US2602095A - Thermoelectric device - Google Patents

Description

Patented July 1, 1952 games 1 York No Drawing. Application June 3,

Serial No. 166,073

6 Claims. 1

The present invention relates to a thermoelectric device. More particularly, it is concerned with an improved thermoelectric element and to thermocouples comprising such element.

An object of the present invention is to provide a thermoelectric alloy having a high thermal electric power which is not materially affected by the presence of impurities.

A further object of the invention is to provide a thermoelectric alloy having good mechanical strength, said alloy being malleable at temperatures below red heat.

These principal objects of the invention and others which will become apparent from the following description are attained in accordance with the present invention by providing a new and improved thermoelectric alloy composed of silver and tellurium and containing more than 63% silver. The alloys found to be useful for obtaining the above mentioned objects are those containing from 63 to 80% silver, preferably from 63 to 65% silver, balance tellurium except for minor impurities.

Investigation of the thermoelectric properties of silver-tellurium alloys has shown that at a point at or near the composition corresponding to 62.8% silver, the polarity of the thermal E. M. F. of the alloy reverses. For example, an alloy with 60% silver has a thermal E. M. F. of plus 150 microvolts per degree 0. against copper, while an alloy with 65% silver has a thermal E. of minus 100 microvolts per degree C. against copper. These alloys of silver and tellurium containing more than 63% silver are also characterized by good mechanical strength, good malleability and an E. M. F. which is not materially affected by the presence of impurities. For ex ample, the 65% silver alloy of tellurium appears to be unique among alloys having such a high thermal E. M. F. in that it is also malleable at temperatures below red heat. At a temperature of about 400 C. this alloy may be hammered from a rod .1" in diameter to a strip about .04" or less in thickness. This property is particularly useful in the manufacture of smaller thermocouple elements as, for example, for instrument thermocouple applications. The 65% silver alloy has a resistivity of about .0048 ohm per centimeter cube.

The thermoelectric alloys of the present inven-.

tion can be made by adding the required amount of silver to molten tellurium in a porcelain crucible. The silver rapidly dissolves when the tellurium is at a temperature barely above its melting point. Thereafter the molten alloy is cast into a suitable form and the cast product formed at an elevated temperature into the required final shape.

While the thermoelectric alloys of the present invention can be used with any suitable second alloy or element in the manufacture of thermocouples, highly eificient thermocouples are those in which the silver-tellurium thermoelectric alloy of the present invention comprises one of the elements while the second element is one having a high positive thermal E. M. F. For this purpose the second element preferably comprises impure tellurium or alloys of silver and tellurium containing less than 62% silver. M. F. of impure tellurium is the highest obtainable in materials which have a resistivity low enough to give a reasonably good efficiency. Since its thermal E. M. F. is positive with respect to copper, ranging from 200' to 550 microvolts per degree C., the combination of impure tellurium and the high silver tellurium alloys provides a thermocouple of maximum efficiency.

The preferred impurities in the tellurium element are up to 1% antimony or bismuth. An alloy of .5% antimony,balance tellurium has a thermal E. M. F. of 215 microvolts per degree C. while an alloy of 1% bismuth, balance tellurium has a thermal E. M. F. of a positive 220 microvolts per degree C. Both form excellent thermocouple combination with the silver-tellurium alloys.

As was indicated hereinbefore, alloys of tellurium and silver containing less than 62.8% silver,

as, for example, an alloy containing silver, has a thermal E. M. F. of plus 150 microvolts per degree C. and these can also be employed with the present thermocouple elements. For better workability alloys containing from 50 to about 62% silver are preferred as they more closely resemble the higher silver alloys'in workability than do the alloys containing less silver.

By the term impurities as used hereinbefore in connection with the alloy of silver and tellurium containing at least 63% silver, it is intended to cover those impurities inherent in commercial tellurium and silver and hence present in the final alloys.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A thermocouple comprising a negative thermoelectric element composed of an alloy consisting of tellurium and silver and containing from 63% to silver.

2. A thermocouple comprising one element The thermal E.

3 composed of an alloy of tellurium and silver containing from 63% to 65% silver.

3. A thermocouple of claim 1 in which the second element is composed of impure tellurium.

4. A thermocouple element of claim 3 in which the impurities are bismuth or antimony.

5. A thermocouple of claim 1' in which the second element is composed of a tellurium-silver alloy containing less than 62% silver.

6. A thermocouple comprising elements composed of alloys of silver and tellurium, one of said elements consisting of an alloy containing 63% to 65% silver, balance tellurium, and the other element consisting of less than 62% silver, balance tellurium.

HAROLD T. FAUS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,232,960 Milnes Feb. 25, 1941 2,264,073 Faus Nov. 25, 1941 2,397,756 Schwartz Apr. 2, 1946 OTHER REFERENCES Addicks: "Silver in Industry," 1940, pages 111, 112, 532, published by Reinhold Pub. Corp.', New York city.

Homing et a1, Review of Scientific Instruments (July 1947), vol. 18, No. 7, pp. 477-478.

Claims (1)

1. A THERMOCOUPLE COMPRISING A NEGATIVE THERMOELECTRIC ELEMENT COMPOSED OF AN ALLOY CONSISTING OF TELLURIUM AND SILVER AND CONTAINING FROM 63% TO 80% SILVER.