PLASMA COATING OF THERMOELECTRIC ACTIVE MATERIAL WITH NICKEL AND TIN

Abstract

The invention relates to a method for producing a thermoelement for a thermoelectric component, in which method: with the aid of a plasma flame, a diffusion barrier made of nickel is applied to a thermoelectric active material; or, with the aid of a plasma flame, a contact-facilitating layer made of tin is applied to a diffusion barrier made of nickel. The invention also relates to a thermoelectric component comprising thermoelements which are produced correspondingly. The aim of the invention is to further develop the conventional plasma spraying technique such that it can be used to produce thermoelements on an industrial scale. To achieve this aim, nickel particles or tin particles are used, which particles conform to a particular specification with regard to their sphericity.

Claims

1. A method for producing a thermoleg for a thermoelectric component, comprising: applying a diffusion barrier of nickel to a thermoelectric active material with the aid of a plasma flame, feeding nickel particles with a mean sphericity of greater than 0.74 to the plasma flame.

2. The method according to claim 1, wherein the nickel particles conform to the following specification with regard to their particle size distribution: D.sub.50 of 0.6 μm to 25 μm.

3. The method according to claim 2, wherein spray-dried and screened nickel particles are used.

4. The method according to claim 1, with the proviso that the plasma flame is a stream of an ionized carrier gas in which the nickel particles are dispersed, wherein a) a carrier gas is selected from the group consisting of nitrogen, hydrogen or mixtures thereof is used; b) the carrier gas is ionized with the aid of an electrical voltage; c) the temperature of the plasma flame lies below 3000 K.

5. The method according to claim 4, with the proviso that the plasma flame is produced in a nozzle, wherein a) the carrier gas is fed into the nozzle with a volumetric flow of 10 Nl/min to 60 Nl/min; b) the carrier gas is ionized in the nozzle by being passed through an electrical discharge induced by the electrical voltage; c) the nickel particles are fed into the nozzle at a feed rate of 1 g/min to 10 g/min; d) the nickel particles are dispersed in the stream of carrier gas, this taking place before or after or during the ionization of the carrier gas; e) the plasma flame leaves the nozzle in the direction of the thermoelectric active material; f) and the nozzle and the thermoelectric active material are moved in relation to one another, while maintaining the same distance, with an advancement of 80 mm/s to 250 mm/s; in such a way g) that the nickel particles fed to the nozzle are deposited on the thermoelectric active material by the plasma flame, and so the diffusion barrier grows on the thermoelectric active material with a layer thickness of 3 μm to 100 μm.

6. The method according to claim 1, wherein, before the application of the diffusion barrier, the thermoelectric active material is treated in the region of the later diffusion barrier with a plasma flame in which no particles are dispersed, the plasma flame without dispersed particles being produced in a way analogous to the plasma flame with nickel particles dispersed in it, with the difference that no nickel particles are fed to the plasma flame without dispersed particles.

7. The method according to claim 1, in which a contact maker layer is applied to a diffusion barrier of nickel with the aid of a plasma flame, wherein the contact maker layer consists of tin, and tin particles with a mean sphericity of greater than 0.72 are fed to the plasma flame.

8. The method according to claim 7, wherein the tin particles conform to the following specification with regard to their particle size distribution: D.sub.50 of 1 μm to 40 μm.

9. The method according to claim 8, wherein spray-dried and screened tin particles are used.

10. The method according to claim 7, with the proviso that the plasma flame is a stream of an ionized carrier gas in which the tin particles are dispersed, wherein a) a carrier gas that is chosen from nitrogen, hydrogen or mixtures thereof is used; b) the carrier gas is ionized with the aid of an electrical voltage; c) the temperature of the plasma flame lies below 3000 K.

11. The method according to claim 10, with the proviso that the plasma flame is produced in a nozzle, wherein a) the carrier gas is fed into the nozzle with a volumetric flow of 10 Nl/min to 60 Nl/min; b) the carrier gas is ionized in the nozzle by being passed through an electrical discharge induced by the electrical voltage; c) the tin particles are fed into the nozzle at a feed rate of 1 g/min to 10 g/min; d) the tin particles are dispersed in the stream of carrier gas, this taking place before or after or during the ionization of the carrier gas; e) the plasma flame leaves the nozzle in the direction of the diffusion barrier; f) and the nozzle and the diffusion barrier are moved in relation to one another, while maintaining the same distance, with an advancement of 80 mm/s to 250 mm/s; in such a way g) that the tin particles fed to the nozzle are deposited on the diffusion barrier by the plasma flame, and so the contact maker layer grows on the diffusion barrier with a layer thickness of 20 μm to 200 μm.

12. The method according to claim 1, wherein the nickel particles and/or the tin particles are fed to the plasma flame with the aid of pneumatic feeding.

13. A thermoelectric component, comprising: at least two thermolegs of thermoelectric active material that are connected in an electrically conducting manner by way of a contact bridge to form a thermocouple, at least one of the thermolegs being obtainable or obtained by a method according to claim 1.

Description

[0124] The invention will now be explained in more detail on the basis of figures. The figures show:

[0125] FIG. 1: a basic diagram;

[0126] FIG. 2: a thermoleg of active material in a passive substrate with an Ni/Sb coating (first working result);

[0127] FIG. 3: a thermoleg of active material in a passive substrate with an Ni/Sb coating (second working result);

[0128] FIG. 4: a thermoleg of active material with an Ni/Sb coating (third working result);

[0129] FIG. 5: a thermoleg of active material with an Ni/Sb coating (fourth working result).

[0130] FIG. 1 shows a basic diagram of the plasma spraying according to the invention. A nozzle 1 comprises a cathode 2 and an anode 3. The cathode 2 is arranged around the anode 3. A high voltage is applied between the cathode 2 and the anode 3. The high voltage is a pulsed DC voltage of 20 kV. The pulse frequency is 20 kHz. There is a spark discharge of the voltage between the anode 3 and the cathode 2.

[0131] A carrier gas 4 flows through the nozzle 1 and is ionized by the discharge of the high voltage between the anode and the cathode. In the region of the mouth of the nozzle 1, a metallic coating material 5 (nickel or tin) is introduced in the form of a powder. This takes place pneumatically with a non-ionized feed gas such as argon. In the nozzle 1, the powdered coating material 5 is dispersed in the carrier gas 4, and so a coating gas stream 6 emerges from the nozzle 1.

[0132] The nozzle is aligned with the thermoelectric active material 7 to be coated. As it approaches, the arc is ignited. By means of the plasma 8, the powdered coating material 5 is deposited on the surface to be coated of the thermoelectric active material 7. A manipulator that is not shown moves the active material 7 in relation to the fixed nozzle 1, and so a layer 9 of coating material grows on the surface of the active material. The relative movement takes place within a space filled with a protective atmosphere, to be more precise in an enclosure of the coating apparatus. Depending on the coating material 5 that is used (nickel or tin), the applied layer 9 is a diffusion barrier or a contact maker layer.

[0133] FIGS. 2 to 5 show various working results, in which a first layer 9 of nickel as a diffusion barrier and on it a second layer 10 of tin as a contact maker layer have been applied according to the invention to thermolegs 11 of thermoelectric active material. In the case of the working results shown in FIGS. 2 and 3, the thermoleg 11 is located in a thermoelectrically passive substrate 12 of a ceramic composite material. The thermolegs 11 in the case of the working results shown in FIGS. 4 and 5 are provided at their flanks, outside their electrical contact area, with an optional protective layer 13, which has likewise been applied according to the invention. Therefore, not only the electrical contact points of the active material can be coated according to the invention, but also other surface areas that are exposed to diffusion and oxidation.

LIST OF REFERENCE NUMERALS

[0134] 1 nozzle [0135] 2 cathode [0136] 3 anode [0137] 4 carrier gas [0138] 5 coating material (powdered) [0139] 6 coating gas stream [0140] 7 thermoelectric active material [0141] 8 plasma [0142] 9 first layer Ni (diffusion barrier) [0143] 10 second layer Sb (contact maker) [0144] 11 thermoleg [0145] 12 substrate [0146] 13 protective layer