Standard Gibbs Energy of Formation of Zn2SiO4.

An experimental study was carried out to determine the standard Gibbs energy of formation of zinc orthosilicate, Δ (Zn2SiO4), for the purpose of controlling zinc vapor pressure by utilizing the equilibrium reaction between Zn2SiO4 and a CO-CO2 gas mixture. A CO-CO2 gas mixture of fixed composition was passed through a column of synthesized granular Zn2SiO4 placed in a uniform temperature zone of a furnace, and the equilibrium CO-CO2-Zn(g) gas mixture from the following reaction Zn2SiO4(s) + 2CO(g) = 2Zn(g) + 2CO2(g) + SiO2(s) was contacted with a molten Cu-Zn alloy placed in the same uniform temperature zone, where another equilibrium was made attain between the gas phase and the molten alloy. From the zinc content and the known thermodynamic data of the alloy, pZn in the gas phase was obtained and from which, being combined with the composition of the CO-CO2 gas mixture, pCO and pCO2 were calculated. Those partial pressures were then used to calculate the standard Gibbs energy change of the above reaction, which was combined with the available standard Gibbs energies of formation of CO, CO2, and SiO2 to determine Δ (Zn2SiO4). The result is as follows : Δ (Zn2SiO4) = 0.613T-1,951(±7) (kJ/mol) [1,423-1,573 K]