CVD OF Y2O3 FROM YCL3-CO2-H2-AR GAS-MIXTURES - AN EXPERIMENTAL-STUDY

The chemical vapor deposition of Y2O3 from YCl3-CO2-H2-Ar gas mixtures is studied in a graphite hot-wall deposition chamber. YCl3 gas flows are generated by vaporization of liquid YCl3 in an argon stream and controlled by recording in situ the mass loss of the YCl3 graphite crucible with a millibalance. The deposits are performed on alumina substrates and the Y2O3-deposition rates are assessed in situ with a microbalance. When [CO2]in/[YCl3]in > 9, the deposits consist of pure Y2O3; otherwise YOCl is the main deposited phase. At P = 4 kPa, the deposition process is rate controlled by surface reactions for T < 1100-degrees-C and 500 < Q(tot) < 1000 sccm, whereas beyond these limits mass transfers across the boundary layer become the rate-limiting phenomena. When controlled by surface reactions, the Y2O3 deposition process is thermally activated with E(a) =616 kJ mol-1, k0 = 4.4.10(11) mg-min-1.cm-2.Pa-5 and the apparent partial reaction orders are n1 = 2; n2 = 2; n3 = 1 and n4 = 0 with respect to YCl3, H2, CO2 and HCl.