Improvement of thermoelectric properties of alkaline-earth hexaborides

Thermoelectric (TE) and transport properties of alkaline-earth hexaborides were examined to investigate the possibility of improvement in their TE performance. As carrier concentration increased, electrical conductivity increased and the absolute value of the Seebeck coefficient decreased monotonically, while carrier mobility was almost unchanged. These results suggest that the electrical properties of the hexaboride depend largely on carrier concentration. Thermal conductivity of the hexaboride was higher than 10 W/m K even at 1073 K, which is relatively high among TE materials. Alloys of CaB₆ and SrB₆ were prepared in order to reduce lattice thermal conductivity. Whereas the Seebeck coefficient and electrical conductivity of the alloys were intermediate between those of CaB₆ and SrB₆ single phases, the thermal conductivities of the alloys were lower than those of both single phases. The highest TE performance was obtained in the vicinity of Ca_0.5Sr_0.5B₆, indicating that alloying is effective in improving the performance.     

Nanostructuration for thermoelectricity: The path to an unlimited reduction of phonon transport

Improvements of the thermoelectric properties in bulk materials have very often relied on the reduction of thermal conductivity, which is mostly based on phonon propagation. Reducing further phonon transport has remained a difficult task due to the fact that current thermoelectric materials are already efficient thermal insulators, and also because of the broadness of the Planckian phonon spectrum. Nanostructuring has provided new paths for decreasing thermal conduction, especially by means of scatterers, be them nano-objects, surfaces, or interfaces. In this chapter, the physics of demonstrated nanoscale methodologies for the reduction of thermal conduction will be proposed together with illustrations from direct simulations.     

Hierarchical nanoporous gold film electrode with extra high surface area and electrochemical activity

This paper describes the fabrication and electrochemical behavior of hierarchical nanoporous gold film (HNPGF) electrode by multi-cyclic electrochemical co-alloying/dealloying of two sacrifice metals (Zn and Sn) with gold. Different from the nanoporous gold film (NPGF) formed in the electrolyte of ZnCl₂ in benzyl alcohol, the HNPGF obtained possessed special hierarchical porous structure and extra high roughness factor of 1250. This study reveals that hierarchical porous gold film electrodes are promising for catalysis.     

X射线荧光光谱法测定超硬铝合金中成分

叙述了用SRS 300型X射线荧光光谱仪测定超硬铝合金中铜、镁、锌、铁、硅、锰、铬、镍、钛、锆的X射线荧光光谱分析方法。试样用车床加工至表面平整、光滑，采用强度校正模型，由计算机拟合回归曲线。此法测定结果与常规湿法化学法测定结果相符。     

Formation and characterization of Rh-Mo bimetallic layers on the TiO2(1 1 0) surface

The investigation of Rh, Mo and Rh-Mo nanosized clusters formed by physical vapor deposition on TiO₂(1 1 0) single crystal was performed by X-ray Photoelectron Spectroscopy (XPS), Low Energy Ion Scattering (LEIS) and Auger Electron Spectroscopy (AES). There was no sign for site-exchange between Mo and Rh atoms during deposition of Mo onto Rh particles at 330 K. Mixing between Ti and Mo ions was facilitated at the Mo particle-titania interface due to reaction at 550-700 K. The redox process between titania and Mo deposit was hindered at 330 K by forming predeposited rhodium layer (Θ_Rh = 2.0 ML), but reached nearly the same extent as without Rh after moderate heating to 600 K. The encapsulation of Rh by titania was complete by about 700 K in the presence of 1.2 ML Mo, in case of Mo-predeposition and Mo-postdeposition as well. Elevating the temperature of TiO₂/Rh-Mo layers above 700 K, these metals form alloy at the Mo-Rh interface irrespective of deposition sequences.