of the sugar: CHR:DGP > CHR:OGP > CHR:HGP > CHR:MGP. Gas phase stabilities determined by CID-MS confirm this relative trend in binding affinities. These findings substantiate the validity and applicability of ESI-MS as a method for investigating noncovalent complex stabilities and thus support research in the field of molecular recognition of carbohydrates by artificial receptors.

Formation of hydrophobic membranes by surface spray assisted NIPS: Effects of solvent/non-solvent and spraying conditions

Membrane distillation has long been a potential desalination technology. Recently, spray-assisted non-solvent induced phase inversion (SANIPS) was proposed as a facile and effective method to prepare microporous hydrophobic membranes for membrane distillation. However, the membrane formation process is not fully disclosed. In this paper, SANIPS is employed to fabricate hydrophobic PVDF membranes. The influencing factors on membrane structure and performance are investigated. Membrane structure is greatly affected by the choice of solvent and non-solvent spray. The interactions between different non-solvent sprays (water and ethanol) and solvents (TEP, NMP and DMF) and the effects of operating conditions on membrane formation are explored. Thermodynamic and kinetic analyses of the membrane formation process suggest that the membrane formation process is dominated by the kinetic factors with water being the spray while thermodynamic factors play the major role with ethanol being the spray. A hydrophobic membrane with water contact angle of 135.93 ± 4.38° and LEP of 2.5 ± 0.4 bar was successfully prepared by using ethanol as the non-solvent spray, which demonstrates a stable desalination performance (initial flux of 19.88 ± 1.39 kg·m−2·h−1 and salt rejection higher than 99.97 %) in vacuum membrane distillation. This study may provide pertinent insights into the rational control of membrane structure and performance of hydrophobic PVDF membranes.

Spray Drying of Inca Peanut Meal Protein Hydrolysate to Produce Protein Powder Drink Mix

The optimal conditions (maltodextrin concentration and inlet air temperature) for spray drying Inca peanut meal protein hydrolysate (IMPH) were determined. The maltodextrin concentration was varied at 5, 10 and 15 % by weight, and inlet air temperature was varied at 150, 160 and 170 °C. The IMPH was subjected to spray drying, where the feed solution was atomized into fine droplets and exposed to a hot air stream, leading to rapid drying and the formation of powder. The moisture, protein, yield, water activity and water solubility index (WSI) of IMPH powder were analyzed. The optimal condition for spray drying IMPH powder utilized 10 % maltodextrin and an inlet air temperature of 160 °C. Under these conditions, the moisture, protein, yield and WSI of IMPH powder were 2.93, 36.93, 38.95 and 99.59 %, respectively, while water activity was 0.41. IMPH powder particles were spherical and non-agglomerate. Inca peanut meal protein powder drink mix (IMPD) with cocoa flavor was the most acceptable. The IMPD with cocoa flavor could be promoted as a high protein and high dietary fiber product. It could be kept at 35 ± 2 °C for 12 weeks, whilst retaining good microbiological properties. HIGHLIGHTS The optimal conditions for spray drying Inca peanut meal protein hydrolysate (IMPH) were determined to be 10% maltodextrin and an inlet air temperature of 160 °C. This resulted in high yield, protein content, and water solubility, while keeping moisture and water activity low. IMPH powder had spherical, non-agglomerated particles, and cocoa-flavored Inca peanut protein powder drink mix (IMPD) was the most preferred in sensory evaluations. The IMPD with cocoa flavor was identified as a high-protein, high-dietary-fiber product, suitable for storage at 35 °C for up to 12 weeks while maintaining good microbiological quality. The study highlights the nutritional benefits of the cocoa-flavored IMPD, which includes essential amino acids, omega-3 fatty acids, and antioxidant properties. GRAPHICAL ABSTRACT

Field evaluation of symbiont-targeted control of Halyomorpha halys in hazelnut crop

Halyomorpha halys has emerged as one of the most damaging pests for hazelnut production. Due to the continuous reduction of available options for chemical control, alternative strategies are required. A promising and sustainable alternative is the use of symbiont-targeted control. Treatment of the egg surface with a biocomplex containing copper, zinc, and citric acid has been shown to effectively prevent the acquisition of the endosymbiont ‘Candidatus Pantoea carbekii’ by H. halys nymphs, resulting in high nymph mortality under laboratory conditions. The aim of this work was to assess the field efficacy of treatments targeting the H. halys symbiont in hazelnut orchards to optimize spray applications. Treatments with the anti-symbiont biocomplex were performed in an orchard infested with H. halys during 2022 and 2023. To assess product efficacy, H. halys egg masses were glued on cardboard tags and hung on different positions of plants canopy before the treatments. The wetting percentage of egg masses according to the position of the egg on the plant canopy was measured; eggs were then reared to evaluate nymphal mortality after hatching. Symbiont acquisition was measured by quantitative PCR. A preliminary test to set the spraying conditions revealed that a higher fan speed induced higher mortality of the newborns from treated egg masses, although it did not affect the wetting rate of cardboards. In addition, cardboard tags hung in the central part of the canopy and those closer to the sprayer showed the highest egg coverage, whereas those in the peripheral row were less covered. However, nymphal mortality was not correlated with the percentage of cardboard tags coverage, although it was correlated with symbiont acquisition. A significant reduction in the percentage of damaged hazelnuts was observed in the treated plot compared to an untreated control, confirming the efficacy of symbiont-targeted control in hazelnut orchards.

Surface preparation by femtosecond laser - An adhesion strength perspective for suspension plasma sprayed ceramic coatings

Surface preparation is very important for the adhesion of thermal sprayed coatings. In this work, the effect of surface preparation on the adhesion strength of suspension plasma sprayed (SPS) Al2O3 coatings is investigated. Aluminum (Al-2024) substrates were micromachined by femtosecond laser (FSL) and also mechanically blasted by conventional grit blasting for surface preparation prior to SPS coating. Surface morphology results showed laser-induced periodic surface structures (LIPSS) produced by FSL, whereas grit blasting produced random irregularities with peaks and undercuts. Surface chemistry analysis showed that the FSL-prepared substrates were functionalized by -OH and O, while the grit-blasted substrates were not functionalized. The prepared substrates were coated by the SPS process under two spray conditions, where one condition was selected to produce a dense coating and the other condition was selected to produce a porous coating. The dense coating showed poor adhesion regardless of surface preparation, while the porous coating showed good adhesion for both grit-blasted and FSL-treated substrates. The adhesion strength of the porous coating was evaluated using the ASTM C-633 pull test protocol. A significant improvement (4.5 factors higher) in adhesion strength was achieved for the FSL-prepared substrates compared to the grit-blasted substrates. The improved adhesion of the FSL-prepared substrates was assessed by surface chemistry and surface morphology analyses of the prepared substrates, as well as by further analysis of the failed samples after the adhesion test and splat analysis. Results from this research showed that FSL has potential as an effective surface preparation technique for SPS.

Optimization of glass spray tempering parameters based on response surface methodology and economic analysis

Glass curtain walls have gained significant popularity as building enclosure structures, owing to their exceptional performance. Consequently, it becomes imperative to reduce energy consumption during the glass tempering process to ensure sustainable development within the construction industry. In this study, an experimental design was conducted using the response surface methodology (RSM). The particle count and cooling energy consumption were selected as the response value, while the influencing factors included four process parameters, namely, the spray distance (H), mist load fraction (f), spray pressure (p), and final cooling temperature (Tz). The second order model fitting of the RSM was used to obtain the polynomial regression equation between each response and each factor. Under the optimized conditions of H = 200 mm, f = 1.03, p = 0.5 MPa, and Tz = 150 °C, the number of fractured glass particles was found to be 234, and the cooling energy consumption was 0.00048 kW·h. Further analysis indicated that under these spray conditions, the net present value was 523.90 k$, and the dynamic payback period was 1.1 years. Compared to traditional air-cooled tempering, spray tempering demonstrated superior economic performance.

Research on the synergy effect of water mist containing additives and flame-retardant system on the syngas explosion inhibition

This paper aimed to study on the synergy of flame-retardant system and mist containing different additives on syngas explosion. By changing the additive condition (its type and mass fraction) and spray condition, the inhibition regular and mechanism of synergy on explosion parameter were revealed. Result indicates that the inhibition effect of mist could be greatly improved after adding additive and the explosion parameter was also visibly reduced. Especially for the impact on the upper end of flame-retardant system. And the intensity order was CTAC>SDS>Tween-20 > Pure miss. As tsp = 400 ms and ω = 0.2 %, the mist containing TWEEN-20 and SDS could greatly reduce (dP/dt)max of upper end, resulting in the decrease extents of 27.6 % and 46.3 %, respectively. After adding CTAC additive, the mist could successfully prevent the propagation of flame. Meanwhile, (dP/dt)max of upper end was decreased by 87.22 % compared with the pure water mist. The inhibition effect was related to additive type and was obviously affected by its mass fraction. Within the range of 0.1 %≤ω ≤ 0.5 % mass fraction, the inhibition effects of three additives all presented a change regular of first reducing then tending to flatten out as the mass fraction increased. Differently, the mass fractions of Tween-20 and SDS additives reaching the optimal inhibition effect were 0.3 % and 0.4 %. But the optimal inhibition effect was 0.2 % for CTAC additive. The explosion parameter was gradually reduced as spray amount increased. And the complete inhibition of explosion could be achieved after adding additive. And the synergy was mainly attributed to the combination of physical and chemical effects and was affect by additive condition.

Research Progress on Numerical Simulation of the Deposition and Deformation Behavior of Cold Spray Particles

It is of significant theoretical and practical value to study the deposition process and deformation behavior of cold-sprayed particles to find the deposition mechanism of cold-sprayed coatings, further improve the coating performance, and expand its application scope. However, observing the deposition process and particle behavior through experiments is difficult due to the brief deposition duration of cold spray particles. Numerical simulation offers a means to slow the deposition process and predict the critical velocity, deformation behavior, bonding mechanism, and residual stress of cold-sprayed particles. This paper uses finite element analysis software, including ANSYS LS Dynamic-2022 R1 and ABAQUS-6.14, alongside various prevalent finite element methods for numerically simulating cold spray particle deposition. These methods involve the Lagrange, Euler, arbitrary Lagrange-Euler (ALE), and Smoothed Particle Hydrodynamics (SPH) to investigate the cold spray particle deposition process. The recent literature primarily summarizes the simulation outcomes achieved by applying these methodologies for simulating the deposition process and deformation characteristics of different particles under varying cold spraying conditions. In addition, the reliability of these simulation results is analyzed by comparing the consistency between the simulation results of single-particle and multi-particle and the actual experimental results. On this basis, these methods’ advantages, disadvantages, and applicability are comprehensively analyzed, and the future simulation research work of particle deposition process and deformation behavior of cold spraying prospects is discussed. Future research is expected to provide a more in-depth study of the micro-mechanisms, such as the evolution of the inter-particle and internal organization of the particles, near the actual situation.

Optimization of HVOF spraying parameters for enhanced Fe-based amorphous coatings: A taguchi approach

In this work, Fe57Cr15Mo8P10C7B3 amorphous coatings (ACs) were fabricated on 316L stainless steel (316L SS) substrate using high-velocity oxygen-fuel (HVOF) spraying technique. The Taguchi's method guided the design of L16 (43) orthogonal experiments to optimize the process parameters, including spraying distance, oxygen flow rate, and kerosene flow rate. Through statistical analyses, including signal-to-noise ratio analysis, analysis of variance (ANOVA), and response surface methodology (RSM), empirical relationships for evaluating the influence of these parameters on coating quality were established, with porosity as the primary metric. Our findings indicate a pronounced sensitivity of the porosity of the ACs to spraying conditions, in which oxygen flow rate has the most significant effect on the porosity of the ACs, while kerosene flow rate has the smallest impact. Meanwhile, it is predicted that a minimum coating porosity of 0.75 % can be achieved under the optimal deposition conditions of the spraying distance of 330 mm, the kerosene flow rate of 6.0 GPH, and an oxygen flow rate of 1900 SCF. Experimental validation confirmed these conditions, yielding coatings with superior coating quality and performance with a minimum coating porosity of 0.68 %, a microhardness of 826 ± 65 HV0.1, improved corrosion resistance in 3.5 wt% NaCl solution with a high self-corrosion potential of −0.37 V, a low self-corrosion current density of 1.08 × 10−6 A/cm2, and a low passivation current density of 1.16 × 10−5 A/cm2, and enhanced wear performance with a wear volume loss of only 4.00 × 10−5 mm3 N−1 m−1 and a friction coefficient of as low as 0.42 ± 0.022. The present study confirms the reliability of Taguchi's method in determining optimal HVOF processing parameters, evidenced by the consistency between theoretical predictions and experimental results.

Research on Film Formation Characteristics by Spraying on Unidiameter Vertical Interpenetrating Cylindrical Surfaces

Unidiameter Vertical Interpenetrating Cylindrical Surfaces (UVICS, also called T-pipe surfaces) are a type of typical complex surface that exists in facilities or equipment such as oil storage tanks and industrial pipelines. The shape and surface characteristics of a component undergoing spraying will have a significant impact on the spray flow field and the resulting coating film. In order to optimize the coating effects of complex surfaces, the Euler-Euler approach was utilized to model a spray film formation process that encompasses both a spray flow field model and a wall adhesion model. Subsequently, the influence of the geometric features, geometric dimensions, lateral air pressure of the spray gun, and spraying distance on the coating film characteristics of this kind of surface were systematically investigated. It is determined that the film thickness uniformity could be enhanced by decreasing the dimensions of the workpiece or increasing the lateral air pressure and spraying distance in an appropriate manner when spraying at the location with the most complex geometric features of UVICS. Furthermore, the optimal parameters under varying spraying conditions were identified. The experiments validated the accuracy of the numerical simulation results and demonstrated the feasibility of this simulation model. The study is of significant value in addressing the challenges associated with film formation during spraying on complex surfaces, developing a comprehensive theoretical framework for air spraying, and expanding the scope of applications for automatic spraying technology.

Process parameters for enhanced microstructure and composition of as-sprayed Yb2Si2O7 environmental barrier coatings via atmospheric plasma spray

Achieving high crystallinity levels, dense, crack-free microstructures with near-stoichiometric phase composition and controlled secondary phase formation are crucial for enhancing the performance of environmental barrier coatings (EBCs). To investigate the impact of APS process parameters on the as-sprayed crystallinity, microstructure, and phase composition of Yb2Si2O7 EBCs, various spraying conditions were explored by adjusting torch power, nozzle size, powder feedrate, stand-off distance, and adding a shroud attachment to the torch. The velocity of particles controlled the density of the EBCs by an interplay between deposition efficiency and splat flattening ratios. Increasing nozzle size from 5/16″ to 1/2″ reduced particle velocity by up to 40 %, resulting in improved deposition efficiencies, porosity levels and coating thickness. However, larger nozzles led to higher silicon evaporation and up to 8 wt% more stable Yb2SiO5 (I2/a) secondary phase was formed. Increasing the stand-off distance from 50 mm had minimal effect on microstructure, but metastable Yb2SiO5 (P21/c) was detected (up to 9 wt%) at longer stand-off distances of 100 and 150 mm. Raising the powder feedrate from 15 gr/min to 60 gr/min improved deposition efficiency (up to 9 %) and density (up to 15 %) of EBCs, yet resulted in higher silicon-depleted phase formation (up to 12 wt%). Adding a shroud to the torch nozzle exit led to severe silicon evaporation and formation of up to 42 wt% and 6 wt% of Yb2SiO5 (I2/a) and Yb2O3, respectively. Moreover, due to the shroud's funnelling effect on smaller particles as well as particle overheating, porous microstructures with up to 28 % porosity levels were formed. High levels of crystallinity (∼75–91 %) were achieved in the as-sprayed condition for all the coatings, indicating real-time crystallization during spraying in all the spraying conditions.

Experimental Investigation for Proton Exchange Membrane Fuel Cells in Marine Salt Spray Environment.

In the maritime setting, Proton Exchange Membrane Fuel Cells (PEMFCs) are subjected to salt spray, posing a risk of contaminating internal components and leading to irreversible degradation in the performance of the PEMFCs. Thus, it is crucial to assess the impact of sodium chloride contamination on PEMFC operation. To address challenges related to prolonged cycle times, high costs, and intricate sample preparation in sodium chloride contamination experiments for PEMFCs, this Article replicates the marine atmospheric conditions using a standard salt spray experimental chamber. The liquid nitrogen fracture method is employed for cost-effective and efficient preparation of experimental samples. The meteorological environment with varying salt content in the salt spray is achieved through precise control of sodium chloride concentration. The Article systematically presents the salt spray experimental method for the membrane electrode assembly (MEA) of PEMFCs. A dedicated salt spray experimental rig was constructed to validate this method for the MEA of PEMFCs. The results indicate that the salt spray experimental method for the MEA of PEMFCs can effectively explore internal component contamination and is well-suited for analyzing the physicochemical effects of NaCl on MEA components, along with their microscopic characterization under salt spray conditions.

An Experimental Study on the Flash Boiling Characteristics of Liquid Ammonia Spray in a Constant Volume Chamber under High Injection Pressure

The spray characteristics of liquid ammonia under various ambient pressures and temperatures were analyzed in a constant volume chamber to cover a wide range of superheat degrees. The injection pressure was set as 70 and 80 MPa with ambient pressure ranging from 0.2 to 4 MPa. The ambient temperature was 500 K. The results showed that the higher the injection pressure, the greater the kinetic energy obtained. The droplet fragmentation was enhanced, and the phenomenon of gradual separation of the gas–liquid region occurred with increasing injection pressure. Under flash boiling spray conditions, the spray developed faster than non-flash boiling and transition flash boiling spray under the same injection pressure. In addition, the flash boiling spray tip penetration of the gas and liquid increased more than that of cold spray, and the fluctuation of the late stage of the injection was relatively large. Therefore, the injection pressure has a greater effect on the spray tip penetration of flash boiling spray. Moreover, ambient pressure greatly influences the flare flash boiling spray. The spray resistance phenomenon was found during the spray development in the flare flash boiling condition. With the increase in ambient pressure, the spray tip penetration of flash boiling spray decreases due to the reduction in the pressure difference inside and outside the spray hole and the restriction of ambient gas. Meanwhile, owing to the low ambient pressure and ambient density, the liquid penetration in the initial phase of the flare flash boiling spray will be abnormally shorter than that of the non-flash boiling spray.

Controlling splat boundary network evolution towards the development of strong and ductile cold sprayed refractory metals: The role of powder characteristics

Feedstock powder characteristics such as composition (specific alloying elements and concentrations and impurity levels), microstructure, thickness/composition of surface oxide layers, and particle size distribution play a crucial role in determining the overall mechanical properties of cold sprayed deposits. Herein, we report on two deposits consolidated via cold spray processing from differently-sourced batches of nominally identical elemental refractory powders under identical spraying conditions, which exhibit bending strength and ductility values that differ by more than a factor of two – and with the weakest sample displaying negligible effective ductility. Through chemical, microstructural and micromechanical characterization of both the feedstock powders and cold sprayed deposits, we consider the possible influences of feedstock characteristics on the mechanical performance of cold spray consolidated deposits. It is shown that while differences in interstitial oxygen and hydrogen content may result in differences in the intrinsic yield characteristics of the feedstock material, both feedstocks maintain the ductile behavior required to induce good metallurgical bonding upon impact of optimally sized powder particles. We conclude that the deposits formed from the two feedstock powders are indistinguishable and exhibit high ductility when characterized locally within the relatively undeformed bulk of a single particle or splat. However, the two sprayed deposits show low ductility or brittle behavior when loaded in tension across intersplat boundary domains comprising material that has undergone extensive deformation. In addition, one feedstock incorporates a broader particle size distribution, with a long tail of larger-than-optimal particles. These larger particles are accelerated below the critical impact velocity, resulting in observed imperfect metallurgical bonding at splat interfaces and higher porosity at such intersplat boundaries. This result, combined with the overall differences in the morphology of the intersplat boundary network between the two deposits, explains the difference in macroscopic mechanical behavior. We conclude that accurate control of the powder feedstock particle size distribution is essential for optimizing the mechanical integrity of cold sprayed refractory elements and alloys.

Sustainable Coating Materials: Exploring the Influence of Adjuvants on Kaolinite Suspension with Insights from Five Local Mining Clays.

Herein, we presented a comprehensive case study on the kaolin suspension derived from mining powder, with a specific emphasis on its mineral constituents within the size range of 2-5 μm and its suitability in spray applications. We have systematically investigated the influence of adjuvants, existing in both organic molecules and polymers, on the sedimentation behavior of clay suspensions. The investigations included the analysis of turbidity, dispersion weight, pH, and surface charge as key parameters. Our findings revealed that the specific presence of PEG-PPG-PEG, PAA, and PSAMA had a notable effect on delaying the suspension of sedimentation by the actual sediment weight as well as enhancing the uniformity of clay coating by the reflection efficiency of coating materials in PPFD units. To enhance sustainability in coating materials, it was essential to elucidate the optimal amounts of adjuvants and the pH levels as they are closely related to the efficacy of tree-coated spraying and soil conditions.