Al2O3 Cr2O3 System Research Articles

Crystal structure evolution and solid solution mechanism of Al2O3-Cr2O3 system under different reaction conditions

The (Al1-xCrx)2O3 solid solution (ACS) is expected to be an low pollution chromium source for high-performance alumina-chromium oxide refractory materials. In this work, the effects of Cr2O3 content and reaction conditions on the solid solution behavior in the Al2O3-Cr2O3 system were explored and the mechanism was revealed. The relationship between the lattice parameters of the formed ACS phase and the content of Cr2O3 was closer to a linear one as the temperature rose, serving as an indicator for a higher degree of reaction. The solid solution reaction between Al2O3 and Cr2O3 was governed by the diffusion processes of Al3+ and Cr3+ at 1300–1500 °C and 1200 °C, respectively, and thus the increase of Cr2O3 content slowed the solid solution reaction at a low temperature whereas promoted it at elevated temperatures. The diffusion process of solid solution reaction within the Al2O3-Cr2O3 system was consistent with the Cater model; The diffusion activation energy (Ea) decreased as the content of Cr2O3 increased at 1300–1500 °C. When the content of Cr2O3 increased from 25 to 60 mol%, the diffusion activation energy decreased from 92.48 to 86.49 kJ/mol−1, which was attributed to the augmentation in the diffusion rate of Cr3+ caused by the increase of Cr2O3 content and its vapor-phase transport mechanism at high temperatures.

Microstructures and property profiles of atmospheric plasma sprayed (Al,Cr,Ti)2O3 solid solution coatings

Ternary compositions of the Al2O3-Cr2O3-TiO2 system are expected to improve the coating properties of the binary compositions, such as Al2O3-Cr2O3. Previous studies have shown that mechanical blends of all three components are not suitable for the formation of solid solutions. Thus, experimental ternary agglomerated and sintered feedstock powders were prepared in this study, which had different Al2O3/Cr2O3 ratios but a similar content of TiO2 (about 8.5 mol%). Atmospheric plasma spraying (APS) was used to prepare coatings from these powders, as well as from commercial powders of the Al2O3-Cr2O3 system. In the experimental feedstock powders, an (Al,Cr)2O3 solid solution was formed, while significant amounts of TiO2 were found to exist separately. During spraying a ternary (Al,Cr,Ti)2O3 solid solution was formed. The deposition efficiency is positively influenced by the use of agglomeration and sintering for feedstock powder preparation and Al2O3-rich solid solutions connected with some porosity in the powder. The coatings were characterized by their microstructure, phase composition, hardness, abrasion and sliding wear resistance, corrosion against H2SO4 and specific DC resistivity. The coating properties depend on the Al/Cr-ratio. All ternary solid solution coatings show a high corrosion resistance. The addition of TiO2 creates the possibility to tailor the electrical resistance.

Effect of Cr2O3 content on viscosity and phase structure of chromium-containing high-titanium blast furnace slag

For several years, ordinary vanadium-titanium magnetite has been rapidly consumed because of its use in smelting. Thus, sources of chromium-containing vanadium-titanium magnetite will need to be developed and utilized in the future. Therefore, the physical and chemical properties of the blast furnace slag that results from smelting chromium-containing vanadium-titanium magnetite should be completely understood. In the present work, the viscous flow characteristics of CaO–SiO2–MgO–TiO2–Al2O3–Cr2O3 system slag were investigated both theoretically and experimentally to promote a better understanding of the effect of Cr2O3 addition on the viscous behavior of slag. With increasing Cr2O3 content, the viscosity first decreases and then increases. When the Cr2O3 content is a maximum of 0.5 wt.%, Cr2O3 serves as a network modifier to simplify the slag structure and reduce the viscosity. When the added amount was a minimum of 1.5 wt.%, perovskite and spinel phases were formed in the slag, resulting in increased viscosity.

Evaluation of mechanical properties of Al2O3–Cr2O3 ceramic system prepared in different Cr2O3 ratios for ceramic armour components

The aim of the present study was to introduce Al2O3–Cr2O3 ceramic system as an armour material by evaluating its performance with static mechanical tests. Cr2O3 was used as an additive to the pure Al2O3 owing to the character of substitutional solid solution formation that would provide increases in mechanical properties. The effect of Cr2O3 addition in different volume ratios (0.5, 1, 5 vol%) on the microstructure and the mechanical properties (elastic modulus, equibiaxial flexural strength, hardness, fracture toughness) of Al2O3 were investigated. Densification behavior and grain size of Al2O3 changed with the amount of Cr2O3, the highest relative density and grain size were obtained for 1 vol% Cr2O3 added Al2O3–Cr2O3 system. A 44% increase in flexural strength was achieved by 0.5 vol% Cr2O3 addition and attributed to the localized compressive stresses because of the grain boundary modification of the larger size of the Cr3+ ions. 1 vol % Cr2O3 addition increased the hardness 13% while the effect of Cr2O3 on toughness was negligible. The fragmentation behavior was discussed as a function of the stored energy at failure and total crack surface area. A shorter crack length for a given stored energy was observed for 0.5 vol% Cr2O3 composition compared to other compositions indicating its fragments would be larger in identical impact conditions increasing the erosion of the projectile.

Resistance of Refractories of the Al2O3–Cr2O3 System Under Liquid-Phase Reduction Conditions of Iron-Containing Technogenic Waste

Results are provided for a laboratory study of the applicability of refractories in the Al2O3–Cr2O3 system in bubble-agitated double-chamber laboratory furnaces during processing of a broad spectrum of iron-containing materials, including technogenic waste. Laboratory tests are conducted for refractory life in a medium of molten iron. Conditions are modeled for exploitation of a refractory in melting and reducing zones of a bubble-agitated type furnace. Optical microscopy is used to study zones and the overall depth of crucible reaction with melt at the melt – refractory crucible interface.

Anomalous densification behavior of Al2O3–Cr2O3 system

Densification behavior of (Al1−xCrx)2O3 (where, x=0, 0.1, 0.3, 0.5) compacts in the temperature range 1000–1700°C under reducing condition were studied. Up to 1300°C, densification behavior followed the normal trend, i.e., bulk density increases with increase in Cr2O3 content. Anomaly in the densification behavior was observed from 1400°C onwards. Al2O3 samples showed high densification; but the addition of 10mol% Cr2O3 resulted in a sharp decrease in densification; while further Cr2O3 addition showed a steady rise in densification. XRD studies revealed the solid solution formation starts at 1400°C. A broad endothermic peak at around 1400°C in DTA thermogram corresponds to the formation of solid solution which actually absorbs extra heat energy resulting less dense Al2O3–Cr2O3 compacts. The average grain size of sintered Al2O3–Cr2O3 samples increases with increase in Cr2O3 content.

Metastable Phase Relationship in the Al2O3-Cr2O3 System and Phase Equilibria of 1:1 Composition at 1200.DEG.C..

(1) A metastable phase relationship in the Al2O3-Cr2O3 system was made by investigating the existing phases in the samples obtained by heating the coprecipitated powders for 10h in the temperature range from 1000 to 1400°C (Fig. 1). There was a metastable two-phase region of AC+CC phases below about 1330°C.(2) Equilibrium state of 1:1 composition at 1200°C was confirmed to be a single phase of the corundum solid solution.(3) TiO2 addition to the 1:1 composition was found to increase the reaction rate from the AC+CC phases into a single corundum phase at 1200°C.

Thermodynamic Modeling of the Isomorphous Phase Diagrams in the Al2O3–Cr2O3 and V2O3–Cr2O3 Systems

The phase diagrams in the Al2O3–Cr2O3 and V2O3–Cr2O3 systems have been assessed by thermodynamic modeling with existing data from the literature. While the regular and subregular solution models were used in the Al2O3–Cr2O3 system to represent the Gibbs free energies of the liquid and solid phases, respectively, the regular solution model was applied to both phases in the V2O3–Cr2O3 system. By using the liquidus, solidus, and/or miscibility gap data, the interaction parameters of the liquid and solid phases were optimized through a multiple linear regression method. The phase diagrams calculated from these models are in good agreement with experimental data. Also, the solid miscibility gap and chemical spinodal in the V2O3–Cr2O3 system were estimated.

The System CaO–“CaCr2O4”–CaAl2O4 in Air and under Mildly Reducing Conditions

The system CaO–chromium oxide in air is reinvestigated and the existence of intermediate phases with chromium in oxidation states >3+ (Ca5Cr3O12, Ca3(CrO4)2, and Ca5(CrO4)3) confirmed. Under reducing conditions these phases are unstable. A metastable, polymorphic form of calcium chromite, δ‐CaCr2O4, is observed. In the CaO‐rich section of the CaO–Al2O3–Cr2O3 system a ternary intermediate phase, chrome‐haüyne, Ca4[(Al,Cr3+)6O12](Cr6+O4), coexists with calcium chromate and calcium aluminate phases. In air, low melting temperatures are preserved in all assemblages containing calcium chromate phases. Under reducing conditions a new ternary phase, Ca6Al4Cr2O15, coexists with CaO, CaCr2O4, chrome‐haüyne, and calcium aluminate phases. The influence of chromium oxide additions on the solidus temperatures of the CaO–Al2O3 system is insignificant.

Kinetics of formation of spinels in the MgO-FeO(Fe2O3)-Al2O3-Cr2O3 system

We investigated the kinetics of spinel-formation in the MgO-FeO (Fe2O3)-Al2O3-Cr2O3 system using a petrographic method for determining the width of a layer of interaction products. The magnitude of the apparent activation energy of the process of spinellide formation was 327.99 kJ/mole.

Microstrain in some oxide crystalline solutions

Abstract Microstrain measurements were made as a function of composition in the Al202 −Cr2O3, and MgO-NiO crystalline solution systems. A maximum in the Al2O3-Cr2O3 system occurred at 30 mole % Al2O3-70 mole % Cr2O3, and in the MgO-NiO system at 40 mole % MgO-60 mole % NiO. Microstrain in the MgO-NiO system was found to be significantly affected by microstrain in the starting materials. The MgO end member possessed relatively large microstrain initially, and, after reaction, enough microstrain from the starting material remained in the MgO-rich compositions to obscure the expected maximum. Upon decomposition, MgCO3 was found to produce MgO with sufficiently low microstrain to make the microstrain maximum easily observable. A theoretical explanation of the position of the microstrain maximum in the plot of microstrain versus composition was sought in terms of lattice energies and strain energies. Good agreement was obtained between experimental data and calculations based on these energy considerations.