Extremely High Surface Area Metallurgical-Grade Porous Silicon Powder Prepared by Metal-Assisted Etching

Abstract

Metallurgical-grade silicon powder (10 m2/g surface area) has been porosified using a metal-assisted chemical etch process based on hydrofluoric acid-ferric chloride chemistry. By controlling the reagent concentrations and ratios, the degree of porosification has been varied. Initiating the reaction at temperatures below 0°C, typically between −15°C and −25°C, yields etched powders with spectacularly increased surface area and pore volume (porosity). The reduced temperature, and its subsequent control, favors pore nucleation and propagation while minimizing bulk chemical etching. Using this process, mesoporous powders with surface areas up to 480 m2/g and pore volumes up to 0.52 ml/g have proved easily achievable at the 10 g batch level.