Development of a Cold Wall Reactor System for the Low‐Pressure Chemical Vapor Deposition of BN on SiC Fiber Tow

A device is developed to coat a SiC fiber tow with BN by low pressure chemical vapor deposition in a cold wall reactor. A motorized spool system is installed to feed the tow into the reactor in preparation for continuous processing in the future. In the present work, the system is used solely to control the mechanical tension of the tow, which is held stationary and heated by microwaves. The heating process induces a temperature gradient, with the temperature decreasing from the core to the surface of the multifilament tow. The precursor gas used is triethylamine borane mixed with ammonia. X‐Ray photoelectron spectrometry analyses demonstrate the feasibility of depositing a boron nitride coating with good purity. Key parameters include the preferred use of N 2 over H 2 as a carrier gas and a sufficiently large reactor diameter. Deposition growth rates are determined in situ by interferometry from non‐contact pyrometric measurements. Deposition kinetic regimes are identified as a function of temperature. The kinetics are limited by chemical reactions up to at least 1500 °C, before being limited by mass transfer and precursor depletion at the highest temperatures.