High-temperature stability of Mg(Al,Cr)2O4 spinel co-existing with calcium aluminates in air |
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| Affiliation: | 1. The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan, 430081, China;2. Centre for Pyrometallurgy, Department of Materials Science & Metallurgical Engineering, University of Pretoria, Pretoria, 0002, South Africa;3. Center for Iron and Steelmaking Research, Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213, USA;1. The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China;2. Department of Ceramic Materials Engineering, University of Bayreuth, Bayreuth 95448, Germany;3. Huaneng Wuhan Power Generation Co, Ltd, Wuhan 430415, China;1. AGH University of Science and Technology, Faculty of Materials Science and Ceramics, al. Mickiewicza 30, 30-059 Kraków, Poland;2. Cracow University of Technology, Institute of Computer Science, al. Jana Paw?a II 37, 31-864 Krakow, Poland;3. The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China;1. Federal University of Sao Carlos, Graduate Program in Materials Science and Engineering, São Carlos, SP, Brazil;2. Materials Microstructure Engineering Group (GEMM), FIRE Associate Laboratory, São Carlos, SP, Brazil;3. RHI Magnesita, Research and Development Center, Praça Louis Ensch, 240, Contagem 32210-902, MG, Brazil;1. Henan Key Laboratory of High Temperature Functional Ceramics, School of Materials Science and Engineering, Zhengzhou University, Zhengzhou, Henan, 450001, China;2. State Key Lab Advanced Refractories, Sinosteel Luoyang Inst. Refractories Res. Co. Ltd., Xiyuan Road 43, Luoyang, 471023, China;3. School of Engineering Management and Real Estate, Henan University of Economics and Law, Jinshui East Road 180, Zhengzhou, 450046, China;4. Technische Universität München, Chair for Construction Chemicals, 85747, Garching, Lichtenbergstraße 4, Germany |
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| Abstract: | Cr2O3 is a well-known corrosion resistant oxide used in refractory applications. However, it can oxidize into toxic and water-soluble Cr(VI) compounds upon reaction with calcium aluminate cement phases in the presence of oxygen, which subsequently causes disposal problems after use. This study describes the extent to which chromium in the spinel Mg(Al,Cr)2O4 phase can be oxidized to Cr(VI) when it reacts with the calcium aluminate cement phases C12A7, CA, CA2 and free CaO at 1300 °C in air, using XRD, XPS and leaching tests (TRGS 613 standard) as analytical tools. On reaction with CaO, the Mg(Al,CrIII)2O4 spinel mainly transformed into hauyne (Ca4Al6CrVIO16) and Ca5Cr3O12 which contains both Cr(IV) and Cr(VI). The reaction of C12A7 and CA with the spinel phase also resulted in the formation of Ca4Al6CrO16. Conversely, the reaction of Mg(Al,CrIII)2O4 spinel with CA2 resulted in the formation of only a trace amount of Cr(VI). Water-soluble Cr(VI) leached in large quantities (>100 mg/L) from samples where the Mg(Al,CrIII)2O4 reacted with either C12A7 or CA. Almost no Cr(VI) leached from the sample when Mg(Al,CrIII)2O4 reacted with CaO, using the standard TRGS 613 leach test, but a significant amount of Cr(VI) was released into solution when leached with a HCl solution for 12 h. Both Cr(IV) and Cr(VI) present in the Ca5Cr3O12 dissolved into acidic solution. Only a small amount of Cr(VI) leached from the sample that resulted when spinel was reacted with CA2, even after a prolonged HCl leach. Cr(III) in spinel Mg(Al,Cr)2O4 is very stable and does not leach in either distilled water or acidic solution. |
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| Keywords: | Refractory castables Calcium aluminates |
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