Dan Xu

Surface modification of heteropoly acid/SPEEK membranes by polypyrrole with a sandwich structure for direct methanol fuel cells

A series of SPEEK/HPW/Ppy-n composite membranes with a sandwich structure were successfully prepared by surface modification with polypyrrole (Ppy) in order to stabilize phosphotungstic acid (HPW) in poly(ether ether ketone)s (SPEEKs) and reduce the methanol crossover. Ppy coatings with a large number of secondary ammonium groups (NH2+) interact with anions of HPW to decrease HPW leaching from the membrane. In addition, the hydrophobic Ppy layers allow for little methanol transport, which leads to a significant decline in methanol crossover with reasonable levels of proton conductivity. The properties of the membranes were investigated in detail by UV, SEM, ac impedance, and TGA. As observed, Ppy-modified membranes were better at immobilizing HPW and exhibited higher selectivities than previously reported SPEEK/HPW composite membranes. All the results indicate that the SPEEK/HPW/Ppy-n composite membranes are excellent candidates for direct methanol fuel cells.

Cross-linked membranes with a macromolecular cross-linker for direct methanol fuel cells

With the goal of reducing water swelling and methanol permeability in sulfonated proton exchange membranes (PEM), bromomethylated poly(ether ether ketone) was synthesized and used as a macromolecular cross-linker. The cross-linking reaction was performed at 195 °C for 5 h and resulted in cross-linked membranes with high cross-linked density. Compared to the pristine membrane, the cross-linked membranes displayed greatly reduced water uptake and methanol permeability. Other properties of the cross-linked membranes, including proton conductivity, mechanical properties, and oxidative stability, were also investigated and compared with the pristine membrane. All the results indicated that the novel macromolecular cross-linker and the resulting cross-linked membranes are promising for fuel cell applications.

New orthorhombic approximants of the Al70Co15Ni10Tb5 decagonal quasicrystal

Three new orthorhombic approximants, C1, C2, and C3, have been found in the Al70Co15Ni10Tb5 decagonal quasicrystal, which was prepared by a method of quenching from the melt under a high static pressure. The lattice parameters of these orthorhombic phases are as follows: C1, a = 2.28 nm, b = 1.60 nm and c = 5.46 nm (B type); C2 a = 6.1 nm, b = 0.4 nm and c = 8.4 nm (P type); C3, a = 6.1 nm, b = 0.4 nm and c = 8.4 nm (B type). The strong diffraction spots in the electron diffraction patterns of these phases show the same intensity modulation as those of the decagonal quasicrystal, implying a close relationship between them.

Orthorhombic phases with large unit cells coexisting with the decagonal quasicrystal in an AlCoNiTb alloy

Elser and Henley suggested that if the irrational golden number [tau] = (1 + [radical]5)/2 associated with the three mutually orthogonal, equivalent twofold axes in an IQC (icosahedral quasicrystal) is approximated by a rational ratio of two consecutive Fibonacci numbers (0, 1, 1, 2, 3, 5, 8, [hor ellipsis], F[sub 0] = 0, F[sub 1] = 1, and F[sub n+1] = F[sub n] + F[sub n[minus]1]), such as F[sub n+1]/F[sub n] = 1/0, 1/1, 2/1, 3/2, 5/3, 8/5, [hor ellipsis], then a cubic crystalline phase generally called an approximant will result. Such an analysis has been extended later to 2-dimensional decagonal quasicrystals (DQCs). If the irradiation [tau] along two mutually orthogonal, non-equivalent, quasiperiodic twofold directions perpendicular to the periodic tenfold axis of a DQC is replaced by rational ratios F[sub n+1]/F[sub n], an orthorhombic approximant with a large unit cell will form. This not only explains the existing orthorhombic Al-TM (transitional metals) phases with large unit cells, such as Al[sub 60]Mn[sub 11]Ni[sub 4] and Al[sub 3]Mn, but also predicts many new approximants with even larger unit cells some of which have been found experimentally afterwards.

The Structure and Light Emitting of Silicon-Doped Boron Nitride Nanotubes

In this paper, we report the structural and optical properties of bamboo-like silicon-doped boron nitride nanotubes. The morphologies and structures of the nanotubes were characterized using electron microscopy and FTIR spectroscopy. Three strong broad peaks centered at 1.76ev, 2.20ev, 2.40ev were observed from the room-temperature PL spectrum of the nanotubes. The spectrum suggested the existence of multifold energy levels within the band gap.

Influence of size of NiO on the electrochemical properties for SOFC anodes

NiO and SDC Powders were Prepared by Sol-Gel Method and then Calcined at 400、600 and 800°C. Nio-SDC Anode Materials were Synthesized by Solid State Reaction According to the Mass Ratio of Nio:SDC=65:35 Ratio . XRD Measurement Showed that Powders Consist of Two Phases, the Cubic Nio and Fluorite Structure Ceria . the Grain Size was Shown to Increase with Increasing Temperature. the Cermet with Ni-SDC Powders Calcined at 400°C Showed the Highest Electric Conductivity and a Lower Degree of Polarization.The Electrical Conductivity was 4155Scm-1 and Overpotential was 0.12V at 600°C.

Preparation and Properties of Ni-Doped Ce0.85Sm0.15O1.925 Ceramics for Use as Electrolytes in IT-SOFCs

The electrolytes materials Ce0.85Sm0.15O1.925-x at.% NiO (x=0, 0.5, 1, 2, 3) were synthesized by means of glycine-nitrate process (GNP). Their structures and ionic conductivities were characterized by X-ray diffraction, SEM and AC impedance spectroscopy. All the electrolytes were found to be ceria based solid solutions of fluorite type structures. Grain size increased with NiO. The grain boundary resistance could be decreased by small addition of NiO. Electrolyte-supported solid oxide fuel cells (SOFC) fabricated with Ni-doped Ce0.85Sm0.15O1.925 electrolytes were studied and compared with other fuel cell with Ce0.85Sm0.15O1.925 (SDC) as electrolytes.

A Steady State Model for the Rheological Behavior of Semisolid Al-6.5wt%Si Alloy

In the present work, The Chen and Fan (CF) model [1] of semisolid metal slurries (SSMS) is improved by modifying the expression of the packing parameter, of the solid particles and then the modified CF (MCF) model is obtained. Subsequently, the MCF model is applied to the Al-6.5wt%Si alloy to investigate its rheological behavior at steady state. The factors which affect the steady state behavior have been studied. It has been shown that the steady state viscosity and the average agglomerate size increase with increasing the solid volume fraction and decreasing the shear rate. The prediction of the model is in good agreement with the experimental results in the literatures qualitatively. The importance of the effective solid volume fraction is shown by explaining the strong coupling between the viscosity and the microstructure. The external flow conditions such as shear rate etc change the agglomeration degree, that is, the effective solid volume fraction and then the viscosity

Two-dimensional pentagon quasicrystal in an Al-Co-Ni-Tb alloy obtained by quenching under high static pressure

A transmission electron microscopy study of quasicrystals was carried out in Al-Co-Ni-Tb alloy which was obtained by quenching under high static pressure and a new two-dimensional pentagonal quasicrystal was discovered. An unique five-fold axis is observed in its diffraction patterns and the periodicity along the five-fold axis is 0.4 nm. Another feature of the pentagonal phase is that no extinction exists in the diffraction patterns along the direction perpendicular to the five-fold axis. A comparison of the high resolution electron microscopy images of the pentagonal phase and the decagonal quasicrystal is given. The effect of high pressure is discussed.

Study on a decagonal quasicrystal and an approximate crystalline phase in Al70Co15Ni10Tb5 obtained by quenching under high static pressure

Abstract A decagonal quasicrystal and a new crystalline approximant of the decagonal quasicrystal have been found in Al 10 Co 15 Ni 10 Tb 5 alloy, which was prepared by a method of quenching from the melt under a high static pressure 7.0 GPa. The lattice parameters of the new crystalline approximant are a = 2.28 nm, b = 1.60 nm, c = 5.46 nm. A lattice image of the approximant was obtained by means of high-resolution electron microscopy and was able to be regarded as an ordered pattern of Penrose tiling. Based on the lattice image, a tiling model of the approximant was put forward.