Key Engineering Materials Vols. 368-372

Abstract: Superhydrophobic ZnO films were prepared by a simple low-temperature solution method, where the ZnO morphology was tuned by hydrofluoric acid. The film topography presents two different length scales: micro flower-like-spheres and nano petals. Such hierarchical structures give the film a superhydrophobic behavior with water contact angle (CA) of 151°, turning into a superhydrophilic one (CA < 5°) after 30 min vacuum ultraviolet (VUV) illumination. The transition from superhydrophobicity to superhydrophilicity is more quickly than the past report using UV illumination because VUV gives higher energy upon the ZnO films. The VUV-illuminated film can be recovered to superhydrophobic through being placed in the dark. Such special wettability can be explained based on ZnO as a photoinduced semiconductor and a photocatalyst. This study will greatly extend applications of ZnO nanomaterials to many important fields, such as microfluidic devices.

Abstract: ZrW2O8 powder was prepared by the solid-state method. A heterogeneous precipitation process was developed to fabricate Cu coated ZrW2O8 composite powders based on a cementation process under 100oC. SEM and XRD were applied to assess the coating quality as well as the phase composition. The result shows that the mean size of ZrW2O8 powders is less than 2 microns. The nanometer compounds are easier formed on the surface of the spheric agglomerated ZrW2O8 powders. The Cu coated ZrW2O8 composite powders can be obtained with flowing hydrogen at 300oC.

Abstract: The mullite sol was prepared using tetraethyoxysilane (TEOS) as raw materials. Aluminum titanate (AT) powders were coated with the sol by dipping. The influence of the concentration of the mullite sol and pH value on the microstructure of the coated AT powders was studied. The results showed that AT powders are coated homogeneously and the thickness of the mullite film is about 0.15 μm when the concentration of the mullite sol is 0.18 mol·L-1 and pH value is 3.0.

Abstract: AlN multilayered films were deposited on Al substrates using RF reactive magnetron sputtering with Al targets under Ar and N2 atmosphere. Circles of deposition and annealing were repeatedly performed. Macrostructure observations, crystallographic analyses and dielectric property measurements were carried out. The grains of AlN film had a worm-like shape. When the number of layers (and cycles) increased, the (100) and (110) oriented grains weakened and the structure of film changed into (002) and (101) oriented. The capacity–frequency (C-f) curves of Cu-AlN-Al-Cu capacitors, measured at 100 Hz - 1 MHz, showed that the dielectric constant and the dielectric loss of AlN decrease with increasing number of cycles, attributed to annealing processes that influences film microstructure and the orientation of worm-like shape grains.

Abstract: The layers of ZrO2-Al2O3 were coated on the surface of SiC fibers (Tyranno SA fiber) by dip-coating process. The citric acid-ethylene glycol solution containing Al and Zr ions was polymerized at 150oC to obtain a polymerized complex precursor. The 2D-woven SiC Tyranno SA fibers were dipped into this precursor few times. Heat treatment for coated fiber was conducted at 800-1200oC for 1 h in air. Thin film of mixed zirconium/aluminum oxides on SiC fibers were successfully elaborated using the sol-gel process. The coated zirconium/aluminum oxides layer of SiC Tyranno SA fiber was about 200-1000 nm. The coated fibers were stable in an oxidizing environment even at high temperatures.

Abstract: Multilayer SiO2 crystals modified by alkoxysilanes were fabricated by the vertical deposition technique combined with self-assembly method. The SiO2 colloidal crystallization was prepared by the traditional Stöber-Fink-Bohn method, and modified by different alkoxysilanes to investigate the properties of the films. The films fabricated by the ordering of SiO2 spheres were investigated by infrared spectrometer, X-ray diffraction, scanning electron microscope, UV-visible spectrophotometer. The results showed that thin film is the face-centered cubic structures and the spheres are [111]-oriented.

Abstract: Ceramic matrix composites reinforced by carbon or SiC-based fibers achieve high toughness and damage tolerance through the disposal of weak fiber coating which can deflect cracks and promote debonding at the fiber/matrix region. The methods for fabrication, as well as different techniques including SEM/EDS, XPS, XRD, AFM, micro Raman for evaluation of properties of the interphase zone are considered. The morphology, composition, topography, roughness, tensile properties of coated carbon and SiC fibers are discussed in details. The behavior of coated fibers is governed by the chemistry, procedure for coating fabrication, nanostructural factors.

Abstract: A study of a catalyst for NOx reduction used for a diesel engine of cars is done frequently currently. In the recent studies, Ag/Al2O3 catalyst system is considered to be a candidate for practical use. The ceramics molding body (ceramics honeycomb etc.) is used as a border brim of these catalysts usually. However, there is a problem. Strength to thermal shock is low. Moreover, it is not easy to go up in the center part until the catalyst operating temperature because thermal conductivity is bad and is obstructed working of the catalyst to the first stage of the reaction for that. In this research, the Ag/Al2O3 catalyst system was coated to stainless steel (SUS304) substrate that forming it is easy and heat conduction rate is good. The aluminum nitrate was used as a binder. After the binder is dissolved in the ion exchange water, the stainless steel substrate coated Ag/Al2O3 catalyst is sintered. In order to optimize coating conditions, the heating temperature, the sintering time, the density of the binder and the amount of the coating powder addition as well as the dip coating frequency were changed, respectively.

Abstract: We have successfully demonstrated that the stress distribution of a metal substrate can be directly displayed by coating SrAl2O4:Eu (SAO), a representative of strong mechanoluminescent materials, on the surface of test objects. An aluminum plate with SAO sensing film had been applied to experimental analysis of stress concentrations, and a numerical calculation via a finite element method confirmed that the observed real time mechanoluminescence images displayed the stress distribution. As a result, visualization of stress distribution on metal surface has been realized by ML images using SAO sensing film, and this novel visualization technique can be applied for viewing the stress concentration in various fields such as modeling, manufacturing and demonstration of an industrial product.

Abstract: Alkaline-earth metal oxides (MgO, CaO, SrO and BaO) were introduced to Na2O-B2O3-Al2O3- SiO2 vitrified bond, and their effects on the properties of the vitrified bond were investigated through the measurements of refractoriness, fluidity and bending strength. The results showed the refractoriness of the vitrified bond was reduced and the fluidity of the bond increased with the addition of alkaline earth metal oxides in the order of CaO>SrO>BaO>MgO. When 2-10wt% MgO, CaO and BaO was added into the bond respectively, the vitrified bond was relatively dense due to high viscosity, and the strength was all improved to some extent. However, when more than 4wt% SrO was added, the strength decreased sharply because of the deterioration of microstructure. It was concluded that the bending strength of the bond was affected by alkaline-earth metal oxides in the order of CaO>MgO>BaO>SrO.