Key Engineering Materials Vols. 280-283

Abstract: In the development of intermediate temperature solid oxide fuel cell (IT-SOFC), the anode supported thin electrolyte with higher conductivity than YSZ is an essential approach in recent years. In this work, we report our route that Ce0.8Sm0.2O1.9 (SDC) as electrolyte and porous NiO-SDC as anode substrate are prepared by a bi-layer tape casting and co-sintering process. The major effort was to adjust and control the shrinkage of the two material layers. It was found that only the specimens with less than 0.1% mismatching of the sintering shrinkage between two layers can result in the flat and crack free samples. In addition, high activity powders were the essential to obtain dense SDC electrolyte. Fuel cells with Sm0.5Sr0.5CoO3 as cathode were tested. The open circuit voltage (OCV) and the power density of the cells confirmed the full densification of the SDC electrolyte on the anode support.

Abstract: Thin wall tubular Lithium aluminate ceramics have special application background. The microwave synthesis of LiAlO2 ultrafine powder, shape forming and microwave sintering of lithium aluminate pipes with 1mm in thickness were conducted in this paper. The results showed: (1) A controllable ratio of alpha to gamma phase LiAlO2 with average particle size of 0.3 µm can be synthesized via microwave radiation at temperature of 650-800°C within an hour; (2) Cold press and cold isostatic press are feasible methods to form LiAlO2 thin-wall tube and their mechanical properties are superior to those molded via hot pressure casting. (3) Lithium aluminate ceramic was successfully fabricated via microwave sintering, a uniform crystal size within 2-4µm, a typical bimodal pore size distribution and a average compressive strength more than 600MPa were obtained at 1300°C for 30min.

Abstract: Nanometer K0.6Sr0.7Zr4P6O24 (KSZP) powders were synthesized from KNO3, Sr(NO3)2, NH4H2PO4 and ZrOCl2·8H2O by a direct co-precipitation method. The as-prepared precipitates and KSZP powders were characterized by thermal analysis, X-ray powder diffraction, granulometer and scanning electron microscope. The crystallization and particle characteristics of the KSZP powder product depend on treatment temperatures and the nanometer KSZP powder can be attained after heat-treated at 900°C. The effects of the sintering conditions on the densification of nanometer KSZP powder and the properties of KSZP ceramics were studied. Under the sintering temperature of 1380°C and the sintering time of 2h and the additive of Nb2O5 2wt%, the KSZP ceramic from the nanometer powder after heat-treated at 900°C has better comprehensive properties.

Abstract: TiO2 thin films were prepared on soda lime glass, fused quartz and stainless steel substrates by liquid phase deposition (LPD) method from a (NH4)2TiF6 aqueous solution upon the addition of boric acid (H3BO3), and then calcined at 500oC for 2 h. The prepared films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It was found that the substrates obviously influenced the element composition and microstructure of TiO2 thin films. Except Ti, O and a small amount of F and N elements, which came from the precursor solution, some Si (or Fe) element in the thin films deposited on soda lime glass and quartz substrates (or on stainless steel substrate) was confirmed. The Si (or Fe) element in the thin films could be attributed to two sources. One was from the SiF6 2- ions (or FeF6 2- ions) formed by a reaction between the treatment solution and soda lime glass or quartz (or stainless steel) substrates. The other was attributed to the diffusion of Si (or Fe) from the surface of substrates into the TiO2 thin films after calcination at 500oC. The Si (or Fe) element in the TiO2 thin films could behave as a dopant and resulted in the formation of composite SiO2/TiO2 (or Fe2O3/TiO2) thin films on the substrates.

Abstract: The aim of the present study is to investigate the physical properties and antibacterial performances of Ag+-doped TiO2 film on stainless steel and effects of surface oxidization. In the experiment, the surface of stainless steel was been oxidized by heat treatment (550°C, 1 hour) before the Ag+-doped TiO2 (anatase) film being formed by sol-gel method. Sample A (filmed after surface oxidization), B (filmed without surface oxidization), C (only surface oxidization) and D (neither oxidized nor filmed) were respectively tested for corrosive resistance, abrasive resistance and adhesiveness, and the samples with different content of argentine was tested for antibacterial performance. Results: 1) Corrosion rates of sample A, B, C and D in 10% FeCl3 solution are respectively 1.65%, 1.87%, 2.02% and 3.28%, suggesting that the film has protected the stainless steel from the corrosion; 2) Scratching using a loaded (150 g) pin makes no crack on surface of sample A, while it results a slight scuffing on surface of sample B, suggesting that the surface oxidization has enhanced the abrasive resistance and adhesiveness of the TiO2 film, which may be due to the bridge-like function of the oxidation film; 3)Antibacterial performance is enhanced as the content of doping argentine increases, exceeding 90% when the argentine reached 3%, and the TiO2 film on the oxidized stainless steel performs better in antibacterial test than untreated one.

Abstract: LiNO3-doped TiO2 thin films on glass-ceramics were prepared by sol-gel dip coating. The influence of LiNO3 addition on the phase transformation temperature was studied. The transformation temperatures of non-crystalline to anatase and anatase to rutile are originally 520°C and 880°C without the addition of LiNO3. By adding 5%LiNO3 the two transformation temperatures decrease to 440°C and 580°C, respectively. The average size of the particles was found to be around 40nm for the LiNO3- doped TiO2 film annealed at 600°C.

Abstract: A new sol-gel method was introduced to prepare titanium oxides (TiO2) photocatalytic thin flms using peroxide (H2O2) and titanyl sulfate (TiOSO4) as raw materials. The TiOSO4 solution was recipitated by adding ammonia solution, then peptized with 30% H2O2 solution to get a yellow, table, neutral, and transparent liquid (peroxo titanic complex sol). When the peroxo titanic complex sol was autoclaved above 80°C for 2h, it changed to a stable, semitransparent sol containing eedle-like, ultra-fine anatase crystals less than 20nm in diameter. Titanium oxide (anatase) films sed for photocatalysis can be prepared on substrates by a dip-coating technique using peroxo titanic omplex and autoclaved sols.

Abstract: In order to meet a need of application of photocatalyst, a slurry dipping method was adopted for nano-TiO2 coating on optical fiber. Three slurry states were designed and their effects on coating quality were investigated. Experimental results showed that paste state may lead to surface cracks in coating. Both flocculent and dispersive slurry states can form high quality coatings whose coating microstructures are different, the former resulted in a loose and thicker coating and the later resulted in a dense and thinner coating, which supplied a basis for further study on effect of photocatalytic reaction and design of photocatalyst reactor.

Abstract: X-ray diffraction (XRD) method to measure the residual stress in the metal substrate surface layer and the medial oxide layer between thin film and metal substrate was introduced and the sol-gel TiO2-SiO2 thin film was successfully prepared on SUS304 stainless steel substrate by dip-coating process. The macro residual stress existing in metal substrate was analyzed by XRD. It turns out that the compressive stress existing in the metal substrate surface layer decreases with the raising of heat-treated temperature and that the compressive stress of metal substrate surface layer and the tensile stress of the medial oxide layer increase with the increase of the withdrawal speeds of the sol-gel dip-coating. Based on the above study, colored stainless steels of high quality were prepared by sol-gel process for the first time.

Abstract: TiO2 is one kind of semiconductor-based photocatalyst. TiO2 shows relatively high reactivity and chemical stability under ultraviolet (UV) light. However TiO2 is poor absorber of photons in the solar spectrum. In order to improve the absorption efficiency, the coatings of TiO2/ZnFe2O4, ZnFe2O4and TiO2 on ITO were prepared by dip coating method, their microstructure, surface properties, photocurrent and photo absorption are investigated in this paper. XRD results show that the phases on the composite coatings are mainly TiO2 and ZnFe2O4 and the main phase on ZnFe2O4 and TiO2 coatings is ZnFe2O4 and TiO2 respectively, the SEM results show that the coatings of TiO2 and TiO2/ZnFe2O4 are distributed evenly on the materials surface and the AFM results show that the grain size is about 20nm. The experimental results also show that the absorption wavelength of composite coatings of TiO2/ZnFe2O4 is 454nm, which is larger than that of TiO2 coatings (370nm). Under the irradiation of Xe lamp light, a photocurrent of 27µA/cm2 on the materials surface could be obtained.