This perspective paper summarizes the authors’ view on how process diagnostics and control can help to gain a deeper insight into thermal spray processes and to better understand the underlying ...mechanisms. The current situation in terms of available process control strategies and suitable sensors is described. In perspective, it is assumed that with suitable models, sensors and machine learning tools, it will be possible to perform a smaller number of experiments to develop coatings with specific target characteristics. In addition, trained machine learning tools can be used to implement an efficient control strategy to produce coatings with high reproducibility and reliability. The corresponding existing knowledge gaps are analyzed to identify needs for future research.
In this work, atmospheric plasma spraying (APS) and suspension plasma spraying (SPS) are employed for developing micro/nano morphologies of superhydrophobic coatings with high water repellence and ...mobility. Accordingly, multiple coatings were developed with different surface morphologies, then by isolating the effect of surface chemistry using a stearic acid treatment, the importance and influence of the achieved morphologies on wetting behavior of the coatings were investigated. Experimental results show that, although coatings developed by the APS process may reach water contact angles as high as 145°, the water mobility of these coatings is low due to relatively large morphological features resulting from the micron-sized feedstock powder. On the other hand, coatings developed by SPS show superior water repellence (manifested through water contact angles as high as 167°) as well as improved mobility (displayed through water sliding angles as small as 1.3°) due to dual-scale submicron/nano (hierarchical) roughness attributed to the submicron size particles in the feedstock. The dynamic behavior of an impinging water droplet is studied and compared to other existing natural and fabricated superhydrophobic surfaces.
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•AAPS and SPS coating techniques are employed to develop submicron-textured, hydrophobic and superhydrophobic TiO2 coatings.•APS coatings show contact angles as high as 145°, but lack the desired water mobility.•SPS coatings show superior water repellence (contact angle ~167°) and improved mobility (sliding angle as ~1.3°).•Morphology and structure of the coatings and their relationship with different wetting behavior of the coatings is studied.•Dynamic wetting of the coatings is shown to be comparable to existing natural and fabricated superhydrophobic surfaces.
This study investigated the performance of photocatalytic titanium dioxide microfiltration membranes with an average pore size of approximately 180 nm and ultrafiltration membranes with an average ...pore size of around 40 nm fabricated with the suspension plasma spray process. The membranes were evaluated for their filtration performance using SiO2 particles of different sizes and polyethylene oxide with molecular weights of 20 kDa to 1000 kDa, and the fouling parameters were characterized. The rejection rate was enhanced by increasing the thickness of the membranes. This effect was more pronounced with the ultrafiltration membranes. The rejection rate of the ultrafiltration membrane was improved significantly after filling the larger pores on the surface with agglomerates of titanium dioxide nanoparticles. The self-cleaning performance of the membranes was assessed under visible light. Both ultrafiltration and microfiltration membranes showed a flux recovery under visible light illumination due to the photocatalytic activity of titanium dioxide. The membranes also show a flux recovery of more than 90%.
Environmental pathogens move from ecological niches to mammalian hosts, requiring adaptation to dramatically different environments. Microbes that disseminate farther, including the fungal meningitis ...pathogen Cryptococcus neoformans, require additional adaptation to diverse tissues. We demonstrate that the formation of a small C. neoformans morphotype—called “seed” cells due to their colonizing ability—is critical for extrapulmonary organ entry. Seed cells exhibit changes in fungal cell size and surface expression that result in an enhanced macrophage update. Seed cell formation is triggered by environmental factors, including C. neoformans’ environmental niche, and pigeon guano with phosphate plays a central role. Seed cells show the enhanced expression of phosphate acquisition genes, and mutants unable to acquire phosphate fail to adopt the seed cell morphotype. Additionally, phosphate can be released by tissue damage, potentially establishing a feed-forward loop of seed cell formation and dissemination. Thus, C. neoformans’ size variation represent inducible morphotypes that change host interactions to facilitate microbe spread.
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•Cryptococcus neoformans exhibits an inducible morphotype within the lungs•This “seed cell” is critical for extrapulmonary organ invasion and dissemination•Alterations in pH and phosphate concentration support seed cell formation in the lungs
Environmental microbes that disseminate during infection must adjust to disparate environments. Denham et al. identify an inducible morphotype that facilitates organ entry by the pathogenic fungus Cryptococcus neoformans. Alterations in phosphate concentration induce this small morphotype, facilitating fungal exit from the lung and dissemination to other organs.
Coating build-up mechanisms and properties of cold-sprayed aluminum-alumina cermets were investigated using two spherical aluminum powders having average diameters of 36 and 81 mum. Those powders ...were blended with alumina at several concentrations. Coatings were produced using a commercial low-pressure cold spray system. Powders and coatings were characterized by electronic microscopy and microhardness measurements. In-flight particle velocities were monitored for all powders. The deposition efficiency was measured for all experimental conditions. Coating performance and properties were investigated by performing bond strength test, abrasion test, and corrosion tests, namely, salt spray and alternated immersion in saltwater tests. These coating properties were correlated to the alumina fraction either in the starting powder or in the coating.
Pathogenic fungi populate a wide range of environments and infect a diversity of host species. Despite this substantial biological flexibility, the impact of interactions between fungi and their ...hosts on the evolution of pathogenicity remains unclear. We studied how repeated interactions between the fungus Cryptococcus neoformans and relevant environmental and mammalian host cells—amoeba and mouse macrophages—shape the evolution of this model fungal pathogen. First, using a collection of clinical and environmental isolates of C. neoformans, we characterized a range of survival phenotypes for these strains when exposed to host cells of different species. We then performed serial passages of an environmentally isolated C. neoformans strain through either amoeba or macrophages for ∼75 generations to observe how these interactions select for improved replication within hosts. In one adapted population, we identified a single point mutation in the adenylyl cyclase gene, CAC1, that swept to fixation and confers a strong competitive advantage for growth inside macrophages. Strikingly, this growth advantage in macrophages is inversely correlated with disease severity during mouse infections, suggesting that adaptation to specific host niches can markedly reduce the pathogenicity of these fungi. These results raise intriguing questions about the influence of cyclic AMP (cAMP) signaling on pathogenicity and highlight the role of seemingly small adaptive changes in promoting fundamental shifts in the intracellular behavior and virulence of these important human pathogens.
•C. neoformans strains vary in their interactions with diverse host species•Serial passaging reveals that fungi adapt rapidly to distinct host-cell environments•A missense mutation in adenylyl cyclase confers increased growth in macrophages•Adaptation to macrophages comes with trade-offs for in vivo pathogenicity
Interactions between environmental microbes, like many fungi, and diverse hosts can fundamentally alter the biology and pathogenicity of these organisms. Using natural genetic variation and laboratory-based evolution, Hilbert et al. reveal the tempo, mode, and mechanisms by which adaptive evolution occurs in a clinically relevant fungal pathogen.
The main objective of this study was to use flash boiling atomization as a new method to inject suspensions with high solid content into the high-power plasma flow. The water-based suspension was ...prepared with submicron titanium oxide particles with an average size of 500 nm. The investigated solid concentrations were 20, 40, 55 and 70 wt%. Two plasma torches operated at 33, 70 and 110 kW were used to investigate the effect of increasing power on the deposited microstructure and deposition efficiency. At low torch power, the deposition efficiency decreased with increasing solid concentration, and deposits with a high number of unmelted particles were obtained with 70 wt% suspensions. At high torch power, the deposition efficiency increased with increasing solid concentration, and dense deposits were obtained with 70 wt% suspensions. XRD analysis was performed on all deposits to determine the distribution of rutile and anatase phases. The percentage of the anatase phase varied from 35.7% to 66.9%, depending on the power input and solid concentration.
The number of research papers as well as of patents and patent applications on cold spray and cold spray related technologies has grown exponentially in the current decade. This rapid growth of ...activity brought a tremendous amount of information on this technology in a short period of time. The main motivation for this review is to summarize the rapidly expanding common knowledge on cold spray to help researchers and engineers already or soon to be involved for their future endeavors with this new technology. Cold spray is one of the various names for describing an all-solid-state coating process that uses a high-speed gas jet to accelerate powder particles toward a substrate where they plastically deform and consolidate upon impact. Cold gas dynamic spray, cold spray, kinetic spray, supersonic particle deposition, dynamic metallization or kinetic metallization are all terminologies found in the literature that designate the above-defined coating process. This review on cold spray technology is divided into two parts. In this article, Part I, patents and patent applications related to this process are reviewed, starting from the first few mentions of the idea at the beginning of the 20th century to its practical discovery in Russia in the 1980s and its subsequent occidental development and commercialization. The patent review encompasses Russian and USA patents and patent applications. Part II will review the scientific literature giving a general perspective of the current understanding and capability of this process.
Surface coatings that operate effectively at elevated temperatures provide compatibility with critical service conditions as well as improved tribological performance of the components. High-entropy ...coatings (HECs), including metallic, ceramics, and composites, have gained attention all over the world and developed rapidly over the past 18 years, due to their excellent mechanical and tribological properties. High-entropy alloys (HEAs) are defined as alloys containing five or more principal elements in equal or close to equal atomic percentage. Owing to the high configurational entropy compared to conventional alloys, HEAs are usually composed of a simple solid solution phase, such as the BCC and FCC phases, instead of complex, brittle intermetallic phases. Several researchers have investigated the mechanical, oxidation, corrosion and wear properties of high-entropy oxides, carbides, borides, and silicates using various coating and testing techniques. More recently, the friction and wear characteristics of high-entropy coatings (HECs) have gained interest within various industrial sectors, mainly due to their favourable mechanical and tribological properties at high temperatures. In this review article, the authors identified the research studies and developments in high-entropy coatings (HECs) fabricated on various substrate materials using different synthesis methods. In addition, the current understanding of the HECs characteristics is critically reviewed, including the fabrication routes of targets/feedstock, synthesis methods utilized in various research studies, microstructural and tribological behaviour from room temperature to high temperatures.
The development of a durable and green icephobic coating plays a vital role in the aviation industry due to the adverse impact of ice formation on aircraft performance. The lack of study into how ...temperature and surface roughness impact icephobicity is the main problem with present icephobic coatings. This study aims to qualitatively evaluate the icephobicity performance of a polytetrafluoroethylene (PTFE) solid lubricant film, as an environmentally friendly solution, with a custom-built push-off test device in different icing conditions utilizing a wind tunnel. The ice-adhesion reduction factor (ARF) of the film has been assessed in comparison to a bare aluminium substrate (Al 6061). The impact of surface energy was investigated by comparing the water contact angle (WCA), the contact angle hysteresis (CAH), and the pull-off force of the PTFE solid lubricant and Al with an atomic force microscope (AFM). The results of ice shear adhesion on the PTFE solid lubricant film showed a significant reduction in the ice adhesion force at various substrate temperatures and surface roughness compared to the bare aluminium substrate. The difference in the ice adhesion between the solid lubricant and aluminium alloy was attributed to the differences in the detachment mechanism. For the PTFE-based solid lubricant, the interfacial detachment mechanism was based on the formation of interfacial blisters towards the centre of the ice. Consequently, upon continued application of the shear force, most of the energy injected would be distributed throughout the blisters, ultimately causing detachment. In the comparison of ice adhesion on PTFE solid lubricant and bare aluminium, the film showed minimal ice adhesion at −6 °C with an adhesion force of 40 N (ARF 3.41). For temperature ranges between −2 °C and −10 °C, the ice adhesion for bare aluminium was measured at roughly 150 N.
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