JPH08158033A - Production of fine-structure thick film material and device therefor - Google Patents

Abstract

PURPOSE: To form a relatively thick film having uniform fine structure simultaneously with the production of a superfine particle. CONSTITUTION: In a plasma furnace fitted with a high-frequency plasma torch 1 using a gaseous mixture of an inert gas with gaseous hydrogen so that the plasma flame 2 is radiated into the furnace, a raw material is gasified by charging the powdery raw material to the plasma generated by the plasma torch 1. The gasified components are associated with each other to form superfine particles having <=1μm particle diameter in the furnace. An aerosol in the furnace which is accompanied with the superfine particles is jetted from a nozzle 18 as a jet stream and the jet stream of the aerosol is projected to a substrate 24. As a result, a sticking layer of the superfine particles is formed on the substrate 24 and is sintered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for forming a thick film having a fine structure by using ultrafine particles, particularly in the field of film formation of metals, ceramics and the like.

[0002]

2. Description of the Related Art Conventionally, plasma spraying has been well known as a film forming method for ceramics or metals. This is a method in which part or all of the raw material particles are melted by plasma and sequentially laminated on the base material, but since the melted particles momentarily solidify on the base material, the laminated coating tends to be porous. is there. Further, since the joining of the base material and the thermal spray coating depends only on the physical meshing, the adhesion strength between the two is not so strong. Furthermore, the raw material particles are hardly evaporated due to the structural limitation of the spray gun, and the molten particles collide with the base material at a high speed, and the particles are crushed to form a laminated body, thus forming a microscopic microstructure. Was practically difficult.

As a film forming method replacing the plasma spraying method, Japanese Patent Publication No. 3-14512 discloses that ultrafine particles (having a particle size of 1 μm or less) are sprayed together with a carrier gas from a small diameter nozzle onto a base surface. A method has been proposed in which the ultrafine particles are attached to a base surface without using an adhesive to form a continuous or discontinuous film having a thickness.

Similarly, in Japanese Patent Laid-Open No. 61-90735, two or more kinds of ultrafine particles are mixed in a carrier gas, and the mixed air stream is sprayed on the adherend, and the aggregate pressure of these ultrafine powders is produced by the spray pressure. A method for producing a green compact is described, in which the green compact is formed, and the green compact is pressed as it is or in a tightly packed state with or without heating.

[0005]

When manufacturing nanomaterials, dispersion-strengthened ceramics, functionally graded materials (materials having different composition ratios in the film thickness direction) using a film-forming technique, the uniformity and physical properties of the structure are obtained. From the viewpoint of improvement, it is required to have a film forming technique capable of controlling a fine structure (particularly, a particle size on the order of μm or less). As mentioned above, the plasma spraying method cannot satisfy this requirement at present.

The above-mentioned Japanese Patent Publication No. 3-14 which teaches to spray ultrafine particles of 1 μm or less with a carrier gas.
According to the methods disclosed in Japanese Patent Laid-Open No. 512 and Japanese Patent Application Laid-Open No. 61-90735, since the raw material is ultrafine particles, a deposited layer of ultrafine particles is formed on the substrate, and its structure is also a fine structure in which ultrafine particles are aggregated. It should be.

However, the proposals in these publications require the use of a nozzle having a very small diameter in order to obtain the required injection pressure. For this reason, for example,
No. 14512, the diameter is 0.01 mm to 1 mm,
It is recommended to use a small diameter nozzle of preferably 0.1 mm, and Japanese Patent Application Laid-Open No. 61-90735 also discloses the use of a nozzle having a diameter of 0.6 mm.

When spraying using such a small diameter nozzle, the spraying area is limited, and the line width obtained when spraying by moving the substrate side or the nozzle side is very small. Become. For example, in the former publication, it is said that a linear film having a diameter of 0.1 mm, which is almost the same as the nozzle diameter, can be obtained, and the line width of 80 to 110 μm is exemplified in the examples. There is a limit in increasing the film thickness of such a thin film, and in fact, the film having a thickness of about 2 μm is also illustrated in the examples.

In addition, in the method of injecting these ultrafine particles with the carrier gas, the ultrafine particles produced in advance must be injected using a special device. That is, the production of ultrafine particles and the film formation using the same are different technologies, and both cannot be performed at the same time. As a result, there are problems that oxidation and agglomeration occur during the storage and handling of ultrafine particles, and that the operation becomes complicated.

When the ultrafine particles are dispersed in such carrier gas, the smaller the particle size of the dispersed particles, the greater the effect of the surface area, and the effect of the surface adsorbed substance or electrostatic energy is greater. Since the particles easily aggregate, it is very difficult to obtain a uniform structure of dispersed particles even in the obtained film.

The present invention is intended to solve such a problem, and an object of the present invention is to provide a method and apparatus for forming a relatively thick film having a uniform microstructure simultaneously with the production of ultrafine particles. is there.

[0012]

According to the present invention, in a plasma furnace in which a high-frequency plasma torch utilizing a mixed gas of an inert gas and hydrogen gas is installed so that its plasma flame radiates into the furnace, A powdery raw material is introduced into the plasma generated by the torch, the raw material is gasified, and the gasified components are associated with each other so that the particle diameter is 1 μm.
Ultra fine particles of m or less are generated in the plasma furnace, aerosol in the furnace accompanied by the ultra fine particles is jetted from a nozzle as a jet flow, and the jet flow of the aerosol is projected onto the substrate to supercharge it on the substrate. Forming an adhesion layer of particles,
Provided is a method of making a microstructured thick film material comprising sintering this adhesion layer.

Further, according to the present invention, as an apparatus for advantageously carrying out the above method, a high-frequency plasma torch is installed so that its plasma flame is radiated into the furnace, and the plasma torch is generated. The powder raw material supply device for continuously supplying the powdery raw material into the plasma, the exhaust path leading from the exhaust port provided in the plasma furnace to the exhaust device, and the aerosol flow in this exhaust path are contracted and exhausted as a jet flow. Provided is an apparatus for producing a fine texture thick film material, comprising a nozzle for injecting into a path and a substrate installed in the exhaust path so as to face the nozzle opening.

[0014]

When the powdery raw material is put into the plasma generated by the plasma torch, the raw material is instantly gasified. The gasified components are associated with each other in the process of diffusing into the furnace from the rear end of the plasma flame together with the plasma gas, and the particle size is 1 μm.
Ultra fine particles of m or less are formed and diffused into the atmospheric gas to form an aerosol.

When the inside of the plasma furnace is exhausted by the exhaust device, this aerosol flows out from the plasma furnace toward the exhaust device as exhaust gas, but a nozzle is provided in the middle of this exhaust passage to pass through the exhaust passage by this nozzle. When the flowing aerosol flow is converged and ejected from the nozzle port, an aerosol jet flow is obtained.

By colliding the jet of the aerosol with the substrate, the ultrafine particles in the aerosol adhere to the substrate and a film made of the ultrafine particles is formed on the substrate.

In this case, even if a nozzle having a relatively large diameter is used as the nozzle for generating the jet of aerosol, the ultrafine particles in the aerosol can be attached onto the substrate. Therefore, the film thickness of the adhesion layer can be increased.
Empirically, it is possible to use a nozzle having a diameter of up to about 30 mm.

Further, the adhering area can be freely expanded by projecting the jet stream onto the substrate while moving the nozzle or the substrate.

As the raw material powder supplied to the plasma torch, powders of metals, alloys, inorganic substances, ceramics or the like are used depending on the composition of the intended thick film material. At that time, if a powder mixture of two or more components is supplied to the plasma torch, a multi-component thick film material is obtained. When the composition ratio of such a mixed powder is supplied to the plasma torch while changing with time, the composition of the ultrafine particles in the generated aerosol also changes with time. Gradient composition films having different component ratios can be obtained.

The thick film thus produced can then be sintered at a sintering temperature according to its composition to obtain a very reliable and strong film. In the case of a multi-component system, A fine texture thick film in which each ultrafine particle is uniformly dispersed is obtained.

[0021]

EXAMPLE FIG. 1 shows the apparatus used to carry out the method of the present invention.

This apparatus comprises a high frequency plasma torch 1,
It has an ultrafine particle production unit for continuously producing ultrafine particles of 1 μm or less by using a plasma furnace 3 attached so that the plasma flame 2 radiates into the furnace. The high frequency plasma torch 1 has an RF coil on the outer circumference, and a plasma gas supply port 5 and a powder supply port 6 are provided on the top of the RF coil via cooling means. As the plasma gas, a mixed gas of Ar gas and hydrogen gas is used, and in this example, 50 k is used as a heat source.
High frequency of W is used. A direct current (DC) plasma jet may be used as long as it is a material that allows contamination of the electrode material.

A raw material powder is continuously supplied from a powder supply device 7 to the powder supply port 6 of the plasma torch 1 by a carrier gas. The powder supply device 7 is of a dispersion feeder type having a rotary hopper 9 and a carrier gas injection nozzle 10 in a closed hopper 8. The rotating container 9 in the hopper is connected to a rotating shaft of a motor 12 via an electronic balance 11, and the number of rotations thereof can be freely changed.
The raw material powder contained in the rotary container 9 is imparted with a rotary motion by the rotation of the container while the gas injection nozzle 10
It is further fluidized by the carrier gas (Ar) injected from.

The powder take-out pipe 13 is inserted in the powdered raw material in the fluidized state, and when the number of revolutions of the container 9 is changed, the open end of the powder take-out pipe 13 is changed according to the increase or decrease in the number of revolutions. The number of colliding particles increases or decreases. As a result, the powder supply amount can be adjusted freely.

In the illustrated example, two powder supply devices 7 are arranged side by side, and a mixer 14 is attached in the middle of each powder extraction pipe 13 so that two types of powder flow fed into each powder extraction pipe 13 are provided. In this example, the powders are merged and supplied to the powder supply port 6 of the plasma torch. These two powder supply devices 7
In the above, if the number of rotations of the rotary container 9 is controlled respectively, the mixing ratio of the two kinds of powders can be adjusted freely. Therefore, the component ratio of the powder raw material charged into the plasma flame 2 of the plasma torch 1 can be changed with time.

The plasma furnace 8 is an airtight furnace having an exhaust port 16, and while the plasma torch 1 is operating to generate ultrafine particles, a fluid in the furnace (atmosphere gas is accompanied by ultrafine particles through the exhaust port 16). Aerosol) is continuously discharged. The discharge of the aerosol is performed through an exhaust path communicating with the exhaust device 17, and a nozzle 18 for forming a jet of aerosol is provided in the middle of the exhaust path.

In the illustrated example, a cooler 19 and a laminating chamber 20 are provided in the exhaust path from the exhaust port 19 of the plasma furnace to the exhaust device 17. The cooler 19 is a container having a water cooling jacket (not shown), and the aerosol is cooled by the passage of the aerosol therein. Further, a surface treatment agent supply device 15 is attached to the cooler 19 so that the surface treatment agent can be introduced into the aerosol as required.

The stacking chamber 20 comprises a closed container to which an aerosol carrying-in pipe 21 and an exhaust pipe 22 are connected. A nozzle 18 is attached to the inner end of the chamber of the aerosol carrying-in pipe 21. 23 are provided. In the illustrated example, the nozzle 18 has its nozzle port oriented vertically downward in the chamber 20, and the substrate 2 in the chamber 20 below this nozzle port.
A substrate installation table 23 is installed so that the 4 can be set horizontally. The installation table 23 can be moved horizontally and vertically. Further, in the chamber 20, a cassette type filter 25 is attached to the exhaust inlet of the exhaust pipe 22. The aerosol transfer path from the exhaust port 19 of the plasma furnace to the nozzle 18 is composed of a water-cooled double tube.

According to the apparatus of the present invention having the above configuration,
The ultra-fine particles generated in the plasma furnace 3 are entrained in the atmosphere gas as they are generated to form an aerosol flow, and this aerosol flow is continuously jetted as a jet flow from the nozzle 18 toward the substrate 24. As a result, the substrate 24
The ultrafine particles are deposited on the upper surface to form a thick film.

In this case, in order to stack the ultrafine particle aerosol in a thick film (for example, 500 to 3000 μm), it is necessary that the ultrafine particles in the aerosol flow at a high speed to some extent and the aerosol flow is laminar. That is, the ultrafine particles suspended in the aerosol are accelerated in the nozzle part and given the kinetic energy necessary for thick film lamination, and further diffuse in the open system and collide with the substrate to lose the kinetic energy and deposit and deposit. However, it is essential that the nozzle diameter be large to some extent in order to stack in a large area.

As shown in the following experimental example, 10 mmφ
10 mm at a flow rate of about 30 m / min using the nozzle
It was possible to stack in the area of φ. When the nozzle diameter is smaller than 3 mm, the flow velocity of the aerosol becomes too high, and when the aerosol collides with the base material, there is a possibility that the superfine particle layer already laminated is blown off. Further, when the nozzle diameter is larger than 30 mm, it is impossible to give kinetic energy for superfine particles to be densely stacked. Therefore, in the device of the present invention, the nozzle diameter is 3 to 30 mm, preferably 5 to 3 mm.
The thickness is preferably 0 mm, and a thick film having an area corresponding to this diameter can be formed. When laminating in a larger area than this, it can be dealt with by appropriately moving the substrate side or the nozzle side.

The behavior of the formation of ultrafine particles by this aerosol will be described below with reference to a typical test example manufactured using this apparatus.

[Operating Conditions] Plasma: RF plasma torch of 50 kW Plasma gas: Mixed gas of (Ar 95% + hydrogen 5%) (100 liters / minute) Carrier gas for carrying the raw material powder: Ar gas (2 liters / minute) Nozzle 18 diameter: 10 mmφ Aerosol flow velocity ejected from nozzle 18: Approximately 30 m / min Here, 5% hydrogen gas is added to the plasma gas because the pinch effect due to the addition of hydrogen gas is used to increase the plasma density. This is to allow it.

[Test Example 1]

Film Forming Test of Finely Dispersed Zirconia Alumina In order to improve the reliability of relatively inexpensive alumina ceramics, studies have been conducted to add high toughness zirconia. As an example of achieving a fine structure according to the present invention, an example in which this fine zirconia uniformly dispersed alumina is experimentally manufactured is shown below.

The alumina raw material powder introduced into the plasma is high-purity alumina (AL160SG) manufactured by Showa Denko KK
1) was used. As the zirconia particles to be dispersed, Yttria partially stabilized zirconia (TZ3Y) manufactured by Tosoh Corporation was used. These raw material powders of alumina and zirconia were weighed at 80:20 (weight ratio), pre-mixed using a V-type mixer, and then fed into the plasma at a feed rate of the mixed powder of 1 g / min by the above-mentioned raw material powder feeder. Introduced to. As a result, a mixed ultrafine particle aerosol in which alumina and zirconia were finely dispersed at an ultrafine particle level (1 μm or less) was generated.

Under the above-mentioned mixed powder supply rate, the concentration was maintained such that the raw material powder particles melted in the high temperature plasma did not adhere to each other to form large particles. And
The raw material powder introduced under these conditions instantly melts from the powder surface in high-temperature plasma, then evaporates from the powder surface, and the vapor is recrystallized by rapid cooling, resulting in ultrafine particles. One of the features of this process is
Since it undergoes a step of instantly evaporating and recrystallizing in plasma,
The composition of the obtained ultrafine particles is the same as that of the raw material powder introduced, and it is possible to obtain uniformly mixed ultrafine particles.

Due to the viscosity of the melt, for example, in the case of alumina or the like, the generated ultrafine particles may be bonded to each other on the surface and may have a fibrous form. Due to causes such as friction with gas,
In some cases, the obtained ultrafine particles are easily charged and aggregate. Therefore, in this example, by bubbling argon gas into ethanol, argon gas containing a very small amount of ethanol vapor was mixed into the aerosol,
Aggregation was prevented by modifying the surface of the ultrafine particles.
As a result, uniform dispersion became very good.

Alumina-zirconia mixed ultrafine particle aerosol generated in the plasma furnace was jetted from the nozzle 18 of the apparatus onto the alumina substrate to prepare a compact having a thickness of about 10 mmφ × 3 mm. Then remove it from the device,
Sintering was performed at 1600 ° C. for 3 hours in the air.

An EMPA image of the obtained thick film sample is shown in FIG. In the figure, EMPA is observed in white small dots.
Is a portion where the characteristic X-ray of zirconium according to is detected. From FIG. 2, it is observed that the ultrafine zirconia particles are uniformly dispersed in the alumina.

Further, FIG. 3 shows the results of particle analysis by image-processing zirconium element mapping based on the EMPA image of FIG. From the results of particle size distribution analysis in Fig. 3, the size of dispersed particles after sintering is mostly around 1.0 μm and up to 2 μm, and particles of the same size are evenly distributed. I understand.

Comparative Example For comparison, a molded body having the same composition as in Test Example 1 was prepared by a pressure molding method, and a sample sintered under the same conditions as in Test Example 1 was prepared.

That is, the same alumina and zirconia raw material powder as in Test Example 1 were premixed in the same composition by using a V-type mixer, dispersed in pure water and sufficiently dispersed and mixed by using an ultrasonic disperser. After that, 2% of PVA-based binder was added as a solid content to form a slurry, and the mixture was granulated by spray drying to a particle size of about 50 μm. Alumina-zirconia raw material powder granulated by such a process is 20 mmφ × 3 m at a molding pressure of about 300 MPa by a die press.
After molding to mt, sintering was performed in the air at 1600 ° C. for 3 hours. Large cracks were generated in the sample after sintering.

Similar analysis results by EPMA of the sample are shown in FIGS. 4 and 5. As shown in the mapping of elemental zirconium in FIG. 4, a large aggregate structure of zirconia was observed as a cluster of white dots. The cause of cracks is considered to be the difference in thermal expansion coefficient between alumina and zirconia. For example, when zirconia dispersed particles are present in agglomerated state as observed in the lower right part of FIG. 4, it is considered that partial stress concentration occurs during sintering and defects such as cracks occur. . Comparing the particle analysis result of FIG. 5 with that of FIG. 3 according to the present invention,
The particle diameter is shifted to a relatively large direction, and this result also proves that the dispersion of the zirconia raw material powder is not good.

Test Example 2 Titanium-Alumina Functionally Gradient Material In this example, a combination of ultrafine particles of metal and ceramics is used as an ultrafine-structure thick film material, and the functional gradient of each ultrafine particle is gradually changed to obtain a functional gradient. An example of trial production of the material is shown.

Alumina raw material powder introduced into the plasma is high-purity alumina (AL160SG) manufactured by Showa Denko KK
1) was used. Furthermore, as the metal of the matrix, titanium powder manufactured by Kojundo Chemical Co., Ltd.
m) was used. These raw material powders were changed from titanium-alumina (80:20) to titanium-alumina (0: 100) in 5 steps at 20% intervals by 5 steps by a raw material powder supply device described in this specification. Introduced into it, a mixed ultrafine particle aerosol in which titanium and alumina were finely dispersed at an ultrafine particle level (1 μm or less) was generated. Also in this example, as in the test example, the feed rate of the raw material powder into the plasma was set to 1 g / min.

The aerosol flow generated in the plasma furnace is continuously ejected from the nozzle 18 as it is to obtain 20 × 3 mm.
It was laminated on a titanium substrate of t to obtain a gradient composition green compact having a thickness of about 500 μm. In this example, the titanium substrate was grounded in order to remove the charge of the charged ultrafine particles and to densify the laminate.

The obtained gradient composition green compact was taken out of the apparatus and sintered at 1200 ° C. under a reduced pressure of 10 ⁻³ Pa for 3 hours. 6 and 7 show the EMPA of the obtained gradient composition thick film.
The analysis results are shown. FIG. 6 shows the mapping results and line analysis results for the aluminum element and FIG. 7 for the titanium element. From these figures, it is clear that titanium and aluminum have compositional gradients with opposite gradients. That is, it can be seen that the surface side of the sample is alumina and the substrate side is titanium, and the composition of the interface is a gradient composition of alumina and titanium. Further, from the size of the white dots showing the detection characteristic X-rays of each element, it can be seen that the size of the crystal particles forming the sample is about 1 μm or less.

[0049]

As described above, according to the present invention,
High-quality nanomaterials, dispersion-strengthened ceramics, functionally graded materials can be produced because thick film materials with ultrafine structures, which could not be obtained by conventional methods, can be produced Etc. can be provided.

[Brief description of drawings]

FIG. 1 is an equipment arrangement system diagram of an apparatus used for carrying out the method of the present invention.

FIG. 2 is an EPMA image photograph showing a microstructure of zirconia uniformly dispersed alumina (20:80) obtained according to the present invention.

FIG. 3 shows the zirconia uniformly dispersed alumina (2
It is a particle size distribution analysis figure of 0:80).

FIG. 4 is an EPMA image photograph of a zirconia-alumina composite material obtained in a comparative example.

5 is a particle size distribution analysis diagram of the sample of FIG.

FIG. 6 is an EPMA image photograph and aluminum element distribution diagram showing aluminum distribution in a titanium-alumina ultrafine structure dispersion functionally graded thick film obtained by the present invention.

FIG. 7 is an EPM showing titanium distribution in a titanium-alumina ultrafine structure dispersed functionally graded thick film obtained by the present invention.
It is an A image photograph and a titanium element distribution chart.

[Explanation of symbols]

 1 Plasma Torch 2 Plasma Flame 3 Plasma Furnace 7 Raw Material Powder Supply Device 16 Exhaust Port of Plasma Furnace 17 Exhaust Device 18 Aerosol Injection Nozzle 19 Cooler 20 Stacking Chamber 23 Substrate Installation Table 24 Substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masato Araiyama, No. 1, Takatani Shinmachi, Ichikawa City, Chiba Prefecture, Nisshin Steel Co., Ltd. New Material Research Center (72) Inventor, Toyokichi Tanaka 7 Takatanimachi, Ichikawa City, Chiba Prefecture Address No. 1 Nisshin Steel Co., Ltd. New Materials Research Center

Claims (7)

[Claims] 1. A plasma furnace in which a high-frequency plasma torch using a mixed gas of an inert gas and hydrogen gas is installed so that its plasma flame radiates into the furnace, and powdered raw material is contained in the plasma generated by the plasma torch. Is charged to gasify the raw material, the gasified components are associated with each other to generate ultrafine particles having a particle size of 1 μm or less in the plasma furnace, and the aerosol in the furnace accompanied by the ultrafine particles is discharged from the nozzle. A method for producing a microstructure thick film material, which comprises jetting as a jet flow, projecting the jet flow of the aerosol onto a substrate to form an adhesion layer of ultrafine particles on the substrate, and sintering the adhesion layer. 2. The method for producing a microstructured film thickness material according to claim 1, wherein the powdery raw material introduced into the plasma is composed of two or more kinds of components, and the composition ratio of each component is changed with time. 3. The method for producing a microstructured film thickness material according to claim 1, wherein the aerosol is sprayed from a nozzle having a diameter of 5 mm or more. 4. A plasma furnace in which a high-frequency plasma torch is mounted so that its plasma flame radiates into the furnace, and a powder raw material supply device for continuously supplying a powdery raw material into the plasma generated by the plasma torch. An exhaust path communicating with an exhaust device from an exhaust port provided in the plasma furnace; a nozzle for contracting the aerosol flow in the exhaust path to inject it into the exhaust path as a jet; and a nozzle opening in the exhaust path. An apparatus for producing a microstructured thick film material, which comprises substrates placed opposite to each other. 5. The apparatus for producing a microstructured thick film material according to claim 4, wherein the nozzle has a diameter of 5 to 30 mm. 6. The raw material supply device comprises two or more powder containers, a pipe leading from each powder container to a raw material supply port of a plasma torch, a mixer provided in the middle of the pipe, and a powder container for each powder container. 6. The apparatus for producing a microstructured thick film material according to claim 4 or 5, comprising a carrier gas source connected thereto, and a device for adjusting the amount of powder sent from each powder container to the pipeline. 7. The apparatus for producing a fine texture thick film material according to claim 4, wherein a zone for contacting the ultrafine particles with the surface treatment agent is provided in the exhaust path upstream of the nozzle.