Novel synthesis and characterization of silicon nitride fibers

Conference · Fri Dec 01 04:00:00 EST 1995

OSTI ID:134942

Vogt, U; Berroth, K; Engeli, G ^[1]

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

A high temperature CVD-process has been developed to produce Si{sub 3}N{sub 4}-fibers for high temperature applications. The reaction 3SiO{sub 2} + 4NH{sub 3} {yields} 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} fibers. 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 fibers can be grown. The length of the amorphouse fibers is up to 15 cm and the diameter in the range of 1-15 {mu}m, depending on the reaction parameters. The oxygen content of the fibers decreases with an increase of crystallinity. 29-Si NMR analysis shows that the oxygen in the fibers is not present as silica, but in the composition of non-stoichiometric silicon oxynitride. The beginning 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 crystallization or recrystallization of the fibers. Tensile strength measurements of flexible amorphous fibers with 15 {mu}m in diameter yield values up to 5 GPa.

• OSTI ID: 134942
• Report Number(s): CONF-9508127--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
66 PHYSICS
ANNEALING
CRYSTAL GROWTH
CRYSTALLIZATION
DISSOCIATION
EVAPORATION
FIBERS
NMR SPECTRA
RECRYSTALLIZATION
SILICA
SILICON NITRIDES
SYNTHESIS
TENSILE PROPERTIES
X-RAY DIFFRACTION