Masayuki Niino

Effect of plasma activated sintering (PAS) parameters on densification of copper powder

Copper (Cu) powder compacts were sintered by plasma activated sintering (PAS), and the effects of PAS parameters on the densification process of these compacts were investigated. A larger direct current caused a higher rate of temperature increase and therefore a higher densification rate of the Cu powder compact. Under a constant electric current, however, higher mechanical pressure resulted in a lower rate of temperature increase and a lower densification rate of the Cu powder compact. When the applied direct current was the same, the rate of temperature increase of the Cu powder compact after application of a 30-s pulse electric current remained higher than that without a pulse electric current. Application of the pulse electric current before application of the direct current was found to be effective in promoting the densification of Cu powder compacts.

A local selection criterion for the composition of graded thermoelectric generators

We present a procedure that locally determines the composition (from a given set of available materials) of a segmented or graded thermoelectric generator leg in order to maximize its output power to a matched load. The method is based on a new interpretation of the electrical output relation, which is organized to resemble a differential output power along the device coordinate. The procedure is applied to calculate the segment length and output power of a segmented bismuth-telluride/iron-disilicide based thermoelectric generator leg.

Recent Development in Nano and Graded Thermoelectric Materials

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.

Feasibility Study of FGM Technology in Space Solar Power Systems (SSPS)

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.

Activities of Laser Propulsion in Japan

This paper describes the status of laser propulsion research and related studies in Japan. Japan covers wide range of laser propulsion research including from ground launching to orbital transfer applications. The current status of Japanese laser propulsion is introduced and the elemental studies of Tohoku University, National Aerospace Laboratory, University of Tokyo, Tokai University and Institute for Laser Technology are presented.

Overview of Studies on Space Solar Power Systems and Elemental Technology Development

Japan Aerospace Exploration Agency (JAXA) has studied Space Solar Power Systems (SSPS) using laser and microwave beams for years since 1998. Current SSPS study undertaken by JAXA consists of three main subjects, SSPS concepts and architectures study, technology demonstration and elemental technology development. In current research of Laser based SSPS (L-SSPS), we have studied some elemental technologies such as ultralight film mirror, wavelength selective mirror, laser generator based on direct solar pumping solid-state laser diode, laser transmission property in atmosphere, photovoltaic generation converting laser energy to electricity and photocatalytic hydrogen generation. This paper presents the introduction of SSPS concepts and architectures study and elemental technology development of L-SSPS.

Technology of Low Cost Production of FGMs

In this paper, we introduced research and development of technology of low cost production of FGMs. This research is designated for development of mass production technology for production of ceramic wares with induction heating (IH) function. Slurry lamination method has advantage in forming graded layers due to its simplicity and easiness. However, this method has a disadvantage to generate cracks during drying process. Therefore, freeze-dry in vacuum was introduced in drying process of slurry lamination. By doing so, mass production could be achieved. In this trial production, we adopted SPS sintering method to production technique. In the future, we will further develop other applications of FGMs into industrial products.

LE-NET and Multi-Purpose Laser Propulsion System

The concept of the Laser Energy NETwork (LE-NET) and the multi-purpose laser propulsion system being studied at NAL are overviewed. The LE-NET can provide abundant energy supplies on earth acting as the effective and long lasting measures against global warming and will cover wide variety of transportation needs by the laser power. The LE-NET needs a Solar Excited Laser (SEL) that directly converts a solar light into a laser beam. The SEL is expected to minimize the SPS weight considerably, leading low-cost realization of the LE-NET.

COMPARISON OF SURFACE AND INTERNAL LASER IRRADIATION OF SOLID PROPELLANT FOR PROPULSION

Laser propulsion mechanism has been studied using a double layered target. Laser ablation is used to generate thrust. Momentum coupling coefficient has been enhanced by at least an order of magnitude. The momentum and temporal profile of force exerted on the targets are measured using pendulum and piezoelectric sensors. It was found that momentum generation from the double layered target exhibits two components. High momentum coupling coefficient is due to the second component which carries large amount of mass with very low velocity.

Life prediction of CIP formed thrust chamber

Abstract The authors previously proposed a new fabrication method of closeout for a regeneratively cooled thrust chamber, the CIP (Cold Isostatic Pressing) forming method, by which a low stiffness closeout is easily obtained. In this study, sintered aluminum alloy was chosen as a porous closeout material which had relatively a lower Youngs modulus and a lighter weight. The forming conditions of the porous closeout and its elastic and plastic behaviors were investigated. Then the fatigue life of the high pressure chamber cooled by liquid hydrogen with the sintered aluminum alloy closeout was analyzed by means of nonlinear FEM (Finite Element Method). The results showed that the optimum design condition for a long-life rocket thrust chamber could be achieved with a low-stiffness closeout consisting of a CIP formed aluminum alloy layer with a porosity of 17% and a TFE (polytetrafluoroethylene) insulation layer with a thickness of 20 mm. The chamber with this low-stiffness closeout had a prolonged fatigue life three times longer than that of a conventional chamber with an electroformed nickel closeout.