silicon for the chemical and solar industry XIII

Silicon for the Chemical and Solar Industry XIII

Kristiansand, Norway, June 13 – 16, 2016

Sistruc: A microstructure model for optimization of silicon

materials

S. Gouttebroze

, Q. Du

, M. M'Hamdi

1) SINTEF Materials and Chemistry, Pb.124 Blindern, 0314 Oslo, Norway

Abstract

Silicon is a key material in various markets such as silicones, photovoltaics, or

aluminium castings. Each market segment has its own requirements in term of

composition, particle shapes, intermetallic phases and more. It is therefore essential to

control and tailor the amounts of major elements to achieve highest downstream

performance, for example reactivity between silicon and methyl chloride to produce

methylchlorosilanes precursors for silicone. Sistruc is a microstructure model

developed by SINTEF in collaboration with Elkem. The model predicts the micro-

segregation and formation of intermetallic phases during the solidification of

metallurgical-grade silicon alloys. The model includes the four major elements Al, Ca,

Fe and Ti in addition to B and P. As an industrial tool, Sistruc is designed to be

extremely fast and user-friendly. In the present paper, an efficient algorithm to solve

the solidification of metallurgical-grade silicon based on simplified phase diagram is

presented. The calibration of the model is explained and the quality of the predictions

is assessed. Finally, an example illustrates the use of Sistruc to optimize the quality of

silicon material in terms of intermetallic content for an industrial case.

Introduction

Liquid metallurgical silicon is produced by reduction of quartz. Impurities are present

from the raw materials used in the production process. During solidification, metallic

impurities will segregate and form intermetallic phases mostly at the grain boundaries.

Depending on the solidification process (especially the cooling rate) and melt quality,

different particles can nucleate and grow. The amount and type of particles present will

affect subsequent processing steps. Indeed metallurgical silicon is not used as a finished

product but as raw material for other processes (for example: i) as an alloying element

for aluminium, ii) as a raw material for chemical industry (e.g. production of silicones),

iii) as a raw material for production of solar and electronic grade silicon. For each

market, the quality and specifications for the solidified silicon are of high importance.

For example, as illustrated by Anglezio [1], the intermetallic compounds affects the