Composite ceramic powders obtained by laser induced reactions of silane and amines
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T. Dikonimos-Makris and R. Giorgi ENEA, Area INN, Dip. Proc. Chim., Mat. non Met. e relat. trat., P.O. Box 2400, AD00100 Roma, Italy
S. Enzo Dip. Chimica Fisica, University of Venice, Italy (Received 18 January 1991; accepted 18 June 1991)
Ultrafine, ternary (Si/C/N) ceramic powders have been produced after CO2 laser initiated reactions between silane and mono- or dimethylamine. Various spectroscopic diagnostics and chemical analyses, including ir spectrophotometry, x-ray photoelectron spectroscopy, and x-ray diffraction analysis have been employed to correlate the parameters involved in gas-phase reactions and the powder final composition.
I. INTRODUCTION Industrial interest in advanced ceramic materials stimulated research for the improvement of their mechanical properties. Recent studies1 suggest that the incorporation of SiC into Si3N4 matrices increases hardness, creep, and oxidation resistance properties compared to those in pure Si 3 N 4 materials. However, the densification process of composite systems is made difficult by the different sintering behaviors of matrix and second phase particles.2 It has been found3 that the chemical homogeneity of the powder favors the densification of the green body and helps reproducibility of the mechanical and physical properties of silicon nitride-silicon carbide composite powders. In this respect, laser synthesis of composite powders from Si/C/N containing gaseous precursors appears to be the ideal method for growing homogeneous mixtures of pure and ultrafine silicon nitride/silicon carbide particles.4"6 Also the laser synthesis process offers the possibility of controlling the composition as well as of doping the material with suitable sintering aids. In this paper we present results on the production of ternary (Si/C/N) synthesized through a reaction between silane and mono- or dimethylamine initiated by ir laser. The experimental apparatus for laser synthesis of ceramic powders is briefly described and the laser-induced process is discussed on the basis of several diagnostics performed on solid products [x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and x-rayinduced Auger electron spectroscopy (XAES), chemical analysis, and ir spectrophotometry]. The use of these
a 'Permanent
address: Institute of Atomic Physics, Laser Department, Bucharest, Romania.
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J. Mater. Res., Vol. 6, No. 11, Nov 1991
http://journals.cambridge.org
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complementary analytical techniques was suggested by the complexity of the reaction and was thought essential to draw significant conclusions on the mechanism of particle formation and growth under different experimental conditions. II. EXPERIMENTAL The experimental apparatus for powder synthesis has been described elsewhere.4 Briefly, a 50 W CO 2 c.w. laser is focused by a Ge lens (f = 5") at the center of the cell onto the reactant gas effusive beam in a single or double pass geometry. In the last configuration the laser radiation is reflected by a spherical Cu mirror (f = 5") and refocused at
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