Gary H. Wiseman

Steric stabilization of Stöber silica dispersions using organosilanes

Organosilanes of the general formula RxSi(OR′)4−x (where R is an alkyl group and R′ = CH3 or CH2CH3) were used to sterically stabilize hexane dispersions of submicrometre silica spheres. The dispersions were characterized according to sediment volume results. For 0.5μm silica particles, the sediment density increased by more than a factor of three up to 50 to 55% of theoretical in the presence of organosilanes with 12 or more carbons in the R group. Solid-state13C nuclear magnetic resonance was used to characterize the powder-dispersant interaction; this technique can distinguish between carbons in the R group of the organosilane and residual organic groups in the silica. Scanning electron micrographs of filter compacts were used to further characterize the dispersions and indicated the presence of primary particles as well as small agglomerates.

Silicon-Nitrogen Polymers and Ceramics Derived from Reactions of Dichlorosilane, H2SiCl2

Silicon nitride, Si3N4, is of great current interest as a material of high thermal and oxidative stability and high hardness for ceramics, electronic and other applications. 1 Silicon nitride may be prepared by the reaction of elemental silicon with gaseous nitrogen or ammonia at elevated temperatures. Ceramic bodies may be produced directly (reaction sintering) or, alternatively, Si3N4 powder may be obtained first and converted to solid bodies by subsequent processing. 1 Chemical vapor synthesis also has served in the preparation of Si3N4 (films or powders), using high temperature reactions of ammonia with chlorosilanes (H2SiC2, HSiC3, SiC14) for this purpose. 2 Solution-phase chemistry also has found application in the synthesis of Si3N4. In particular, the reaction of ammonia with silicon tetrachloride, carried out in an inert solvent, has been the subject of investigations by a number of groups of workers.3 This ammonolysis reaction initially produces a solid, insoluble, cross- linked product, [Si(NH)2]x, together with four molar equivalents of ammonium chloride. Pyrolysis of this product at 1250°C gives α-Si3N4, but the fact that [Si(NH)2]x is a nonvolatile, insoluble solid brings some limitations to its practical applications.

Hexamethylsilirane: IV. Nucleophillic ring opening by alkyllithium reagents

Abstract Alkyllithium reagents (methyl-, n-butyl- and t-butyl-) react at 0°C with hexamethylsilirane to give RSiMe 2 CMe 2 CMe 2 Li as the initial product. In a second step this reagent metalates methyl substituents on silicon to give RSi(CH 3 )(CH 2 Li)CMe 2 CMe 2 H as the final product.