Silicon nitride fibres synthesised by a gas-phase process

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:175577

Vogt, U; Kuebler, J; Engeli, G ^[1]

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1. Swiss Federal Laboratories for Materials Testing and Research (EMPA), Duebendorf (Switzerland)

A high temperature CVD-process has been developed to produce Si{sub 3}N{sub 4}-fibres for high temperature applications. The reaction 3SiO{sub 2} + 4NH{sub 3} {r_arrow} Si{sub 3}N{sub 4} + 6H{sub 2}O operates at temperatures above 1400{degrees}C by evaporation Of SiO{sub 2} to SiO and dissociation of NH{sub 3} into active nitrogen and hydrogen atoms. The active nitrogen atoms react with unbounded Si atoms thus forming Si{sub 3}N{sub 4} fibres. The growth process is mainly influenced by the reaction temperature, reaction time and the gas flow rate in the reaction chamber. Depending on the reaction parameters temperature and time, amorphous or crystalline fibres can be grown. The oxygen content of the fibres decreases with an increase of crystallinity. 29-Si-NMR analysis shows that the oxygen in the fibres is not present as silica, but in the composition of non-stoichiometric silicon oxynitride. The commencement of oxidation in air could be established at 1230{degrees}C by DTA/TG analysis. Annealing experiments in argon at 1500{degrees}C for 16 hours show no crystallisation or recrystallisation of the fibres. Tensile strength measurements of flexible amorphous fibres yield values up to 5 GPa.

• OSTI ID: 175577
• Report Number(s): CONF-9501103--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANNEALING
CHEMICAL VAPOR DEPOSITION
GAS FLOW
NMR SPECTRA
RECRYSTALLIZATION
SILICON 29
SILICON NITRIDES
TEMPERATURE DEPENDENCE
TENSILE PROPERTIES
TIME DEPENDENCE