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Influence of Isothermal Chemical Vapor Deposition and Chemical Vapor Infiltration Conditions on the Deposition Kinetics and Structure of Boron Nitride
Author(s) -
Leparoux Marc,
Vandenbulcke Lionel,
Clinard Christian
Publication year - 1999
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1999.tb01894.x
Subject(s) - chemical vapor deposition , chemical vapor infiltration , boron nitride , mass transfer , isothermal process , materials science , kinetics , chemical engineering , nitride , boron , diffusion , deposition (geology) , supersaturation , chemistry , mineralogy , porosity , composite material , nanotechnology , layer (electronics) , thermodynamics , organic chemistry , paleontology , physics , chromatography , quantum mechanics , sediment , biology , engineering
An experimental study has been performed to gain some insight into the correlations between the deposition conditions and the structure of boron nitride (BN) coatings that are used in ceramic‐matrix composites. BN has been deposited at 700°C from BCl 3 ‐NH 3 ‐H 2 mixtures on various substrates, by using chemical vapor deposition (CVD) and isothermal‐isobaric chemical vapor infiltration (ICVI) processes, simultaneously in the same reactor. A kinetic study has shown that the CVD process is governed either by a combination of mass transfer with chemical kinetics at low flow rates or by the heterogeneous kinetics only at high flow velocities. In contrast, the limiting contribution of mass transfer always is observed for the ICVI process. The influence of diffusion cages that are positioned around the fibrous preforms is reported. The structure of BN deposits has been studied as a function of the various deposition conditions via transmission electron microscopy. The chosen CVD conditions lead to a poor organization of the BN deposits. Fairly well‐organized BN coatings are deposited on all fibers of a fibrous preform via ICVI. The results are discussed in terms of supersaturation and deposition yields. The use of diffusion cages and the adjustment of the inlet composition and mass flow rate seem to be very important to obtain the best BN organization and thickness uniformity.