The spontaneous ignition of alkyl silanes

Abstract

The spontaneous ignition temperatures of a number of alkyl silanes have been determined and compared with the chemical structures of these compounds. A ‘drop’ technique, based on the method described by Wiezevich et al., was used. Because of the need for standardization of the experimental procedure in this type of method, the spontaneous ignition temperatures were determined at a fixed delay time of five seconds, and with a fuel air ratio controlled between the limits of two and three times the stoichiometric requirement. With these conditions, the repeatability of the results was, in general, good. These results permit a qualitative discussion of the possible influence of silicon-hydrogen bonds on the ease of oxidation as indicated by differences in the spontaneous ignition temperatures. Thus with the ethyl silanes the ease of oxidation decreases in the order Et 2SiH 2>Et 3SiH>Et 4Si The same order was found by Schalla et al. for the methyl silane series. The differences in spontaneous ignition temperatures are less pronounced in the n-propyl series, and still less pronounced in the n-butyl series and in the n-amyl series. These results suggest that the silicon-hydrogen bonds have less influence on the ease of oxidation i n the higher homologues. The relative effect of primary, secondary and tertiary silicon-hydrogen bonds is shown by comparing the ease of oxidation in a series of silanes containing 5 carbon atoms ( n-amyl, n-propyl ethyl, di-ethyl methyl silanes) and 6 carbon atoms ( n-hexyl, n-butyl ethyl, di- n-propyl and tri-ethyl silanes). In both series the ease of oxidation decreases in the order primary>secondary>tertiary In isomeric dialkyl silanes, such as di- n-propyl and n-butyl ethyl silanes, the greater the symmetry of the molecule about the SiH 2 group, the more resistant it is to oxidation.