Ferro Silicon Magnesium is a kind of master alloy of magnesium with iron and silicon. It is mainly used as spheroidizing agent of graphite in cast iron and is also applied to the production of low carbon steel. It is characterized by stable chemical composition, small fluctuations, high alloy purity, low magnesium oxide content, dense alloy structure, no air shrinkage, and reasonable particle size distribution. It is a popular additive in the nodular cast iron abroad.
During the Pidgeon process, dolomite is dissolved in molten ferrosilicon to produce ferro-silicon magnesium (FeSiMg). The reaction between the two compounds is very fast and produces a large amount of Ca vapor that serves as an effective reducing agent for MgO. The vapor pressure of the Ca vapor is 13 Pa at 1150 degC, and it increases with increasing temperature.
The vapor pressure of Ca-Si liquid alloy is lower at 1300 degC, but it was still sufficient to reduce MgO, since the Gibbs free energy was slightly higher at this temperature. Moreover, the vapor pressure of Ca vapor was not affected by the molar ratio of dolomite/ferrosilicon.
In the present work, the molar ratio of dolomite/ferrosilicon was changed to increase or decrease the reduction rate. Depending on the molar ratio of dolomite to ferrosilicon, the reduction rate varied from 15 to 50 percent. As the dolomite/ferrosilicon molar ratio decreased, the reduction rate remarkably increased. It could be attributed to the diffusion of Si into dolime in the presence of an increase of reductant particles. It was also possible that the contact area between dolomite and ferrosilicon reduced the diffusional resistance.
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