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.

The Stoichiometry of Electroless Silicon Etching in Solutions of V2O5 and HF

“…[2] When performed under conditions for the formation of porous silicon (por-Si), the process is known as stain etching. It can be initiated by a variety of more suitable oxidizing agents [3] and can be used for the low-cost production of nanocrystalline por-Si powder [4] or Si nanocrystals. [5] Nonetheless, we still lack the most basic chemical understanding of this reaction: the reaction stoichiometry is unknown.…”

Drug Delivery with Porous Silicon

“…The cost of silicon wafers used in microelectronics is high because of the strict demands for high purity. These demands are well beyond that what would be needed for biomedical applications, and although it is possible to produce low-cost PSi from metallurgical grade silicon (Loni et al 2011;Chadwick et al 2012), it is not yet clear if this type of PSi can be used for biomedical purposes. Quite recently, a new promising approach to produce low-cost PSi has been started to explore, namely, magnesium-induced reduction of silicon dioxide to silicon (Bao et al 2007 and chapter "▶ Porous Silicon Formation by Porous Silica Reduction"), which may open a way to produce low-cost PSi with an environmentally friendly process (Batchelor et al 2012).…”

Luminescent Properties of Porous Silicon

“…Film thicknesses of 10-20 μm were easily obtained in as short as 60 min of etching. Subsequently, Loni et al (2011) showed that this approach could be used for porosification of metallurgical-grade silicon powder (10 m 2 /g surface area). Using stain etching in FeCl 3 :HF solution at reduced temperature (up to -25°C), mesoporous powders with surface areas up to 480 m 2 /g and very high chemical reactivity were prepared.…”