A Study on the Formation and Reduction of Fayalite (Fe₂SiO₄)

Abstract

In this work, the rate of formation of fayalite (Fe₂SiO₄) from mixture of ferrous oxide and α-quartz was measured. The influence of various oxide additions on the formation of fayalite was also studied. These synthetized samples were reduced with H₂ or in graphite crucible. The rate of reduction was measured, and reduction products were investigated with X-ray diffraction.
The results obtained are as follows:
1) The rate of formation satisfies with JANDER'S equation.
2) The formation of fayalite was generally delayed by additions. The stoichiometric molar ratio of FeO/SiO₂ was altered as a result of the reaction of added compounds with FeO and Si0₂.
3) Especially, the formation of fayalite was delayed when magnetite and tridymite co-existed with fayalite as a reaction product.
4) The rate of reduction agrees with MCKEWAN'S equation, during the early period of reduction. When the reduction proceeds further with formation of amorphous SiO₂, MCKEWAN'S equation was not valid, since fayalite reduction is prevented by amorphous SiO₂.
5) FeO was reduced first in the samples which contain FeO and additions. The rate of reduction of fayalite was influenced little by additions.
6) It is found that fayalite is decomposed into Fe and Fe₂-xSiO₄-y at the primary stage of reduction. When Fe₂-gSiO₄-y was reduced further, it changed to amorphous SiO₂ at low temperature, and α-crystobalite at high temperature.