メタ珪酸塩ガラスのイオン構造

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This is the second paper in a series of articles concerning "Thermodynamic Approach to the Structure of Silicate Glasses". By applying the method presented in the first paper of the series [This Journal, 68, 204-210 (I960)], calculations of free-energy changes and equilibrium constant? have been made for reactions of forming metasilicate building units of sodium, calcium and magnesium from the combination of other types of silicate building units including SiO_2 at temperatures of 298°-1,500°K. The values of equilibrium constant, K, for the above types of reactions of forming sodium metasilicate building unit were decreased with the increase of temperature and were also decreased, at a given temperature, with the decrease in difference of the silicon-oxygen ratio, A'si, between each reactant and the resultant ; for example, the values of log_<10> K for the reaction, n [(4Na^+)(SiO_4^<4->)] (N_<Si>=0.250)+n[SiO_2] (N_<Si>=0.500)⇄2 [(2nNa^+) (Si_nO_<3n>^<2n->)] (N_<Si>=0.333), at 298° and 1,100°K were respectively 3.37 and 0.74, the values of log_<10> for the reaction, n [(6Na^+)(Si_2O_7^<6->)] (N_<Si>=0.286)+[(2nNa^+)(Si_<2n>O_<5n>^<2n->)](N_<si>=0.400) ⇄ 4[(2/zNa+)(Si_nO<3n>^<2n->)](N_<Si>=0.333), at 298° and 1,100°K respectively 0.59±0.30 and 0.04±0.26, and the values of log_<10> K for the reaction, n [(14Na^+)(Si_6O_<19>^<14->)] (N_<Si>=0.316)+[(2nNa^+)(Si_<2n>O_<5n>^<2n->)] (N_<Si>=0.400) ⇄ 8 [(2nNa^+)(Si_nO_<3n>^<2n->)](N_<Si>=0.333), at 298° and 1,100°K respectively 0.29±0.37 and -0.02±0.32, where n denoted an integer and (Si_2O_7^<6->) and (Si_6O_<19>^<14->) were linear silicate anions. The effect of replacing sodium oxide component by calcium and/or magnesium oxides on the value of K for the reactions of forming metasilicate building unit was almost within the range of suggested errors. It can be said, therefore, that the value of K for the reactions does not depend predominantly on the kind of cations Na^+, Ca^<2+> and Mg^<2+>, but depends mainly on both the temperatureat which the reactions occur and the N_<Si> ratios of the reactants. The micro-inhomogeneity expected for the ionic structure of metasilicate glasses including one or more oxides of sodium, calcium and magnesium in the internal equilibrium state at and above room temperature, can be concluded from the above results as follows: The glasses have the "micro- inhomogeneous structure" containing different types of SiO_4 groups, among which one or more types of SiO_4 groups of linear silicate building units may be included ; the structural micro-inhomogeneity of the glasses is increased with temperature; at an given temperature the difference in the structural micro-inhomogeneity may be approximately negligible among the metasilicate glasses of 2-4 component systems including one or more oxides of sodium, calcium and magnesium; the smaller the difference of the N_<Si> ratio of silicate building unit from 0.333, the larger may be the activity of the SiO_4 group of the building unit in the glass concerned. When the temperature of the metasilicate glasses having equilibrium ionic structure at high temperature is lowered, the structure of the glasses may be changed toward the internal equilibrium state corresponding to the lowered temperature. It is repuired from the above conclusions that this structural change involves the process of decreasing the micro-inhomogeneity in ionic structure. However, the rate of the change is decreased with decreasing temperature and, at a temperature below the transformation range, may become extremely slow or almost negligible because of the approach to the near completion of the "frozen-in" state of structure. It is, therefore, expected that the ionic structure of metasilicate glasses at a temperature below the transformation range may be more microinhomogeneous than in the internal equilibrium state corresponding to the temperature.
社団法人日本セラミックス協会の論文
1964-03-01

メタ珪酸塩ガラスのイオン構造

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