ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Model straight pores with rectangular cross-section (size ranging from 60 to 320 μm) have been infiltrated with pyrocarbon resulting from the cracking of C3H8 or CH4 under pulse chemical vapour infiltration (P-CVI) conditions. Three main parameters control the quality of the pore infiltration: temperature and pressure, as previously known for regular CVI under isothermal/isobaric conditions (I-CVI) and, additionally, the residence time t R, which appears to be the key parameter in P-CVI. There is a direct correlation between t R, on the one hand, and both the PyC thickness gradient and anisotropy along the pores, on the other hand. The experimental results are explained on the basis of a qualitative model assuming two competing deposition mechanisms, depending on whether PyC is formed from small and H-rich molecules (akin to C3H8) (low t R values) or from large aromatic H-poor intermediates resulting from the maturation of the gas phase (high t R values). The use of CH4 (more stable thermally than C3H8) slows down the maturation process and favours in-depth infiltration. The best infiltrations, similar to and even better than those reported for I-CVI, are achieved under low t R, T, P conditions but require a very large number of pulses. P-CVI is an efficient way to control the microstructure of the deposit.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00351432
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