Morphology Of Oxide Research Articles

The origin of different morphology of internal oxide precipitates in ferritic and austenitic steels

The internal oxide precipitates were supposed to be spherical in Wagner's original theory, while the following research demonstrated that this assumption is an exception rather than the truth, which caused deviations in the application of this theory. In this study, the internal oxide precipitates have a needle-like and a near-spherical morphology in a Fe-9Cr ferritic and a Fe-17Cr-9Ni austenitic steels after exposure to 600 °C deaerated steam for 600 h, respectively. The nano-to-atomic scale characterization shows that the morphology of the internal oxide precipitates is controlled by the structure of the interfaces between the metal matrix and the internal oxide, while the interface structure is mainly affected by the crystallographic structure of the two phases and their orientation relationship. In addition, the internal oxide precipitation-induced volume expansion and the outward Fe diffusion-induced volume shrink occur simultaneously during the oxidation process. The stress status in the internal oxidation zone (IOZ) is the competing result of the two factors, which could dynamically affect the high-temperature oxidation. The results obtained in this study suggest that there is potential to control the distribution, morphology, and interface structure of the internal oxide precipitates by selecting appropriate base metal and internal oxide-forming element, in order to obtain better high-temperature oxidation-resistant materials.

Chemical looping conversion of methane via Fe2O3-LaFeO3 calcined from LaFe-MOF precursor

The effective utilization of natural gas resources is a promising option for the implementation of the “dual carbon” strategy. However, the capture of carbon dioxide with relatively lower concentration after the combustion of natural gas is the crucial step. Fortunately, the lattice oxygen is used for chemical cycle conversion of methane to overcome the shortcomings mentioned above. A method was proposed to synthesize perovskite for methane cycle conversion using metal organic framework as a precursor. Morphology and pore structure of Fe2O3-LaFeO3 composite oxides were regulated by precursor synthesis conditions and calcination process. Moreover, the chemical looping conversion performance of methane was evaluated. The results showed that the pure phase precursor of La[Fe(CN)6]·5H2O was synthesized with the specific surface area of 23.91 m2·g−1 under the crystallization of 10 h and the pH value of 10.5. Fe2O3-LaFeO3 was obtained by controlled calcination of La[Fe(CN)6]·5H2O and Fe2O3 with variable mass ratio. The selectivity of CO2 can reach more than 99% under the optimal parameters of methane chemical looping conversion: m(Fe2O3):m(LaFeO3) = 2:1, the reaction temperature is 900 °C, the lattice oxygen conversion is less than 40%. Fe2O3-LaFeO3 still has good phase and structure stability after five redox reaction and regeneration cycles.

Effect of applied potential on the optical and electrical properties of Cu2CoO3

The effect of the applied potential on the crystallography, morphology, optical, and electrical properties of copper-cobalt oxide (Cu2CoO3) co-electrodeposited on ITO (Indium Tin Oxide) substrate has been studied. The electrochemical behavior of Cu2CoO3 using cyclic voltammetry showed that the co-electrodeposition of Cu2CoO3 occurred at a negative potential of - 0.70 V versus SCE, following a quasi-reversible reaction controlled by the diffusion process. Chronoamperometry (CA) revealed that the nucleation and growth mechanism of Cu2CoO3 follows the instantaneous three-dimensional process according to Scharifker and Hill model. X-ray diffraction (XRD) analysis indicated that the resulting layers at different applied potentials exhibited an orthorhombic structure with a preferred orientation of the crystallites (011) plan. The morphology of the surface changes with potential applied. Furthermore, the optical properties of the copper and cobalt oxide films were investigated using UV-visible spectroscopy; showing that the band gap energy for all the materials increases when the applied potential decreases. The Cu2CoO3 layers obtained are p-type semiconductors. The acceptor density (NA) increases with decreasing applied potential.

Ultrafast synthesis of K cations inserted birnessite-type MnO2 electrode in ethanolamine based deep eutectic solvents with improved supercapacitor performance

Specific capacitance of energy storage devices depends on the electrode materials and various manganese oxides have recently been developed and attracted much attention due to their superior electrochemical performance with high capacitance, energy density, and cyclic stability. Herein, K cations inserted birnessite-type MnO2 was ultrafast synthesized by a facile room temperature wetchemical method under ethanolamine based deep eutectic solvents (DESs), where monoethanolamine (MEA), diethanolamine, and triethanolamine were used as hydrogen bond donor (HBD) and choline chloride (ChCl) was acted as hydrogen bond acceptor. The results indicate that K+ can be pre-inserted into the layers of birnessite-type MnO2 during the preparation process by the addition of ethanolamine based DESs. The morphology, crystallinity, and porosity of manganese oxides can be effectively adjusted by changed types of HBD in the DESs. The mesoporous granular K+ pre-inserted birnessite-type MnO2 prepared in [ChCl:2MEA] (MnOx-CM) with a high specific surface area of 220 m2/g and electrical conductivity exhibits the best electrochemical performance with high specific capacitance of 290 F/g at the current density of 0.1 A/g. The pre-inserted K+ ions participating in the redox process of birnessite-type MnO2 can efficiently improve the electrochemical energy storage and cycling stability. Thus, the MnOx-CM can still maintain 92.5% capacity retention after 8000 cycles.

Pressure-Controlled Layer-by-Layer to Continuous Oxidation of ZrS2(001) Surface

Understanding oxidation mechanisms of layered semiconducting transition-metal dichalcogenides (TMDC) is important not only for controlling native oxide formation but also for synthesis of oxide and oxysulfide products. Here, reactive molecular dynamics simulations show that oxygen partial pressure controls not only the ZrS2 oxidation rate but also the oxide morphology and quality. We find a transition from layer-by-layer oxidation to amorphous-oxide-mediated continuous oxidation as the oxidation progresses, where different pressures selectively expose different oxidation stages within a given time window. While the kinetics of the fast continuous oxidation stage is well described by the conventional Deal-Grove model, the layer-by-layer oxidation stage is dictated by reactive bond-switching mechanisms. This work provides atomistic details and a potential foundation for rational pressure-controlled oxidation of TMDC materials.

Bio-assembled MgO-coated tea waste biochar efficiently decontaminates phosphate from water and kitchen waste fermentation liquid

Crystal morphology of metal oxides in engineered metal-biochar composites governs the removal of phosphorus (P) from aqueous solutions. Up to our best knowledge, preparation of bio-assembled MgO-coated biochar and its application for the removal of P from solutions and kitchen waste fermentation liquids have not yet been studied. Therefore, in this study, a needle-like MgO particle coated tea waste biochar composite (MTC) was prepared through a novel biological assembly and template elimination process. The produced MTC was used as an adsorbent for removing P from a synthetic solution and real kitchen waste fermentation liquid. The maximum P sorption capacities of the MTC, deduced from the Langmuir model, were 58.80 mg g−1 from the solution at pH 7 and 192.8 mg g−1 from the fermentation liquid at pH 9. The increase of ionic strength (0–0.1 mol L−1 NaNO3) reduced P removal efficiency from 98.53% to 93.01% in the synthetic solution but had no significant impact on P removal from the fermentation liquid. Precipitation of MgHPO4 and Mg(H2PO4)2 (76.5%), ligand exchange (18.0%), and electrostatic attraction (5.5%) were the potential mechanisms for P sorption from the synthetic solution, while struvite formation (57.6%) and ligand exchange (42.2%) governed the sorption of P from the kitchen waste fermentation liquid. Compared to previously reported MgO-biochar composites, MTC had a lower P sorption capacity in phosphate solution but a higher P sorption capacity in fermentation liquid. Therefore, the studied MTC could be used as an effective candidate for the removal of P from aqueous environments, and especially from the fermentation liquids. In the future, it will be necessary to systematically compare the performance of metal-biochar composites with different metal oxide crystal morphology for P removal from different types of wastewater.Graphical

Green and sustainable recycling of MnCo2O4/Mn3O4/Li(Mn0.75Ni0.25)2O4 mixed oxide from of spent Li-ion and Zn–MnO2 batteries and evaluation of its photocatalytic properties

In this study, MnCo2O4/Mn3O4/Li(Mn0.75Ni0.25)2O4 spinel-like mixed oxide was synthesized by green recycling of spent Li-ion and Zn–MnO2 batteries. The first step consisted of leaching the cathode of Li-ion batteries and the cathode of Zn–MnO2 batteries with citric acid and glucose. Then, Li-ion cathode leachate was mixed with Zn–MnO2 cathode leachate. Leachate mixture received the addition of oxalic acid, yielding oxalate precursor material, which was calcined at 450 °C for 3 h to afford MnCo2O4/Mn3O4/Li(Mn0.75Ni0.25)2O4. Mixed oxide structure, composition, and morphology were determined by X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP OES), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic properties of mixed oxide were evaluated in the decolorization of a model dye (methylene blue) under UV radiation. System using UV radiation + H2O2 + catalyst reached decolorization efficiency >93% in 120 min of reaction. This study provides a possible solution for two environmental liabilities (batteries and wastewater), and the results reported here are of scientific, economic, environmental, and social interest.

Insight into the origin of oxidation behaviors of carbon fiber reinforced carbon aerogel composites with different porous skeletons

Carbon fiber reinforced carbon aerogel (C/CA) composites are promising lightweight insulators for the thermal protection of aerospace vehicles at ultra-high temperatures. However, it is seriously lack of understanding their oxidation behaviors despite its importance for the applications in oxygen-containing environments. Herein, we fabricate two kinds of C/CA using resorcinol-formaldehyde (RF) and phenolic resin (PR) as precursors and investigate the effects of original and heat-treated skeletons on their oxidation behaviors. The results show that the composites derived from RF have the lower mass losses at 600−800 °C after 35-min oxidation with an apparent activation energy of 50.80 kJ mol−1 than the counterparts derived from PR with the value of 40.14 kJ mol−1. It can be explained by the existence of more impurities and macropores as well as the larger residual tensile stress in C/CA from PR. The temperature-dependent oxidation morphology evolution is similar to the time-dependent evolution, changing from the gradually enlarged pores, to the formed grooves and even island-like structure. However, the composites from RF have reversely the higher mass losses when they were heat treated at 1600 and 2300 °C, which is attributed to its relatively lower crystallinity and larger mesopore surface area. The significant increase in crystallinity and decrease in impurities and specific surface area are the main explanations for the remarkably lower oxidation rates after heat treatment. The oxidation behaviors of C/CA are jointly governed by the carbon-oxygen reaction and diffusion within pores; and the residual stress exerts a role to different extent.

Features of technological synthesis and properties of ZnO-Cd based materials for photocatalytic applications. Review

In this review, the current state of ZnO-Cd based materials for photocatalytic applications is summarized. Relevant technological synthesis methods such as pulsed laser deposition, magnetron sputtering, electrodeposition, sol-gel, metalorganic chemical vapor deposition, evaporating, spray pyrolysis, reflux are considered, and recent developments in effective and reproducible synthesis technology of nano- and microstructured zinc oxide, doped with cadmium and solid solutions of Zn1‑xCdxO for photodecomposition of organic pollutant molecules are discussed. The synthesis technology and level of Cd doping has a significant effect on the structure and morphology of zinc oxide and, as a result, on the optical and photocatalytic properties. The figures of merit, the theoretical limitations and rational control of the concentration of the cadmium alloying impurity is necessary to create a material with balanced optical properties and photocatalytic activity. Lastly, the importance of doping ZnO by isovalent Cd impurity significantly improves its photocatalytic properties due to a narrowing of the band gap, a decrease in the rate of recombination of electron-hole pairs, which increases the efficiency of spatial charge separation, the formation of active oxide radicals and an increase in the specific surface area. Thus, ZnO-Cd based materials are the most promising photocatalytic materials for organic pollutants.

Fabrication of Flexible Supercapacitor Electrode Materials by Chemical Oxidation of Iron-Based Amorphous Ribbons.

A flexible electrode constructed from Fe-based amorphous ribbons decorated with nanostructured iron oxides, representing the novelty of this research, was successfully achieved in one-step via a chemical oxidation method, using a low concentration of NaOH solution. The growth of metal oxides on a conductive substrate, which forms some metal/oxide structure, has been demonstrated to be an efficient method for increasing the charge transfer efficiency. Through the control and variation of synthetic parameters, different structures and morphologies of iron oxide were obtained, including hexagonal structures with a hollow ball shape and rhombohedral structures with rhombus-like shapes. Structural and morphological characterization methods such as X-ray diffraction and SEM morphology were used on the as-synthesized composite materials. The supercapacitor properties of the as-developed amorphous ribbons decorated with Fe2O3 nanoparticles were investigated by cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy. The flexible supercapacitor negative electrode demonstrates a specific capacitance of 5.96 F g-1 for the 0.2 M NaOH treated sample and 8.94 Fg-1 for the 0.4 M NaOH treated sample. The 0.2 M treated negative electrodes deliver 0.48 Wh/kg at a power density of 20.11 W/kg, and the 0.4 M treated electrode delivers 0.61 Wh/kg at a power density of 20.85 W/kg. The above results show that these flexible electrodes are adequate for integration in supercapacitor devices, for example, as negative electrodes.

High-efficiency tin perovskite solar cells by the dual functions of reduced voltage loss and crystal regulation

Environment friendly tin perovskite solar cells (TPSCs) have become a promising candidate due to their low toxicity and similar electronic configuration to lead counterparts. However, the easily generated defects due to the Sn2+oxidation and poor morphology originated from rapid crystallization are both barriers for tin-based devices in the enhancement of photovoltaic performance. Here, phenethylammonium chloride (PEACl) is introduced for post-treating FASnI3 films, which plays dual roles in adjusting film topography and passivating defects in bulk and interface of films. First, the film morphology can be improved by eliminating SnF2 impurities. In addition, a small amount of two-dimension perovskite can be formed in the films, inducing preferred orientation in secondary crystallization, well-matched energy level, and effective defect passivation. Finally, the FASnI3-based devices with PEACl treatment obtained a champion conversion efficiency of 11.63% with an average value of 10.76%, along with the obvious enhanced open circuit voltage and fill factor. In contrast, the pristine FASnI3 devices range from 6.92% to 9.40% with an average value of 7.96%. This work not only deepens our understanding of the suppression of defects in tin-based perovskites but also paves a facile way to ameliorate film morphology and interfaces to fabricate promising tin perovskites and devices.

Controlled synthesis of 3D urchinlike niobium tungsten oxide nanostructure for fast hydrogen ion storage

The shear crystal structure through metal doping can effectively promote the transport speed of ions and electrons in metal oxides, which has important dynamic significance for the design of high-performance energy storage materials. Herein, a 3D urchinlike niobium tungsten oxide (NWO) nanostructure as an efficient hydrogen ion storage material is reported for the first time, which exhibits a capacity of 88mAh g−1 at 20 °C (1 °C = 100 mA g−1). The large specific capacity of the 3D urchinlike NWO nanostructure is ascribed to the reversible reaction of a great quantity of W6+, W5+ and W4+ in the process of protonation and deprotonation processes. In addition, hydrogen ions can still be stored in large and stable quantities, even at rates as high as 100 °C (75 mAh g−1 at 100 °C). The improvement of hydrogen ion storage properties is arising from an optimized morphology of niobium tungsten oxide via tuning of the crystal structure. The high specific superficial area 3D urchinlike shape with rich one-dimensional nanostructures significantly shortens charge-carrier transport distances, ensuring rapid interfacial electronics movement to polish up ion storage kinetics. Consequently, this crystallographic shear structure strategy to boost hydrogen ion storage capacity may be universal and is likely to pave the way toward highly capacity hydrogen ion energy storage systems.

Direct observation of the ultrafast formation of cation-disordered rocksalt oxides as regenerable cathodes for lithium-ion batteries

Lithium-rich cation-disordered rocksalt (DRX) oxides offer promising prospects of satisfying boosting demand for high performance lithium-ion batteries. We introduce a time- and energy-saving high temperature shock synthesis for fast fabrication of these materials, which occurs through formation of binary oxides undergoing transformation to DRX oxides. Variations of morphology, elemental distribution, and microstructure of DRX oxides during the synthesis were followed using the in-situ transmission electron microscopy. The compositional space of DRX oxides varied from binary to senary, demonstrating that the high temperature shock strategy is a general process for their synthesis. Moreover, we demonstrated how the cycling life of DRX oxide cathodes applied in lithium-ion batteries could be extended through recrystallization of their collapsed lattice structure, and this regeneration process was accomplished using the same high temperature shock strategy. The specific capacity of the regenerated cathodes could be recovered to 91.4% of the initial value. Thus, our study offers a general strategy for not only synthesizing DRX oxides but also regenerating the respectively spent cathodes to extend the cycling life of lithium-ion batteries.

Effects of the phase, morphology, band gap and hydrogen evolution of vanadium oxide with reduced graphene oxide

Effects of the phase, morphology, band gap and hydrogen evolution of vanadium oxide with reduced graphene oxide

Particle and Phase Analysis of Combusted Iron Particles for Energy Storage and Release

The combustion of metal fuels as energy carriers in a closed-cycle carbon-free process is a promising approach for reducing CO2 emissions in the energy sector. For a possible large-scale implementation, the influence of process conditions on particle properties and vice versa has to be well understood. In this study, the influence of different fuel-air equivalence ratios on particle morphology, size and degree of oxidation in an iron-air model burner is investigated by means of small- and wide-angle X-ray scattering, laser diffraction analysis and electron microscopy. The results show a decrease in median particle size and an increase in the degree of oxidation for leaner combustion conditions. The difference of 1.94 μm in median particle size between lean and rich conditions is twentyfold greater than the expected amount and can be connected to an increased intensity of microexplosions and nanoparticle formation for oxygen-rich atmospheres. Furthermore, the influence of the process conditions on the fuel usage efficiency is investigated, yielding efficiencies of up to 0.93. Furthermore, by choosing a suitable particle size range of 1 to 10 μm, the amount of residual iron content can be minimized. The results emphasize that particle size plays a key role in optimizing this process for the future.

High-Performance Layered Oxides for Sodium-Ion Batteries Achieved through Combined Aluminum Substitution and Surface Treatment

Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries that combine, in a better way, high performance with environmental requirements. However, their cycling stability is still far from desirable. Herein, we demonstrate a rational approach to control the cycling stability of sodium-deficient nickel manganese oxides, Na2/3Ni1/2Mn1/2O2, with two- and three-layer stacking through Al substitution and Al2O3 treatment. Layered Na2/3Ni1/2Mn1/2O2 oxide displays a limited ability to accommodate aluminum in its structure (i.e., up to 8 at. %). The substitution of Ni ions with electrochemically inactive Al3+ ions and keeping the amount of Mn ions in Na2/3Ni1/2−xAlxMn1/2O2 leads to the stabilization of the two-layer stacking and favors the participation of lattice oxygen in the electrochemical reaction in addition to Ni ions. This results in an increase in the specific capacity of the Al-substituted oxides. Furthermore, the kinetics of the cationic migration between layers occurring during oxide cycling was manipulated by oxide morphology. The best cycling stability is observed for Na2/3Ni0.42Al0.08Mn1/2O2 having a column-like morphology of stacked plate-like particles along the common faces. The treatment of the layered oxides with Al2O3 mitigates the Mn dissolution reaction during electrode cycling in the NaPF6-based electrolyte, thus contributing to a high cycling stability.

Investigation of correlation of oxide layer surface morphology and magnesium degradation using a gas atmosphere dependent nanosecond laser processed model

In biomedical applications, degradation behavior of Magnesium (Mg) and its alloys is crucial for its outcomes. Various methods have been adopted to regulate Mg metals degradation, in which oxide layer generation has been considered to be a reliable strategy. However, correlation of magnesium oxide layer surface morphology and magnesium degradation is difficult to clarify due to interruption of oxide layer thickness and co-effect of other surface characteristics. In this work, Mg samples with two distinctive oxide layer morphology were prepared by nanosecond laser processing under N2 and CO2 atmospheres, coupled with essential surface and cross-section characterizations using SEM, AFM, TEM, XPS, XRD, and contact angle instrument. Furthermore, oxide layer morphology dependent Mg degradation behavior was investigated by electrochemical experimental, hydrogen precipitation, and pH tests. Results indicated that by changing laser treatment processing gas atmosphere, magnesium oxide morphology generated on sample surface could be tailored while maintaining consistency in thickness and composition. Larger particle size, surface roughness and wettability of magnesium oxide can decrease degradation rate.

Controlled thermal pre-treatment of ZMG232G10® for corrosion mitigation under simulated SOFC interconnect exposure conditions

The IT-SOFC candidate interconnect material ZMG232G10® was thermally pre-treated in air and in H2 – 3% H2O to mitigate dual atmosphere corrosion. Bare and pre-treated steel samples were exposed to a dual atmosphere exposure condition (dry air/metal/4% H2 – N2 (bal.) + 3% H2O) for 500 h at 600 °C. Corrosion products and oxide morphology developed on the air-exposed surfaces were analyzed. Pre-treatments of the metal in oxidizing (air) and reducing (H2 – 3% H2O) gas atmospheres provide improved passivation against dual atmosphere corrosion compared to bare steel. The uniform and iron-free oxide scale developed during the pre-treatment of alloy in the low pO2 H2 – 3% H2O gas atmosphere provides an effective diffusion barrier against the outward transport of cations and oxidation of iron observed under dual atmosphere conditions.

Phase-field modeling of alloy oxidation at high temperatures

Oxide growth is a complex process involving transport of reactive species, heterogeneous reactions, and microstructure evolution. Predicting oxidation kinetics, especially the oxide morphological change has been a longstanding challenge. Here we develop a phase-field model for predicting the oxide growth kinetics of a multicomponent alloy during high temperature oxidation, focusing on internal oxidation (non-protective) and its transition to external oxidation (protective). The predicted kinetics and oxide morphology are analyzed and compared to the classical Wagner's theory and an existing analytical model by Zhao and Gleeson. Some assumptions used in the analytical models and the limitation are discussed. In addition, it is demonstrated that the morphology and distribution of the initial oxide nuclei play an important role in the later stage oxide connectivity and thus the transition to external oxidation.

Compositing graphene oxide with carbon fibers enables improved dynamical thermomechanical behavior of papers produced at a large scale

This article discusses the morphology and thermomechanical properties of graphene oxide (GO) paper sheets and GO paper composites reinforced with carbon fibers. GO paper was fabricated using GO paste obtained by the condensation of GO aqueous solution synthesized using the Hummers' method. Carbon fibers were implemented to improve the mechanical properties of the pristine GO paper. All the investigated papers were subjected to thermal treatment to check thermo-related morphological and mechanical properties. The results presented in this study allowed for the deeper insight into morphological, structural, and mechanical volume and surface-related properties of pristine GO and GO-based composite materials reinforced with carbon fibers. We showed that there are two important factors that should be taken into consideration for the design and fabrication of GO-based papers. These factors were the concentration of the reinforcing agent and the thermal reduction of the papers. Both factors have influenced the final properties of the resulting GO-based papers. For the first time, it was revealed how the addition of the reinforcing material affects the GO paper thermal expansion coefficient.