JP2023064826A - Composite thermal spray material, production method thereof, and electrode using the same - Google Patents

Abstract

To provide a composite thermal spray material capable of suppressing oxidation during thermal spraying.SOLUTION: A composite thermal spray material 1 is granulated by using a metal particle 2 with an oxide film 3 whose surface is oxidation-treated, and an oxide mineral 4. The metal particle 2 is Ni-Cr alloy, and the oxide mineral 4 is bentonite. The metal particle with an oxide film whose surface is oxidation-treated by being heated at 600°C-800°C for 1-3 hours, is formed, and the composite thermal spray material 1 is granulated by using the metal particle with the oxide film, and the oxide mineral.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a composite thermal spray material, a manufacturing method thereof, and an electrode using the same.

Thermal spraying is one of the methods of forming metal coatings. Metal particles for thermal spraying are introduced into a plasma flame, a combustion flame, or the like, given heat and kinetic energy, and ejected toward the surface of the substrate, which is a target. However, when thermally sprayed in the air, the metal particles are oxidized, and the properties of the metal particles may not be exhibited sufficiently in the thermal spray coating.

Therefore, Patent Document 1 discloses a thermal spray particle having a coating layer formed by a surface treatment agent on the surface of a base particle made of metal. As the surface treatment agent, one capable of forming a coating layer having an oxidation-inhibiting ability on the surface of the base particles is used. It is described that this prevents the base particles of the core from being oxidized even when exposed to a high-temperature oxidizing atmosphere during the thermal spraying process, and a good metal coating can be obtained.

JP 2010-133021 A

There is an electrically heated catalyst (EHC) as an exhaust purification device for purifying exhaust gas discharged from an engine of an automobile or the like. As an example of an EHC, a cylindrical carrier made of ceramics having a honeycomb structure on which a catalyst such as platinum or palladium is supported is electrically connected to the carrier, and a pair of electrodes are arranged opposite to each other on the outer peripheral surface of the carrier. Some have electrodes.

Each electrode comprises an underlayer, a metal foil, and a fixing layer. The underlayer is formed on the outer peripheral surface of the carrier over the entire electrode formation region. On the base layer, a plurality of metal foils extending in the circumferential direction of the carrier over the entire formation region of the base layer are arranged at predetermined intervals along the axial direction of the carrier.

As a fixing layer for fixing the metal foil to the base layer, a thermal spray coating made of a composite thermal spray material of metal and ceramics is formed so as to cover the metal foil. If the fixed layer is formed by thermal spraying in the atmosphere, there is concern that the metal will be oxidized and the performance of the electrode will be degraded.

Therefore, it is desired to prevent the metal particles from being oxidized during thermal spraying, and an inert gas such as Ar is used as a gas shield to reduce the oxygen content in the flame. However, there is a problem that the provision of the shielding device increases the cost of gas and increases the manufacturing cost. Moreover, Patent Document 1 is a technique for suppressing oxidation of thermal spray particles having metal as a base particle, and cannot be applied to a composite thermal spray material.

The present invention has been made in view of such problems, and an object of the present invention is to provide a composite thermal spray material capable of suppressing oxidation during thermal spraying, a method for producing the same, and an electrode using the same. That is.

A composite thermal spray material according to a first aspect of the present invention is granulated using metal particles with an oxide film, the surfaces of which are oxidized, and an oxide mineral.

In the composite thermal spray material according to the second aspect of the present invention, the metal particles are either Ni--Cr alloy or MCrAlY alloy (where M is at least one of Fe, Co and Ni).

In the composite thermal spray material according to the third aspect of the present invention, the oxide mineral is either bentonite or mica.

A method for producing a composite thermal spray material according to a fourth aspect of the present invention includes heating metal particles at 600° C. to 800° C. for 1 to 3 hours to form oxide film-coated metal particles having surfaces oxidized, A composite thermal spray material is granulated using the metal particles with oxide film and the oxide mineral.

In the method for producing a composite thermal spray material according to the fifth aspect of the present invention, the metal particles are produced by gas atomization.

An electrically heated catalyst device according to an aspect of the present invention includes a composite thermal spray material granulated using metal particles with an oxide film, the surfaces of which are oxidized, and oxide minerals, on a substrate. It includes a thermally sprayed coating formed by thermal spraying in the air and fixing the metal foil.

According to the present invention, it is possible to provide a composite thermal spray material capable of suppressing oxidation during thermal spraying, a method for producing the same, and an electrode using the same.

It is a figure which shows the structure of an electrically heated catalyst apparatus. It is a figure explaining the composite thermal-spraying material which concerns on embodiment. FIG. 4 is a diagram showing changes in the cross-sectional state of metal particles with oxidation treatment temperature. It is a figure which shows the elemental-analysis result of a metal particle. 4 is a graph showing structural analysis results of metal particles by XRD (X-ray Diffraction). It is a figure which shows the cross-sectional state of the metal particle surface when oxidation treatment is performed at 800 degreeC for 3 hours in air|atmosphere. FIG. 4 shows a composite thermal spray material granulated using metal particles and oxide minerals; It is a figure which shows the example thermal-spraying in air|atmosphere. FIG. 4 is a diagram showing a cross-sectional structure of a thermal spray coating thermally sprayed in the atmosphere using the composite thermal spray material according to the embodiment; It is a figure explaining the thermal-spraying material of a comparative example. FIG. 10 is a diagram showing an example of thermal spraying in a state where the plasma flame is gas-shielded; FIG. 6 is a diagram showing a cross-sectional structure of a thermal spray coating thermally sprayed in a gas shielded state using a thermal spraying material of a comparative example; FIG. 5 is a diagram showing a cross-sectional structure of a thermal spray coating thermally sprayed in the atmosphere using a thermal spray material of a comparative example;

Embodiments of the present invention will be described below with reference to the drawings. Equivalent components in each figure are denoted by the same reference numerals, and overlapping descriptions are omitted.

The composite thermal spray material according to the embodiment is used, for example, as an electrode of an electrically heated catalytic device that is provided on the exhaust path of an automobile or the like and purifies the exhaust gas emitted from the engine. First, an electrically heated catalyst device according to an embodiment will be described with reference to FIG. FIG. 1 is a diagram showing the configuration of an electrically heated catalyst device 100 according to an embodiment. As shown in FIG. 1, an electrically heated catalyst device 100 includes an electrode 10 and a carrier 20 .

The carrier 20 is a porous member that supports a catalyst such as platinum or palladium. The carrier 20 is made of conductive ceramics such as SiC (silicon carbide). The carrier 20 has a cylindrical outer shape and a honeycomb structure inside. The exhaust gas passes axially through the interior of the carrier 20 as indicated by the arrows.

A pair of electrodes 10 are provided on the outer peripheral surface of the carrier 20 so as to face each other. Power is supplied to each electrode 10 from a power source such as a battery. By supplying electric power to the pair of electrodes 10, the carrier 20 can be heated by applying current. Electrode 10 includes underlayer 11 , metal foil 12 and anchoring layer 13 .

The underlayer 11 is a thermal spray coating formed over both longitudinal ends of the carrier 20 . The underlayer 11 is in physical contact with and electrically connected to the carrier 20 . A metal foil 12 is provided on the underlying layer 11 . The metal foils 12 are extended in the circumferential direction of the carrier 20 over the area where the base layer 11 is formed, and a plurality of metal foils 12 are arranged at predetermined intervals along the axial direction of the carrier 20 . The metal foil 12 is made of metal such as Fe--Cr alloy.

The fixing layer 13 is a button-shaped thermal spray coating formed to cover the metal foil 12 to fix the metal foil 12 to the base layer 11 . A plurality of fixing layers 13 are arranged at predetermined intervals along the longitudinal direction of the metal foil 12 (the circumferential direction of the carrier 20). The fixing layer 13 is in physical contact with and electrically connected to the metal foil 12 and the underlying layer 11 . In the metal foils 12 adjacent to each other, the fixing layers 13 are arranged at different positions in the longitudinal direction of the metal foils 12 .

In the electrically heated catalyst device 100 , the catalyst supported on the carrier 20 is activated by electrically heating the carrier 20 with the pair of electrodes 10 . As a result, harmful substances such as unburned HC (hydrocarbon), CO (carbon monoxide), and NOx (nitrogen oxide) in the exhaust gas passing through the carrier 20 are purified by catalytic reaction.

The composite thermal spray material according to the embodiment is used for the base layer 11 and the fixing layer 13, which are thermal spray coatings. That is, the composite thermal spray material according to the embodiment is thermally sprayed to fix the metal foil 12 to the carrier 20 to form a thermal spray coating. Since the metal foil 12 is energized, the matrix of the thermal spray coating must be metal. The thermal spray coating also has a dispersed phase in the metal matrix to lower the Young's modulus. Note that the contents described in International Publication No. 2013/038449 can be appropriately applied to the thermal spray coating containing the metal matrix and the dispersion layer.

Here, with reference to FIGS. 10 and 11, problems of the comparative example will be described. FIG. 10 is a diagram explaining a thermal spray material of a comparative example. FIG. 11 is a diagram showing an example of thermal spraying in a state where the plasma flame is gas-shielded.

As shown in FIG. 10, the thermal spray material 1A of the comparative example is obtained by kneading metal particles 2 forming a metal matrix and particles of an oxide mineral 4 forming a dispersed phase using a polymeric adhesive 5 as a medium. It is compounded by the embedded granulation method. A thermal spray coating is formed by plasma thermal spraying using this thermal spray material. As described above, in the electroheating type catalyst device, the metal foil for energization is fixed with a sprayed coating made of a sprayed material that is a composite of metal and oxide mineral. During thermal spraying, if the metal in the thermal spray material is oxidized, the electrical resistance of the thermal spray coating increases, making electrical heating difficult. Also, when a Ni--Cr alloy is used as the metal, the Cr component on the metal surface decreases due to oxidation during thermal spraying, so the oxidation resistance at high temperatures decreases, and the thermal spray coating deteriorates due to oxidation.

In order to suppress the metal particles contained in the thermal spray material from being oxidized during flight through the plasma flame, a low-pressure thermal spraying method or, as shown in FIG. Gas shield method is adopted. However, the low-pressure thermal spraying method is costly in terms of equipment such as a vacuum pump. Further, in the gas shield method shown in FIG. 11, since it is necessary to use a large amount of inert gas such as Ar so as to surround the plasma flame, gas costs are high. Thus, any method has the problem that the production cost of thermal spraying becomes very high.

Accordingly, the inventors devised the following composite thermal spray material. A composite thermal spray material according to an embodiment will be described with reference to FIG. FIG. 2 is a diagram illustrating a composite thermal spray material according to an embodiment. As shown in FIG. 2 , the composite thermal spray material 1 according to the embodiment uses metal particles 2 with oxide films 3 in which the surfaces of the metal particles 2 are oxidized, and oxide minerals 4 to form a polymer-based material. is granulated using the adhesive 5 as a medium.

The metal particles 2 form a thermal spray coating matrix for energizing the metal foil 12 . In order to withstand use at high temperatures, the metal particles 2 are Ni—Cr alloys (where the Cr content is 20 to 60% by mass), MCrAlY alloys (where M is At least one of Fe, Co, and Ni) is preferable. The Ni—Cr alloy and MCrAlY alloy may contain other alloying elements. Note that the granulated composite thermal spray material may contain the metal particles 2 with the oxide film 3 remaining.

The oxide mineral 4 constitutes a dispersed phase for reducing the Young's modulus of the metal matrix. As the oxide mineral 4, one having a layered structure and containing an oxide such as SiO ₂ or Al ₂ O ₃ as a main component is used. Specifically, the oxide mineral 4 is preferably made of bentonite, mica, or a mixture thereof.

An example in which a Ni-50Cr alloy is used as the metal particles 2 and bentonite is used as the oxide mineral 4 will be described below. A Cr passivation film on the surface is known as an anticorrosive action of stainless steel. The inventors of the present invention thought that a similar effect could be expected for suppressing oxidation of Ni-50Cr particles by thermal spraying, and studied the oxidation phenomenon of Ni-50Cr particles in the air.

Almost no oxide film is formed on the surface of the Ni-50Cr particles produced by the gas atomization method. Therefore, the state of formation of the oxide film on the surface of the Ni-50Cr particles due to changes in the oxidation treatment conditions in the atmosphere was investigated. FIG. 3 shows changes in the cross-sectional state of Ni-50Cr particles when the oxidation treatment temperature is 600°C, 700°C, 800°C, 900°C and 1075°C. FIG. 4 is a diagram showing the results of elemental analysis of Ni-50Cr particles without oxidation treatment and after oxidation in air at 600° C., 700° C., and 800° C. FIG.

As shown in FIGS. 3 and 4, no oxide film was observed on the surface of the Ni-50Cr particles that had not been oxidized in the initial stage. It was confirmed that The higher the temperature, the thicker the oxide film, but at 900° C. or higher, particles adhered to each other. For this reason, the oxidation treatment temperature is preferably 600° C. to 800° C. in terms of production.

FIG. 5 is a graph showing the structural analysis results of Ni-50Cr particles by XRD (X-ray Diffraction). As shown in FIG. 5, it was confirmed that the oxidized Ni-50Cr particles contained Cr oxide (Cr ₂ O ₃ ).

As an example, Ni-50Cr particles obtained by the gas atomization method were subjected to oxidation treatment in the atmosphere at 800° C. for 3 hours, thereby adding Cr oxide (Cr ₂ O ₃ ) to the surface of the Ni-50Cr particles by about 0.0. A thickness of about 2 to 1 μm was formed. FIG. 6 shows the cross-sectional state of the Ni-50Cr particles at this time. FIG. 7 shows a photograph of a composite thermal spray material granulated using Ni-50Cr particles with a Cr oxide film and bentonite particles.

When a composite thermal spray material using such Ni-50Cr particles with an oxide film is put into a plasma flame, the Cr oxide film on the surface of the Ni-50Cr particles acts as a barrier, suppressing the oxidation of the Ni-50Cr particles and suppressing the thermal spray coating. The total amount of oxides can be reduced. Therefore, the manufacturing cost can be reduced without using a large amount of shielding gas.

Next, the oxidation state of the thermal spray coating of the embodiment and the thermal spray coating of Comparative Examples 1 and 2 were compared. In the embodiment and Comparative Examples 1 and 2, the particle size of the primary particles (raw materials) of the Ni-50Cr alloy and the bentonite was 10 to 45 μm. again. Ni-50Cr alloy: Bentonite was granulated at a ratio of 60 wt%:40 wt%, and the particle size of the formed secondary particles (powder) was adjusted to 30 to 120 µm.

In the embodiment, a composite thermal spray material obtained by granulating Ni-50Cr particles heated at 800° C. for 3 hours and bentonite was used. In the embodiment, as shown in FIG. 8, plasma spraying was performed in the air.

In Comparative Examples 1 and 2, as described with reference to FIG. 10, a thermal spray material obtained by granulating bentonite and Ni-50Cr particles without oxidation treatment was used. In Comparative Example 1, as shown in FIG. 11, plasma spraying was performed using a gas shield method. In Comparative Example 2, plasma spraying was performed in the air.

Thermal spraying conditions for all of the embodiment and Comparative Examples 1 and 2 were as follows.
・Plasma gas: Ar—H ₂ , gas flow rate Ar: 60 L/min, H ₂ : 10 L/min
・Plasma current: 600A, plasma voltage: 60V
・ Powder supply amount: 30 g / min
・Spraying distance: 150mm

In addition, about the comparative example 1, the following was added to the thermal spraying conditions.
・Ar gas shield: flow rate 50 m ³ /Hr

FIG. 9 (Embodiment), FIG. 12 (Comparative Example 1), and FIG. 9, 12, and 13 were subjected to image processing to measure the area ratio of gray oxide present in the white metal as the oxide ratio in the sprayed coating.

A comparison of FIGS. 9 and 12 reveals that the thermal spray coating of the embodiment and the thermal spray coating of Comparative Example 1 have substantially the same oxide ratio. 9 and 13, it was found that the oxide ratio in the thermal spray coating of the embodiment was reduced to about 1/4 of the oxide ratio in the thermal spray coating of Comparative Example 2.

Thus, in the embodiment, the target oxide rate could be achieved without using an expensive gas shield. In addition, the cost of oxidizing the metal particles is 1/10 or less of that of gas shielding. Therefore, according to the present embodiment, it is possible to achieve both reduction in overall manufacturing cost and quality assurance.

Furthermore, using the composite thermal spray material according to the embodiment, the electrically heated catalyst device 100 in which the electrode 10 was formed was subjected to thermal durability evaluation and current application evaluation. It was confirmed that no abnormality such as oxidation deterioration of the thermal spray coating in the electrode 10 occurred.

Here, a method for manufacturing a composite thermal spray material according to the embodiment will be described.
First, a Ni—Cr alloy (where the Cr content is 20 to 60% by mass) or an MCrAlY alloy (where M is at least one of Fe, Co, and Ni) constituting a metal matrix is formed by a gas atomization method or the like, Metal particles 2 having a small specific surface area are granulated. The metal particles 2 preferably have a large particle size from the viewpoint of suppressing oxidation during thermal spraying, and preferably have a small particle size in order to uniformly disperse the dispersed phase in the thermal spray coating.

Next, the metal particles 2 are heated in the atmosphere at 600° C. to 800° C. for 1 to 3 hours to oxidize the surfaces of the metal particles 2 . Thereby, the oxide film 3 can be formed so as to cover the surfaces of the metal particles 2 .

Also, approximately spherical particles of the oxide mineral 4 made of bentonite or mica that constitute the dispersed phase are granulated by a spray drying method or the like. Bentonite has the property of absorbing moisture and swelling, and mica has water of crystallization. Therefore, the particles are sintered at a temperature of 1000 to 1100° C. in a hydrogen atmosphere to remove moisture in the particles.

Then, the metal particles 2 with an oxide film and the oxide mineral 4 are compounded by a kneading granulation method using a polymeric adhesive 5 as a medium. After that, it can be sintered at a temperature of 1000 to 1100° C. in a hydrogen atmosphere to produce a composite thermal spray material.

As described above, according to the embodiment, the metal particles of the raw material are oxidized in advance in the air to form an oxide film on the surface, thereby eliminating oxidation in the thermal spray coating without using a costly gas shield. can be reduced to the same extent.

By using such a composite thermal spray material to fix the metal foil of the electrically heated catalyst device, it is possible to suppress an increase in the electrical resistance of the thermal spray coating. In addition, it is possible to improve oxidation resistance at high temperatures, and to suppress oxidation deterioration of the thermal spray coating.

It should be noted that the present invention is not limited to the above embodiments, and can be modified as appropriate without departing from the scope of the invention.

REFERENCE SIGNS LIST 1 Composite Thermal Spray Material 2 Metal Particle 3 Oxide Film 4 Oxide Mineral 5 Adhesive 10 Electrode 11 Base Layer 12 Metal Foil 13 Fixed Layer 20 Carrier 100 Electric Heating Catalyst Device

Claims (6)

granulated using metal particles with an oxide film, the surface of which is oxidized, and an oxide mineral,
Composite thermal spray material. The metal particles are either a Ni—Cr alloy or an MCrAlY alloy (where M is at least one of Fe, Co, and Ni),
The composite thermal spray material of claim 1. The oxide mineral is either bentonite or mica,
A composite thermal spray material according to claim 1 or 2. heating the metal particles at 600° C. to 800° C. for 1 to 3 hours to form oxide film-coated metal particles whose surfaces are oxidized;
granulating a composite thermal spray material using the oxide film-coated metal particles and the oxide mineral;
A method for manufacturing a composite thermal spray material. The metal particles are produced by a gas atomization method,
The manufacturing method of the composite thermal spray material according to claim 4. A metal foil is fixed on a base material by thermally spraying a composite thermal spray material granulated using metal particles with an oxide film, the surface of which is oxidized, and an oxide mineral, in the air. including a thermal spray coating that
Electrodes for electrically heated catalytic converters.

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