EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Zircon (ZrSiO4) is a ceramic material whose properties make it especially interesting to be applied in thermal and environmental barrier coatings at a competitive cost. However, its decomposition at high temperature during the deposition step has so far limited its use by plasma spraying from powder feedstocks.

The aim of the present work is to assess the potential of using suspensions instead of powder feedstocks in plasma spraying in order to obtain coatings in which a high proportion of zircon is preserved. For that purpose, aqueous suspensions were prepared at different solids contents from a commercial zircon powder with a d50 = 1 µm. The chosen contents were 10 vol.% and 30 vol.%. Liquid feedstocks used in plasma spraying must fulfil two requirements, i.e. very good physical and chemical stability and low viscosity. Therefore, different proportions of an ammonium poly(acrylate) were added to the suspensions to stabilise them. The optimum amount of dispersant was determined through zeta potential and rheological measurements. The liquid feedstocks were deposited by suspension plasma spraying (SPS) on metallic substrates testing different spraying distances. The topography of the coatings was analysed by confocal microscopy, their surface and cross-section were observed by scanning electron microscopy, the different crystalline phases were determined by X-ray diffraction and the thermal conductivity was measured by means of a laser flash equipment.

The results showed that a significant amount of zircon phase is preserved in the final coatings. Additionally, a clear effect of both the feedstock solids content and the spraying distance on the thermal decomposition of zircon particles was observed. Thus, different microstructures and proportion of crystalline phases in the resulting coatings were obtained giving rise to some thermal conductivity variations.

This work has been supported by the Spanish Ministry of Science, Innovation and Universities (RTI2018-099033-B-C3, MCIU/AEI/FEDER, UE).