KINETICS OF DEPOSITION OF ZIRCONIA-BASED CERAMICS FROM ZRCL4-H2-CO2-AR GAS-MIXTURES

The kinetics of deposition of zirconia from the overall reaction: ZrCl4(g)+2H2(g)+2CO2(g) --> ZrO2(s)+2CO(g)+4HCl(g) was studied from an experimental standpoint. A specially designed chemical vapor deposition reactor, equipped with a microbalance and accurate devices for controlling the experimental parameters (and especially the gas phase composition), was used to measure reliable growth rates of the ZrO2 films over wide ranges of temperature, pressure, total flow rate and gas phase composition. The influence of the partial pressures of ZrCl4, H2, CO2, Cl2, HCl and argon was quantitatively investigated and the data used to derive kinetic laws. Finally, a tentative model of the chemical deposition process is proposed. It assumes three steps: (i) chemisorption of CO2 on the substrate, (ii) reaction of adsorbed CO2 with H2 molecules resulting in H2O adsorbed species and (iii) reaction of one ZrCl4 Molecule with two H2O adsorbed species yielding zirconia and HCl, the third step being considered as the rate limiting step.