Corrosion of magnesia–chrome brick in molten MgO–Al2O3–SiO2–CaO–FetO slag

The corrosion of magnesia–chrome (MgO–Cr₂O₃) brick in molten MgO–Al₂O₃–SiO₂–CaO–Fe_tO slag has been characterized using a dynamic rotary slag corrosion testing for various test cycles at 1650 °C. The open porosity decreases from 15.3 to 4.0% for three cycles, then it gradually increases from 4.0 to 4.8% when the test is extended to nine cycles, in which the permeating depth of the slag maintains at about 20 mm. The XRD pattern of the permeated layer shows the presence of the MgO, MgCr₂O₄ and CaMgSiO₄ phases. In the interior of the permeating layer cracks are formed and corrosion starts at the pores and cracks of MgO and decreases gradually. However, at 20–40 mm beneath the permeated layer edge, different shapes of MgO particles are found.     

Thermisch gespritzte Schichten im System Al2O3–Cr2O3–TiO2 – ein Update

With exception of ZrO₂, the individual oxides and binary compositions in the system Al₂O₃–Cr₂O₃–TiO₂ are the most important oxide materials for the preparation of thermally sprayed coatings. In this contribution selected results of recent own research activities are summarized. This includes the comparison of microstructures, phase compositions, and properties of coatings, deposited by atmospheric plasma spraying (APS) and high velocity oxy‐fuel (HVOF) spraying. The possibilities arriving from the use of suspensions as feedstock are reviewed. Special attention is paid to the advantage of use of binary compositions in this system. Tribological, electrical and corrosion properties of the coatings are discussed.     

High‐Capacity and High‐Rate Discharging of a Coenzyme Q10‐Catalyzed Li–O2 Battery

Discharging of the aprotic Li–O₂ battery relies on O₂ reduction to insulating solid Li₂O₂, which can either deposit as thin films on the cathode surface or precipitate as large particles in the electrolyte solution. Toward realizing Li–O₂ batteries with high capacity and high rate capability, it is crucially important to discharge Li₂O₂ in the electrolyte solution rather than on the cathode surface. Here, a soluble electrocatalyst of coenzyme Q₁₀ (CoQ₁₀) that can efficaciously drive solution phase formation of Li₂O₂ in current benchmark ether‐based Li–O₂ batteries is reported, which would otherwise lead to Li₂O₂ surface‐film growth and premature cell death. In the range of current densities of 0.1–0.5 mA cm^?2_areal, the CoQ₁₀‐catalyzed Li–O₂ battery can deliver a discharge capacity that is ≈40–100 times what the pristine Li–O₂ battery could achieve. The drastically enhanced electrochemical performance is attributed to the CoQ₁₀ that not only efficiently mediates the electron transfer from the cathode to dissolve O₂ but also strongly interacts with the newly formed Li₂O₂ in solution retarding its precipitation on the cathode surface. The mediated oxygen reduction reaction and the bonding mechanism between CoQ₁₀ and Li₂O₂ are understood with density functional theory calculations.     

Fe2O3–TiO2 Nano‐heterostructure Photoanodes for Highly Efficient Solar Water Oxidation

Harnessing solar energy for the production of clean hydrogen by photo­electrochemical water splitting represents a very attractive, but challenging approach for sustainable energy generation. In this regard, the fabrication of Fe₂O₃–TiO₂ photoanodes is reported, showing attractive performances [≈2.0 mA cm⁻² at 1.23 V vs. the reversible hydrogen electrode in 1 M NaOH] under simulated one‐sun illumination. This goal, corresponding to a tenfold photoactivity enhancement with respect to bare Fe₂O₃, is achieved by atomic layer deposition of TiO₂ over hematite (α‐Fe₂O₃) nanostructures fabricated by plasma enhanced‐chemical vapor deposition and final annealing at 650 °C. The adopted approach enables an intimate Fe₂O₃–TiO₂ coupling, resulting in an electronic interplay at the Fe₂O₃/TiO₂ interface. The reasons for the photocurrent enhancement determined by TiO₂ overlayers with increasing thickness are unraveled by a detailed chemico‐physical investigation, as well as by the study of photo­generated charge carrier dynamics. Transient absorption spectroscopy shows that the increased photoelectrochemical response of heterostructured photoanodes compared to bare hematite is due to an enhanced separation of photogenerated charge carriers and more favorable hole dynamics for water oxidation. The stable responses obtained even in simulated seawater provides a feasible route in view of the eventual large‐scale generation of renewable energy.     

Fundamental Understanding of Water‐Induced Mechanisms in Li–O2 Batteries: Recent Developments and Perspectives

Modern sustainability challenges in recent years have warranted the development of new energy storage technologies. Practical realization of the lithium–O₂ battery holds great promise for revolutionizing energy storage as it holds the highest theoretical specific energy of any rechargeable battery yet discovered. However, the complete realization of Li–O₂ batteries necessitates ambient air operations, which presents quite a few challenges, as carbon dioxide (CO₂) and water (H₂O) contaminants introduce unwanted byproducts from side reactions that greatly affect battery performance. Although current research has thoroughly explored the beneficial incorporation of CO₂, much mystery remains over the inconsistent effects of H₂O. The presence of water in both the cathode and electrolyte has been observed to alter reaction mechanisms differently, resulting in a diverse range of effects on voltage, capacity, and cyclability. Moreover, recent preliminary research with catalysts and redox mediators has attempted to utilize the presence of water to the battery's benefit. Here, the key mechanism discrepancies of water‐afflicted Li–O₂ batteries are presented, concluding with a perspective on future research directions for nonaqueous Li–O₂ batteries.     

Determining crystallization kinetic parameters of Li2O–Al2O3–SiO2 glass from derivative differential thermal analysis curves

The kinetic parameters such as crystallization activation energy, E, and the frequency factor, ν, of Li₂O–Al₂O₃–SiO₂ glass were determined by a new non-isothermal method. The method is described by the equation

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, where β is the heating rate and T_f is the inflection-point temperature of differential thermal analysis (DTA). The value of T_f is determined as the maximum peak temperature on derivative differential thermal analysis (DDTA) curves. Values of E and ν of Li₂O–Al₂O₃–SiO₂ glass were also determined by two existing non-isothermal methods, namely the Kissinger plot and the Ozawa plot, and compared with those determined by isothermal method. Values of E and ν determined by the proposed equation were 332 kJ/mol and 1.4×10¹³ s⁻¹, respectively. They are excellent agreement with the isothermal analysis results, 336 kJ/mol and 1.8×10¹³ s⁻¹, respectively. In contrast, both the Kissinger equation and the Ozawa equation give much higher values of E and ν.     

Rationalizing the Effect of Oxygen Vacancy on Oxygen Electrocatalysis in Li–O2 Battery

Albeit the effectiveness of surface oxygen vacancy in improving oxygen redox reactions in Li–O₂ battery, the underpinning reason behind this improvement remains ambiguous. Herein, the concentration of oxygen vacancy in spinel NiCo₂O₄ is first regulated via magnetron sputtering and its relationship with catalytic activity is comprehensively studied in Li–O₂ battery based on experiment and density functional theory (DFT) calculation. The positive effect posed by oxygen vacancy originates from the up shifted antibond orbital relative to Fermi level (E_f), which provides extra electronic state around E_f, eventually enhancing oxygen adsorption and charge transfer during oxygen redox reactions. However, with excessive oxygen vacancy, the negative effect emerges because the metal ions are mostly reduced to low valence based on the electrical neutral principle, which not only destabilizes the crystal structure but also weakens the ability to capture electrons from the antibond orbit of Li₂O₂, leading to poor catalytic activity for oxygen evolution reaction (OER).     

Catalytic CVD growth of Si–C and Si–C–O alloy films by using alkylsilane and related compounds

Cat-CVD method has been applied to the growth of Si–C and Si–C–O alloy thin films. Growth mechanism has been studied with emphasis on the effects of filament materials. Growth rates and alloy compositions were measured for W, Ta, Mo and Pt filaments at the filament temperatures ranging from 1300 to 2000 °C. Si_1−xC_x films with x ranging from 0.38 to 0.7 could be grown by using single molecule source Si(CH₃)₂H₂ (dimethylsilane). Si–C–O ternary alloy films was successfully prepared by using Si(OC₂H₅)₄ (tetraethoxysilane) and Si(CH₃)₂(OCH₃)₂ (dimethyldimethoxysilane) molecules.     

Synthesis and microstructure of boron-doped alumina membranes prepared by the sol–gel method

Pure and boron-doped γ-Al₂O₃ membranes have been synthesized by the sol–gel method. The thermal stability of the unsupported alumina membrane was studied by determining the pore structure (including average pore size, pore volume and BET surface area). The average pore size of the pure alumina membrane increased sharply after sintering at temperatures higher than 1000°C. Addition of 16% boron can considerably stabilize the pore structure of the unsupported alumina membrane. The pore diameter for the B-doped membrane was stabilized within 13 nm after sintering at 1200°C for 5 h. The substantial increase in the pore size for the pure alumina membrane at the sintering temperature of 1000–1200°C was accompanied by the phase transformation from γ-Al₂O₃ to -Al₂O₃. The addition of boron can raise the temperature of this phase transformation significantly and, thus, improves the thermal stability of the membranes.     

Protecting the Li‐Metal Anode in a Li–O2 Battery by using Boric Acid as an SEI‐Forming Additive

The Li–O₂ battery (LOB) is considered as a promising next‐generation energy storage device because of its high theoretic specific energy. To make a practical rechargeable LOB, it is necessary to ensure the stability of the Li anode in an oxygen atmosphere, which is extremely challenging. In this work, an effective Li‐anode protection strategy is reported by using boric acid (BA) as a solid electrolyte interface (SEI) forming additive. With the assistance of BA, a continuous and compact SEI film is formed on the Li‐metal surface in an oxygen atmosphere, which can significantly reduce unwanted side reactions and suppress the growth of Li dendrites. Such an SEI film mainly consists of nanocrystalline lithium borates connected with amorphous borates, carbonates, fluorides, and some organic compounds. It is ionically conductive and mechanically stronger than conventional SEI layer in common Li‐metal‐based batteries. With these benefits, the cycle life of LOB is elongated more than sixfold.     

Sensitivity enhancement for H2 gas detection using a SnO2–Ag2O–PdOx nanocrystalline system

Thick film H₂ sensors were fabricated using SnO₂ loaded with Ag₂O and PdO_x. The composition that gave highest sensitivity for H₂ was in the wt.% ratio of SnO₂:Ag₂O:PdO_x as 93:5:2. The nano-crystalline powders of SnO₂–Ag₂O–PdO_x composites synthesized by sol–gel method were screen printed on alumina substrates. Fabricated sensors were tested against gases like H₂, CH₄, C₃H₈, C₂H₅OH and SO₂. The composite material was found sensitive against H₂ at the working temperature 125 °C, with minor interference of other gases. H₂ gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on SnO₂–Ag₂O–PdO_x nanocrystalline system exhibited high performance, high selectivity and very short response time to H₂ at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of H₂.     

Mikrostruktur und Eigenschaften HVOF‐gespritzter Schichten im System TiO2 – Cr2O3

Microstructure and properties of HVOF‐sprayed coatings of the TiO₂ – Cr₂O₃ system Thermally sprayed titanium oxide coatings are known for their good tribological properties and their electrical conductivity. The latter is due to oxygen deficiency from the stoichiometric composition TiO₂. These lattice defects can be ordered and are called crystallograhic shear planes. These structures are known as Magnéli phases. At high temperature in oxygen‐containing atmospheres the material forms isolating TiO₂, therefore the application under such conditions is restricted. At the titania‐rich side of the system TiO₂‐Cr₂O₃ also compounds with the structure of Magnéli‐phases are formed. According to information from the literature, these phases are stable in oxygen‐containing atmospheres and are therefore promising for corresponding coating applications at elevated temperatures. In this paper first results of systematic studies of microstructure and properties of HVOF‐sprayed coatings are presented.     

Electronic Structure and Magnetic Properties of New Rare-earth Half-metallic Materials AcFe₂O₄ and ThFe₂O₄: Ab Initio Investigation

Electronic structure and magnetism of the rare-earth metals Ac and Th doped Fe₃O₄ Fe_1-xRe_xFe_2-yRe_yO₄(Re=Ac, Th; x=0, 0.5, 1; y=0, 0.5, 1.0, 1.5, 2.0) are investigated by first-principle calculations. AcFe₂O₄, FeAc₂O₄ and ThFe₂O₄ are found to be II B-type half-metals. The large bonding-antibonding splitting is believed to be the origin of the gap for AcFe₂O₄, FeAc₂O₄ and ThFe₂O₄, resulting in a net magnetic moment of 9.0μ_B, 4.0μ_B and 8.1μ_B, respectively, compared with 4.0μ_B of Fe₃O₄. Also, the conductance of AcFe₂O₄ and ThFe₂O₄ are both slightly larger than that of Fe3O4. It can be predicted that the new rare-earth half-metals AcFe₂O₄ and ThFe₂O₄ have wider application ground in spin electronic devices due to their larger magnetoresistance and higher conductivity than that of Fe₃O₄. The half-metallic feature can be maintained up to the lattice contraction of 8%, 3% and 4% for Fe₃O₄, AcFe₂O₄ and ThFe₂O₄, respectively.