JPH0529666A - Coated thermocouple - Google Patents

Abstract

(57) [Abstract] [Purpose] To make a thermocouple with a thin insulating layer, compact size, excellent flexibility, and no gas adsorption source. [Structure] A metal oxide layer 2 is provided outside the thermocouple element 1, and a heat-resistant organic resin layer 3 is provided outside the metal oxide layer 2. The metal oxide layer is prepared by using a sol-gel method to prepare a sol in which metal oxide precursor fine particles are dispersed, immersing a thermocouple wire in the sol, and applying the thermocouple wire as a cathode to energize the metal oxide. It is formed by depositing precursor fine particles of and heat treating it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated thermocouple used for temperature measurement.

[0002]

2. Description of the Related Art Thermocouples are of a type in which a conductor is passed through a ceramic insulator tube, or a heat-resistant alloy tube made of a stainless alloy, etc., filled with fine particles of metal oxides such as magnesium oxide. 2. Description of the Related Art A sheath thermocouple of a type in which a thermocouple wire is passed has been conventionally known.

[0003]

The thermocouple, which is insulated by using the ceramic insulator tube, has the drawback of being poor in flexibility and being bulky. Further, when used in a high vacuum, the insulator is inherently porous and has a large surface area, so that it has a problem of adsorbing a large amount of gas.

Since the sheath thermocouple is composed of a heat-resistant alloy tube and a thermocouple wire, there are problems that the outer diameter is large and the terminal is difficult to process.

An object of the present invention is to provide a thermocouple having a thin insulating layer, compact size, excellent flexibility, and no gas adsorption source.

[0006]

The coated thermocouple according to the present invention is characterized in that the thermocouple wire is coated with a metal oxide layer, and the heat-resistant organic resin layer is coated outside the metal oxide layer. I am trying.

The metal oxide layer is prepared by preparing a sol in which metal oxide precursor fine particles are dispersed by a sol-gel method, immersing the thermocouple wire in the sol, and energizing the thermocouple wire as a cathode. Then, the precursor fine particles of the metal oxide are attached, and the precursor particles can be formed by heat treatment.

The heat resistant organic resin layer is preferably a compound selected from the group consisting of polyimide, polyamideimide and silicon resin. This heat-resistant organic resin layer functions as an effective protective layer of the metal oxide layer in an environment of about 300 ° C. or lower, and improves flexibility and abrasion resistance.

In the present invention, an organic compound salt and / or a metal inorganic salt can be added in order to increase the dielectric constant of the dispersion medium of the sol.

In the present invention, the sol into which the thermocouple wire is immersed is preferably prepared by the hydrolysis reaction and condensation reaction of the metal alkoxide or metal carboxylic acid ester corresponding to the metal oxide.

The metal oxide preferably contains at least one compound selected from the group consisting of silicon oxide, aluminum oxide, zirconium oxide, and magnesium oxide.

Further, the ceramic powder is preferably at least one compound selected from the group consisting of mica powder, silicon oxide, silicon nitride, silicon carbide, aluminum oxide, boron nitride and aluminum nitride.

The surface of the thermocouple wire is preferably oxidized by heating. By such an oxidation treatment, the adhesion of the metal oxide layer to the thermocouple wire can be enhanced.

FIG. 1 is a sectional view showing an embodiment of the present invention. Referring to FIG. 1, around the thermocouple wire 1,
A metal oxide layer 2 is provided. A heat resistant organic resin layer 3 is provided around the metal oxide layer 2.

[0015]

The thermocouple is a temperature measuring technique utilizing the thermoelectromotive force by the Seebeck effect, and the magnitude of this thermoelectromotive force is due only to the composition of two kinds of metals in contact with each other.
For this reason, it is impossible to form an alloy such as stainless steel, to which ceramics are likely to adhere, on the surface of the thermocouple element wire, as described in Japanese Patent Application No. 1-322376.

In the present invention, the thermocouple element wire is immersed in a sol in which the fine particles of the metal oxide precursor are dispersed, and the thermocouple element wire is used as a cathode to energize the fine particles of the metal oxide precursor to generate electricity. It is electrophoresed and forced to adhere to the surface of the thermocouple wire.

In a preferred embodiment of the present invention, an organic compound salt and / or an inorganic salt is added to increase the electrophoretic efficiency of the sol. This increases the electrophoretic efficiency, and the precursor particles of the metal oxide can be attached to the surface of the thermocouple element with a lower applied voltage and / or a shorter energization time. As a result, a thick ceramic coating can be formed.

As an organic compound salt for increasing the dielectric constant of the dispersion medium, there is an organic ammonium salt used for a phase transfer catalyst. As the metal inorganic salt, at least one compound selected from the group consisting of aluminum, magnesium, potassium, and zirconium nitrates, sulfates, chlorides, and hydroxides can be used.

To obtain a larger film thickness, fine powder of ceramics may be mixed in the sol of the precursor of the metal oxide. As the ceramic fine powder, at least one kind of compound selected from the group consisting of mica powder, silicon oxide, silicon nitride, silicon carbide, and aluminum nitride can be used.

Further, the metal oxide layer is originally poor in toughness and is prone to bending fracture during severe bending. In this invention, since the metal oxide layer is covered with the highly heat-resistant organic resin layer having high flexibility, the coated thermocouple as a whole is extremely flexible.

The thermocouple of the present invention has a thin insulating layer and is compact. Further, since it is excellent in flexibility and does not adsorb a large amount of gas, it can be used even in vacuum.

[0022]

Example 1 First, each wire of a positive leg (alloy mainly containing nickel and chromium) and a negative leg (alloy mainly containing nickel) of a CA thermocouple having a diameter of 0.32 mm was first exposed to the atmosphere. 80
Heat treatment was performed at 0 ° C. for 15 minutes. Next, a mixed solution of 5 mol% tetrabutoxyzirconium, 8 mol% water, 10 mol% glacial acetic acid, and 77 mol% butyl alcohol was prepared,
Furthermore, it stirred at room temperature for 2 hours, and prepared the sol liquid. To 100 ml of this sol solution, 2 g of yttrium nitrate hexahydrate was added at room temperature.

When the above-mentioned thermocouple wire was immersed in the sol prepared as described above and a DC voltage of 200 V was applied for 2 minutes, a white gel of about 70 μm was formed as a gel on the surface of the thermocouple wire. A film formed.

The gel-coated plus-leg and minus-leg thermocouple wires were set to 900 ° C.
After heat treatment for 10 minutes, it was rapidly cooled. After cooling, thickness 5
A yttria partially stabilized zirconia film having a thickness of μm was formed.

Next, a polyimide varnish (P
16% by weight of N-methyl-2-
What was diluted with pyrrolidone to make 5% by weight was applied onto a ceramic-coated thermocouple wire. 2. In a furnace at 400 ° C.
A polyimide film having a thickness of 3 μm was formed by passing through at 5 m / min and firing.

The dielectric breakdown voltage of the obtained product was measured and found to be 1.6 kV. Regarding the flexibility, no crack was generated in the film even when the obtained thermocouple element was wound around a cylinder having a diameter of 1 mm. In the one-way wear test, 502g, reciprocating type (w = 0.6kg)
Then, it was 12 times, and the wear resistance also showed good results.

When the ends of the thermocouple wires of the positive leg and the negative leg were fusion-bonded and used as a thermocouple, 70
Good results were obtained up to 0 ° C.

Example 2 A thermocouple element wire having a positive leg (alloy mainly containing nickel and chromium) and a negative leg (alloy mainly containing nickel) of a CA thermocouple having a diameter of 0.16 mm was prepared.

4 mol% tetraethyl orthosilicate,
Nitric acid was added dropwise to a mixed solution of 40 mol% of water and 56 mol% of ethyl alcohol in an amount of 1/100 of the molar number of tetraethylorthosilicate, and the temperature was adjusted to 2 at 80 ° C.
Prepare a sol that has reacted for a period of time, and have a nominal particle size of
An electrolytic solution was prepared by mixing 5 g of the mica powder of.

When the above thermocouple element wire was immersed in the sol prepared as described above and a DC voltage of 350 V was applied for 2 minutes, a white film of about 20 μm was formed as a film on the surface of the thermocouple element wire. The membrane was purified.

The gel-coated positive and negative leg thermocouple wires were heated at 100 ° C.
After heating for 1 hour, it was quenched. After cooling, thickness 18 μm
The silicon oxide / mica composite film of No. 3 was formed.

Next, silicone resin H-19-2 (Toray
Dow Corning) was diluted in xylene to give a 10% solution. This silicone resin solution
Apply to the outside of the thermocouple wire with the mica composite film formed,
It was baked by heating at 00 ° C. for 5 minutes. By repeating this coating and heating and baking 5 times, a coating film having a film thickness of 10 μm was obtained.

When the obtained thermocouple element was evaluated, the dielectric breakdown voltage was 1.0 kV, and the flexibility was such that even if this element wire was wound around a cylinder having a diameter of 1 mm, no crack was generated in the film. Met.

When the ends of the plus leg and minus leg thermocouple wires were fusion-bonded and used as a thermocouple, 70
Good results up to 0 ° C were obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

[Explanation of symbols]

1 thermocouple wire 2 Metal oxide layer 3 Heat-resistant organic resin layer

Claims (9)

[Claims] 1. A sol in which a thermocouple wire and metal oxide precursor fine particles are dispersed is prepared by a sol-gel method, and the thermocouple wire is immersed in this sol to form the thermocouple wire. A metal oxide precursor fine particles are deposited by energizing as a cathode, and a metal oxide layer is provided outside the thermocouple wire by heat-treating it, and provided outside the metal oxide layer. And a heat-resistant organic resin layer to be coated. 2. The coated thermocouple according to claim 1, wherein the sol contains an organic compound salt in order to increase the dielectric constant of the dispersion medium of the sol. 3. The coated thermocouple according to claim 1, wherein the sol contains an inorganic salt of a metal in order to increase the dielectric constant of the dispersion medium of the sol. 4. The coated thermocouple according to claim 1, wherein the sol contains ceramic powder. 5. The coated thermocouple according to claim 1, wherein the sol is prepared by a hydrolysis reaction and a polymerization reaction of a metal alkoxide or a carboxylic acid ester of a metal corresponding to the metal oxide. 6. The coated thermocouple of claim 1, wherein the metal oxide layer comprises at least one compound selected from the group consisting of silicon oxide, aluminum oxide, zirconium oxide and magnesium oxide. 7. The ceramic powder is mica powder,
The coated thermocouple according to claim 4, which is at least one compound selected from the group consisting of silicon oxide, silicon carbide, silicon nitride, aluminum oxide, boron nitride and aluminum nitride. 8. The coated thermocouple according to claim 1, wherein the surface of the thermocouple wire is oxidized by heating. 9. The heat-resistant organic resin layer is polyimide,
The coated thermocouple according to claim 1, comprising at least one selected compound consisting of polyamide-imide and silicone resin.