SYNTHESIS OF CERAMIC OXIDE POWDERS IN A MICROWAVE PLASMA-DEVICE

Synthesizing oxide ceramic powders by application of a microwave plasm a is a great advantage. There are two ways the microwave plasma can be used: The first is as a source of heat for the pyrolysis of solutions and the second is to excite gas reactions to obtain nanosized powders . Both applications are superior to standard methods. A microwave cavi ty well suited for these experiments and its operating characteristics are described. Using a microwave plasma as a source of heat for pyrol ytic decomposition of nitrates in aqueous solutions leads to a fine-gr ained product with particle sizes from 100 to 1000 nm. Crystallite siz es in those particles are in most cases less than 10 nn. This is demon strated with zirconia-based ceramics, such as ZrO2 - 3 mol % Y2O3 -20 Mol % Al2O3. Depending on the conditions during pyrolysis, it is possi ble to obtain a product in which alumina is either dissolved in zircon ia or the onset of the phase separation is observed. The energy effici ency of this process is better than 80%. If the reactants are gaseous, e.g., ZrCl4, ft is possible to produce powders with mean particle siz es of about 4 nm. In the case of zirconia, these particles are monocry stalline with a cubic structure. This structure is not in equilibrium under the experimental conditions.