Recovery of V<Subscript>2</Subscript>O<Subscript>5</Subscript> from Bayer liquor by ion exchange

A new technology was developed to recover V2O5 from Bayer spent liquor by ion exchange.The experimental results show that in the conditions of 105°C and 0.20-0.25 mass ratios between CaO in lime and Al2O3 in spent liquor, the precipitation rate of vanadium in Bayer liquor is more than 85%.The vanadium-bearing precipitation is leached by NaHCO3 solution.The leaching rate of vanadium can reach 85% in the conditions of 95°C, 40 g·L-1 of NaHCO3 concentration, and ventilating of CO2.The 201 × 7 type of resin has...     

Phase Transformations During Li-Insertion into V<Subscript>2</Subscript>O<Subscript>5</Subscript> at Elevated Temperature

Recent interest in developing cathode materials for an elevated temperature operation of Li-ion batteries has motivated researchers to explore the possibility of using layered V₂O₅ as a potential candidate because of its high capacity and cyclic stability. Despite a wide lithiation voltage window of V₂O₅ (between 1.0 V and 4.0 V), compositional fluctuations, metal dissolution, and so on contribute to capacity loss at high temperatures. A first discharge of V₂O₅ to voltages below 2.0 V has been observed to be associated with a series of phase transformations at both room temperature and high temperature and has been characterized here. From structural characterization of harvested electrodes post–first discharge, a new Li-rich phase was observed to be formed at 120°C and the composition was estimated.     

Synthesis and Characterization of New Bismuth Lead Vanadate Pb<Subscript>2</Subscript>BiV<Subscript>3</Subscript>O<Subscript>11</Subscript>

It has been shown that BiVO₄ and Pb₂V₂O₇ react with each other, forming a new compound of the formula Pb₂BiV₃O₁₁ at molar ratio equal to 1:1. This compound has also been obtained from PbO, Bi₂O₃, and V₂O₅, mixed at a molar ratio of 4:1:3. It melts congruently at a temperature of 725 ± 5 °C and crystallizes in the triclinic system with unit-cell parameters: a = 0.710076 nm, b = 1.41975 nm, c = 1.42972 nm, α = 134.552°, β = 97.2875°, γ = 89.6083°, and Z = 4.     

Phase Relations in the System TiO<Subscript>2</Subscript>-V<Subscript>2</Subscript>O<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> under Oxidizing and Reducing Conditions

The target of this work was to investigate the phase development in the catalyst system consisting of TiO₂ (Anatase) and V₂O₅ (Shcherbinaite) under several gas atmospheres. Thus a set of V₂O₅/TiO₂ specimens was prepared by ball milling and exposed to subsequent annealing in air and feed gas in the temperature range from 400 to 700 °C. The XRD-results showed that the initial phases Anatase and Shcherbinaite remain stable for all atmospheres containing oxygen. In the temperature range above 525 °C the formation of a Rutile solid solution (Rutile-ss) containing VO _x species takes place. However, under reducing conditions (lower oxygen partial pressure) the reduction of V₂O₅ to V₂O₃ was found by X-ray diffraction measurements. There is no miscibility up to 1300 °C followed by the formation of V₂TiO₅ (Berdesinskiite). SEM images underline the reduction by monitoring the change in morphology with respect to the V-containing phases. TiO₂ remains without much alteration. The two phases V₂Ti₇O₁₇ and V₂Ti₃O₉ (Schreyerite) as described in mineralogy have not been observed in these experiments. The knowledge of phase relations helps to find the appropriate processing conditions and to understand the aging phenomena of catalysts.     

Phase Formation of the Yttrium Aluminates in the Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiC System

Phase formation sequence of the yttrium aluminates in the Y₂O₃-Al₂O₃-SiC ternary system as temperature increases were investigated via x-ray diffraction (XRD). Results showed that YAM (monoclinic), YAP (perovskite) and YAG (garnet) were the yttrium aluminates presented in the solid-state reacted samples at a fixed Al₂O₃:SiC ratio of 1:1. Formation of the yttrium aluminates depended on the temperature. The YAM, YAP and YAG started to form below 1150 °C, at 1300 °C, and at 1450 °C, respectively. Accordingly, two behavior phase diagrams of the Y₂O₃-Al₂O₃-SiC ternary system were recognized, one is in the temperature range of 1150-1300 °C and the other is in 1300-1450 °C, respectively. Thereafter, the phase equilibrium was reached in the temperature range of 1450-1700 °C. Effects of SiC on the phase formation processes in the ternary system were discussed.     

Phase Relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> System in the Solid State. The Crystal Structure of AlVO<Subscript>4</Subscript>

Phase relations in the ternary oxide system Al₂O₃-V₂O₅-MoO₃ in the solid state in air have been investigated by using the x-ray diffraction (XRD) and differential thermal analysis/thermogravimetric (DTA/TG) methods. It was confirmed that in the subsolidus area of the Al₂O₃-V₂O₅-MoO₃ system, there exist seven phases, that is Al₂O₃, V₂O_5(s.s.), MoO₃, AlVO₄, Al₂(MoO₄)₃, AlVMoO₇, and V₉Mo₆O₄₀. Seven fields, in which particular phases coexist at equilibrium, were isolated. The crystal structure of AlVO₄ has been refined from x-ray powder diffraction data. Its space group is triclinic, , Z = 6, with a = 0.65323(1) nm, b = 0.77498(2) nm, c = 0.91233(3) nm, α = 96.175(2)°, β = 107.234(3)°, γ = 101.404(3)°, V = 0.42555 nm³. The crystal structure of the compound is isotypic with FeVO₄. Infrared (IR) spectra of AlVO₄ and FeVO₄ are compared.     

Microstructure and Thermomechanical Properties of Atmospheric Plasma-Sprayed Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating

In this study, a Yb₂O₃ coating was fabricated by the atmospheric plasma spray technique. The phase composition, microstructure, and thermal stability of the coating were examined. The thermal conductivity and thermal expansion behavior were also investigated. Some of the mechanical properties (elastic modulus, hardness, fracture toughness, and flexural strength) were characterized. The results reveal that the Yb₂O₃ coating is predominantly composed of the cubic Yb₂O₃ phase, and it has a dense lamellar microstructure containing defects. No mass change and exothermic phenomena are observed in the thermogravimetry and differential thermal analysis curves. The high-temperature x-ray diffraction results indicate that no phase transformation occurs from room temperature to 1500 °C, revealing the good phase stability of the Yb₂O₃ coating. The coefficient of thermal expansion of the Yb₂O₃ coating is (7.50-8.67)?×?10^?6 K^?1 in the range of 200-1400 °C. The thermal conductivity is about 1.5 W m^?1 K^?1 at 1200 °C. The Yb₂O₃ coating has excellent mechanical properties and good damage tolerant. The unique combination of these properties implies that the Yb₂O₃ coating might be a promising candidate for T/EBCs applications.     

The effect of boron oxide on the crystallization behavior of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel phase during the cooling of the CaO-SiO<Subscript>2</Subscript>-10 mass.% MgO-30 mass.%Al<Subscript>2</Subscript>O<Subscript>3</Subscript> systems

The microstructural characteristics of the CaO-SiO₂-B₂O₃-10 mass.% MgO-30 mass.% Al₂O₃ systems solidified during slow cooling from 1600 °C were investigated using SEM-EDS and a thermochemical computation package. The effect of boron oxide on the crystallization behavior of the spinel in the aluminosilicate system was observed because boron oxide is believed to become a potential flux to reduce the melting point of the liquid oxides. The primary crystalline phase was spinel, mainly MgAl₂O₄, irrespective of the boron content. The liquidus temperature T _L continuously decreased as the boron oxide content increased, indicating that the boron oxide decreased the activity of the MgAl₂O₄ spinel phase in liquid melts at high temperatures. The size of the spinel crystals increased as the temperature range for the solid + liquid coexisting region, viz. the mushy zone, increased. In the present systems, because the T _L continuously decreased with the increase in the boron oxide content, the viscosity of the liquid oxide may have affected the crystallization behavior of the spinel during cooling. Based on these results, an injection of a small amount of B₂O₃ flux into molten steel containing liquid aluminosilicate inclusions is not recommended because large spinel crystals can originate from the changes in the thermophysical properties of the liquid inclusions due to the incorporation of boron oxide into the aluminosilicate networks.     

Synthesis and thermal expansion of 4J36/ZrW<Subscript>2</Subscript>O<Subscript>8</Subscript> composites

Gas atomized 4J36 alloy powder was milled for 72 h then mixed with ZrW₂O₈ powder and sintered at 600°C for 4 h under argon atmosphere. 4J36/ZrW₂O₈ composites containing 10 vol.%, 20 vol.%, 30 vol.%, and 40 vol.% ZrW₂O₈ were fabricated, the relative density of which ranged from 70% to 80%. Thermal expansion coefficients of the composites decreased as the amount of ZrW₂O₈ increased, in agreement with the rule of the mixture. The coefficient of thermal expansion of the 4J36/40 vol.%ZrW₂O₈ composite in 25–100°C is 0.55 × 10⁻⁶/°C.     

Nanostructural Free-Volume Effects in Humidity-Sensitive MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Ceramics for Sensor Applications

Technologically modified spinel MgO-Al₂O₃ ceramics were prepared from Al₂O₃ and 4MgCO₃·Mg(OH)₂·5H₂O powders at sintering temperatures of 1200, 1300, and 1400 °C. Free-volume structural effects in MgO-Al₂O₃ ceramics and their electrophysical properties were studied using combined x-ray diffraction, scanning electron microscopy, Hg-porosimetry, and positron annihilation lifetime spectroscopy. It is shown that increasing of sintering temperature from 1200 to 1400 °C results in the transformation of pore size distribution in ceramics from tri- to bi-modal including open macro- and meso(micro)pores with sizes from ten to hundreds nm and nanopores with sizes up to a few nm. Microstructure of these ceramics is improved with the increase of sintering temperature, which results in decreased amount of additional phases located near grain boundaries. These phase extractions serve as specific trapping centers for positrons penetrating the ceramics. The positron trapping and ortho-positronium decaying components are considered in the mathematical treatment of the measured spectra. Classic Tao-Eldrup model is used to draw the correlation between the ortho-positronium lifetime and the size of nanopores, which is complementary to porosimetry data. The studied ceramics with optimal nanoporous structure are highly sensitive to humidity changes in the region of 31-96% with minimal hysteresis in adsorption-desorption cycles.     

Oxidation Behavior of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Spinel-Coated Interconnects in Wet Air

Corrosion of boilers and heat exchangers is accelerated in the presence of vanadium, sodium, and sulfur from low-grade fuels. Several iron- and nickel-based alloys were immersed in 60 mol% V₂O₅–40Na₂SO₄ salt for 1000 h in order to investigate their degradation behavior at 600 °C in air. Materials performance was analyzed by means of substrate recession rate and metallographic characterization. Their corrosion mechanism is characterized by the formation of a sulfide/oxide layer adjacent to the metal, the dissolution of scale oxides in the molten deposit, and their precipitation near the outer surface of the deposit. High Ni- and Cr-containing alloys show the lowest metal loss rates. Al addition was detrimental due to low-melting eutectic AlVO₄–V₂O₅ formation. Fe–Cr-based alloys showed the highest metal loss rates. In such alloys, high Cr additions (above 20%) did not improve the performance due to the negative synergetic effect by simultaneous dissolution of Fe₂O₃ and Cr₂O₃. The predominant salt composition at the corrosion front varied from vanadate rich to sulfate rich during the exposure. This change in the attacking salt makes it difficult to find a protective material for mixed sulfate–vanadate-induced corrosion.     

Microstructure and Thermal Properties of Atmospheric Plasma-Sprayed Yb<Subscript>2</Subscript>Si<Subscript>2</Subscript>O<Subscript>7</Subscript> Coating

In the present work, Yb₂Si₂O₇ powder was synthesized by solid-state reaction using Yb₂O₃ and SiO₂ powders as starting materials. Atmospheric plasma spray technique was applied to fabricate Yb₂Si₂O₇ coating. The phase composition and microstructure of the coating were characterized. The density, open porosity and Vickers hardness of the coating were investigated. Its thermal stability was evaluated by thermogravimetry and differential thermal analysis (TG-DTA). The thermal diffusivity and thermal conductivity of the coating were measured. The results showed that the as-sprayed coating was mainly composed of crystalline Yb₂Si₂O₇ with amorphous phase. The coating had a dense structure containing defects, such as pores, interfaces and microcracks. The TG-DTA results showed that there was almost no mass change from room temperature to 1200 °C, while a sharp exothermic peak appeared at around 1038 °C in DTA curve, which indicated that the amorphous phase crystallized. The thermal conductivity of the coating decreased with rise in temperature up to 600 °C and then followed by an increase at higher temperatures. The minimum value of the thermal conductivity of the Yb₂Si₂O₇ coating was about 0.68 W/(m K).     

Effect of water intercalation on the structure and electrophysical properties of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6.9</Subscript>

The influence of water vapors and plastic deformation on the structure and electrophysical properties of YBa₂Cu₃O_6.9 (123) has been studied. It has been established that, at T = 200°C, the introduction of water into the structure of YBa₂Cu₃O_6.9 leads to its transition into a defect tetragonal phase of the 124 type as a result of the formation of planar stacking faults. After annealing at T = 930°C, these defects are partially retained and are efficient centers of pinning in the magnetic fields applied perpendicularly to the c axis, which makes it possible to increase (by an order of magnitude) the critical current density in the high-textured ceramics at 77 K in the external magnetic field of 5–10 T. The plastic deformation of the hydrated ceramics favors the reverse transition of the arising 124 phase to the 123 phase at T = 930°C and is accompanied by a recrystallization of the material, which leads to the appearance of a texture and an increase the critical current density.     

Fabrication of Al matrix composite reinforced with submicrometer-sized Al<Subscript>2</Subscript>O<Subscript>3</Subscript> particles formed by combustion reaction between HEMM Al and V<Subscript>2</Subscript>O<Subscript>5</Subscript> composite particles during sintering

To fabricate an Al-V matrix composite reinforced with submicron-sized Al₂O₃ and Al_xV_y (Al₃V, Al₁₀V) phases, high energy mechanical milling (HEMM) and sintering were employed. By increasing the milling time, the size of mechanically milled powder was significantly reduced. In this study, the average powder size of 59 μm for Al, and 178 μm for V₂O₅ decreased with the formation of a new product, Al-Al₂O₃-Al_xV_y, with a size range from 1.3 μm to 2.6 μm formed by the in-situ combustion reaction during sintering of HEM milled Al and V₂O₅ composite powders. The in-situ reaction between Al and V₂O₅ during the HEMM and sintering transformed the Al₂O₃ and Al_xV_y (Al₃V, Al₁₀V) phases. Most of the reduced V reacted with excess the Al to form Al_xV_y (Al₃V, Al₁₀V) with very little V dissolved into Al matrix. By increasing the milling time and weight percentage of V₂O₅, the hardness of the Al-Al₂O₃-Al_xV_y composite sintered at 1173 K increased. The composite fabricated with the HEMM Al-20wt.%V₂O₅ composite powder and sintering at 1173 K for 2 h had the highest hardness.     

Control of microwave dielectric properties in 0.42ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript>−0.58TiO<Subscript>2</Subscript> ceramics by the quantitative analysis of phase transition

Phase constitutions of ZnNb₂O₆−TiO₂ mixture ceramics were significantly changed according to the sintering temperature. Phase transition procedures and their effect on the microwave dielectric properties of 0.42ZnNb₂O₆−0.58TiO₂ were investigated using X-ray powder diffraction and a network analyzer. The fractions of the phases composing the mixture were calculated by measuring integral intensities of each reflection. The structural transitions in 0.42ZnNb₂O₆−0.58TiO₂ were interpreted as the association of two distinct steps: the columbite and rutile to ixiolite transition present at lower temperatures (900–950°C) and the ixiolite to rutile transition at higher temperatures (1150–1300°C). These transitions caused considerable variation of microwave dielectric properties. Importantly, τ_f was modified to around 0 ppm/°C in two sintering conditions (at 925°C for 2 hr and at 1300°C for 2 hr), by the control of phase constitution.     

Tunneling magnetoresistance in sintered Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> samples diluted with Fe and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Electric transport and magnetoresistance characteristics were investigated for Fe₃O₄-x Fe(x=0, 10, 20 wt.%) samples and Fe₃O₄-α-Fe₂O₃ samples sintered at 500°C. For composition dependence of Fe₃O₄-x Fe samples, the largest room temperature MR, 3.3% at 10 kOe, was obtained from a Fe₃O₄-10 Fe sample. For the surface heat treatment dependence of Fe₃O₄ powders, the largest room temperature MR, 4% at 10 kOe, was obtained from a Fe₃O₄-α-Fe₂O₃ sample sintered with Fe₃O₄ powders heated at 200°C in air. It was found that these enhanced MR ratios always appear together with the appropriate excess resistance which is regarded as the tunneling barrier. These enhanced MR ratios of Fe₃O₄-10 Fe and Fe₃O₄-α-Fe₂O₃ samples can be explained by the increased interparticle contact sites and the appropriate thickness of α-Fe₂O₃, respectively.     

Effects of alkali and alkaline-earth oxides on thermal, dielectrical, and optical properties of zinc borate glasses for transparent dielectric

The development of a transparent dielectric layer with a low dielectric constant is essential for improving the luminous efficacy of plasma display panels (PDPs). In this study, a ZnO-B₂O₃-SiO₂-Al₂O₃ glass containing alkaline-earth oxides and an alkali oxide was fabricated as a candidate Pb- and Bi-free transparent dielectric layer with a low dielectric constant. The thermal, electrical, and optical properties of these glasses were characterized. The changes in the properties in this glass system were investigated according to the alkalineearth oxides (RO)/alkali oxide (R₂O) ratio. The glass transition temperature (T_g), the coefficient of thermal expansion (CTE), and the dielectric constant of the glasses varied from 480°C to 540 °C, 7.9 to 10.6 × 10⁻⁶ /K, and 7.4–8.2, respectively. As the RO/R₂O ratio was increased, the T_g value increased, the CTE and transmittance decreased, and the dielectric constant increased slightly. The T_g or CTE can be calculated from other known values in these system glasses without requiring numerous experiments. The T_g and CTE are inversely proportional to each other and a constant was obtained by multiplying the two values.     

Phase Stability of Ce-Modified La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> Coatings and Chemical Compatibility with YSZ

Ce-modified La₂Zr₂O₇ powders, i.e., La₂Zr₂O₇ (LZ), La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3), and La₂(Zr_0.3Ce_0.7)₂O₇ (LZ3C7), were used to produce thermal barrier coatings by atmospheric plasma spray process. The chemical compatibility of the CeO₂-doped La₂Zr₂O₇ with the traditional YSZ was investigated in LZ-YSZ powder mixtures and LZ-YSZ bilayer coatings by x-ray diffraction and scanning electron microscope. The powder mixtures and coatings were aged at 1200 and 1300 °C for 100 h. The results showed that LZ and LZ7C3 presented single pyrochlore structure after the heat treatments at both 1200 and 1300 °C. For LZ3C7, however, fluorite structure was observed at 1300 °C, indicating a poor phase stability of LZ3C7 at the elevated temperature. The results further showed that La₂(Zr_0.3Ce_0.7)₂O₇ reacted with YSZ in the bilayer ceramic coatings due to the diffusion of cerium, zirconium, and yttrium. While for La₂Zr₂O₇(LZ) and La₂(Zr_0.7Ce_0.3)₂O₇, a better chemical compatibility with YSZ was shown.     

Experimental Study and Thermodynamic Re-optimization of the FeO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> System

Phase equilibria and thermodynamic data in the FeO-Fe₂O₃-SiO₂ system were critically reviewed. New experiments were undertaken to resolve discrepancies found in previous data. The liquid oxide/slag phase was described using the modified quasichemical model. New optimized parameters of the thermodynamic models for the Gibbs energies of slag and other phases in the selected system were obtained. The new parameters reproduce all available phase equilibria and thermodynamic data within the experimental error limits from 298 K (25 °C) to above the liquidus temperatures at all compositions and oxygen partial pressures from metal saturation to 1 atm of O₂. This study was carried out as part of the development of a self-consistent thermodynamic database for the Al-Ca-Cu-Fe-Mg-Si-O-S multi-component system.     

Influence of water vapor on the formation of pinning centers in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> upon low-temperature annealing

The influence of the double heat treatment (T = 300 and 930°С) on the critical parameters of highly textured YBa₂Cu₃O_6.96 and YBa₂Cu₃O_6.8 ceramics has been investigated. It has been shown that, upon low-temperature annealing in humid air, planar stacking faults are formed in these ceramics. These defects are partly retained after reduction annealing (at T = 930°С) and are efficient pinning centers in magnetic fields applied parallel and perpendicular to the c axis. Due to the absorption of water, the oxygen content is increased in the ceramics, which is accompanied by an increase in the critical temperature of superconducting transition up to 94 K for YBa₂Cu₃O_6.96 and up to 90 K for YBa₂Cu₃O_6.8. Optimal conditions of the double annealing have been established, after which the critical-current density increased to j _c ≥ 10⁴ А/сm² in an external magnetic field of up to 6 T. The low-temperature treatment in the neutral atmosphere saturated by water vapors deteriorates the current-carrying capacity of the highly textured ceramics, which is connected with the disappearance of texture due to the copper reduction and the precipitation of impurity phases.