Shockwave fabrication of thermoelectric materials

Abstract

The explosive consolidation of semiconductor powders results in thermoelectric materials having reduced thermal conductivity without a concurrent reduction in electrical conductivity and thereby allows the construction of thermoelectric generators having improved conversion efficiencies of heat energy to electrical energy.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the priority date of U.S. Provisional Patent Application 61 / 007,319, entitled “High efficiency electricity generation from a thermal gradient” which was filed on Dec. 12, 2007. The specifications of that application are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This invention relates to the shockwave fabrication of thermoelectric materials as a means for deriving an enhanced performance. The consolidation of micro and nano-scale powders through explosive means results in a material that impedes thermal energy transmission through lattice vibrations (phonons) without negatively impacting electrical conductivity, the result being an improvement in thermoelectric conversion efficiency.[0004]2. Background of the Invention[0005]Energy is a quantity that has many forms, with electrical energy having the attractive property that it may be easily transmitted through co...

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Benefits of technology

[0017]In order to reduce the mean free path of phonons it is desirable for the semiconductor thermoelectric to have small crystalline structure, that is, many grain boundaries that would serve to block phonon transmission while preserving the ability for electron transmission. In this sense, we desire a “pseudo-glassy” material. One way to accomplish this is through shock wave consolidation of a powder mixture. As contrasted with powder compaction and sinterning techniques, consolidation allows complete particle to particle bonding, thus producing a monolith of homogeneous properties. Shock consolidation requires the very rapid collapse of the gaps between the powder particles as well as the rapid deposition of energy at the particle surfaces. These processes must be close to adiabatic. The ultra rapid deformation and energy deposition is accomplished in time durations of microseconds by the passage of an explosively produced shock wave. The amplitude of the shock wave has to be sufficient to bond the powders but should not be so high as to produce extensive melting and cracking on subsequent reflections. The correct choice of explosive material and experimental geometry can ensure an acceptable result.

[0019]Prior art approaches to the preparation of thermoelectric materials using melts will exhibit a polycrystalline structure that does nothing to inhibit phonon transport. Prior art approaches that use powder compaction will have limited interparticle bonding. Accordingly, the present invention has the following objects and advantages for the manufacture of thermoelectric materials:a. It maximizes interparticle bonding and thereby enhances electrical conductivity;b. Thermoelectric materials are produced adiabatically, discouraging the formation of crystalline structures;c. It results in a reduced lattice thermal conductivity; andd. It yields an improved performance thermoelectric material.

Problems solved by technology

Prior art approaches that use powder compaction will have limited interparticle bonding.

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