Baijun Yan

Structure and Crystallization Kinetics of Glassy CaO-Al2O3-SiO2-CaF2-Na2O Mold Fluxes with Varying Basicity

The structure and the crystallization kinetics of CaO-Al2O3-SiO2-CaF2-Na2O mold fluxes with varying basicities were investigated by solid-state 29Si nuclear magnetic resonance with magic angular spinning (MAS-NMR) and differential thermal analysis (DTA) technique, respectively. 29Si MAS-NMR study indicated that the increase of basicity decreased the degree of polymerization of mold fluxes. With the increasing basicity, Q0, Q2, and Q3 gradually decreased, while Q1 gradually increased, and the overall degree of polymerization was reduced. Crystallization analysis showed the cuspidine first crystallized from glass, and wollastonite crystal crystallized at elevated temperature for the samples with basicity (defined as CaO/SiO2 mass ratio) values of 0.9 and 1.0, respectively. Only cuspidine was found to crystallize from glass for the samples with basicity values of 1.1 and 1.2, indicating that the crystallization of wollastonite was suppressed with the increase of basicity. Crystallization kinetics analysis by DTA and field emission scanning electron microscopy equipped with energy dispersive spectroscopy investigation showed that growth mechanism of cuspidine is mainly of the diffusion-controlled three-dimensional growth with the increasing number of nuclei during heating. Activation energies for growth of cuspidine decreased with the increasing basicity of mold flux, which indicated that the crystallization ability was enhanced with the increase of basicity. The relationship between structure and crystallization of mold fluxes was established.

Thermodynamics of Mn in Cu-Mn Melts

The present work aimed to measure the thermodynamic data of manganese in Cu-Mn melts over a broad manganese concentration range, using the equilibrium among the liquid copper/MnO(s)/CO-CO2 gas mixture in the temperature range from 1673xa0K to 1873xa0K (1400xa0°C to 1600xa0°C). Darken’s quadratic formalism was introduced to correlate the activity coefficient of manganese in copper to composition, and the excess molar Gibbs energy change of mixing of Cu-Mn melts was described satisfactorily by Redlich–Kister type polynomial.

Activity of MnO in MnO-CaO-SiO2-Al2O3-MgO Molten Slags

The activities of MnO in the MnO-CaO-SiO2-Al2O3 (10, 20, and 30xa0mass pct)-MgO (5xa0mass pct) melts at 1873xa0K (1600xa0°C) were measured by equilibrating the melts with liquid copper under an oxygen partial pressure controlled by CO/CO2 gas mixture with a volume ratio of 99/1. Over the investigated composition range, MnO shows a negative deviation from Raoultian behavior. On the basis of the experimental data, the activity coefficient of MnO in this multicomponent melts was evaluated using the following quadratic formalism based on regular solution model:

Study of Chromium Oxide Activities in EAF Slags

RTln {gamma_{{text{MnO}}({text{s}})}} = sumlimits_j {{alpha_{ij}}x_j^2} + sumlimits_j {sumlimits_k {( {{alpha_{ij}} + {alpha_{ik}} - {alpha_{jk}}}){x_j}{x_k} + I{^prime}} } .

Study of MnO Activity in CaO-SiO2-MnO-Al2O3-MgO Slags

RTlnγMnO(s)=∑jαijxj2+∑j∑k(αij+αik-αjk)xjxk+I′. The values of the conversion factor, I′, for the melts containing 10, 20, and 30 mass pct Al2O3 were determined to be 6950, 2715, and 12092xa0J/mol, respectively. Iso-activity contours for MnO in the five component system were calculated using the quadratic formalism, and they showed a good agreement with the experimental data.

Reply to the “Discussion of Determination of Activities of Niobium in Cu-Nb Melts Containing Dilute Nb”

The activity coefficients of niobium in Cu-Nb melts were measured by equilibrating solid NbO2xa0with liquid copper under controlled oxygen potentials in the temperature range of 1773xa0K to 1898xa0K (1500xa0°C to 1625xa0°C). Either CO-CO2xa0gas mixture or H2-CO2xa0gas mixture was employed to obtain the desired oxygen partial pressures. Cu-Nb system was found to follow Henry’s law in the composition range studied. The temperature dependence of Henry’s constant in the Cu-Nb melts could be expressed as follows:

Experimental Determination of the Liquidus in the High-Basicity Region in the Al2O3(25 mass pct)-CaO-MgO-SiO2 and Al2O3(35 mass pct)-CaO-MgO-SiO2 Systems

log gamma_{{{text{Nb(l}})}}^{0} = frac{3305}{T} + 0.72.