Development of a Simple Manufacturing Process for Thermoelectric Particles to Produce Electricity from Waste Heat
Low Cost Power Generation Technology with Dramatically Reduced Energy Waste
2011.12.16
(2012.01.13 Update)
National Institute for Materials Science
Mitsuba Corporation
Thermoelectric generation is a technology in which electricity is generated directly from waste heat discharged by automobile engines and factory furnaces, enabling effective utilization of this large untapped energy source. A simple, low cost method of manufacturing particles for use in this process was developed as a result of a collaborative research effort.
Abstract
- Thermoelectric generation is a technology in which electricity is generated directly from waste heat discharged by automobile engines and factory furnaces, enabling effective utilization of this large untapped energy source. A simple, low cost method of manufacturing particles for use in this process was developed as a result of a collaborative research effort. The Dr. Yukihiro Isoda, who is a Senior Researcher in the Battery Materials Unit (Unit Director: Kazunori Takada) of the National Institute for Materials Science (NIMS; President: Sukekatsu Ushioda) and Dr. Naoki Shiota, a Researcher in the Research Division (Division Director: Shinichi Nagashima) of Mitsuba Corporation (Mitsuba; President and COO: Tsuneo Akuto) have participated in this joint venture.
- Particles of Mg2Si, which is a compound of magnesium and silicon, have attracted attention as a material for use in waste heat recovery by thermoelectric generation of electricity. In the past, two methods have generally been used to produce these particles. One was a melting synthesis process, in which particles were produced by crushing ingots of the compound obtained by directly melting the raw materials. The second was a mechanical alloying process, in which the raw material powder and steel balls were introduced into a pot and rotated at high speed. Both of these conventional processes have certain drawbacks. Problems in the melting synthesis process include deviations in the chemical composition due to the Mg evaporation. The evaporation occurs because of the boiling point of Mg (1090°C) being close to the melting point of Mg2Si (1085°C), contamination by impurities and oxidation in the crushing process etc. In the mechanical alloying process, dust explosion is a danger, as Mg powder is used in the raw material. Also impurities may be introduced from the pot and balls, and the size of the obtained particles is small.
- Here we present a simple synthesis process for Mg2Si compound particles. The process is developed by incorporating lump Mg and Si powder in a carbon board, and heating the mixture in an electric furnace to a temperature at which only Mg melts. Large-scale equipment is not required, and all problems of the conventional processes are not present because a crushing process is not necessary. Manufacturing costs are greatly reduced, and the size of the synthesized particles can be controlled freely simply by changing the particle size of the Si powder raw material.
- The thermoelectric particles which are produced by sintering particles of the Mg2Si compound, enable waste heat power generation by producing electricity from waste heat that had been discharged without use in the past. That includes waste heat from incinerators, melting furnaces, smelters, and other industrial furnace, automobiles, and many other sources. Using this manufacturing process, it is now possible to supply the particles at less than 1/3 of the current price, and further cost reductions will be targeted in the future by development of a mass production technology.
- This achievement will be announced on December 20, 2011 at Session T: Energy Materials Frontier at the 21st Academic Symposium of MRS-Japan (MRS: Materials Research Society) held in Yokohama beginning December 19.
Figure: Performance index of thermoelectric materials currently in use and the new Mg2Si compound developed by NIMS.