Synthesis of Lanthanum Hexaaluminate (LaMgAl11O19) Powder in order to plasma spary coating on the nickel superalloy as Thermal Barrier coating

Lanthanum hexaaluminate (LaMgAl11O19) as a new thermal barrier coating due to the properties and superior features is selected as a preferred composition instead of yttria -stabilized zirconia (YSZ) Composition. In this paper, synthesis of this composition by solid state reaction method was investigated then it was prepared to coat by atmospheric plasma spraying (APS) method. Scanning electron microscope with X-ray microanalysis (SEM-EDS), differential thermal analysis (TGA/DTA), X-ray diffraction (XRD) were used to characterize of the synthesized powder, granules and free standing as-sprayed LaMgAl11O19 coating. In this research first, α-Al2O3 powder was used as a raw material. The results showed that this material was not suitable for the synthesis of this compound. Therefore γ-Al2O3 powder was used. As a result of that, a single phase compound with plate-like morphology was formed and the synthesis temperature was 1330 Cº. Also α-Al2O3, LaAlO3 and MgAl2O3 compounds were formed at 850-1100 ºC that the final phase transformation was occurred due to reaction between these three compounds.
From the phase analysis results, it can be concluded that the main role of γ -Al2O3 phase in structure is to reduce the synthesis temprature of MgAl2O4 spinel phase to a temperature of less than 1100 ºC.
Also chemical analysis results of granules and APS coating with optimal parameters indicated the existence of single phase structure and the second phase was not found.