A Study Of The Oxidation Behavior Of Crystalline Silicon Powders

Crystalline silicon dusts widely exist in the process of high purity silicon production and wafer production, including the process of cutting and grinding. Also, the metallurgical purification technologies for solar grade silicon are often based on the silicon powders by grinding from the metallurgical grade silicon. So it's very important to study the oxidation behavior of silicon powders, especially for the use and storage of the silicon powder, the recovery of sawing and grinding kerfs and the development of metallurgical purification technologies.In the present work, the oxidation behaviors of crystalline silicon powders in air, ultrapure water, PEG, admixture of water and PEG, acidic solution, have been studied by means of TGA, XRD and EDX. The results show that no observable oxidation happened in the dry air at 200℃, while in water for some time above 80℃amorphous SiO₂ formed on the silicon powder and the oxidation is strongly influenced by the temperature and time stay in the water. Also, a lot of Si atoms dissolved in water when oxidation, which result in reduce of silicon mass. Compared with water and aqueous solution, PEG showed better protection from oxidation for the silicon powder to some extent. In different acidic solution, the oxidation situation of silicon powder is very different. Dilute HCl solution can effectively inhibit the oxidation of silicon powders. On the other hand, notable oxidation happened on the silicon powders in Dilute HF solution (1:100 and 2:100) for 3 days at 90℃. Hydrophilic amorphous SiO₂ formed and a lot of "islands" appeared on the surface of the silicon powders. However, the concentrated HF solution (1:5) can remove the oxide and the "islands" formed in the dilute HF solution.In addition, oxidation of kerf loss particles formed in two different slicing processes was investigated. The band sawing kerfs are compacted in spheres and the XRD result show that notable oxidation of the sawing kerfs occurred in band sawing process. With the extension of the storage time, the amorphous oxide increase. While the amorphous oxide changed to crystalline after treatment at 1500℃. Also the results showed that lots of SiC particles and PEG in the wire sawing kerfs and no detectable oxidation of the sawing kerfs was observed. The PEG can be cleaned by washing with ultrapure water, as a result, dispersed powder at the micron level can be obtained. The XRD results show that no observable oxidation happened on the wire sawing kerfs after 3 days in the ultrapure water at 90℃, which is different from the solar grade silicon powders.