Thermoelectric generators

The AEG sponsored research ia the program known as Systems for Nuclear AuxiHary Power (SNAP) as early as the 1950s. Most of the systems developed iavolved the radioisotope plutonium-238 as a heat source for a thermoelectric generator. Such electrical suppHes permitted radio transmission to earth from spacecraft such as Pioneer and l qyager. 

Table 2. Summary of Radioisotope Thermoelectric Generators Successfully Launched by the United States from 1961 to 1990...

Antimonides of formulas CdSb and Cd2Sb2 have been reported. Both are usually prepared by direct union of the elements, the former is a hole-type semiconductor (9), with properties shown in Table 1, and finds use as a thermoelectric generator. Reagent-grade material costs 2.00/g in small lots. The band gap energy is 0.46 eV (2.70 J.m) (31) is 138 kj/mol (33.0 kcal/mol). Dicadmium triantimonideCd2Sb2, is a metastable, white... 

Skrabek, E.A., High temperature insulations for radioisotope thermoelectric generators. In Proc. of 13th Intersociety Energy Conv and Eng Conf, vol. 2, ASME, New York, 1978, pp. 1712 1716. 

The power supply is usually a transformer/rectifier that converts a.c. power to d.c. Typically the d.c. output will be in the range 15-100 V and 5-100 A although 200 V/200 A units are not unknown. Thus fairly substantial driving voltages and currents are available. Where mains power is not available, diesel or gas engines, solar panels or thermoelectric generators have all been used to provide suitable d.c. 

Where a.c. supplies do not exist, other sources of power can be used such as d.c. generators, and either diesel or gas driven. Alternatively, thermoelectric generators may be considered if the power requirement is relatively low. Thermo-electric generators are available in relatively small outputs only as shown in Table 10.28. They have the advantage of being completely self-contained since they are powered by taking off some of the gas which passes through the pipeline. 

Rare earth sulfides, selenides, and tellurides show semiconducting properties and have potential for application in thermoelectric generation. Thin film chalcogenides of various rare earths have been prepared by multisource evaporator systems [233]. 

Bloom, J. 13 Watt Curium Fueled Thermoelectric Generator for Hard Lunar... 

Figure 4.10 Direct thermoelectric generators will compete in efficiency with internal combustion engines when thermoelectric materials with figures of merit ZT of the order of 2 are available at temperatures above 900 K.

The most important apphcation of this metal is as control rod material for shielding in nuclear power reactors. Its thermal neutron absorption cross section is 46,000 bams. Other uses are in thermoelectric generating devices, as a thermoionic emitter, in yttrium-iron garnets in microwave filters to detect low intensity signals, as an activator in many phosphors, for deoxidation of molten titanium, and as a catalyst. Catalytic apphcations include decarboxylation of oxaloacetic acid conversion of ortho- to para-hydrogen and polymerization of ethylene. 

Radioisotope thermoelectric generators (RTGs) are sometimes used as power sources for space systems. In April 1964, a United States RTG navigational satellite, SNAP 9A, reentered the atmosphere and burned up at high altitude over the Mozambique Channel, releasing 629 trillion becquerels (TBq), equivalent to 17,000 Ci, of Pu and 0.48 TBq of Pu (Whicker and Schultz 1982a Richmond 1989). In January 1978, a Soviet RTG satellite, Kosmos 954, reentered the atmosphere over Canada and spread radiouranium across parts of that country (Richmond 1989). The amount of radioactive materials in space applications is expected to increase (Richmond 1989). 

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