Manufacturing of solar selective coatings for solar tower receivers by compact plasma spray.

The present work aims to study the feasibility to deposit selective absorbing coatings by using low-power plasma spraying systems. Three powders systems, namely pure chromium carbides, WOKA 7104 that is a commercially available mixture of chromium carbide and Ni20Cr metallic particles, and Manganese/Cobalt/Oxygen spinel were investigated, and the effect of processing parameters on the coating morphology and absorptance were assessed. The design of experiments approach was applied for the selection of the processing parameters. The results indicate that the compact plasma spray was not able to process the pure chromium carbide without the application of a bond coat, achieving a poor or null deposition for almost all process configurations. Woka and MnCoO spinel attained an average value of absorptance between 0.85 and 0.91, strongly influenced by the current and the plasma gas rate, which in turn dictate the power absorbed by the plasma equipment. Satisfactory values for absorptance and coating thickness can be achieved after optimization of the processing parameters, however, the results indicated that morphological characteristics and optical performance can have a competitive behavior, and their maximation can not be reached simultaneously. Therefore, requirements in mechanical and optical performances need to be balanced when the optimization of the deposition process is wanted. [ABSTRACT FROM AUTHOR]