Formation of CaZrO₃ at the interface between CaO–SiO₂–MgO–CaF₂(–ZrO₂) slags and magnesia refractories: Computational and experim

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• 作者：Joo Hyun Park
• 关键词：Calcium zirconate ; Refractory ; Thermodynamic calculation ; Zirconia ; Activity
• 刊名：Calphad
• 出版年：2007
• 出版时间：June 2007
• 年：2007
• 卷：31
• 期：2
• 页码：149-154
• 全文大小：1190 K

文摘

The formation behaviour of calcium zirconate (CaZrO₃) at the interface between the CaO–SiO₂–MgO–CaF₂(–ZrO₂) slags (B(=(mass % CaO) /(mass % SiO₂)) = 2.0) used in the AOD converter and the MgO refractories has been computed by employing a commercial thermodynamic software. The solubility of zirconia (ZrO₂) in the liquid CaO–SiO₂-7 mass % MgO slag phase is relatively small, viz. about 2–3 mass % and the CaZrO₃ phase is formed at about B>1.5. The region of fully liquid phase extends to the composition saturated by dicalcium silicate (Ca₂SiO₄) and cubic ZrO₂ (B1.2). The effect of 7 mass % CaF₂ addition on the solubility of ZrO₂ in the liquid slag phase was computed to be negligible, while the liquid phase exists through the entire compositions. In addition, the region of fully liquid phase extends to the more basic composition range (10928f4350c607b"" title=""Click to view the MathML source"">B1.5), where the saturating phases are the Ca₂SiO₄ and CaZrO₃. The thermodynamic calculations indicate CaZrO₃ not to form at (mass % ZrO₂) /(mass % MgO) ((=Z/M))<0.6. In the “ Liquid+Ca₂SiO₄+MgO” region, the activity of SiO₂ in the liquid phase is nearly fixed because the activity of CaO in the liquid phase is unaffected by the activity of ZrO₂. However, with higher ZrO₂ activity from the increase in the Z/M ratio, the activity of CaO in the liquid phase is expected to decrease due to the formation of CaZrO₃. The formation behaviour of CaZrO₃ in the slags, computed based on the Gibbs energy minimization principles, could experimentally be confirmed by employing the XRD and SEM–EDS analysis.