Development of colloidal suspension spraying application to the fabrication of dense YSZ coatings for SOFCs

Kurzfassung

The colloidal suspension spraying is being considered as an alternative coating process to the plasma spraying for SOFCs. It consists in spraying a suspension with nanoparticles of the required material through an air atomizing bi-fluid nozzle. After drying, the green coating are sinterd in air to obtain the final microstructure. In this work, the implementation of this process was investigated for the coating of dense electrolyte for SOFCs applications. First of all, an optimization of the layering process was made by modelling. A strategy consisting in coating several layers with a shift of the nozzle was successfully applied to obtain homogeneous coating. An optimum was found for 4 layers coating. Experimentally, standard suspensions were sprayed on top of various substrates in order to characterize the homogeneity of the coating. By changing the air pressure of the atomization, the parameters yielding to a semi-elliptic distribution of the spray pattern gave the best results in term of homogeneity in agreement with the modelling. The samples were sintered in air at 1300 °C (due to technical limitation with oven), but it was unfortunately not possible to obtain fully dense layer because of the low sintering temperature. However homogeneous coatings with 10 μm in thickness were obtain and suggest the opportunity to obtain dense films with a thickness between 5 and 10 μm. Major improvement could be achieved by optimizing the formulation of the suspension in order to increase the compacity of the green layers and avoid defects. In parallel to these tasks, the development of a software and the design of an automated system was made in order to control the spraying process with a computer.