JPH0472054A - Method and furnace for forming oxide film on metal - Google Patents

Abstract

PURPOSE:To form an oxide film (black rust) having high radiation rate and free from deterioration by carrying out the oxidation treatment, by heating, of iron material, stainless steel material, etc., in the atmospheres in two stages, the former stage and the latter stage, and regulating oxygen concentration in the former stage so that it is higher than that in the latter stage. CONSTITUTION:An oxide film is formed on the surface of a metallic material composed essentially of iron by means of oxidation treatment by heating. At this time, as the atmosphere in the initial stage, an oxygen-containing gas is introduced into the field in the state where a reducing gas consisting of carbon monoxide and/or hydrogen is contained, and oxygen concentration in the former stage is regulated so that it is higher than that in the latter stage. Further, the concentration of reducing gas in the latter stage is regulated so that it is higher than that in the former stage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming a high-quality oxide film on the surface of a metal material and a furnace for the same.

[Prior Art] In recent years, in color cathode ray tubes, the market demands improved brightness and clarity of reproduced images. In response, one measure to improve brightness is to increase the kinetic energy of the electron beam that irradiates each picture element that emits fluorescence, which constitutes the image plane that reproduces the image of a color cathode ray tube.

However, in this method, the electron beam collides with the shadow mask, which is a color selection electrode built into the cathode ray tube, and the temperature of the shadow mask itself increases by 40 to 80 degrees.
As a result, the shadow mask becomes thermally distorted and color purity decreases on the image plane.

As a countermeasure, an oxide film (black rust) is formed on the surface of a shadow mask made of iron material to improve the heat emissivity.

A means for forming an oxide film on the surface of a shadow mask made of iron material is high-temperature oxidation using water vapor or carbon dioxide gas. In high-temperature oxidation using water vapor, the emissivity is 0.3 that of iron.
However, this high-temperature oxidation using water vapor results in a backlash process, resulting in poor productivity. On the other hand, high-temperature oxidation using carbon dioxide gas can be carried out continuously in a tunnel furnace.

This tunnel furnace is an oxide film forming furnace that is generally used to form an oxide film on the surface of metal materials, as shown in Figure 4. Tropical, [C] is a cold zone, (5) is a mesh belt that guides the iron material to be surface-treated into the furnace (moving parts are not shown), 02)
is the space filled with combustion gas introduced into the furnace, (
6) is a smoke tower that exhausts the atmosphere inside the furnace, (1), (2),
(3) both indicate the position where combustion gas is introduced into the furnace. The iron material is placed on the mesh belt (5) and moves from the container to (B) to (0). Fig. 5 shows the actual temperature when the material is oxidized at high temperature by this furnace.

The combustion gas supplied into the furnace is DX gas obtained by mixing and burning natural gas and air, and its composition (volume %) is COz
10.5%, GO1.5%, )121.2%, )12
00.8%, the remainder being N2.

However, in such a method, an appropriate processing temperature (
(approximately 600° C.), an oxide film of sufficient thickness cannot be formed.

On the other hand, in the oxidizing atmosphere of this combustion gas, the
A method of improving the quality of the oxide film by treating it at 00°C and further adding air was disclosed in Japanese Patent Application Laid-Open No. 61-116.
It is disclosed in Japanese Patent No. 734. In addition, in connection with this, it is possible to add oxygen, etc. to the atmosphere inside the furnace.
This method is disclosed in Japanese Patent Publication No. 767, Japanese Patent Application Laid-open No. 57-57448, Japanese Patent Publication No. 18734-1987, and the like.

[Problem to be solved by the invention] However, although these treatments with carbon dioxide gas can be carried out continuously in a tunnel furnace as shown in Fig. 4, if the emissivity of the iron material is low, the emissivity is 0.3 to 0. .4, A<but
It has the disadvantage of not being able to maintain a degree of 0.5 to 0.6 degree.

On the other hand, in order to suppress the deformation of the shadow mask due to thermal strain, there is a method of using Invar material (iron material containing N13B%) with a small coefficient of thermal expansion, but even if the Invar material is oxidized at high temperature with carbon dioxide gas, the emissivity remains low. The reality is that the oxide film, which is as low as 0.3 to 0.4, cannot be replaced.

In addition, the shadow mask used in color cathode ray tubes is
In the color cathode ray tube manufacturing process, heat treatment is performed in air at 350 to 450 degrees Celsius two to three times, but this heat treatment process has the disadvantage that the oxide film changes from black rust to red rust and that the emissivity deteriorates by around 0.1. be.

The present invention was made to solve the above-mentioned problems, and it is made of high-quality material that has a high emissivity through high-temperature oxidation with carbon dioxide gas and whose emissivity does not deteriorate even when heat treated in air at around 400°C. The purpose of this study is to establish an oxide film forming method and an oxide film forming furnace for forming an oxide film.

[Means for Solving the Problems] The present invention is a method for forming an oxide film on the surface of a metal material containing iron as a main component by thermal oxidation treatment. A method for forming an oxide film on a metal, characterized in that an atmosphere containing at least one of hydrogen and hydrogen is introduced into an atmosphere containing oxygen or a gas containing oxygen, and a method for heating and oxidizing a metal material containing iron as a main component. The present invention relates to a metal oxide film forming furnace, which is characterized in that it is provided with means for making the atmosphere of the heating oxidation treatment different between the first stage and the second stage of the treatment.

[Function/Example] In the method of the present invention, the heating oxidation treatment is carried out in an oxidizing atmosphere such as in combustion gas, and the atmosphere at the initial stage of the treatment contains at least one of carbon monoxide and hydrogen. An atmosphere is created in which oxygen or a gas containing oxygen, such as air, is introduced into a field containing conditions. The initial stage is
For example, when using Invar material, the belt speed is 30011111.
In the case of processing at 1/min, this refers to the stage from the entrance of the tunnel furnace to about 5 m inside.

The oxygen introduced into the heating atmosphere is
Hydrogen and carbon monoxide, which are reducing compositions contained in combustion gas, are changed into oxidizing compositions by the reaction shown in . (The combustion start temperature of hydrogen is 580 to 600°C, and the combustion start temperature of carbon monoxide is 640 to 660°C.) 2(H2) + (02) −2(H2O)
(I12(Co) + (02) -2(CO2)
(11 The iron contained in the metal material becomes
> + (H2) [[)3
<PeO> + (H2O) -<Pe5o4>
+ (H2) ([V)2<Pe304> +
(H2O)-3<Fe2O3> + (H2)
The CO2 system is <Pe> 10 (CO2) - <FeO> + (Co
) (gD3<PeO) +(CO2)
−<Pe5O4> +(Co) m2<F
e3O4> + (CO2) -3<Fe2e3>
+ (Co)■ o2 system is 2<Pe> + (02)= 2<FeO>
E6<FeO> + (0
2) −2<Fe50<> (X)
4< Pe5Oa > + (02) −6<
In the present invention, oxidation of Fe304 (black rust), which is generally more stable than Fe2O3 and FeO against oxidation and reduction, is applied to the surface of the metal material. In order to scale the film, the oxidizing property is strengthened in the first stage of the thermal oxidation treatment under conditions such as temperature, atmosphere, and time, and the Fe2O3
The conditions are controlled to reduce Fe50+ to Fe50+.

For example, the heating oxidation treatment can be carried out using a furnace in which the treatment atmosphere can be made different for the first stage and the second stage, as shown in Figure 1, which will be described later. Atmosphere and/or (1) It is carried out in an atmosphere in which the reducing gas concentration in the latter stage of the thermal oxidation treatment is higher than the reducing gas concentration in the earlier stage.

Metal materials containing iron as a main component used in the present invention include iron materials (those containing 99% or more of iron, the same shall apply hereinafter), Invar materials (iron materials containing 36% Ni, the same shall apply hereinafter), stainless steel materials, etc. In addition to materials commonly used as masks, there are various materials that can form an oxide film.

The atmosphere containing at least one of carbon monoxide and hydrogen may include at least one of carbon monoxide and hydrogen, such as combustion gas (combustion gas of hydrocarbon gas and air).
Examples include an atmosphere containing 1 to 2% by weight of carbon monoxide species and 0.5 to 1.5% by weight of hydrogen species.

Gases in which the content of at least one of carbon monoxide and hydrogen is less than the lower limit or higher than the upper limit are difficult to produce in the reaction tower. In addition, when iron material is used as the metal material, it is preferable to contain hydrogen from the viewpoint of improving the reaction rate, and when using Invar material, it is preferable to contain carbon monoxide or carbon monoxide and hydrogen to increase the oxidizing power. It is preferable because it becomes stronger.

The dew point of the atmosphere is 35 to 45°C when iron material is used.
is preferred. If the dew point is less than 35°C, sufficient oxidizing power may not be obtained, whereas if it exceeds 45°C, oxidation is likely to occur and it is difficult to put it into practical use. Moreover, when using Invar material, the temperature is preferably 40 to 50°C. Figure 6 shows the relationship between dew point and water vapor amount.

The combustion gas that forms the atmosphere described above is consumed by reaction with oxygen and metal materials, so for example, in a furnace with an opening of approximately 1.5 to 2 m x 0.2 m, the combustion gas is approximately 315 to 385 Nm/hour. continue to be supplied.

The amount of oxygen or oxygen-containing gas introduced is 13.5 to 1
B, 5NTl1/hour is preferred.

By introducing oxygen or a gas containing oxygen only in the initial stage of the thermal oxidation treatment, the oxidizing nature of the atmosphere in the first stage of the treatment is strengthened, oxidation is promoted, and an oxide film of Fe304 is formed.

The temperature setting in the place where oxygen or a gas containing oxygen is introduced is preferably 580°C or higher when iron material is used;
-600 degreeC is more preferable. If the temperature is less than 580°C, hydrogen becomes difficult to burn. Further, when using an Invar material, the temperature is preferably 640° C. or higher, and more preferably 640 to 650° C., since both hydrogen and carbon monoxide can be burned. The actual temperature of the metal material being processed is
Due to the reaction, the temperature is about 50 to 100°C higher than the set temperature.The heating time is σ゛f′<
The first stage (where the oxygen concentration is high and/or the reducing gas concentration is low) is preferably 10 to 30 minutes, more preferably 11 to 19 minutes, and particularly preferably 13 to 17 minutes.

If the time is less than 10 minutes, oxidation tends to be insufficient, and if it exceeds 30 minutes, peeling tends to occur. In addition, the latter stage (low oxygen concentration and/or high reducing gas concentration) is 5 to 3
0 minutes is preferable, 3 to 11 minutes is more preferable, 6 to 9 minutes
minutes is particularly preferred. If the treatment time is less than 5 minutes, reduction tends to be insufficient, and if it exceeds 30 minutes, peeling tends to occur.

On the other hand, when using Invar material, the first stage of treatment is
25 minutes is preferable, 18 to 22 minutes is more preferable, and the second stage is preferably 5 to 15 minutes, and even more preferably 8 to 12 minutes.

Note that preheating and gradual cooling are performed as appropriate before and after the heating and oxidation treatment.

When forming an oxide film on iron material, the dew point should be lower as described above, and the heating time should be 0.3 to
It is preferable to increase the thickness by 0.5 times in order to avoid making the oxide film too thick. When the oxide film thickness exceeds 3 -, peeling tends to occur, and there is a possibility that a discharge phenomenon between the electrodes (25 kV) that accelerates the emission of electron beams in the color cathode ray tube may occur.

The method of the present invention is not limited to a method using a furnace in which the atmosphere can be made different between the first stage and the second stage of treatment, as shown in FIG. The treatment may be carried out in two furnaces.

By the method of the present invention as described above, a denser oxide film mainly composed of Fe304 (black rust) with a thickness of 0.5 to 3 mm can be formed on the surface of a metal material. For example, in conventional composite gas oxidation treatment, iron material has a
Invar and stainless steel materials, which were only in the 0.3 to 0.4 range, can be increased to about 0.6 to 0.7.

Here, FIG. 7 shows the relationship between the emissivity of a shadow mask using an Invar material and the local doming rate (the amount of movement due to thermal strain during electron beam operation, which indicates the image quality of a color cathode ray tube). From FIG. 7, it can be seen that the emissivity of the shadow mask made of Invar material on which the oxide film is formed by the method of the present invention is 0.
．． Since the emissivity is about 6 to 0.7, it can be seen that the local doming rate is improved by about 30% compared to when the emissivity is 0.4.

Next, an oxide film forming furnace of the present invention suitable for carrying out the above-mentioned oxide film forming method will be explained based on FIG. 1, which is a typical example thereof.

In Figure 1, the preheating zone is the preheating zone, (Bl) and (B2) are the heating zone, and (C) is the cooling zone.
2) is separated by a convex wall 0). (1) is the position where oxygen or oxygen-containing gas is supplied into the furnace; [2);
+31 indicates a position where a composite gas mainly composed of carbon dioxide, which is an oxidizing gas, is supplied. (4) is a space filled with the composite gas introduced into the furnace. The temperature of the heating zone (B1) shall be at least 650°C. The size and shape of the space between the upper and lower convex walls (2) are not particularly limited, as long as they allow passage of at least the mesh belt (5) and the metal material to be processed. In the device shown in FIG. 1, a person (B1
), (B2), and (C) are sent in this order. The exhaust tower (6) is provided with a control valve (7) for adjusting the pressure inside the furnace, and the atmospheric pressure inside the furnace is controlled by the convex wall (D) as a boundary (B1).
The atmospheric pressure is set so that ) and (B2) are equal or (B2) is higher. Further, at least one stainless steel thin plate curtain (8) is hung on the mesh belt (5) at the outlet and inlet portions of the furnace. It is preferable that a plurality of thin plate curtains (8) be provided at a pitch of several (up to) in order to prevent outside air from entering.

In the apparatus shown in FIG. 1, since the convex wall (the cross-sectional area inside the heating furnace such as a DJ) is provided with a boundary portion that is smaller than other portions, the supply amount of each gas is controlled, for example, in the front stage,
100±10 Nm at 37 hours and 350±l in the latter stage, respectively.
By adjusting ONm'/hour, it is possible to make the atmosphere different between the first stage and the second stage of the thermal oxidation treatment.

Note that if the atmospheric pressure in the latter stage is made higher than the atmospheric pressure in the former stage, the atmosphere can be made different between the former stage and the latter stage of the treatment without providing a boundary such as a convex wall [Dl].

As another example of the oxide film forming furnace of the present invention, a gas rich in oxygen is introduced into which air is introduced in the first stage of the heating oxidation process, and a gas with a weakly oxidizing and reducing composition (CO, H2) is used in which air is not introduced into the second stage. As shown in Fig. 3, the furnace can more effectively realize an atmosphere in which oxidation and reduction can take place.The heating atmosphere in the first and second stages is separated, and an exhaust port (9) having a control valve (7) is used. ) can be used as a furnace. As shown in FIG. 3, it is preferable to separate the atmosphere by using a thick plate 01 made of stainless steel or the like at the boundary between the front stage and the rear stage.

Example 1 Using the furnace shown in FIG. 1, an oxide film was formed on a shadow mask made of Invar material with a plate thickness of 0.2 mm.

The atmosphere inside the furnace was 150±10℃, (B1) and (B
2) was controlled at 650±10°C, and (C) was controlled at 200±IO°C.

From position (1), use a vibrator to air (relative humidity 65-75)
%) was introduced at a flow rate of 15NTIl/hour, and from position (2), a composite gas (DX gas obtained from natural gas) with the composition shown in Table 1 and the dew point controlled at 48±3°C was added at 1.05NTI/hour.
A composite gas with a composition shown in Table 1 and a dew point controlled at 48±3° C. was introduced from position (3) at a flow rate of 3508·rd7 hours. In addition, the CO concentration and 02 concentration during treatment are as follows: (B1) The first half is Co: 0.0%, 0
2: 6.7%, second half Co: 0.1%, 02.10
%, (B2) or CO・1.1%, 02: 6400
It was ppm.

[Left below] The convex wall (which is the boundary between the atmospheres of (B1) and (B2))
D) was approximately the same size as the space of the preheating section (8) and slow cooling section fc). The internal pressures of the furnaces (B1.) and (B2) were adjusted by adjusting the control valves (7) of the respective exhaust ports (6) so that the internal pressures were at least the same. The belt speed was adjusted to 300 mm/min so that the heating time for (Bl) was approximately 18 minutes and the heating time for (B2) was approximately 12 minutes.

The resulting shadow mask contains Pe3 with a thickness of 1uIrl.
Oxide film mainly composed of 04 (ratio based on X-ray diffraction intensity:
Fe5Oa / Fe2O3 / Fe-30 / O /
7[]) was formed, and the emissivity was 0.65. By manufacturing a color cathode ray tube using the obtained shadow mask, a color cathode ray tube with image quality improved by about 3090 points compared to a conventional method using a shadow mask (emissivity 0.45) was obtained.

FIG. 2 shows the actual temperature trend of the Nyadou mask in the treatment of Example 1. In FIG. 2, the horizontal axis shows the elapsed time for oxidation treatment, the vertical axis (1 on the scale indicates 100°C, 5 indicates 650°C) shows the actual temperature, and t shows the factor for standardizing the measurement results. Part E) of the second solid temperature curve is one of the important parts of the present invention. The temperature of the atmosphere at this position (position (1) where air is introduced) is 1° below the set temperature when there is no shadow mask to be oxidized.
It was confirmed with a thermocouple that the temperature was 0 to 30°C higher. Also,
The actual temperature of the shadow mask and the ambient temperature were almost the same, and were 50 to 100° C. higher than the set temperature. This is the part where air is introduced into the furnace and has a high air concentration, where the oxygen (O2) contained in the air and the carbon monoxide (CO) and hydrogen (H2) contained in the composite gas are mixed. Combustion occurs at the temperature in the furnace as shown in the above equation (It) or equation +1), and the reducing gas is converted to an oxidizing gas, and together with other oxidizing gases (oxygen, carbon dioxide, water vapor), the above equation (
It shows that the reaction shown by Il[l~(XI) is occurring. Then, in the next part (B2), the complex gas atmosphere reduces the expensive oxidation from Fe2O3 to Fe3O4.

Example 2 Using a shadow mask made of iron material with a plate thickness of 0.2+++m, the set temperature was changed to 600°C, and the dew point of the composite gas was set to 40°C.
The temperature was changed to ±30°C, and the heating time for (B1) and (B2) were made 0.75 times that of Example 1. Oxide film (ratio according to X-ray diffraction intensity: Fe50* / Fe
A shadow mask having an emissivity of 0.7 and having an emissivity of 20s/Fe-40/20/40) was manufactured.

The actual temperature trend of the shadow mask in the process of Example 2 was similar to the actual temperature curve shown in FIG.
However, in the figure, 1 on the scale of the vertical axis is 100 degrees Celsius, and 5 is 60 degrees Celsius.
0°C).

Examples 3 to 7 The material of the shadow mask, the dew point of the composite gas, the set temperature of (B1) and (B2), and the total heating time of (B1) and (B2) were changed as shown in Table 2. A heating oxidation treatment was performed in the same manner as in Example 1 to form an oxide film. Table 2 shows the emissivity of the obtained shadow mask.

Kanayama Example 8 An oxide film was formed in the same manner as in Example 1 except that the set temperatures of (Bl) and (B2) were changed. The emissivity of the obtained shadow mask is shown in FIG.

Example 9 An oxide film was formed in the same manner as in Example 1 except that the dew point of the composite gas was changed. FIG. 9 shows the emissivity of the obtained shadow mask.

Example 10 An oxide film was formed in the same manner as in Example 1 except that the total heating time in (B1) and (B2) was changed.

The emissivity of the obtained shadow mask is shown in FIG.

[Effects of the Invention] According to the oxide film forming method of the present invention, the emissivity of iron materials, Invar materials, stainless steel materials, etc. is high, and the emissivity is high at 350 to 450°C in air.
It is possible to continuously form an oxide film (black rust) that does not change in quality even after heat treatment. Furthermore, by using the oxide film forming furnace of the present invention, the oxide film forming method described above can be easily carried out.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the oxide film forming furnace of the present invention, Fig. 2 is a graph showing the actual temperature trend of metal materials treated by the method of the present invention, and Fig. 3 is an explanatory diagram of the oxide film forming furnace of the present invention. Figure 4 is an explanatory diagram of a conventional oxide film forming furnace, Figure 5 is a graph showing the actual temperature trend of iron materials processed by the conventional method, and Figure 6 is
Figure 7 is a graph showing the relationship between dew point and water vapor content, Figure 7 is a graph showing the relationship between emissivity and local doming rate, and Figure 8 is a graph showing the relationship between emissivity and local doming rate.
Figures 1 to 10 are graphs showing the relationship between emissivity and set temperature, composite gas dew point, or heating time in the examples of the present invention, respectively. (Main symbols in the drawing) (1): Positions for supplying oxygen or oxygen-containing gas (2), (3): Positions for supplying composite gas, etc. (4):
Position 2 where the space filled with compound gas etc. is placed on the 0 line'): Position 4 where compound gas is fitted4F: Space filled with compound gas etc. Male 1 protector

Claims (2)

[Claims] (1) A method of forming an oxide film on the surface of a metal material whose main component is iron by thermal oxidation treatment, in which the atmosphere at the initial stage of the thermal oxidation treatment is changed to at least one of carbon monoxide and hydrogen. A method for forming an oxide film on a metal, characterized by creating an atmosphere in which oxygen or a gas containing oxygen is introduced into a field containing oxygen. (2) A furnace for heating and oxidizing metal materials containing iron as a main component, characterized in that the furnace is provided with means for making the atmosphere of the heating and oxidation treatment different between the front stage and the rear stage of the treatment. Oxide film forming furnace.