Characterization of some pyrolysed polycarbosilanes by transmission electron microscopy

Abstract

The exploration, either complete or radial, ofrecipro­cal space has long been used by one of us [1-3] tocharacterize poorly organized materials, such asturbostratic carbons, or amorphous ones [4].Particles the order of magnitude of resolution, i.e,0.5 nm in size, could also be identified in a mixture ofphases [5], These techniques of transmission electronmicroscopy (TEM) use one ofail the scattered beamsemitted by the specimen, selected by a suitable objec­tive aperture displaced relative to the selected-areaelectron diffraction (SAD) pattern. The regions emit­ting agiven beam or portion ofadiffraction ring appearin the image as bright domains in a dark field (DF).After having successfully applied these techniques tocommercial SiC fibres [6), the present letter will pre­sent results obtained from pyrolysed polycarbosilanes(PCS).Fourdilferent polymers (Table 1) were pyrolysed upta 1000° C in an alumina boat, under an argon Flow.A heating rate of4° Cmin-'without residence time atmaximum temperature was used.For TEM examination, specimens were dusted onan amorphouscarbon film, as thinly as possible. Arterheat-treatlllent, samples were most1y SiC.Polymer A, is a commercial PCS purehased fromNippon Carbon Co, A, is a Yajima's Mark 1 PCS[7], obtained by then110lysis of polydimethylsilane(PDMS) in an autoclave at 470° C.