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UBC Theses and Dissertations

Thermodynamics of hydrogen in electroslag remelting Chattopadhyay, Subrata


Oxide ion activities in binary CaF₂ - CaO and ternary, CaF₂ -CaO - Al₂O₃ and CaF₂ - CaO -SiO₂, slags were determined by CO₂-slag equilibrium experiments at 1400°C. The carbonate capacity of these slags was computed and compared with the sulfide1 capacity data available in the literature. The similarity in their trends suggests the possibility of characterizing carbonate capacity as an alternative basicity index for fluoride-based slags. The optical basicity of these slags is difficult to define, and with the assumption of CaF₂ as an inert diluent, this parameter did not show any distinct relationship with carbonate capacity. Slag-D20 equilibrium experiments were performed at 1400°C with binary ( CaF₂ - CaO ) and ternary ( CaF₂ - CaO - Al₂O₃ and CaF₂ - CaO -SiO₂) slags to determine water solubility at two different partial pressures of D₂O. A new technique of slag sampling was employed using a quartz tube. A new and reliable method of water analysis in ESR slags was developed. The new water solubility data were higher than the previous data by an order of magnitude, however, the solubility data showed a linear relationship with the square root of water vapour partial pressure. Also, the solubility was at a maximum in binary slags and a minimum in ternary slags containing SiO₂ with N[sub CaO]/N[sub SiO₂]≤2. These experimental findings were used along with literature data to generate a new equilibrium ratio for hydrogen distributed between the slag and the metal during an ESR process. This information was further extended to compute the maximum permissible water content in an initial ESR slag for the production of an ESR ingot with an acceptable level of hydrogen.

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