High-Temperature Chemical Stability of Cr(III) Oxide Refractories in the Presence of Calcium Aluminate Cement
Al<sub>2</sub>O<sub>3</sub>-CaO-Cr<sub>2</sub>O<sub>3</sub> castables are used in various furnaces due to excellent corrosion resistance and sufficient early strength, but toxic Cr(VI) generation during service remains a concern. Here, we investigated...
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| Autores principales: | , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
MDPI AG
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/b072899da87c4a728dc3a0273c77190a |
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| Sumario: | Al<sub>2</sub>O<sub>3</sub>-CaO-Cr<sub>2</sub>O<sub>3</sub> castables are used in various furnaces due to excellent corrosion resistance and sufficient early strength, but toxic Cr(VI) generation during service remains a concern. Here, we investigated the relative reactivity of analogous Cr(III) phases such as Cr<sub>2</sub>O<sub>3</sub>, (Al<sub>1−x</sub>Cr<sub>x</sub>)<sub>2</sub>O<sub>3</sub> and in situ Cr(III) solid solution with the calcium aluminate cement under an oxidizing atmosphere at various temperatures. The aim is to comprehend the relative Cr(VI) generation in the low-cement castables (Al<sub>2</sub>O<sub>3</sub>-CaO-Cr<sub>2</sub>O<sub>3</sub>-O<sub>2</sub> system) and achieve an environment-friendly application. The solid-state reactions and Cr(VI) formation were investigated using powder XRD, SEM, and leaching tests. Compared to Cr<sub>2</sub>O<sub>3</sub>, the stability of (Al<sub>1−x</sub>Cr<sub>x</sub>)<sub>2</sub>O<sub>3</sub> against CAC was much higher, which improved gradually with the concentration of Al<sub>2</sub>O<sub>3</sub> in (Al<sub>1−x</sub>Cr<sub>x</sub>)<sub>2</sub>O<sub>3</sub>. The substitution of Cr<sub>2</sub>O<sub>3</sub> with (Al<sub>1−x</sub>Cr<sub>x</sub>)<sub>2</sub>O<sub>3</sub> in the Al<sub>2</sub>O<sub>3</sub>-CaO-Cr<sub>2</sub>O<sub>3</sub> castables could completely inhibit the formation of Cr(VI) compound CaCrO<sub>4</sub> at 500–1100 °C and could drastically suppress Ca<sub>4</sub>Al<sub>6</sub>CrO<sub>16</sub> generation at 900 to 1300 °C. The Cr(VI) reduction amounting up to 98.1% could be achieved by replacing Cr<sub>2</sub>O<sub>3</sub> with (Al<sub>1−x</sub>Cr<sub>x</sub>)<sub>2</sub>O<sub>3</sub> solid solution. However, in situ stabilized Cr(III) phases as a mixture of (Al<sub>1−x</sub>Cr<sub>x</sub>)<sub>2</sub>O<sub>3</sub> and Ca(Al<sub>12−x</sub>Cr<sub>x</sub>)O<sub>19</sub> solid solution hardly reveal any reoxidation. Moreover, the CA<sub>6</sub> was much more stable than CA and CA<sub>2</sub>, and it did not participate in any chemical reaction with (Al<sub>1−x</sub>Cr<sub>x</sub>)<sub>2</sub>O<sub>3</sub> solid solution. |
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