Thermodynamics of oxide-sulfate melts: the system PbO-PbSO₄

Activities in the PbO-PbSO₄ melts at 1253 K have been measured by emf and gas-equilibration techniques. The activity of PbO was directly obtained from the emf of the solid oxide cell, Pt, Ni-NiO/CaO-ZrO₂/Auo.92PbO.08, PbOx-PbSO4(1-x), Ir, Pt for 1.0 >XPbO > 0.6. The melt and the alloy were contained in closed zirconia crucibles. Since the partial pressure of SO₂ gas in equilibrium with the melt and alloy was appreciable (>0.08 atm) atXPbO < 0.6, activities at lower PbO concentrations were derived from measurements of the weight gain of pure PbO under controlled gas streans of Ar + SO₂ + O₂. The partial and integral free energies of mixing at 1253 K were calculated and found to fit a subregular model: ΔGEPbO =X²PbSO₄ {-42,450 + 20,000X2PbSO₄} J mol-1 ΔGEPbO =X²pbSO {-12,450 - 20,000XPbS} J mol^-1 ΔG^EpbSOXPbSO₄ {-32,450XPbS - 22,450XPbSO₄ } J mol^-1. The standard free energy of formation of liquid PbSO₄ from pure liquid PbO and gaseous SO₃ at 1 atm at 1253 K was evaluated as -88.02 (±0.72) kJ mol^-1

Some observations of the reactions between molten oxides and solid carbon

Observations of the reactions between molten metal oxides and various forms of carbon have been made using X-ray transmission and optical techniques. Particular attention has been paid to the wetting characteristics and the reaction rates between the melts and carbon. The critical slag surface tension for complete wetting of metallurgical coke is predicted. The results also indicate that non-wetting oxide melts are reduced by a gas ferrying mechanism between the carbon and the melt. On the other hand, oxides which wet the carbon surface appear to be reduced through separate and parallel electrochemical reactions