MECHANOCHEMICAL REACTION OF METALLURGICAL GRADE SILICON WITH GASEOUS HYDROGENCHLORIDE IN A VIBRATION MILL

A vibration mill for simultaneous chemical reaction and comminution wa s developed, which is heatable up to 450 degrees C and resistant to pr essures up to 2 MPa. This apparatus will be named ''reaction mill'' to characterize the combination of the two process steps. The possible a ccelerations exceed up to 65 g and amplitudes of 7 mm are adjustable, The chemical reaction, which takes place in this reaction mill, is the hydrochlorination of metallurgical grade (MG) silicon, where chlorina ted silanes of the form SiHxCl4-x are formed; trichlorosilane SiHCl3 a nd silicontetrachloride SiCl4 are the main products of this reaction, Additionally the by-product FeCl2 is formed by the hydrochlorination o f the main impurity iron Fe. This FeCl2 becomes very important, becaus e it is regarded as reaction inhibitor. The examinations of the combin ed hydrochlorination and comminution have shown, that a reported induc tion period in the starting phase of the chemical reaction, carried ou t singularly, can be reduced to a minimum. On the other hand, it could be noticed, that the lower temperature limit, which is necessary to s tart the reaction, could be lowered essentually, On one hand, this is explained by the enlargement of the reactive surface during comminutio n and on the other hand, by a mechanical activation of the MG silicon, Furthermore, the mechanical removal of the reaction inhibiting produc t-layer of FeCl2 could be determined to have a positive effect to the reaction.