Friday, September 26, 2008
2008 R&D 100 Winner
Thermoelectric materials are used in solid-state devices to convert heat into electricity based on the Seebeck effect, which describes voltage develops when a material (typically semiconductors and metals like bismuth telluride alloys) is subject to a temperature difference. They are also used in cooling and heat pumping devices based on the Peltier effect, the reversible cooling and heating phenomena at the interface of two materials when an electrical current is applied. Conversion efficiency is often represented by a dimensional numerical figure-of-merit ZT, but this level has been stuck near 1 since the 1950s. However, GMZ Energy, Newton, Mass., Massachusetts Institute of Technology, Cambridge, and Boston College, Chestnut Hill, Mass., have produced High Performance Thermoelectric Materials that accomplish appreciable figures-of-merit increases: 1.2 at 25°C, 1.4 at 100°C, and 0.8 at 250°C.
The key to their approach is a proprietary ball-milling process that converts bismuth antimony telluride into nanoparticles which are then hot-pressed into bulk ingots. Why nanoparticles? The researchers believed they could replicate the high ZT levels found in complex superlattices. Consistent nanoparticle size, averaging about 20 nm dia, keeps ZT high, and the manufacturing process itself is cost effective.
Technology
Thermal materials
Developers
GMZ Energy
Massachusetts Institute of Technology
Boston College
