Materials Science Forum Vols. 534-536

Abstract: Ru-C nano-composite films were prepared by metal-organic chemical vapor deposition (MOCVD), and their microstructures and their electrode properties for oxygen gas sensors were investigated. Deposited films contained Ru particles of 5-20 nm in diameter dispersed in amorphous C matrix. The AC conductivities associating to the interface charge transfer between Ru-C composite electrode and YSZ electrolyte were 1000-10000 times higher than that of conventional paste-Pt electrodes. The electro-motive-force (emf) values of the oxygen gas concentration cell constructed from the nano-composite electrodes and YSZ electrolyte showed the Nernstian theoretical values at low temperatures around 500 K. The response time of the concentration cell at 500 K was 900 s.

Abstract: Dispersion-strengthened copper with TiB2 was produced by ball-milling and spark plasma sintering (SPS).Ball-milling was performed at a rotation speed of 300rpm for 30 and 60min in Ar atmosphere by using a planetary ball mill (AGO-2). Spark-plasma sintering was carried out at 650°C for 5min under vacuum after mechanical alloying. The hardness of the specimens sintered using powder ball milled for 60min at 300rpm increased from 16.0 to 61.8 HRB than that of specimen using powder mixed with a turbular mixer, while the electrical conductivity varied from 93.40% to 83.34%IACS. In the case of milled powder, hardness increased as milling time increased, while the electrical conductivity decreased. On the other hand, hardness decreased with increasing sintering temperature, but the electrical conductiviey increased slightly

Abstract: The p-type (Bi0.2Sb0.8)2Te3/(Pb0.7Sn0.3)Te functional gradient material (FGM) was fabricated by hot-pressing the mechanically alloyed (Bi0.2Sb0.8)2Te3 and the 0.5 at% Na2Te-doped (Pb0.7Sn0.3)Te powders. Also, the n-type Bi2(Te0.9Se0.1)3/PbTe FGM was processed by hot-pressing the mechanically alloyed Bi2(Te0.9Se0.1)3 and the 0.3 wt% Bi-doped PbTe powders. With △T larger than 300°C, the p-type (Bi0.2Sb0.8)2Te3/(Pb0.7Sn0.3)Te FGM exhibited larger thermoelectric output power than those of the (Bi0.2Sb0.8)2Te3 and the 0.5 at% Na2Te-doped (Pb0.7Sn0.3)Te alloys. For the n-type Bi2(Te0.9Se0.1)3/PbTe FGM, the thermoelectric output power superior to those of the Bi2(Te0.9Se0.1)3 and the 0.3 wt% Bi-doped PbTe was predicted at △T larger than 300°C.

Abstract: The shrinkage variation of Low Temperature Cofired Ceramics(LTCC) limits the size of the substrates that impose limitations on embedded passive components. This paper focuses on the method of minimizing or controlling planar shrinkage and reducing distortion during firing. The laminated sheets of alumina and glass were sintered at varying temperature, and depending on the amount of the glass ceramics. When the sintered of multi-layer structure with Al2O3/Glass/Al2O3, the glass infiltrated entirely into Al2O3 layer at the temperature of about 950°C or higher.

Abstract: This study deals with the co-sintering of copper oxide added ANT with alumina tapes and silver ink. AgNb1/2Ta1/2O3 (refered ANT 22) was synthesized using niobium oxide with fine and large grain size to examine the effect of the granulometry on the tape casting. The resulting multilayers were co-fired between 850 and 900°C. Phase identification was investigated by XRD. Energy Dispersive Spectroscopy was performed to study the interdiffusion between the layers. Permittivity and dielectric losses were measured at 50 kHz for both tape cast samples and bullk material. No interdiffusion was observed between ANT/silver and ANT/alumina and this is a very promising result for LTCC applications.

Abstract: In order to obtain materials for electronic applications that exhibit both excellent thermal conductivity and low coefficient of thermal expansion (CTE), copper matrix composites have been reinforced by short high modulus graphite fibers. The lack of fiber/matrix interaction prevents any degradation of the carbon reinforcement during the elaboration steps and the normal use of these materials. Elaboration conditions, such as mixing conditions of the short carbon fibers and the copper powder, dimension and shape of the two powders, and finally densification atmosphere, temperature, pressure and time, have been optimized. Main parameters involved in the thermal properties of the Cu/C composite materials have been analyzed and adjusted. CTE is mainly related with the carbon volume fraction; CTE ranging from 9 to 13 10-6/°C can be reproductively obtained with carbon volume fraction ranging from 50% to 20%. Thermal conductivity properties are more complex and are linked mainly with 1) the porosity level inside the material, and 2) the orientation, properties and volume fraction of the carbon fibers. For short carbon fibers, in plane thermal conductivity ranging from 200 to 550 W/mK have been reproductively measured associated with thermal conductivity through-thickness ranging from 150 to 300 W/mK.

Abstract: We investigated on the additive effect of carbon nanotube in the sulfur electrode on the first discharge curve and cycling property of lithium/sulfur cell. The sulfur electrode with carbon nanotube had two discharge plateau potentials and the first discharge capacity about 1200 mAh/g sulfur. The addition carbon nanotube into the sulfur electrode did not affect the first discharge behavior, but improved the cycling property of lithium/sulfur cell. The optimum content of carbon nanotube was 6 wt% of sulfur electrode.

Abstract: Attempts have been made to describe the influence of production process parameters on the microstructure and properties of W - Ag and Mo - Ag composites. The compositions of powder mixtures are W + 30% Ag and Mo + 30%Ag. Silver additions assists densification during sintering by a liquid phase sintering process. The main goal of this work is to compare properties and microstructure of as-sintered and as-infiltrated composites.

Abstract: In the present work, Cu-TiB2 nanocomposite powders were synthesized by combining high-energy ball-milling of Cu-Ti-B mixtures and subsequent self-propagating high temperature synthesis (SHS). Cu-40wt.%TiB2 powders were produced by SHS reaction and ball-milled. The milled SHS powder was mixed with Cu powders by ball milling to produce Cu-2.5wt.%TiB2 composites. TiB2 particles less than 250nm were formed in the copper matrix after SHS-reaction. The releative density, electrical conductivity and hardness of specimens sintered at 650-750°C were nearly 98%, 83%IACS and 71HRB, respectively. After heat treatment at 850 to 950°C for 2 hours under Ar atmosphere, hardness was descedned by 15%. Our Cu-TiB2 composite showed good thermal stability at eleveated temperature.

Abstract: In recent years, power generating systems using thermoelectric elements have become attractive as an effective method of using industrial waste heat, at a temperature of around 773K, to produce energy. However, in order to develop a module usable under such a high temperature, certain concerns have to be overcome, e.g. thermal stress, diffusion of the connecting interfaces, etc. In this research, using an FeSi2 with diffusion barrier layers and a SiGe element produced by a powder metallurgy process, the module structure and installation method were optimized for application in PM sintering furnaces. As a result, from a viewpoint of heat stress at high temperatures and contact thermal resistance, it is confirmed that the optimal structure is the skeleton structure using Cu substrate on the cooling side, which has excellent heat conductivity and the optimal installation method is to adopt a carbon sheet and a mica sheet to the high temperature side, where Si grease is applied to the low temperature side, under pressurized condition. The power of the developed modules indicated 0.5W in an FeSi2 module and 3.8 W with a SiGe module at 827K, respectively. Moreover, neither breakage nor deterioration were observed after 30 heat cycles test simulating sintering furnace.