Amorphous boron carbide coatings have been prepared by chemical vapor deposition from CH4/BCl3/H-2 precursor mixture at low temperature (800-1050 degrees C) and reduced pressure (12 kPa). A kinetic study has been conducted to determine the kinetic law (including apparent activation energy and reaction orders) related to the deposition within the regime controlled by the chemical reactions. On the basis of an in situ gas phase analysis by Fourier transform infrared spectrometry and a thermodynamic study of the homogeneous equilibrium, the HBCl2 species has been identified as an effective precursor of the boron element. The evidence of correlations between the various experimental approaches has supported a discussion on the chemical process involved. (c) 2006 The Electrochemical Society.