US20120205010A1

US20120205010A1 - Corrosion control method of metal

Info

Publication number: US20120205010A1
Application number: US13/369,323
Authority: US
Inventors: Katsumi Mabuchi; Haruo Akahoshi
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2011-02-16
Filing date: 2012-02-09
Publication date: 2012-08-16
Also published as: JP2012167342A; JP5372983B2

Abstract

The present invention provides a method of preventing a metal from corroding by giving a high corrosion resistance in the state of retaining the functions of the metal surface, a surface of a thin film material particularly. A stable silane coupling layer which has a robust bond is formed on a metal surface by using a silane coupling agent and an oxidizer in combination.

Description

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent application serial No. 2011-030359, filed on Feb. 16, 2011, the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a surface treatment to prevent a metal surface from corroding, and to a metal material produced by the surface treatment.
2. Description of Related Art
As a surface treatment for corrosion resistance heretofore been applied, there is a chromate treatment using a substance including hexavalent chromium such as chromic acid or dichromic acid. From the viewpoint of environmental problems in recent years however, a surface treatment including hexavalent chromium is restricted and the development of a chromium-free surface treatment is vigorously worked on. As such a surface treatment as not using hexavalent chromium, a method of processing a metal surface with a solution of at least one trivalent chromium chelated complex is known as described in Japanese Patent Application Laid-Open No. 2004-3019 for example. As a technology of using an inorganic component other than chromium, a treatment with a metal surface treatment agent having a vanadium compound and a metal compound containing at least one kind of metal selected from zirconium, titanium, molybdenum, tungsten, manganese, and cerium is disclosed in Japanese Patent Application Laid-Open No. 2002-30460 for example. As corrosion protection methods using a silane coupling agent for example, a method of processing a metal plate with an aqueous solution containing an organic functional silane of a low concentration and a cross-linking agent is disclosed in U.S. Pat. No. 5,292,549, a method of preventing a metal from corroding with a bifunctional polysulfur silane is disclosed in Japanese Patent Application Laid-Open No. 2002-519505, and a method of applying long-term coating to a metal substrate by bringing the metal substrate into contact with a solution containing aminosilane and multisilyl functional silane and then removing the solvent is disclosed in Japanese Patent Application Laid-Open No. 2007-291531. Further, Japanese Patent Application Laid-Open No. 2007-291531 discloses a method of producing a chromium-free surface-treated steel sheet excellent in corrosion resistance, fingerprint resistance, blackening resistance and paint adhesiveness with a surface treatment agent containing a specific resin compound (A), a cationic urethane resin having at least one kind of cationic functional group selected from primary to tertiary amino groups and a quaternary ammonium base (B), one or more kinds of silane coupling agents having specific reactive functional groups (C), and a specific acid compound (E); and having the contents of the cationic urethane resin (B) and the silane coupling agent (s) (C) controlled in prescribed ranges.

SUMMARY OF THE INVENTION

The present invention is characterized by forming a silane coupling layer on a metal substrate by bringing the metal substrate into contact with a solution containing an organic functional silane at least partially hydrolyzed, an oxidizer and a solvent, and then removing the solvent.
The present invention can make it possible to realize a surface being excellent in corrosion resistance and having the heretofore functions of a metal surface by applying a silane coupling agent in combination with an oxidizer to a metal, in particular to a transition metal or a metallic alloy thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a surface treatment to prevent a metal surface from corroding, or to a method for producing a metal material and to the metal material produced by the surface treatment, and particularly to a surface of a thin film of a metal.
The method provides a surface not only having an improved corrosion resistance but also being excellent in thermal resistance, solvent resistance, slidability and smoothness by using a single or plural organic functional silane(s) and an oxidizer in combination and hence forming an organic coating layer on a metal surface. The metal surface to which the present invention is applied is a surface showing the characteristics of being very smooth and having functionality as it is represented by a surface of magnetic disk which is coated with the thin film of the metal on a substrate.
It is required to provide a surface not only having an improved corrosion resistance but also being excellent in thermal resistance, solvent resistance and slidability. However, the methods of using a trivalent chromium chelated complex, a vanadium compound or the like of the above related arts have the following problems:
A thick film of about several microns is formed although a corrosion resistance comparable to a chromate film can be obtained in spite of the fact that the self-repairability is low. A processed metal disappears during processing when it is applied to a thin film because the treatment environment is in a strong acidic region. Primary functions of the metal surface are lost since a thick product is deposited on the surface even when the processed metal does not disappear.
In the corrosion protection method using a silane coupling agent, a product having satisfactory corrosion resistance, thermal resistance, solvent resistance and slidability is not obtained. In particular, the product is weak in the satisfactory corrosion resistance. An additional problem is that an organic functional silane is easily removed by rinsing or the like because it does not bind well to the metal surface. Further, plural silane coupling agents are applied sequentially and a larger number of processes are applied in many cases, in order to enhance corrosion resistance by using the silane coupling agents. Thus, they are energetically inefficient and require a lot of time. Consequently, there are many problems in practical applications. For that reason, comprehensively satisfactory surface treatment agent and surface treatment method are strongly demanded.
An object of the present invention is to provide a method of preventing a metal from corroding by giving a high corrosion resistance in the state of retaining the functions of the metal surface.
A metal corrosion protection method intended in the present invention provides a surface not only having an improved corrosion resistance but also being excellent in thermal resistance, solvent resistance and slidability; and gives a surface maintaining the heretofore characteristics of being very smooth and having functionality as it is represented by a magnetic disk surface. Consequently, the characteristics necessary as a coated substance are as follows:
(1) To show a corrosion protection action of a metal or an alloy thereof to be processed,
(2) To form a smooth and dense film having defects of a smallest possible number, and
(3) To retain the heretofore functions of a metal surface.
one of the characteristics of the item (3) is to have a structure not causing the deterioration of a magnetic recording characteristic caused by the increase of a magnetic distance between a magnetic head and a magnetic recording medium if a hard disk is taken as an example, and another of the characteristics of the item (3) is to have the sensing function as it is, if a sensor is taken as an example.
Although a corrosive environment is basically air-based or water-based, corrosion resistance in a wide pH environment is required since there exist factors such as acidification or alkalization caused by an ambient material, atmospheric pollutants or the like which are decomposed or dissolved, and interfusion of chlorides.
With regard to the item (1), as a result of various studies, we found that a surface excellent in not only corrosion resistance but also thermal resistance, solvent resistance, slidability and smoothness can be obtained by retaining a silane coupling layer stably on the metal surface. Further, we found that it is important to form an ultrathin oxide on the metal surface in order to retain the silane coupling agent stably on the metal surface. There are the following three methods for forming the ultrathin oxide on the metal surface and forming the silane coupling layer thereon:
[1] To make an oxidizer having the function of oxidizing the metal coexist in a solution containing the silane coupling agent,
[2] To immerse the metal in a solution having the function of oxidizing the metal before immersing the metal in a solution containing the silane coupling agent, and
[3] To oxidize the metal in a dry environment before immersing the metal in a solution containing the silane coupling agent.
With regard to the item (2), an ultrathin oxide is formed on the surface of the metal and BTSE molecules form a strong coordination bond with the oxide when a silane coupling agent, for example, 1,2-bis(triethoxysilyl)ethane (hereunder refer to as BTSE) is used and a hydrogen peroxide solution is used as an oxidizer. And then a covalent bond is formed among the BTSE molecules by applying a heat treatment and thereby a robust BTSE molecule film is formed on the metal surface. Hence a very dense film not having defects and moreover being excellent in adhesiveness is formed.
With regard to the item (3), it is possible to highly inhibit corrosion in the state of having a surface unchangingly retaining the characteristics of being very smooth and having functionality since BTSE is arrayed in the order of molecules.
The present invention makes it possible to form a stable silane coupling layer on the metal surface by using the silane coupling agent and the oxidizer in combination. And thereby the present invention makes it possible to provide a surface being excellent in corrosion resistance and moreover unchangingly retaining the functions of the metal surface.
The present invention can be classified roughly into two methods.
One is a method of forming a silane coupling layer on a metal surface by immersing a subject metal in a solution containing a silane coupling agent and an oxidizer in combination.
The other is a method including the following steps: applying an oxidation treatment to a surface of a subject metal by exposing it in a dry environment, or forming oxide on the surface by immersing the subject metal in a solution containing an oxidizer beforehand; and then forming the silane coupling layer on the surface by immersing the oxidation-treated metal in a solution containing the silane coupling agent.
The methods are hereunder described separately.
(1) With regard to the method of making the silane coupling agent coexist with the oxidizer

[Solvent]

Since the solubility of some silane coupling agents to water is restricted, a solvent containing one or two or more alcohols is used in order to improve the solubility of the silane coupling agents basically. The alcohols further improve stability of a treatment solution and wettability of the metal substrate. The silane coupling agents have to be hydrolyzed basically and hence a solvent having a high degree of affinity with water is preferably used. Specifically, used are methanol, ethanol, propanol, butanol, and isomers thereof; ketones such as acetone, methyl ethyl ketone and diethyl ketone; ethers such as dimethyl ether, ethyl methyl ether, diethyl ether and tetrahydrofuran; and glycols such as ethylene glycol, propylene glycol and diethylene glycol.

[Oxidizer]

Any of ordinary oxidizers can be used. An oxidizer is required to have an ability to oxidize a metal surface as a matter of course. If the oxidizability is excessively large however, a solvent described above is also oxidized and hence the type and the concentration of the oxidizer are very important. Then of course, since a main component of the solution is the solvent stated above and only a quantity of water corresponding to a quantity necessary for hydrolyzing a silane coupling agent stated below exists, the oxidizer should have an oxidizing action even with a low concentration and moreover should have a high solubility. Hydrogen peroxide; chloric acid, perchloric acid, persulfuric acid and nitric acid and salts of those acids; diammonium cerium nitrate, etc. are used.

[Silane Coupling Agent]

Substances used as the silane coupling agents are classified roughly into the following two types.
One type is represented by the structure of X¹ _3-nSiR′SiX² _3-n. In the structure, n is 0 or 1, and X¹and X²are selected from the group consisting of hydrolysable groups (or hydrolytic groups) (methoxy, ethoxy, methoxyethoxy, propyl, butyl, isobutyl, s-butyl, t-butyl and acetyl) and both the X¹and X²may be either an identical substance or different substances. Then R′ is selected from alkyl, alkenyl, and alkenyl having at least one amino group or S group substituted in place of a hydrogen atom.
Examples are bis(triethoxysilyl)ethane (BTSE: (H₅C₂O)₃S₁—CH₂CH₂—Si(OC₂H₅)₃); bis(triethoxysilyl)propylamine (BTSPA: (H₅C₂O)₃Si—(CH₂)₃—NH—(CH₂)₃—(OC₂H₅)₃); and bis(triethoxysilyl)propyltetrasulfide (BTSPS: (H₂C₂O)₃Si—(CH₂)₃Si—(CH₂)₃—Si(OC₂H₅)₃).
The other type is represented by the structure of X¹ _3-nR_nSiZ as an organic functional silane. In the structure, n is 0 or 1, X¹is selected from the group consisting of hydrolysable groups (methoxy, ethoxy, methoxyethoxy, propyl, butyl, isobutyl, s-butyl, t-butyl and acetyl), Z is selected from the group consisting of organic functional groups represented by amino, mercapto, phenyl, vinyl, epoxy, methacryl, isocyanate, ureide and sulfa, and alkyl groups, and R is a methyl group.
Examples are vinyl silane (CH₂═CHSi(OCH₂CH₃)₃); 3-glycidoxypropyltrimethoxysilane (CH₂— (O)—CHCH₂OCH₂CH₂CH₂Si(OCH₃)₃); 3-mercaptopropyltriethoxysilane (HSCH₂CH₂CH₂Si(OCH₂CH₃)₃); 3-aminopropyltriethoxysilane (H₂NCH₂CH₂CH₂Si(OCH₂CH₃)₃); Phenyltriethoxysilane (C₂H₅O)₃Si—C₆H₅); 3-methacryloxypropyltriethoxysilane (CH₂—C(CH₃)COOCH₂CH₂CH₂SOCH₂CH₃)₃); 3-isocyanatepropyltriethoxysilane (O═C=NCH₂CH₂CH₂Si(OCH₂CH₃)₃); decyltrimethoxysilane (CH₃(CH₂)₉Si(OCH₃)₃); and 3-ureidepropyltriethoxysilane ((C₂H₅O)₃SiC₃H₆NHC(O)NH₂)
In addition to those, octadecyltriethoxysilane, bis (triethoxysilyl)ethane, bis(triethoxysilyl)hexane, bis(triethoxysilyl)ethylene, and bis(trimethoxysilyl)ethylbenzene are also effective. The silane coupling agents stated above are hydrolyzed at least partially or preferably completely. The concentration of such a silane coupling agent is about 0.05 to 10 wt % and preferably 0.2 to 1 wt %. Since the silane coupling agent has to be hydrolyzed, it is necessary to add water. An appropriate quantity of water used is in the range of several % to 10% of a whole treatment liquid. In the case of a hydrogen peroxide solution, it is not necessary to add water since it is added usually in the state of about 30% and water is already included in hydrogen peroxide itself.
The treatment liquid is applied basically by immersion but can also be applied by splaying or roll coating.

[pH Adjuster of Silane Coupling Solution]

A pH of a silane coupling solution is largely related to a hydrolysis reaction rate and an oxide generation rate. Here, pH is referred to as “a potential Hydrogen”. Although pH is maintained preferably at about 7 or lower from the viewpoint of hydrolysis reaction, oxides can stably exist, for example, in the range of pH 7 to 13 with regard to Co, pH 8 to 12 with regard to Ni, and pH 7 to 12 with regard to Fe respectively according to the Pourbaix diagram (Atlas of Electrochemical Equilibria in Aqueous Solutions, Marcel Pourbaix, NACE International Cebelcor) and hence pH of a treatment solution is preferably maintained in the range of 3 to 12. As a pH adjuster, hydroxide such as potassium hydroxide, ammonia, sulfuric acid, hydrochloric acid, nitric acid, etc. are appropriately used.
(2) With regard to the method of immersing the metal in the silane coupling agent solution after oxidation treatment is applied

[Oxidizer]

Any of ordinary oxidizers can be used. An oxidizer is required to have an ability to oxidize a metal surface as a matter of course. Unlike the method (1), when a treatment is applied in a wet environment, the method does not require the coexistence of a solvent and hence a strong oxidizer can be used. Oxidizers used in a wet environment are hydrogen peroxide solution, permanganic acid, chloric acid, dichromic acid, bromic acid, nitric acid, hypochlorous acid and salts of those, peracetic acid, ozone water, etc. In a dry environment, a method of applying air oxidation during heating and a method of applying oxidation by ozone are used.

[Silane Coupling Agent]

A silane coupling agent described in the method (1) can be used. Although the silane coupling agent has to be hydrolyzed in the method (1), it is not necessary to dear to add water since many hydroxyl groups exist on the surface of generated oxide and they cause the hydrolysis reaction of a silane coupling agent in the case of applying oxidation treatment by the method (2) that is a wet method. In the case of generating oxide in a dry environment however, it is necessary to add water in the same manner as the method (1).

[pH Adjuster of Silane Coupling Solution]

Since it is not necessary to generate oxide in the event of silane coupling unlike the method (1), pH may simply be adjusted while attention is focused only on accelerating hydrolysis reaction. The pH may be maintained preferably at 7 or lower in order to accelerate the hydrolysis reaction and yet preferably at 3 to 6 if possible. As a pH adjuster, hydroxide such as potassium hydroxide, ammonia, sulfuric acid, hydrochloric acid, nitric acid, etc. are suitably used.
In the case of adopting the method (1) or (2), appropriate time for immersing a metal in a silane coupling agent is about one hour. In the case where the concentration of the silane coupling agent is not more than 1 wt % or another case however, corrosion resistance may sometimes improve when the immersion time is prolonged to about 24 hours.
After the silane coupling treatment, a metal surface is cleaned with the solvent used (not containing the oxidizer and the silane coupling agent) and successively dried by air blowing Otherwise it is also possible to dry the metal surface by maintaining the temperature in the range of room temperature to 50° C.
Further, it is possible to improve corrosion resistance by applying a heat treatment as post-treatment after the silane coupling treatment. The heat treatment is applied preferably at a temperature of 100° C. to 200° C. for 30 minute to 2 hours and yet preferably at a temperature of 100° C. to 150° C. for 30 minute to 1 hour.
Furthermore, it is possible to further improve corrosion resistance by applying the silane coupling treatment several times again after the heat treatment or after the drying. On this occasion, the first silane coupling treatment liquid and the succeeding silane coupling treatment liquid may not be identical to each other.
Corrosion evaluation is carried out as follows.
Each of specimens is prepared by forming titanium oxide on a silicon wafer as a tight layer by sputtering, successively applying a subject metal, for example, cobalt, nickel or iron, thereon by sputtering, and thus forming a film. Silane coupling layers are formed by the two methods described above. Some of the specimens are subjected to a heat treatment, for example, at 100° C. for 1 hour in the air after the silane coupling layer is formed.
Corrosion resistance is evaluated by the following two methods.
(1) Constant Temperature and Humidity Test
A silane coupling treated sample is left for 96 hours under the condition of high temperature and high humidity of 65° C. and 90% or more in relative humidity RH. A specimen produced by forming a film on a silicon wafer of 2.5 inches is used. Successively, the number of corrosion points in the region between 14 mm and 25 mm in radius is counted with an optical surface analyzer and the specimen is graded as follows.
A specimen having a count number of less than 50 is graded as “A”, a specimen having a count number of 50 or more to less than 200 is graded as “B”, a specimen having a count number of 200 or more to less than 500 is graded as “C”, and a specimen having a count number of 500 or more is graded as “D”. A grade of “B” or better is desirable for a practical use.
Here, an expression that “P is 50 or more to less than 200” is referred to as “50≦P<200”.
(2) Electrochemical Test
A sample subjected to silane coupling treatment is sealed while a part 1 cm²in area of the sample is not sealed. The sample is immersed in a borate aqueous solution of pH 7.47 or a 3% NaCl aqueous solution. When the sample is immersed for 10 minute and potential is stabilized, the potential is scanned at a scanning rate of 30 mV/min in an anode direction while a low potential of −100 mV from the immersion potential is used as a benchmark and an electric current is measured. After the measurement, a corrosion current density is obtained with the Tafel's relational expression. Comparing a corrosion current density in an untreated case, a case where the corrosion current density is less than 10% is evaluated as “A”, a case where it is 10% or more to less than 20% is evaluated as “B”, a case where it is 20% or more to less than 50% is evaluated as “C”, and a case where it is 50% or more is evaluated as “D”.
Concrete examples to which the present invention is applied are hereunder explained in reference to tables.

Comparative Examples 1-4

With regard to untreated Co, Ni, Fe and Cu, as shown in Comparative Examples 1-4 (Table 1), the evaluation results of the corrosion resistance in the constant temperature and humidity test are the grade “D” and the corrosion resistance is very poor. The test results are used as the benchmark of the following corrosion evaluation results.

TABLE 1

	Silane coupling treatment	Corrosion evaluation

	Silane				Constant	Electrochemical
	coupling	Coexisting			temperature	measurement

Comparative		agent/	oxidizer/		Immersion	and humidity		NaCl
example No.	Specimen	concentration	concentration	pH	time	test	Borate	solution

1	Co	—	—	—	—	D	—	—
2	Ni	—	—	—	—	D	—	—
3	Fe	—	—	—	—	D	—	—
4	Cu	—	—	—	—	D	—	—

Examples 1-4

In Examples 1-4, Co, Ni, Fe and Cu are used as specimens and a silane coupling layer is formed on each of the metals with a treatment liquid produced by adding 1 wt % BTSE as the silane coupling agent and 30% H₂O₂by 10% as the coexisting oxidizer. The pH is set at 4.2 and immersion time is set at 1 hour. Ethanol is used as the solvent. The corrosion evaluation results of Co, Ni and Cu are all “A” in the constant temperature and humidity test and the electrochemical test (in borate) and good corrosion resistance is shown. The corrosion evaluation of Fe is “B” in the constant temperature and humidity test and the electrochemical test and a dramatically good corrosion resistance is shown in comparison with the untreated case although the corrosion resistance is somewhat lower than the other metals. The similar results are obtained even when acetone, toluene or ethyl ether is used as the solvent.

TABLE 2

	Silane coupling treatment	Corrosion evaluation

	Silane				Constant	Electrochemical
	coupling	Coexisting			temperature	measurement

Example		agent/	oxidizer/		Immersion	and humidity		NaCl
No.	Specimen	concentration	concentration	pH	time	test	Borate	solution

1	Co	BTSE/1 wt %	30% H₂O₂/10%	4.2	1 h	A	A	A
2	Ni	BTSE/1 wt %	30% H₂O₂/10%	4.2	1 h	A	A	A
3	Fe	BTSE/1 wt %	30% H₂O₂/10%	4.2	1 h	B	B	B
4	Cu	BTSE/1 wt %	30% H₂O₂/10%	4.2	1 h	A	A	A

Examples 3 and 5-6

In Examples 3 and 5-6, an influence of the immersion time on the corrosion evaluation is shown when Fe is used as the specimens and a silane coupling layer is formed on the metal by using a treatment liquid produced by adding 1 wt % BTSE as the silane coupling agent and 30% H₂O₂by 10% as the coexisting oxidizer. Ethanol is used as the solvent. Whereas the corrosion evaluation is “B” in every test in the case where the immersion time is 1 hour (Example 3), the corrosion evaluation is “A” in the constant temperature and humidity test in the case where the immersion time is 4 hours, and the corrosion evaluation is “A” in all the tests by applying 24 hour immersion, and thus it is obvious that the corrosion resistance improves as the immersion time increases.

TABLE 3

	Silane coupling treatment	Corrosion evaluation

	Silane				Constant	Electrochemical
	coupling	Coexisting			temperature	measurement

Example		agent/	oxidizer/		Immersion	and humidity		NaCl
No.	Specimen	concentration	concentration	pH	time	test	Borate	solution

3	Fe	BTSE/1 wt %	30% H₂O₂/10%	4.2	1 h	B	B	B
5	Fe	BTSE/1 wt %	30% H₂O₂/10%	4.2	4 h	A	B	B
6	Fe	BTSE/1 wt %	30% H₂O₂/10%	4.2	24 h	A	A	A

Examples 7-15

In Examples 7-15, the corrosion evaluation results are shown when Co is used as the specimens and a silane coupling layer is formed on each of the metals by using a treatment liquid produced by using various kinds of silane coupling agents of 1 wt % and adding 30% H₂O₂by 10% as the coexisting oxidizer. Ethanol is used as the solvent. The silane coupling agents used are a multifunctional silane series, a vinyl silane series, a ureide series, an epoxy silane series, amercapto silane series, a sulfur silane series, etc. In any of the cases, the corrosion evaluation result is “A” and a good corrosion resistance is shown. Although data are not shown here, similar results are obtained also in the cases of Fe, Ni and Cu.

TABLE 4

	Corrosion evaluation

Silane coupling treatment

Constant

Electrochemical

Coexisting

temperature

measurement

Example		Silane coupling	oxidizer/		Immersion	and humidity		NaCl
No.	Specimen	agent/concentration	concentration	pH	time	test	Borate	solution

7	Co	BTSPA/1 wt %	30% H₂O₂/10%	4.2	1 h	A	A	A
8	Co	BTSPS/1 wt %	30% H₂O₂/10%	4.5	1 h	A	A	A
9	Co	3-aminopropyltriethoxysilane/1 wt %	30% H₂O₂/10%	9.5	1 h	A	A	A
10	Co	Octadecyltriethoxysilane/1 wt %	30% H₂O₂/10%	4.6	1 h	A	A	A
11	Co	Phenyltriethoxysilane/1 wt %	30% H₂O₂/10%	5.0	1 h	A	A	A
12	Co	Vinylsilane	30% H₂O₂/10%	6.0	1 h	A	A	A
13	Co	3-mercaptopropyltriethoxysilane	30% H₂O₂/10%	4.3	1 h	A	A	A
14	Co	3-glycidoxypropyltrimethoxysilane	30% H₂O₂/10%	5.0	1 h	A	A	A
15	Co	3-ureidepropyltriethoxysilane	30% H₂O₂/10%	8.5	1 h	A	A	A

Example 12

In Examples 3 and 16-19, the influence of pH on the corrosion evaluation is shown when Co is used as the specimens and a silane coupling layer is formed on the metal by using a treatment liquid produced by adding 1 wt % BTSE as the silane coupling agent and 30% H₂O₂by 10% as the coexisting oxidizer. Ethanol is used as the solvent. In the case where pH is 1.5, since the dissolution rate of Co is large and Co elutes when the immersion time is 1 hour, the immersion time is set at 5 minute. Whereas the corrosion evaluation is “B” in the constant temperature and humidity test, the corrosion evaluation is “C” in the electrochemical test. Although it is confirmed that the corrosion resistance improves in comparison with the case of no treatment, the corrosion inhibition action is small. This is because the pH of the solution is low and hence oxide is insufficiently formed on Co. In the cases where the pH of the treatment solution is 4.0 or more, the corrosion evaluation results are “A” and a good corrosion resistance is shown. Although data are not shown here, similar results are obtained also in the cases of Fe, Ni and Cu.

TABLE 5

	Corrosion evaluation

Silane coupling treatment

Constant

	Silane				temperature	Electrochemical
	coupling	Coexisting			and	measurement

Example		agent/	oxidizer/		Immersion	humidity		NaCl
No.	Specimen	concentration	concentration	pH	time	test	Borate	solution

16	Co	BTSE/1 wt %	30% H₂O₂/10%	1.5	5 min	B	C	C
1	Co	BTSE/1 wt %	30% H₂O₂/10%	4.2	1 h	A	A	A
17	Co	BTSE/1 wt %	30% H₂O₂/10%	8.0	1 h	A	A	A
18	Co	BTSE/1 wt %	30% H₂O₂/10%	10.2	1 h	A	A	A
19	Co	BTSE/1 wt %	30% H₂O₂/10%	12.2	1 h	A	A	A

Examples 20-23

In Examples 20-23, the influence of the type of the oxidizer on the corrosion evaluation is shown when Co is used as the specimens and a silane coupling layer is formed on the metal by using 1 wt % BTSE as the silane coupling agent and changing the coexisting oxidizer. Ethanol is used as the solvent. The oxidizers used are ammonium persulfate, sodium perchlorate, diammonium cerium nitrate and sodium chlorate. Those are strong oxidizers and hence the concentration is set so as to be lower than the case of using hydrogen peroxide. The corrosion evaluation results are “A” in both the constant temperature and humidity test and the electrochemical test in the case of using any of the oxidizers and a good corrosion resistance is shown. Although data are not shown here, similar results are obtained also in the cases of Fe, Ni and Cu.

TABLE 6

	Corrosion evaluation

Silane coupling treatment

Constant

	Silane					temperature	Electrochemical
	coupling	Coexisting				and	measurement

Example		agent/	oxidizer/	Water		Immersion	humidity		NaCl
No.	Specimen	concentration	concentration	concentration	pH	time	test	Borate	solution

20	Co	BTSE/1 wt %	Ammonium	1.0 wt %	6.0	1 h	A	A	A
			persulfate
21	Co	BTSE/1 wt %	Sodium	0.02 wt %	4.0	1 h	A	A	A
			perchlorate
22	Co	BTSE/1 wt %	Diammonium	0.005 wt %	7.0	1 h	A	A	A
			cerium nitrate
23	Co	BTSE/1 wt %	Sodium	0.05 wt %	4.0	1 h	A	A	A
			chlorate

Examples 24-26

In Examples 24-26, the results of the corrosion evaluation of specimens produced by using Co and Fe as the specimens and forming a silane coupling layer on each of the metals by using a treatment liquid produced by adding 1 wt % BTSE as the silane coupling agent and 30% H₂O₂by 10% as the coexisting oxidizer and then applying heat treatment are shown. Although the corrosion test evaluation results are “B” in the case of Fe shown in Example 3, the corrosion evaluation result comes to be “A” by applying the heat treatment. Further, the corrosion evaluation result is still “A” in the case of Co and hence it is understood that the corrosion resistance improves by applying the heat treatment. This is because the condensation reaction is accelerated.

TABLE 7

	Corrosion evaluation

Silane coupling treatment

Constant

	Silane				Post	temperature	Electrochemical
	coupling	Coexisting			treatment	and	measurement

Example		agent/	oxidizer/		Immersion	(heat	humidity		NaCl
No.	Specimen	concentration	concentration	pH	time	treatment)	test	Borate	solution

24	Fe	BTSE/0.2 wt %	30% H₂O₂/10%	4.2	1 h	100° C./1 h	A	A	A
25	Fe	BTSE/5 wt %	30% H₂O₂/10%	4.2	1 h	150° C./1 h	A	A	A
26	Co	BTSE/10 wt %	30% H₂O₂/10%	4.2	1 h	100° C./1 h	A	A	A

Examples 27-31

Examples 27-30 relate to the method (2) described earlier. Oxidation pretreatment is applied in a wet environment before silane coupling treatment is applied. The oxidizers are 30% H₂O₂in 10% concentration, ammonium persulfate in 10% concentration, sodium perchlorate in 10% concentration, and sodium permanganate in 10% concentration. The oxidation treatment is applied in a wet environment. As the silane coupling agent, BTSE (immersion time 1 hour, the solvent is ethanol) of pH 4.2 is used. As stated earlier, since many hydroxyl groups are introduced on the surface to be used by the oxidation pretreatment, water for hydrolysis may not be added to the BTSE solution. In any of the cases, the corrosion evaluation result is “A” and a good corrosion resistance is shown. Although data are not shown here, similar results are obtained also in the cases of Fe, Ni and Cu.

TABLE 8

	Corrosion evaluation

Silane coupling treatment

Constant

	Oxidation pretreatment	Silane			temperature	Electrochemical
	(wet treatment)	coupling			and	measurement

Example		Oxidizer/	Oxidation	agent/		Immersion	humidity		NaCl
No.	Specimen	concentration	time	concentration	pH	time	test	Borate	solution

27	Co	30% H₂O₂/10%	1 h	BTSE/0.2 wt %	4.2	1 h	A	A	A
28	Co	Ammonium	1 h	BTSE/5 wt %	4.2	1 h	A	A	A
		persulfate/10%
29	Co	Sodium	1 h	BTSE/10 wt %	4.2	1 h	A	A	A
		perchlorate/10%
30	Co	Sodium	1 h	BTSE/10 wt %	4.2	1 h	A	A	A
		permanganate/10%

Examples 31-32

Examples 31-32 relate to the method (2) described earlier. Oxidation pretreatment is applied in a dry environment before the silane coupling treatment is applied. As the oxidizer, air or ozone is used. As the silane coupling treatment agent, BTSE (immersion time 1 hour, the solvent is ethanol and 10% H₂O) of pH 4.2 is used. Since the silane coupling agent has to be hydrolyzed, water is contained by 10% in the silane coupling treatment liquid. In any of the cases, the corrosion evaluation result is “A” and a good corrosion resistance is shown. Although data are not shown here, similar results are obtained also in the cases of Fe, Ni and Cu.

TABLE 9

	Oxidation	Corrosion evaluation

pretreatment

Silane coupling treatment

Constant

(dry treatment)

Silane

temperature

Electrochemical

Oxidizer/

coupling

and

measurement

Example		concentration,	Oxidation	agent/		Immersion	humidity		NaCl
No.	Specimen	temperature	time	concentration	pH	time	test	Borate	solution

31	Co	Air/200° C.	0.5 h	BTSE/0.2 wt %	4.2	1 h	A	A	A
32	Co	Ozone/40° C.	0.1 h	BTSE/5 wt %	8.0	1 h	A	A	A

Comparative Examples 5-13

Comparative Examples 5-13 are the cases of evaluating corrosion when treatment is applied with a silane coupling agent not containing an oxidizer. Although an oxidizer is not contained, water is added by 10% in order to hydrolyzing the silane coupling agent. The main solvent is ethanol. In the case where treatment is applied with any of the silane coupling agents, the corrosion evaluation is “C” or lower in both the constant temperature and humidity test and the electrochemical test and corrosion resistance is not shown. Although data are not shown here, similar results are obtained also in the cases of Fe, Ni and Cu.

TABLE 10

	Corrosion evaluation

		Constant	Electrochemical
	Silane coupling treatment	temperature	measurement

Comparative		Silane coupling		Immersion	and humidity		NaCl
example No.	Specimen	agent/concentration	pH	time	test	Borate	solution

5	Co	BTSE	4.2	1 h	C	D	D
6	Co	BTSPA/1 wt %	4.2	1 h	C	D	D
7	Co	BTSPS/1 wt %	4.5	1 h	D	D	D
8	Co	3-aminopropyltriethoxysilane/1 wt %	9.5	1 h	C	D	D
9	Co	Octadecyltriethoxysilane/1 wt %	4.6	1 h	D	D	D
10	Co	Phenyltriethoxysilane/1 wt %	5.0	1 h	D	D	D
11	Co	Vinylsilane	6.0	1 h	D	D	D
12	Co	3-mercaptopropyltriethoxysilane	4.3	1 h	D	D	D
13	Co	3-glycidoxypropyltrimethoxysilane	5.0	1 h	D	D	D

Comparative Examples 14-17

In Comparative Examples 14-17, corrosion evaluation results in the case of not applying silane coupling treatment but applying only oxidation treatment are shown. The corrosion evaluation is “D” in both the constant temperature and humidity test and the electrochemical test and corrosion resistance is not shown. Although data are not shown here, similar results are obtained also in the cases of Fe, Ni and Cu.

TABLE 11

	Corrosion evaluation

		Constant	Electrochemical
	Oxidation treatment	temperature	measurement

Comparative		Oxidizer/	Immersion	and humidity		NaCl
example No.	Specimen	concentration	time	test	Borate	solution

14	Co	30% H₂O₂/10%	1 h	D	D	D
15	Co	Ammonium	1 h	D	D	D
		persulfate/10%
16	Co	Air/200° C.	0.5 h	D	D	D
17	Co	Ozone/40° C.	0.1 h	D	D	D

Examples 33-35 and Comparative Examples 17-19

In Examples 33-35, the results of measuring and identifying the surfaces of Co after treatment by XPS (X-ray photoelectron spectroscopy) in the case of the series of a silane coupling agent and an oxidizer showing corrosion resistance are shown. Then in Comparative Examples 17-19, the results of measuring and identifying the surfaces of Co after treatment by the XPS in the case of the treatment with only a silane coupling agent not showing corrosion resistance are shown. It is understood that the proportion of oxide in the O1s peak is large and a larger quantity of oxide is generated in the examples showing corrosion resistance in comparison with the comparative examples not showing corrosion resistance. A similar result is obtained also in the case of applying oxidation pretreatment shown in Example 27. Consequently, it is understood that it is necessary either to make the oxidizer coexist or to apply oxidation treatment beforehand in order to obtain the corrosion resistance with the silane coupling agent.

TABLE 12

	Silane coupling treatment	Post

		Silane coupling	Coexisting			treatment	O1s waveform analysis
Example		agent/	oxidizer/		Immersion	(heat	result by XPS (%)

No.	Specimen	concentration	concentration	pH	time	treatment)	Oxide	—OH—CO₃C═O	C—O

33	Co	BTSE/1.0 wt %	30% H₂O₂/10%	4.2	1 h	—	36	57	7
34	Co	BTSE/1.0 wt %	30% H₂O₂/10%	4.2	24 h	—	40	52	8
35	Co	BTSE/1.0 wt %	30% H₂O₂/10%	4.2	1 h	100° C./1 h	37	58	6

TABLE 13

	Silane coupling treatment	Post

		Silane coupling	Coexisting			treatment	O1s waveform analysis
Comparative		agent/	oxidizer/		Immersion	(heat	result by XPS (%)

example No.	Specimen	concentration	concentration	pH	time	treatment)	Oxide	—OH—CO₃C═O	C—O

17	Co	—	—	—	—	—	22	71	7
18	Co	BTSE/1.0 wt %	—	4.2	1 h	—	28	66	6
19	Co	BTSE/1.0 wt %	—	4.2	24 h	—	28	61	11

Examples 36-38

In Examples 36-38, alloys containing various transition metals are used as the specimens and a silane coupling layer is formed on each of the metals with a treatment liquid produced by adding 1 wt % BTSE as the silane coupling agent and 30% H₂O₂by 10% as the coexisting oxidizer. The pH is set at 4.2 and immersion time is set at 1 hour. Ethanol is used as the solvent. The corrosion evaluation results of the alloys containing the various transition metals are all “A” in both the constant temperature and humidity test and the electrochemical test (in borate) and a good corrosion resistance is shown. The similar results are obtained even when acetone, toluene or ethyl ether is used as the solvent.

TABLE 14

	Corrosion evaluation

Silane coupling treatment

Constant

	Silane				temperature	Electrochemical
	coupling	Coexisting			and	measurement

Example		agent/	oxidizer/		Immersion	humidity		NaCl
No.	Specimen	concentration	concentration	pH	time	test	Borate	solution

36	Co85/Cr5/Pt10	BTSE/1 wt %	30% H₂O₂/10%	4.2	1 h	A	A	A
37	Fe85/Ni15	BTSE/1 wt %	30% H₂O₂/10%	4.2	1 h	A	A	A
38	Cu70/Ni30	BTSE/1 wt %	30% H₂O₂/10%	4.2	1 h	A	A	A

Claims

1. A corrosion control method of a metal, the method comprising the steps of:

bringing a metal substrate into contact with a solution containing an organic functional silane at least partially hydrolyzed, an oxidizer and a solvent; and

removing thereafter the solvent on the metal substrate, and thereby forming a silane coupling layer on the metal substrate.

2. A corrosion control method of a metal, the method comprising the steps of:

applying an oxidation treatment to a metal substrate;

bringing thereafter the metal substrate into contact with a solution containing an organic functional silane at least partially hydrolyzed and a solvent; and

removing thereafter the solvent on the metal substrate and thereby forming a silane coupling layer on the metal substrate.

3. A corrosion control method of a metal, the method comprising the steps of:

immersing a metal substrate in a solution containing an oxidizer;

bringing thereafter the metal substrate into contact with a solution containing at least one kind of organic functional silane, and thereby forming a silane coupling layer on the metal substrate.

4. The corrosion control method according to claim 1 or 3, wherein the oxidizer is at least one kind selected from the group consisting of hydrogen peroxide; chloric acid, perchloric acid, persulfuric acid and nitric acid and salts thereof; ammonium persulfate; and diammonium cerium nitrate.

5. The corrosion control method according to claim 2, wherein an oxidizer used in the oxidation treatment is air or ozone.

6. The corrosion control method according to claim 1, further comprising a step of:

applying a heat treatment after forming the silane coupling layer on the metal substrate.

7. The corrosion control method according to claim 2, further comprising a step of:

8. The corrosion control method according to claim 3, further comprising a step of:

9. The corrosion control method according to claim 2 or 3, wherein the organic functional silane is represented by the following chemical formula (1) or (2),

X¹ _3-nR_nSiZ (1)

X¹ _3-nSiR′SiX² _3-n (2)

(in the expression: n is 0 or 1; X¹and X²are selected from hydrolytic groups (methoxy, ethoxy, methoxyethoxy, propyl, butyl, isobutyl, s-butyl, t-butyl and acetyl) and both the X¹and X²may be either an identical substance or different substances; Z is selected from organic functional groups represented by amino, mercapto, phenyl, vinyl, epoxy, methacryl, isocyanate, ureide and sulfa, or alkyl groups; R is a methyl group; and R′ is selected from alkyl, alkenyl, and alkenyl having at least one amino group or S group substituted in place of a hydrogen atom).

10. The corrosion control method according to any one of claims 1 to 3, wherein the metal substrate is Fe, Co, Ni or Cu, or an alloy thereof.