Suppressing Hydrogen Evolution by Aqueous Silicon Powder Dispersions by Controlled Silicon Surface Oxidation

Abstract

Aqueous silicon dispersions are used to produce pyrotechnic time delay compositions.The propensity of the silicon to react with water and to produce hazardous hydrogen gas must be suppressed. To this end, the effect of air heat treatment temperature on the rate of corrosion of silicon was investigated. It was found that four hour heat treatments at temperatures below 350°C provided significant passivation. This is attributed to the removal of the hydroxyl groups present on the SiO 2 surface scale layer. It was found that thickening the silica layer, by heat treatment at higher temperatures, causes a further reduction in the amount of hydrogen released. However, differential thermal analysis (DTA) studies showed that excessive silicon surface oxidation increased the ignition temperature and reduced the heat release of a near-stoichiometric Si-lead chromate pyrotechnic composition.

Review of Gasless Pyrotechnic Time Delays

“…[49a], Tichapondwa et al [139] investigated the effect of pH, adding organic corrosion inhibitors, controlled air oxidation of the silicon powder before slurrying and the introduction of competing cathodic reactions as means of eliminating hydrogen formation when silicon powder was slurried in water. Hydrophobization of the silicon particle surface by organic silane coatings was found to be the best strategy resulting of up to a 97 % reduction in hydrogen production [49a].…”

“…This is particularly prominent in nano-sized materials where the oxide layer may account for a significant portion of the particle volume. Focused ion beam-scanning electron microscopy (FIB-SEM) has been shown to be an effective method of quantifying the extent of oxide formation on silicon powder [139]. In this method, an ion beam derived from a gallium source is used to mill the silicon particles into half, the particle cross-section can then be viewed and the thickness of the oxide layer determined.…”

Suppressing Hydrogen Evolution by Aqueous Silicon Powder Dispersions Through the Introduction of an Additional Cathodic Reaction

“…Hydrogen evolution studies where performed using the procedure described by Tichapondwa et al (2012). However, 0.1 M metal salt solutions where added to the Si in place of distilled water.…”

“…organic surface modification (Tichapondwa et al, 2011) and controlled silicon air oxidation (Tichapondwa et al, 2012). Figure 6 shows the amount of hydrogen evolved following a 1 h exposure of neat and silane-treated silicon powders to distilled water.…”

“…These results were then compared with those obtained for other methods of suppressing of hydrogen evolution (Tichapondwa et al, 2011 andTichapondwa et al 2012).…”