Cr2O3 System Research Articles

Subsolidus area of the MgO–P2O5–Cr2O3 system: Synthesis, properties and application of magnesium–chromium phosphates as colouring substances

Subsolidus area of the MgO–P2O5–Cr2O3 system: Synthesis, properties and application of magnesium–chromium phosphates as colouring substances

Analysis of phase equilibria in liquid chromium-manganese steels in the presence of calcium. Report 1. Phase diagrams of oxide systems.

The metallurgical industry produces a wide range of chromium-manganese steels, deoxidized and modified with calcium. To determine the non-metallic inclusions (NI) that can form in the Fe–Ca–Cr–Mn–C–O system, it is necessary to study the double and triple phase diagrams included in the FeO–CaO–MnO–Cr2O3 system. Divalent chromium oxide, which is also included in the oxide melt in the Fe–Ca–Cr–Mn–C–O system, practically does not occur in the literature as a component of double or triple state diagrams; therefore, the activity of chromium(II) oxide was equated to its ion fraction and state diagrams with it were not considered in this work. The state diagrams of oxide systems FeO–CaO, FeO–MnO, FeO–Cr2O3, CaO–MnO, MnO–Cr2O3, and FeO–MnO–Cr2O3 were previously studied by the authors. In this work, the state diagrams of the CaO–Cr2O3, FeO–CaO–Cr2O3, FeO–CaO–MnO, and CaO–MnO–Cr2O3 systems are calculated and plotted. The mixing energies are selected to determine activities in solid (theory of regular ionic solutions) and liquid (theory of subregular ionic solutions) oxide solutions to calculate the coordinates of the liquidus and solidus lines of these state diagrams. The enthalpy (103.4 KJ/mol) and entropy (21.958 J/(mol•K)) of melt-ing of calcium chromite CaCr2O4 are specified. The invariant points of the state diagrams of the FeO–CaO–Cr2O3 and CaO–MnO–Cr2O3 systems have been determined. The study of double and triple phase diagrams belonging to the FeO–CaO–MnO–Cr2O3 system will make it possible to determine all possible NIs that can form in chromium-manganese steels in the presence of calcium under equilibrium conditions.

The novel ternary phase CaAl2±xCr2±xO7 in the Al2O3–CaO–Cr2O3 system: What is the chromium solubility?

Recently, in the Al2O3–CaO–Cr2O3 system, a Cr3+ ternary phase named wuboraite (CaAl2Cr2O7) was synthesized for the first time in an air atmosphere, which later showed an undetermined hint of solid solubility between Cr3+ and Al3+ in different atmosphere. In the present investigation, the solubility limits (or x values) of the CaAl2±xCr2±xO7 were determined by conducting high-temperature equilibrium experiments in both air and N2 atmospheres with the various proportionate mixtures of CaO, Al2O3, and Cr2O3, and subsequently using powder X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis. In the air atmosphere, the Cr richest end-member of the Wuboraite solid solution phase is CaAl1.77Cr2.23O7 (or x = 0.23), while that of Al richest end-member is CaAl2.18Cr1.82O7 (or x = 0.18). Whereas, in the N2 atmosphere, the Cr richest end-member of the wuboraite solid solution phase is CaAl1.77Cr2.23O7 (or x = 0.23), while that of Al richest end-member is CaAl2.15Cr1.85O7 (or x = 0.15).

Study on diffusion kinetics of chromium and nickel electrochemical co-deposition in a NaCl–KCl–NaF–Cr2O3–NiO molten salt

Abstract The process of preparing surface composite by molten salt co-deposition is the result of the mass transfer of active particles in molten salt, electrochemical reduction, and solid diffusion. In this study, we prepared Cr–Ni alloy/low-carbon steel surface composites in NaCl, KCl, NaF, Cr2O3, and NiO melt salt system successfully, and analyzed the entire diffusion dynamics process, aiming to find out the limiting links and provide ideas for further improving the preparation efficiency. The results show that chromium and nickel ions are simultaneously reduced on the cathode surface through two and one steps, respectively. And an alloy layer with Fe content of 64.52 wt%, Ni content of 28.96 wt%, and Cr content of 6.52 wt% is formed on the surface of low-carbon steel substrate. The average diffusion coefficients of chromium and nickel atoms in the surface composites are 1.16 × 10−14 and 1.44 × 10−14 m2·s−1. The mass transfer process in molten salt is the limiting link in the whole preparation process.

REFINEMENT OF THE FOUR-COMPONENT SYSTEM MgO – CaO – Al2O3 – Cr2O3 SUB-SOLIDUS STRUCTURE INCLUDING THE Сa6Al4Cr2O15 COMPOUND

The results of theoretical calculations of the subsolidus structure of the four-component system MgO – CaO – Al2O3 – Cr2O3 are presented, taking into account the three-component compound Сa6Al4Cr2O15. Thermodynamic and geometric topological analysis methods were used to establish stable conodes in the specified system. When dividing the concentration tetrahedron MgO – CaO – Al2O3 – Cr2O3 into elementary ones with the involvement of a geometro-topological analysis, it is possible to make an unambiguous closure to the elementary tetrahedron of faces with incident edges (connodes) through a common vertex. The use of this method allows to minimize the number of necessary thermodynamic calculations. The tetrahedra of the MgO – CaO – Al2O3 – Cr2O3 system, taking into account the stable phases, is caused by the presence of three "internal" conodes passing through the three-dimensional space of the concentration tetrahedron: Сa6Al4Cr2O15 – MgO; MgCa3Al4O10 – CaCr2O4, CaCr2O4 – MgAl2O4, which determine the presence of 14 elementary tetrahedra in the subsolidus region. The lengths of conodes and volumes of elementary tetrahedra were calculated taking into account barycentric coordinates and elements of Euclidean geometry. The phases included in the composition of the tetrahedron with the largest relative volume and the smallest asymmetry CaCr2O4 – СaAl2O4 –MgAl2O4 – MgO (185.6 ‰ and 2.55, respectively) have the highest probability of existence in the system, which will allow the development of a sustainable technology for creating composite materials based on calcium aluminochromite cement, with periclase as an aggregate, without special techniques dosage of initial components. At the same time, in the event of a violation of the technological process, magnesium aluminate spinel will be synthesized in the composition of the unformed material, which will not lead to deterioration of the performance characteristics of the composite used. It should be noted that elementary tetrahedra with a high degree of asymmetry, which require appropriate dosage accuracy when predicting the phase composition of synthesized composite materials, are located in areas of the system that are not technologically advantageous from the point of view of obtaining unformed refractories based on special binder materials, and are interest for materials scientists in the ceramic and refractory industries.

Formation mechanisms of Wuboraite (CaAl2Cr2O7) in air and Ar atmosphere

Recently, a new high-temperature ternary Cr(III) phase (Wuboraite, CaAl2Cr2IIIO7) was synthesized in the Al2O3–CaO–Cr2O3 system. However, its formation & chemical transformation mechanism is yet to be explored in detail. And here, we investigated the system between 500 and 1600 °C under the air and argon (Ar) atmosphere via solid-state reaction using XRD, TG-DSC, XPS, and leaching tests. Wuboraite formation starts at different temperatures (∼1500 & ∼1100 °C) under different atmospheres (air and Ar). The intermediate compounds, CaCrVIO4 and CaCr2IIIO4, formed under air and Ar atmospheres, play a crucial role in wuboraite conversion given proper temperature and stoichiometry.

THERMODYNAMIC MODELING OF PHASE EQUILIBRIA AT STEEL ALLOYED WITH MANGANESE AND CHROME

In order to analyze the phase equilibria that are realized in the Fe–Mn–Cr–C–O system at the liquid metal existence temperatures, an extensive material on the thermodynamics of the interaction reactions of components dissolved in liquid iron has been generalized and systematized, and a database of mutually consistent data has been created. For the first time, the thermodynamic modeling of liquidus line coordinates has been performed and state diagrams for MnO–Cr2O3 and FeO–MnO–Cr2O3 systems have been plotted. The temperature for MnCr2O4 incongruent melting ( = 1812°С) and the enthalpy and entropy for formation of this compound from the components of the oxide melt of the MnO–Cr2O3 system were calculated ( = 190.77 kJ/mol and ( = 75.62 J/(mol•K), respectively). It is shown that for the FeO–MnO–Cr2O3 system phase diagram, there are extensive areas of equilibrium for the oxide melt with solid oxides solutions FeO, MnO and solid solutions of chromites FeCr2O4, MnCr2O4 with variable composition. The energy parameters of the theory of subregular ionic solutions were determined and used for calculation of the activities of oxide melt components (FeO, Cr2O3, MnO). The data obtained made it possible to refine the boundaries of the liquid metal composition in areas, which is in equilibrium with specific oxide phases. It is shown that at steelmaking temperature (1600°C) and contents of manganese and chromium in liquid iron about 1 wt. %, the formation of spinels’ solid solution inclusions is possible. Increasing the temperature to 1800°C (for example, when metal is blown with oxy-gen) can shift the equilibrium towards the formation of liquid oxide inclusions. The obtained results can be used in modeling of steel alloying with manganese and chromium. The effect of carbon on the nature of the phase equilibria that are realized in the system is taken into account. It is shown that already at a carbon content in the liquid metal at the level of 0.1–0.2 wt. %, there is a wide range of metal compositions that are in equilibrium with the gas phase {CO, CO2}. The obtained results can be used in modeling of the processes of steel alloying with manganese and chromium

Finite element analysis of stress evolution during the high temperature oxidation of Ni30Cr+ Cr2O3 systems

The present article describes the finite element analysis of mechanical evolution during high temperature oxidation of a metallic alloy. The concerned phenomena are the stress evolutions with time and space in Ni30Cr + Cr2O3 system during oxidation in the range 800–1000 °C. The forming of an oxide layer on chromium-based alloys in oxidizing environments for high temperature applications provides a good protection against further oxidation. During this oxidation, stresses develop in both oxide layer and metallic substrate, which may cause further layer cracking or spallation and limit the lifetime of alloys in such a challenging environment. In order to investigate the stress distributions, a full thermomechanical model is implemented in the commercial finite element software Abaqus/Standard through a UMAT FORTRAN subroutine. The time-dependent stress is especially calculated and compared to experimental results from bibliography. Different temperatures are considered to estimate their influence on the different phenomena and quantities of the mechanical state. Numerical values of stresses as well as for material parameters are provided in this study.

Stress distribution in depth of NiCr + Cr2O3 systems using high-energy synchrotron X-rays in transmission mode

NiCr alloys develop chromia layers in oxidizing high temperature environments. The stress in oxide layer was largely explored, whereas too few works were devoted to the stress distribution in the underlying metallic substrate. To determine the stress distribution in a duplex oxide-metallic substrate system, a variant of sin2ψ method in transmission mode using high-energy synchrotron X-rays has been developed. 103.4 keV synchrotron X-rays have been used to penetrate 6 × 6 × 0.4 mm and Ø6 × 0.9 mm samples with different oxidation conditions. In order to obtain the stress gradient from the top surface to the bottom surface, the patterns of diffraction were collected and then were analyzed by a complete data processing. The stress varies towards the surface in a non-linear manner, especially near the interface zone. In order to better understand the stress distribution of such a duplex oxide-metallic substrate system, the stress caused by chromium diffusion is investigated by proposing numerical values for coupling coefficient, which finally can partially explain the stress variation near the interface zone.

New high-entropy oxide phases with the magnetoplumbite structure

In the studied BaO–SrO–CaO–La2O3–Fe2O3–TiO2–Al2O3–Mn2O3–CoO–In2O3–Ga2O3–Cr2O3 system there were synthesized three new high-entropy magnetoplumbite phases by solid-state sintering in air at 1300, 1350, and 1400 °C.The average composition of the high-entropy phases obtained at 1350 °C can be described by the formulas:Ba0.48Sr0.30Ca0.05La0.15Fe1.62Ti1.78Al1.55Mn1.45Co1.11In1.29Ga1.52Cr1.71O19;Ba0.39Sr0.37Ca0.05La0.18Fe2.88Ti1.60Al1.69Mn1.09Co0.92In1.20Ga1.27Cr1.38O19;Ba0.37Sr0.29Ca0.05La0.28Fe5.85Ti1.15Al0.97Mn0.74Co0.56In0.85Ga0.94Cr0.97O19.The data obtained indicate that a significant portion of calcium was not incorporated into the high-entropy phase. This must be taken into account in the course of subsequent experimental work on the creation of homogeneous phases necessary for the study of their electrical and magnetic properties.

The phases of the Moon: Modelling crystallisation of the lunar magma ocean through equilibrium thermodynamics

Despite some 50 years of intense research on samples returned from the Apollo missions and lunar meteorites, along with remote-sensing and Earth-based observations, many questions regarding the formation and evolution of the Moon persist. These include the detailed compositional and density structure of the lunar mantle and the source and petrogenesis of the diverse suite of extrusive and intrusive igneous rocks. There is broad agreement that the primary internal structure of the Moon reflects crystallisation of a lunar magma ocean (LMO), and that an inverted density gradient within the mantle cumulates led to some reorganisation of layers by partial convective overturn. Experimental studies have provided invaluable constraints on crystallisation of the LMO, but are limited by the relatively small number of experiments that can practically be undertaken. Here we use recently-developed thermodynamic models for minerals and melt in the K2O–Na2O–CaO–FeO–MgO–Al2O3–SiO2–TiO2–Cr2O3 system to model crystallisation of a full-moon LMO based on two existing end-member bulk compositions—Taylor Whole-Moon (TWM), and Lunar Primitive Upper Mantle, LPUM—on which many experimental studies have been based. We follow several recent studies in considering equilibrium crystallisation of the first 50 vol.% and fractional crystallisation thereafter. Our results match well with experimental studies, and provide detailed constraints on the major oxide composition, mineralogy and density structure based on the two starting compositions that, while exhibiting some similarities, show important differences. The more fertile TWM composition contains significant quantities of garnet in the deep mantle, whereas the LPUM composition has none. By contrast, prior to any gravitational overturn, the uppermost mantle cumulates for TWM are strongly silica-undersaturated and contain abundant aluminous spinel, whereas those for LPUM are silica-saturated. For both starting compositions, with the exception of TiO2 and Na2O, our modelled compositions of the final dregs of fractionated melt show a reasonable match with existing estimates on the composition of urKREEP. Modelled partial melts of the upper-mantle cumulates at low to moderate melt fractions have major oxide compositions that match well with low- and intermediate-Ti lunar basalts. The correspondence is particularly good for picritic (green) glasses that likely represent melts derived from deeper levels within the upper mantle. The wide spread in TiO2 concentrations in lunar basalts and basaltic glasses is consistent with density-driven reorganisation involving ilmenite. Our simulations provide thermodynamically-robust estimates of the compositional, mineralogical and density structure of the lunar interior that are unprecedented in their detail, and which provide the foundation for several lines of future research addressing the origin and secular evolution of the Moon.

Calculation and evaluation of temperatures and eutectic compositions of multicomponent sections of the CaO—Al2O3—Fe2O3—Cr2O3 system

The predicted service temperatures and eutectic compositions of the polycomponent sections of the CaO—Al2O3—Fe2O3—Cr2O3 system were calculated and evaluated. According to the results of geometrical topological studies of this system, the CaAl2O4—CaFe2O4—CaCr2O4—Ca4Al2Fe2O10 tetrahedron has the largest relative volume and the smallest degree of asymmetry. However, the composition of this tetrahedron includes two compounds that do not have hydraulic activity; this will adversely affect the cement strength. Presence of CaFe2O4 will significantly reduce the composition melting point, that why the CaAl2O4—Ca12Al7O33—CaCr2O4—Ca4Al2F2O10 tetrahedron is of more interest. The calculations result of temperatures and eutectic compositions of triple and tetra-component sections of the CaAl2O4—Ca12Al7O33—CaCr2O4—Ca4Al2F2O10 region of the CaO—Al2O3—Fe2O3—Cr2O3 system are presented. The phases that make up this tetrahedron are highly likely to exist in the CaO—Al2O3—Fe2O3—Cr2O3 system, which will allow us to develop a stable technology for the oil-well cementing materials based on calcium-ferro-alumina chromate cement without special techniques for ensuring high accuracy of the starting components dosage. The paper presents graphic images of the liquidus surface of polycomponent sections of optimal region of system. Selected areas are the most suitable for producing oil-well binding materials with an elevated temperature in application. It was found that, composite materials based on this system can be used at temperatures above 1350 °C. Based on the analysis of temperatures and eutectics compositions of polycomponent section, the use of rational area compositions for producing high-temperature resisting oil-well cement has been proved.

Inhibition of Cr6+ by the formation of in-situ Cr3+ containing solid-solution in Al2O3–CaO–Cr2O3–SiO2 system

The pseudo-ternary Al2O3–CaO–Cr2O3 system is of great interest due to various pyrometallurgical applications. However, Cr3+ might be oxidized into toxic and carcinogenic Cr6+ during service, causing harm to humans and the environment. So, doping an adequate amount of SiO2 could suppress the generation of Cr6+. In this experiment, the Al2O3–CaO–Cr2O3 ternary system was doped with different amounts of SiO2 (0–47 wt%) and heat-treated at 1400 °C in the air atmosphere. The reaction mechanism and the phase evolution process were studied by implementing XRD, SEM-EDS, leaching tests, XPS, and associated software. In the Al2O3–CaO–Cr2O3 system under the air atmosphere, chromium primarily exists as a Cr3+ compound CaAl2Cr23+O7 and a Cr6+ compound Ca4Al6Cr6+O16 as a secondary phase. The Cr6+ leaching process was diffusion-controlled and more effective at elevated temperatures. However, Ca4Al6Cr6+O16 disappeared with the addition of SiO2. With the increase of SiO2 content, Cr2O3 tends to be in the Cr3+ form with gehlenite phase (Ca2(Al, Cr)2SiO7) and anorthite phase (Ca(Al, Cr)2Si2O8), thereby inhibiting the Cr6+. Nevertheless, the investigated compositions in the quaternary systems do not exhibit Cr6+ in the air atmosphere at 1400 °C.

Effect of basicity and chromium oxide on the viscosity of boron-containing slags

The main diluent for chromium-containing slags is CaF2. However, fluorspar disadvantages make it necessary to search for a replacement. As a substitute, boron oxide allows to improve slag physical properties and environmental situation. The paper presents the experimental study results of the chemical composition and temperature influence on viscosity of slags of CaO–SiO2–Cr2O3 system containing 8% MgO, 3% Al2O3 and 6% B2O3. It was found that a slag free of chromium oxide with basicity of 1.0 has a sufficiently high fluidity of 0.2–0.6 Pa·s in a wide temperature range of 1200–1350°C, due to high concentration of low-melting phases, reaching 22%, and only 11 % high-melting. A slag with 18% Cr2O3 and the same basicity retains a low viscosity of 0.1–1.0 Pa·s but at higher temperature of 1450–1570 °C due to increase in high-melting compound content to 27%. The viscosity of a slag with basicity of 2.5 without chromium oxide is 0.07–1.0 Pa·s in a narrow temperature range of 1650–1700°C and 0.14–1.0 Pa·s for a ‘shorter’ slag with 18% Cr2O3 and same basicity in even narrower range of 1650–1670°C. These slags have the highest high-melting phase content of about 50%.

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.

Co-existence of a Cr3+ phase (CaAl2Cr2O7) with hydraulic calcium aluminates at high temperature in the Al2O3–CaO–Cr2O3 system

Obtaining a stable Cr3+ phase at higher temperatures in the presence of hydraulic calcium aluminates (the phases found in calcium aluminate cement, CAC) in the Al2O3–CaO–Cr2O3 system remains a significant challenge in many application areas, as the formation of toxic, carcinogenic, and water-soluble Cr6+ compounds often occur. To address the issue, recently, we synthesized a high-temperature stable Cr3+ ternary compound (CaAl2Cr2O7) with space group P3 (143). In the present work, we investigated the formation-stability of CaAl2Cr2O7 with in-situ calcium aluminate phases at 1500 °C under the CO2 atmosphere in the Al2O3–CaO–Cr2O3 system through solid-oxide reactions route varying Cr2O3 content (at constant Al2O3:CaO ratio). It co-existed with hydraulic calcium aluminates and other phases over the full investigated composition range of 2.76–68.3 mol% Cr2O3 (5–80 wt%). Apart from CAC phases (CaAl2O4, CaAl4O7), major Cr3+-phases are CaAl2Cr2O7 and (Al,Cr)2O3 while (α,β)-CaCr2O4 and Ca(Al,Cr)12O19 formed as minor phases. At a constant Al2O3:CaO ratio of 5.6:4.4 mol% (7:3 wt%), the formation of the CaAl2Cr2O7 phase increases with Cr2O3 content (up to the investigated composition of 26.43 mol%) and then decreases gradually. The solid solubility of Al and Cr in the CaAl2Cr2O7 phase limited over a narrow range, and presumably dependent more on heat treatment condition rather than composition as reflected from the lattice parameter calculations. Though XRD revealed the presence of only Cr3+-phases in the partial CO2 atmosphere, however, traces of Cr6+ could be detected using XPS and leaching tests. However, leachable Cr6+ content (0.095–1.252 mg/L) were much below the United States Environmental Protection Agency (US-EPA) permissible limit of 5 mg/L. The formation mechanism of the CaAl2Cr2O7 and other phases with plausible reactions were also discussed.

Thermodynamic Modeling of Phase Equilibria in the FeO-Al<sub>2</sub>O<sub>3</sub>-Cr<sub>2</sub>O<sub>3</sub> and MgO-Al<sub>2</sub>O<sub>3</sub>-Cr<sub>2</sub>O<sub>3</sub> Systems

Thermodynamic modeling of phase equilibria and further construction of a full projection of the liquidus surface in the FeO–Al2O3–Cr2O3 and MgO–Al2O3–Cr2O3 systems were carried out. Theories of sub-regular ionic solutions, regular ionic solutions and ideal ionic solutions were used for calculation. Values of energy parameters of the used thermodynamic models were obtained in the course of the research. These values might be applicable for further modeling of more complex oxide slag systems which are formed in the process of manufacture of chromic steels. Calculated phase diagrams for the FeO–Al2O3–Cr2O3 and MgO–Al2O3–Cr2O3 systems were compared with available data from literature sources.

Delamination Morphology Maps of Chromium Oxide Scales Formed on Cr-Based Alloys

The delamination processes occurring in chromia scales formed on Ni-30Cr and Fe-47Cr alloys were studied. Delamination is the result of the competition between growth stresses evolution during heating, thermal stresses during cooling, and stress release phenomena, leading to high residual stress in the oxide film. Delamination in chromia has been found to occur due to type and amount of residual stresses generated at the end of heating-induced chromia growth and subsequent cooling-induced differential shrinkage. The mapping of the residual stresses in the oxide films at the microscopic scale around the delaminations allow to classify the latter into three different groups: buckles of Type 1, buckles of Type 2, and spalls. Using the stress relaxation magnitude, an assessment of the interfacial toughness of the metal/oxide systems was carried out, thanks to the buckling and crack propagation theory in the oxide. From the value obtained, microscopic observations, and the residual stress maps, a diagram describing the spalling of the buckles for chromia scales is proposed, as well as the delamination maps of Fe-47Cr/Cr2O3 and Ni-30Cr/Cr2O3 systems specifying the conditions of existence of the obtained delamination features.

Effect of Fe2O3 on the size and components of spinel crystals in the CaO−SiO2−MgO−Al2O3−Cr2O3 system

The stability of chromium in stainless steel slag can be enhanced by increasing the spinel crystal size. The effect of Fe2O3 on the size of spinel crystals in the CaO−SiO2−MgO−Al2O3−Cr2O3 system was investigated using lab experiments carried out in a carbon tube furnace. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM−EDS) and X-ray diffraction (XRD) were used to analyze the microstructure, components, and the mineral phases of synthetic slags. FactSage 7.1 was used to calculate the crystallization process of the molten slag. The results showed that the addition of Fe2O3 promoted the precipitation of spinel crystals and inhibited the formation of dicalcium silicate. The size of spinel crystals increased from 2.74 to 8.10 µm and the contents of chromium and iron in the spinel varied as the Fe2O3 addition was increased from 0 to 20wt%. Fe2O3 thermodynamically provided the spinel-forming components to enhance the formation of FeCr2O4, MgFe2O4, and Fe3O4. The addition of Fe2O3 increased the fraction of liquid phase in a certain temperature range and promoted diffusion by decreasing the slag's viscosity. Therefore, Fe2O3 is beneficial to the growth of spinel crystals in stainless steel slag.

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.