固体亜鉛ケイ酸塩中のZnOに関する熱力学的研究

鉄還元揮発法による亜鉛製錬の基礎研究 (第4報)

抄録

Phase relations of solid ZnO-SiO₂, ZnO-SiO₂-CaO, ZnO-SiO₂-Al₂O₃ and ZnO-SiO₂-MgO systems at 1073K have been determined by the X-ray diffraction and X-ray microanalysis studies of quenched samples. And the e.m.f. measurements using the stabilized zirconia solid electrolytes have been carried out to determine the activities of zinc oxide in solid ZnO-SiO₂ and ZnO-SiO₂-CaO systems, the activities of zinc in liquid Au-Zn alloys and the standard free energy of formation of Cu₂0 and ZnO. The results are summarized as follows:(1) In ZnO-SiO₂ system, the activities of zinc oxide were represented by a single value of azno=1.0 over the range Nzno=0.67-1.0, while at Nsio=0.33-1.0 they showed also a single value but of around 0.2 at 973 and 1073 K. The standard free energy change of formation of Zn₂SiO₄ from ZnO and SiO₂ was determined as follows:
ΔG^°_r/J·mol^-1 (Zn₂SiO₄)=-46590+16.79T/K (973-1073K).
(2) In ZnO-SiO₂-CaO system, the activities of zinc oxide showed a single value of azno=1.0 in the compositions near the pure ZnO at 973-1073K. In ZnO-SiO₂-Al₂O₃ and ZnO-SiO₂-MgO systems, solid solubilities of SiO₂, Al₂O₃, MgO in ZnO phase were negligible small and it was considered that the activities of zinc oxide showed a single value of aznO=1.0 in the compositions near the pure ZnO.
(3) In liquid Au-Zn alloys, the activities of zinc showed considerable negative deviation from Raoult's law at 1023, 1073K and agreed well with published data.
(4) The standard free energy of formation of Cu₂0 and ZnO were determined as follows:ΔG^°Cu 2O/J·mol^-1=-166690+71.03T/K±100 (871-1317K)
ΔG^°znO/J·mol^-1=-355940+108.53T/K±190 (823-1073K).