Thermopower on the Cheap
December 21, 2012
Things are precise in a laboratory environment. You weigh things out to five, or six, decimal places, you control temperature to a tenth of a degree, and you mark time to the second. Then, when the specification for your miracle material is sent to the factory, there's cigarette ash in the crucible, and things are over-annealed while the crew is on a coffee break. Six Sigma supposedly fixed most of these problems in the better companies, but scientists are never surprised when laboratory properties are not reproduced in commercial material.
As I wrote in a previous article (Coal, July 23, 2012), this isn't a problem for some materials, since they're just dug out of the ground and used in their pristine state. The most important of these is coal, and if we didn't have coal, we wouldn't have had the Industrial Revolution.
Another example is kieselguhr, also known as diatomaceous earth. This material, the fossil shells of diatoms, is a useful mixture of silica (SiO2, 80-90%), alumina (Al2O3, 2-4%) and iron oxide (Fe3O4, 0.5-2%). This nice mix of inorganic oxides makes diatomaceous earth a good material for thermally insulating high temperature furnaces.
Diatomaceous earth is used as an abrasive, as a filtration medium, a support medium for catalysts, and a filler for plastics. The absorbency of diatomaceous earth makes it useful for cat litter, and also as a way to stabilize nitroglycerin to form dynamite.
Diatomaceous earth is about as close to a free lunch as a materials scientist can get, and it makes you wonder what other things might be made from other inexpensive minerals. A team of scientists from Michigan State University and UCLA has just developed a thermoelectric material based on an inexpensive mineral known as tetrahedrite.[1-2]
Tetrahedrite, one of the most abundant minerals, has the chemical formula, (Cu,Fe)12Sb4S13. As can be seen from the formula unit, it exits in both copper-rich and iron-rich forms, and bismuth (Bi) is known to substitute for the antimony (Sb). All this can be expected from the atomic radii of the atoms (Cu = 135 pm; Fe = 140 pm; Sb = 145, Bi = 160), although bismuth is a tight fit. The mineral takes its name from its tetrahedron-shaped crystals.
I've written about thermoelectric materials in several previous articles, most recently concerning the power source of the Curiosity rover (Curiosity Rover Power, November 5, 2012). Thermoelectric materials make use of the Seebeck effect to convert a temperature differential to electric power. Thermocouples, as used for temperature measurement, do this same trick, but not very efficiently. thermoelectric devices are constructed from junctions of n- and p-doped semiconductors (see figure), but the leading material for this purpose, bismuth telluride, is still relatively inefficient.
Says Donald Morelli, a professor of chemical engineering and materials science at Michigan State University and leader of the research team,
|A thermoelectric cell.|
Bismuth and tellurium, common material components in such cells, are mildly toxic.
(Image by author, rendered using Inkscape.)
"Typically you'd mine minerals, purify them into individual elements, and then recombine those elements into new compounds that you anticipate will have good thermoelectric properties... But that process costs a lot of money and takes a lot of time. Our method bypasses much of that."
Their material is quite unlike the typical thermoelectric material, which is composed of rare elements and demands careful doping to achieve high efficiency. In fact, the research team was able to use natural tetrahedrite, itself, to make inexpensive thermoelectric devices; however, small chemical modifications produced highly efficient thermoelectric materials.
It's reported that the dimensionless figure of merit of this material is near unity, which puts it on par with the best thermoelectrics available (see figure). This research was supported by the Office of Science of the U.S. Department of Energy. Thermoelectric modules are commercially available, so you can experiment with this technology yourself.
- Xu Lu, Donald T. Morelli, Yi Xia, Fei Zhou, Vidvuds Ozolins, Hang Chi, Xiaoyuan Zhou and Ctirad Uher, "High Performance Thermoelectricity in Earth-Abundant Compounds Based on Natural Mineral Tetrahedrites," Advanced Energy Materials, vol. 2, no. 11 (November, 2012), DOI: 10.1002/aenm.201200650.
- Energy savings - easy as dirt, heat, pressure, Michigan State University Press Release, November 27, 2012.
- Thermoelectric Power Generation Products, Tellurex Corporation.
Permanent Link to this article
Linked Keywords: Arithmetic precision; laboratory; weight; decimal; temperature; Celsius; degree; second; specification; cigarette ash; crucible; annealing; coffee break; Six Sigma; scientist; coal; Industrial Revolution; kieselguhr; diatomaceous earth; fossil; shell; diatom; silica; alumina; iron oxide; inorganic; oxide mineral; oxide; thermal insulation; furnaces; sediment core; Deep Sea Drilling Project; micrometer; Hannes Grobe; Alfred Wegener Institute for Polar and Marine Research; Wikimedia Commons; abrasive; filtration; catalyst support; support medium; catalysis; catalyst; filler; plastic; absorption; absorbency; cat litter; nitroglycerin; dynamite; free lunch; materials science; materials scientist; Michigan State University; University of California, Los Angeles; UCLA; thermoelectric effect; thermoelectric; tetrahedrite; chemical formula; Cu; Fe; copper; iron; bismuth; antimony; atomic radius; tetrahedron; Curiosity rover; Seebeck effect; electric power; thermocouple; energy conversion efficiency; junction; n-type semiconductor; p-type semiconductor; semiconductor; bismuth telluride; bismuth; tellurium; toxic; Inkscape; Donald Morelli; professor; chemical engineering and materials science; doping; dimensionless figure of merit; Office of Science; U.S. Department of Energy.
Latest Books by Dev Gualtieri
Thanks to Cory Doctorow of BoingBoing for his favorable review of Secret Codes!
Blog Article Directory on a Single Page
- Soybean Graphene - March 23, 2017
- Income Inequality and Geometrical Frustration - March 20, 2017
- Wireless Power - March 16, 2017
- Trilobite Sex - March 13, 2017
- Freezing, Outside-In - March 9, 2017
- Ammonia Synthesis - March 6, 2017
- High Altitude Radiation - March 2, 2017
- C.N. Yang - February 27, 2017
- VOC Detection with Nanocrystals - February 23, 2017
- Molecular Fountains - February 20, 2017
- Jet Lag - February 16, 2017
- Highly Flexible Conductors - February 13, 2017
- Graphene Friction - February 9, 2017
- Dynamic Range - February 6, 2017
- Robert Boyle's To-Do List for Science - February 2, 2017
- Nanowire Ink - January 30, 2017
- Random Triangles - January 26, 2017
- Torricelli's law - January 23, 2017
- Magnetic Memory - January 19, 2017
- Graphene Putty - January 16, 2017
- Seahorse Genome - January 12, 2017
- Infinite c - January 9, 2017
- 150 Years of Transatlantic Telegraphy - January 5, 2017
- Cold Work on the Nanoscale - January 2, 2017
- Holidays 2016 - December 22, 2016
- Ballistics - December 19, 2016
- Salted Frogs - December 15, 2016
- Negative Thermal Expansion - December 12, 2016
- Verbal Cues and Stereotypes - December 8, 2016
- Capacitance Sensing - December 5, 2016
- Gallium Nitride Tribology - December 1, 2016
- Lunar Origin - November 27, 2016
- Pumpkin Propagation - November 24, 2016
- Math Anxiety - November 21, 2016
- Borophene - November 17, 2016
- Forced Innovation - November 14, 2016
- Combating Glare - November 10, 2016
- Solar Tilt and Planet Nine - November 7, 2016
- The Proton Size Problem - November 3, 2016
- Coffee Acoustics and Espresso Foam - October 31, 2016
- SnIP - An Inorganic Double Helix - October 27, 2016
- Seymour Papert (1928-2016) - October 24, 2016
- Mapping the Milky Way - October 20, 2016
- Electromagnetic Shielding - October 17, 2016
- The Lunacy of the Cows - October 13, 2016
- Random Coprimes and Pi - October 10, 2016
- James Cronin (1931-2016) - October 6, 2016
- The Ubiquitous Helix - October 3, 2016
- The Five-Second Rule - September 29, 2016
- Resistor Networks - September 26, 2016
- Brown Dwarfs - September 22, 2016
- Intrusion Rheology - September 19, 2016
- Falsifiability - September 15, 2016
- Fifth Force - September 12, 2016
- Renal Crystal Growth - September 8, 2016
- The Normality of Pi - September 5, 2016
- Metering Electrical Power - September 1, 2016
Deep Archive 2006-2008