JPH06104594B2 - Heat resistant insulation tube - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an insulating tube having excellent heat resistance, which is used as a protective tube for thermocouples and the like.

(Prior art) In the field of ceramics, 10
A 0 atmosphere pressure sintering furnace and a HIP furnace are often used, but in temperature control particularly in the firing process, measuring instruments such as thermocouples and radiation thermometers are used. Since these measuring instruments are installed in a furnace and exposed to an atmosphere exceeding 2000 ° C, it is strongly desired to improve the strength against heat.

Therefore, at present, as shown in the sectional view of FIG. 1, the thermocouple 1 is put in a cylindrical protective tube 2 made of carbon, boron nitride or the like for use.

However, all of the above-mentioned conventional protection tubes have low strength, and particularly carbon has a high reactivity, and the components of the protection tube are leached out, leached out, and adversely affect the object to be measured.

(Object of the Invention) The present invention was devised to solve the above problems, and an object thereof is to provide an inexpensive protective tube having excellent heat resistance. Another object of the present invention is to provide a protective tube in which the strength of the film is improved while the adhesion between the film to be provided and the substrate is increased, and the base material component is completely sealed.

(Structure of the Invention) According to the present invention, the outer surface of an insulating tube-shaped substrate made of graphite is coated with pyrolytic boron nitride through an intermediate layer, and the intermediate layer has a thermal expansion coefficient of the graphite and the pyrolytic nitride. The strength and heat resistance of the insulating tube itself can be improved by using at least one selected from the group consisting of SiC, B ₄ C having an intermediate value with boron, and randomly oriented boron nitride.

Hereinafter, the present invention will be described in detail.

According to the present invention, graphite, which is low in cost and excellent in workability, is used as a substrate, and a film of pyrolytic boron nitride (hereinafter, simply referred to as PBN) is provided on the surface of the graphite substrate. PBN is electrically insulating,
Since it has excellent thermal conductivity and thermal shock resistance, and particularly excellent chemical stability and oxidation resistance at high temperatures, the protective tube itself can have excellent heat resistance. However, the coefficient of thermal expansion between the base graphite and PBN varies depending on the orientation of the PBN film, but there is a difference of about 2 to 10 × 10 ^-6 / ° C.
Even if a film is provided, it tends to peel off due to repeated heating-cooling cycles.

According to the present invention, the thermal expansion coefficient and PB of such a graphite substrate
In order to prevent peeling of the PBN film due to the difference in thermal expansion coefficient from N, as shown in the partial sectional view of FIG.
It is important to provide the intermediate layer 4 in order to reduce the difference in thermal expansion.

The intermediate layer 4 is selected to have an intermediate value between the thermal expansion coefficients of graphite and PBN. In the present invention, a combination of at least one selected from SiC, B ₄ C or randomly oriented boron nitride is included. Among these intermediate layer components, when the carbide is formed as a reaction product with the substrate (carbon), the substrate component can be sealed by the intermediate layer and carbon leaching can be prevented. Further, the randomly oriented boron nitride can control the thermal expansion coefficient of the film within the range of about 2 to 30 × 10 ⁻⁶ / ° C. depending on the orientation of the BN film, that is, the ratio of the a-axis orientation and the c-axis orientation. This can be changed depending on the substrate temperature or the composition of the reaction gas at the time of film formation. Furthermore, the above intermediate layer can be continuously formed in the same reaction tank from the intermediate layer to the formation of the PBN film in accordance with the vapor phase growth method, especially the CVD method. Adhesion with each film is also improved.

The intermediate layer may be composed of a plurality of layers. Preferably, SiC and B ₄ C are provided as the first layer from the base material, and randomly oriented boron nitride is provided as the second layer. According to this structure, the components of the base material can be reliably sealed by the first layer, and the thermal expansion coefficient is adjusted to an intermediate expansion coefficient between the upper and lower layers by the second layer, so that the adhesion from the base material to the PBN film is improved. Can be improved more reliably.

To produce the heat-resistant insulating tube of the present invention, by placing a substrate made of graphite in the reaction vessel to control the substrate temperature of 500 to 1500 ° C., SiH ₄ as there reaction gas, SiCl ₄ or the like of Si When a gas containing or a gas containing boron such as BCl ₃ and these and H ₂ gas are introduced, a Si or B film is formed on the substrate. At that time, due to the reaction with the carbon of the substrate, SiC or B ₄ C
Is generated. After that, a PBN film is produced by continuously introducing three kinds of gases of BCl ₃ , NH ₃ , and H _{2 at} a predetermined ratio. Randomly oriented boron nitride has a substrate temperature of 500 to 1500 ° C. and a reaction gas ratio of NH ₃ / B in forming a BN film.
By setting the Cl ₃ ratio in the range of 1 to 20, the orientation of BN can be randomly controlled and its thermal expansion coefficient can be controlled to a value close to that of graphite.

When the intermediate layer has a plurality of layers, the reaction gas may be exchanged appropriately.

The thickness of the intermediate layer and the PBN film can be appropriately set, but it is preferable that the thickness of the intermediate layer is 1 to 100 μm and the PBN film is 0.01 to 1 mm from the viewpoint of adhesion strength and cost.

Hereinafter, the present invention will be described with reference to the following examples.

Example 1 A U-shaped insulating tube-shaped compact made of highly dense graphite was prepared, placed in a CVD reaction tank, heated to 900 ° C., and SiH ₄ gas was added thereto at a pressure of 30 Torr. It was introduced and a silicidation reaction was carried out for 1 hour. As a result, silicon carbide was formed on the entire surface of the graphite compact with a film thickness of 10 μm.

After that, BCl ₃ gas, NH ₃ gas and H ₂ gas were continuously supplied to the reaction chamber at 10 CC / min, 10 CC / min and 100 CC / min, respectively.
At a pressure of 20 Torr to cause a catalytic reaction for 10 hours to form a 200 μm thick P film on the entire surface of the silicon carbide film.
A BN film was formed.

In the obtained insulating tube into N ₂ by installing a thermocouple and Ar in
The measurement was performed up to 2000 ° C, but it showed excellent heat resistance without peeling of the film.

Example 2 A molded body similar to that of Example 1 was prepared and placed in a reaction tank.
BCl ₃ 10CC / min, H ₂ 150CC / m at a pressure of 5 Torr
The mixed gas was introduced at a flow rate of in, and the boration reaction was performed for 1 hour to form a B ₄ C intermediate layer of 5 μm. More continuously,
Under the same conditions, NH ₃ gas was introduced at a flow rate of 10 CC / min, and 200 μm
A PBN film was formed.

When a thermocouple was installed in the obtained insulating tube and the measurement was carried out in the same manner as in Example 1, excellent heat resistance was exhibited even at 2000 ° C., and no trouble occurred.

Example 3 A molded body substrate made of graphite was placed in a CVD reaction tank, the substrate was heated to 800 ° C., and NH ₃ , BCl ₃ , and H ₂ were each added at 10 CC / min,
1 at 10 CC / min (NH ₃ / BCl ₃ = 1), 150 CC / min pressure 1 Torr
A BN film having a thermal expansion coefficient of 4 × 10 ₋₆ / ° C. and having a random orientation was formed in a thickness of 5 μm. After that, set the substrate temperature to 1500 ℃
The reaction was performed for 10 hours under exactly the same conditions except that
The PBN film of was formed.

When a thermocouple was installed in the obtained insulating tube and measurement was performed under the same conditions as in Example 1, excellent heat resistance was exhibited without peeling of the film.

Example 4 As in Example 1, the molded body was placed in a reaction tank and heated to 1500 ° C., and the pressure was 5 Torr and BCl ₃ 10 cc / min. The H ₂ shaped molded body was placed in the reaction tank and heated to 1500 ° C. Pressure 5 Torr and BCl ₃ 10cc /
After introducing a mixed gas at a flow rate of 150 cc / min for min and H ₂ to perform a boration reaction for 1 hour to form a 3 μm intermediate layer of B ₄ C,
The substrate is heated to 800 ℃ and NH ₃ , BCl ₃ and H ₂ are added at 20cc / mi each.
Reaction was carried out for 2 hours at a pressure of 1 Torr of n, 10 cc / min (NH ₃ / BCl ₃ = 2) 150 cc / min to form a randomly oriented BN film having a thermal expansion coefficient of 4 × 10 ₋₆ / ° C. and a thickness of 10 μm.

After that, the reaction was performed for 5 hours under exactly the same conditions except that the substrate temperature was raised to 1500 ° C. to form a PBN film of 150 μm.

A thermocouple was installed in the obtained insulating tube and the measurement was performed in N _2. However, even at 2000 ° C, heating up to 2000 ° C without any problem-
Cooling was repeated 10 times to show excellent heat resistance and film adhesion without any change.

(Effect of the invention) As described above, the heat-resistant insulating tube of the present invention, SiC, B ₄ C having a coefficient of thermal expansion intermediate between pyrolytic boron nitride and graphite on the graphite substrate surface or randomly oriented boron nitride The PBN layer is firmly adhered to the substrate by coating the pyrolytic boron nitride (PBN) through the intermediate layer composed of at least one of the
It has excellent heat resistance and strength, is inexpensive, and has a long life.

The insulating tube of the present invention can be applied to various fields such as a crucible and a mold in addition to a thermocouple protection tube that is measured in a high temperature region such as a firing furnace.

[Brief description of drawings]

FIG. 1 is a sectional view of a conventional insulating tube used for protecting a thermocouple, and FIG. 2 is a partial sectional view of the insulating tube of the present invention. 1 ... Substrate 3 ... Pyrolytic boron nitride film 4 ... Intermediate layer

Claims (1)

[Claims] 1. A heat-resistant insulating tube in which a pyrolytic boron nitride is coated on the outer surface of an insulating tube-shaped substrate made of graphite via an intermediate layer, wherein the intermediate layer has a thermal expansion coefficient with that of the graphite. It has an intermediate value with that of boron nitride, and SiC, B ₄ C
And a heat-resistant insulating tube comprising at least one selected from the group of randomly oriented boron nitride.