Performance Research of Magnesium Base Lanthanum Hexaaluminate Prepared by Co-Precipitation
Ying LI1,2,Chao SUN1,Jun GONG1()
1. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2. University of Chinese Academy of Sciences, Beijing 100049, China
Cite this article:
Ying LI,Chao SUN,Jun GONG. Performance Research of Magnesium Base Lanthanum Hexaaluminate Prepared by Co-Precipitation. Acta Metall Sin, 2019, 55(5): 657-663.
Thermal barrier coatings are widely used on turbine blades to provide high temperature insulation, oxidation and corrosion protection. Thermal barrier coatings are composed of matrix, oxide layer, bonding layer and ceramic layer. The lanthanum magnesium hexaaluminate with magnetoplumbite structure have a high aspect ratio, large specific surface area and strong resistance to high temperature sintering, and it can be used as ceramic layer of thermal barrier coatings. In this work, the former powders of lanthanum magnesium hexaaluminate was prepared at synthesized temperature of 60 ℃, pH=11.5. Comparing with the conventional chemical co-preparation synthesis, the synthesized temperature was raised and the pH value for synthesizing was reduced, which resulted in improving production efficiency of former powders. And the lanthanum magnesium hexaaluminate powders for ceramic layer of thermal barrier coating was prepared after the precursor powders were calcinated at 1500 ℃ for 5 h. The phase structure of reaction products, morphology of the powders, full width at half maximum and spectral intensity were analyzed by XRD, SEM, TEM and XPS. The results showed that the magnetoplumbite structured formation generation was elevated much more efficiency if the former powders were precipitated at higher temperature. Since the bonding energy of La, Mg, Al and O atoms increased, the kinetic energy of electrons decreased, therefore, chemical composition of the reaction products were steady near 1500 ℃. During the crystallization process of lanthanum magnesium hexaaluminate, the spinel layer was generated firstly and mirror layer was consequently produced. In the process of producing pure magnetoplumbite phase powders, the full width at half maximum of LaAlO3 formula and MgAl2O4 formula were increased and the activation energy of the crystal structure was higher than that before reaction, which was beneficial to improve anti-sintering performance and thermal stability of the ceramic coating.
Fig.1 XRD spectra of the precursor powder prepared at synthesized temperature of 60 ℃, pH=11.5 (a) and room temperature, pH=12.5 (b) after calcinated at different temperatures for 5 h
Fig.2 SEM image (a) and bright field TEM image (b) of the LaMgAl11O19 powder prepared at synthesized temperature of 60 ℃, pH=11.5 and calcinated at 1500 ℃ for 5 h
Temperature / ℃
Al2p
Mg1s
La3d
O1s
1000
73.17
1302.92
836.91
532.06
1100
73.24
1302.99
837.02
532.10
1200
73.23
1303.43
837.14
532.20
1300
73.10
1303.11
837.20
532.13
1400
73.05
1303.46
837.07
532.02
1500
73.41
1303.48
837.24
532.20
Table 1 Atom bonding energies of calcined powder at different temperatures
Fig.3 XPS survey spectra of the LaMgAl11O19 powder prepared at synthesized temperature of 60 ℃, pH=11.5 and calcinated at 1500 ℃ for 5 h
Fig.4 XPS spectra of the La3d (a)、Al2p (b)、Mg2p (c) and O1s (d) of the LaMgAl11O19 powder prepared at synthesized temperature of 60 ℃, pH=11.5 and calcinated at 1500 ℃ for 5 h
Fig.5 Full width at half maximum (FWHM) of La2O3, LaAlO3 and MgAl2O4 (a) and chemical bonds content ratio of LaAlO3 and La2O3 (b)
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