JPH0730459B2 - Ceramic coating method on metal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for coating a metal with a ceramic. In recent years, it has become popular to apply a ceramic coating to a metal in order to improve heat resistance and oxidation resistance, and various proposals have been made for applying a ceramic coating that is difficult to peel even when exposed to high temperatures. The present invention is
The present invention relates to a method for ceramic coating of metal, which comprises performing pretreatment of metal to achieve such properties.

(Prior Art) In recent years, it has become popular to apply ceramic coating to a metal material that is required to have heat resistance and oxidation resistance.

According to pages 206 to 209 of "Survey research on development of ceramic coating technology and usage trends in new industrial fields (Japan Industrial Technology Association, published in March 1985)", carbide-based materials such as TiC and SiC , Nitrides such as TiN, Si ₃ N ₄ , borides such as TiB ₂ , oxides such as Al ₂ O ₃ , MoSi ₂
It is described that by coating a metal with a ceramic such as a silicide, the properties of the metal are significantly improved with respect to heat resistance and oxidation resistance.

In addition, as a method of coating ceramics on a metal, a radiation method, an ion sputtering method, a chemical vapor deposition method (CV
D method), coating drying method, coating baking method and the like. The coating and baking method includes a method of treating at a high temperature of 677 to 871 ° C. using a glass frit (see Japanese Patent Publication No. 55-26714) and a method of treating at the ordinary baking temperature of an inorganic paint.

In any of these methods, a ceramic surface is directly coated on a mechanically or chemically cleaned metal surface.

In this regard, according to the above-mentioned “Ceramics coating .. Research study”, it is said that for metal alkoxide-based paints, the base only needs to be cleaned with an alkali (page 25), and for alkali metal silicate-based paints, roughening by sandblasting. In addition to that, it is said that it is necessary to introduce a reactive chemical bond into the paint to react with the underlying metal, and in the coating agent for high temperature, it is important to bond the ceramic and the metal by a chemical bond. It is explained.

As a kind of silicone paint, a heat-resistant paint using modified silicone varnish as a binder and alumina / silica short fibers as a ceramic has recently been marketed (Nikkei New Material, 1986, 5-19, p. 101). It has been introduced that one of the features of this paint is that the paint film can follow the expansion of the metal.

(Problems to be solved by the invention) In the conventional methods, except for the CVD method, the adhesion between the coating film and the base metal is not sufficient, and the thermal expansion coefficient of the metal and the ceramic is high under the high temperature intended for the use of the ceramic coating. However, there was a problem that the ceramic coating peeled off due to the difference in temperature and the oxidation of the base metal.

On the other hand, there has been a device from the viewpoint of enhancing the reaction between the coating material (ceramic) and the metal, but this method has the limitation of application due to the chemical composition of the metal and the coating material. By such a non-limiting means, it is possible to prevent the ceramic coating coated on the metal from peeling off at high temperature and to prevent the base metal from being oxidized at high temperature.
It is an object of the present invention to provide a ceramic coating method that can be sufficiently put to practical use.

(Means for Solving Problems) In order to solve problems such as peeling of a ceramic coating at high temperature and high temperature oxidation of a base metal, the present inventors first
Attempts have been made to clean the metal surface as much as possible by the conventional method, but the above problems could not be solved. Therefore, as a result of studying various surface treatments as a pretreatment before performing the ceramic coating, when the ceramic coating is applied after forming the aluminum phosphate coating, the oxidation of the base metal at high temperature is suppressed, and It was found that the coating did not peel off at elevated temperatures.

The aluminum phosphate coating described here is Japanese Patent Publication No. Sho 53-6.
In Japanese Patent No. 945, the present applicant has found that a pH of 1.5 containing aluminum ion 0.01 to 10 g / l phosphate ion 1 to 100 g / l.
Which it was proposed a film forming method by which a chemical conversion treatment or an electrolytic treatment in an acidic phosphate solution to 5, the main component of the coating is aluminum phosphate (AlPO ₄ .XH ₂ O).

The invention of this publication, as described in the section of "Detailed Description of the Invention", is for the purpose of rust prevention treatment of steel materials,
Previous phosphates such as zinc, manganese, calcium,
It has been proposed to form a film in place of the chromate film, and acrylic resin paint is only mentioned as a specific example of the coating.

(Function) Since it is a serious finding by the present inventor that the aluminum phosphate coating is excellent as a ceramic coating base, the function of the aluminum phosphate coating will be described in detail.

FIG. 1 is a graph showing the results of thermogravimetric changes and differential thermal analysis up to 500 ° C. of the aluminum phosphate coating prepared by the method described in the above publication. The aluminum phosphate coating is amorphous AlPO ₄ .XH ₂ O, but as shown in FIG.
XH ₂ O is lost (about 12% weight loss) at around 50 ° C to 200 ° C, and then AlPO ₄ becomes stable at high temperatures up to 500 ° C.

That is, adsorbed water is lost at 50 to 100 ° C, and crystal water is lost at around 150 ° C, but there is no weight change at 200 ° C or higher, and thus thermally stable AlPO ₄ is shown. In the present invention, the drying temperature of the aluminum phosphate coating is not specified, and even if the coating is dried at room temperature, water, crystal water, etc. contained in the coating will be scattered during the subsequent baking of the ceramic coating. It is assumed that it does not affect the adhesion of the coating.

Although the temperature of the surface of the base material becomes high due to baking, CVD, etc. at the time of coating the ceramic, AlPO ₄ does not decompose beyond the above-mentioned dehydration, and acts as a base for improving the adhesion with the ceramic coating.

When the metal surface is cleaned and the ceramic coating is applied as in the conventional method, the metal surface is oxidized in the heat resistance test,
Also, the ceramic coating is peeled off. On the other hand, in the case where a ceramic coating is applied on the aluminum phosphate coating, the ceramic coating is not peeled at all in the heat resistance test, and the oxidation of the metal is suppressed. This further enhances the performance of the ceramic coating as a heat resistant coating, which is the original purpose of the ceramic coating.

Hereinafter, a specific configuration of the present invention will be described in detail.

The aluminum ion used in the treatment liquid for the aluminum phosphate coating is prepared by adding an aluminum compound such as aluminum nitrate, aluminum hydroxide or aluminum sulfate to the acidic phosphoric acid solution as a solid or liquid and then adjusting the pH. Aluminum ion content in solution is 0.01-10
g / l It is preferably 0.2 to 3 g / l. If it is less than 0.01 g / l, the amount of aluminum phosphate coating adhered is small, and if it exceeds 3 g / l, it is economically disadvantageous. Acidic phosphoric acid solution is phosphoric acid or first
Sodium phosphate, dibasic sodium phosphate, etc. are diluted with water and adjusted to contain 1 to 100 g / l, preferably 5 to 50 g / l as phosphate ions. For example, caustic soda after addition of aluminum compound to phosphoric acid solution, PH due to caustic potash, ammonia, etc.
= Adjust to 1.5 to 5.0. If the pH is less than 1.5, the etching effect of the metal to be treated is large, and if the pH exceeds 5.0,
This is disadvantageous because a large amount of aluminum phosphate and aluminum hydroxide precipitates in the bath. If necessary, as an oxidant and a film promoter, nitrate ion 0 to 20 g / l, preferably 1 to 5 g / l, chlorate ion 0 to 20 g / l, preferably 1 to 5 g / l
1 and nickel ions 0 to 5 g / l, preferably 0.01 to 2 g / l can be contained in the acidic phosphoric acid solution. Further, in order to increase the coating weight, 0-10 g / l of sulfate ion can be contained.

Examples of the metal used in the present invention include metal materials such as iron, steel, stainless steel plate, heat resistant steel, aluminum and aluminum alloys which can be etched by phosphoric acid and need to have improved heat resistance.

The operation of forming a film is as follows: a metal is immersed or sprayed in the above-mentioned acidic phosphoric acid solution heated to 30 to 90 ° C for 1 to 5 minutes to form a film in the same manner as a normal chemical conversion treatment, or a metal to be treated is used. Carbon metal, aluminum, or stainless steel is used for both poles or counter electrodes of a certain metal. Distance between poles 20 to 500 m / m Current density 0.1 to 20 A / dm ² , preferably 3 to 5 A / dm ² , energizing time 5 seconds to 5 minutes AC electrolytic formation is carried out. Further, the metal to be treated can be used as a cathode, and the counter electrode can be subjected to cathodic electrolytic formation using the above electrode, and if necessary, dip formation can be used in combination with electrolytic formation.

After forming the film in this way, dry baking
It is desirable to carry out at a temperature of 0 ° C or higher.

A ceramic coating is applied on top of this coating, but there is no particular limitation as a ceramic coating agent as long as the temperature during baking or use of the coating becomes high and the heat resistance of AlPO ₄ can be utilized. However, as the type of ceramic, it is possible to adopt a carbide type, a nitride type, a boride type, an oxide type, a silicide type, a mixture or compound type thereof, and an alkali metal silicate type,
A metal alkoxide type, a silica sol type, a silicone type or the like can be adopted. Further, when the ceramic coating method is a coating and baking method, it is possible to obtain coating film adhesion almost equal to that of the conventional CVD method. However, the heat resistance of the aluminum phosphate coating is utilized during the ceramic coating because the substrate becomes hot even in the CVD method. Further, the substrate may be heated to 200-400 during the ceramic coating.

Further, the same effect as above can be expected in the ion sputtering method or the radiation method.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 conversion treatment specimens: SPCC steel plate (70 × 150 × 0.8mm) treatment solution ^{_{composition: PO 4 - 22.8g / l Al}} 3+ 0.8g / l NO 3 - 3.1g / l sodium hydroxide the processing solution Neutralize with and adjust pH to about 2.5.

Treatment conditions: Immersion treatment Temperature 60 ° C. Treatment time 3 minutes Under the above treatment conditions, a test piece whose surface had been cleaned in advance was subjected to chemical conversion treatment, followed by washing with water and drying, and as a result, a coating having a coating weight of 1 g / m ² was obtained. Then, a commercially available ceramic coating agent (GLASCA 90, manufactured by Nichiban Kenkyusho Co., Ltd., a metal alkoxide-based (colorless transparent) ceramic coating agent, ceramic component-alkoxysilane: 19 to 23%) is dip-coated on this, 1
It was baked at 50 ° C. for 30 minutes to form a colorless and transparent ceramic coating. The film thickness was 5 μm.

Example 2 electrolyzed specimen: SPCC steel plate (70 × 150 × 0.8mm) treatment solution ^{_{composition: PO 4 3- 25g / l Al}} 3+ 1.2g / l NO 3 - Sodium hydroxide 9.0 g / l the treatment liquid It was neutralized with and adjusted to pH 2.5.

Treatment conditions: Treatment temperature 65 ° C Current density 5A / dm ² Current flow time 30 seconds Pole ratio 1: 1 Interelectrode distance 40mm Counter electrode carbon plate DC electrolysis treatment was performed with the test plate whose surface was cleaned under the above conditions as the cathode. . Then, after washing with water and drying, the same ceramic coating as in Example 1 was applied thereon. Further, as a comparison, a non-treated (steel plate whose surface was only cleaned by degreasing) coated with the same ceramic coating as in Examples 1 and 2 was prepared.

These untreated test pieces of Example 1 and Example 2 were heated at 250 ° C. for 4 hours.
Table 1 shows the results of examining the appearance by heating in an oven at 00 ° C and 500 ° C for 2 hours and then allowing to cool at room temperature. The oxidative discoloration of the metal surface was visually observed through the transparent ceramic coating or when the coating was peeled off, with respect to the metal surface at the peeled portion.

As is clear from the above test results, when the aluminum phosphate coating is formed before the ceramic coating, the effect that the high temperature adhesion of the coating is excellent and the discoloration of the base metal is suppressed is provided. The main reason is that the heat resistance of the aluminum phosphate coating is a major factor.

Example 3 After performing the chemical conversion treatments of Examples 1 and 2, various commercially available ceramic coatings shown in Table 2 were applied and subjected to the test. The results are shown in Table 3.

Test method 1. Corrosion resistance a. Method: Perform salt spray test b. Evaluation: ASTM-D714-56 Evaluation of coating film blister generation
Evaluation by replacing the standard blister with rust Rust size: (excellent) 10 No change> 0 Large rust (inferior) Rust area: (excellent) F density small>M>MD> D Full surface rust (inferior) 2. Heat resistance Evaluation b. Method: After surface treatment and ceramic coating, heat in oven at each temperature and cool to room temperature. B. Evaluation: Visual observation of adhesion of ceramic coating and change of test plate substrate Coating adhesion: (excellent) 5 No peeling> 0 Overall peeling of substrate: (excellent) 5 No change> 0 Blueing Various ceramics in Table 2 All the coatings were applied by a dipping treatment, baking was performed under each condition, and the test was performed. The results are shown in Table 3.

(Effect of the invention) When ceramic coating is applied without pretreatment, the metal surface is oxidized and the ceramic coating peels off, but the aluminum phosphate coating does not peel off up to 500 ° C. Oxidation of the metal surface is also suppressed.

The heat resistance achieved by such a coating and baking method is comparable to the conventional CVD method. Therefore, the method of the present invention does not have the drawbacks of the CVD method in that the processing temperature is high, the material is thermally deformed, the processing time is 2 to 8 hours, the productivity is low, and the apparatus cost is high. Is the way. That is, when the present invention is applied to the coating and baking method, it has advantages that the processing method is simple, the productivity is high, and the application range is wide.

In addition, the method of the present invention is applicable to the CVD method,
In this case, the adhesion is further improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the heating temperature, the thermogravimetric change and the differential thermal analysis result of the aluminum phosphate coating.

Claims (2)

[Claims] 1. A ceramic coating method for a metal, which comprises subjecting a metal material to chemical conversion treatment or electrolytic treatment to form an aluminum phosphate coating film, and then applying a ceramic coating on the coating film. 2. The above-mentioned treatment is carried out in an acidic phosphoric acid solution having a pH of 1.5 to 5.0 containing 0.01 to 10 g / l of aluminum ions and 1 to 100 g / l of phosphate ions. The method according to item 1.