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Abstract: Crystallization kinetics of the newly developed Al2O3‐Y3Al5O12 (YAG) amorphous ceramic coating fabricated by atmospheric plasma spraying (APS) were investigated via differential scanning calorimetry (DSC) under non‐isothermal conditions. The phase compositions and microstructure of the as‐sprayed coating were characterized by X‐ray diffraction (XRD) and Scanning electron microscopy (SEM). The glass transition temperature Tg, the onset temperature of crystallization Tc and the peak temperature of crystallization Tp presented heating rate dependence. The related kinetic parameters of activation energies (Eg, Ec, Ep) and Avrami exponents (n) were quantified using various methods including Kissinger, Augis–Bennett, Ozawa and Matusita–Sakka, etc., to understand the phase transition mechanism and crystallization process in depth. A series of parameters including devitrification interval ΔT, thermal stability (Tc, Ec), nucleation resistance Ec/RTg and fragility index F were quantified in order to evaluate the nucleation mechanism, crystallization behavior and thermal stability of Al2O3‐YAG amorphous ceramic coating. Excellent thermal stability was witnessed in the studied coating. Furthermore, the YAG crystalline phases can be reasonably controlled and independently precipitated from the amorphous matrix via proper annealing. [ABSTRACT FROM AUTHOR]

In recent years, numerous techniques have been developed to mimic nacre-like hierarchical architectures in order to improve the damage tolerance of materials. We present herein a simple strategy to fabricate such a hierarchical architectured Al2O3–Y2O3 composite coating via atmospheric plasma spraying. The evolution of the phase and microstructure of the Al2O3–Y2O3 composite coating were characterized under conditions of high-temperature exposure in air at 800-1350 °C. The hardness and porosity of several typical coatings were determined. In situ formation of dense hierarchical architectured Al2O3–YAG composite coating with improved hardness was achieved after heat treatment at 1350 °C. Compared with Al2O3 coating, elevated toughness was found for the hierarchical architectured Al2O3–YAG composite coating, which can be ascribed to the distribution of YAG phase that contributed to crack termination and deflection, and microbridging. After thermal aging treatment at 1350 °C, the hierarchical architectured Al2O3–YAG composite coating was quite stable after 100 h of thermal exposure. Furthermore, the Al2O3–Y2O3 composite coating exhibited superior sintering resistance compared with the Al2O3 coating. [ABSTRACT FROM AUTHOR]

Abstract: Lanthanide hexaaluminates including LaMgAl11O19, NdMgAl11O19, SmMgAl11O19 and GdMgAl11O19 were synthesized via Sol–Gel method. Due to the anisotropic crystal growth, these oxides crystallize in the form of platelets and the platelet thickness increases with the decrease of rare-earth ionic radius. It was observed that the thermal-shock resistances of LaMgAl11O19, NdMgAl11O19 and SmMgAl11O19 oxides were superior to 8YSZ as proved by water quenching tests. In addition, the thinner the platelet, the more interstices are retained in the sintered specimen, and the better thermal-shock resistance the oxide has. Based on SEM images, it can be seen that the SmMgAl11O19 sample exhibits a mixture of the intergranular and transgranular fracture after thermal cycling failure. [Copyright &y& Elsevier]

In this study, the process optimization of sprayed powders and deposition performance for amorphous Al2O3–Y3Al5O12 (YAG) coatings was investigated. The solid-state reaction mechanism of the nano-sized Al2O3 and Y2O3 powders with eutectic molar ratio was studied by multiple step-by-step heating cycle calcination processes. The calcination process could be adjusted according the dominant control factors like chemical reaction rate or ion diffusion rate. Finally, the actual deposition performance of the calcined powders (Al2O3/YAG) was examined by atmospheric plasma spraying (APS). XRD, SEM and DTA were used to characterize the powders and the as-sprayed coatings. The results showed that the reaction of Al2O3–Y2O3 system is a high temperature solid reaction dominated by Al3+ diffusion, the initial reaction process was usually belong to chemical kinetic range, then the reaction will be transformed from chemical kinetic range to diffusion dynamic range with the temperature increasing. The process optimization of powders was very effective, and the deposition effect of coating was effective. [ABSTRACT FROM AUTHOR]

Abstract: Lanthanum zirconate (La2Zr2O7, LZ) powders with the addition of various Y2O3 contents for potential thermal barrier coatings (TBCs) application were synthesized by solid-state reaction. The structure evolution, sintering-resistance and thermophysical properties of the synthesized powders and sintered ceramics were systematically studied. X-ray diffraction (XRD) results indicate that LZ containing 3–12wt.% Y2O3 mainly keeps a pyrochlore-type structure, and two new phases of LaYO3 and Y0.18Zr0.82O1.91 are also detected. Raman spectra confirm that the higher the Y2O3 content, the easier is the formation of LaYO3. With the increase of Y2O3 content, the linear thermal expansion coefficients (TEC) of different La2O3–ZrO2–Y2O3 ceramics may gradually decrease. Additionally, LZ ceramics doped with 3wt.% Y2O3 have the lowest relative density and the highest sintering-resistance among all samples, implying that it is the best candidate for TBCs among those samples in this investigation. [Copyright &y& Elsevier]

Abstract: Oxide ceramics with high sintering-resistance above 1473 K have very important applications in thermal barrier coatings (TBCs), catalytic combustion and high-temperature structural materials. Lanthanum zirconate (La2Zr2O7, LZ) is an attractive TBC material which has higher sintering-resistance than yttria stabilized zirconia (YSZ), and this property could be further improved by the proper addition of ceria. The composite La2(Zr0.7Ce0.3)2O7 (LZ7C3) has the highest sintering-resistance, and it is observed that fine particles of the second phase in the composite concentrate at the grain boundary to prevent the grain growth of the main phase. The formation of hollow fibers is helpful to the further improvement of sintering-resistance of LZ7C3, and this technique may be widely applied to protect the catalyst support against thermal sintering. [Copyright &y& Elsevier]

Abstract: Lanthanum–zirconium–cerium composite oxide (La2(Zr0.7Ce0.3)2O7, LZ7C3) coatings were prepared under different conditions by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, surface and cross-sectional morphologies, cyclic oxidation behavior of these coatings were studied. Elemental analysis indicates that the coating composition has partially deviated from the stoichiometry of the ingot, and the existence of excess La2O3 is also observed. The optimized composition of LZ7C3 coatings could be effectively achieved by the addition of excess CeO2 into the ingot or by properly controlling the deposition energy. Meanwhile, when the deposition energy is 1.15×104–1.30×104 J/cm2, the coating has a similar X-ray diffraction (XRD) pattern to the ingot, and the thermal cycling life of the coating is also superior to other coatings. The spallation of the coatings occurs either within the ceramic layer approximately 6–10.5μm above its thermally grown oxide (TGO) layer or at the interface between ceramic layer and bond coat. [Copyright &y& Elsevier]

Abstract: Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La2Zr2O7 (LZ) and yttria stabilized zirconia (YSZ) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, surface and cross-sectional morphologies and cyclic oxidation behavior of the DCL coating were studied. Both the X-ray diffraction (XRD) and thermogravimetric–differential thermal analysis (TG–DTA) prove that LZ and YSZ have good chemical applicability to form a DCL coating. The thermal cycling test at 1373K in an air furnace indicates the DCL coating has a much longer lifetime than the single layer LZ coating, and even longer than that of the single layer YSZ coating. The failure of the DCL coating is a result of both the bond coat oxidation and the thermal strain between bond coat and ceramic layer generated by the thermal expansion mismatch. Additionally, the compressive stress initiated during cooling is also an important factor to control the cleavage of the interface between the LZ and YSZ coatings. Since no single material that has been studied so far satisfies all the requirements for high temperature TBCs, DCL coating is an important development direction of TBCs. [Copyright &y& Elsevier]

Abstract: Electrospinning was employed to fabricate polymer–ceramic composite fibers from solutions containing poly(vinyl pyrrolidone) (PVP), Ce(NO3)3⋅6H2O and ZrOCl2⋅8H2O. Upon firing the composite fibers at 1000 °C, Ce0.67Zr0.33O2 fibers with diameters ranging from 0.4 to 2 μm were synthesized. These fibers exhibit strong resistance to sintering. They still have specific surface area around 11.8 m2/g after being heated at 1000 °C for 6 h. [Copyright &y& Elsevier]

Electrospinning was employed to fabricate polymer–ceramic composite fibers from solutions containing polyvinyl pyrrolidone (PVP) and . Upon firing the composite fibers at 800°C, In2O3 fibers with diameters ranging from 200 to 400nm were synthesized. This indium oxide calcined at 800°C is a body-centered cubic cell. The photoluminescence (PL) properties of the as-formed In2O3 nanofibers were investigated. The In2O3 nanofibers show a strong PL emission in the ultraviolet (UV) region under shorter UV light irradiation. [Copyright &y& Elsevier]