JPS6272584A - Composite method for refractories - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a composite method for refractories in which the surface of an inorganic material is coated with, for example, a 5iJ4 film.

(Prior Art and its Problems) For example, in the production of a high-purity Si material, impurity components from a container that comes into contact with the molten metal during the melting and solidification steps deteriorate the quality of the material. Therefore, in a Si melting crucible or a Si solidification mold, 5iJa powder is used as a mold coating agent on the inner surface in order to produce a high purity Si ingot. However, since inorganic binders such as phosphates have traditionally been used as adhesives for coating molds, diffusion of impurities from the container can be suppressed, but there is a problem of impurities entering from the binder. there were. In addition, the coating film itself becomes porous during the dehydration process during the drying period after application.
Its role as a buffer layer was insufficient.

Furthermore, the adhesion of the coating film was unstable, and components were likely to penetrate through contact with the container material. In any case, with the conventional method, it was difficult to secure high-purity ingots, and a large amount of black rind had to be cut.

By the way, in order to avoid the diffusion and permeation of components from the container during the melting and solidification process of Si, the container material must be highly heat resistant, resistant to getting wet by molten metal (and chemically resistant). Stable 5i3Nn is suitable.However, 5iJ4 as a ceramic material is made by molding and firing 5i3Na powder into the desired shape, or by reaction-sintering Si powder after molding, so most of it is sintered. Various substances (Y, 03, MgO1Al2O2, Fe2O,, BN
etc.), and most take the form of a Mi weave that binds 5isNa particles as an oxide.

Therefore, diffusion of Y, Mg, AI, Fe, B, etc. occurs, and in particular, a large amount of O is supplied to the Si substrate. Therefore, it is not perfect in terms of blocking the intrusion of impure components, and the material itself is expensive, so it cannot be put to practical use on an industrial scale and is still in the trial stage. Under these circumstances, it has been desired to form a S:J< film with good adhesion and high purity for this type of container.

In recent years, thermal spraying, especially ceramic thermal spraying, has developed as a surface treatment method that coats various materials to impart new functions.

However, in the case of thermal spraying in the atmosphere, 1) nitrides have a high melting point (>2000℃), 2) they do not have a melting point in the atmosphere and are easily oxidized and decomposed, and 2) the powder shape is acicular, making gas transport difficult. For this reason, many are thermally sprayed with cermet.

Recently, systems called reduced-pressure thermal spraying and vacuum thermal spraying have been developed, but these also focus on preventing oxidation of powder, which represents a breakthrough in cermet thermal spraying. Especially 5
Formation of the iJa film itself is considered impossible.

On the other hand, surface treatment methods include various deposition methods such as PVD and CVD, and the nitride films produced are of extremely high quality. However, the formation rate of the resulting film is up to 50
μm/day, and film formation tends to be uneven depending on the shape of the deposition surface.Furthermore, the sample size is limited by the size of the deposition container, making it difficult to use on a full-scale basis. There are many faces.

However, according to this method, the amount of bores in the membrane can be reduced.

As a result of various experiments and research, the present inventors established a method for easily manufacturing a composite material coated with a nitride film by combining a metal film formation step and a film nitridation step. .

That is, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a composite method for refractories that can easily coat the surface of an inorganic material with a nitride or carbonitride film. be.

(Means for Solving the Problems) The present invention applies St, Ti, Zr, and AI metal powder to the surface of an inorganic material in the air or in an N2 gas atmosphere using static gas, N2 gas, or a mixture thereof as a working gas. The gist of this method is to heat-treat the sprayed base material at 800 to 1400°C in an N2 atmosphere after plasma spraying.

That is, in the method of the present invention, a gas plasma spray machine is used as a spray gun in the step of spraying to generate a metal film. Then, N2 gas, Ar gas, or a mixed gas thereof is used as the working gas.

The so-called primary gas is N2 gas or Ar gas, and the secondary gas is static gas or N2 gas.

By the way, the selection of these quantitative ratios is determined mainly by the relationship between the properties of the working plasma and the physical properties of thermal spraying. I used them differently from the perspective of improving the. That is, diatomic gases such as N2 gas are advantageous in securing the amount of heat, and monatomic gases such as static gas are advantageous in obtaining plasma with a high flow rate. Further, in the case of a mixed gas of these, characteristics of both sides can be obtained, resulting in improved film properties.

Note that He gas and N2 gas can be used as secondary gases for the same purpose, but they are unfavorable in terms of economy and work safety, and furthermore, they require high voltage, so the ratio of amounts cannot be adjusted arbitrarily. In addition, operating plasma using 0□ gas, CO2 gas, or air is excluded from the viewpoint of preventing oxidation of St powder, which is a thermal spray material, because it becomes a 02-ion state. However, from the perspective of preventing oxidation, shield spraying,
The vacuum thermal spraying method is effective, and at the same time the thermal spraying substrate is preheated, which greatly contributes to the adhesion rate.

The mixing ratio of N2 gas and gauge gas is the flow rate ratio of 10010 to 0/1.
00, and the N2 gas flow rate ratio (Nz/Ar) is 1OO10.
~50150, the output current is 700'~
400A, and 50150~O/100, that is, Ar
When the gas flow rate ratio (Ar/Nz) is 10010 to 50150, the output current needs to be 700 to 100OA. That is, when the N2 gas ratio is large, the negative electrode of the thermal spray gun tends to be rapidly worn out, and the sprayed film is contaminated with W ions from the electrode. Furthermore, when the Ar gas ratio is large, although the thermal load exerted on the electrode is small, it is necessary to set the output to a high output in order to ensure the maximum plasma flow rate. In either case, it can be said that high current is desirable for thermal spraying metals due to functional limitations of the gun structure.
80KW type) was used.

The particle size of the metal powder, which is the thermal spray material, is suitably in the range of 100 to 5 μm. In other words, if it exceeds 100 μm, the melting of the powder will be incomplete and the adhesion rate will decrease, and the pore size between the particles stacked as a film will increase and the adhesion strength will decrease, and if it is less than 5 μm, the adhesion strength will decrease. This is because it becomes difficult to transport the gas guided to the plasma flame, and particles may be overheated and evaporated in the plasma flame, making it unsuitable. On the other hand, if we consider the penetration of N ions into the metal film during nitriding or the volume expansion during nitriding, the pore diameter in the film will be 10 to 2μ.
The range of m was appropriate, and the particle size of the powder was optimal in the range of 50 to 15 μm. Further, in view of the above-mentioned volumetric expansion, the thickness of the sprayed film is limited to 0.5 μm.

The amount of pores in the sprayed film must be adjusted so that the apparent porosity is within 10% in order to promote reaction sintering by Nt gas aeration, and the powder particle size is also important in this respect.

The pores formed in the sprayed film basically depend on the particle size, but they can also be adjusted depending on the construction conditions.

In other words, if the axis of the thermal spray gun, that is, the core axis of the plasma flame, is set within the range of 67 to 85 degrees with respect to the surface of the substrate to be thermally sprayed,
The shadow effect during the stacking of droplets facilitates the formation of pores.

However, if the angle exceeds 85°, the shadow-effe
ct does not appear, and if it is less than 67 degrees, the film becomes porous and cannot be used for practical use, or if thermal spraying is performed with low-velocity plasma using N2 gas as the primary gas, the number of pores in the stack increases. At this time, pore formation can be adjusted by changing the amount of Ar gas added to adjust the speed.

Therefore, in order to obtain the desired film properties, it is necessary to adjust the physical properties of the thermal spray material as well as the construction conditions.
It can be said that the most suitable gas types are gas and N2 gas.

Next, the step of heat treatment in a nitriding atmosphere is carried out in a heating furnace that is sealed sufficiently to block the atmosphere.

In this case, a resistance heating furnace or an electric furnace using a carbon heating element is effective because it is not affected by nitriding. However, N
In consideration of the generation of two gases, etc., it is necessary to exhaust the amount of gas input during heating. For this reason, it is necessary to take precautions such as installing a piping system with a flashback prevention valve in the exhaust hole.

The higher the N2 partial pressure, the more nitriding progresses, but if a sufficient heat treatment time of 10 hours or more is allowed, the required nitriding can be obtained.

For example, a heat treatment time of 10 hours is required for a film having a film thickness Q, jam, and a pore volume of 7.5%. In terms of speed, nitriding can be achieved within a range of 10 to 20 μm/hour.

Considering the melting point (1410°C) of metal S+, the heat treatment temperature must be 1400°C or lower. Further, in order to obtain the required nitriding rate, a temperature of 800° C. or higher is required. When NH3 is used, nitriding can be obtained even at temperatures above 500°C, but in this case a catalyst such as Fe is required, and in the case of coating a crucible for Si melting, it is unsuitable due to the contamination of impurities. . In addition, in the case of a furnace using a carbonaceous heating element, Si3
SiC may also be produced together with N. This is due to the influence of CO generated at the initial stage of heating, and is due to the influence of CO generated during the heating process.
If the gas is degassed at 0° C., the amount of SiC produced will be reduced. however,
When the base material is carbon-based, SiC generation at the film interface cannot be avoided. The same applies when oxygen ions are contained in the base material. However, nitridation progresses almost completely on the film surface in contact with the N2 atmosphere, and the film function, which is the object of the invention, can be ensured. Therefore, in order to remove oxygen in the atmosphere during the heating process up to 800° C., it is necessary to once reduce the pressure in the furnace to 10-'torr or less to promote N2 or NH3 substitution.

Such nitriding treatment of metal films is applicable not only to Si but also to Ti, Z, etc.
It can be widely applied to metal films such as r, A1, etc., and is extremely effective as a method for compositing materials. In addition, if 5iJi is deposited on the obtained 5j3N4 coated material, Si3N4 will precipitate in the film and reduce the amount of pores, and the material will be double coated, including a high-grade Si3N4 thin film, and will have multiple functions. is enhanced.

(Function) In the method of the present invention, after plasma spraying Sis Ti5Zrx Al metal powder onto the surface of an inorganic material, the sprayed base material is subjected to N
Since the heat treatment is performed in a 2 atmosphere, the surface of the inorganic material can be easily coated with a nitride or carbonitride film.

(Example 1) Metallic Si (purity 99.5%) was pulverized to a particle size of 75 to 50 μm as a thermal spraying material, and an artificial graphite plate and a fused silica plate were used as base materials, and the surface was polished with #60 alumina grid. Sprayed on things. The working gas is N2 as a thermal spraying condition.
Gas: 76Nl/min, ^rGas: 1. ONI/min, operating a plasma with an output current of 600A,
A film of μm was formed.

Further, heat treatment was performed at 1350° C.±20° C. for 20 hours in a Tamman furnace in an N2 gas atmosphere with Po=100 ppm or less to obtain a 5iJa film with a content of about 60%. The results are shown in Table 1 below.

Table 1. Thermal spraying conditions and film properties for 1j6W1)* Number of times of thermal cycling
Material 5S-41) was fixed on the film with epoxy resin, and the torsional strength was measured using a torque wrench.The torque was used to quantify the strength of the film coated with a conventional phosphoric acid binder.
The ratio is shown as 00. In addition, the thermal shock resistance is 1
The coatings were heated in a furnace at 000°C for 15 minutes, left in the air for 15 minutes, and then charged into the furnace again to give the coating a shock of rapid heating and cooling.

As is clear from Table 1 above, nitride (
The SisN4) film is significantly superior in both adhesion strength ratio and thermal shock resistance compared to nitride films produced by conventional methods.

(Example 2) Metal Ti (purity 90%, remainder Fe) was applied to the surface of a blast furnace carbon block with an apparent porosity of 20.2%.
The thermal spraying material is pulverized to a particle size of μm, and Ar gas 5
Using a mixed gas of ONl/min and N2 gas of 7.2NI/min as working gas, a plasma with an output current of 800 to 900Δ was operated to form a film of 50 μm on the entire surface of the carbon block. These carbon blocks are Po, = 1%
Heat treatment was performed for 25 hours in an electric furnace under an atmosphere of Note that in the furnace, carbon blocks were embedded in coke grains, and electricity was applied while blowing Nt gas. The amount of N2 gas blown at this time was 0.6 to 0.9 r//min per 1 rrr of furnace internal volume. As a result, the Ti film is made of Ti(Co, 4, No, h)
titanium carbonitride film. Adhesive strength and thermal shock resistance were tested using the same method as described above (Example 1) on pieces cut out from carbon blocks. T as a comparison material
The material was prepared by coating iN powder mixed with a sodium silicate solution. The results are shown in Table 1 above.

As is clear from Table 1 above, in the case of Example 2, both the bond strength ratio and the thermal shock resistance are significantly superior compared to the conventional method.

(Example 3) (Example 1) The obtained fused silica plate was placed in a sealed furnace, and after reducing the furnace pressure to 10-'torr, 5iC1n gas was added to 2O
It was aerated with N1/min, heated at a temperature increase rate of 10°C/min, maintained at 870°C, and then heat-treated for 10 hours.

As a result, the amount of 5iJa increased to 65%, the amount of pores decreased from 0.10 cc/g to 0.04 cC/g, and a sealing effect was obtained.

(Effects of the Invention) As explained above, according to the present invention, a nitride or carbonitride film with excellent adhesion strength and thermal shock resistance can be easily obtained, and therefore a composite material with excellent functions can be obtained. It has great effects.

Claims (1)

[Claims] (1) Ar under air or N_2 gas atmosphere
After plasma spraying Si, Ti, Zr, and Al metal powder onto the surface of an inorganic material using gas, N_2 gas, or a mixture thereof as a working gas, heat-treating the sprayed base material at 800 to 1400°C in an N_2 atmosphere. A composite method for refractories characterized by: