Search Results (486)

A cold-sprayed Cr₂AlC coating was deposited on an H13 tool steel substrate, and the electrochemical corrosion behavior in 3.5 wt.% NaCl solution was experimentally investigated. Electrochemical tests, including open circuit potential and potentiodynamic polarization measurements, revealed that the Cr₂AlC coating significantly improved the corrosion resistance of H13 steel, exhibiting a more positive open circuit potential and a reduced corrosion current density compared with the bare H13 steel substrate. Post-corrosion surface morphology analysis by scanning electron microscopy showed extensive pitting corrosion on the substrate surface, while no obvious corrosion damage was observed on the coating surface. X-ray photoelectron spectroscopy (XPS) analysis further confirmed the formation of a passive film composed of chromium and aluminum oxides on the coating surface, indicating a protective passivation mechanism. The enhanced corrosion performance is attributed to a synergistic mechanism involving both a physical barrier provided by the coating and surface passivation induced by the Cr/Al-based oxide layer. This work highlights the potential of cold-sprayed Cr₂AlC coating as an effective corrosion protection solution for steel substrates in chloride-containing environments. Full article

The 2011 Fukushima accident highlighted the vulnerability of traditional Zr alloy fuel cladding under loss-of-coolant accident (LOCA) conditions, prompting the development of accident-tolerant fuel (ATF) systems. A promising near-term solution involves depositing protective coatings on existing Zr alloy cladding. Among various deposition techniques, cold spray technology has emerged as one of the leading methods due to its solid-state, low-temperature process, which minimises thermal degradation and allows for the deposition of a wide range of high-performance materials. This review provides a comprehensive examination of recent advances in cold-sprayed coatings for ATF cladding, beginning with an overview of the fundamentals of cold spray technology and its specific advantages for nuclear applications. The core of the review critically analyses three primary coating systems: Cr, FeCrAl alloys, and MAX phase composites, with a particular focus on Cr coatings, as they have been more extensively studied compared to the other two material systems. Key coating properties, including microstructure of the coating-substrate interface, mechanical properties, thermal conductivity, oxidation resistance, irradiation tolerance, and performance under normal operation and simulated LOCA conditions, are discussed in detail, with particular emphasis on the potential of cold-sprayed Cr coatings to enhance Zr alloy cladding. Cr coatings demonstrate significant improvements in oxidation resistance and irradiation stability, but also face challenges such as high-temperature interfacial reactions. To address these issues, promising solutions, such as diffusion-barrier bilayer systems, are being explored. Additionally, the review discusses FeCrAl and MAX phase composite coatings, highlighting their promising long-term performance under extreme conditions. The review concludes with recommendations for further research to optimise cold spray processes and ensure the robustness of coatings in operational reactor environments. Full article

Identifying the factors limiting cold resistance in augustinegrass is essential for expanding this shade-tolerant tropical turfgrass into temperate regions. We hypothesized that leaf potassium content is closely associated with its cold tolerance. To test this, we first analyzed the correlation between leaf potassium content and cold resistance across 30 germplasms, which confirmed a positive relationship and suggested that low potassium may limit cold tolerance. We then applied foliar potassium at 0, 15, 30, and 60 mM to increase leaf potassium content and evaluate its effect on cold resistance. The 15 mM treatment was most effective, increasing whole-plant fresh weight by 91.5% under cold stress compared to the control. To understand the underlying physiological mechanism, we measured the impact of foliar potassium on four key processes: photosynthesis (chlorophyll content, fluorescence, enzyme activity, stomatal aperture, gas exchange, and carbon assimilation products), osmotic adjustment (proline), membrane stability (relative conductivity and MDA), and ROS scavenging (SOD and CAT activity). Foliar potassium significantly enhanced photosynthetic performance; increased soluble sugars, starch, and proline; reduced MDA; and boosted both SOD and CAT activities. Pearson correlation analysis linked most physiological indicators to improved fresh weight. Critically, multiple linear regression identified leaf CAT activity as the primary factor, explaining 80% of the variation in cold resistance. qPCR analysis confirmed that CAT gene expression matched the increased enzyme activity. Field trials validated that a 15 mM potassium foliar spray effectively enhances cold tolerance. These findings demonstrate that leaf potassium is a major limiting factor for cold resistance in augustinegrass, and that foliar application of 15 mM potassium represents an effective management strategy, primarily by enhancing leaf CAT activity to improve ROS scavenging and overall stress tolerance. Full article

Postharvest fruit losses significantly impact producers and distributors. Although synthetic preservatives mitigate these losses, consumer safety concerns and regulatory restrictions drive interest in alternative approaches. Propolis, rich in polyphenols, exhibits antioxidant and antimicrobial activities, making it a promising natural strategy to preserve fruit quality. This study aimed to evaluate the effects of the pre- and postharvest applications of Portuguese propolis extracts on the preservation of postharvest quality of ‘Rocha’ pear, an exclusively Portuguese variety of major economic importance. Treatments were applied by spraying the fruits one month before and at harvest. After five months of cold storage, the main quality parameters, phenolic content, antioxidant capacity, physiological disorders, and microbial contamination were assessed. The results showed that the application of propolis extract, either 30 days before or immediately after harvest, reduces the total microbiological load on the fruit’s epidermis (~1-log to 2-log reduction, after treatment). Moreover, the treatment enhanced the preservation of key quality attributes, including a reduction in water loss of up to 44%, a 13–33% decrease in firmness loss relative to the control, and a lower incidence of physiological disorders during postharvest storage. Furthermore, the application of propolis can enhance the production of fruits with higher levels of bioactive compounds, while also adding value to a bee product that is often underappreciated by most beekeepers. Full article

The medical field now uses mRNA therapeutics to deliver fast programmable treatment options through versatile vaccination platforms. The worldwide adoption of mRNA therapeutics faces a major obstacle because these molecules require extreme cold storage and transportation systems. mRNA stability establishes a fundamental scientific and industrial challenge which requires researchers to unite formulation design with process control and material engineering for cold-chain independence. Current knowledge about RNA hydrolysis and lipid oxidation and water-mediated degradation is combined with new methods for solid-state stabilization through lyophilization and spray-freeze-drying and thin-film technologies. Mechanism such as vitrification, water replacement and excipient RNA interactions are assessed to establish the fundamental chemical properties needed for extended product stability. Advanced mRNA development strategies are also examined, including self-amplifying and circular RNA structures and nano-glass and metal–organic frameworks and artificial intelligence-based predictive design for creating stable mRNA formulations at room temperature. This review examines manufacturing and regulatory and logistical obstacles which affect real-world implementation of mRNA therapeutics through assessments of production scale and product quality tests and packaging strength and tropical environment testing. The combination of research findings presents a path to develop mRNA medicines which maintains their effectiveness when stored at 25 °C or above, thus enabling worldwide access to RNA-based treatments. The development of mRNA into a durable therapeutic platform requires scientists to merge molecular research with process development and regulatory standardization. Full article

The quality of the feedstock powder plays a key role in determining the properties of coatings produced by cold spray (CS). However, most commercially available powders are not specifically designed for CS, which makes it difficult to tailor powder characteristics for optimal performance. In this study, we examined the cold sprayability of five copper (Cu) powders manufactured using electrolysis, gas atomization, and mechanical grinding. The powders were characterized in terms of their microstructure, particle shape, and size distribution to evaluate how the production method influences powder properties. Powder flowability was measured using a shear cell test, while mechanical properties and deformability relevant to CS were assessed through nano-indentation. The results showed that gas-atomized powders with equiaxed grain structures offered the best combination of flowability and deformability, making them the most suitable for CS. Their spherical particle shape resulted in a lower surface area compared to the irregular electrolytic powder, which reduced inter-particle surface forces and allowed for smoother powder flow. Nano-indentation measurements indicated that the mechanically ground powder with ultra-fine grains and the gas-atomized powder containing fine dendrites had the highest nano-hardness values (HIT = 2.1 ± 0.15 GPa and 1.6 ± 0.1 GPa, respectively). In contrast, the porous electrolytic Cu powder showed the lowest hardness (HIT = 0.7 ± 0.2 GPa). These trends were confirmed by microstructural analysis of the deposited coatings. Coatings produced from the irregular electrolytic powder exhibited limited particle deformation, weak inter-particle bonding, and the highest porosity. Conversely, spherical gas-atomized powders produced much denser coatings. In particular, the powder with the most uniform spherical shape and no microsatellite particles resulted in the lowest coating porosity due to its superior deformation behavior upon impact. Full article

Artisanal colonial cheese (ACC) produced from raw milk is a rich reservoir of autochthonous lactic acid bacteria (LAB), but strain-level evidence supporting safe downstream application and technological stability remains limited. In this study, 10 LAB isolates from ACC were screened for phenotypic safety, antimicrobial susceptibility, and probiotic-related traits, and their viability was further assessed after inulin-based spray-drying microencapsulation under different storage temperatures. All isolates showed no hemolytic or mucinolytic activity and did not produce gelatinase, supporting an initial safety profile, and all strains were sensitive to at least two antimicrobial classes. Strain prioritization identified Lacticaseibacillus casei LAB06, LAB09, and LAB10 and Lactiplantibacillus plantarum LAB03 as the most robust candidates for downstream development because they maintained stable cell counts throughout simulated gastrointestinal digestion. Inulin spray-drying yielded structurally stable microcapsules and supported refrigerated storage, with substantially lower viability losses at 4 °C than at 25 °C; notably, L. plantarum LAB01 and LAB02 showed the best refrigerated shelf-life, remaining above 6.0 log CFU/g after 45 days. Together, these results position ACC as a source of promising LAB candidates and highlight cold-chain-compatible microencapsulation as a strategy to support safe functional food development with potential public health benefits. Full article

Pintle injectors offer variable thrust capability and combustion stability advantages for liquid rocket engines. This study presents experimental and numerical investigation of spray characteristics for a liquid–liquid pintle injector using water as simulant. Ten cold flow tests covering total momentum ratio (TMR) from 0.36 to 2.76 captured spray angle variations from 26° to 80°. Computational fluid dynamics (CFD) simulations using Ansys Fluent 2025 R1 with the Volume of Fluid method and dispersed interface modeling showed good agreement with experimental spray angles for TMR > 0.74 (error < 8%), but demonstrated increasing discrepancy at lower TMR values (up to 62% error at TMR = 0.36). This deviation indicates limitations of steady-state RANS models in capturing unsteady, fuel-dominated flow regimes. The experimental dataset provides validation benchmarks for CFD modeling and contributes to injector design optimization for sounding rocket applications. Full article

The AZ31 magnesium alloy is an attractive lightweight metallic material, but its low corrosion resistance and wear resistance significantly limit its widespread application in fields such as aerospace, the automotive industry, and mechanical engineering. Moreover, most coating systems currently cannot restore their original functions and dimensions after localized damage. Based on this, this study combined cold spray (CS), micro-arc oxidation (MAO), and magnetron sputtering (MS) to develop a high-performance and repairable composite modification strategy. First, a 5056 aluminum alloy coating was prepared on AZ31 via CS, followed by the growth of a hard alumina (Al₂O₃) coating via MAO and a diamond-like carbon (DLC) coating via MS on the 5056 aluminum alloy surface. The microstructure, phase composition, hardness, tribological properties, and electrochemical corrosion behavior of the coatings were evaluated using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD), Vickers hardness testing, ball-on-disk dry sliding wear testing, and potentiodynamic polarization testing in a 3.5% sodium chloride solution. The CS 5056 aluminum alloy coating reduced the corrosion current density of AZ31 from 4.098 × 10⁻⁵ A/cm² to 2.714 × 10⁻⁶ A/cm². The MAO alumina coating increased the hardness of AZ31 from 68.60 HV_0.05 to 1614.00 HV_0.05 and decreased the wear rate from 1.703 × 10⁶ μm³/(N·m) to 2.038 × 10³ μm³/(N·m). The DLC coating further reduced the average coefficient of friction of the alumina coating from 0.48 to 0.27, decreased the wear rate to 6.979 × 10² μm³/(N·m), and lowered the corrosion current density from 3.020 × 10⁻⁶ A/cm² to 8.860 × 10⁻⁹ A/cm². This indicates that the three-phase composite coating achieves synergistic improvements in the corrosion and wear resistance of AZ31 through complementary advantages. Additionally, the thick CS aluminum alloy underlayer provides potential repairability, enabling the restoration of function and dimensions after damage without compromising the magnesium substrate. Overall, the proposed 5056Al/Al₂O₃/DLC composite coating strategy offers a reliable protective approach for AZ31 components and is expected to further expand their application fields. Full article

This paper reviews the fracture mechanics parameters associated with the variability in the crack growth curves associated with forty-two different tests that range from additively manufactured (AM) steels to cold spray additively manufactured (CSAM) 316L steel. As a result of this review, it is found that, to a first approximation, the effects of different building processes and R-ratios on the relationship between ΔK and the crack growth rate (da/dN) can be captured by allowing for changes in the fatigue threshold and the apparent cyclic toughness in the Schwalbe crack driving force (Δκ). Whilst this observation, when taken in conjunction with similar findings for AM Ti-6Al-4V, Inconel 718, Inconel 625, and Boeing Space Intelligence and Weapon Systems (BSI&WS) laser powder bed (LPBF)-built Scalmalloy^®, as well as for a range of CSAM pure metals, go a long way in making a point; it is NOT a mathematical proof. It is merely empirical evidence. As a result, this review highlights that for AM and CSAM materials, it is advisable to plot the crack growth rate (da/dN) against both ΔK and Δκ. The observation that, for the AM and CSAM steels examined in this study, the da/dN versus Δκ curves are similar, when coupled with similar observation for a range of other AM materials, supports a prior study that suggested using fracture toughness measurements in conjunction with the flight load spectrum and the operational life requirement to guide the choice of the building process for AM Ti-6Al-4V parts. The observations outlined in this study, when taken together with related findings given in the open literature for AM Ti-6Al-4V, AM Inconel 718, AM Inconel 625, and BSI&WS LPFB-built Scalmalloy^®, as well as for a range of CSAM-built pure metals, have implications for the implementation and certification of limited-life AM parts. Full article

Today, PHB and its copolymers—potential plastic substitutes—are produced by fermenting sugar, which is not scalable to the volumes of plastic consumption. PHB from CH₄ can offer a sustainable process route, with CH₄ potentially produced from a variety of waste biomass streams through anaerobic digestion, gasification, and methanation. The high molar mass (M_w) of PHB is a key determinant of its mechanical properties, and strain, culture conditions and downstream processing influence it. In this work, the strain Methylocystis sp. GB 25 (DSMZ 7674) was grown on natural gas as the sole carbon and energy source and air (1:1) in a loop reactor with 350 L active fermentation volume, at 35 °C and ambient pressure. After two days of continuous growth, the bacteria were limited in P and N for 1, 2, and 2.5 days to determine the optimal conditions for PHB accumulation and the highest Mw as the target. The biomass was then centrifuged and spray-dried. For downstream processing, chloroform solvent extraction and selected enzymatic treatment were deployed, yielding ~40% PHB from the biomass. The PHB obtained by solvent extraction exhibited high average weight molar masses of M_w ~1.1–1.5 × 10⁶ g mol⁻¹. The highest M_w was obtained after one day of limitation, whereas enzyme treatment resulted in partially degraded PHB. Cold chloroform maceration, interesting due to energy savings, did not achieve sufficient extraction efficiency because it was unable to extract high-molar-mass PHB fractions. The extracted PHB has a high molar mass, more than double that of standard commercial PHB, and was characterized by DSC, which showed a high degree of crystallinity of up to 70% with a melting temperature of close to 180 °C. Mechanical tensile properties measurements, as well as dynamic mechanical thermal analysis (DMTA), were performed. Degradation of the PHB by enzymes was also determined. Methanotrophic PHB is a promising bioplastics material. The high M_w can limit and delay polymer degradation in practical processing steps, making the material more versatile and robust. Full article

The impact and solidification of multiple molten droplets on a cold substrate critically influence the quality and performance of thermally sprayed coatings. We present a Smoothed Particle Hydrodynamics (SPH) model that couples fluid-solid interaction, wetting, heat transfer and phase change to simulate multi-droplet impact and freezing. The model is validated against benchmark cases, including the Young–Laplace relation, wetting dynamics, single-droplet impact and the Stefan solidification problem, showing good agreement. Using the validated model, we investigate two droplets—either centrally or off-centrally—impacting on a cold surface. Simulations reveal two distinct solidification patterns: convex pattern (CVP), which results in a mountain-like splat morphology, and concave pattern (CCP), which leads to a valley-like shape. The criterion for the two patterns is explored with two dimensionless numbers, the Reynolds number $Re$ and the Stefan number $Ste$. When $Re\le 17.8$, droplets tend to solidify in CVP; at higher Reynolds numbers $Re\ge 18.8$, they tend to solidify in CCP. The transition between the two patterns is primarily governed by $Re$, with $Ste$ exerting a secondary influence. For example, when droplets have $Re=9.9$ and $Ste=5.9$, they tend to solidify in a convex pattern, whereas at $Re=19.8$ and $Ste=5.9$, they tend to solidify in a concave pattern. Also, the solidification state of the first droplet greatly influences the subsequent spreading and solidification of the second droplet. A parametric study on CCP cases with varying vertical and horizontal offsets shows that larger vertical offsets accelerate solidification and reduce the maximum spreading factor. For small vertical distances, the solidification time increases with horizontal offset by more than 29%; for large vertical distances the change is minor. These results clarify how droplet interactions govern coating morphology and thermal evolution during thermal spraying. Full article

Frost accumulation on heat exchangers severely limits the efficiency and reliability of air-source heat pumps (ASHPs) in cold, humid environments. Superhydrophobic coatings fabricated via electrostatic spraying offer a promising energy-free strategy for frost suppression. In this study, a robust superhydrophobic coating was deposited on the heat exchanger of a residential ASHP using this scalable technique. Under low-temperature heating conditions (2/1 °C), the coated exchanger delayed frost completion by a factor of 2.83 and shortened defrosting time by 33.3% compared to a conventional hydrophilic counterpart. These improvements translated to a 6.24% increase in average heating capacity and a 2.83% gain in the coefficient of performance (COP). Although the thicker superhydrophobic coating resulted in a marginal 3.1% reduction in cooling capacity during free-cooling operation, the significant enhancements in frost resistance and heating performance underscore its practical value. This work demonstrates that electrostatic spraying is a viable and effective method for fabricating high-performance superhydrophobic heat exchangers, paving the way for more efficient and frost-resistant ASHPs. Full article

This work investigates the penetration behavior of SiC particles into Digital Light Processing (DLP)-printed thermoset substrates under low-pressure cold-spray conditions, aiming to enhance surface hardness and wear resistance. A coupled simulation framework was established in which particle acceleration was obtained from CFD using ANSYS Fluent, and high-speed impact and embedding were modeled through ANSYS Explicit Dynamics. Two particle diameters (25 μm and 60 μm) were examined across inlet pressures from 2 to 5 bar to evaluate both the continuous influence of pressure and the two-level effect of particle size. Mesh convergence was achieved at a resolution of d_p/20, ensuring numerical stability and computational efficiency. The results showed a strong dependence of penetration depth on pressure and particle size: for 25 μm particles, penetration increased from 0.76 d_p at 2 bar to 1.53 d_p at 5 bar, while 60 μm particles exhibited deeper absolute embedding due to their significantly higher kinetic energy. Response-surface analysis further revealed nonlinear pressure effects and a predominantly linear size-dependent shift. Experimental validation at 3 bar confirmed a penetration depth of approximately 1 d_p, demonstrating good agreement between simulation and physical observation. Overall, the validated workflow provides quantitative insight into particle–substrate interaction in thermoset polymers and offers a practical basis for controlled particle embedding as a surface-strengthening strategy in additive manufacturing. Full article

Many special structures such as pipeline, revolving gears, and tanks suffer from biofouling used in marine environment, which could induce serious results in the ship system such as blockage and stuck, consequently lead to failure of the mechanical system and power system. Generally, coatings with antifouling agents are used for protecting metal structures from biofouling, but coatings are not conveniently applicable in the high velocity flowing seawater and narrow space. Electrochlorination and electrolysis of copper and aluminum anode are usually used in these circumstances, but the electric power will lead to stray current corrosion to the component. For the sake of convenience and safety, Cu-Ti pseudo alloy antifouling anode was proposed in this work for antifouling in pipeline and other narrow spaces without external electric power. Four Cu-Ti pseudo alloy antifouling anodes with different Ti contents (mass fraction) of 0 wt.%, 5 wt.%, 10 wt.%, and 15 wt.% were investigated with computational method, and a 15 wt.% Ti content Cu-Ti pseudo alloy antifouling anode was prepared by cold spray, and the microstructure and composition of the anode were observed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Electrochemical tests were conducted to obtain the corrosion potential, potentiodynamic polarization curve, and micro zone electrochemical information in natural seawater, and the Cu ions releasing behavior were analyzed using inductively coupled plasma (ICP). The results indicated that in natural seawater, copper particles, and titanium particles on the surface of anode samples can form micro galvanic couples. With the increase in Ti mass fraction, the number of micro primary cells composed of copper particles and titanium particles increases, and the corrosion rate of Cu particles increased. When the Ti mass fraction is 15%, the corrosion rate is the fastest, and the copper ion release rate increases by nearly ten times, reaching 147 μg/(cm²·d). This method can effectively accelerate the releasing rate of Cu ions in Cu-Ti pseudo alloy anode and promote the antifouling effect. Full article