Microstructure Oxidation Research Articles

Influence of micro-arc oxidation on the microstructure and dielectric properties of anodic aluminum oxide

To improve the dielectric performance of the anodic alumina film used in aluminum electrolytic capacitors, this study comparatively investigated the microstructure and dielectric properties of anodic aluminum oxide obtained through micro-arc oxidation (MAO) and conventional anodic oxidation (CAO). It is found that from the perspective of microstructure, the internal structure of the MAO treated oxide film has more and larger pores than that of CAO. This was attributed to the generation and overflow of numerous oxygen bubbles from within the oxide film at the locations where plasma sparks occurred during the process, thus forming larger pores. Regarding dielectric properties, the leakage current of the oxide film after MAO treatment was significantly reduced compared to CAO, with reductions of 58%, 56%, 64%, and 74% for the tested electrolytes Y1–Y4, respectively.

Is Low Polydispersity Always Beneficial? Exploring the Impact of Size Polydispersity on the Microstructure and Rheological Properties of Graphene Oxide.

Graphene oxide (GO) is a promising material widely utilized in advanced materials engineering, such as in the development of soft robotics, sensors, and flexible devices. Considering that GOs are often processed using solution-based methods, a comprehensive understanding of the fundamental characteristics of GO in dispersion states becomes crucial given their significant influence on the ultimate properties of the device. GOs inherently exhibit polydispersity in solution, which plays a critical role in determining the mechanical behavior and flowability. However, research in the domain of 2D colloids concerning the effects of GO's polydispersity on its rheological properties and microstructure is relatively scant. Consequently, gaining a comprehensive understanding of how GO's polydispersity affects these critical aspects remains a pressing concern. In this study, we aim to investigate the dispersions and structure of GOs and clarify the effect of polydispersity on the rheological properties and yielding behavior. Using a rheometer, polarized optical microscopy, and small-angle X-ray scattering, we found that higher polydispersity in the same average size leads to overall improved rheological properties and higher flowability during yielding. Thus, our study can be beneficial in the employment of polydispersity in the processing of GO such as 3D printing and fiber spinning.

Retraction: Effects of thermal aging atmospheres on oxidation activity, element composition and microstructure of diesel soot particles.

[This retracts the article DOI: 10.1039/D3RA05340G.].

Oxidation behaviour of Ti-V-Cr-Nb-Ta and Al-Ti-V-Cr-Ta refractory high entropy alloys: Effects of Nb and Al substitutions

Refractory high entropy alloys (RHEAs) are candidate materials for nuclear and other high-temperature applications, due to their high-temperature strength, good irradiation resistance, and high melting temperatures. However, a significant issue with current RHEAs is that those exhibiting good mechanical properties tend to show poor oxidation resistance, and vice versa. In this paper, the oxidation kinetics of four RHEAs (20Ti-20V-20Cr-20Nb-20Ta, 25Ti-25V-5Cr-20Nb-25Ta, 20Al-20Ti-20V-20Cr-20Ta, and 14Al-24Ti-24V-14Cr-24Ta alloys) were investigated in an air atmosphere at 1000 °C. As-prepared and oxidised samples were characterised by a combination of state-of-the-art microscopy techniques. By replacing Nb with Al, the two Al-containing alloys were observed to form a less porous oxide microstructure, showing significant improvement in their oxidation resistance. As a result of oxygen/nitrogen ingress during oxidation and associated phase-segregation at high temperatures, the hardness of the underlying metal matrix of the RHEAs increased by approximately 5 GPa.

Microstructure characterization of plasma electrolytic oxidation coating on Hf-Nb-Ta-Zr high entropy alloy

The morphology, composition, and microstructure of plasma electrolytic oxidation (PEO) coating on Hf-Nb-Ta-Zr high entropy alloy (HEA) were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, glow discharge optical emission spectroscopy (GDOES) and transmission electron microscopy (TEM). The formation mechanism of PEO coating was analyzed. It was found that a dense PEO coating of ∼4 μm thick on the HEA surface was formed, which consisted of tetragonal and monoclinic ZrO2 phases, tetragonal and monoclinic HfO2 phases, Nb2O5 and Ta2O5 phases. The PEO coating from the alloy substrate to the surface contained five distinctive layers: amorphous barrier layer, nanocrystalline layer, columnar grain layer, amorphous outer layer, and top porous layer. Their formation was ascribed to the different cooling rates of the melt in the different depths of the discharge channel across the coating. Meanwhile, the formation of an amorphous barrier layer near the HEA substrate was also related to the mutual migration and diffusion of Hf4+, Nb5+, Ta5+, Zr4+ and O2− besides the rapid cooling of melt in the bottom of the discharge channel. The columnar grains of ∼70 nm wide were mainly composed of the monoclinic ZrO2 and monoclinic HfO2 phases, but both the amorphous layers enrich the Ta and Nb elements. It was believed that the high-content Ta and Nb in the HEA enhanced the formation of the amorphous layers.

The effect of heating rate on microstructure and electrochemical performance of nickel-rich layered oxides cathode materials

Nickel-rich layered oxides have attracted significant attention as promising cathode materials for lithium-ion batteries due to their high specific capacity, rate capability, and relatively low cost. However, the material still faces challenges such as harsh synthesis conditions, easy cation mixing and large residual alkali on the surface, severely limiting its practical applications. To overcome these drawbacks, this study successfully synthesized a series of LiNi0.8Co0.1Mn0.1O2 (NCM) cathode materials with different heating rates. The results indicate that appropriately reducing the heating rate can improve the cycling performance of the material and reduce cation mixing and surface residual alkalinity. Specifically, among the four samples, the LiNi0.8Co0.1Mn0.1O2 sample (NCM-2 °C min-1) exhibites a lower Li⁺/Ni²⁺ mixed arrangement and fewer surface residual alkalis, demonstrating good cycling performance and rate capability. The NCM-2 °C min-1 sample provides an excellent initial discharge capacity of 210.4 mAh g⁻¹ under 0.1 C conditions, and it achieves the highest capacity retention rate (85.9%) after 100 cycles at 1 C, while the capacity retention rates for NCM-1 °C min-1, NCM-3 °C min-1, and NCM-4 °C min-1 are 75.4%, 75.2%, and 71.2%, respectively. NCM-2 °C min-1 sample also showed excellent rate performance, especially at high rates. The discharge capacity remains at 151.6 mAh g-1 at 10 C, which is much higher than that of other samples (149.3 mAh g-1 for NCM-1 °C min-1, 123.5 mAh g-1 for NCM-3 °C min-1, and 120.6 mAh g-1 for NCM-4 °C min-1). The research of synthesis technology has important guiding significance for the synthesis of high-stability high-nickel layered oxide materials.

(Invited) IrOx Nanoparticle Catalysts on a Unique Microstructure of Doped Tin Oxide to Dramatically Boost the Oxygen Evolution Reaction Activity for PEM Water Electrolysis

Proton exchange membrane water electrolyzers (PEM WEs) has a potential to produce high-purity green hydrogen. PEMWEs have been commercialized with the use of high loadings of the noble metal Ir-based anode catalyst for the oxygen evolution reaction (OER). To lower the Ir loading amount, it is critically important to develop efficient catalysts with increased Ir utilization and higher OER activity. One-dimensional Ir oxide nanorod/nanoparticles catalysts supported on doped SnO2 with a unique microstructure were invented to show their exceptionally high activity in the OER catalysis, with the Ir-mass specific activity being 10 times higher than that of commercial IrOx catalyst at 1.5 V vs. RHE.[1] The experiment also found that the OER activation energy was greatly lower than that of commercial Ir oxide. The interaction between Ir oxide nanorod/nanoparticles and doped SnO2 support occurs a lower degree of Ir oxidation which allows the surface terminal oxygens to be closer together while allowing facile desorption of nonreactive oxygenated species. The electronic state of Ir oxide nanorod/nanoparticles catalysts could play an important role in facilitating the crucial step of the OER, thereby enhancing the OER activity. These priorities of the catalysts would promise the reduction of the Ir usage in PEMWEs.Reference[1] G. Shi, T. Tano, D.A. Tryk, T. Uchiyama, A. Iiyama, M. Uchida, K. Terao, M. Yamaguchi, K. Tamoto, Y. Uchimoto and K. Kakinuma, ACS Catalysis, 13 (2023) 12299. Figure 1

Graphene Oxide Surface Modification of Reverse Osmosis (RO) Membrane via Langmuir-Blodgett Technique: Balancing Performance and Antifouling Properties.

The reverse osmosis water treatment process is prone to fouling issues, prompting the exploration of various membrane modification techniques to address this challenge. The primary objective of this study was to develop a precise method for modifying the surface of reverse osmosis membranes to enhance their antifouling properties. The Langmuir-Blodgett technique was employed to transfer aminated graphene oxide films assembled at the air-liquid interface, under specific surface pressure conditions, to the polyamide surface with pre-activated carboxylic groups. The microstructure and distribution of graphene oxide along the modified membrane were characterized using SEM, AFM, and Raman mapping techniques. Modification carried out at the optimal surface pressure value improved the membrane hydrophilicity and reduced the surface roughness, thereby enhancing the antifouling properties against colloidal fouling. The flux recovery ratio after modification increased from 65% to 87%, maintaining high permeability. The modified membranes exhibited superior performance compared to the unmodified membranes during long-term fouling tests. This membrane modification technique can be easily scaled using the roll-to-roll approach and requires minimal consumption of the modifier used.

Oxidation mechanism and microstructure evolution of invar alloy with high temperature annealing process

The high temperature oxidation behavior of Fe–36Ni Invar alloy in the forged billet stage and hot rolled rod stage in the compressed air atmosphere has been systematically studied. The results show that the oxide layer can be divided into the external oxide layer composed of Fe2O3, Fe3O4 and NiO, and the inner transition oxide layer composed of FeO, Fe2O3, Fe3O4 and NiO. In addition, hot rolled rod samples treated by solution and rolling have higher oxidation resistance. The mechanism of O diffusion during oxidation is analyzed, and it is found that the O atom adsorbed on the surface of the substrate diffuses into the grain along the grain boundary. The grain boundary is the optimal path for O diffusion to the interior of the material, which results in the degree of intergranular oxidation of the alloy being greater than the degree of intragranular oxidation. In summary, the oxidation resistance of Invar alloy can be improved by proper solution treatment and avoiding the formation of grain boundary cracks during production.

Microstructure, mechanical properties and interfacial features of graphene oxide reinforced 7075 composites fabricated by ultrasonic assisted casting

Graphene oxide reinforced 7075 (GO/7075) composites were successfully prepared via ultrasonic assisted casting. In this study, the microstructure, mechanical properties and interfacial structure of GO/7075 composites with varying GO contents were investigated. The experimental results showed that GO could refine grain size and produce many dislocations at the GO/Al interface, and was well bonded with Al matrix. Meanwhile, a few rod-like Al4C3 phases were observed at the active prism planes of GO in the composite. When the content of GO reached 1.0 wt%, the optimal mechanical properties of GO/7075 composites were obtained. The yield strength and ultimate tensile strength of 1.0 wt% GO/7075 composites were 212.3 MPa and 285.6 MPa, which were 61.8 % and 41.1 % higher than those of 7075 alloy, respectively. The thermal mismatch strengthening and load transfer strengthening were the main strengthening mechanisms. Moreover, in order to control the interfacial reaction between GO and Al matrix, the thermodynamic/kinetic condition and growth mechanism for the formation of Al4C3 were analyzed in details.

Sol-gel derived ZnO film as a gas sensor: Influence of UV processing versus a thermal annealing

While preparing oxide layers as gas sensors by a sol-gel approach, a high-temperature annealing makes a challenge to apply in numerous applications like flexible electronics with a heavy influence on the oxide microstructure. Therefore, its replacing by UV irradiation combined with a mild heating as “photo-annealing” paves the way to develop soft protocols when designing oxide-based gas sensors bearing a fine nanocrystallinity. Herein, we consider hierarchical sol-gel derived ZnO films which were a subject of conventional annealing and photoannealing to compare their gas-sensor performance when exposed to alcohol vapors. It is found that films obtained by photoannealing have an X-ray amorphous character, in contrast to ones being thermally annealed; although, the hierarchical organization of both samples revealed by SEM is almost identical. The DFTB modeling performed for ZnO crystal exposed to alcohol molecules and water has indicated the chemiresistive effect to be enhanced with a molecular weight of analytes. These observations were validated in experiment with sol-gel ZnO layers which exhibited an alcohol response in sub-ppm concentration range down to 10 ppb. To selectively compare the impact of various alcohols, we successfully applied a linear-discriminant analysis to the vector signal of the on-chip multisensor array.

Investigation of zinc oxide doped microstructures with cobalt via electrochemical deposition

The present paper reports electrochemical elaboration of zinc oxide microstructure doped with cobalt (CZO) at various [Co2+]/[Zn2+] (Co/Zn) concentration ratios onto ITO substrates at a pH of 6.5. All Mott-Schottky plots of electrochemical analysis showed that all electrodeposited CZO samples exhibited n-type semiconducting behaviours. XRD spectra revealed that all electrodeposited CZO samples crystallized in the typical hexagonal wurtzite structure with a preferential orientation along the (100) plane with descending crystalline size versus increasing cobalt dopants amount. Reviewing SEM images, notable changes were found on granular morphologies of CZO samples because of doping changing. EDX showed proportionality between the increase of final Co/Zn ratio in the CZO samples and the increase of starting Co/Zn concentration ratio within the initial depositing solutions. UV–Vis measurements indicated that transmittances of most CZO samples were above 80 % in the visible range and their optical band gaps were high and limited between 3.60 and 3.64 eV.

Pyramid-like zinc oxide microstructures as humidity sensor

Pyramid-like zinc oxide microstructures as humidity sensor

Effects of element addition on the microstructure and thermophysical properties of seven-principal cations rare-earth high-entropy oxide

Three new rare-earth high-entropy oxides with compositions of (Y1/7La1/7Nd1/7Sm1/7Gd1/7Yb1/7Lu1/7)2O3 (7HEO), (Y1/8La1/8Nd1/8Sm1/8Gd1/8Yb1/8Lu1/8Ce1/8)2O3 (8HEO) and (Y1/10La1/10Nd1/10Sm1/10Gd1/10Yb1/10Lu1/10Ce1/10Zr1/10Hf1/10)2O3 (10HEO) were prepared using a solid-state reaction method combined with conventional sintering at 1600 °C for 10 h 7HEO has a monoclinic structure. The addition of Ce into 7HEO not only leads to the phase transformation from monoclinic to bixbyite structure, but also contributes to the grain refinement. When the three elements of Ce, Zr and Hf are added into 7HEO, a second fluorite-structured phase forms and further promotes the grain refinement. 10HEO and 8HEO have a higher thermal conductivity compared with 7HEO in 25–600 °C. When the temperature reaches 900 °C, the thermal conductivity of 8HEO is lower than that of 7HEO. The addition of Ce or Ce/Zr/Hf into 7HEO causes the weakening of the bond strength and the increase of the bond length of cation-O2- in the samples, which in turn increases the thermal expansion coefficient. Moreover, 7HEO possesses a better oxygen barrier property compared with 8HEO and 10HEO. The hardness and Young's modulus of 7HEO are lower than those of 8HEO and 10HEO.

In situ steam oxidation of nickel phosphide/carbon composite nanofibers as anode materials for lithium-ion batteries

The synthesis of self-standing nickel phosphide/carbon (NixP/C) composite nanofibers is accomplished through a one-pot electrospinning and in situ steam oxidation after the carbothermal reduction process. Control over the levels of in situ steam oxidizers in the forms of crystal water and nitrates in the precursor fibers is achieved by systematically adjusting the drying temperature before the high-temperature heat treatment. This led to structural modifications in the final products analyzed through comprehensive characterizations. Mechanistic insights into the in situ steam oxidation process are provided, emphasizing its potential in optimizing electrode materials. Electrochemical assessments reveal significantly improved performance in the sample prepared from the media with optimal content of oxidizers, attributed to a tailored surface oxide layer, electronic configuration, and microstructure, enabling enhanced reaction kinetics and minimizing volume expansion. This results in exceptional cycling stability and notable capacity retention during prolonged charge-discharge cycles. Thus, NixP/C achieves the highest initial charge capacity of 719.5 mAh g−1 with an initial Coulombic efficiency of 61% and maintains a high capacity of 590.7 mAh g−1 after 100 cycles at a current density of 0.1 A g−1.

Remote‐Controllable Lateral Electropolymerization of Conducting Polymers via Dual‐Electrode ADC‐Bipolar Electrochemistry

AbstractThe electrolysis of aromatic molecules is a useful method for the synthesis and deposition of conducting polymers. However, this method cannot be applied to diverse large‐area electronic devices because films grow vertically on the surface of an electrically connected working electrode. Herein, the remote‐controllable lateral electropolymerization of 3,4‐ethylenedioxythiophene using direct‐current voltage superimposed alternating‐current voltage (ADC)‐bipolar electrochemistry is reported. The use of shape‐designed dual bipolar electrodes and systematic optimization of the process parameters led to the fabrication of uniform poly(3,4‐ethylenedioxythiophene) (PEDOT) films on 2‐inch glass wafers and flexible plastic substrates. The oxidation levels and microstructures of ADC‐electropolymerized PEDOTs with various supporting electrolytes are investigated and correlated with their thermoelectric properties. A soft thermocouple and resistive‐type gas sensor based on an ADC‐electrodeposited PEDOT are demonstrated to monitor cerebral temperature in a brain replica and to sense nitrogen dioxide gas, respectively.

3D Nanoprinting of Heterogeneous Metal Oxides with High Shape Fidelity.

3D nanoprinting can significantly enhance the performance of sensors, batteries, optoelectronic/microelectronic devices, etc. However, current 3D nanoprinting methods for metal oxides are suffering from three key issues including limited material applicability, serious shape distortion, and the difficulty of heterogeneous integration. This paper discovers a mechanism in which imidazole and acrylic acid synergistically coordinate with metal ions in water. Using the mechanism, this work develops a series of metal ion synergistic coordination water-soluble (MISCWS) resins for 3D nanoprinting of various metal oxides, including MnO2, Cr2O3, Co3O4, and ZnO, as well as heterogeneous structures of MnO2/NiO, Cr2O3/Al2O3, and ZnO/MgO. Besides, the synergistic coordination effect results in a 2.54-fold increase in inorganic mass fraction within the polymer, compared with previous works, which effectively mitigates the shape distortion of metal oxide microstructures. Based on this method, this work also demonstrates a 3D ZnO microsensor with a high sensitivity (1.113 million at 200ppm NO2), surpassing the conventional 2D ZnO sensors by tenfold. The method yields high-fidelity 3D structures of heterogeneous metal oxides with nanoscale resolution, paving the way for applications such as sensing, micro-optics, energy storage, and microsystems.

Multiphase manganese-based layered oxide for sodium-ion batteries: structural change and phase transition

Sodium-ion batteries (SIBs) are recognized as a leading option for energy storage systems, attributed to their environmental friendliness, natural abundance of sodium, and uncomplicated design. Cathode materials are crucial in defining the structural integrity and functional efficacy of SIBs. Recent studies have extensively focused on manganese (Mn)-based layered oxides, primarily due to their substantial specific capacity, cost-effectiveness, non-toxic nature, and ecological compatibility. Additionally, these materials offer a versatile voltage range and diverse configurational possibilities. However, the complex phase transition during a circular process affects its electrochemical performance. Herein, we set the multiphase Mn-based layered oxides as the research target and take the relationship between the structure and phase transition of these materials as the starting point, aiming to clarify the mechanism between the microstructure and phase transition of multiphase layered oxides. Meanwhile, the structure-activity relationship between structural changes and electrochemical performance of Mn-based layered oxides is revealed. Various modification methods for multiphase Mn-based layered oxides are summarized. As a result, a reasonable structural design is proposed for producing high-performance SIBs based on these oxides.

Exploring microstructures of metal-doped oxides via simulated Raman spectrum

Solid solution of metal-doped oxide has been widely used in material industry and catalysis process. Its performance is highly correlated with the distribution of doped ions. Due to the complex distribution of doped ions in solid solution and its variation with temperatures, to obtain the microstructures of metal-doped ions in solid solution remains a substantial challenge. Taken Ce1-xZrxO2 as a model, the global structure searching, structures proportion with temperature determined by Boltzmann distribution, and the weighted simulation Raman spectra were integrated to explore the microstructures of metal-doped solid solution oxides. It was further verified by application into rutile and anatase TiO2 mixture, indicating that the present method is feasible to deduce the microstructure of metal composite oxides. We anticipate that it provides a powerful solution to explore microstructures of solid solution and complex metal oxides.

On corrosion of zirconium alloy in dissolved oxygen water: The role of Cu addition

It is significantly important to improve the corrosion resistance of Zr-Sn-Nb alloys in dissolved oxygen (DO) high temperature water by compositional modification. Here, the effect of Cu addition on the corrosion behaviors of Zr-0.5Sn-0.2Nb-0.4Fe-0.2Cr alloy was studied by using an autoclave circulating water loop at 360 °C/20 MPa up to 250 days. The oxide microstructures were characterized by a combination of SEM, TEM, STEM-EELS and PED. The results showed that compared with 0Cu alloy and 0.07Cu alloy, 0.13Cu alloy shows better corrosion resistance and its final weight gain after 250 days exposure is even lower than that of commercial Zr-4 alloy. The oxides for 0.07Cu and 0.13Cu alloys show more ordered crystals, thinner oxide and less lateral cracks, and the columnar grains show a stronger {10–3} texture, compared to Cu-free counterpart. The t-Zr2Cu SPPs have oxidized in the oxygen-rich layer below the O/M interface. The Cu ions tend to diffuse towards the grain boundary of dense columnar grains and maybe strengthen the grain boundaries, avoiding the defect generation under intrinsic stress in the oxide.