Chemical Vapour Transport, Calculation of CTR, Thermodynamic Data Five phases exist in the system Co-Si: Co3Si, aand /?-Co2Si, CoSi and CoSi2. The phases a-Co2Si and CoSi could be prepared by chemical transport with iodine as transport agent in the temperature range between Ti (700 °C) and T2 (900 °C). In a attempted systematic clarification of the chemical transport reactions of all phases in the system, the effective transport equilibria were determined. Thermodynamic data show satisfactory agreement bet ween calculation and experiment.