Suppressing H₂Evolution by Silicon Powder Dispersions

Abstract

Silicon dispersions in water 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 surface modifications and medium pH on the rate of corrosion of silicon were studied at ambient temperature. It was found that the rate of hydrogen evolution increased with increasing pH. Silanes proved to be more effective silicon corrosion inhibitors than alcohols, with vinyl tris (2-methoxyethoxy) silane producing the best results. DTA studies were performed using a near-stoichiometric amount of lead chromate as oxidant. Comparable combustion behaviour was observed when both the fuel and the oxidant powders were either uncoated or silane modified. Mixtures of neat oxidant with silane coated silicon showed poor burn behaviour and this was attributed to poor particle-particle mixing owing to the mismatch in surface energies.

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

“…Neat silicon produced 13.7 ± 1.0 mmol H 2 /kg Si in one hour when ultrasonically agitated. This represents a 65 % increase in the hydrogen gas output compared to the result previously reported using magnetic stirring for the same powder (Tichapondwa et al, 2011). Figure 7 shows a two-step inhibition process with an initial step decrease to 9.3 ± 0.4 mmol H 2 /kg Si for silicon heated at 75 °C.…”

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

“…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.…”

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

“…The results show that neat silicon produced 13.7 AE 1.0 mmol H 2 kg À1 silicon in 1 h when ultrasonically agitated. This represents a 65 % increase in the hydrogen gas output compared to the result previously reported using magnetic stirring [19] for the same powder. Table 1 shows that the d 50 of the neat and heat-treated silicon particles decreased after 1 h ultrasonic agitation.…”

An assessment of the viability of hydrogen generation from the reaction of silicon powder and sodium hydroxide solution for portable applications

“…The rate of reaction of an untreated silicon powder with water is thus negligible unless some method of removing the oxide layer is employed. The overall reaction of silicon with water has been described in previous work by Tichapondwa et al [18,19] and is represented by Equations (1) and (2).…”