Patent GB-827724-A (GB)
Title: Improvements in or relating to thermoelectric heat pumps
IPC: H01L35/16
Filed: 1955-12-07
Abstract: 827,724. Thermocouples. MINNESOTA MINING & MANUFACTURING CO. Dec. 7, 1955 [Dec. 15, 1954; June 1, 1955], No. 35169/55. Addition to 814,594. Class 37. In a thermoelectric heat pump comprising a source of voltage and a plurality of electrical conductors joined in circuit to provide a pair of thermoelectric junctions, one of the conductors is a material consisting of a base alloy of lead with one or more of the elements sulphur, selenium and tellurium and a small amount of a promoter additive. The base alloy is non- stoichiometric lead telluride containing 37- 38.05% by weight of tellurium, non-stoichiometric lead selenide containing 26.5-27.55% of selenium, non-stoichiometric lead sulphide containing 12.9-13.37% of sulphur, or a ternary alloy consisting of a mixture of the above mentioned lead tellurium and lead selenium, or lead selenium and lead sulphur alloys having a composition lying within the shaded part of Fig. 3 or Fig. 4 respectively. Small amounts of the following promoters are added to these alloys to increase the conductivity; bismuth, manganese, zirconium, titanium, aluminium, gallium, chlorine, bromine, iodine, uranium, or tantalum to lead tellurium alloys; iodine, chlorine, bromine, zirconium, silicon, titanium, indium, gallium, aluminium, copper, gold, fluorine, bismuth, antimony, columbium or tantalum to lead selenium alloys; and zirconium, indium, bromine, chlorine, iodine, titanium, bismuth, antimony, gallium, uranium, columbium or tantalum to lead sulphur alloys, appropriate combinations of these being used in the tenary alloys. Alternatively the conductivity type of the alloys which are normally N-type may be altered by small additions of the following promoters: sodium, potassium, arsenic or thallium to lead tellurium; sodium or potassium to lead selenium; and silver to lead sulphur. The alloys must not contain more than 0.001% of impurities other than the promoters mentioned and selenium, sulphur, and tellurium. The maximum amount of each promoter which is effective in improving the heat pump properties of the alloys is given in the Specification. The aforementioned alloys may be made by sealing a mixture of the elements in an evacuated chamber and agitating it while heating to the melting point of the mixture, then cooling and casting into graphite or quartz moulds in an inert atmosphere, e.g. argon or carbon dioxide under pressure. The ingots are then machined and annealed in a reducing atmosphere. Alternatively the elements are melted together in an open crucible in an inert or reducing atmosphere, additional sulphur, selenium or tellurium being added to make up for evaporation losses, and are then cast and annealed. The required purity is achieved either by use of pure raw materials or by application of the zone melting technique to the ingots. Pure lead is in the latter case added to the purified ingots to restore the composition. The alloys are thought to consist of a first phase consisting of crystals containing a minute excess of lead, cemented together by a second phase consisting primarily of lead. A preferred heat pump consists of N- and P-type elements of the above type connected through a metal bar.