Oxide Solid Solutions Research Articles

Creep anisotropy reduction and improvement via post-heat treatment in yttrium-added Hastelloy-X fabricated by laser powder bed fusion

The development of laser powder bed fusion (LPBF) has made it possible to produce complex three-dimensional components for high-temperature applications. The LPBF process needs to be refined to address several key factors, such as high-temperature elongation, microstructure heterogeneity, and mechanical anisotropy. Hastelloy-X Ni-based superalloy was used to illustrate these issues in this study. First, 0.046 wt.% of yttrium (Y) was added to Hastelloy-X (HX-y) to prevent grain boundary embrittlement. The second step involves two kinds of post-heat treatments; i) at 850 °C for 2 h (DA) for carbides and ii) solution heat treatment at 1240 °C for 8 h upon aging at 850 °C for 2 h (HTA). The creep properties of the samples were compared at 900 °C/ 80 MPa to understand the effect of Y addition and post heat treatments. The HX-y specimen was strengthened by solid solution and dispersion of Y-rich oxides, together with stabilization of oxygen-based contamination at the grain boundaries. The DA and HTA HX-y specimens had better creep properties than the HX specimens. The HX-y specimen showed superior creep properties to the HX specimen due to the presence of carbides M6C and Cr23C6 inside grains and at grain boundaries. However, carbides remained stable even at high temperatures within grains and at grain boundaries. Nevertheless, the HTA HX-y specimen exhibited superior isotropic creep properties. As a result of grain boundary pinning, serrated grain boundaries prevented grain boundary sliding. In contrast, HX specimens exhibited poor creep properties. This study confirmed that the optimal addition of Y together with the optimization of post-heat treatment drastically enhances the creep properties of materials fabricated by the LPBF process.

Electronic and Lattice Engineering of Ruthenium Oxide towards Highly Active and Stable Water Splitting

AbstractThe development of efficiently active and stable bifunctional noble‐metal‐based electrocatalysts toward overall water splitting is urgent and challenging. In this work, a rutile‐structured ruthenium‐zinc solid solution oxide with oxygen vacancies (Ru0.85Zn0.15O2‐δ) is developed by a simple molten salt method. With naturally abundant edges of ultrasmall nanoparticles clusters, Ru0.85Zn0.15O2‐δ requires ultralow overpotentials, 190 mV for acidic oxygen evolution reaction (OER) and 14 mV for alkaline hydrogen evolution reaction (HER), to reach 10 mA cm−2. Moreover, it shows superior activity and durability for overall water splitting in different electrolytes. Experimental characterizations and density functional theory calculations indicate that the incorporation of Zn and oxygen vacancies can optimize the electronic structure of RuO2 by charge redistribution, which dramatically suppresses the generation of soluble Rux>4 and allows optimized adsorption energies of oxygen intermediates for OER. Meanwhile, the incorporation of Zn can distort local structure to activate the dangling O atoms on the distorted Ru0.85Zn0.15O2‐δ as proton acceptors, which firmly bonds the H atom in H2O* to stabilize the H2O and considerably improves the HER activity.

Self-supported iridium-ruthenium oxides catalysts with enriched phase interfaces for boosting oxygen evolution reaction in acid

Developing highly efficient low-noble-metal loading electrocatalysts for acidic oxygen evolution reaction (OER) remains a great challenge. Herein, we developed a novel self-supported IrmRunOx/Ti electrode exhibiting an amorphous film encapsulated with a small number of crystalline nanoparticles for efficient acidic OER. The as-synthesized Ir0.95Ru0.05Ox/Ti electrode exhibits an excellent OER performance with an overpotential of 200 mV at 10 mA cm−2, a Tafel slope of 46.8 mV dec-1, and robust stability of 192 h in 0.1 M HClO4. The enriched heterogeneous interfaces between the amorphous phase and crystalline phase enhance the stability and activity of the solid solution oxides. The high density of oxygen vacancies on the surface, together with the strong electronic interaction contribute to boosting the OER. This work provides some valuable insights into developing efficient Ir-based catalysts for acidic water splitting.

High-temperature chemical expansion of Pr0.1Ce0.9O2-δ thin films determined by Differential Laser Doppler Vibrometry

The chemical expansion of thin-film praseodymium‑cerium oxide solid solutions (Pr0.1Ce0.9O2−δ, PCO10) is investigated at temperatures ranging from 500 °C to 800 °C and oxygen activities down to about 10−22. Differential Laser Doppler Vibrometry (D-LDV) in combination with periodic electrochemical pumping of oxygen is used to detect very small displacements of the sample surface. With decreasing pumping frequency, the film approaches chemical equilibrium, which is nearly reached at 700 °C below 0.01 Hz. D-LDV enables direct measurement of film thickness changes as well as the bending of the underlying substrates due electrochemically induced lateral mechanical stress. The substrate bending is found to be more than an order of magnitude larger than the film thickness change, increasing the detection limit by the same factor. The thickness change of the thin film is calculated from the measured displacement of the sample surface and compared with directly measured values. Thin-film literature data available for low oxygen activities up to 650 °C agree with our measurements. In addition, the thickness change of the film is determined from the displacement at different sample positions, which validates previous measurements. Finally, thin film chemical expansion is found to be larger by a factor of about 2 than the corresponding bulk value in agreement with predictions from a mechanical model that the out-of-plane expansion of a constrained film is increased.

The effect of abrasive additives on the tribotechnical properties of lubricants for the wheel–rail system

The paper studies the polishing power of a tribochemically active abrasive material based on a solid solution of iron and aluminum oxides, as well as a solid solution of aluminum and iron oxides modified by zirconium oxide and yttrium oxide additives, and the tribotechnical properties of a lubricant doped with these abrasive materials. The modified Al2O3·Fe2O3·ZrO2·Y2O3 powders prove to have an essentially higher polishing power producing a considerably lower surface roughness than that of the unmodified Al2O3·Fe2O3 powder. By varying the content of the modifying oxides, one can change the tribochemical activity of the abrasive powder and select the best composition depending on the material to be polished. The addition of these abrasive powders is shown to have an essential effect on the tribotechnical properties of the lubricant for the wheel–rail contact. The laboratory testing of the lubricant compositions suggests their effective applicability to the wheel–rail contact.

Hydration activity and expansibility of different divalent metal oxide solution compositions in steel slag

Steel slag (SS) accounts for 15–20% of steelmaking output; its application in cement concrete has been limited because of poor stability. In this study, the divalent metal oxide solid solution (RO phase) in SS was analogue synthesised to study its hydration activity and expansibility. The results showed that the hydration activity and expansibility of magnesium oxide (MgO) in the analogue-RO phase is affected by the content of ferrous oxide (FeO); with the increase of molar ratio (x) of iron oxide to magnesium oxide in the analogue-RO phase, the autoclave expansion rate and hydration activity of the cement paste decreased. When x ≤ 0.5, the RO phase had high hydration activity and could cause poor soundness of SS. When x = 1, the RO phase had low hydration activity and could cause slight expansion of SS. When x ≥ 2, the RO phase had no hydration activity and could not cause any expansion of SS. The control of different analogue-RO phase compositions induced different hydration and expansibility, which provided a theoretical basis for the influence of the RO phase on the soundness of SS and enabled measures to be proposed to reduce the expansion of SS, thereby promoting high-volume utilisation of SS in cement and concrete.

Non-contact thermometer behavior of (Y0.5In0.5)2O3:Yb3+,Er3+ solid solution.

Oxides are physically and chemically stable. Non-contact thermometer-Yb3+-Er3+ ions co-doped solid solution (Y0.5In0.5)2O3, is prepared by the regular solid method. The structural results obtained by XRD indicate that a pure phase solid solution (Y0.5In0.5)2O3 has been obtained. The solid solution (Y0.5In0.5)2O3 has a similar crystal structure, especially Y2O3 and In2O3 with the same space group (Ia3̄). Green emission from 500 to 600 nm is due to Er3+ 4f-4f transitions: 4S3/2 → 4I15/2 at 567 nm and 2H11/2 → 4I15/2 at 528 nm. Red emissions from 630 to 720 nm are attributed to Er3+: 4F9/2 → 4I15/2. UC luminescence changes greatly with laser diode power and Er3+ and Yb3+ content. Furthermore, the two-photon process is confirmed to be dominant between Yb3+ and Er3+ in oxide solid solution (Y0.5In0.5)2O3. Optical temperature sensitivity is also investigated systematically in order to explore the application of the oxide solid solution (Y0.5In0.5)2O3. The temperature-dependent green fluorescence at 528 and 567 nm was investigated with the range of 313-573 K. 0.316% K-1 is the maximum absolute sensitivity at 503 K, which is higher than most Yb3+/Er3+ co-doped systems. In addition, the solid solution (Y0.5In0.5)2O3:Yb3+,Er3+ has better thermal stability and stronger UC emission than a simple substance with excellent temperature sensing performance. It indicates that Yb3+-Er3+ ions co-doped (Y0.5In0.5)2O3 solid solution is a good candidate for optical temperature sensing.

EFFECT OF SILVER ADDITION TO HIGH-ENTROPY ALLOYS AL0.5COCRCU0.5FENI AND AL0.5COCRCUFENI ON THEIR MICROSTRUCTURE, PHASE COMPOSITION, MICROHARDNESS AND SURFACE OXIDE LAYER FORMATION

High-entropy alloys (HEAs) consisting of five or more components in an equimolar ratio are attracting increasing attention due to a unique combination of various properties. Alloying HEAs with small amounts of certain elements (most often rare earth, trace or noble metals) is a promising way to improve the characteristics of such alloys and control their properties. This paper reports the results on the microstructure, phase composition, and microhardness of cast AgxAl0.5CoCrCuyFeNi HEAs (x = 0, 0.1; y = 0.5, 1.0). The effect of silver addition on the oxidation behavior of the studied HEAs at 700°C was determined. The morphology, phase and chemical composition of the resulting oxide film were studied. It was shown that the introduction of silver improves the mechanical characteristics of the alloys, but deteriorates the oxidation resistance due to the formation of copper-silver eutectic in the alloy microstructure, leading to a change in the morphology and phase composition of the formed oxide layer. Along with the solid solution of (Al, Cr)2O3 oxides and CuCr2O4, NiCr2O4 spinels, the addition of silver leads to the formation of copper oxide CuO and a small amount of silver oxide Ag2O in the surface film.

Inserted hydrogen promotes oxidation catalysis of mixed Ru0.3Ti0.7O2 as exemplified with total propane oxidation and the HCl oxidation reaction

The solid solution of a reducible oxide with a (non or) less reducible oxide may open the way to incorporate substantial amounts of hydrogen by the simple exposure to H2 at elevated temperatures, as exemplified by the mixture of RuO2 and TiO2.

Hydrothermal conversion of mixed uranium(IV)-cerium(III) oxalates into U1-xCexO2+δ·nH2O solid solutions.

Uranium-cerium oxide solid solutions, U1-xCexO2+δ·nH2O, were prepared through hydrothermal conversion of mixed U(IV)-Ce(III) oxalate precursors, cerium being used as a surrogate for plutonium. Whatever the starting pH, the fluorite-type structure of AnO2 was obtained after heating at 250 °C for 24 h. The initial pH of the reaction media appeared to affect significantly the oxide morphology: for pH ≤ 2, the powder was found to be composed of microspheres, whereas for more alkaline pH values, agglomerates of nanocrystallites were found. Furthermore, a study of the hydrothermal treatment duration (T = 250 °C, pH = 8, t = 1-48 h) showed that fluorite-type mixed dioxides started to form after only 1 h, and then became single phase after 3 h. SEM and TEM/EDS analyses revealed that the cationic distribution narrowed with time to finally form highly homogeneous mixed oxides. Such a preparation route was then applied to various cerium incorporation rates and it was found that the formation of U1-xCexO2+δ·nH2O mixed oxides was possible for 0.1 ≤ x ≤ 0.75. In all the systems investigated, the speciation of uranium and cerium was questioned in both the solid and liquid phases. Thermodynamic calculations and evaluation of the O/M ratio in the final oxides led us to understand the complex redox behaviour of uranium and cerium in solution during hydrothermal processes and to propose a conversion mechanism.

High activity and excellent durability of oxygen-vacancy-rich ruthenium manganese oxide solid-solution nanowires for the oxygen evolution reaction in acidic media

Oxygen vacancy-rich solid-solution RuxMn1−xO2 nanowires have been reported to be efficient catalysts for acidic oxygen evolution reaction. They only need an overpotential of 200 mV to drive 10 mA cm−2 and show no obvious activity drop for >600 h.

Competitive adsorption of oxygen-containing intermediates on ruthenium–tin solid-solution oxides for alkaline oxygen evolution

A ruthenium–tin solid-solution oxide is constructed to regulate the strong adsorption of *O intermediates on Ru sites through competitive adsorption between Sn atoms and Ru atoms.

Strontium effect on the nature of phase equilibria in liquid metal containing calcium and aluminum

The use of complex strontium-containing alloys with alkaline-earth metals for steel out-of-furnace treatment makes it possible to increase the efficiency of the refining process and steel modifying. In this work based on the binary phase diagrams of SrO – CaO, SrO – Al2O3 , Al2O3 – CaO binary systems and data on possibility of the solid solution formation, the phase diagram of the SrO – Al2O3 – CaO system is modeled in the temperature range 1600 – 2600 °С. When constructing liquidus lines, the theories of perfect solutions (for solid solutions of strontium and calcium aluminates), regular solutions (for solid solutions of oxides) and irregular ionic solutions (for oxide melt) were used to calculate the activity of components. Thermodynamic analysis of the Fe – Sr – Ca – Al – O system was carried out as applied to the refining steel processes with alloys containing calcium and strontium at a temperature of 1600 °C. The simulation results showed that in in the process of refining the aluminium-deoxidized steel, a complex mechanism of interaction of active elements with oxygen will be realized. The interaction of calcium and strontium with oxygen occurs both for elements dissolved in iron and along the boundary of the gas phase containing calcium and strontium with the liquid iron melt. As a result of the interaction of calcium and strontium with oxygen in the presence of aluminium (0.05 %), the probability of formation of liquid oxide melts SrO – Al2O3 – CaO is high, which greatly facilitates the removal of reaction products from the melt. The resulting non-metallic inclusions are most likely to be complex calcium and strontium aluminates, which, due to the presence of strontium, are easily assimilated by slag. The formation of undesirable corundum inclusions during metal processing with complex alloys containing strontium and calcium is unlikely.

Iridium-titanium oxides for efficient oxygen evolution reaction in acidic media

Active and highly stable oxygen evolution reaction (OER) electrocatalyst for PEM-based water electrolysis are currently in high demand. Herein, we report a rutile iridium-titanium oxide solid solution (IrTiOx) through a facile one-step annealing of a Ti-based metal-organic framework precursor. The composite exhibits excellent OER activity and stability in acidic media, with a low overpotential of 296 mV at 10 mA cm−2 while the OER activity was retained during a 100-h galvanostatic stability test at a constant current of 10 mA cm−2 in 0.5 M H2SO4, outperforming the state-of-the-art IrO2-based electrocatalysts. We further demonstrate the structure evolution of iridium-titanium oxide during OER operations. In contrast to the initial uniform distribution of Ir and Ti over the entire architecture, after OER stability test, a hollow morphology is formed, in which the particle surface is covered with an IrOx-rich layer and entire particle becomes hollow. We ascribe the structure evolution to the Ir/Ti leaching and redeposition during the OER operations. We propose that the structure evolution of iridium-titanium oxide during the electrochemical process is responsible for the high OER activity and stability of IrTiOx.

Hydrotalcite-derived nickel–gallium alloy catalysts with enhanced resistance against metal sintering for methane decomposition

Catalytic methane decomposition is a promising way to convert methane into COx-free hydrogen and value-added carbon nanomaterials, but the development of a sintering-resistant catalyst is a challenge. In this study, Ni–Ga/Al2O3 alloy catalysts with different Ga/Ni atomic ratios were prepared from Ni3−xGaxAl (x = 0–1.2) hydrotalcite-like compounds (HTlcs) as precursors and tested for methane decomposition. Structural and physicochemical properties of the as-prepared and used catalysts were characterized by ICP, N2 physical adsorption, XRD, H2-TPR, H2 chemisorption, STEM-EDX, SEM, TEM, and Raman techniques. The results indicate that upon calcination at 500 °C, Ni–Ga–Al HTlcs are transferred to rock-salt Ni(Ga,Al)O oxide solid solutions, and reduction with H2 at 800 °C leads to single-phase and composition-uniform Ni–Ga alloy particles with an average crystal size of 8–10 nm. In catalytic methane decomposition at 600 °C, the alloying Ni with a suitable amount of Ga effectively enhances the catalyst life and carbon yield. Especially, Ni2.4Ga0.6Al shows the highest carbon yield of 61.1 g-C/g-cat, approximately 4.4 times that of the Ga-free Ni counterpart. Meanwhile, Ni–Ga alloying has a marked influence on the CNTs geometry, giving herringbone-like CNTs with small diameters and thin walls. It is gratifying to find that the Ni–Ga/Al2O3 catalyst exhibits good resistance against sintering under the adopted reaction condition, which accounts for the formation of uniform CNTs of smaller size. The findings provide guidelines for the control of carbon morphology and geometric size in methane decomposition.

Geometrical Engineering of Spinel Oxide Solid Solution to Enhance the Oxygen Evolution Reaction

Thanks to their outstanding activity, spinel oxides are generally regarded as a potential noble metal-free electrocatalyst as a substitute for noble metals in the oxygen evolution reaction. The design and regulations of octahedral geometry have been considered to be the most feasible strategy to enhance the OER performance on spinel oxides. In this report, to promote the catalytic activity of OER, two strategies have been applied to regulate the octahedral geometry of spinel oxide solid solution, including construction of a large number of active sites by filling the foreign cations into the unoccupied octahedral interstices and exposure of multiple active sites. The as-prepared iron foam (IF)-supported solid solution of MoxNi1–xFe2O4 (the atomic ratio of Mo:Ni is 1.05:10) nanosheets (MNFO NS/IF) exhibits efficient catalytic activity (achieving low overpotentials of 250 and 281 mV at current densities of 10 and 100 mA cm–2), fast kinetics (with a lower Tafel slope of only 36.9 mV dec–1), and high durability (maintaining the OER performance at 100 mA cm–2 over 120 h).

Ferromagnetism in LaMnO3-LaFeO3-LaCoO3 mixed spin perovskite oxide solid solution

The solid solution polycrystalline powder sample of LaMnO3 - LaFeO3 – LaCoO3 was synthesized via mixed-oxide method in 1:1:1 ratio by mass by following two step synthesis process (I) synthesis of LaMnO3, LaFeO3 and LaCoO3 by sol – gel method and (II) synthesis of LaMnO3 - LaFeO3 – LaCoO3 polycrystalline solid solution powder by solid state reaction method. The resulting solid solution crystallizes as a blend of orthorhombic and cubic crystal structure (Space group: Pna21 + Pm 3‾ m). The magnetic characterization in this mixed spin oxide solid solution reveals ferromagnetic nature from 50 K to 300 K. The appearance of stepped hysteresis loop (M − H plot) with two magnetic saturation states at 50 K is the characteristic exclusively exhibited by mixed spin oxide solid solution. Above 50 K only single magnetic saturation state exists with persistent hysteresis loop, thus, confirming the ferromagnetic nature up to 300 K.

The Electrophoretic Deposition of Nanopowders Based on Yttrium Oxide for Bulk Ceramics Fabrication

In the present work, a study was carried out to investigate the key factors that determine the uniformity, mass, thickness, and density of compacts obtained from nanopowders of solid solutions of yttrium and lanthanum oxides ((LaxY1−x)2O3) with the help of the electrophoretic deposition (EPD). Nanopowders were obtained by laser ablation of a mixture of powders of yttrium oxide and lanthanum oxide in air. The implemented mechanisms of the EPD and factors of stability of alcohol suspensions are analyzed. It has been shown that acetylacetone with a concentration of 1 mg/m2 can be used as a dispersant for stabilization of isopropanol suspensions of the nanoparticles during the EPD. It was shown that the maximum density of dry compacts with a thickness of 2.4 mm reaches 37% of theoretical when EPD is performed in vertical direction from a suspension of nanopowders with addition of acetylacetone.

Organic ligand-assisted synthesis of Ir0.3Cr0.7O2 solid solution oxides for efficient oxygen evolution in acidic media

Construction of strong interactions between oxides is compelling for modulating the active sites towards acidic oxygen evolution reaction (OER) electrocatalysts. Here, a solid solution oxide electrocatalyst constructed by alloying of IrO2 and CrO2 (labeled as Ir0.3Cr0.7O2) is reported with an overpotential of 255 mV at a current density of 10 mA cm−2 for OER in 0.5 M H2SO4 solution, which is much lower than that of the state-of-the-art IrO2 (357 mV). The mass activity at 1.50 V vs. RHE is 47 folds than that of IrO2, and it can maintain such OER stability for more than 200 h. Detailed analysis concludes that the organic ligands-assisted synthesis of Ir0.3Cr0.7O2 can enlarge the surface-active area and provide more active sites for water oxidation, while the leaching of Cr and its strong interaction with Ir sites resulting in the formation of high chemical state oxides of Ir with superior activity for acidic OER. It is found that the significantly increasement of oxygen vacancies content during electrochemical test together with the two points mentioned above jointly promote the water oxidation activities of Ir0.3Cr0.7O2 electrocatalyst in acidic media.

Understanding the protective ability of the native oxide on an Fe-13 at% Cr alloy at the atomic scale: A combined atom probe and electron microscopy study

We have performed high-resolution structural and chemical characterization of the native oxide films formed on a ferritic Fe- 13 at% Cr alloy at different stages of growth. The steady-state protective oxide film was found to be 5–6 nm thick, epitaxially grown, with a cubic spinel-structure ((Fe, Cr)3O4) and a Baker-Nutting orientation-relationship with the underlying alloy. Composition evolution within the oxide during growth, measured by atom probe tomography, has been explained on the basis of the low solid-state mobility of Cr3+ cations. We propose that the miscibility gap in the Fe-Cr spinel oxide solid-solution can be used to explain the reduced driving force for oxide-layer thickening with time.