Zircon (ZrSiO₄) is an inexpensive and easily available ceramic material well known for its excellent thermal properties, such as low conductivity and thermal shock resistance. This makes it a suitable candidate for thermal barrier coatings (TBCs). The challenge of this material to produce TBCs is the decomposition that it undergoes at high temperatures. Nevertheless, recent studies have demonstrated the possibility of obtaining zircon-based coatings by means of the suspension plasma spraying (SPS) technique, resulting in tetragonal zirconia as the major phase and considerable amounts of retained zircon. The aim of the present work focuses on obtaining zircon-based coatings by SPS from suspensions with mixtures of zircon and alumina or titania nanoparticles that may react with the by-products of zircon decomposition. In this way, coatings based on the ZrSiO₄/ZrO₂ system are obtained with the in-situ development of new reinforcing crystalline phases such as mullite or zirconium titanate.
 
The stability of all suspensions and colloidal sols was studied by zeta potential measurements as a function of both the pH and the concentration of different polyelectrolytes (cationic and anionic). Aqueous suspensions with a total solids content of 20 vol.% were prepared for suspension plasma spraying. The rheological study was performed optimising the deflocculant content and the sonication time. For this purpose, the corresponding flow curves were measured at room temperature (25ºC) using a rotational rheometer and a microfluidic chip type rheometer in order to evaluate the viscosity over a wide range of shear rates.
 
The optimised suspensions were plasma sprayed on metal substrates using fixed spraying parameters. The topography and surface roughness of the coatings were analysed by confocal microscopy, their microstructure was observed by scanning electron microscopy and the development of crystalline phases was evaluated by X-ray diffraction. The coatings exhibit the typical microstructure derived from suspensions deposited by plasma spraying. It is worth noting that a significant proportion of the starting zircon is retained in the final coatings, as well as the in-situ development of new mullite or zirconium titanate reinforcing phases. Finally, the thermal conductivity of all the coatings was determined.
 
This work has been supported by the Spanish Ministry of Science and Innovation (PID2021-124521OB-I00, MCIU/AEI/FEDER, UE).