DE1064537B - Thermocouple, especially for electrothermal refrigeration, and process for its manufacture - Google Patents

Description

GERMAN

Materials for thermocouples have recently become known which, in addition to a relatively high differential thermal efficiency, have a relatively small lattice heat capacity, i.e. a small Wicdemann-Franz-Lenz number (WFL number), and thus have significantly improved effectiveness. 2. B. alloys made from the compounds BijTej and Sb, Tc ₁ have been proposed. The dimensions that have become known up to now provide for compositions in which the bismuth portion predominates over the alloys or in which these two proportions do not or only slightly differ from one another.

The subject of the invention is a thermocouple, in particular for refrigeration. in the case of the solid solution (mixed crystal) of the compounds Bl ₁ Te and Sb ₂ Te, at least on the leg axis, there is an antimony content between 24 and 36 atom percent and a bismate content between 4 and 16 atom percent. These are texnary systems of form

Thermocouple, especially for the

electrothermal refrigeration,

and its method of manufacture

Corresponds to the aforementioned Bi * and Sb-Antdten a JT value between 1.2 and 1.8.

A composition with 28 atomic percent of antimony and 12 atomic percentages is particularly advantageous Bismuth (χ = 1.4).

The invention is based on the surprising experimental finding that maximum effectiveness can be achieved when the antimony and bismuth proportions are measured in the manner indicated above. The advantages of the dimensioning according to the invention can be seen from the table. In particular, it can be seen from this that dnc maximum effectiveness can be achieved in a composition with 28 atomic percent antimony and 12 atomic percent bismuth . For example, a plastic limb with a Bi ₃ Tc ₃ limb doped conductively by adding 0.1 percent by weight of AgI, you get a Peltier element with an overall effect of 2.1.10 degrees corresponds to a theoretically possible temperature reduction of 80 ° C (cold solder joint - 0 ° C).

In the table, columns 1 and 2 are in atomic percentages the Antimony · and Bismutanteik ·. in, column 3 the different tbermokraft (α), in column 4 the 10 * fachc WFL number and in column 5 the lO'Kiehv Effectiveness (x) given. The effectiveness is like follows defined;

Applicant:

Siemens-Schuckertwerke

Corporation,

Berlin and Erlangen "

Erlangen, Wemer-von-Siemens-Str. 50

Dlpl.-Phys. Ulrich Blrkhalz, Nuremberg, has been recognized as an egg end

electrical conductivity and K is the thermal conductivity.

Sb- bi- 2 ₉ WFL- Jt-10 » 32 Zihl-IO » proportion of
in acomp% 20th , .WGr * Degree-* I. 16 ) 4th S. 8th 12th +202 8.5 1.68 20th 8th + 153 4.65 1.77 24 4th + 146 3.55 1.91 28 + 146 3.14 2.05 32 + 136 3.06 2.04 36 + 108 2.67 1.30

χ s = ■

where α means the differential thcrino force, ο dit-

The effectiveness gives a direct measure of the brewing power of a substance as thermoelectric Component, in particular for the measurable temperature difference in the door

♦ S l) i) i.-itinn. furthermore for the power supply in the case of the clcktrotlK-rmischen cooling and the thcrmoek-ktris ^ licii Stronicnecugui ^.

The tliernioelekirisclicn componentCB of the Thennock niiiitfs according to the invention can after a dvr iK-ktinnten Hersiellungiveriahren for Tl »cnno · ck-matte can be divided into sections. Is particularly advantageous you see »! l) ckanine Hcrstcllurp according to the pulvernutaHurKisclicii method (x. B. German patent 8, V6iM3>. Here.

WiMl

that the solid solution of the compounds Bi ₂ Te ₃ and Sb ₂ Te _{3 is} produced by melting, then pulverized and then further processed by the powder metallurgical process to form the thermocouple limb.

According to a further invention, the thermoelectric properties can be adapted in a predetermined manner in the manufacture of the thermocouple according to the powder metallurgical process by suitable dimensioning of the sintering conditions, especially the grain size, the liquid pressure, the sintering temperature, time and atmosphere. In particular, the defect electron concentration can be reduced. This makes it possible to dimension the sintering conditions in terms of achieving the optimal charge carrier concentration. The optimal charge carrier concentration is understood here to mean that charge carrier concentration which results in such an electronic thermal conductivity (K _ei ) that the condition known from the theory of the Peltier effect

α =

+ - ^ - 1 u V / degree ^k )

is met as far as possible. K ₀ means the lattice thermal conductivity.

In the case of the composition with 28 atomic percent antimony and 12 atomic percent bismuth given above as particularly favorable, z. B. α values of 200 to 300 μV / degree can be achieved by varying the sintering 3c temperature between 250 and 500 ° C and the pressing pressure between 2 and 8 t / cm ² ; the sintering time is 1 hour, the grain size of the starting powder is below 60 μ. The α value of the molten material is 145 μV / degree.

Claims (5)

Patent claims: 1. Thermocouple, especially for electrothermal refrigeration, in which at least one leg consists of a solid solution (mixed crystal) of the compounds Bi ₂ Te ₃ and Sb ₂ Te ₃ , characterized in that the antimony content between 24 and 36 atomic percent and the bismuth content between 4 and 16 atomic percent is measured. 2. Thermocouple according to claim 1, characterized in that the antimony content of the leg from de »solid solution of the compounds Bi ₂ Te ₃ and Sb ₂ Te ₃ is dimensioned to 28 and the bismuth content to 12 atomic percent. 3. A method for producing a thermocouple according to claim 1 or 2, characterized in that the leg or legs are made from the solid solution of the compounds Bi ₂ Te ₃ and Sb ₂ Te ₃ in a manner known per se by the powder metallurgical process. 4. The method according to claim 3, characterized in that the solid solutions of the compounds Bi ₂ Te ₃ and Sb ₂ Te _{3 produced} by the melting route, then pulverized and then further processed by the powder metallurgical process to form the thermocouple leg. 5. The method according to claim 3 or 4, characterized in that the conditions of the powder metallurgical Process, in particular grain size, pressing pressure, sintering temperature, sintering time and sintering atmosphere, in the sense of achieving the optimal charge carrier concentration can be adjusted. © 909 610/85 8.