GAS-TO-PARTICLE CONVERSION IN THE PARTICLE PRECIPITATION-AIDED CHEMICAL-VAPOR-DEPOSITION PROCESS .2. SYNTHESIS OF THE PEROVSKITE OXIDE YTTRIUM CHROMITE

In the particle precipitation-aided chemical vapor deposition process, an aerosol is formed in the gas phase at elevated temperatures. The particles are deposited on a cooled substrate. Coherent layers with a controlled porosity can be obtained by a simultaneous heterogeneous reaction, which interconnects the deposited particles. The synthesis of submicrometer powder of the perovskite oxide yttrium chromite (YCrO3) by pas to particle conversion, which is the first step of the PP-CVD process, has been investigated, and preliminary results are shown. The powders have been synthesized using yttrium trichloride vapor (YCl3), chromium trichloride vapor (CrCl3), and steam and oxygen as reactants. The influence of the input molar ratio of the elements on the composition and characteristics of the powders has been investigated. Phase composition has been determined by X-ray diffraction (XRD). The powders have been characterized by transmission electron microscopy (TEM) and sedimentation field flow fractionation (SF3). At a reaction temperature of 1283 K the powders consist of chromium sesquioxide (Cr2O3), or a mixture of Cr2O3 and YCrO3. At stoichiometric input amounts of metal chlorides and steam the formation of YCrO3 seems to be favored. Two typical particle size distributions have been observed. The primary particle size ranges from 5 to 30 nm for small particles, and from 40 to 250 nm for large particles, depending on the process conditions. The particles tend to be agglomerated. The weight of the agglomerates is independent of the primary particle diameter.