Abstract: The Cu/W functionally graded material (FGM) was produced by vibration of W
agglomerates in order to obtain the W skeleton with a gradient in porosity, which after pressureless sintering was infiltrated with molten Cu. Certain sintering mechanisms are suggested for these complex W structures. The segregation of two different sizes of W agglomerates was controlled by vibration time. Different vibration duration resulted in different types of microstructure: skeleton type microstructure after shorter vibration time and graded type microstructure after extended vibration times. The final Cu-infiltrated FGMs were characterized microstructurally and their
electrical resistivity (r) was measured using the 4-probe technique. The values of r were in between those for pure W and Cu, depending strongly on the vibration times of the initial W agglomerates, and exhibiting particular r vs. T (K) behavior.
Abstract: In 2003, a joint research project entitled “Nano and graded thermoelectric
materials/Photovoltaic-thermoelectric-wind power generation” is established in cooperation among research institutes from Japan and China. The major research institutes include State Key Laboratory of Advanced Technology for Materials Synthesis and Processing (Wuhan University of Technology, China), Shanghai Institute of Ceramics (Chinese Academy of Sciences, China), State Key Laboratory of New Ceramics and Fine Processing (Tsinghua University, China), Japan Aerospace Exploration Agency (JAXA, Japan) and Foundation for Promotion of Japanese Aerospace Technology (JAST, Japan). The main aim of this project is to develop a photovoltaic-thermoelectric-wind power generation system with high efficiency solar energy conversion. The key works of the project include: (1) fabrication of high efficiency nano thermoelectric materials with a maximum figure of merit Z≥1.3; (2) design and fabrication of nano graded thermoelectric material/component with efficiency conversion larger than 12% for wide temperature range and (3) design and construction of photovoltaic- thermoelectric coupled power generation system. The recent progress about the joint research project is reported in this paper. Emphasis is put on the mechanism, design and fabrication of high efficiency nano graded thermoelectric materials. The future research plan is also mentioned in brief.
Abstract: Typical conductive polymers of poly(3-alkylthiophenes) were synthesized by oxidative polymerization. Alkyl side chains were CnH2n+1 with n=4, 6, 8, 12. The regioregularity with the HT linkage was larger than 99% based on NMR analysis. Completely regioregular head-to-tail (HT) poly(3-alkylthiophenes) were obtained. We have evaluated the effect of side chain size on the thermoelectric properties of Seebeck coefficient and electrical conductivity. The results were as
follows: 1) Seebeck coefficient decreased with an increasing electrical conductivity. 2) High Seebeck coefficient >1mV/K was observed at low electrical conductivity <10-2S/cm. 3) The small side chain caused the higher electrical conductivity in the range of electrical conductivity <10- 1S/cm.
Abstract: In this paper, we reported that lead telluride (PbTe) with continuous carrier
concentration gradient, in which PbI2, Al and Zr were doped, were successfully fabricated by the unidirectional solidification method. The carrier concentration was optimized by adjusting the relation between the dopants and the carrier concentration gradient. The carrier concentration for the ingots was estimated from the resistance results which were measured by the one-probe method. The result shows that the carrier concentration was large at the initiation side and small at termination side of the solidified ingots. The degree of the carrier concentration gradient can be controlled by the holding time at a liquid state and the cooling rate from the liquid state. The carrier concentration gradient can be largely affected by the
Al-dopant. The samples 0.07mol%PbI2-0.05mol%Zr-0.07mol%Al-PbTe, which were made from a liquid phase at 1200K held for 1h and cooled at 98K/h, showed a carrier concentration gradient ranging from 2×1024 to 1.5×1025 /m3. The effective maximum power for this continuous FGM is 20% larger than that of jointed FGM.
Abstract: Every thermoelectric material shows high performance at a specific narrow temperature range. The temperature range with high performance can be expanded by joining the materials with different peak temperature. This is the concept of a functionally graded material (FGM) for thermoelectric materials. Bismuth telluride is the best material for cooling devices at around room temperature. Then we investigated the thermoelectric cooling properties for bismuth telluride with two step graded structure. FGM samples were fabricated by three methods. The first FGM was synthesized by in situ method. The second one was fabricated by joining in a hot-press equipment. The last one was composed by joining with solder. Thermoelectric cooling properties were evaluated by observing the maximum temperature drop to electric current when the high temperature side was kept constant. The large temperature difference was obtained when the proper configuration of thermoelectric materials along the temperature gradient were performed. The coincidence of optimum electrical currents of composing materials is also essential to obtain the high cooling performance.
Abstract: Commercial off-the-shelf (COTS) thin-film solid-polymer Li-ion battery cells appear to posses the requisite physical characteristics for dual use as both electrical energy-storage devices and structural members under a finite load. One realistic application could be small electric unmanned vehicles where the power requirements are in the range of 10 to 100 watts and the mechanical loads are relatively small. We tested the multifunctional feasibility of COTS battery cells by designing a specific mechanical testing protocol based on realistic use in unmanned vehicles. Our characterization protocol included randomized bending and shear testing and generation of energy-power relation (Ragone) plots of the COTS cells. The results indicate that multifunction applications of COTS Li polymer battery cells are feasible; however, battery packaging geometry and bonding are critical design issues.
Abstract: In this paper, we introduce research and development in SSPS (aimed at global energy supply) in Japan. To build SSPS, we must develop ultra lightweight materials and high efficiency energy conversion materials. Feasibility of adapting FGM concept for those new demands and advanced research theme for future FGM research are also introduced in this paper.
Abstract: Titania surfaces were produced via a combined tape and slurry casting process. They were structured in the mm-µm range using structuring the gypsum, embossing the green ceramic, and lasering the sintered ceramic. The resulting structures were analyzed upon surface roughness and optically characterized by SEM. The ra values lay between 19-28 µm. Fibroblasts were seeded onto these structures, incubated for one and three days, and the number of cells was compared using
polystyrol petri-dishes and borosilicate glass cover slips as references. It was demonstrated that the structure of the ceramic had an influence on the cell behaviour: larger cell numbers could be observed for the structured ceramics.
Abstract: A numerical approach to study the crack propagation in symmetric step-wise graded
Alumina/Zirconia composites subjected to a residual stress field is presented in this work. The finite element method is used to calculate the stress intensity factor for cracks developing from the surface and to determine the effects of the thermal residual stresses. The results show that a suitably conceived stacking sequence induces in the laminate a residual stress field able to provide increased toughness and reliability of the structure by making the crack propagation stable below a given threshold stress. Moreover a lower bound on stress, below which no crack propagation occurs, can be identified.