Yuan Run-zhang

Chemistry reaction processes during combustion synthesis of B2O3–TiO2–Mg system

Abstract In this paper, combustion synthesis method was used to synthesize TiB2 ceramic powder from various oxides. Thermal analysis methods were employed to reveal the chemical reaction processes, a high-speed image recorder was used to monitor and analyze the features of combustion processes. Study results indicated that in B2O3–TiO2–Mg system, B2O3 was reduced to elemental B and MgB2 in one step and TiO2 was reduced to element Ti through following steps: TiO2→Ti3O5→Ti2O→Ti, and then, TiB2 was formed by reaction Ti+2B→TiB2 and Ti+MgB2→TiB2+Mg. In synthesis processing, Mg plays a important role in controlling the mineral phase component of synthesized production and combustion processing. The propagating combustion wave model was found to become unstable with increasing diluent additive amount in raw mixture.

Synthesis, structure and ferroelectric property of a new niobate: Sr6CrNb9O30

Abstract A new niobate Sr 6 CrNb 9 O 30 was found in the ternary system SrOCr 2 O 3 Nb 2 O 5 . The transparent crystal which has a green color and a need-like shape can be grown by the flux method. The crystal structure was determined by x-ray diffraction analysis and dielectric measurement, and it belongs to the orthorhombic tungsten bronze structure at room temperature with space group Cmm2, and unit cell parameters a=1.7505(4) nm, b=1.7510(1) nm, c=7.768(4)nm, Z=4. Dielectric constant measurement show that Sr 6 CrNb 9 O 30 has two phase transitions, paraelectric to ferroelectric at 110°C and ferroelectric to ferroelastic at 205°C.

The formation and stability of γ-aluminium oxynitride spinel in the carbothermal reduction and reaction sintering processes

Several methods of manufacturing γ-aluminium oxynitride spinel (ALON) powder are discussed in this paper. In the carbothermal reduction process, ALON is an intermediate compound, and powders with a high ALON content may be produced in flowing nitrogen below 1650 °C if process parameters are carefully controlled. In addition, ALON may be produced when Al2O3/C mixtures are heated in a coke powder bed above 1650 °C. In the reaction sintering process, ALON is unlikely to form below 1600 °C in a flowing nitrogen atmosphere or in a coke powder bed, owing to the instability of ALON and the fact that the solid–solid reaction does not readily occur unless additives, e.g. MgO, MgAl2O4, are employed.

A Self-Humidifying Composite Membrane with Self-Assembled Pt Nanoparticles for Polymer Electrolyte Membrane Fuel Cells

A method for preparing a self-humidifying composite membrane for the polymer electrolyte membrane fuel cells (PEMFCs) is presented. In this method, perfluorosulfonylfluroride resin is impregnated into a PTFE porous support and positively charged poly(diallymethylammonium)-Pt nanoparticles are self-assembled into the composite membrane to form a self-humidifying layer. The self-assembled Pt nanoparticles were dispersed uniformly in the composite membrane and serve as the catalytic center for the combination reaction between the crossover hydrogen and oxygen, effectively self-humidifying the membrane. The self-assembly of Pt nanoparticles has little adverse effect on the proton conductivity of the composite membrane. The composite membrane with self-assembled Pt nanoparticles improves significantly the performance of PEMFCs as compared to that of the composite membrane without self-assembled Pt nanoparticles. The results show that optimum loading of the self-assembled Pt nanoparticle is about 8.87-9.57 μg/cm 2 under conditions of the present study.

Carbothermal reduction synthesis of aluminium oxynitride spinel powders at low temperatures

Abstracts are not published in this journal

Effect of raw materials on carbothermal reduction synthesis of γ-aluminum oxynitride spinel powder

The effect of starting Al2O3 materials on synthesis of γ-aluminum oxynitride spinel (γ-AlON) powder by carbothermal reduction has been investigated. Whether using Al(OH)3, boehmite, dried gel, or calcined alumina as an alumina source, the reaction rate is faster than that using α-Al2O3. That is because the oxygen distribution in γ-Al2O3 is cubic close packed as the non-metal arrangement in AlON spinel is whereas that in α-Al2O3 is hexagonal close packed. When hydrated aluminas used lose structural water and transform into γ-Al2O3 in heating cycle, γ-Al2O3 is easily reduced and nitrided into AlON spinel after a slight adjustment in the cation positions and proportions is made in the reduction process of alumina. The particle morphology of the product after carbothermal reduction was strongly influenced by the type of alumina source employed, which suggests the mechanism of Al2O3/C powder mixtures in a flowing N2 stream is the absorption of aluminum-containing gas, such as Al(g), Al2O(g), etc., on the surface of aluminum oxide in the initial stages, followed by reaction with N2 gas to form AlON and AlN phases with nucleation, and growth on Al2O3 particle surfaces.

Nafion/Silicon oxide composite membrane for high temperature proton exchange membrane fuel cell

Nafion/Silicon oxide composite membranes were produced via in situ sol-gel reaction of tetraethylorthosilicate (TEOS) in Nafion membranes. The physicochemical properties of the membranes were studied by FT-IR,TG-DSC and tensile strength. The results show that the silicon oxide is compatible with the Nafion membrane and the thermo stability of Nafion/Silicon oxide composite membrane is higher than that of Nafion membrane. Furthermore, the tensile strength of Nafion/Silicon oxide composite membrane is similar to that of the Nafion membrane. The proton conductivity of Nafion/Silicon oxide composite membrane is higher than that of Nafion membrane. When the Nafion/Silicon oxide composite membrane was employed as an electrolyte in H2/O2 PEMFC, a higher current density value (1 000 mA/cm2 at 0.38 V) than that of the Nafion1135 membrane (100 mA/cm2 at 0.04 V) was obtained at 110 °C.

Fractal analysis of gas diffusion layer in PEM Fuel Cells

The aim of this study is to show how fractal analysis can be effectively used to characterize the texture of porous solids. The materials under study were carbon papers, the backing material of the gas diffusion layer (GDL) in Proton Exchange Membrane Fuel Cell (PEMFC). The fractal dimensions were calculated by analyzing data from mercury porosimetry. The polytotrafluoroethylene (PTFE) treated carbon paper shows a significantly high fractal dimension value than pure sample, and the high fractal dimension signifies that the physical complexity of the pore surface is enhanced. The fractal dimension can be used as a valid parameter to monitor the textural evolution of the samples as the treatment progresses, as this behaves in a similar way to other textural parameters. The use of fractal analysis in conjunction with the results of classical characterization methods leads to a better understanding of textural modifications in the processing of materiah.

Synthesis and evaluation on performance of hydrogen storage of multi-walled carbon nanotubes decorated with platinum

By means of chemical reduction, nanoparticles of platinum were deposited on the surface of multi-walled carbon nanotubes (MWCNTs). The performance of hydrogen storage of as-prepared MWCNTs decorated with platinum was investigated. The results indicate that: (1) Hydrogen uptake is more quick and intense for decorated MWCNTs than that for not decorated ones at 10.931 MPa and room temperature. The saturation of hydrogen uptake of the former only lasts about 30 min, while the latter needs about 150 min; (2) The amount of hydrogen uptake of decorated MWCNTs is about 1.13wt%, which is larger than that of not decorated ones (about 0.54wt%); (3) However, more than 37% hydrogen absorbed by decorated MWCNTs is chemisorbed.

Studies on Preparation and Performance of Sodium Silicate/Graphite Conductive Composites

Sodium silicate/graphite conductive composites are prepared by mold pressing at room temperature. The effects of graphite content, size of graphite particles, mold pressing pressure, and mold pressing time on the electrical conductivity of composites are discussed. The density and the water content are composites with different graphite content and are also investigated. The optimized preparation conditions are determined. The results show that the electrical conductivity, the density, and the water content of sodium silicate/graphite composite bipolar plate for proton exchange membrane fuel cell (PEMFC) is >100 s/cm, 1.8g/cm3, and 9 wt%, respectively. The density of this composite bipolar plate material is smaller than that of another bipolar plate. This composite bipolar plate material contains gel capillary pores and has sufficient hydrophilicity, which can humidify the proton exchange membrane during the operating process of PEMFC.