Amorphization of Silicon during Mechanical Treatment of Its Powders: 1. Process Kinetics

Abstract

The kinetics of silicon amorphization in the process of mechanical treatment of powders in a vibrating micromill was studied by the X-ray diffraction. The treatment was carried out in the argon atmosphere, the apparatus energy intensity was equal to 18 W/g, and the amount of consumed energy (dose) was as high as 510 kJ/g (14 MJ/mol). The analysis of the shape of X-ray diffraction patterns and the dynamics of the changes in silicon atomic structure were described within the framework of three-fraction model. Fraction 1 composed of large crystalline blocks comprising particles of initial powder; the second fraction is represented by nanocrystalline blocks with the dimensions of not less than 8 nm; and the third fraction is an amorphous phase. A decrease in the content and sizes (from 10²to 25 nm) of initial microcrystals of fraction 1 is accompanied by the formation of X-ray amorphous phase 3. Nanocrystalline blocks of fraction 2 are none other than the intermediate products. They are first accumulated synchronously with the amorphous phase and then disintegrated with a decrease in their sizes from 8 to 4 nm. At the initial stage of experiment, at the dose up to 15 kJ/g and the degree of amorphization up to 40%, the energy yield of the formation of amorphous phase amounts to 1 ± 0.1 mol/MJ. At the end of experiment (the dose varies from 20 to 510 kJ/g), the yield drops by tens of times, and the content of amorphous phase reaches 70–80%.