Formation Of Complex Oxides Research Articles

High-Temperature Oxidation of NbTi-Bearing Refractory Medium- and High-Entropy Alloys.

The oxidation of six NbTi-i refractory medium- and high-entropy alloys (NbTi + Ta, NbTi + CrTa, NbTi + AlTa, NbTi + AlMo, NbTi + AlMoTa and NbTi + AlCrMo) were investigated at 1000 °C for 20 h. According to our observation, increased Cr content promoted the formation of protective CrNbO4 and Cr2O3 oxides in NbTi + CrTa and NbTi + AlCrMo, enhancing oxidation resistance. The addition of Al resulted in the formation of AlTi-rich oxide in NbTi + AlTa. Ta addition resulted in the formation of complex oxides (MoTiTa8O25 and TiTaO4) and decreased oxidation resistance. Meanwhile, Mo's low oxygen solubility could be beneficial for oxidation resistance while protective Cr2O3/CrNbO4 layers were formed. In NbTi + Ta, NbTi + AlTa and NbTi + CrTa, a considerable quantity of Ti-rich oxide was observed at the interdendritic region. In NbTi + AlCrMo, the enrichment of Cr and Ti at the interdendritic region could fasten the rate of oxidation. Compared to the recent research, NbTi + AlCrMo alloy is a light-weight oxidation-resistant alloy (weight gain of 1.29 mg/cm2 at 1000 °C for 20 h and low density (7.2 g/cm3)).

Performance Degradation and Protective Effects of Atomic Layer Deposition for Mg‐based Thermoelectric Modules

AbstractThermoelectric technology has witnessed a resurgence in recent years due to increasing demands for sustainable energy sources and efficient cooling systems. Recently, the introduction of Te‐free thermoelectric modules using non‐toxic, abundant materials including p‐type MgAgSb and n‐type Mg3(Sb,Bi)2 marked a significant breakthrough. Despite promising performance, questions persist regarding long‐term robustness and stability, especially in harsh environments. In this study, a thorough exploration of thermoelectric modules is conducted, focusing on their performance degradation under various conditions. Through elemental mapping analysis, degradation mechanisms are identified within the modules during cycling in argon environments, where atomic migrations and the formation of complex oxides at contact regions are key factors. Furthermore, cycling tests in air reveal significant degradation, prompting the exploration of protective strategies. Surface coatings using atomic layer deposition (ALD) emerge as a promising solution, particularly by HfO2, demonstrating superior protective effects. Furthermore, re‐soldering effectively restores module performance is found, highlighting the importance of developing advanced soldering techniques to promote magnesium‐based thermoelectric technology as a sustainable alternative to Bi2Te3. These findings emphasize the importance of exploring novel contact materials and demonstrate the potential of ALD as a universal approach to enhancing module reliability and robustness.

The Inhibition Action of Some Brij-Type Nonionic Surfactants on the Corrosion of OLC 45 in Various Aggressive Environments.

The corrosion protection property of three Brij-type surfactants, namely, Brij 35, Brij 56 and Brij 58P, was considered on OLC 45 carbon steel in a 0.5 M H2SO4 medium. The efficacy for these organic compounds was examined using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods, scanning electron microscopy (SEM) procedures, and Fourier transform infrared (FT-IR) spectroscopy. We hypothesized that these surfactants hinder the corrosion for OLC 45 samples through a protecting mechanism owing to the adsorption of organic molecules that form an inhibitive film or through the formation of complex oxides. These surfactants exhibited an appreciable protective effect against OLC 45 corrosion, operating as mixed inhibitors, as could be demonstrated by their influence on the electrochemical characteristics of the metallic substrates. The adsorption of surfactants over the substrates zone conformed to the representation of the Langmuir isotherm. The effect of temperature on the electrochemical comportment of the OLC 45 specimens in H2SO4 without and with Brij at 800 ppm was examined in the temperature interval of 293 to 333 K. The negative estimate of thermodynamic attributed as Gibbs free energy of adsorption presented the spontaneity of the adsorption activity. The investigation with FT-IR and SEM established the adsorption of Brij and the constitution of the corrosive components on the OLC 45 surface. Electrochemical determinations of these surfactants indicated its anticorrosion inhibition performance and the highest inhibition of 96% was reached when the Brij 35 concentration was at 800 or 1000 ppm, while for Brij 56 and Brij 58P, the highest inhibition was obtained when their concentrations were 500, 800, or 1000 ppm.

Design of Refractory High Entropy Alloys TiZrHfNbX (X=Cr/Ta) system, using thermodynamic calculations

Refractory high entropy alloys (RHEAs) are materials with novel concept that do not use a specific element as a base material and mixture of multiple elements in near equal amounts. This concept is expected to be adopted for use in aerospace heat-resistant materials that can be used at higher temperatures than currently available. We focused on the TiZrHfNbCr system as a new high-temperature structural material. We carried out thermodynamic calculation using the CALPHAD method and proposed compositions of TiZrHf(NbCr)2 and TiZrHf(NbCr)7 in addition to the equimolar composition (TiZrHfNbCr). These alloys are fabricated by arc melting, and microstructures in TiZrHf(NbCr)7 alloys, predicted by CALPHAD were observed in SEM images. Although some agglomeration of Nb is recognized by observation, microstructures of TiZrHf(NbCr)2 were also good agreement with the prediction by CALPHAD. From the results of TiZrHfNbCr, TiZrHf(NbCr)2 and TiZrHf(NbCr)7, complex oxides were formed and small weight gains were observed compared to other alloys (e.g., ZrTi and NbTa). The effect of formation of complex oxide to the oxidation behavior of these alloys will be discussed in the presentation.

Role of High-Valence Fe(IV), Cu(III), and Bi(V) Forms in the Processes of the Phase Formation of Complex Oxides

Role of High-Valence Fe(IV), Cu(III), and Bi(V) Forms in the Processes of the Phase Formation of Complex Oxides

Microstructure, mechanical properties and oxidation behavior of NbTaTi and NbTaZr refractory alloys

This study reports the microstructure, phase composition, mechanical properties and oxidation behavior of NbTaTi and NbTaZr ternary equiatomic alloys. These ternary components, together with earlier reported NbTiZr and MoNbTi, are commonly observed in refractory high entropy alloys (RHEAs) with a single-phase BCC or multi-phase crystal structures. Therefore, the reported information about these ternary alloys is thought to be useful for the development of advanced RHEAs. While NbTiZr and MoNbTi are single-phase BCC structures, NbTaTi and NbTaZr are multi-phase alloys. NbTaTi consists of a BCC matrix and discontinuous, Ti-rich precipitates with BCC and FCC crystal structures. NbTaZr consists of a co-continuous spinodal mixture of two BCC phases, one of which is rich in Ta and Nb and another is rich in Zr, and it also contains a Zr-rich HCP phase in the form of coarse grain-boundary particles. NbTaTi has compression yield stress of 724 MPa at 25 °C, 268 MPa at 800 °C and 129 MPa at 1200 °C. NbTaZr is stronger, with the compression yield stress of 1027 MPa at 25 °C, 530 MPa at 800 °C and 183 MPa at 1200 °C. Both alloys show rapid oxidation with formation of complex oxides during holding at 1200 °C.

Antimicrobial effects by silver–indium–tantalum oxide thin film in visible light

This study focuses on the antimicrobial effects in silver-indium-tantalum oxide (Ag–InTaO) thin films. A stack of alternated layers of Ag (7 ​nm), In2O3 (14 ​nm) and Ta2O5 (10 ​nm) was sequentially deposited by sputtering. Then this as-deposited stack of films was rapidly annealed at three selected temperatures 700, 800 or 900 ​°C for 5 ​min to allow the formation of complex oxides. Results from material characterization indicate that annealing help to form complex oxides, intermetallic compounds and Ag particles on the top surface. These features lead to the improved antimicrobial effect against E. Coli. under visible light by Ag–InTaO.

Phase stability of Yb-Gd-Si ternary alloys at elevated temperature

A ternary alloy with an Yb-Gd-Si composition was designed using thermodynamic calculation software. The ternary alloy with two different steady-state phases (Yb:Gd:Si = 25:18:57 and 19:23:58 at%) was successfully fabricated using arc melting. Oxidation tests were carried out at 1200 °C for 1, 2, 4, and 8 h in air. Thermogravimetric and microstructural analyses indicated that weight gain during oxidation at 1200 °C was suppressed compared with that for the Yb–Si alloy (Yb3Si5) owing to the formation of complex oxides in the Yb2O3–Gd2O3–SiO2 system. In addition, the phase stability of Yb-Gd-Si was higher than that of Yb3Si5 because the growth of a eutectic phase in Yb-Gd-Si during oxidation was prevented compared with Yb3Si5. The addition of Gd in Yb–Si alloy was effective in improving phase stability and oxidation behavior.

Complex oxides of copper and manganese as the base material for catalytic suppression of waste gases

The composite material “ionite-sorbed ions” was obtained by ion exchange technology. The conditions for obtaining the composite material “ionite-sorbed ions” are studied. In the thermolysis of cationite with sorbed ions, the synthesis of complex oxide is carried out between ions located at atomic distances from each other. This facilitates and accelerates the formation of complex oxide. Thermolysis of carboxyl cationite KB-4P-2 with sorbed copper and manganese ions was performed at temperatures from 250-950°C . Control of the thermolysis mechanism of the composite material “ionite-sorbed ions” was carried out using thermograms. According to the scanning electron microscopy data, the obtained powder of complex copper and manganese oxide has a good crystallite structure. Data x-ray diffraction analysis confirmed the crystallization of a complex oxide of copper and manganese in orthorhombic crystal structure. A method for the synthesis of complex copper and manganese oxide powder based on the thermolysis process of the composite material “ionite-sorbed ions”, which has catalytic properties, has been developed.

Solubilization of Rhodium in Hydrochloric Acid Using an Alkali Metal Salt Method

Acids such as aqua regia, a 3:1 mixture of hydrochloric acid (HCl) and nitric acid, that contain strong oxidizing agents are used in the dissolution-based recovery of platinum group metals (PGMs). However, nitrate-nitrogen emission has become subject to increasingly strict environmental regulations in recent years. Accordingly, we herein propose a dissolution process for PGMs via the formation of complex oxides using HCl alone. We prepared complex oxides of alkali metals and rhodium (Rh), which is particularly hard to dissolve, and investigated their dissolution behaviors in HCl. Rh-containing complex oxides were prepared by calcining Rh powder and alkali metal salts in air, and dissolution tests using HCl were conducted on the complex oxides obtained. It was found that Rh-containing complex oxides were completely dissolved under appropriate calcination and dissolution conditions.

Modeling of the reaction interdiffusion in the polycrystalline systems with limited component solubility

that may be accompanied by the processes of mutual diffusion and phase formation. Controlled technological process of forming coatings with the given properties entails the necessity of forecasting the evolution of the phase composition. This in turn requires the development of algorithms and quantitative models of the processes. Reactive mutual diffusion in polycrystalline metal (oxide film systems with limited component solubility) has not been simulated before. The simulation allows selecting the annealing conditions (time and temperature) necessary for the inclusion and uniform distribution of metal in the oxide lattice. A quantitative model of the interaction in a multi-layer system metal — polycrystalline oxide of the other metal under conditions of limited solubility is developed. The model is based on the concepts of mutual diffusion of the components and the bulk reactions of the formation of complex oxides. The developed model was applied to the analysis of the process of modifying thin films of titanium oxide with transition metals. The model allowed us to perform a numerical analysis of the experimental concentrations of the component distributions in polycrystalline Co - Ti02 and Fe - Ti02 thin-film systems. The individual diffusion coefficients of the studied metals and titanium under conditions of vacuum annealing were determined. The model provides a good description of the basic systematic features of the process: the appearance of titanium in the metal film and deep penetration of Fe and Co into the film of titanium oxide. It also explains the fact that complex oxides are formed not by layer-by-layer growth at the metal-oxide interface, but throughout the entire thickness of Ti02 film. The results of analysis of the processes of interracial interaction in layered systems accompanied by the reaction mutual diffusion can be used to predict the evolution of the phase composition, as well as to control the technological processes of obtaining materials with the desired properties.

Formation mechanisms of Y–Al–O complex oxides in 9Cr-ODS steels with Al addition

For the Al-alloyed 9Cr-ODS steels consolidated by spark plasma sintering and annealed at 800 °C, the Y–Al–O oxides, interface structure and orientation relationships between the oxides and the matrix are studied by high-resolution transmission electron microscope technique. It is found that the spark plasma sintering can serve as a useful and effective tool to investigate the transition states in complex oxide formation. Monoclinic Y4Al2O9 (YAM), orthorhombic YAlO3 (YAP), cubic Y3Al5O12 (YAG) and Y2O3 nanoparticles are identified. Both YAM and YAG can directly precipitate from the Y2O3 particles. One individual Y2O3 particle will produce several YAM particles, while only one YAG particle can be formed within one Y2O3 particle. The majority of identified Y–Al–O oxides exhibit partially coherent interfaces with the matrix, and multiple orientation relationships are revealed.

Direct Reduction of Iron from Crystal Lattice of a Complex Oxide

This work studied a decomposition and reduction of complex carbonate (sideroplesite) siderite lump ore from the Bakal’s deposit. The decomposition caused formation of complex oxides (Fe,Mg,Mn)O and (Fe,Mg,Mn)O·Fe2O3, and it preceded the Fe reduction; the weight loss during the decomposition process reached about 32%, being followed by the formation of a large number of pores. As the pores and micro-pores provide deep penetration of the carbon monoxide in the bulk of the ore lumps, it seemed that the pores would allow reduction of this ore without difficulties. However, during reduction experiments it was discovered that the distribution of the reduction process and formation of the metal phase were not connected with the pores’ distribution. The reduction process developed via an electrochemical mechanism, and the channels of the distribution of the reduction process were oxides of metals which were difficult to reduce under the presented experimental conditions; these oxides were mostly represented by the magnesia and silica compounds. The high rate of the iron reduction from the complex iron-manganese-magnesium oxides was explained by the high rate of distribution of the negatively charged anion vacancies forming on the surface of the oxide, due to reaction with a reducing agent.

Strengthening of Al0.3CoCrFeMnNi-based ODS high entropy alloys with incremental changes in the concentration of Y2O3

The high-entropy alloy (HEA) composite Al0.3CoCrFeMnNi based on the face-centered-cubic (FCC) system and reinforced with 0–3 vol% Y2O3 was processed by mechanical alloying followed by spark plasma sintering (SPS). The compressive yield strength of the Al0.3CoCrFeMnNi high-entropy alloy (HEA) increased phenomenally, from 0.98 GPa (0 vol% Y2O3) to 1.76 GPa (3 vol% Y2O3). A quantitative analysis by atom probe tomography (APT) suggested the in-situ formation of complex oxide resulting from the reaction of Y2O3 with the HEA matrix during processing, enhancing the strength. Using the dispersion-barrier hardening model, the strengthening by dispersoids in Al0.3CoCrFeMnNi with Y2O3 was calculated, and closely matched the experimental results.

Investigation on the effect of nano-ceria on the epoxy coatings for corrosion protection of mild steel in natural seawater

PurposeThis paper aims to investigate the effect of introducing nano-ceria (CeO2) particles to the epoxy coatings on mild steel in natural seawater.Design/methodology/approachThe epoxy–ceria nanoparticles were coated with mild steel using a wire-wound draw-down bar method. The effects of ceria nanoparticles on the corrosion resistance of epoxy-coated samples were analyzed using scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS).FindingsLocalized measurements such as oxygen consumption and iron dissolution were observed using SECM in natural seawater in the epoxy-coated sample. The increase in film resistance (Rf) and charge transfer resistance (Rct) values by the addition of nano-ceria particles in the epoxy coating was measured from EIS measurements after wet and dry cyclic corrosion test. Scanning electron microscope (SEM)/energy dispersive X-ray spectroscope (EDX) analysis showed that complex oxides of nano-ceria were enriched in corrosion products at a scratched area of the coated mild steel after corrosion testing. Focused ion beam-transmission electron microscope (FIB-TEM) analysis confirmed the presence of the nanoscale oxide layers of ceria in the rust of the steel.Research limitations/implicationsThe tip current at −0.70 V for the epoxy–CeO2-coated sample decreased rapidly because of cathodic reduction of the dissolved oxygen. The increase in film resistance (Rf) and charge transfer resistance (Rct) values by the addition of nano-ceria particles in the epoxy coating were measured from EIS measurements after wet and dry cyclic corrosion test.Practical implicationsThe presence of complex oxide layers of nano-ceria layers protects the coated steel from rusting.Social implicationsThe use of this nano-ceria for corrosion protection is environment-friendly.Originality/valueThe results of this study indicated the significant effect of nano-ceria particles on the protective performance and corrosion resistance of the epoxy coating on mild steel. The dissolution of Fe2+ was lower in the epoxy–ceria nanoparticle-coated mild steel than that of the epoxy-coated mild steel resulting in a lower anodic current of steel. The increase in film resistance and the charge transfer resistance showed that the nano-ceria particles and the formation of complex oxides provide better barrier protection to the coating metal surfaces.

ИК-СПЕКТРОСКОПИЯ ПЛЕНОЧНОЙ СИСТЕМЫ Fe–TiO2, ПОЛУЧЕННОЙ МЕТОДОМ МАГНЕТРОННОГО РАСПЫЛЕНИЯ

Проведен сравнительный анализ оптических спектров отражения-поглощения (RAS) и нарушенного полного внутреннего отражения (ATR) пленочной системы Fe-TiO2, полученной методом реактивного магнетронного распыления с последующим отжигом в вакууме и при атмосферном давлении в потоке кислорода. Показано, что смещение характеристических колебаний связи Ti–O в сторону меньших частот связано с присутствием в кристаллической структуре TiO2 катионов Fe+3. Установлено, что полосы поглощения, обусловленные деформационными колебаниями связи Fe-OH, наблюдаются только в спектрах ATR и смещены в сторону больших частот по сравнению с индивидуальными оксидами железа, что свидетельствует об образовании сложных оксидов в пленочной системе Fe-TiO2.
 Результаты исследований получены на оборудовании Центра коллективного пользования научным оборудованием ВГУ.

Interdiffusion and phase formation in the Fe–TiO2 thin-film system

The interaction of magnetron-sputtered metal iron with titanium-oxide films upon isothermal vacuum annealing is studied by X-ray phase analysis, secondary-ion mass spectrometry, atomic-force microscopy, and mathematical simulation. A mechanism for the formation of complex oxides at grain boundaries is suggested. The mechanism is based on the reaction diffusion of metal iron into titanium oxide. A quantitative model of reaction interdiffusion in two-layer polycrystalline metal–oxide film systems with limited component solubility is developed. From numerical analysis of the experimental distributions of the metal concentrations in the Fe–TiO2 film system, the individual diffusion coefficients are determined. It is found that, under the conditions of vacuum annealing at 1073 K, the diffusion coefficients of iron and titanium are 8.0 × 10–13 and 3.0 × 10–15 cm2 s–1, respectively.

Formation Mechanism of Complex Oxide Inclusions in 55SiCr Spring Steels

In the current study, formation mechanism of complex oxide inclusions in spring steels is studied. The complex oxides are extracted from steel samples with different methods, including two‐dimensional observation on a polished cross section of steel samples, acid etching, and non‐aqueous solution electrolytic extraction to reveal the three‐dimensional morphology of inclusions. Most of the oxide inclusions are characterized as MgO or MgO · Al2O3 in a core covered with liquid components. Thermodynamic calculation is performed using Factsage 7.0 software. Both MgO, MgO · Al2O3 solid inclusions, and liquid inclusions are observed in the molten steel. Based on the wettability between the molten steel, solid MgO inclusions, and liquid inclusions, a mechanism for the formation of complex oxides is suggested, that is, the solid core is wrapped by liquid inclusions in the molten steel.

Regularities of formation of complex oxides with the fluorite structure in the ZrO2–Y2O3 system

The crystal and local structures of the complex oxides (1–x)ZrO2 ∙ xY2O3 (YSZ) (x = 0.08–0.40) prepared by precipitation from solutions of metal salts followed by heat treatment in air were comprehensively studied by X-ray diffraction and Raman spectroscopy. Despite the same crystal structure type of the YSZ powders (cubic system, space group \(Fm\overline 3 m\) (225)), there are differences in the local structure of the samples. Comparison of the Raman spectra recorded at different laser excitation wavelengths provided the conclusion that the peaks observed in the Raman spectra of the YSZ samples with high yttrium content (x = 0.18–0.40) are likely to be due to luminescence of the powders.

Production and characterization of a tool steel-PSZ composite by mechanical alloying and spark plasma sintering

Abstract Tool steel matrix composites show improved hardness and remarkable wear resistance but generally also a systematic lower fracture toughness than the base material. The present work deals with the feasibility and characterization of a powder metallurgical hot work tool steel reinforced with partially stabilized zirconia (PSZ). Selection of PSZ as the reinforcement is aimed at improving the strength and fracture toughness of the composite by taking advantage of the transformation toughening effect of PSZ. The specimens were produced by mechanical alloying (MA) followed by spark plasma sintering (SPS) using two different types of PSZ, different volume fractions (10 and 20 vol %) and sizes of reinforcement. The influence of processing parameters on density and microstructure was investigated. The chemical stability of the tool steel-PSZ system was also studied looking at the possible formation of complex oxides and precipitates during the fast consolidation by SPS.