Microstructure Oxidation Research Articles

Polymer-derived SiAlOC coating to improve the high-temperature resistance of chromium

Cr and its alloys are interesting materials for applications at temperatures higher than 1000 °C. However, challenges such as limited oxidation resistance and nitridation still restrict their usage as high-temperature structural materials. The present work investigates the influence of a 0.6 μm thin SiAlOC sol-gel coating on the oxidation resistance and kinetic of Cr at 950 °C for 50 h and 1050 °C for up to 100 h of exposure time in dry synthetic air using thermogravimetric analysis. The resulting oxide scale and microstructure were extensively studied by combining different techniques such as EPMA, XRD, SEM, Raman spectroscopy, FT-IR, and STEM. Overall, a reduction in mass gain and an improved scale adhesion was observed. The interaction of coating and substrate causing nanosized Cr2O3 and cristobalite formation in the SiAlOC coating was further supported by investigations of bulk materials.

A Comparative Study on High-Temperature Oxidation Behavior, Microstructure Characterization, and Texture of UNS R30155 Superalloy Weldment Joint Using Pulsed Current and Constant Current Gas Tungsten Arc Welding

A Comparative Study on High-Temperature Oxidation Behavior, Microstructure Characterization, and Texture of UNS R30155 Superalloy Weldment Joint Using Pulsed Current and Constant Current Gas Tungsten Arc Welding

Oxide and Heat Treatment Microstructure Evolution of Melted Mark on Copper Wire under Various Heat Treatment Conditions

Oxide and Heat Treatment Microstructure Evolution of Melted Mark on Copper Wire under Various Heat Treatment Conditions

Temperature-dependent oxidation kinetics and mechanical properties degradation of Cf/ZrB2-SiC composites

The oxidation kinetics and microstructures evolution of Cf/ZrB2-SiC composites are investigated by experimental characterizations. An empirical model containing multi-reaction systems is further established for predicting the specimen mass evolution during isothermal oxidantion. Based on the morphological observations and in-situ tensile responses, three oxidation mechanisms of carbon phase controlled by reaction and diffusion kinetic are categorized as uniform, non-uniform and superficial oxidation. The relationship between fracture modes and internal fibers microstructures indicates that the structural origin of the fracture mode transition is the toughening mechanism transition of fibers on the ceramics matrix induced by oxidative damage.

Multi-Scale Characteristics of Coal Secondary Spontaneous Combustion Under Different Pre-Heating Oxygen Concentrations by TG and FTIR Analysis

ABSTRACT The study aimed to explore the influence of pre-oxidation oxygen concentration on the mass variation and microstructure of coal oxidation using TG and FTIR experiments. The objective was to comprehend the thermal effects and mechanisms of coal oxidation under distinct pre-oxidation conditions. Employing fuzzy mathematics and multiple linear regression equations, the study sought to elucidate the influence mechanism of pre-oxidation oxygen concentration on the thermal effect. The findings reveal that pre-oxidation did not alter the overall weight loss pattern during the spontaneous combustion process of coal, yet significantly accelerated the rate of weight loss. Furthermore, the dry cracking temperature experienced a notable advancement. Through FTIR experiments, it was observed that pre-oxidation activated the reactivity of C=O, -CH2-, and aromatic hydrocarbons, thus leading to more intense reactions. The key functional groups influencing the mass change were identified as aromatic hydrocarbons and hydrogen bonds. Notably, the pre-oxidation effect on the thermal impact was most pronounced when the pre-oxidation oxygen concentration reached 15%.

Influences of adding Y2Ti2O7 and HfH1.98 nanoparticles on the microstructure and mechanical properties of oxide dispersion strengthen steels

Adding Y2O3 will make Al-containing oxide dispersion strengthened (ODS) steels produce coarse Y-Al-O particles, which deteriorates their mechanical properties. Herein, Y2Ti2O7 nanoparticles and Hf hydride nanoparticles (NPs) were successfully prepared by hydrogen plasma-metal reaction (HPMR) method and added together in the Fe-Cr-Al ODS steel to replace the traditional Y2O3 NPs. The microstructure of matrix and oxide in ODS steels has been characterized by scanning transmission electron microscopy (STEM) and high resolution transmission electron microscopy (HRTEM). The oxide NPs in FHYT-0.6 (Fe-14Cr-4.5Al-2 W-0.35HfH1.98–0.6Y2Ti2O7, wt%) are made of Y2Ti2O7 (semi-coherent with the matrix and about 10 nm) and HfO2 (incoherent with the matrix and about 26 nm). The size of oxide dispersoid in FHYT-0.6 is reduced to 8.8 nm and the number density is greatly increased to 9.4 × 1023 m−3 compared with FTYT-0.6 (Fe-14Cr-4.5Al-2 W-0.35Ti-0.6Y2Ti2O7, wt%) and FTY-0.6 (Fe-14Cr-4.5Al-2 W-0.35Ti-0.6Y2O3, wt%). The tensile strength at room temperature of FHYT-0.6 is 1194 MPa, which is 24.1 and 14.1% higher than the FTY-0.6 and FTYT-0.6, respectively. Our work has proved that the mechanical properties of the alloy can be significantly improved by adding Y2Ti2O7 and HfH1.98 NPs, which provides a new idea for manufacturing high-performance ODS steels.

Effect of annealing treatment on microstructure of micro arc oxidation ceramic film on Al-Mg-Sc alloy

The effect of annealing treatment on the microstructure of micro arc oxidation (MAO) ceramic film prepared on Al-Mg-Sc alloy was studied. Results suggested that the difference of microstructure of Al-Mg-Sc alloy after various ageing treatment mainly focused on the evolution of dislocation density and the precipitation of β phase (Al3Mg2), and this difference induced the component transformation of surface oxide film from Al2O3 and MgO to MgO and MgAl2O4.Meanwhile, when the other parameters were kept constant, the relevant relations between the microstructure evolution and precipitation phase and the substrate induced the changes of electrical conductivity, then determining the characteristics of MAO ceramic film. Without sacrificing any strength, the optimal MAO ceramic film owning the higher thickness and lower porosity was obtained on Al-Mg-Sc alloy after annealing treatment at room temperature, and tightly bonded to the substrate, which provided a theoretical basis for subsequent research to improve the corrosion resistance of Al-Mg-Sc alloy.

Oxidative stability and physicochemical changes of dark chocolates with essential oils addition

This research aimed to evaluate the oxidative stability and rheological properties of dark chocolates with the addition of essential oils (EO) of Cymbopogon citratus, Pimpinella anisum, and Mintostachys mollis. For this purpose, before the inclusion in chocolates, the EO were chemically characterized to identify the most important volatile compounds. We added essential oils of P. anisum, C. citratus and M. mollis to dark chocolates (cocoa 70%) at doses of 10, 12 and 14 μL per 500 g, separately. These chocolates were evaluated for oxidative activity, hardness, microstructure, rheological and melting properties and antioxidant capacity. It was found that C. citratus EO (10 μL/500 g of chocolate) improve the oxidative stability of the chocolates at 90 days of storage at 25 °C (230 meq O2/kg), while higher concentrations promote lipid oxidation. The incorporation of essential oils improves the antioxidant capacity, likewise, it changes the rheological, thermal, and microstructural properties. Therefore, essential oils can improve the physicochemical characteristics of dark chocolates allowing greater stability in oxidative fat and thus increase the shelf life.

Effects of negative voltage on microstructure, electrical insulating, anti-corrosion, and thermal physical performance of plasma electrolytic oxidation coating on SiCp/Al composite

PEO coating microstructure on SiCp/Al composites under the influence of negative pulse are comparatively studied. Results show that the cross-sectional porosity is significantly reduced to 5.1%. The electrical insulation performance of coatings initially improves and then declines as the negative voltage rises from 0 V to 120 V, which is attributed that either an excessively low or excessively high negative voltage is insufficient to improve the internal defects of the coating. Among all the coatings, the coating obtained at +500 V/−80 V (i.e., N80) possesses better electrical insulation (with breakdown voltage of 736 ± 15 V, dielectric strength of 16.3 ± 0.3 V/μm, electrical resistivity of 1.51 × 1011 Ω∙cm), better dielectric performance, higher optical band gap value, making it appropriate for usage as electronic packaging or dielectric materials. The impedance modulus at low frequency of N80 coating is two to three times higher than that of N0, N40, and N120 coating, providing a long-term anti-corrosion ability for the substrate, during the 72-hour immersion. Additionally, the coatings display a high infrared emissivity in the waveband of 8–20 μm (>0.9) to achieve good radiation and heat dissipation effect. Thus, a reasonable negative voltage used in coating preparation does effectively diminish internal structural defects, enhancing coating performance.

Effect of α-Al2O3 Additive on the Surface Micro-Arc Oxidation Coating of Ti6Al4V Alloy.

α-Al2O3 nanoparticles can enter a micro-arc oxidation coating and participate in the coating-formation process through chemical reaction or physical-mechanical combination in the electrolyte. The prepared coating has high strength, good toughness and excellent wear and corrosion resistance. In this paper, 0, 1, 3 and 5 g/L of α-Al2O3 nanoparticles were added to a Na2SiO3-Na(PO4)6 electrolyte to study the effect on the microstructure and properties of a Ti6Al4V alloy micro-arc oxidation coating. The thickness, microscopic morphology, phase composition, roughness, microhardness, friction and wear properties and corrosion resistance were characterized using a thickness meter, scanning electron microscope, X-ray diffractometer, laser confocal microscope, microhardness tester and electrochemical workstation. The results show that surface quality, thickness, microhardness, friction and wear properties and corrosion resistance of the Ti6Al4V alloy micro-arc oxidation coating were improved by adding α-Al2O3 nanoparticles to the electrolyte. The nanoparticles enter the coatings by physical embedding and chemical reaction. The coatings' phase composition mainly includes Rutile-TiO2, Anatase-TiO2, α-Al2O3, Al2TiO5 and amorphous phase SiO2. Due to the filling effect of α-Al2O3, the thickness and hardness of the micro-arc oxidation coating increase, and the surface micropore aperture size decreases. The roughness decreases with the increase of α-Al2O3 additive concentration, while the friction wear performance and corrosion resistance are improved.

Effect of precursor particle size of NiO-YSZ electrodes in its physico-chemical and electrical conductivity properties for solid oxide electrochemical cells

Electrodes play an important role in the overall performance of solid oxide electrochemical cells (SOC), such as for fuel cell or electrolysis cell applications. Desirable properties of the electrode include good morphological features with high electronic and ionic conductivity. In this study, in order to investigate the effect of precursor particle size on the microstructure and conductivity properties of nickel oxide and yttria-stabilized zirconia (NiO-YSZ), precursors were prepared with different particle sizes using a planetary ball mill via varying the milling speed and milling time. From the particle size analysis (PSA) of the milled samples based on the studied milling parameters, it was observed that the milling time had a significant effect on the resulting ball-milled samples compared to the effect of the milling speed. However, upon sintering to obtain the NiO-YSZ electrode composites, the effect of milling speed, in terms of grain size, can be observed. From the XRD patterns, major peaks can be attributed to cubic phases of NiO and YSZ; however, traces of ZrO2 impurity peaks can be seen for the precursor sample with higher milling speed. SEM-EDX analyses support the more agglomerated morphology for the sample with longer milling duration and larger grains for those with higher milling speed. The obtained total bulk conductivities for the sample milled at 400 rpm (10 h) is about 1.27x10-1 S/cm, and for the 400 rpm (20 h) is about 1.77x10-1 S/cm with Ea of 0.88 eV and 0.27 eV, respectively.

High-temperature oxidation behavior of Cu64Zr36 metallic glass powders

Cu64Zr36 metallic glass powders were prepared via gas atomization. The high-temperature oxidation behavior of Cu64Zr36 metallic glass powders under the influence of internal factors (powder particle size) and external factors (oxidation temperature and oxidation time) was experimentally investigated by using XRD, DSC, TGA, SEM and TEM. The oxidation kinetics, oxide phase, surface morphology and microstructure of metallic glass powders were analyzed. The results show that Cu64Zr36 metallic glass powders form multiple layers of surface oxides after oxidation and the major components of the surface oxides are t-ZrO2, m-ZrO2, Cu2O and CuO. The oxidation kinetics follows a double-stage parabolic rate law. The oxidation process is dominated by the inward diffusion of O anions and the outward diffusion of Cu cations. Thermodynamic analysis shows that the Gibbs free energy change of the oxidation reaction increases with the decrease of particle size, leading to a more rapid and thorough oxidation of the powder with a smaller particle size.

Growth of 3D nanowall-like structures of FeVO4 by controlling reaction rate for effective CO2 reduction using UV-visible light

We report the synthesis of FeVO4 oxide microstructures with a large amount of polar surfaces using a single-step facile chemical method by growing of FeVO4 microstructures. It was found that nanowall-like morphology of FeVO4 transformed into nanorods and dense-like structure with nanosheets. The morphological analysis revealed that nanorods, nanowall-like, deformed nanowalls, and dense nanostructure shapes were formed on the substrate after 5 h, 10 h, 15 h, and 20 h of the reaction, respectively. The structural analysis confirms the formation of dual phases (volume fraction of FeVO4 = 82 % & Fe2O3 = 18 %) inside the grown structures. Photocatalytic CO2 reduction was measured under irradiation with UV–vis light using the structures as catalysts. The nanowall-like structure exhibited exceptional amount of CO (202 μmol g−1) as compared to particulate FeVO4 (9 μmol g−1) and other nanostructures (nanorods = 93 μmol g−1, deformed nanowalls = 82 μmol g−1 and dense nanostructure = 58 μmol g−1). The enhanced performance for 3D (three dimensional) nanowall-like structure was attributed to light scattering, oxygen vacancies, and increased optical absorbance as compared to other morphologies obtained. Along with the morphology, the formation of heterojunction aroused from the dual phase i.e. FeVO4 and Fe2O3 might have contributed in efficient charge separation. Finally, the development of FeVO4 semiconductor applications for CO2 reduction and its use as a new medium for carbon neutralization are made possible by the increase in active sites and electrical conductivity.

Effect of Y2O3 addition on the microstructure and mechanical properties of an Al1.8CoCrCu0.5FeNi BCC HEA

The present study investigated the influence of Y2O3 addition by mechanical alloying (MA) on the microstructure evolution of a BCC High Entropy Alloy (HEA). The characterisation and mechanical properties of the alloy were explored using X-ray diffraction, SEM, EBSD, and nano-indentation. The sintered Al1.8CoCrCu0.5FeNi HEA shows a microstructure formed by an ordered BCC phase (Al-rich) and a second disordered BCC (Cr-rich), while a minor FCC (Cu-rich) appears. These BCC phases show a wide morphology evolution from cuboidal and wave-like structures to irregular shapes. The minor FCC phase also adopts several morphologies as the MA is performed. The introduction of oxide reinforcements and microstructure refinement through mechanical alloying yields a change in phase quantification and grain structure. In accordance with the hardness and elastic modulus values from ordered/disordered BCC phases, the disordered BCC shows higher values than the ordered one. The grain size reduction as well as the solid solution strengthening from the microstructure evolution consequence of the MA are shown to be the main contributors to the increase in hardness and elastic modulus in the consolidated samples.

Superhydrophobic Surface Designing for Efficient Atmospheric Water Harvesting Aided by Intelligent Computer Vision.

Atmospheric water harvesting (AWH) is a possible solution for the current water crisis on the Earth, and the key process of AWH has been widely applied in commercial dehumidifiers. To improve the energy efficiency of the AWH process, applying a superhydrophobic surface to trigger coalescence-induced jumping could be a promising technique that has attracted extensive interest. While most previous studies focused on optimizing the geometric parameters such as nanoscale surface roughness (<1 μm) or microscale structures (10 μm to a few hundred μm range), which might enhance AWH, here, we report a simple and low-cost approach for superhydrophobic surface engineering, through alkaline oxidation of copper. The prepared medium-sized microflower structures (3-5 μm) by our method could fill the gap of the conventional nano- and microstructures, simultaneously act as the preferable nucleation sites and the promoter for the condensed droplet mobility including droplet coalescence and departure, and eventually benefit the entire AWH performances. Moreover, our AWH structure has been optimized with the aid of machine learning computer vision techniques for droplet dynamic analysis on a micrometer scale. Overall, the alkaline surface oxidation and medium-scale microstructures could provide excellent opportunities for superhydrophobic surfaces for future AWH.

Enhanced-Performance Asymmetric Supercapacitor Based on a Multidimensional Hierarchically Assembled NiMoO4/ZnMoO4/NF Electrode

The multidimensional microstructure of bimetallic oxides shows a synergistic effect and enhanced energy storage performance compared to their monometallic oxides with a single microstructure. One-dimensional (1D) NiMoO4/ZnMoO4 nanorods self-assembled from two-dimensional (2D) ultrathin NiMoO4 nanosheets loaded with zero-dimensional (0D) ZnMoO4 nanoparticles were evenly grown on the surface of Ni foam (NZMO/NF) by combining hydrothermal method and heat treatment. The NZMO/NF electrode for supercapacitors shows a high specific capacity of 2064.07 F g–1 at 2 mA cm–2 and an excellent capacity maintenance of 99% after 10 000 cycles. Such exceptional performances can be boiled down to its distinctive structural design of multidimensional hierarchy. In addition, the asymmetric pseudocapacitor assembled with NZMO/NF and AC exhibits not only a maximum energy density of 47.4 Wh kg–1 but also a relatively good cyclability (91.74% capacitance retention after 12 000 cycles), demonstrating a promising application as supercapacitor electrode materials.

A novel characterization method for oxidation products of TiBw reinforced TA15 matrix composite

The manuscript presented the application of in-situ TAG (high-temperature oxidation analyzer) and TG-MS-FTIR (Thermogravimetry, Mass spectrometer and Fourier transform infrared spectrometer) techniques for further characterization of TiBw oxidation products in TA15 matrix composite. The volatile ingredient and chemical bonding measurement results revealed the existence of B2O3 and H3BO3, which generated during the oxidation process of TiBw/TA15 composite. Compared with TiCp/TA15 composite, the cyclic oxidation kinetic and microstructure observation results indicated that TiBw/TA15 composite had superior oxidation resistance, which resulting from well-designed network structure.

Synthesis and microstructure of BaMnO3 oxide obtained from coordination precursor

We report here on a new coordination heterometallic [MnII–BaII] polymer with 2,3-pyridinedicarboxylic bridging ligand and its application as single-source for access to perovskite oxide BaMnO3. The structure and magnetic properties of both coordination compound and the obtained oxide have been investigated. The tridentate and pentadentate 2,3-pyridinedicarboxylic ligands bridge MnII and BaII heteroatoms forming a 3D coordination polymer. The XRD and EDX results confirm the formation of the hexagonal phase of pure BaMnO3 perovskite.The magnetic and EPR spectroscopy measurements of 2 show characteristic structural and magnetic transitions reported for 2H–BaMnO3.

Combined effect of Ru on the oxidation behavior and microstructure stability of a single crystal superalloy

The isothermal oxidation behavior and the microstructure stability was studied at 900 °C, 1000 °C and 1100 °C of the two alloys with and without Ru. The curves of oxidation weight gain show that the oxidation resistance decreases sharply with the addition of Ru. A multi-layered scale formed on the alloy surface, and it generally consisted of an external layer of NiO, an intermediate layer of spinel and an Al2O3 inner layer. The oxidation rate at 1100 °C is significantly higher than that at the other two temperatures due to more serious cracking and peeling of oxide scale. Compared with Ru-free alloy, the oxide layer of Ru-containing alloy is thicker and the oxide layer spallation more seriously. The oxide of Ru was found in the spinel layer and the vaporization of the oxide makes the scale spallation. Surprisingly, a large number of TCP phases were found in alloy matrix, especially in 2Ru alloy. This indicates that poor oxidation resistance will lead to a decline in microstructure stability.

Microstructure and properties of graphene oxide reinforced copper-matrix composite foils fabricated by ultrasonic assisted electrodeposition

In this paper, graphene oxide (GO)/Cu composite (GO/Cu) foils with high thermal and mechanical properties were prepared by ultrasonic-assisted direct current electrodeposition. The effect of ultrasonic power and graphene concentration on the microstructure and properties of the composite foils was systematically investigated. It was found that the average grain size can be refined by both the addition of GO reinforcement and ultrasonic treatment. Under the optimized preparation condition with 120 W ultrasonic power and GO concentration of 0.8 g/L GO in plating solution, the average grain size was about 0.26 μm and illustrated strong crystallographic orientation of (220). In addition, the GO content in the composites was increased from 0.67 wt% without ultrasonic treatment to 1.72 wt%, and it was uniformly dispersed in the composite foil with ultrasonic effect. Compared with pure copper foil, the hardness value of the GO/Cu composite foil nearly doubled to 74.6 HV0.1, the average friction coefficient was decreased from 0.87 to 0.72 and the tensile strength of the composite foil was improved to 239 MPa with an elongation of 17%. Meanwhile, the thermal conductivity with optimized condition increased 39.8% to 556.57 W m−1 K−1. The improved mechanical and thermal properties of the GO/Cu composite foil were mainly ascribed to the grain refinement, change of preferred orientation and the presence of reduced GO reinforcement as a network in the composite foil.