Zhang Lianmeng

Synthesis and Thermoelectric Properties of Polyaniline

Electrical conductivity and seebeck coefficient at different temperatures, and thermal conductivity at room temperature for various doped polyaniline (PAn) samples were measured, and the thermoelectric figure of merit ZT was calculated. The effects of preparation methods and temperature on thermoelectric properties were discussed. The results show that the electrical conductivity and the seebeck coefficient of PAn are strongly dependent on the preparation conditions and temperature. The electrical conductivity becomes larger and the seebeck coefficient becomes smaller as PAn molecular weight increase. Redoping by organic acid and HCl results in an increase in both electrical conductivity and Seebeck coefficient of PAn, and therefore ZT value. The electrical conductivity increases and the seebeck coefficient decreases as the temperature increases when T<Td (dedoping temperature). The decreasing of the electrical conductivity and increasing of the seebeck coefficent take place by dedoping when T>Td. The thermal conductivity is lower, and insensitive to the sample preparation conditions.

Effect of nanocomposite structure on the thermoelectric properties of 0.7-at% Bi-doped Mg2Si nanocomposite

Nanocomposites offer a promising approach to the incorporation of nanostructured constituents into bulk thermoelectric materials. The 0.7-at% Bi-doped Mg2Si nanocomposites are prepared by spark plasma sintering of the mixture of nanoscale and microsized 0.7-at% Bi-doped Mg2Si powders. Microstructure analysis shows that the bulk material is composed of nano- and micrograins. Although the nanograin hinders electrical conduction, the nanocomposite structure is more helpful to reduce thermal conductivity and increase the Seebeck coefficient, hence improving thermoelectric performance. A dimensionless figure of merit of 0.8 is obtained for the 0.7-at% Bi-doped Mg2Si nanocomposite with 50-wt % nanopowder, which is about twice larger than that of the sample without nanopowder.

Experimental Investigation on the Damping Behaviors of Epoxies with Different Epoxy Value

In this article, five different epoxies including a new kind of flexible epoxy having low glass transition temperatures (11 ∼ 28°C) were prepared using polyamine as curing agent. Damping mechanical tests show that compared with other common available epoxies, the flexible epoxy has high loss factor over broad frequency and temperature range. Activation energy corresponding to glass transition process of different epoxies has been calculated from the temperature corresponding to tan δmax values, obtained at different measurement frequencies. The maximum value of loss factor is 0.71 and the Tg varies from 11 to 28°C, indicating the flexible epoxy can be used as damping polymer materials in common temperature or frequency range.

Fabrication and mechanical properties of TiC/TiAl composites

TiC/TiAl composites with different TiC content were fabricated by rapid heating technique of spark plasma sintering (SPS). The effect of TiC particles on microstructure and mechanical properties of TiAl matrix was investigated. The results indicate that grain sizes of TiAl matrix decrease and mechanical properties are improved because of the addition of TiC particles. The composites display a 26.8% increase in bending strength when 10wt% TiC is added and 43.8% improvement in fracture toughness when 5wt% TiC is added compared to values of TiC-free materials. Grain-refinement and dispersion-strengthening were the main strengthening mechanism. The improvement of fracture toughness was due to the deflexion of TiC particles to the crack.

Effects of solid-state reaction synthesis processing parameters on thermoelectric properties of Mg2Si

The Mg2 Si-matrix thermoelectric material was synthesized by low temperature solid-state reaction. This paper studies the effects of holding time and reaction temperature on the particle size and the properties of the material, and also studies effects of doping elemental Sb, Te and their doping seqence on the properties of the material. The result shows that excessively high temperature and elongated holding time of solid-state reaction are harmful, there is a range of particle size to ensure optimum properties and the doping sequence of Sb or Te without influencing the properties.

Effect of Nb on the mechanical properties of Ti/Al2O3 composite

Ti/Al2O3 composite with improved mechanical properties was synthesized by the spark plasma sintering. The effect of Nb on the microstructure of the composite was analyzed by TEM, SEM and so on. The experimental results indicate that the bending strength, fracture toughness, micro-hardness and relative density of the composite are 897.29MPa, 17.38MPa·m1/2, 17.13GPa and 99.24% respectively when adding 1.5vol Nb. The bending strength is improved by reason of forming dislocation ring and transfering fracture mode from integranular to mixture fracture of intergranular and transgranular. The crack propagating is mainly the deflection bridging. It indicates a reduction of crack driving force and an increase in crack growth resistance, which results in toughness enhanced.

Hydrothermal synthesis and characterization of inorganic/organic hybrid complex containing tungstophsphate

A new complex [Cu(C12H8N2)2]1.5PW12O40·1.5H2O was synthesized under hydrothermal conditions. The complex was characterized by the elemental analysis, SEM, X-ray powder diffraction analysis, IR, UV-Vis spectroscopy, and TG thermal analysis, respectively. The experimental result shows that the heteropolyanion is of a Keggin structure containing coordinated cations. Photochromism studies show that the electron transfer takes place from the organic compound to the heteropolyanion.

Liquid Phase Sintering （LPS） and Dielectric Constant of α-Silicon Nitride Ceramic

The spark plasma sintering (SPS) was applied to prepare α-Si3N4 ceramics of different densities with magnesia, silicon dioxide, alumina as the sintering aids. The mechanism of liquid phase sintering (LPS) was discussed and the factors influencing the density of the prepared samples were analyzed. The dielectric constant of sintered samples was tested. The experimental results show that the density can be controlled from 2.48 g/cm3 to 3.09 g/cm3 while the content of the sintering aids and the sintering temperature alter and the dielectric constant is closely dependent on the density of obtained samples.

Spark effect on the densification of SiCp/Al composites by SPS

SiCp/Al composites containing high volume fraction of SiC particles were fabricated by spark plasma sintering (SPS), and their thermophysical properties, such as thermal conductivity (TC) and coefficient of thermal expansion (CTE), were characterized. The electric field in the vacuum column was calculated and the generation condition of the spark was analyzed. Spark can be generated by a low current if the cavity in the green body is large enough. A high relative density of the composites was successfully achieved through the optimization of sintering parameters. The measured TCs of the SiCp/Al composites fabricated by SPS are higher than 195 W/ m · K.

Mechanical and thermal properties of polysiloxanes and NBR blend elastomer

A series of elastomers, based on NBR, polysiloxanes (PS) were prepared and characterized by tensile tests, thermogravimetry (TG) and differential scanning calorimetry (DSC). Two kinds of vulcanizing agent, DMDBH (2,5-dimethyl-2,5-di(t-butyl perory) hexane) and DCP (dicumylperoxide) were used to investigate the influence of different vulcanizing agents on properties of PSINBR. The addition of PS to NBR was found to improve the thermal stability and decrease the tensile strength of NBR. The tensile strength decreased considerably while the elongation at break increased obviously with the increase of PS content. The series using DMD-BH as vulcanizing agent showed a higher tensile strength and elongation at break than the series using DCP as vulcanizing agent. Simultaneity the thermal stability increased with the increase of PS content.