Summer 2011 Intern Project- Armin Moosazadeh

NANOSTRUCTURED SILICON GERMANIUM FOR THE EFFICIENT CONVERSION OF WASTE HEAT TO ELECTRICITY


Armin Moosazadeh

Mechanical Engineering
UC Santa Barbara

Mentor: Matthew Snedaker
Faculty Advisors: Martin Moskovits and Galen Stucky
Department: Chemistry and Biochemistry

The thermoelectric effect provides a method to covert thermal energy to electrical energy and vice-versa.  This phenomenon may be exploited in order to improve energy efficiency, by applying it for refrigeration or generation of electricity from waste heat.  Silicon germanium alloys (SiGe) are the standard materials used for thermoelectric generators at high temperatures.  The thermoelectric efficiency of these alloys may be improved through nanostructuring; whereby, the average grain size is on the order of the phonon’s mean free path, resulting in increased phonon scattering and a significant reduction of the lattice thermal conductivity.  Unfortunately, the current means to produce high performance SiGe nanocomposites involves high energy ball milling of elemental Si and Ge, which is expensive and energy intensive, preventing it from being implemented on an industrial scale.   We are developing a mild and green method to produce SiGe nanocomposites with competitive thermoelectric properties.  Thermoelectric characterization of a bulk powder requires pelletization.  The resulting pellet’s thermoelectric properties are dependent upon the pellet’s density and phase segregation; therefore, we are developing a method that will allow us to monitor the densification of a thermoelectric pellet during hot pressing through in-situ resistance measurements from a two-wire method and density measurements from a displacement gauge.   We report our progress on developing this method, which we anticipate will allow us to optimize hot pressing conditions and better understand how the thermoelectric properties of our materials change as a function of temperature and pressure.

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