The content and uniformity of impurities and precipitates have an important role in the efficiency of solar cells made of multicrystalline silicon. We developed a transient global model of heat and mass transfer for directional solidification for multicrystalline silicon and a dynamic model of SiC particles and silicon nitride precipitation in molten silicon based phase diagrams. Computations were carried out to clarify the distributions of carbon, nitrogen and oxygen based on segregation and the particle formation in molten silicon during a directional solidification process. It was shown that the content of SiC precipitated in solidified ingots increases as a function of the fraction solidified. It was also clarified from the results that Si2N 2O was first formed near the melt-crystal interface, since oxygen concentration in the melt decreases and nitrogen concentration in the melt increases with solidification of the molten silicon. Si3N4 was formed after Si2N2O had been formed.