Yan Jiang

Crystallinity and morphology changes of a-WO3 films

Abstract The crystalline property changes of a-WO 3 films deposited by reactive sputtering are studied using HREM, STM and other techniques. The results indicate that cyclical electrochemical hydrogen insertion and extraction weakens the amorphous feature and increases the crystalline properties of the as-deposited a-WO 3 films. The degree of these changes is strongly correlated with the degree of electrochemical cycling of the a-WO 3 film. STM analysis reveals that the morphology of saturated colored a-WO 3 films consists of very fine grains (ca. 20 nm) with voids in the film, whereas the morphology of unsaturated colored a-WO 3 film consists of relatively compact large (ca. 110 nm) clusters. H 2 O compounds are formed in both coloring and bleaching process of the a-WO 3 film electrochemical cycles.

Oxidation protection of (ZrTa)B2–SiC–Si coating for graphite materials

ABSTRACT To protect graphite materials from oxidation, a dense (ZrTa)B2–SiC–Si coating was for the first time prepared on graphite substrate by slurry dipping and vapour silicon infiltration process. (ZrTa)B2 phase was synthesised by in-situ reaction using ZrC, TaC, B4C, phenolic resin and Si as raw materials. The phase compositions and microstructure of the obtained coating were analysed by XRD and SEM. The isothermal oxidation tests demonstrated that the in-situ coating had excellent oxidation resistance ability, after oxidation for 468 and 347u2005h at 1273 and 1773u2005K, respectively, the weight gains were 0.07% and 0.33%, respectively. No signs of oxidation of graphite substrate were found after oxidation, and two layers could be observed in the coating, namely, oxide layer containing Zr and Ta oxides and (ZrTa)B2–SiC–Si layer. A model for the evolution of the oxide layer was proposed to interpret the oxidation failure mechanism of the coating.