Papers by Author: Wen Hao Fan

Abstract: Abstract. Ca3CO4O9/x wt.%SiO2 composites were prepared by using field-activated pressure-assisted synthesis(FAPAS) process. The effects of nano-SiO2 addition on the microstructure and thermoelectric properties of the Ca3CO4O9 were investigated. With an increasing of the of SiO2 content, the size of Ca3Co4O9 particles decreased. The Seebeck coefficient decreased after the doping of nano-SiO2. The electrical conductivity firstly increased and then decreased with increasing amount of nano-SiO2 and the highest value belong to the Ca3CO4O9/0.5 wt.% SiO2 - sample. With the highest electric conductivity and slightly decreased Seebeck coefficient, the Ca3CO4O9/0.5 wt.%SiO2-sample achieved the highest power factor of 0.349 mw/mk2 at 800 °C, which is 8% higher than the value of pure Ca3CO4O9 reported in the literature.

Abstract: In the present study, Mg₂Si nanoparticles of high purity were successfully synthesized through low-temperature reaction by using MgH₂ and Si powders as rawmaterials. The size of Mg₂Si particles is about 50nm. The bulk nanocomposites xSiO₂/Mg₂Si_0.8Sn_0.2(x = 0, 0.1, 1 and 2wt. %) were followed by field-Activated and pressure-assisted synthesis (FAPAS). The effects of SiO₂ addition on the microstructure and thermoelectric properties of Mg₂Si_0.8Sn_0.2 were studied. The field emission scanning electron microscopy shows that the nanometer-sized SiO₂ particles disperse homogeneously in Mg₂Si_0.8Sn_0.2 matrix. Among all of the samples, 1wt. % SiO₂/Mg₂Si_0.8Sn_0.2 exhibits the best figure of merit (ZT = 0.25 at 573 K), which is 24% higher than that of the sample without SiO₂, indicating that the thermoelectric properties of Mg₂Si_0.8Sn_0.2 can be enhanced effectively by the dispersion of nanometer-sized SiO₂.

Abstract: The formation energy, structure relaxation and electronic structure of Mg₂Si and Y-doped Mg₂Si are investigated using first-principle calculations based the density functional theory. The general gradient approximation was used to treat the exchange and correlation potential. The calculated electronic structure shows that Mg₂Si is a semiconductor with a direct gap of 0.27eV at G point. The preferential substitution site of Y inside Mg₂Si is determined to be Mg. Y-doping makes the Si atoms around the impurity outward relaxation and increases the Seebeck coefficient, electrical conductivity and thermal conductivity of Mg₂Si crystals simultaneously.

Abstract: Iron disilicide (-FeSi2, and -FeSi2+Cu0.1wt%) were prepared by a field-activated pressure assisted synthesis(FAPAS) method from elemental powders and the thermoelectric properties were investigated. The average grain size of these products is about 0.3m. The thermal conductivity of these materials is 3-4wm-1K-1in the temperature range 300-725K. These products’ figure of merit is 28.50×10-4 in the temperature range 330-450K. The additions of Cu promote the phase transformation of -Fe2Si5 + -FeSi → β-FeSi2 and shorten the annealing time. It is proved that FAPAS is a benign and rapid process for sintering of -FeSi2 thermoelectric materials.

Abstract: Iron disilicide（-FeSi2）compounds were synthesized by field-activated pressure assisted synthesis (FAPAS) process, and their thermoelectric properties were measured. Fine microstructure with small pores was obtained in the fabricated samples. The average grain size was approximately 0.3 m. The thermal conductivity in the temperature range of 300-725 K was 3-4 Wm-1K-1, which was considerably lower than that of the same materials synthesized by other methods including SPS process. Lower thermal conductivity provided a higher figure of merit, ZT of 28.50×10-4 in the temperature range of 330-450 K.