Key Engineering Materials Vols. 280-283

Abstract: Sr(NO3)2, Fe(NO3)3 and citric acid (the mole ratio was 1:1:2) were mixed in water to form sol. Alumina substrate, which had been treated by ultrasonic cleaner, were dipped in the sol and pulled out, and the coating film was heated for 1h at 900oC. Through seventeen times treatment, SrFeO3-d thin film was coated on the alumina substrate. The remainder sol was dried and heated at 400oC, 800oC, 900oC for 2 h. The thin films and the powders were characterized by XRD. The morphologies of thin films were observed by SEM. The results showed that SrFeO3-δ was formed at 900oC on alumina substrate and the grain size was 100 ~ 200 nm. The oxygen sensitivity was measured in the temperature range of 377 ~ 577oC under different oxygen partial pressures. SrFeO3-δ thin film showed p-type conduction. The response time was less than 2 min when being exposed to a change from N2 to 0.466% O2 at 377oC.

Abstract: Tungsten oxide thin films were prepared by an inorganic-sol-gel dip-coating process, where the sol was obtained by adding citric acid, as chelating agent, to the ammonia solution of tungstic acid. The resultant thin films were a mixture of monoclinic and tetragonal phases of WO3 and, after being pretreated at 600°C and sintered at 650°C, the average grain size of the polycrystalline films was about 500 nm. The gas-sensing properties of WO3 thin films were tested at temperatures ranging from 500° to 600°C and in nitrogen gas containing 5vol% O2 or 5vol% H2. The WO3 sensors exhibited a good sensitivity and response speed at the temperature of 550°C.

Abstract: A SO2 sensor based on Na-b-Al2O3 interfaced with an auxiliary electrode of Na2SO4 formed in situ and a solid mixture of Fe3O4, Fe2O3, 3Na2O.5Fe2O3 as the reference electrode was developed. The sensor displayed a Nernstian response to changes in the partial pressure of SO2.

Abstract: A glass system according to the molar formula (70% mole V2O5- (15-x)% mole P2O5-15% mole B2O3), where x = 0, 1, 2.5, 5 and 7.5 % mole Fe2O3, was prepared by melting the pure powder chemicals at porcelain crucibles at 1000Co for three hours until the homogenous glass was obtained. The samples were quenched in air and heat-treated at 500 Co for 1, 2 and 3 h. The density, the molar volume, the electrical conductivity and magnetic properties were measured before and after the heat-treatment. The crystalline phases due to heat-treatment were determined using x-ray diffraction. The heat-treatment causes change of BO3 to BO4 and forming non-bridging oxygen. Replacing the phosphorus oxide with the iron oxide increases the magnetic properties while the conductivity increase up to 5% mole and then decreases. The changes of electrical and magnetic properties with heat-treatment time have a random behavior due to the change of the structure if the samples with heat treatment.

Abstract: The humidity control ceramics were prepared by selective leaching and sintering of Suzhou kaolin clay. Effects of sintering temperature and solid/liquid ratio of selecting leaching of the kaolin clay on the humidity controlling properties of ceramics were analyzed. It was found that the ceramic had the best properties when the kaolin clay was sintered at 1000oC for 2 hours and leached with the solid/liquid ratio being 1:50. Water vapor adsorption isotherms of the ceramic possessed a sharp increase in the relative humidity between 45 and 85%.

Abstract: The effects of glass additives on the sintering and properties of Ni/(Ba0.92Sr0.08)TiO3 composites were investigated. Due to the addition of glass additives, Ni/ceramic composites with low room-temperature resistivity and obvious PTC effect were obtained at a low sintering temperature. It was shown that glass-additives could form liquid phase that aided the solution and diffusion of solid atoms, acting as sintering aids to accelerate the sintering and lower the sintering temperature. The room-temperature resistivity decreased first and increased later with the increasing content of glassadditives, which was explained by two functions of glass-additives, decreasing interface contact resistance as sintering aids and adding volume resistance as insulators. Moreover, a suitable amount of glass-additives could enhance the PTC effect unexpectedly, which was attributed to the decrease of the contact resistance existing at the ceramic/ceramic interface.

Abstract: Ni/BaTiO3 composite was prepared by decomposition of NiC2O4·2H2O/BaTiO3 precursor, which was prepared by precipitating of nickel in the form of oxalate into the BaTiO3 slurry. The composite must be sintered in reducing atmosphere. Otherwise NTC effect would be introduced. The prepared composite almost had no PTC effect. But PTC effect of the Ni/BaTiO3 composite can be effectively renewed by heat-treatment in air. Under a proper composition and method, the composite shows low room-temperature resistivity (ρRT=6.0 Ω·cm) and obvious PTC effect (ρmax/ρmin=102).

Abstract: The influence of grahtite and bakelite content of Graphite/Bakelite/BaTiO3-based PTC ceramic composite on their properties was studied. It was found that the composite's room- temperature resistivity was decreased and the PTC intensity was assured. This method offered a new way to solving the problem of high room-temperature resistivity of the BaTiO3-based PTC ceramic.

Abstract: High-performance PTCR ceramics with low resistivity (8Ω.cm) at room temperature and around four orders magnitude of the PTCR jump were obtained by adding BaCO3 and Pb3O4(B-P) in BaTiO3. The influence of adding B-P on the sintering behavior, the microstructure and the electrical properties of BaTiO3-based PTCR was investigated. The phase constituent in the sintered ceramics was analyzed by XRD and it was shown that the metallic layered Ba3Pb2O7 phase was synthesized during the sintering. Analysis suggested that making the weak reduction atmosphere at the grain boundary may decrease the grain-boundary resistivity.

Abstract: Nickel/graphite/BaTiO3 PTC composites with lower room-temperature resistivity and higher resistance jump were fabricated by adding graphite and nickel powders into BaTiO3 PTC ceramics. Characteristics and conductive mechanism of the composites were discussed based on the experimental results.