Oxidation state of iron in silicate glasses and melts: a thermochemical model

https://openresearch-repository.anu.edu.au/bitstream/1885/139076/1/1-s2.0-S0009254117306782-main.pdf

Zinc isotope composition of the Earth and its behaviour during planetary accretion

In order to describe and quantify the reactivity of silicate melts, the ionic notation provided by the Temkin formalism
has been historically accepted, giving rise to the study of melt chemical equilibria in terms of completely
dissociated ionic species. Indeed, ionic modelling of melts works properly as long as the true extension of the
anionic matrix is known. This information may be attained in the framework of the Toop-Samis (1962a,b) model,
through a parameterisation of the acid-base properties of the dissolved oxides. Moreover, by combining the
polymeric model of Toop and Samis with the «group basicity» concept of Duffy and Ingram (1973, 1974a,b,
1976) the bulk optical basicity (Duffy and Ingram, 1971; Duffy, 1992) of molten silicates and glasses can be split
into two distinct contributions, i.e. the basicity of the dissolved basic oxides and the basicity of the polymeric
units. Application to practical cases, such as the assessment of the oxidation state of iron, require bridging of the
energetic gap between the standard state of completely dissociated component (Temkin standard state) and the
standard state of pure melt component at P and T of interest. On this basis it is possible to set up a preliminary
model for iron speciation in both anhydrous and hydrous aluminosilicate melts. In the case of hydrous melts, I
introduce both acidic and basic dissociation of the water component, requiring the combined occurrence of H+
cations, OH- free anions and, to a very minor extent, of T-OH groups. The amphoteric behaviour of water revealed
by this study is therefore in line with the earlier prediction of Fraser (1975).

/pdf/polymerisation-basicity-oxidation-state-and-their-role-in-bs02ckqwcw.pdf

Polymerisation, basicity, oxidation state and their role in ionic modelling of silicate melts

Evaporation of moderately volatile elements from silicate melts: experiments and theory

Liquidus-phase equilibrium data of the present authors for the PbO-ZnO-SiO2 system, combined with phase equilibrium and thermodynamic data from the literature, were optimized to obtain a self-consistent set of parameters of thermodynamic models for all phases. The modified quasichemical model was used for the liquid slag phase. From these model parameters, the optimized ternary-phase diagram was back-calculated.

Thermodynamic optimization of the systems PbO-SiO2, PbO-ZnO, ZnO-SiO2 and PbO-ZnO-SiO2

The activity of ZnO in ZnO-SiO2 and CaO-ZnO-SiO2 melts has been measured at 1560 °C using a transpiration technique with CO-CO2 mixtures as the carrier gas. The activities of ZnO in dilute solution in 42 wt pct SiO2−38 wt pct CaO-20 wt pct A12O3 in the range 1400° to 1550 °C and in 62 wt pct SiO2−23.3 wt pct CaO−14.7 wt pct A12O3 at 1550 °C have also been measured. The measured free energies of formation of ZnO-SiO2 melts are significantly more negative than published estimated values and this, together with the behavior observed in the system CaO-Al2O3-SiO2, indicate that ZnO is a relatively basic oxide. The results are discussed in terms of the polymerization model of binary silicate melts and ideal silicate mixing in ternary silicate melts. The behavior of ZnO in dilute solution in CaO-Al2O3-SiO2 melts is discussed in terms of the possibility of the fluxing of ZnO by iron blast furnace slags.

R. A. Reyes

Papers

The thermodynamic activity of ZnO in silicate melts