Effect of substituting CaO with BaO on the viscosity and structure of CaO‐BaO‐SiO₂‐MgO‐Al₂O₃ slags

Abstract

In this study, the effect of CaO and BaO substitution on the viscosity and structure of CaO‐BaO‐SiO2‐MgO‐Al2O3 slags was investigated. The results showed that the viscosity increased with an increase in the BaO substitution concentration, which was correlated to an increase in the degree of polymerization (DOP) of the slag structural units as the activation energy increased from 207.9 to 263.8 kJ/mol for viscous flow. Deconvolution and area integration of the Raman spectrum of the slag revealed that the ratio of Q3/Q2 (Qi, i is the number of O0 in a [SiO4]‐tetrahedral unit) increased and NBO/Si (nonbridging oxygen per unit silicon atom) decreased with higher BaO content. It was also observed from the 27Al magic angles pinning nuclear magnetic resonance (27Al MAS‐NMR) spectrum that the relative proportion of AlIV increased, while that of AlV decreased because of the decrease in the percentage of nonbridging oxygen (O−), indicating the polymerization of the slag. O1s X‐ray photoelectron spectroscopy (XPS) was also carried out to semi‐quantitatively analyze the various types of oxygen anions present in the slag. The XPS results correlated well with the results obtained from the analysis of the Raman and 27Al MAS‐NMR spectra of the slags and its viscous behavior.

Experimental determination of phase equilibria in the CaO‐BaO‐SiO2‐12 mol pct. Al2O3‐13 mol pct. MgO system at 1573 K and 1623 K

“…Due to the large difference in the molar mass between BaO (153 g/mol) and CaO (56 g/mol), when investigating the influence of equal mass substitution of CaO with BaO at generally less than 15 mass pct., the precipitated crystals did not contain Ba 2+ , but the crystallization temperature of the precipitated phase gradually decreased according to Yan et al and Xiao et al Although a partial substitution of an equal mass of CaO with BaO can lower the melting point of mold fluxes inhibiting crystallization, this does not suggest that an unrestricted substitution amount of CaO with BaO can occur with a continuous decrease in the crystallization temperature. In the region where BaO is used to substitute CaO to gradually lower the crystallization temperature, the increasing viscosity of the molten slags should also be considered . Therefore, the feasible amount of BaO used in the mold fluxes depends on the combination effect of the decreasing crystallization temperature and the increasing viscosity of the mold fluxes.…”

“…The calculated X p × Z/R k values of the cations are given in Table , where lower X p × Z/R k values pertain to the higher basic tendency cations appearing as network modifiers, that is, octahedral structural units, while higher X p × Z/R k values pertain to the higher acidic tendency cations appearing as network formers, that is, tetrahedral structural units . The lower activity of Ca 2+ and the limited mass transfer rate caused by higher viscosities at reduced (C + B)/S ratios with a higher degree of polymerization of the slags may facilitate Ba 2+ cations with the strongest basic tendency to substitute Ca 2+ and bond with cations with acidic tendency in order to form Ba‐containing phases.…”

“…Recent works have reported on the substitution behavior of CaO with BaO in the mold fluxes . Due to its similar physiochemical properties, BaO (melting point at 2196 K, 1923°C) substitution of CaO (melting point at 2845 K, 2572°C) in mass pct.…”

“…Recent works have reported on the substitution behavior of CaO with BaO in the mold fluxes. [14][15][16][17] Due to its similar physiochemical properties, BaO (melting point at 2196 K, 1923°C) substitution of CaO (melting point at 2845 K, 2572°C) in mass pct. can result in lower melting temperatures of multicomponent mold fluxes, which can inhibit their crystallization tendencies.…”

Effect of CaF2, B2O3 and the CaO/SiO2 mass ratio on the viscosity and structure of B2O3‐containing calcium‐silicate‐based melts

“…[45][46][47][48][49][50][51] From the FTIR analysis, the existence and estimated depth of the trough at specific wavenumbers can be assigned to the silicate and borate structural units. The non-bridged oxygen per tetrahedral cation (NBO/T) and in particular the ratio of Q 3 /Q 2 can be correlated with the DOP, as described previously.…”