Search Results (89)

Critical-size bone defects do not heal spontaneously and require external support, making bone regeneration a central challenge in tissue engineering. Polymeric/ceramic composite scaffolds offer a promising approach to mimic the structural and biological properties of bone. In this study, we aimed to evaluate the effect of different doping oxides in bioactive glass (BG) on the performance of polycaprolactone (PCL)-based composite scaffolds for bone tissue engineering applications. Composite scaffolds were fabricated using solvent casting, hot pressing, and salt-leaching techniques, combining PCL with 25 wt% of BG or doped BG containing 4 mol% of tantalum, zinc, magnesium, or niobium oxides, and 1 mol% of copper oxide. The scaffolds were characterized in terms of morphology, mechanical properties, and in vitro biological performance. All scaffolds exhibited a highly porous, interconnected structure. Mechanical compression tests indicated that elastic modulus increased with ceramic content, while doping had no measurable effect. Cytotoxicity assays confirmed biocompatibility across all scaffolds. Among the tested materials, the Zn-doped BG/PCL scaffold uniquely supported cell adhesion and proliferation and significantly enhanced alkaline phosphatase (ALP) activity—an early marker of osteogenic differentiation—alongside the Nb-doped scaffold. These results highlight the Zn-doped BG/PCL composite as a promising candidate for bone regeneration applications. Full article

To address the technical challenge of high polymer gel viscosity reducers losing viscosity at elevated temperatures and difficulty in controlling fluid loss, a polymer-based nano calcium carbonate composite high-temperature tackifier named GW-VIS was prepared using acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), N-vinylpyrrolidone (NVP), and nano calcium carbonate as raw materials through water suspension polymerization. This polymer gel can absorb water well at room temperature and has a small solubility. After a long period of high-temperature treatment, most of it can dissolve in water, increasing the viscosity of the suspension. The structure of the samples was characterized by infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy, and their performance was evaluated. Rheological tests indicated that the 0.5% water suspension had a consistency coefficient (k = 761) significantly higher than the requirement for clay-free drilling fluids (k > 200). In thermal resistance experiments, the material maintained stable viscosity at 180 °C (reduction rate of 0%), and only decreased by 14.8% at 200 °C. Salt tolerance tests found that the viscosity reduction after hot rolling at 200 °C was only 17.31% when the NaCl concentration reached saturation. Field trials in three wells in the Liaohe oilfield verified that the clay-free drilling fluid supported formation operations successfully. The study shows that the polymer gel has the potential to maintain rheological stability at high temperatures by forming a network structure through polymer chain adsorption and entanglement, with a maximum temperature resistance of up to 200 °C, providing an efficient drilling fluid for deep oil and gas well development. It is feasible to select nano calcium carbonate to participate in the research of high-temperature resistant polymer materials. Meanwhile, the combined effect of monomers with large steric hindrance and inorganic materials can enhance the product’s temperature resistance and resistance to NaCl pollution. Full article

With the continuous progress of global renewable energy, the reliability of the performance of heat storage materials is becoming increasingly important. In this study, graphene oxide (GO) was used as an additive to investigate its influence on the heat storage performance of quaternary nitrate molten salt. Quaternary nitrate molten salts doped in different proportions of 0.5, 1.0, 1.5, and 2.0 wt.% were prepared by the high-temperature hot melting method, and their properties were characterized in detail. The results show that the optimal concentration value of graphene oxide nanosheets is 1.0 wt.%, at which point the thermal parameters such as the specific heat capacity and thermal conductivity of the molten salt are optimal. Meanwhile, differential scanning calorimetry and thermogravimetric analysis tests verified the enhanced effect of the thermal performance. Furthermore, transmission electron microscopy and scanning electron microscopy analyses indicated that the insertion and encapsulation of nanosheets in the channel structure between nitrate crystals were effective. The modification methods used in this paper can enhance the thermophysical properties of nitrates. Meanwhile, the methods proposed in this paper can provide new ideas for the practice of heat-requiring systems. Full article

The present study was focused on assessing the molten salt-induced hot corrosion resistance of selective laser melting (SLM) manufactured Inconel 625 at 900 °C for 96 h and investigating the possibility of improving the superalloy’s corrosion resistance by applying a pre-oxidation heat treatment. The material’s hot corrosion properties were assessed in a heat-treated state (heat treatments performed at 1000 °C/1 h and 1150 °C/1 h, respectively) with and without pre-oxidation. The heat treatment at 1000 °C promoted the columnar dendrite morphology evolution, while the heat treatment at 1150 °C promoted the equiaxed dendrite morphology evolution. At 1150 °C, microstructural features specific to conventional manufactured material developed (annealing twin boundaries). They are considered a sign of anisotropy reduction due to equiaxed grains forming and it is believed that the internal stress in the material is reduced. High-temperature pre-oxidation heat treatment at 900 °C for 96 h ensured the formation of protective oxide scales with a reduced thickness (1.74 μm in the case of samples’ heat-treated at 1000 °C, and 2.22 μm in the case of samples’ heat-treated at 1150 °C, respectively). Experimentally, based on weight gain and oxide scale analysis, it was proven that pre-oxidation can improve the hot corrosion resistance of SLM manufactured Inconel 625 by forming a stable and protective oxide scale on the surface of the alloy before exposure to molten salts. The preformed oxide layer acts as a barrier for the corrosive species, reducing the formation of detrimental compounds, especially Mo-rich sulfides. Based on the tests, an improvement in corrosion resistance of up to 33.94% was observed in samples heat-treated at 1150 °C with pre-oxidation compared to samples heat-treated at 1000 °C without pre-oxidation. Full article

This study evaluates the effects of three mechanical pre-treatment methods on S235JRG2 steel sheets: blasting with a synthetic corundum (F40), blasting with steel shot (S170), and grinding with synthetic corundum (P40). Untreated samples served as a reference. The analysis of mechanical pre-treatments focused on surface integrity, including measurements of surface roughness parameters Ra and Rz (ISO 21920-2) and subsurface microhardness (ISO 6507-1). Zinc coatings were assessed through mechanical testing (cupping test, ISO 1520) and corrosion testing in a neutral salt spray environment (ISO 9227), with results evaluated using digital image analysis. Experimental findings indicate that electroplated zinc deposition rates are influenced by surface roughness, while subsurface microhardness has no significant effect. In contrast, for hot-dip galvanizing, both parameters impact the process. The mechanical properties of electroplated zinc coatings are further affected by steel surface integrity, whereas hot-dip zinc coatings are primarily governed by intermetallic phase formation, making the influence of steel surface integrity statistically negligible. Corrosion testing revealed that blasting with a synthetic corundum is particularly unsuitable, as it leads to numerous inhomogeneities in both coating types, accelerating corrosion degradation. Full article

The use of composite coatings containing solid lubricants is widely reported in the literature, in particular thermally sprayed coatings containing silver. However, these coatings are often limited in their maximum operating temperature due to the melting point of silver and due to reactions between the components at temperatures above 500 °C. In this study, a novel coating is proposed, which consists of an MCrAlY-based matrix and the addition of components (Cu, Mo, and BaF₂) to improve the wear resistance at elevated temperatures. The coatings were sprayed by high-velocity oxy-fuel, heat-treated at 1040 °C, and tribologically tested at room and elevated temperatures. Raman spectroscopy and scanning electron microscopy were used on worn and unworn regions of the coating to characterize the changes in microstructure caused by wear. The coatings were also exposed to oxidation and hot corrosion conditions to evaluate the resistance to high-temperature environments. The results have shown an improvement in wear rates of the coatings upon heat treatment and the formation of a smooth tribolayer at 300 °C. The as-sprayed coating was able to withstand the attack by molten salts without exposing the substrate, and minor weight gain was observed, indicating that the MCrAlY matrix was effective to protect the coating and the substrate against damages induced by salt penetration. Full article

This paper presents a novel and effective approach for the rational selection of zinc coatings in industrial applications. The corrosion behaviors of three types of zinc coatings were investigated through salt spray testing in the laboratory. Corrosion failure characteristics of the coatings were analyzed using corrosion morphology observation, electrochemical analysis, corrosion product identification, and weight loss measurements. Additionally, the environmental impacts of the production processes for the three coatings were evaluated. Among the three coatings, the thermally sprayed zinc–aluminum coating exhibited the best corrosion resistance in the salt spray test, while the hot-dip zinc coating showed the poorest performance. The electrochemical characteristics of the coatings at various stages of corrosion were examined using polarization curves, revealing the changes in corrosion current and corrosion potential that corresponded to the failure progression of the coatings. The corrosion products of the thermally sprayed zinc–aluminum coating primarily included ZnO, Al₂O₃, Zn(OH)₂, and ZnAl₂O₄ phases. In contrast, the corrosion products of the thermally sprayed zinc coating and the hot-dip zinc coating predominantly consisted of ZnO and Zn(OH)₂ phases. Finally, the environmental impact indicators of the three coatings were assessed using the IMPACT2002+ method. Full article

The aim of this study was to assess the germination and growth of two strains of Bacillus cereus following the artificial inoculation of six selected hot dishes with spores which were then stored at temperatures of 40, 50, and 60 °C for 0.5, 1.0, 2.0, 2.5, 3.0, and 4.0 h. The water activity of the prepared meals varied between 0.967 and 0.973 and the salt content between 0.74 and 1.40%. The pH value of four dishes exceeded 6.0, but for two (tomato sauce and ratatouille) it was 4.6. The tested strain DSM 4312 showed good growth abilities and attained a population exceeding 6.0 log CFU/g within 4 h at 40 °C in foods with pH values > 6.0. The study demonstrated that a drop in food temperatures to 40 °C is risky, while no growth of B. cereus was detected within 4 h at 50 and 60 °C. The growth rate of B. cereus is conditioned not merely by environmental conditions (temperature, pH values, food composition), but also by the bacterial strain. Full article

The article compares the properties of coatings (cataphoretic, hot-dip zinc, and thermo-diffusion zinc) applied to steel components used in the automotive industry. The research focused on the analysis of corrosion resistance, hardness measurements, and tribological properties conducted on steel guides used in trailer and truck body structures as well as fasteners (M12 × 40 bolts). The base surfaces were cleaned chemically. Corrosion resistance was tested in a salt chamber, while coating thickness was measured using the magnetic induction method. Coating hardness (HV 0.02) was assessed with a microhardness tester, and tribological properties were tested under dry friction conditions. The results showed that the zinc coatings demonstrated corrosion resistance far superior to paint coatings. Full article

This study involved the investigation of the mechanical and tribological behaviors of DIN 1.2344 and WP7V tool steels, quenched in a salt bath after austenitization at 1050 °C, followed by triple tempering for 2 h. The selection of tempering temperatures produced two hardness levels under four metallurgical conditions, with the hardest level found only for WP7V steel (54 and 57 HRC). The mechanical properties were evaluated using Rockwell C, Vickers, and nanoindentation methods, along with unnotched impact tests, according to the SEP 1314 guidelines. Wear tests were conducted in a tribometer configured for a reciprocating setup, with a frequency of 5 Hz, a load of 25 N, and a time of 60 min, at room temperature and at 200 °C. As counterbodies, alumina balls of 5 mm in diameter were used. Wear tracks were evaluated through scanning electron microscopy, EDS, interferometry, and Raman spectroscopy. Friction and wear behaviors were affected by the variation in temperature for softer steels (DIN 1.2344 and WP7V of 48.5 HRC): the higher the temperature, the better the tribological performance. The harder steels were not sensitive to temperature testing. These effects depend on maintaining iron oxide (hematite) at the point of contact. The wear rates determined for the hardest material (57 HRC), considering its impact resistance, make it unsuitable for severe conditions such as hot stamping. Full article

This study investigated the moisture absorption and mechanical degradation of epoxy-based polymer systems with Mg-Al/NO₃ layered double hydroxide (LDH) nanoparticles content up to 5 wt%. Such systems are developed for multilayer corrosion protective coatings. A sorption model was developed to calculate the moisture concentration field in the multilayer structures using Fick’s law of diffusion. The finite-difference method was used for the numerical solution. Epoxy/LDH nanocomposites were prepared using various dispersion methods with solvents, wetting agents, and via a three-roll mill. Moisture absorption was measured under different environmental conditions, including temperatures up to 50 °C and salinity levels up to 26.3 wt% salt solution. The results showed that equilibrium moisture content increased by 50% in hot water, while it was reduced by up to two times in salt solution. The diffusion coefficient in hot water increased up to four times compared to room temperature. The numerical algorithm was validated against experimental data, accurately predicting moisture distribution over time in complex polymer systems. Mechanical tests revealed that the elastic modulus did not change after water exposure; however, the ultimate strength decreased by 10–15%, especially in specimens with 5 wt% LDH. Full article

This paper presents the results of studies on the growth kinetics, microstructure (SEM/EDS) and corrosion behavior of coatings obtained by hot-dip galvanizing process in baths containing Bi additive. The coatings for testing were produced on low-silicon steel in a Zn bath containing 0.04, 0.12 and 0.4 wt.% Bi. The corrosion resistance of the coatings was determined comparatively in standard Neutral Salt Spray Tests (NSST) (ISO 9227) and sulfur dioxide test (SDT) in a humid atmosphere (ISO 22479). Potentiodynamic tests and electrochemical impedance spectroscopy measurements were conducted. It was found that the addition of 0.04 and 0.12 wt.% Bi reduces the total thickness of the coatings and the thickness of intermetallic layers, while the content of 0.4 wt.% Bi in the bath increases the thickness of the layers forming the coating. Direct corrosion tests (NSST and SDT) and electrochemical tests showed that the addition of Bi to the zinc bath reduces the corrosion resistance of the coatings. The corrosion resistance of the coatings decreases with increasing Bi concentration in the zinc bath. In the microstructure of the coatings, it was found that Bi precipitates mainly on the surface of the coating, but also on the cross-section of the outer layer and ζ intermetallic layer. Bi precipitates, due to their cathodic nature, affect the reduction of the corrosion resistance of the coatings with the increase of their content in the bath. Full article

TiAl alloys are used in high-temperature components such as the turbine blades of aeroengines because of their excellent properties. However, TiAl alloys are prone to thermal corrosion when in near-ocean service. In order to solve this problem, a hot-corrosion-resistant CrAl/NiCoCrAlY/AlSiY gradient composite coating was prepared on the surface of the TiAl alloy. The phase composition and morphology of the coating were analyzed. Hot corrosion tests of the traditional NiCoCrAlY coating and CrAl/NiCoCrAlY/AlSiY gradient composite coating on a TiAl substrate were performed. The samples were coated with 75%Na₂SO₄ + 25%NaCl salt film and treated at 950 °C for 100 h, and the corrosion products were analyzed. The results indicate that compared with the TiAl substrate and traditional NiCoCrAlY-coated samples, the composite coating showed better hot corrosion resistance, only slightly cracking, and no corrosion loss occurred. This is mainly because the continuous Al₂O₃ layer can effectively resist the damage caused by the melting reaction in salt, and the Cr-rich layer can not only slow the mutual diffusion of elements but also generate a good corrosion resistance chromium oxide protective layer under serious corrosion. Moreover, the corrosion mechanism of the TiAl substrate, traditional NiCoCrAlY coating, and experimental composite coating was analyzed in detail. Full article

The materials used in concentrating solar power (CSP) systems are becoming of interest because of the high energy efficiency of energy storage. Molten salts can be used as both heat-storage media and heat-transfer fluid in a CSP system. In molten salts, steel alloys used in vessels and pipelines are highly vulnerable to hot corrosion. To protect steel alloys, applying a coating is an excellent strategy to extend the life of the alloy. NiCrAl coatings are well-suited for high-temperature environments. The purpose of this study was to investigate the corrosion behavior of NiCrAl with Si addition coatings on AISI304 in molten salt. NiCrAl coatings with and without Si addition were deposited using the high-velocity oxygen fuel (HVOF) technique. The corrosion test was performed using an immersion test in modified solar salt with 0.5% NaCl at 400–600 °C. Gravimetric methods evaluate the weight change for immersion tests. At 400 °C, an increased amount of weight gain due to the oxidation reaction and molten salt infiltration was observed. At 600 °C, the corrosion reaction was more dominant, and apparent oxidation was decreased; however, oxidation products NiO and sodium aluminum silicate were detected. Si addition supports the formation of the protective oxide sodium aluminum silicate, which inhibits molten salt oxidation reaction and molten salt infiltration. Full article

This article presents the results of research on the growth kinetics, microstructure (SEM/EDS/XRD), and corrosion behavior of Zn-5Al coatings obtained using a high-temperature hot dip process on B500B reinforcing steel. The corrosion resistance of the coatings was determined using the neutral salt spray (NSS) test (EN ISO 9227). Based on chemical composition tests in micro-areas (EDS) and phase composition tests (XRD), corrosion products formed on the coating surface after exposure to a corrosive environment containing chlorides were identified. In the outer layer of the coating, areas rich in Zn and Al were found, which were solid solutions of Al in Zn (α), while the diffusion layer was formed by a layer of Fe(Al,Zn)₃ intermetallics. The growth kinetics of the coatings indicate the sequential growth of the diffusion layer, controlled by diffusion in the initial phase of growth, and the formation of a periodic layered structure with a longer immersion time. The NSS test showed an improved corrosion resistance of reinforcing bars with Zn-5Al coatings compared to a conventional hot-dip-galvanized zinc coating. The increase in corrosion resistance was caused by the formation of beneficial corrosion products: layered double hydroxides (LDH) based on Zn²⁺ and Al³⁺ cations and Cl⁻ anions and simonkolleite—Zn₅(OH)₈Cl₂·H₂O. Full article