Ceramics-Silikáty 22, (4) 293 - 302 (1978)

The paper presents a discussion of a structural model of highly dilute solutions of CaO.MgO.2SiO₂ in 2CaO.MgO.2SiO₂. The melt of pure C₂MS₂ probably comprises mainly pyrosilicate anions besides the Ca²⁺ and Mg²⁺ cations. When liquid CMS₂ is added to C₂MS₂ melt the [(SiO₃)^2-]_p metasilicate chains are split into type [(Si₂O₆)_u.O]^(4u+2)-. The weight of the dissociated chains was determined:

a) from the Le Chatelier-Šreder relation between equilibrium concentration (activity), equilibrium temperature and heat of fusion of akermanite. The value of ΔH_tus,A,theor (0, T_eq(0,0)), calculated by means of the equation using the formal "formula" weight of diopside, amounted to 502 kJ.mol^-1. Substitution of the corrected mole fractions with about four-fold molar weight of diopside yielded the value ΔH_tus,A,theor (0, T_eq(0,0)) = 125,5 kJmol^-1, which is practically identical with the experimental value of 123.9 ± 5.5 kJmol^-1 [4]. The standard deviation was estimated at ± 10 % as usual in this type of calculations. The agreement between the two values was not affected by the introduction of the assumption according to which solid solutions o CMS₂ are formed in C₂MS₂ at a concentration of CMS₂ y ≤ 0.05;

b) from the course of isothermic dependence of C₂MS_2- activity on concentration.