Yuqi Wu

Oxidation behavior of laser remelted plasma sprayed NiCrAlY and NiCrAlY–Al2O3 coatings

Abstract Two types of plasma sprayed coatings (NiCrAlY and NiCrAlY–Al 2 O 3 ) were remelted by continuous wave CO 2 laser. A homogeneous dense remelted layer without voids, cavities, unmelted particles and microcracks was formed. As a result of isothermal oxidation tests at 1000°C, the weight gains of laser remelted coatings, especially laser remelted NiCrAlY–Al 2 O 3 coatings, were obviously lower than plasma sprayed coatings. The effects of both laser remelting and incorporation of Al 2 O 3 second phase in NiCiAlY matrix on high temperature oxidation resistance of plasma sprayed coatings was discussed.

Structural-Dependent Photoactivities of TiO2 Nanoribbon for Visible-Light-Induced H2 Evolution: The Roles of Nanocavities and Alternate Structures

Bicrystalline dehydrated nanoribbon (DNR) with alternate structure of TiO(2)(B) and anatase has been prepared by a short-time annealing method. It is photoactive for photocatalytic H(2) evolution from water in the visible region sensitized by a novel heteropoly blue sensitizer. The effects of annealing temperature and time on the DNR phase transformation process have been investigated. These results reveal that the nanocavity structure of TiO(2)(B) exhibits a narrow band gap and improves its absorbance coefficient in the visible region. The alternate structures of TiO(2)(B) and anatase improve interfacial electron separation and transfer. Compared with normal phase junction, the smoothing alternate joints in the band structure of DNR-600-30 provide an effective route for the movement of holes and electrons. This unique alternate bicrystalline structure has a significant advantage on its applications in photocatalysis and nanodevices.

The roles of density-tunable surface oxygen vacancy over bouquet-like Bi2O3 in enhancing photocatalytic activity

Bouquet-like hierarchical Bi2O3 photocatalyst materials with high-density surface oxygen vacancy are synthesized via a hydrothermal method by the synergetic control of NaOH and a polyvinyl alcohol (PVA) stabilizer. The OH(-) ion addition led to the formation of more relaxed PVA macromolecular clusters, as a result, a thinner PVA film was formed, the species adsorbed on the surface of the produced Bi2O3 crystal nucleus could tune both the surface microstructure size and oxygen vacancy density via controlling the velocity, transfer and reaction of the OH(-) ions. The significant enhancement of photocatalytic performances could be attributed to the high density of the surface oxygen vacancy which was propitious to the charge separation efficiencies, distribution characteristic, and its role in a photo-redox reaction. A turnable-bending self-assembly mechanism was proposed to clarify the formation process of the bouquet-like hierarchical structure.

Oxidation behavior of thermal barrier coatings obtained by detonation spraying

Thermal barrier coatings (TBCs) have been successfully obtained by detonation spraying, through optimizing the spray parameters (especially the ratio of C2H2 to O-2). The oxidation behaviors of detonation sprayed TBCs at 1000 and 1100 degreesC were studied. The results indicated that the detonation sprayed TBCs were uniforin and dense, with a few microcracks in the ceramic coats and a rough surface of bond coats. At the high temperature, the dense detonation sprayed ceramic coats with low porosity could obviously decrease the diffusive channels for oxygen and reduce the oxygen pressure (PO2) at the ceramic/bond coat interface. Under the lower oxygen pressure at the interface, it was advantageous to the formation of a continuous protective Al2O3 layer and the growth of a thermally grown oxide layer (TGO) obeyed the fourth power law

The role of a metallic copper interlayer during visible photocatalytic hydrogen generation over a Cu/Cu2O/Cu/TiO2 catalyst

The role of metallic copper as a co-catalyst is still uncertain, which is an interesting problem in photocatalytic hydrogen evolution. There is debate over the role of Cu+, Cu2+ and metallic Cu during photocatalytic hydrogen generation. Herein, we identified that the metallic copper interlayer between Cu2O and TiO2 played a key role in the hydrogen evolution process. By fabricating the metallic Cu interlayer via in situ reduction of Cu2O/TiO2, efficient charge transfer took place over the Cu/Cu2O/Cu/TiO2 catalyst, while a retarded electron transfer was found over the Cu/TiO2 catalyst. This interlayer structure provides a bridge for photoelectron transfer from th`e conduction band of TiO2 to Cu2O, significantly prolonging the life-time of electron transfer. In addition, the ratio of metallic Cu and Cu2O could be easily adjusted by the loading amount of Cu2O on TiO2, and that the ratio affects the photocatalytic hydrogen evolution activity. A high transient photocurrent and long fluorescence lifetime (0.365 ns) were achieved over the Cu/Cu2O/Cu/TiO2 catalyst when the molar ratio of the interlayer metallic Cu to Cu2O was 0.99. Under the same reaction conditions, the photocatalytic hydrogen generation activity of the Cu/Cu2O/Cu/TiO2 catalyst was three times than that observed with the Cu/TiO2 catalyst with good stability.

Inhibition of the excited-state Rose Bengal (RB) nonradiative process by introducing DMSO for highly efficient photocatalytic hydrogen evolution

An excited-state Rose Bengal (RB) nonradiative process caused by proton-induced quenching makes the capacity of photoelectrons to reduce water weak, which crucially influences the efficiency of hydrogen generation for RB-sensitized photocatalytic systems. In this work, we introduced a low content of dimethyl sulfoxide (DMSO) to form a water–DMSO mixture solvent, which significantly inhibited the nonradiative process. The lifetime of the excited electrons was increased remarkably. The hydrogen generation activity in a water–DMSO mixture solvent was 4.48 times higher than that in the single water solvent. The highest apparent quantum efficiency (AQE) of 44.3% was reached at 550 nm. A small amount of DMSO could break the partial network through hydrogen bonding, increase the RB hydrophobicity, and suppress the excited-state RB nonradiative process.

Detonation gun sprayed thermal barrier coatings

Abstract: Detonation gun spraying (D-gun spraying) is believed to be a promising new spraying technology in thermal barrier coatings (TBCs) for application to aircraft turbines. This chapter focuses mainly on two issues of aircraft turbine applications. It discusses first the low thermal conductivity of the new type of D-gun sprayed YSZ top coating. The failure mechanism of thermal shock cycling aimed at improving the lifetime of D-gun sprayed TBCs is then described.