Deposition Mechanisms of Thick Lanthanum Zirconate Coatings by Spray Pyrolysis

Abstract

An aqueous nitrate-based precursor solution was deposited on stainless steel substrate by spray pyrolysis to produce thick lanthanum zirconate coatings for thermal barrier coating application. The as-deposited, dried, and further annealed coatings were characterized by thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The influence of the substrate temperature on the film formation and microstructure has been carefully studied for a better understanding of the deposition mechanisms. A temperature range corresponding to the deposition of an ionic salt liquid was found to be critical to obtain thick crack-free green coatings. Further heat treatment was necessary to decompose the nitrate species into an oxide coating with a fine porous microstructure.

Lanthanum zirconate based thermal barrier coatings: A review

“…In addition to the two methods mentioned above, there are other techniques to deposit LZ coatings, such as suspension plasma spray (SPS) and spray pyrolysis [7,32,33].…”

“…The main deposition 12 parameters were standoff distance of the substrate and the concentration of the suspension feedstock. A liquid solution was used as a feedstock material instead of powder, which provided the possibility of tailoring the coating composition and the deposition of the doped multilayered coatings [33]. As shown in Fig.…”

“…7b, many pores and cracks were spotted in the microstructure of the SPS deposited coatings [32]. Weber et al fabricated the LZ coating using the spray pyrolysis method [33]. Zirconyl oxynitrate hydrate (ZrO(NO3)2·xH2O) and lanthanum nitrate hexahydrate (La(NO3)3·6H2O) were dissolved in deionized water and further mixed in a molar ratio of 1:1 of La and Zr.…”

Thermal and mechanical properties of crack-designed thick lanthanum zirconate coatings

“…By air atomizing a precursor solution on a heated substrate, thin or thick films or coatings can be deposited and, by adjusting the process parameters, the microstructure can be tailored. In particular, the substrate temperature has a significant influence on the film formation [20; 21], and the deposition of thick crack-free coatings by spray pyrolysis of an aqueous precursor solution is only possible in a suitable substrate temperature interval corresponding to the deposition of ionic salt precipitates [22]. Further cracking of thick coatings occurs during the decomposition of the precursor salts in the deposited coatings due to the associated volumetric shrinkage.…”

“…previously cleaned with ethanol by a non-commercial spray pyrolysis unit developed at NTNU and described elsewhere [22]. With this setup, a precursor solution was fed to the spray unit using a peristaltic pump and further atomized on a heated substrate by a two-fluid nozzle using synthetic air (0.5 bar) as a carrier gas.…”