JPH05299156A - High-melting point metal heater and its manufacture - Google Patents

Abstract

PURPOSE:To provide a high-melting point metal heater capable of being used for a long time in the oxidizing atmosphere. CONSTITUTION:The base material of a heater is made of at least one kind of metal or alloy of W, Re, Mo, Ta, Nb, Ni, Cr, and a film mainly made of zirconia is formed on the surface of the base material. A sol containing a zirconium element is coated on the surface of the base material of the heater, then it is heat-treated at 200 deg.C or above. The heater capable of being used for a longer time than high-melting point metal heaters used in the past is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory metal heater which can be used for a long time even in an oxidizing atmosphere and a method for producing the same.

[0002]

2. Description of the Related Art In the steel industry, when a refractory is used, it is sometimes necessary to preheat the refractory so that cracks or cracks do not occur in the refractory due to a rapid thermal change. .. For example, especially in direct contact with molten steel,
In the case of the tip of the immersion nozzle where a sudden temperature change occurs, in such a case, the refractory is often heated to a high temperature of about 1500 ° C, and a gas burner or a high melting point metal heater is often used for heating. It is used. However, it is difficult to heat the gas burner to a high temperature of about 1500 ° C., and the efficiency is not very good. Even with a high melting point metal heater, oxidation is very likely to occur, and it has been difficult to use it for a long time.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to improve the oxidation resistance of a refractory metal heater capable of heating more efficiently than the above gas burner, and to improve the oxidation resistance in an oxidizing atmosphere. The present invention also provides a refractory metal heater that can be used for a long time and a method for manufacturing the same.

[0004]

According to the present invention, the base material of the heater is made of at least one metal or alloy of W, Re, Mo, Ta, Nb, Ni and Cr, and the surface of the base material is mainly zirconia. A high melting point metal heater characterized by having a film made of W, Re, Mo, T
A high melting point metal heater characterized by coating a surface of a base material of a heater made of at least one metal or alloy of a, Nb, Ni and Cr with a sol containing zirconium element and then heat-treating at 200 ° C. or higher. Is a manufacturing method.

The present invention will be described in detail below. In the present invention, the purity of refractory metal such as tungsten (W), rhenium (Re), molybdenum (Mo), tantalum (Ta), niobium (Nb), nickel (Ni), chromium (Cr), or an alloy thereof is high. Although it is not particularly limited, it is preferably 95% or more in order to prevent the melting point from lowering, and is preferably processed into a mold such as a wire or a flat plate for use as a heater. The composition of the alloy is not particularly limited as long as it is an alloy based on the above-mentioned refractory metal, but examples of suitable alloys include tungsten molybdenum, tungsten rhenium, and nichrome.

The coating mainly formed of zirconia formed on the surface of the heater substrate includes not only zirconia alone but also zirconia partially stabilized or stabilized by so-called stabilizers such as yttrium, magnesium, calcium and cerium. It is meant to include.

The sol containing zirconium element used to form the oxidation resistant coating on the surface of the heater substrate may be a sol prepared by any method as long as it contains zirconium element. For example, a sol made by hydrolysis of zirconium oxychloride known as a known method, a sol made of zirconium alkoxide, or the like can be used.
A sol or the like in which zirconium alkoxide is hydrolyzed with hydrogen peroxide solution containing an acid, a transparent precursor thereof is evaporated to dryness, and dispersed again in an organic solvent, is preferable. This is because the solvent is an organic substance, so that it dries quickly, the coating surface becomes smooth, and the adhesion strength is higher than that in the case of water such as a sol produced by hydrolysis of zirconium oxychloride.

By heating the refractory metal heater of the present invention by heat treatment or energization and raising the temperature, the coating film becomes crystalline zirconium oxide, but zirconium oxide, that is, zirconia, has a melting point of 2715.
Since it has a high melting point among those of ℃ and ceramics and is an oxide, it can be used even in an oxidizing atmosphere at high temperature. Further, since the thermal expansion coefficient of zirconia is relatively close to that of metal, cracking and peeling are less likely to occur. That is, the sol used to form the oxidation resistant coating on the surface of the heater substrate needs to contain the element zirconium.

A sol containing magnesium, calcium, yttrium or cerium or a salt thereof can be added to the sol as a stabilizer. From the viewpoints of economic efficiency, price, strength, etc., a sol having a composition of zirconia partially stabilized with magnesium is desirable.

As a method for coating the substrate sol of the heater made of the metal, known methods such as brush coating, dip coating and spin coating can be used. The film thickness of the coating is affected by the usage environment of the heater, etc., but it is desirable that the film thickness is approximately 5 μm or more. However, since dip coating and spin coating have a thin coating thickness of about 0.5 μm, drying and coating may be repeated several times to increase the coating thickness to a desired thickness.

The coated sol is subjected to a heat treatment in order to improve the adhesion between the coating film and the substrate.
The treatment temperature at this time varies depending on the type of metal and the type of sol, but a temperature of 200 ° C. or higher is required. However, if heat treatment is performed at an excessively rapid heating rate, cracks may occur, so it is desirable that the heating rate be about 200 ° C./h or less. The high melting point metal heater manufactured by the above method is
It can be used for a long time even in an oxidizing atmosphere.

[0012]

[Function] The base material of the heater is W, Re, Mo, Ta, N
In a high melting point metal heater, which is made of at least one metal or alloy of b, Ni, and Cr and has a zirconia coating formed on the surface of the substrate, the zirconia coating film on the surface of the substrate is , Melting point 2
It has a high melting point of 715 ° C. among ceramics, and since it is an oxide, it can be used for a long time even in an oxidizing atmosphere at high temperature. Furthermore, since the thermal expansion coefficient of zirconia is relatively close to that of metal, cracking and peeling are less likely to occur.

[0013]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 100 g of zirconium oxychloride was dissolved in 200 ml of distilled water and kept at a temperature of 80 ° C. for about 1 day with stirring, and zirconium oxychloride was hydrolyzed to prepare a zirconia sol. Yttrium nitrate was added thereto so that the composition of the coating after heat treatment would be 30 mol% yttria-zirconia, and the amount of solvent (water) was adjusted to adjust the viscosity of the sol to 10 cp.
It was adjusted to be about s. Using the sol, a W wire having a purity of 99.5% and a diameter of 0.5 mm was coated. The method at that time was a dip coating method, and the pulling rate was 2 mm / s. Since the film thickness was about 0.5 μm in one coating, after repeating dip coating and drying 10 times, the temperature was raised to 500 ° C to improve the adhesion with the substrate, and the high melting point metal heater was used. And The coating was partially stabilized zirconia and had a thickness of about 6 μm.

When the prepared W wire heater was wound around the tip of the immersion nozzle made of refractory and used for preheating,
It was possible to raise the temperature to 1500 ° C. The immersion nozzle was pulled out from the heater, and the cross section of the heater was observed with an optical microscope. No discoloration due to oxidation was observed in the W metal inside. No cracking or peeling was observed in the coating film.

Example 2 5 mol of zirconium normal butoxide (commercial 90% butanol solution) was mixed with hydrogen peroxide contained in hydrogen peroxide solution (containing 30 wt% of hydrogen peroxide) in an amount of 10 mol times that of zirconium normal butoxide. Hydrogen peroxide water was added to the mixture, and nitric acid was immediately added to the zirconium normal butoxide in an amount of 0.75 mol times. After vigorous stirring, it became a transparent zirconia sol precursor after about 1 hour. The precursor was evaporated to dryness with an evaporator and ethanol was added to obtain a zirconia sol. Magnesia sol (brucite sol) was heat-treated on the zirconia sol to prepare a sol having a composition in which the coating film was 8 mol% magnesia-zirconia, that is, partially stabilized zirconia. This sol was adjusted to a viscosity of about 100 cps by adjusting the amount of ethanol, and brushed 5 times to give Nb having a purity of 99.9%.
The wire was coated. 200 ° C after drying for 1 day
The temperature was raised to increase the adhesion to the metal, and a high melting point metal heater was obtained. When conducting a current test in the atmosphere using the heater, the temperature of the heater rises to 1800 ° C.
No change in electric current or disconnection due to oxidation did not occur even when electricity was applied for 50 kV for a time.

Comparative Example 1 A commercially available W wire having a purity of 99.5% was subjected to a 50 kV energization test. Ten minutes later, after the temperature rose to about 1000 ° C., sparks occurred from the W wire and the wire was broken. As a result of observing the cross section with an optical microscope, discoloration occurred due to oxidation, and the strength was so low that it could be easily broken by hand.

[0017]

According to the present invention, a heater that can be used for a longer period of time than a conventional high melting point metal heater is formed by coating a surface of a substrate of a heater with a sol containing elemental zirconium and then performing heat treatment. It can be manufactured by forming a coating mainly composed of zirconia.

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[Procedure amendment]

[Submission date] June 3, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

[0013]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 100 g of zirconium oxychloride was dissolved in 200 ml of distilled water and kept at a temperature of 80 ° C. for about 1 day with stirring, and zirconium oxychloride was hydrolyzed to prepare a zirconia sol. Yttrium nitrate was added thereto so that the composition of the coating after heat treatment would be 3.0 mol % yttria-zirconia, and the amount of solvent (water) was adjusted to adjust the viscosity of the sol to 10
Adjusted to be about cps. Using the sol, a W wire having a purity of 99.5% and a diameter of 0.5 mm was coated. The method at that time was a dip coating method, and the pulling rate was 2 mm / s. Since the film thickness was about 0.5 μm in one coating, after repeating dip coating and drying 10 times, the temperature was raised to 500 ° C to improve the adhesion with the substrate, and the high melting point metal heater was used. And The coating was partially stabilized zirconia and had a thickness of about 6 μm.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tsuneharu Kanematsu 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Co., Ltd. Technology Development Division (72) Inventor Kazuo Hamai 20-1 Shintomi, Futtsu-shi, Chiba Shinnihon Steel Engineering Co., Ltd.

Claims (2)

[Claims] 1. The heater base material is W, Re, Mo, T
A refractory metal heater, which is made of at least one metal or alloy of a, Nb, Ni, and Cr and has a coating film mainly made of zirconia formed on the surface of the base material. 2. The base material of the heater is W, Re, Mo, T
A refractory metal characterized in that the surface of a substrate of a heater made of at least one metal or alloy of a, Nb, Ni and Cr is coated with a sol containing elemental zirconium and then heat-treated at 200 ° C. or higher. Heater manufacturing method.