Towards a Better Understanding of the Chemical Reactions Between Iron Carbide and Silicon Carbide

Abstract

This article contains the research results of the equilibrium interaction of iron carbide (Fe₃C) with silicon carbide (SiC) in a temperature interval of 700-2000 K with the formation of iron silicides (Fe₃Si, Fe₅Si₃, FeSi, FeSi₂ ), by using the program of the Finnish metallurgical company Outokumpy HSC Chemistryj-5.1 for  Windows with regard to the electrothermal production of ferrosilicium from siliceous and carboncontaining raw materials. On the basis of the received regression equations connecting the Gibbs energy change with the temperature and the silicon content in a ferroalloy, the response surfaces (change of the Gibbs free energy - ∆G_T⁰) and their horizontal sections for three groups of ferroalloys were constructed with the program Mathcad. The silicon content in the first group of alloys is 14.3-23%, in the second group of alloys – 23-33.3% and in the third group of alloys – 33.3-42.8%. It was established, that the reactions between Fe₃C and SiC with the formation of iron silicides in the range of temperatures 700-2000 K are possible, and the probability of these reactions increases with increasing the mole ratio Fe₃C/SiC from 0.166 to 1.0. As a result of the reactions the low-silicon ferrosilicium can be obtained, answering to a grade FS20 with Si content from 19 to 27% and consisting of a mixture of Fe₃Si and Fe₅Si₃, and also the ferrosilicium corresponding to a grade FS25 with a Si content from 23 to 29% and consisting of a mixture of Fe₅Si₃ and FeSi. It was found, that at the technological temperature of 1900-2000 K the maximum Si content in the received ferrosilicium can’t be more than 37.7-38.8%. Production of the medium-silicon and the high-silicon ferrosilicium answering to grades FS45- FS90 from the Fe₃C-SiC mixture is impossible from a thermodynamic point of view. The received information extends our knowledge about the iron silicides formation during the electrothermal production of ferrosilicium with a silicon content in the alloy from 19 to 90%.