Abstract
Deposition of silicon carbide (Sic) into two types of capillaries
(1.5 mm dia. x 6 mm depth, 1.0
mm dia. x 4 mm depth) has been attempted by a vertical hot-wall-type
chemical vapour infiltration
(CVI) process using an SiCl4-CH4-H2 system. Dependence of the deposition
temperature (Tdep) and
the total gas pressure (Ptot) on the thickness distribution of Sic
in the two types of the capillaries (parallel
and perpendicular to the gas stream) was studied. Activation energy
of the deposition of Sic was 42
Wmol in the Tdep range of 1673 to 1773 K, and 167 Wmol in the Tdep
range of 1573 to 1673 K. The
most suitable CVI condition was a Tdep below 1673 K accompanied by
the reaction-rate controlled
process. The uniformity of the film thickness obtained at Ptotbelow
0.13 kPa was lower than that obtained
at Ptot below 13 kPa. The lower the Ptot and the closer the deposition
was to the capillary entrance,
the higher the vorticity in the two types of capillaries became. The
film thickness at the capillary
entrance increased coincident with the increase in vorticity. Vorticity
in the capillaries perpendicular
to the gas stream was higher than that parallel to the gas stream.
In the diffusion-rate controlled
process (Tdep>1673 K), in which decreasing Ptot was accompanied by
increasing vorticity,
film thickness uniformity in the capillary decreased Results of the
CVI experhen& and the gas flow
simulation suggest that lower vorticity under reaction-rate controlled
conditions is important for obtaining
uniformity of Sic thickness in the capillaries.
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