Delgado A.,University of Texas at El Paso |
Cordova S.,University of Texas at El Paso |
Lopez I.,University of Texas at El Paso |
Nemir D.,TXL Group, Inc. |
Shafirovich E.,University of Texas at El Paso
Journal of Alloys and Compounds | Year: 2016
Magnesium silicide (Mg2Si) is a promising intermetallic compound for applications such as light-weight composite materials and thermoelectric energy conversion. It is difficult, however, to synthesize high-quality Mg2Si on a large scale. Self-propagating high-temperature synthesis (SHS) is an attractive pathway, but it is difficult to ignite the low-exothermic Mg/Si mixture and achieve a self-sustained propagation of the combustion wave. In the present paper, mechanical activation was used to facilitate the ignition. Magnesium and silicon powders were mixed and then milled in a planetary ball mill in an argon environment. The mixtures were compacted into pellets and ignited at the top in a reaction chamber filled with argon. Depending on the pellet dimensions and diameter-to-height ratio, two modes of combustion synthesis, viz., thermal explosion and SHS, were observed. In both modes, Mg2Si product was obtained. Thermocouple measurements have revealed that the exothermic reaction stages include two self-heating events separated by a long period of relatively slow interaction. To clarify the reaction mechanisms, differential scanning calorimetry was used, which also revealed two peaks of exothermic reaction in the milled Mg/Si mixture. The first peak is explained by the effect of mechanical activation. Explosive-based shockwave consolidation was used to increase the product density. Thermophysical properties of the obtained material were determined using a laser flash apparatus. © 2015 Elsevier B.V. All rights reserved.
TXL Group, Inc. | Date: 2012-04-06
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.
Agency: National Aeronautics and Space Administration | Branch: | Program: STTR | Phase: Phase I | Award Amount: 100.00K | Year: 2009
Thermoelectric (TE) generators/refrigerators have the advantages of lack of moving parts, quiet operation, and flexibility in deployment, but their use has been limited because of their relatively low conversion efficiency. Two major loss components are conductive (phonon) heat transfer through the TE lattice and parasitic losses at fabrication interfaces. Shock wave consolidation of thermoelectric nanopowders to produce TE devices will reduce both loss sources, leading to enhanced efficiency devices. The conversion efficiency of a TE device will always be thermodynamically limited by the Carnot ratio of (Th-Tc)/Th, where Th and Tc are the temperatures of the hot and cold junctions. Present technology thermoelectric devices can provide conversion efficiencies up to a third of the Carnot limit. With the restrictions on phonon transport acruing from nanopowder consolidation, conversion efficiencies of over 50% of the Carnot limit should be possible.
TXL Group, Inc. | Date: 2010-08-03
Thermoelectric generating apparatus used for converting heat energy to electrical energy, namely, thermoelectric generation module.
Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase I | Award Amount: 150.00K | Year: 2015
ABSTRACT: Phase 1 research will validate an approach for material synthesis that combines mechanical alloying with explosive powder consolidation to produce bulk materials with novel properties. The main advantage to the approach is that it can be applied to diverse material systems, including the creation of alloys with otherwise insoluble constituents. An additional advantage is that it has a straightforward path for scale up to industrial levels of production. In Phase 1, elemental powders of bismuth, antimony and tellurium will be mechanically alloyed, both with and without inert nanoinclusions, to produce a powder with particles that are in a highly non-equilibrium state. Explosive powder consolidation will allow the imposition of dynamic pressures in excess of 10 GPa to accomplish densification and interparticle bonding without the attendant grain growth and loss of non-equilibrium features that occur with other powder metallurgy approaches. A series of post-consolidation heat treatments for the step restoration of the material to the equilibrium state allows a characterization of bulk properties as a function of departure from equilibrium. The specific application addressed in Phase 1 is the development of high performance p-type thermoelectric material, a choice that not only has immediate market potential but that also allows microstructural assessment through measurements of bulk quantities such as thermopower, electrical conductivity and thermal conductivity. BENEFIT: Non-equilibrium materials produced by shockwave synthesis may exhibit unique properties such as increased ductility, higher strength and higher melting point. A specific application that will benefit is in the production of thermoelectric materials where the high incidence of grain boundaries and lattice defects will reduce thermal conductivity and increase the figure-of-merit, Z. A higher Z thermoelectric material has an immediate home in generation and Peltier heat pumping applications.