Copper-Silicon Structures for Selective Catalytic Formation of Silanes

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9317580 Falconer This is a study of the mechanism and intermediates of the Rochow direct synthesis reaction between silicon and methyl chloride catalyzed by copper. This reaction can serve as a model for understanding the class of solid-catalyzed gas-solid reactions. When it is run industrially in large fluidized bed reactors, it forms dimethlydichlorosilane, the precursor to silicone polymers, with selectivity as high as 90% It is very sensitive to material properties such as surface composition, the form of the catalyst, concentrations of promoters, and impurities; the objective of this work is to determine which materials and properties improve activity and selectivity. Reaction kinetics are measured at atmospheric pressure in a small reactor attached to an ultrahigh vacuum system equipped for surface analysis and sample treatment. Single-crystal silicon surfaces are used so that the planar surfaces and the pits formed on reacted surfaces can be characterized at various stages by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, optical microscopy, Auger spectroscopy, chemical treatment, and temperature-programmed desorption. The effects of silicon-oxide layers, silicon crystal face, zinc and tin as promotors, and aluminum, iron, and calcium as impurities are determined. Parallel studies in a fluidized bed reactor will be conducted at the Elkem Development Center in Sewickley, PA. Silicone polymers are ubiquitous in modern technology with wide application as sealants, lubricants, hydraulic fluids, dielectrics, and other applications. High-quality polymer requires a pure monomer, in this case dichlorodimethylsilane, and it is this issue that is addressed here. The contamination of the monomer by other silanes formed as byproducts in the direct synthesis reaction is presently a problem. This effort is coordinated with Elkem Corp., a major supplier of dichlorodimethlysilane. Supplementary support for this effort is provided by Dow-Corning Corp., a major consumer of dichlorodimethlysilane.