Thermodynamic stabilities of intermediate phases in the Ca–Si system

Electrolytic Reduction of SiO2 Granules in Molten CaCl2

“…According to the binary phase diagram for the Ca-Si system, 52 there are five intermetallic compounds at 1123 K (CaSi 2 , Ca 3 Si 4 , CaSi, Ca 5 Si 3 , and Ca 2 Si), while another compound (Ca 14 Si 19 ) appears above 1173 K. Brutti et al measured the temperature dependence of the equilibrium partial pressure of Ca metal by the Knudsen method, and reported the thermodynamic data for the Ca-Si compounds. 53 The partial pressures of Ca for each reaction and temperature calculated from the literature are listed in Table 2. Since the experimental temperature in the present study was 1123 K, the calculations were conducted at 1123, 1173, 1223, and 1273 K. Here, the partial pressure from pure Ca(l) was calculated using the value from pure Ca(s) below 960 K reported in Ref.…”

“…Since the experimental temperature in the present study was 1123 K, the calculations were conducted at 1123, 1173, 1223, and 1273 K. Here, the partial pressure from pure Ca(l) was calculated using the value from pure Ca(s) below 960 K reported in Ref. 53 and the standard Gibbs energy of the fusion of Ca reported in JANAF. 54 The electrochemical equilibrium of the two Ca-Si alloys, alloy A and alloy B, in the molten CaCl 2 system is expressed as:…”

“…The equilibrium potential, E ðalloy A=alloy BÞ , is given by the Nernst equation: The calculated potentials from the thermodynamic data 53 are listed in Table 3. Since the formation of Ca-Si compounds occurs at potentials more negative than 0.503 V vs. Ca 2+ /Ca at 1123 K, the reduction of SiO 2 to Si without Ca-Si formation is possible at potentials more positive than 0.503 V. Thus, the electrolysis potentials were set at 0.70, 0.60, and 0.50 V in this study.…”

Lattice stability of Ca, Sr and Yb disilicides

“…Experimentally, the CaeSi and the SreSi phase diagrams have been investigated by Manfrinetti et al [12] and Palenzona and Pani [13], their thermodynamic properties of formation at standard pressure and temperature have been derived by Brutti et al [14] and Balducci et al [15] and the high-pressure phase transitions for Ca, Sr and Ba disilicides have been reported by Imai and Kikegawa [16] and Bordet et al [10]. Theoretically, using density functional theory (DFT) within the local density approximation (LDA), various authors have investigated the structure and thermodynamic properties of several AEM silicides [6,17e19].…”

Vapor pressures and thermodynamic properties of strontium silicides

“…The insufficiency of reliable thermodynamic data has been emphasized in [3]. Practically only the binaries Mg-Si, which apparently exhibits the only intermediate phase Mg 2 Si [4][5][6], and Ca-Si [7] have been studied extensively so far.…”