Search Results (218)

The tribocorrosion behavior of AZ31 and WE43 was investigated during sliding wear tests in Hank’s balanced salt solution (HBSS) and pure water. While wear volume increased monotonically with load in air and water, HBSS exhibited a distinct non-monotonic trend; the maximum material loss occurred at the minimum load (0.98 N) and decreased at 2.94 N before rising again. This indicates that at low loads, degradation is primarily driven by accelerated chemical dissolution (tribocorrosion) rather than by purely mechanical abrasion. The magnitude of wear followed the order [HBSS] > [air] > [water] in the low-load range (0.98–1.96 N), whereas it shifted to [air] > [HBSS] > [water] in the high-load range (2.94–5.88 N). A comparison of the wear rate of the alloys shows that the wear rate in HBSS differs from that in water, depending on the hardness of the substrate, similar to conditions in air. Notably, the specific wear rate decreased as test duration increased under low loads, further suggesting that corrosion-induced volume loss significantly outweighs mechanical wear in this regime. The static corrosion test revealed that volume loss during tribocorrosion was higher than that under static corrosion conditions. While the deposition of corrosion products affected net volume loss, chemical dissolution remained the primary driver of the observed wear trends at low loads. Electrochemical data from anodic polarization curves confirmed that the specimen tested under a 0.98 N load exhibited lower corrosion resistance. Mechanistically, it was suggested that Cl⁻ ions contributed to the overall increase in wear, while NaHCO₃ specifically contributed to the increase in wear in the low-load range. Full article

The present study demonstrates that the corrosion behavior of dental cobalt–chromium (Co–Cr) alloys is strongly influenced by the interaction between microstructure, manufacturing technique, and oral chemical environment. A comparative investigation was conducted on Co–Cr specimens fabricated using four technological routes: conventional casting, CAD/CAM machining, Selective Laser Melting (SLM), and Direct Metal Laser Sintering (DMLS). The study included microstructural characterization, evaluation of generalized corrosion behavior using the rotating electrode technique, assessment of localized crevice corrosion, and quantitative analysis of the release of twenty metallic cations. Extraction tests were performed for 168 h in two media simulating aggressive oral environments: 0.07 N HCl (acidic medium) and a fluoride-containing electrolyte (0.1% NaF + 0.1% KF). Electrochemical measurements were recorded in the current density range of 10⁻¹⁰ to 10⁻⁷ A/cm², while released cation concentrations were quantified at the µg/L level. All alloys exhibited very low corrosion current densities (icorr in the 10⁻⁸ to 10⁻⁹ A·cm⁻² range), confirming overall good corrosion resistance. Among all manufacturing routes, CAD/CAM specimens demonstrated the highest electrochemical performance, with a wide passivity domain extending up to approximately 740 mV/SCE. A statistical interaction analysis between extraction media and manufacturing techniques was performed using the non-parametric Mann–Whitney (MW) U test. Among the analyzed elements, only chromium showed a statistically significant difference between media (p < 0.05), with an approximately 25-fold-higher release in acidic conditions compared with the fluoride medium, confirming the predominant role of proton-induced destabilization of the protective Cr₂O₃ passive film. In contrast, fluoride-containing media induced selective release of elements such as Cu (3× higher), W (2.5× higher), and Mo (1.4× higher), associated with complexation phenomena. The manufacturing route significantly influences corrosion behavior. Although additive manufacturing technologies (SLM/DMLS) enable highly accurate and customized prosthetic designs, rapid solidification and microstructural heterogeneities may increase susceptibility to localized corrosion compared with more homogeneous CAD/CAM materials. Clinically, these findings suggest that future restorative strategies should incorporate corrosion-aware material selection within digital workflows. As digital dentistry evolves, predictive models integrating patient-specific oral conditions may assist clinicians in selecting the most appropriate material system for long-term performance. In conclusion, the long-term success of dental Co–Cr prosthetic devices depends not only on mechanical strength and precision of fit, but also on sustained electrochemical stability in the complex oral environment. Full article

The corrosion behavior of hot-press-formed (HPF) B-pillar components fabricated from Al–Si-coated boron steel was investigated with an emphasis on the forming-induced crack morphology. The specimens were extracted from the inner and outer surfaces of the top, flat, and radius regions. Microstructural characteristics and coating cracks were examined using optical microscopy, as well as field-emission scanning electron microscopy (FE-SEM) in combination with energy-dispersive spectroscopy (EDS), and corrosion behavior was evaluated using cyclic corrosion immersion and potentiodynamic polarization tests in a 3.5 wt.% NaCl aqueous solution. The Al–Si coating exhibited a multilayered structure composed of alternating Al- and Fe-rich layers. The crack morphology strongly depended on the local stress state: wide macrocracks were mainly formed on the outer surface of the radius region under tensile deformation, whereas the narrow microcracks predominated on the inner surface subjected to compressive deformation. Cyclic corrosion immersion tests showed that the corrosion propagated preferentially along the coating cracks and was more severe on the inner surfaces, where narrow microcracks promoted aggressive crevice corrosion owing to chloride ion accumulation and local acidification. By contrast, wider macrocracks on the outer surface mitigated crevice corrosion by allowing electrolyte exchange. Potentiodynamic polarization tests indicated similar corrosion rates for all regions; however, the outer radius region exhibited a relatively noble corrosion potential owing to oxide film formation on the locally exposed substrate areas. These results demonstrate that the crack morphology induced by curved forming is a key factor governing the corrosion behavior of HPF B-pillar components. Full article

Metal Injection Molding (MIM) enables complex orthodontic-bracket geometries but can introduce surface and geometric discontinuities that act as initiation sites for crevice and pitting corrosion. The effect of acidic, kombucha-like exposure on corrosion and repassivation was assessed for MIM-316L brackets relative to a commercial comparator, and the coupling between surface quality (roughness and wettability) and localized damage at scanning electron microscopy (SEM)-identified hot-spots was examined. Kombucha was characterized by pH and titratable acidity. Surfaces were characterized by SEM, areal roughness metrics (R_a, S_a, S_z, and A2), and wettability by sessile-drop goniometry. Electrochemical behavior in artificial saliva was measured using open-circuit potential and cyclic potentiodynamic polarization (ASTM F2129/G59), and a qualitative magnetic check was included as a pragmatic quality-assurance screen. Exposure in kombucha reduced breakdown and repassivation potentials and increased passive current density, with the strongest effects co-localizing geometric discontinuities. Commercial brackets exhibited markedly poorer surface quality (notably higher S_z), amplifying acidity-driven susceptibility. These findings indicate that, under acidic challenges, surface/geometry quality dominates corrosion behavior; non-magnetic-phase compliance and simple chairside screening (e.g., magnet test), alongside tighter manufacturing controls on roughness and edge finish, should be incorporated into clinical and industrial quality assurance (QA). Full article

Welding repair of cracks in FSX-414 cobalt-based alloy, used in high-temperature components, poses significant challenges due to the presence of surface oxide films within the cracks. By comparing the formation of oxide films on the external surface and inside the narrow crevice of FSX-414 alloys preserved at 900 °C for up to 1000 h, we found that the oxide film growth rate on the external surface was slightly larger than that inside the narrow crevice, and the latter slowed down after 672 h. Additionally, the oxide films on both surfaces were mainly composed of O and Cr elements, providing excellent protection to the underlying metal and resulting in minimal internal oxidation. A compositional transition region formed between the oxide film and the base metal. The width of the transition region decreased with heating duration and was narrower in the external surface sample, leading to a steeper composition gradient between the oxide film and the inner metal. With prolonged exposure, increasing numbers of “pores” rich in W and O appeared near the oxide films, creating channels that connect the oxide layer with the internal metal and accelerate material degradation. “Pores” extended deeper into the metal within the narrow crevice compared to those on the surface. Prior to welding repair, channels composed of W and O near the oxide films must be cleaned along with the oxide layer itself, and the removal of oxide from narrow cracks poses greater difficulty. Full article

The enamel of teeth affected by Molar–Incisor Hypomineralization (MIH) has been reported to have a higher protein content. Though a glass hybrid is recommended for restoring teeth with MIH in children, there is a lack of in vitro research on the influence of deproteinization on its marginal integrity. Therefore, this study aimed to evaluate whether enamel pretreatment with 5.25% NaOCl reduces the size of the marginal crevice of such restorations. Out of eight extracted teeth with severe MIH, restored using a glass hybrid (Equia Forte HT/GC), half underwent deproteinization. A stereoscopic and a scanning electron microscope (SEM) were used for sections analysis. The median value of the marginal crevice measured using stereoscopic microscopy (n = 17) was significantly lower for the deproteinized (6.78 μm) than for the standard-prepared specimens (12.61 μm), p = 0.008. On SEM images, the median marginal crevice (n = 10) was 69.40 μm versus 156.77 μm for the deproteinized and standard groups, respectively. The differences, however, were not statistically significant. This study only partially confirmed the hypothesis that pretreatment with NaOCl reduces marginal crevices between the Equia Forte HT material and hypomineralized hard tissues. Further studies on the effect of deproteinization on the marginal adaptation of glass hybrid materials are needed. Full article

High concentrations of hydrogen isotopes have been observed at the ends of CANDU Zr-2.5Nb pressure tubes in the region associated with the rolled joints with 403 stainless steel end fittings. These concentrations are above current regulatory limits, causing concerns over how long pressure tubes should remain in service. This paper reviews two differing interpretations of the mechanisms for these high concentrations, leading to two conclusions. Ingress after about 30 y is attributed to pressure tube sag creating a crevice between the end fitting and the top of the tube that provides a window for hydrogen isotopes to enter from the annulus gas under reducing conditions. Small additions of oxygen should close this window. A new mechanism is suggested to explain deuteride precipitates past the rolled joint contact region after about 30 y. Surprisingly, the mechanism relies on deuterium and protium diffusing in solution at the same rate, i.e., no mass-dependent isotope effect. Full article

Owing to its corrosion resistance, stainless steel is a sustainable alternative to carbon steel as a structural material in challenging seawater environments. Studies on carbon steel indicate that among all marine corrosion zones (i.e., atmospheric zone, splash zone, tidal zone, and immersed zone), the rate of corrosion is particularly high in the splash zone, above the seawater level, due to the recurrent splashing of seawater with high levels of oxygen and chloride content. Nevertheless, the information on the extent of localized corrosion (i.e., pitting and crevice corrosion) on stainless steel in the splash and tidal zones is scarce and, in most cases, limited to standard austenitic grades. In this work, we present the pitting and crevice corrosion results on lean duplex, duplex, and super duplex stainless steels after two years of field exposure in the North Sea (site at Heligoland South Harbour). The standard austenitic grade 1.4404 (316L) was also exposed as a reference material in atmosphere and splash zone conditions. Parallel exposure of coupons in splash, tidal, and immersed zones allows comparison of the extent of corrosion in each zone and enables proper material selection for structural applications in marine environments. Full article

The migration of the long-lived isotope technetium-99 (half-life 2.1 × 10⁵ years) presents a significant challenge for the deep geological disposal of radioactive waste. This study investigates the immobilization of technetium by carbon steel corrosion products under aerobic and anaerobic conditions simulating the Yeniseysky site (Krasnoyarsk Region, Russia), a proposed location for a Deep Geological Repository (DGR). Over time, the degradation of barrier materials is expected to allow low-salinity solutions to be brought into contact St3 steel, the intended container material for vitrified radioactive waste in the Russian context, leading to crevice corrosion. The findings demonstrate that carbon steel containers act not merely as a physical barrier but also as a chemical barrier by facilitating the reductive immobilization of technetium. The most effective reduction of technetium was observed in the presence of ferrihydrite as a corrosion product under both aerobic and anaerobic conditions, as indicated by distribution coefficient (K_d) values ranging from 1.4 × 10³ to 1.6 × 10³ cm³/g. However, the presence of bentonite clay can diminish the efficiency of this process by adsorbing corrosion products, resulting in a 50% reduction in the distribution coefficients. In contrast, leaching products from aluminophosphate glass and cement had a less pronounced effect on technetium immobilization, causing a decrease in distribution coefficients of no more than 30%. The results of this research can be applied to model the long-term behavior of technetium in the evolving environment of a geological radioactive waste repository. Full article

Stingless bees, particularly Tetragonula pagdeni, are vital for both ecosystems and the economy due to their pollination services and nest products. However, little is known about their nesting habits. This study investigated the nesting ecology of Tetragonula pagdeni in West Bengal, India. The species was found inhabiting a variety of landscapes, including agricultural, forest, rural, semi-urban, and urban areas, with a greater abundance in rural areas featuring mixed vegetation. Colonies, which were eusocial, perennial, and cavity-nesting, occupied diverse substrates, including tree trunks, building walls, rock crevices, electric poles, and field ridges—tree trunks and walls being the most common. Wild nests were located at heights ranging from 0 to 13.46 m, mostly around 2 m. Nest entrances varied in shape (circular, oval, slit-like, or irregular), with a longest opening axis of 10.50 ± 2.94 mm, and were oriented in multiple directions. Internally, nests measured 198.31 ± 86.36 mm in length and 142.73 ± 17.28 mm in width. Nests featured brood zones surrounded by honey and pollen pots, along with structure-supporting elements like the involucra and pillars. Brood cells were light brown and oval; those for workers and drones were similar, while queen cells were larger. Honey pots were light to dark brown, oval, dome-shaped, or irregular. Each involucrum was a thin, flat sheet, and the pillar was short, narrow, thread-like. These findings offer valuable insights into the distribution, nesting behaviour, and nest architecture of Tetragonula pagdeni, supporting its conservation and sustainable management. Full article

Centrostephanus longispinus (Philippi, 1845) is a sea urchin widely distributed across the tropical and temperate Atlantic Ocean (including the Caribbean) and Mediterranean Sea. Although it is present along the Alboran Sea coastline (Western Mediterranean), it is generally considered rare and is listed under conservation and protection lists and conventions due to fragmented populations threatened by seabed degradation. This study provides the first density and size distribution data for this echinoid in the circalittoral and bathyal bottoms of the Alboran Sea, aiming to relate its presence to seabed features, environmental variables, and human pressures. A series of 131 (62 ROV and 69 TASIFE transects) underwater image transects were collected during CIRCAESAL expeditions (2021, 2023, 2024) using a ROV and a photogrammetric sledge from infralittoral to bathyal bottoms (17–856 m depth). Images were processed with OFOP software to quantify and classify individuals by size classes, depth, substrate, seafloor roughness, micro-habitat, and coverage of key benthic structuring species. A total of 524 individuals of C. longispinus were detected in 13 transects, with the highest densities recorded at 48–100 m depths in rough, rocky substrates with crevices and a moderate to low coverage of key benthic structuring species. Differences in habitat use were also observed across depth strata: individuals in shallower zones tend to remain hidden within crevices and structurally complex substrates, displaying a more cryptic behaviour, whereas those in deeper strata rely less on refuge and occupy less complex habitats. The largest aggregations occurred near the Guadiaro Canyon, outside the “Estrecho Oriental” Special Area of Conservation (SAC), suggesting this area may serve as a population reservoir deserving conservation. Despite these findings, ecological knowledge of C. longispinus remains limited, and future studies should improve the knowledge gaps, particularly in the eastern and southern Alboran Sea. Full article

Selenium-enriched Dendrobium huoshanense C. Z. Tang et S. J. Cheng is a precious medicinal herb that combines traditional therapeutic value with modern nutritional benefits. However, its wild populations primarily inhabit special habitats like cliffs and rock crevices, resulting in limited yield and low selenium content. This study optimized an in vitro selenium-enriched cultivation system for D. huoshanense, investigating the regulatory mechanisms of selenium on physiological metabolism by modulating exogenous selenium concentrations, and determining the spatiotemporal distribution and speciation of selenium in plantlets. The results showed the optimal medium composition was as follows: MS + IBA (0.1 mg/L) + NAA (0.6 mg/L) + 7% agar + 30% sucrose + 100 g/L banana homogenate + 3 mg/L sodium selenite (pH 5.8). Under these conditions, roots served as the primary selenium accumulation sites at 30 and 60 days of cultivation. After 90 days, selenium redistribution occurred from storage organs (roots) to metabolically active organs (leaves). Organic selenium constituted 83.70% of total selenium, comprising 44.90% selenoproteins, 29.20% selenopolysaccharides, and 9.60% other organic forms. The contents of selenomethionine (SeMet), methylselenocysteine (MeSeCys), and selenocysteine (SeCys₂) were 0.63 ± 0.04, 0.20 ± 0.11, and 0.28 ± 0.06 mg/kg, respectively. Using plant tissue culture technology, we successfully cultivated selenium-enriched D. huoshanense, and investigated its growth metabolism, selenium translocation mechanisms, and selenium speciation. These findings provide theoretical foundations for developing selenium-enriched medicinal materials and have significant implications for enhancing the medicinal value of D. huoshanense. Full article

Columnar-structured thermal barrier coatings deposited via the suspension plasma spray process have attracted significant attention due to their long thermal cycling life and high cost-effectiveness. In this work, the effects of suspension properties, including solvent type, viscosity, and particle size, on the formation of different coating microstructures were investigated via a comparative study. Two different kinds of solvents (water and ethanol) and particles of different sizes (D50 = 0.45 μm and 1.2 μm) were used to prepare suspensions for coating deposition, respectively. When using suspensions containing small-sized particles as feedstock, coatings deposited from the ethanol-based suspension showed columnar microstructures with inter-column crevices, while the water-based suspension resulted in cracked–columnar microstructures, showing a mixture of columns and cracks. When the large-sized particles were used to prepare the suspension, both the ethanol-based suspension and the water-based suspension resulted in homogeneous coating microstructures. The formation mechanism of different microstructures was investigated by modelling the diverted plasma jet and the in-flight particle movement during the impingement period. Particles smaller than 2 μm were strongly affected by the diverted plasma gas, showing obvious oblique impinging trajectories, while particles larger than 3 μm kept their original trajectories and impinged on the substrate orthogonally. The formation mechanism of different microstructures was elaborated by analyzing the impinging trajectories of particles transitioning from different suspensions. Full article

Grade 304L stainless steel canisters are susceptible to crevice corrosion in marine environments. In the present study, white emery was utilized to create a simulation of dust accumulation. The corrosion testing was conducted at two distinct temperatures (35 °C and 45 °C) and three levels of relative humidity (45%, 55%, and 70% relative humidity). The chloride deposition density levels tested were 0.1 g/m² and 1 g/m². The test durations were 8000 h and 23,000 h. It is evident that with a chloride deposition density of 0.1 g/m² at a temperature of 45 °C and a relative humidity of 70%, the onset of stress corrosion cracking (SCC) occurred after 8000 h in the white emery deposition tests. In contrast, at a 1 g/m² chloride deposition density, the polytetrafluoroethylene (PTFE) crevice former test specimen exhibited continuous transgranular SCC within the same period. These quantitative findings emphasize the critical roles of salt load and environmental severity in the initiation of SCC. Full article

In order to reveal the adaptation strategies of karst forest plants to “high-calcium (Ca)–low-phosphorus (P) heterogeneous” habitats, the dominant shrubs and herbs in the Maolan karst area were taken as the research objects. The carbon (C), nitrogen (N), P, potassium (K), Ca, and magnesium (Mg) contents of plant components and their stoichiometric ratios in different microhabitats were systematically measured, and the environmental driving factors were analyzed by redundancy analysis (RDA) and variance partitioning analysis (VPA). The results showed that there were no significant differences in the plant nutrient contents and stoichiometric ratios in different microhabitats, but there were significant differences with respect to the components. The contents of N, P, K, and Mg in shrub leaves were significantly higher than those in branches and roots, while the contents of C/N, C/P, and C/K in branches and roots were significantly higher than those in leaves. The K content of herb leaves was significantly higher than that of roots. This reflects the functional differentiation of plant components and the different trade-off strategies for resource acquisition and storage. The stoichiometric characteristics of shrub leaves are dominated by species characteristics, while herb leaves are controlled by leaf tissue density (LTD), and soil-exchangeable Ca has a significant regulatory effect on the roots of both plant forms. Shrubs directly obtain bedrock slow-release nutrients through deep roots penetrating rock crevices and combine high C/N and C/P to improve nutrient utilization efficiency, forming a “mechanical resistance priority–metabolic cost optimization” adaptation strategy. Herbs respond to environmental fluctuations through functional trait plasticity and achieve rapid growth with high specific leaf area (SLA) and low LTD. Full article