Solubility Of Fe2O3 Research Articles

Preparation and characterization of corundum-based ceramics for thermal storage

Corundum-based ceramics were prepared by two methods. The first used Fe2O3 and TiO2 as additives to react with α-Al2O3. The second made full use of Al2O3, SiO2 and TiO2 in calcined bauxite, and Fe2O3 was used as an additive. The SiO2-TiO2-Fe2O3 system was designed to influence corundum. The effects of Fe2O3, TiO2 and SiO2 on physical properties, phase transformation, microstructure, thermophysical properties and thermal shock resistance were investigated. Results showed that Fe2O3 and TiO2 realized densification sintering through entering in the lattice of corundum, and the solubility of Fe2O3 was higher than that of TiO2. In addition, the excess TiO2 tend to synthesize iron aluminum titanate in the grain boundaries, which could refine the grains and improve the mechanical properties. The SiO2-TiO2-Fe2O3 system reduced significantly the sintering temperature, but the imperfect microstructure impaired the properties. Corundum-based ceramics prepared by Fe2O3, TiO2 and α-Al2O3 had the optimal properties. The thermal conductivity and thermal storage density were 14.81 W/(m·K) (25 °C), 837 kJ/kg (25–800 °C), respectively. No cracks were formed after 30 thermal shock cycles (1100 °C-room, air cooling), and the bending strength increased by 2.59%. This study supports the application of corundum-based ceramics as a promising thermal storage candidate.

Solubility of Metal Oxides in Na2o-B2O3 Melts Associated with Basicity

1. Introduction Molten salts have been used as slag, and as an oxidation inhibitor in the steel production process at high temperature. Steels and refractories are corroded by adherence of fused salts such as molten oxide to their surfaces at the solid-liquid interface. For example, casting nozzles made of refractory oxides are corroded by molten oxide used in continuous casting molds. Dissolution of oxides on the surface of materials in molten salts is thought to be the cause of hot corrosion1). So, it is necessary to understand the corrosion behavior to clarify the dissolution behavior of oxides in melts. The basicity of the fused salts, which is similar to pH in aqueous solution, is one of the dominant influencing factors in the dissolution behavior of metal oxides. In the range of basic of fused salts, metal oxides are dissolved via a basic dissolution reaction, and in the range of acidity, an acidic dissolution reaction dominates in melts1). Dissolution of metal oxides in molten Na2SO4 at 1173 K associated with basicity defined by Na2O activity is well known as an example of reaction of metal oxides with fused salts1). To clarify the dissolution behavior of protective oxide scales in a molten sulfate film under a corrosion environment of gas turbine blades and vanes, the dissolution behavior of metal oxides such as Fe2O3 and Cr2O3 in molten Na2SO4 was investigated. In the case of molten oxides, dissolution reactions of metal oxides in molten sodium silicate used in the steel process were investigated2). However, researches on the dissolution reaction of metal oxides in borate melt, which steel slag comprises, are not sufficient. In this study, the correlation between the basicity and the solubility of Fe2O3 and Cr2O3 in Na2O-B2O3 melt was investigated using the method applied to molten Na2SO4 3). 2. Experimental In order to measure the solubility of Fe2O3 and Cr2O3 powders in binary fused Na2B4O7-B2O3 melts at 1173 K and 1373 K in air, salts and oxide powders were placed in a platinum crucible and heated at 1173 K and 1373 K. The temperature of the platinum crucible was measured by an R-type thermocouple with a wire diameter of 0.2 mm. The basicity of the melt was measured by a basicity sensor using a solid electrolyte, and a coil of platinum wire was immersed and drawn out of the melt to quench the melt sample. To determine the quantity of soluble Fe or Cr in the melt, the quenched samples were analyzed by ICP-AES. To secure the chemical equilibrium of the melts, measurements were conducted after heating at 1173 K and 1373 K in air for more than 86.4 ks. 3. Results For the entire range of the tested basicity, the solubility of Fe2O3 was one order of magnitude higher than that of Cr2O3. The solubility of both Fe2O3 and Cr2O3 decreased as the basicity of the melt increased. From the oxides’ solubility dependence on the melt basicity, both Fe2O3 and Cr2O3 are suggested to dissolve by the basic dissolution reaction. Comparing the solubility of oxides with the same basicity at 1173 K and 1373 K suggests the possibility of organizing the solubility of oxides in Na2O-B2O3 melts in air by their basicity. References 1) R. A. Rapp et al.: JOM 1994. December 47-55 2) H. Khedim et al.: J. Non-Crysta. Solids. 356 (2010) 2734-2741 3) R. Toki et al.: Mater. Trans. 57 (2) (2016) 143-147

1173 K における Na<sub>2</sub>O-B<sub>2</sub>O<sub>3</sub> 系溶融塩の Fe<sub>2</sub>O<sub>3</sub>, Cr<sub>2</sub>O<sub>3</sub> の溶解度測定

1173 K における Na<sub>2</sub>O-B<sub>2</sub>O<sub>3</sub> 系溶融塩の Fe<sub>2</sub>O<sub>3</sub>, Cr<sub>2</sub>O<sub>3</sub> の溶解度測定

Thermodynamics of leaching roasted jarosite residue from zinc hydrometallurgy in NH4Cl system

The thermal decomposition process of jarosite residue and the solubility of various oxides presented in the decomposed residue in NH4Cl-H2O system were studied. The results of heat decomposition of jarosite residue show that the insoluble ZnFe2O4 phase in the residue can be decomposed at temperatures ranging from 500 °C to 650 °C for 1 h. The OLI Systems software was used to study the thermodynamics of the solubility of various metal oxides existing in the decomposed residue in NH4Cl-H2O system. The results show that the solubility of ZnO, PbO, CdO, CuO and Ag2O is high, while the solubility of Fe2O3 is less than 10−4 mol/L in the pH range from 4.0 to 9.0. The calculated data are in accordance with the experimental results.

Chemical Equilibrium and Critical Phenomena: The Solubilities of Iron(III) Oxide and Cobalt(II,III) Oxide in Isobutyric Acid + Water Near the Consolute Point

The solubilities of iron(III) oxide, formula Fe2O3, and cobalt(II,III) oxide, formula Co3O4, have been determined in the liquid mixture, isobutyric acid + water, along the critical isopleth at temperatures above the upper critical solution temperature near 299 K. When plotted in van’t Hoff form with ln s versus 1/T, the measurements of solubility, s, lie on a straight line for values of the temperature, T, in kelvin, which are sufficiently in excess of the critical solution temperature, Tc. The sign of the slope, (∂ ln s/∂(1/T)), indicates that in the case of both oxides, the dissolution reaction is endothermic. When the temperature is within 1K of Tc, however, the slope departs from its constant value and appears to diverge toward negative infinity. The principle of critical-point universality predicts that a divergence in (∂ ln s/∂(1/T)) is to be expected for T near Tc in those cases where the stoichiometry of the dissolution reaction involves both components of the solvent; moreover, the Gibbs–Helmholtz equation predicts that, if the heat of solution is endothermic, the sign of the divergence should be negative. Both of these predictions are confirmed by the solubilities of Fe2O3 and Co3O4 measured as a function of temperature along the critical isopleth of isobutyric acid + water.

Oxygen-ion diffusion and electrical conduction of La2Mo2−2x Fe x O9−δ systems

Based on the novel oxygen ion conductor La2Mo2O9, a series of Fe-doped samples of La2Mo2−x FexO9−δ (x = 0, 0.025, 0.05, 0.1) was prepared by conventional solid-state reaction method. The structure, phase transition, oxygen ion diffusion and electrical conductivity were studied with X-ray diffraction (XRD), differential scanning calorimeter (DSC), direct current (dc) resistivity, and dielectric relaxation (DR) measurements. One DR peak associated with the short-distance diffusion of oxygen vacancies was observed in both temperature and frequency spectra. The activation energy for oxygen ion diffusion in Fe-doped La2Mo2O9 samples was smaller than that in un-doped samples. Fe doping can increase the ionic conductivity of La2Mo2−xFexO9−δ samples as well as the ionic transference number in the temperature range from 680°C to 400°C in comparison with the un-doped samples, although the electronic conductivity slightly increases. It is found that because of the small solubility of Fe2O3 in La2Mo2O9 (<5%), Fe doping cannot suppress the phase transition that occurred around 570°C, but 2.5% K doping at La site at the same time (e.g. in sample La1.95K0.05Mo1.95Fe0.05O9−δ) can completely suppress this phase transition and increase conductivity at lower temperatures.

Solubility of Metal Oxides under Control of Basicity by Electrolysis in Fused Na&lt;SUB&gt;2&lt;/SUB&gt;SO&lt;SUB&gt;4&lt;/SUB&gt;

The dissolution behavior of NiO, Co3O4, Fe2O3, Fe3O4, SiO2, Al2O3 and Cr2O3 powders under the control of the O2− activity of fused Na2SO4 by electrochemical polarization was investigated. As a result, the increase in the quantity of electricity for the anodic reaction with increasing polarization potential for the platinum electrode caused an increase in the basicity(−log aNa2O) of the fused Na2SO4, while the increase in the quantity of electricity for cathodic reaction with decreasing polarization potential caused a decrease in basicity of the fused Na2SO4. The solubility of NiO and Co3O4 in fused Na2SO4 increased in the anodic potential region. However, their solubility did not increase in the cathodic potential region. The solubility of Fe2O3 and Fe3O4 slightly increased in the anodic potential region. The solubility of SiO2 did not increase in the anodic potential region, whereas the solubility of SiO2 increased with a decrease in the polarization potential in the cathodic potential region. The solubility of Al2O3 and Cr2O3 increased in the cathodic and anodic potential regions. The solubility of Al2O3 was larger than that of Cr2O3. We found that the resistance of acid and basic dissolution for oxides could be estimated by the electrochemical polarization method.

Lead Zirconate‐Lead Titanate Piezoelectric Ceramics with Iron Oxide Additions

An investigation of the effects of small additions of Fe2O3 to lead zirconate‐lead titanate ceramics with compositions between 45 and 60 mol% lead zirconate has shown that, with 2 moles of PbO to balance each mole of Fe2O3, the solubility of Fe2O3 was about 0.8 wt% in compositions near the tetragonal‐rhombohedra1 boundary. The dielectric constant and dissipation factor for both rhombohedra1 and tetragonal materials were decreased by addition of iron oxide, whereas the mechanical quality factor and frequency constant were increased. The dependence of the electromechanical properties on grain size was qualitatively similar for both undoped and iron oxide‐doped materials; the presence of iron oxide inhibited grain growth and lowered the limiting grain size below which the electromechanical properties change rapidly with grain size.

On the Phase Diagram of the Condensed System BaO-Fe2O3

The equilibrium of the system BaO-Fe2O3 has been studied by ordinary mineralographic methods. In some of the specimens of this system, the dissociation of Fe2O3 has been observed, and hence in such cases, the experiments were conducted under 1 atm. pressure of oxygen.The results obtained in the present studies are summarized in Fig. 1. The existence of three compounds BaO⋅6Fe2O3, BaO⋅Fe2O3 and 2BaO-Fe2O3 was confirmed. The two binary eutectic reactions, Liquid ?? BaO.6Fe2O3+BaO⋅Fe2O3 at 1370°C and Liquid ?? BaO⋅Fe2O3+2BaO⋅Fe2O3 at 1330°C ware observed at the composition of 60.0 mole% and 41.2 mole% Fe2O3 respectively.BaO.6Fe2O3 (85.7mole% Fe2O3) forms a solid solution by the dissolution of BaO⋅Fe2O3. The BaO: Fe2O3 ratio of the solid solution was 18.2: 81.8 mole at 1350°C and 16.7: 83.3 mole at 800°C, but the solubility of Fe2O3 in this phase was not observed. The solubility range of BaO.Fe2O3 phase is very narrow and the solubility of BaO⋅Fe2O3 in 2BaO⋅Fe2O3 was not observed. The compound BaO⋅6Fe2O3 is a hexagonal lattice, a =5.877, c=23.02Å, BaO⋅Fe2O3 a tetragonal lattice, a=6.02, c=9.45Å, and 2BaO⋅Fe2O3 a cubic lattice, a=8.07Å.