Calculation and Characterization of Silicon-Boron Phases in Metallurgical Grade Silicon

Introduction

It is a challenge that boron is removed in upgrading metallurgical grade silicon (MG-Si) to solar grade silicon (SoG-Si) with a metallurgical process. In this research, the Si-B binary system is thermodynamically assessed and characterized by using the CompuTherm Pandat software, which is helpful to the boron removal in refining MG-Si to SoG-Si.

Methods

The Si-B binary system was thermodynamically assessed and characterized by using the CompuTherm Pandat software. The SEM-EDS and XRD technologies were used.

Results

The solution phases, including Liquid, diamond-Si and ??-B were treated as substitutional solution phases, of which the Gibbs energies were expressed with Redlich?CKister polynomial functions. Meanwhile, the compounds, SiB₃, SiB₆, SiB_n, were modeled as stoichiometric compounds. The thermodynamic parameters formulating the Gibbs energies of various phases were obtained and the equilibria and transition of the phases were discussed. According to XRD technology, the intermediate phase SiB₄ was obtained and observed. It was tested that the phase SiB₄ existed objectively although it is not found in the assessed Si-B binary phase diagram.

Discussion

The existent forms for Si-B phases in the MG-Si melt were forecast and tested to be SiB₆ and Liquid.