| Commercial ferrosilicon alloys with Si content greater than 33 wt% tend to evolve toxic phosphine gas (PH3) and are susceptible to spontaneous disintegration. Previous work showed that the maximum gas generation occurs at around 55 to 60wt% Si, at which composition ferrosilicon alloys have the most pronounced tendency to spontaneous disintegration. This research work focuses on investigating the effect of Si content on the microstructure, PH3 gas evolution and spontaneous disintegration behavior of Si-rich ferrosilicon alloys (with wt% Si ≥55).; The high temperature FeSi2.4 phase is present in FeSi55-95 alloys. The mechanisms that contribute to the formation of preexisting microcracks in this phase are revealed through a microstructural study. FeSi55 is a single-FeSi 2.4 phase alloy, and the anisotropic coefficient of thermal expansion (CTE) values of FeSi2.4 along different crystallographic directions are responsible for microcrack formation in this alloy. The different CTE's between the Si and FeSi2.4 phases has a much greater effect on microcrack formation in FeSi65-95 alloys, which results in much higher Microcrack densities than those in the FeSi55 alloy.; The distribution of phosphorus in ferrosilicon alloys was studied. Phosphorus in ferrosilicon alloy exists in two parts, i.e., reactive phosphides and inert phosphorus in the solid solution. Reactive phosphides in FeSi65-95 alloys are present at the interfaces of the Si and FeSi2.4 phases. However, phosphides are within the FeSi2.4 phase in the FeSi55 alloy. These phosphides are usually associated with preexisting microcracks in the FeSi 2.4 phase. The reactive phosphide fraction decreases with the increasing Si content in ferrosilicon alloys due to the increased inert phosphorus dissolved in the Si phase.; Both the PH3 amount and spontaneous disintegration rate decrease with increasing Si content. The increased thickness of Si plates as Si content increases is considered to be responsible for it. |
