A different consideration for Na₂SiF₆ formation/dissociation and its relation with silicon fluoride vaporization in the steelmaking process

Due to contamination and corrosion problems caused by silicon fluoride vaporization in steelmaking plants, the formation/dissociation of Na2SiF6 has become the subject of many studies. In all the previous works, it has been assumed that silicon tetrafluoride (SiF4) is the only gas species formed during processing by the use of slags and fluxes in the steel industry. In the present work, it is proposed that during the thermal composition of Na2SiF6, SiF4 is not the only gas species formed. Based on a study on the kinetics of decomposition of Na2SiF6 in nitrogen and on thermodynamic predictions, it is proposed that Na2SiF6 decomposes endothermically into various gaseous species (SiF4, SiF3, SiF2, SiF, and Si, denoted by SiFx) through a series of complex reactions of zero-order with respect to the gaseous products, with activation energy of 156kJmol-1 and a rate-determiningstep given by the chemical reaction itself. The gaseous species are formed through a set of simultaneous reactions represented by the general equation [image omitted] where x varies from 0 to 4 and n, given by (2-0.5x), takes the values 0, 1/2, 1, 3/2, and 2 and NaF is sodium fluoride.