The reaction of silicon with water and possible applications

Silicon powder is a classic fuel in pyrotechnic compositions. However, it is also being discussed as a carbon-free fuel with high gravimetric and volumetric energy density. Analogous to base metals such as aluminium or magnesium, it reacts exothermically with water to form hydrogen. In the reaction, 1.76 m 3 of hydrogen is produced per kilogram of silicon. Therefore, many patents exist that propose particularly highly porous or nanometric silicon particles as hydrogen storage at low or moderate temperature in a hydrolyses. At the same time, 11.9 MJ/kg of heat is released, which has so far been considered as waste heat to be dissipated. In this study micrometresized silicon particles were first burned in high-temperature water steam in a laboratory-scale burner with the intention of utilizing both the hydrogen and the heat release. Branched chains of nanoscale silica particles were collected as main reaction product like commercially available fumed silica, which commonly is produced by the combustion of silicon tetrachloride. The reaction product can be explained based on reaction kinetics calculations carried out in parallel. They show that gaseous silicon monoxide is formed in a first step, which suddenlycondenses during oxidation to silica to form so-called primary nanoparticles, which combine to form chain-like and more complex structures. A promising application for the combustion of silicon with steam appears to be in the propulsion of overseas passenger ships and freighters.