Shunjie Deng

Porous α-Al2O3 thermal barrier coatings with dispersed Pt particles prepared by cathode plasma electrolytic deposition

Porous α-Al2O3 thermal barrier coatings (TBCs) containing dispersed Pt particles were prepared by cathode plasma electrolytic deposition (CPED). The influence of the Pt particles on the microstructure of the coatings and the CPED process were studied. The prepared coatings were mainly composed of α-Al2O3. The average thickness of the coatings was approximately 100 μm. Such single-layer TBCs exhibited not only excellent high-temperature cyclic oxidation and spallation resistance, but also good thermal insulation properties. Porous α-Al2O3 TBCs inhibit further oxidation of alloy substrates because of their extremely low oxygen diffusion rate, provide good thermal insulation because of their porous structure, and exhibit excellent mechanical properties because of the toughening effect of the Pt particles and because of stress relaxation induced by deformation of the porous structure.

Direct preparation of La2Zr2O7 microspheres by cathode plasma electrolysis.

La2Zr2O7 microspheres were directly prepared by cathode plasma electrolysis (CPE) in the electrolyte of Zr(NO3)4·5H2O and La(NO3)3·6H2O. Compared with high temperature sintering methods, the energy of plasma was completely used by CPE and made it possible to prepare the microspheres without calcining. The diameters of microspheres were mostly in the range of 0.5-5μm and the microspheres consisted of fluorite and pyrochlore structures of La2Zr2O7. Moreover, the microspheres possessed potential photocatalytic activity and fluorescence property, owing to the high crystallinity and large surface area of the microspheres.

Al2O3 Microspheres Prepared by Cathode Plasma Electrolysis

Al2O3 microspheres were prepared by cathode plasma electrolysis (CPE) in an aqueous solution of Al(NO)3·9H2O. Compared with high-temperature calcination methods, the CPE method afforded the preparation of microspheres directly at room temperature. The results showed that regular microspheres formed under relatively high concentrations of Al(NO)3·9H2O. The microspheres, with diameters mostly in the range of 5–30 μm, consisted of γ-Al2O3 and α-Al2O3. The possible formation mechanism included the following processes: (1) Al(OH)3 intermediate was formed during the cathodic reactions; (2) plasma energized the intermediate to Al2O3; and (3) microspheres formed under the effect of the surface tension.

La2Zr2O7 TBCs toughened by Pt particles prepared by cathode plasma electrolytic deposition

La2Zr2O7 thermal barrier coatings (TBCs) with dispersed Pt particles were prepared by cathode plasma electrolytic deposition (CPED) with ceramic balls added to the cathode region. Compared with the conventional CPED, when ceramic balls are used in the cathode region, the plasma discharge ignition current density decreases approximately 62-fold and the stable plasma discharges occur at the whole cathode surface. Such TBCs with a thickness of 100 μm exhibit a crack-free surface and are composed of pyrochlore-structured La2Zr2O7. Cyclic oxidation, scratching, and thermal insulation capability tests show that such TBCs not only exhibit high resistance to oxidation and spallation but also provide good thermal insulation. These beneficial effects are attributed to the excellent properties of TBCs, such as good thermal insulation because of low thermal conductivity, high-temperature oxidation resistance because of low-oxygen diffusion rate, and good mechanical properties because of the toughening effect of Pt particles.