Thermoelectric structural composites and thermocouples using them
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Thermoelectric structural composites and thermocouples using them Shoukai Wang, Sihai Wen, Victor H. Guerrero and D.D.L. Chung Composite Materials Research Laboratory University at Buffalo, The State University of New York Buffalo, NY 14260-4400, U.S.A. ABSTRACT The tailoring of the sign and magnitude of the absolute thermoelectric power was achieved in structural composites by the choice of the reinforcing fibers and of the particulate filler between laminae. The resulting thermoelectric structural composites included continuous carbon fiber polymer-matrix composites and short fiber cement-matrix composites. In addition, it resulted in thermocouples in the form of structural composites. The fibers and interlaminar filler impacted the thermoelectric behavior in the longitudinal and through-thickness directions respectively. INTRODUCTION This work involves taking structural composites as a starting point and modifying these composites for the purpose of enhancing the thermoelectric properties. The resulting composites are multifunctional. Because structural composites are used in large volumes, the rendering of the thermoelectric function to these materials means the availability of large volumes of thermoelectric materials. The thermoelectric function also means that the structure can sense its temperature without the need for embedded or attached thermometric devices. This paper addresses the tailoring of the thermoelectric properties of cement-matrix composites containing short and randomly oriented fibers, and polymer-matrix composites containing continuous and oriented fibers. In both cases, the fibers serve as the reinforcement. Two routes are used in the tailoring. One route involves the choice of fibers. The other route, which only applies to the polymer-matrix composites, involves the choice of the interlaminar filler, which refers to the particulate filler between the laminae. The former route impacts the thermoelectric properties in any direction for a composite containing randomly oriented fibers. In the case of a composite containing oriented continuous fibers, the former route impacts mainly the thermoelectric properties in the fiber direction of the composite, whereas the latter route impacts mainly the thermoelectric properties in the through-thickness direction. TAILORING BY THE CHOICE OF CONTINUOUS FIBERS Polymer-matrix composites with continuous oriented fibers are widely used for lightweight structures. Glass and polymer fibers are not conductive electrically and are therefore not suitable for the thermoelectric function. Carbon fibers can be n-type or p-type even without intercalation. Intercalation increases the carrier concentration, thus making the fibers strongly n-type or strongly p-type [1]. A drawback of intercalated graphite is the instability due to intercalate desorption or reaction with environmental species. For the case of bromine (an electron acceptor) as the intercalate, the instability due to desorption can be overcome by the use of a residue compound [2-4]. For the case of an alk
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