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Environmental hazards due to alkali elution can be mitigated by investigating the dissolution kinetics of calcium silicate mineral phases in water. This study demonstrated the effect of the silicate skeleton structure on the dissolution kinetics of calcium silicate mineral phases in water. The time dependence of the Ca-Si relative release ratio during leaching indicated the preferential elution of Ca to Si in the initial stage of dissolution. The formation of a Ca-depleted layer on the surface of the leached sample was confirmed by X-ray photoelectron spectroscopy and time-of-flight secondary-ion mass spectrometry. The elution kinetics of Ca and Si were determined by the semi-infinite diffusion model and the detachment reaction of the intermediate phase that was formed on the surface of the mineral by hydration, respectively. Furthermore, the nanoscale intermediate phase was observed by transmission electron microscopy. The diffusion coefficient of Ca in the leached layer and the reaction-rate coefficient of Si were obtained from the elution kinetics of Ca and Si, respectively, and these decreased with the increase in the degree of polymerization of the silicate skeleton structure that varied in the following sequence: calcio-olivine (γ-Ca2SiO4) > rankinite (Ca3Si2O7) ≈ wollastonite (β-CaSiO3) > pseudowollastonite (α-CaSiO3). more...

Phase equilibria of the ternary CaO-ZnO-SiO2 system have been investigated at 1170 °C to 1691 °C for oxide liquid in equilibrium with air and solid oxide phases: tridymite or cristobalite SiO2 (up to two immiscible liquids), pseudowollastonite (CS) CaSiO3, rankinite (C3S2) Ca3Si2O7, dicalcium silicate (C2S) (Ca, Zn)2SiO4, tricalcium silicate (C3S) (Ca, Zn)3SiO5, lime (Ca, Zn)O, zincite (Zn, Ca)O, willemite Zn2SiO4 and hardystonite (melilite) Ca2ZnSi2O7, covering the ranges of concentrations not studied before. High-temperature equilibration on primary phase (silica) or inert metal (platinum) substrates followed by quenching and direct measurement of the Ca, Zn and Si concentrations in the phases with the electron probe X-ray microanalysis (EPMA) has been used to accurately characterize the system. Liquidus phase equilibrium data of the present authors for the CaO-ZnO-SiO2 system are essential to obtain a self-consistent set of parameters of thermodynamic models for all phases. more...

The pseudoternary section “FeO”-ZnO-(CaO + SiO2) with a CaO/SiO2 weight ratio of 0.71 in equilibrium with metallic iron has been experimentally investigated in the temperature range from 1000 °C to 1300 °C (1273 to 1573 K). The liquidus surface in this pseudoternary section has been determined in the composition range of 0 to 33 wt pct ZnO and 30 to 70 wt pct (CaO + SiO2). The system contains primary-phase fields of wustite (FexZn1−xO1−y), zincite (ZnzFe1−zO), fayalite (FewZn2−wSiO4), melilite (Ca2ZnuFe1−uSi2O7), and pseudowollastonite (CaSiO3). The phase equilibria involving the liquid phase and the solid solutions have also been measured. more...

Phase-equilibrium data and the liquidus for the system “MnO”-CaO-(Al2O3-SiO2) at a manganese-rich alloy saturation have been determined in the temperature range from 1423 to 1723 K. The results are presented in the form of a pseudoternary section “MnO”-CaO-(Al2O3 + SiO2) with an Al2O3/SiO2 weight ratio of 0.41. The following primary phases are present in the range of conditions investigated: 3Al2O3·2SiO2; SiO2; MnO·Al2O3·2SiO2; (Mn,Ca)O·SiO2; 2(Mn,Ca)O·SiO2; MnO·Al2O3; (Mn,Ca)O; α-2CaO·SiO2; α′-2CaO·SiO2; 2CaO·Al2O3·SiO2; CaO·SiO2, and CaO·Al2O3·2SiO2. The presence of alumina in this system is shown to have a significant effect on the liquidus compared to the system “MnO”-CaO-SiO2, leading to the stabilization of the anorthite and gehlenite phases. more...

The pseudoternary sections FeO-ZnO-(CaO + SiO2) with CaO/SiO2 weight ratios of 0.33, 0.93, and 1.2 in equilibrium with metallic iron have been experimentally investigated in the temperature range from 1000 degreesC to 1300 degreesC (1273 to 1573 K). The liquidus surfaces in these pseudoternary sections have been experimentally determined in the composition range from 0 to 33 wt pct ZnO and 30 to 70 wt pct (CaO + SiO2). The sections contain primary-phase fields of wustite (FexZn1-xO1+y), zincite (ZnzFe1-zO), fayalite (Fu(w)Zn(2-w)SiO(4)), melilite (Ca2ZnuFe1-uSi2O7), willemite (ZnvFe2-vSiO4), dicalcium silicate (Ca2SiO4), pseudowollastonite and wollastonite (CaSiO3), and tridymite (SiO2). The phase equilibria involving the liquid phase and the solid solutions-have also been measured. more...