CHEMICAL-VAPOR-DEPOSITION OF HAFNIUM CARBIDE AND CHARACTERIZATION OF THE DEPOSITED LAYERS BY SECONDARY-NEUTRAL MASS-SPECTROMETRY

The paper describes an alternative high temperature coating for carbon fibre reinforced carbon and carbon fibre reinforced silicon carbide. Hafnium carbide layers were obtained in a thermally stimulated chemica l vapour deposition (CVD) reactor on non-porous substrates by reaction of hafnium tetrachloride, methane and addition of hydrogen. Thermodyn amic modelling of the reaction HfCl4 + H, + CH4 --> HfC, HfCl4-x, C, H CI shows the possibility of depositing a nearly carbon-free hafnium ca rbide layer. These theoretical calculations could be proved experiment ally in a thermally activated CVD process. The important carbon conten t in the hafnium carbide layers could be measured by means of secondar y-neutral mass spectrometry, which was employed because of its outstan ding capability to provide elementary concentrations at the parts-per- million level with a depth resolution of a few nanometres. The carbon- to-hafnium ratio of the deposited layer closely agreed with the thermo dynamic predictions.