Al2O3 Oxide Research Articles

Research of the microstructure glass–metal boundary obtained under influence by ultrashort pulse lasers

The article research the microstructure of the welded layer obtained by exposure to an ultrashort laser pulse on a glass-metal joint. The study of the weld made it possible to identify the effect of thermal diffusion of the chemical elements of glass and metal into the joint zone in a ratio of 50 : 50% of each material. The size of the transition layer of the welded joint between glass and metal was 2–3 microns. The results of the work also show that when combining chromium-nickel stainless steel with borosilicate glass, bonds of the Fe–O–Si type are formed, and the connection of a 6000 series aluminum alloy with borosilicate glass leads to the formation of aluminum oxides Al2O3.

Enhanced mechanical properties and oxidation resistance in Ti-rich medium entropy alloy via Al2O3 addition

Lightweight high/medium entropy alloys (H/MEAs) have attracted significant attention for their potential applications in lightweight high-temperature materials. Incorporation of oxides or oxygen atoms is an effective strategy for enhancing the mechanical and oxidation resistance performance of H/MEAs. Therefore, this work investigated the microstructure, phase compositions, mechanical properties, and oxidation resistance of Ti-V-Cr medium entropy alloys with varying Al2O3 oxide content. The results showed a notable improvement in mechanical performance and enhanced oxidation resistance with the addition of Al2O3. The incorporation of Al2O3 oxides contributed to fine grain strengthening, interstitial strengthening, phase separation and transformation, collectively enhancing performance of the alloy. The 0.6 wt.% Al2O3-added Ti-25V-15Cr alloy achieved a balance between strength and ductility, with a density of 5.111 g/cm3, a yield strength of 1371 MPa, and a plasticity exceeding 40%, even in the as-cast state. The 1.2 wt.% Al2O3 alloy exhibited a high yield strength of 1471 MPa and plasticity over 15%. Additionally, the 0.6 wt.% Al2O3-added alloy displayed superior oxidation resistance at 700 °C. The incorporation of Al2O3 did not change the oxidation mechanism of the Ti-25V-15Cr alloy but reduced the oxidation extent on the surface by forming oxides of the same type with varying morphologies.

Synthesis and characterization of new continuous phosphate glass fibers intended for structural engineering applications: Structure/property relationships

Nowadays, phosphate glass fibers (PGF) are considered quite competitive respective to conventional glass fibers. This work focus on the development of PGF fibers intended for structural engineering applications such as composite reinforcement for building and automotive fields. For this purpose, two series of phosphate glasses based on 52P2O5-24CaO-13MgO-(11-(X+Y+Z)) K2O-XAL2O3-YF2O3-ZTiO2; (X=1; 3; 5, Y=0; 5, Z=0; 1 mol %) were processed and transformed into phosphate glass fibers by melt spinning. The resulting fibers were characterized. XRD analysis confirmed the non-crystalline nature of phosphate glasses. In addition, the substitution of K2O by Al2O3 and by the combination of Al2O3, Fe2O3 and TiO2 in the composition of phosphate glass could lead to a significant increase in fiber density from 2,16 g/cm3 to 2,80 g/cm3. The stability of the produced phosphate glass fibers was examined using two methods: weight loss at 37°C and dissolution kinetics under different pH levels (4, 7, and 12). The results showed that the chemical resistance of the PGF fibers was improved with up to 99% increase respective to the original formulation. In addition, the mechanical properties of the spinnable phosphate glass manufactured by replacing K2O oxide by Al2O3 oxide were improved, such a substitution led to a maximum tensile strength and modulus of 2668 MPa and 140 GPa, respectively. Therefore, the tensile proprieties were improved by 75% compared to the original formulation. This comparative study between phosphate glass fibers (PGF) and traditional fibers highlight similar tensile strength but combined to notable enhancements in chemical stability through cation addition, expanding their potential use in composite and biomedical materials. Finally, a correlation analysis of mechanical performances was carried out. It was observed that the results obtained using the statistical methods were consistent with the experimental data.

Matrizes cimentícias com o uso de resíduos de construção e demolição para redução do impacto ambiental de blocos de pavimentação

The construction industry is responsible for the intensive consumption of natural resources and the generation of large volumes of construction and demolition waste (CDW), which are often disposed of improperly. This research developed concrete blocks using recycled CDW aggregates, promoting sustainability and circular economy by reusing these materials in urban infrastructure. Waste was collected from a recycling plant over five months, selecting Brita 1, Brita 0, and Pó de Brita to compose the concrete mixes. Particle size distribution, bulk density, and specific gravity tests were performed, and blocks and specimens were molded with 100% replacement of natural aggregates by CDW. The compressive strength tests were carried out at 14 and 28 days, while the abrasion test was performed only at 28 days. X-ray fluorescence (XRF) and Scanning electron microscopy (SEM) were used to characterize the products. The results indicated a compressive strength of 34.3 MPa at 28 days, close to the minimum required by the standard (35 MPa). XRF analysis showed a predominance of SiO₂, CaO, Al₂O₃, Fe₂O₃, MgO, SO₃, and K₂O oxides, all within normative limits. Leaching and solubilization tests, conducted according to NBR 10005 and NBR 10006, classified the waste as non-hazardous and non-inert. This study demonstrates that using CDW in concrete block production is a viable and sustainable alternative, contributing to waste reduction, material reuse, and the development of sustainable urban infrastructure.

Study on the growth mechanism of Pt nanoparticles in oxides: Role of metal-oxide interactions

Strong interactions of metal nanoparticles (NPs) with oxide matrices can dramatically enhance the thermal stability of metal NPs. However, how metal-oxide interactions control the growth of metal NPs remains unclear. Here, the growth of Pt NPs with respect to metal-oxide interactions was investigated by encapsulating them in different Al2O3 and SiO2 oxides. Pt NPs encapsulated in Al2O3 exhibited excellent thermal stability than those in SiO2. Quantitative thermodynamic calculations revealed that metal-oxide interactions strongly governed the driving force for the coalescence of Pt in Al2O3 and SiO2. The kinetic analysis further showed that stronger Pt-Al2O3 interactions controlled the Ostwald ripening of Pt NPs by restricting the diffusion of Pt atoms in oxides, leading to a higher growth activation energy of Pt in Al2O3 than SiO2. These findings explain the different sinter resistance of metal NPs when encapsulated in different oxides, providing valuable insights for enhancing the thermal stability of metal NPs.

Enhanced Photovoltaic Efficiency through 3D-Printed COC/Al₂O₃ Anti-Reflective Coversheets

In the past few years, there has been a considerable growth in the utilization of solar cells to produce electrical power to fulfil the growing worldwide energy demands. An optical loss is a crucial factor that impacts the performance of the photovoltaic conversion process. This loss occurs when incoming sunlight is reflected back on the outer layer of the photovoltaic cells. The application of antireflective materials on the photovoltaic substrates can enhance the absorption of sunlight and minimize the reflection. Currently, there is no ideal anti-reflective coating for solar cells that can allow the transmission of sunlight without any reflection. In this research, a transparent cyclic-olefin-copolymer (COC) was used to fabricate anti-reflection (AR) coversheet by fused deposition modelling process (3D printing). Further, the aluminium oxide Al2O3 powder was added at the proportions of 1wt%, 2wt%, 3wt%, and 4wt% to the COC polymer to increase the anti-reflection characteristics. The structural, morphological, mechanical (tear strength), electrical and temperature characteristics were studied. The performance of COC with aluminium oxide (COCA) coversheets was evaluated, and the findings revealed a considerable increment in power conversion efficiency (PCE) of 17.21% (sunlight exposure) and 18.34% (neodymium light) for COCA3 coversheets. As seen, the COCA3 sample exhibit lower electrical resistance of 3.88 ×10-3 Ω cm, carrier concentration (36.91×1020 cm-3) and higher hall mobility (13.67 cm2/Vs). The findings from the investigations demonstrated that the utilization of COC with Al2O3 powder (COCA) can be a suitable antireflective coversheet material for boosting the performance of polycrystalline silicon photovoltaic cells.

Hydrogen production from energetic poplar and waste sludge by electrohydrogenesis using membraneless microbial electrolysis cells

Membraneless microbial electrolysis cells (MECs) are potentially considered to produce biohydrogen (bioH2) in a green manner and simultaneously minimize agricultural and wastewater facility wastes. However, effective, sustainable, and cost-effective system configuration and improvement of operating variables, working at ambient conditions, are needed to make the MEC a sustainable process. Therefore, this study investigates the bioH2 production from poplar leaves and anaerobic sludge mixture by incorporating nanomaterials comprising Al2O3, MgO, and Fe2O3 metal oxides at various dosages. Moreover, the effects of applied cell voltage (0.5–1.5 V) and inoculum amount (20–40 mL) on bioH2 production and organic matter removal performance are evaluated. The maximum bioH2 production value is 417 mL at an applied voltage of 1.5 V with a chemical oxygen demand (COD) removal efficiency of 37.6 % under operating times of 5 min using 40 ml of inoculum. The bioH2 production of the MEC system is reduced with the decrease in inoculum amount. The highest bioH2 production of 828 mL is obtained at improved conditions in the presence of 1 g of Fe2O3 metal oxide. Overall, this study provides the potentiality of simultaneous waste minimization and bioH2 production under ambient conditions that highlight the waste-to-energy pathway for membraneless and green bioelectrochemical process.

Influence of NiCrAlY coating on anti-corrosion of M951 alloy

M951 alloy is a cast nickel-based super-alloy widely used in gas turbines and aircraft engines, thus a suitable high temperature protective coating must be applied on its surface to enhance the corrosion resistance. In this research, NiCrAlY coating was deposited on M951 by arc ion plating. TGA at 1100 °C, cyclic oxidation at 1000 °C and hot corrosion in molten Na2SO4+25 wt% K2SO4 salt at 850 °C of M951 bare alloy and NiCrAlY coating specimens were investigated respectively. After TGA and cyclic oxidation, mixed oxides of NiO, NiAl2O4, Nb2O5 and Al2O3 formed on M951 surface, which spalled seriously during cyclic oxidation process. Thin, continuous and adhesive α- Al2O3 formed on the surface of NiCrAlY coating after both oxidation process. In molten Na2SO4+25 wt%K2SO4 salt at 850 °C, catastrophic corrosion occurred for the M951 alloy only after 10 hours, while thin and continuous θ- Al2O3 film formed on the surface of the NiCrAlY coating. In a word, NiCrAlY coating greatly improved the high temperature oxidation and hot corrosion resistance of the M951 superalloy. This study will further refine the oxidation and corrosion behaviors of M951 superalloy under different high temperature protective coatings and provides theoretical and experimental basis for the application of M951 superalloy in corrosive environments.

Aluminum droplets on Ni substrates: Evaluating high-temperature oxidation at the liquid/gas interface

In reactive wetting aluminum (Al)/nickel (Ni) systems, oxides at liquid/gas (L/G) interfaces received less attention compared to intermetallic compounds forming at liquid Al/solid Ni interfaces yet potentially significantly influencing wetting properties. Between 900 and 1250 °C, we observed that the shape of sessile Al droplets with dense oxides at the L/G interface and intense interactions at liquid Al/solid Ni interfaces deviates from a spherical cap and can be used as a way to characterize the oxide evolution. This approach reveals a critical temperature of 1100 °C under a PO2 level of 3.9 × 10−9 atm and a vacuum level of ∼2 × 10−2 mbar. Above it, Al2O3 oxides at the L/G interface are eliminated as Al2O gas, while at lower temperatures, they develop as a mixture of Al2O3 oxides and Al-Ni intermetallic compounds with Ni being dissolved from the substrate. At high temperatures (above 1200 °C), despite oxide-free L/G interfaces, non-spherical cap shapes were also obtained due to the formation of sharp edges at the contact line triggered by the growth of intermetallic compounds. The coupling between the droplet shapes and the interfacial interactions is further confirmed by in-situ observation of oxides, analysis of quenched samples and thermodynamic calculations. The proposed method can be potentially applied to multiple reactive wetting systems (e.g. Sn/Cu, Al/Fe, Mg/Ni systems), which are crucial for high-temperature processes such as soldering, coating, and processing of metal matrix composites.

Evaluation of the corrosion and oxidation resistance of NiCoCrAlY cladding on CMSX-4 by laser cladding

This study uses laser cladding to investigate the hot corrosion and oxidation behavior of CMSX-4 claddes with NiCoCrAlY powder. High-temperature oxidation tests were conducted at 1050°c for 50, 100, 150, and 200 h on 4 samples, while 6 samples underwent hot corrosion testing at 850°c for 6 h. The innovative application of laser cladding enables the creation of a γ′ and β interdendritic phase microstructure. High-temperature oxidation tests reveal a growth rate of 0.05 μm/h in oxide layer thickness between 50 and 200 h, accompanied by a surface weight increase rate of approximately 0.8 mg/cm2.h. The oxide layer's regeneration, continuity, and density are observed at 200 h, highlighting the innovative potential of this technique. Fracture oxidation is observed at 150 h in some TGO layer regions, but at 200 h of oxidation, the TGO layer's regeneration, continuity, and dense TGO was observed at the cladding interface. The TGO forms at 1050°c consist of Al2O3, Cr2O3, and CoO oxides, with Al2O3 as the main oxide phase. The study's findings demonstrate the ability of laser cladding to enhance the thermal protection of CMSX-4, showcasing a promising innovation in the field.

Clarifying the effects of composition and phase stabilization on the oxidation resistance in AlCoCrFeNiTi series high-entropy alloys at 1100 °C

The application of high entropy alloys in thermal barrier coating (TBC) systems offers a viable solution for mitigating interfacial instability arising from the elevated-temperature interdiffusion within the bonding layer/matrix. Nevertheless, the elucidation of the phase stability under elevated temperatures and the intricate interplay among thermal-mechanical-chemical factors in HEAs remain lacks clarity. Herein, a set of AlxCo10.5Cr10Fe25Ni(50-x)Ti4.5 HEAs featuring desirable high-temperature phase stability, oxidation resistance, and spalling resistance at 1100 °C were meticulously designed. And the effects of phase composition and thermodynamics on the evolution of surface oxides in these HEAs were investigated. Specifically, the formation of the unfavorable σ phase between 860 and 1200 °C is avoided through the composition adjustment. The oxidation resistance is governed by the presence of large-size columnar grains and the spalling resistance of the Al2O3 oxide film. The spalling resistance is mainly linked to the configuration sequence (Spinel→FeAlTiO5→TiO2) of the outer oxide layer and the phase transition of the matrix either to FCC or BCC. Meanwhile, the formation of FeAlTiO5 assumes a crucial role in the optimization of spalling (>770 h) and oxidation resistance (2.6×10−12 g2·cm−4·s−1) within an Al20Co10.5Cr10Fe25Ni30Ti4.5 alloy. These findings provide guidance for the development of TBC systems endowed with exceptional properties tailored for engineering applications.

A generalized master sintering curve based on nucleation-limited densification kinetics

The master sintering curve was developed assuming diffusion-limited coarsening and densification kinetics. A key limitation of the model is that it is only valid for a single set of initial conditions, i.e., grain size and density. Recent in situ sintering experiments suggest that densification follows nucleation-limited kinetics. A model for sintering can be formulated based on a thermodynamic energy balance between interfacial energy dissipation and work required to overcome the nucleation barrier. A feature of this model is that it inherently relates coarsening and densification, providing a basis for formulating a generalized master sintering curve that is not sensitive to initial conditions. This paper develops the model and demonstrates its practical application to several oxide systems, including ZnO, Al2O3, and Y2O3-doped tetragonal ZrO2.

Enhancing high-temperature chloride molten salts corrosion resistance of 310S steel with Si-added Ni–Al coating

Ni–Al based coating is one of the common high temperature and corrosion resistant protective coatings. In the present paper, the effect of Si content on the formation of Al2O3 layer and the corrosion resistance of Ni–Al coating to chloride molten salt was studied. The research results show that the Ni–Al coatings with varying Si content mainly form NiAl2O4 and Al2O3 oxide layers after pre-oxidation, and form a three-layer structure after molten salt corrosion. The appropriate amount of Si added to the Ni–Al coating can promote the formation of the α-Al2O3 layer during pre-oxidation and thermal corrosion, improving the corrosion resistance of the coating to high temperature chloride molten salt, and hindering the diffusion of Cr elements. Particularly, the Ni–Al coating with Si content of 1.2 at.% has the thickest and densest Al2O3 protective layer, showing the best corrosion resistance. The simulation results shows that compared with the Ni–Al coating without Si, the Cl atoms in the Si-added Ni–Al coating need to overcome greater energy barriers to diffusion during the molten salt corrosion process, which also indicates that the addition of Si can improve the corrosion resistance of the coating.

Wear Properties of Ni3Al-Ni3V-Zr-Ni5Zr Alloys under Different Atmospheres

The study examines the friction and wear properties of Ni3Al-Ni3V-Zr-Ni5Zr alloys under varying gas conditions. The alloy was tested in the presence of oxygen and carbon dioxide using a controlled atmosphere wear tester. The study revealed that the wear environmental embrittlement resulted from the diffusion of reactive atomic hydrogen into the interior of the Ni3Al-Ni3V alloy. The addition of Zr elements decreased the proportion of Al elements on the surface of the Ni3Al-Ni3V-Zr-Ni5Zr alloy and reduced the proportion of H atoms produced by the chemical reaction between atmospheric water vapour and Al elements. This inhibited the environmental embrittlement and improved the performance of the Ni3Al-Ni3V-Zr-Ni5Zr alloy. The wear performance of Ni5Zr alloy is superior to that of Ni3Al-Ni3V. When exposed to air in an air environment, the surface of Ni3Al-Ni3V-Zr-Ni5Zr alloy forms a protective Al2O3 oxide film on the workpiece, resulting in a reduction of the friction coefficient and wear rate of the alloy. The wear mechanism of the alloy is mainly oxidation wear and abrasive wear. In an oxygen environment, the surface of the alloy generates a significant amount of Al2O3 oxide film. The flaking of the oxide film leads to an increase in the friction coefficient and wear rate of the alloy. In a carbon dioxide environment, the surface of the alloy undergoes severe deformation, and plough lines become apparent. This is accompanied by flaking Si3N4 abrasive chips adhering to the surface of the alloy, which intensifies the wear of the alloy. The primary wear mechanism is abrasive wear. Therefore, the friction coefficient and wear rate of the Ni3Al-Ni3V-Zr-Ni5Zr alloy in the atmosphere are optimal.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ПОСТТЕРМООБРАБОТКИ НА СТРУКТУРУ АЛИТИРОВАННОГО СЛОЯ НА ТИТАНЕ ВТ1-0

The study results of the post-heat treatment effect on the structure of the aluminized layer on VT1-0 titanium are presented. It is shown that the coating after heat treatment at 700 and 850 °C for 20 h consists of two layers. In the outer layer, rounded TiAl3 particles are separated by aluminum oxide Al2O3. A continuous diffusion zone of ~10 μm thickness is formed at the boundary with titanium, consisting of several layers representing TiAl2, TiAl and Ti3Al aluminides.

Microstructural Stability and High-Temperature Oxidation Behavior of Al0.25CoCrCuFeNi High Entropy Alloy

Al0.25CoCrCuFeNi is a high-entropy alloy composed of transition metals, specifically designed for high-temperature applications owing to its favorable mechanical properties, high melting point, and excellent high-temperature resistance. This alloy has been identified as a promising material for space exploration, particularly in the fabrication of combustion chambers and rocket nozzles by the National Aeronautics and Space Agency. Ongoing alloy development involves modifying the elemental composition. This study reduced aluminum content in the equiatomic AlCoCrCuFeNi alloy to Al0.25CoCrCuFeNi, followed by isothermal oxidation treatments at 800, 900, and 1000℃. A series of experiments were conducted to investigate the microstructure stability and oxidation behavior of the Al0.25CoCrCuFeNi alloy. The alloying elements were melted using a single DC electric arc furnace, followed by homogenization at 1100°C for 10 hours in an inert atmosphere. Subsequently, samples were cut into coupons for isothermal oxidation testing at the desired temperatures for 2, 16, 40, and 168 hours. The oxidized samples were characterized using XRD (x-ray diffraction), SEM (scanning electron microscopy) equipped with EDS (energy-dispersive X-ray spectroscopy), optical microscopy, and Vickers hardness testing. The as-homogenized alloy consisted of two constituent phases: an FCC (face-centered cubic) phase in the dendritic region and a copper-rich FCC phase in the inter-dendritic region. The oxides formed during the oxidation process included Al2O3, Cr2O3, Fe3O4, CoO, CuO, NiO, and spinel oxides (Co,Ni,Cu)(Al,Cr,Fe)2O4), with distinct formation mechanisms at each temperature.

Aluminide Coatings by Means of Slurry Application: A Low Cost, Versatile and Simple Technology

The present study focused on demonstrating the versatility of the slurry deposition technique to produce aluminide coatings to protect components from high-temperature corrosion in a broad temperature range, from 400 to 1400 °C. This is a simpler and low-cost coating technology used as an alternative to CVD and pack cementation, which also allows the coating of complex geometries and offers improved and simple repairability for a lot of industrial applications, along with avoiding the use of non-hazardous components. Slurry aluminide coatings from a proprietary water-based-Cr6+ free slurry were produced onto four different substrates: A516 carbon steel, 310H AC austenitic steel, Ti6246 Ti-based alloy and TZM, a Mo-based alloy. The resulting coatings were thoroughly characterised by FESEM and XRD, mainly so that the identification of microstructures and appropriate phases was reported for each coating. The importance of surface preparation and heat treatment as key parameters for the coating final microstructures was also evidenced, and how those parameters can be optimised to obtain stable intermetallic phases rich in Al to sustain the formation of a protective Al2O3 oxide scale. These coating systems have applications in diverse industrial environments in which high-temperature corrosion limits the lifetime of the components.

Achieving excellent mechanical and antioxidant properties in MoAlB ceramics through spark plasma sintering-high-frequency (SPS-HF) sintering

A fully dense MoAlB ceramic was synthesized utilizing MoAlB powder through SPS-HF technology. The Vickers hardness, fracture toughness and bending strength of the MoAlB ceramic reached 14.08 GPa, 6.70 MPa m1/2 and 407 MPa, respectively. The electrical conductivity and thermal conductivity of the MoAlB ceramic at room temperature were measured to be 3.20 × 106 S m−1 and 23.50 W m−1 K−1, respectively. The ceramic exhibited excellent high-temperature oxidation resistance at 800–1200 °C for up to 64 h. Even after 64 h of oxidation at 800 °C and 1000 °C, the thickness of the oxide layer was only 2.09 µm and 2.20 µm, respectively. The oxidation behavior was controlled by a diffusion process. The rapid formation of a continuous and dense Al2O3 oxide layer effectively inhibited the inward diffusion of oxygen and the oxide layer is well bonded to the matrix.

A study of the effect of volume fraction of Alumina Oxide on the thermal conductivity values of polyester resin particulate composites

This study aims to calculate the thermal conductivity of unsaturated polyester resin when adding aluminum oxide Al2O3 as a filler in different quantities of 10%, 20%, and 30% to the resin and to study the effect of these additives on the thermal conductivity (K) of this resin material. The behavior was changed based on Fourier's thermal conductivity law when calculating the resin's K value before and after adding aluminum oxide. The results showed an increase in thermal insulation with an increase in the percentage of aluminum oxide in the resin with a decrease in the thermal conductivity value. The lowest value obtained was 0.23 W/m.c when the percentage of alumina oxide was 30% at the highest applied temperature of 50 °C. This was illustrated through the graphs that summarize the relationship between thermal conductivity and temperature based on different percentages of aluminum oxide.

Effects of Al Content on the Mechanical Properties and Corrosion Behavior of Ni-Al Coatings on 310S Heat-Resistant Steel for CSP Plants

Material selection is crucial in concentrated solar power technology due to the significant impact of high-temperature corrosion. The Ni-Al coating on the steel is an effective approach to corrosion resistance. The alterations in microstructure, hardness, toughness, adhesion, and corrosion inhibition properties of Ni-Al coatings were examined across varying Al concentrations after oxidation processes. Cracks appeared on the surface of coatings with preoxidation Al content ranging from 9.9 at% to 23.3 at%, and no continuous Al2O3 oxide film was formed. Notably, as the Al content rose to 41.0 at%, and a continuous α-Al2O3 oxide film was successfully formed. It showed the best toughness and elastic modulus (181.6 GPa), and relatively high coating hardness (8.0 GPa). The corrosion results show that when the Al content is 41.0 at%, the corrosion resistance of high-temperature molten chloride salt is the best. The oxidation layer formed by the preoxidation has a blocking effect on the migration of elements from the molten salt into the coatings. The results provide a route to fabricate Ni-Al coatings that possess integrated strength, toughness, and corrosion resistance suitable for protective coating applications in concentrated solar power systems.