XRFS Determination of Total Silicon, Silicon Dioxide and Others Impurity Elements in Industry Silicon with Sample Preparation by Fusion

The method of sample preparation by fusion in a Li₂B₄O₇-lined crucible was applied to the XRFS analysis of industrial silicon for determination of total silicon, silicon dioxide and others impurity elements (Al, Fe, Ca, Mg and Ti). Before the fusion procedure, the sample (1.000 0 g) should be ignited directly at 700℃ to 750℃ to give the value of ignition loss and to expell carbon in the sample. 0.200 0 g of the ignited sample was mixed thoroughly with 1.700 g of Li₂CO₃ and 0.1-0.3 mL of 600 g·L^-1 NH₄NO₃ solution, and the mixture was transferred into the Li₂B₄O₇-lined crucible and preoxidized for 10 to 12 min at 710℃ to 720℃. The preoxidized mixture together with the lined crucible was then transferred into a Pt-Au crucible in which 3.000 g of boric acid had been added preliminarily, and 0.1-0.4 mL of 400 g·L^-1 NH₄Br solution was added and the fusion procedure was carried out in a sample fusion apparatus, for 8 min under stationary mode and followed for 12 min under shaking mode. After cooling, a glassy slice of the melt of the sample was demoulded from the crucible. Five melts of calibration samples (equivalent to 0.200 0 g of each sample) were prepared by mixing oxides of determined elements, and treated in the same way as the fusion of sample. Linear relationships between values of XRF intensity and mass fraction of each components were kept in definite ranges. A formula for calculation of SiO₂ in the sample was proposed. The proposed method was applied to analyze 5 samples of industrial silicon, giving results in consistency with the values given by wet analysis.