Tim Holgate

Thermal Conductivity and Combustion Properties of Wheat Gluten Foams

Freeze-dried wheat gluten foams were evaluated with respect to their thermal and fire-retardant properties, which are important for insulation applications. The thermal properties were assessed by differential scanning calorimetry, the laser flash method and a hot plate method. The unplasticised foam showed a similar specific heat capacity, a lower thermal diffusivity and a slightly higher thermal conductivity than conventional rigid polystyrene and polyurethane insulation foams. Interestingly, the thermal conductivity was similar to that of closed cell polyethylene and glass-wool insulation materials. Cone calorimetry showed that, compared to a polyurethane foam, both unplasticised and glycerol-plasticised foams had a significantly longer time to ignition, a lower effective heat of combustion and a higher char content. Overall, the unplasticised foam showed better fire-proof properties than the plasticized foam. The UL 94 test revealed that the unplasticised foam did not drip (form droplets of low viscous material) and, although the burning times varied, self-extinguished after flame removal. To conclude both the insulation and fire-retardant properties were very promising for the wheat gluten foam.

Thermoelectric performance of NiyMo3Sb7−xTex(y≤0.1, 1.5≤x≤1.7)

Mo3Sb7−xTex is a high temperature thermoelectric material, reported to reach figure of merit (ZT)=0.8 at 1023 K. Various p-type samples of NiyMo3Sb7−xTex were prepared with y≤0.1 and 1.5≤x≤1.7 via high temperature reactions at 993 K. Adding transition metal atoms into the empty cube formed by Sb atoms significantly alters the band structure and thus the thermoelectric properties. Electronic band structure calculations indicate that adding Ni slightly increases the charge carrier concentration, while higher Te content causes a decrease. Thermoelectric properties were determined on pellets densified via hot pressing at 993 K. Seebeck as well as electrical and thermal conductivity measurements were performed up to 1023 K. The highest ZT value thus far was obtained from a sample of nominal composition Ni0.06Mo3Sb5.4Te1.6, which amounts to 0.93 at 1023 K.

Increasing the Efficiency of the Multi-mission Radioisotope Thermoelectric Generator

The National Aeronautics and Space Administration’s Mars Science Laboratory terrestrial rover, Curiosity, has recently completed its first Martian year (687 Earth days) during which it has provided a wealth of information and insight into the red planet’s atmosphere and geology. The success of this mission was made possible in part by the reliable electrical power provided by its onboard thermoelectric power source—the multi-mission radioisotope thermoelectric generator (MMRTG). In an effort to increase the output power and efficiency of these generators, a newly designed enhanced MMRTG (eMMRTG) that will utilize the more efficient skutterudite-based thermoelectric materials has been conceptualized and modeled, and is now being developed. A discussion of the motivations, modeling results and key design factors are presented and discussed.

Kinetics, Stability, and Thermal Contact Resistance of Nickel–Ca3Co4O9 Interfaces Formed by Spark Plasma Sintering

Incorporating oxide thermoelectric (TE) materials into TE power generation modules necessitates study of the interfaces between the oxide TE elements and the interconnect materials used to transfer current between them. In this study, interfaces between pure nickel and undoped calcium cobaltate (Ca3Co4O9) have been formed directly by spark plasma sintering (SPS). An intermediate NiO phase is formed during the SPS processes, which grows during post-heating with Co entering from the cobaltate side to form a graded Ni1−xCoxO interfacial layer. The electrical and thermal transport across these interfaces, as well as the long-term chemical stability of the intermediate layers, have been studied and are discussed.

A systems integrated approach to thermal modeling of an enhanced MMRTG

A systems integrated thermal model of an enhanced Multi-Mission Radioisotope Thermoelectric Generator (eMM-RTG) was performed utilizing Sinda 2014 from MSC Software. A comprehensive physics model was added to the Sinda solver which includes, among others, the Seebeck effect, Peltier effect, Thomson effect, Joule heating, and thermal radiation in all the applicable components. The added physics enables the computation of the power output of the eMMRTG. A custom tool was developed to rapidly and efficiently create the necessary Sinda input files allowing for parameterization and optimization of geometries and materials with ease. The methods and select results are presented and discussed.