JPH08100250A - Surface treatment of copper member - Google Patents

Abstract

PURPOSE: To suppress the rise of natural potential and to prevent pitting corrosion by forming an oxidized coating film on a copper member by oxidation under heating in an oxygen-contg. atmosphere. CONSTITUTION: A copper member such as a copper tube is heated in an oxygen- contg. atmosphere such as air to form a corrosion resistant oxidized coating film of about 10-500nm thickness on the surface of the copper member. Since this oxidized coating film formed by surface treatment acts as a barrier to electronic conduction, even when an active oxygen producing field is formed, a cathode reaction is not accelerated, the rise of natural potential does not occur and pitting corrosion is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for a copper member, and more particularly to a surface treatment method for a copper member which forms a good corrosion resistant oxide film on the surface of a copper pipe or the like to prevent pitting corrosion.

[0002]

2. Description of the Related Art Copper pipes are used in addition to water and hot water supply pipes,
Widely used for heat transfer tubes such as air conditioners and heat exchangers. Copper tubes used for such purposes are generally shipped as products after bright annealing is performed in a reducing atmosphere in the final stage of the manufacturing process. Due to this bright annealing, the product copper tube has a beautiful metallic luster, but the oxide film on the surface is in an extremely thin state.

[0003]

When such a copper pipe is used for pipes such as water supply pipes and hot water supply pipes and heat transfer pipes, leakage due to pitting corrosion may occur.

Conventionally, regarding the pitting corrosion of the copper tube, the natural potential of the copper tube is a critical value (190 mV based on the silver / silver chloride reference electrode).
Although it is known that pitting corrosion occurs when the value exceeds the above, the inventors of the present invention have studied the factors that cause pitting corrosion in the conventional copper pipes from the viewpoint of materials, and as a result, the copper pipes conventionally provided are We found that the spontaneous potential could easily exceed the critical value and cause pitting corrosion.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a surface treatment method for a copper member which can remarkably improve the pitting corrosion resistance of a copper pipe.

[0006]

According to a first aspect of the present invention, there is provided a surface treatment method for a copper member, wherein a copper member is heated in an oxygen-containing atmosphere to form a corrosion resistant oxide film on the surface of the copper member. .

According to a second aspect of the present invention, there is provided a surface treatment method for a copper member, wherein the oxide film formed has a thickness of 1
It is characterized in that it is 0 to 500 nm.

Hereinafter, the present invention will be described in detail.

In the present invention, a copper member such as a copper pipe is heated in an oxygen-containing atmosphere such as air, oxygen-enriched air, or oxygen atmosphere, preferably in air, to oxidize the surface and to corrode the surface. Form an oxide film. The thickness of the oxide film is 10 to 500 nm, preferably about 20 to 100 nm.

The heating temperature for forming this film is
If it is too low, the corrosion resistant oxide film is not sufficiently formed and the effect of preventing pitting corrosion becomes low. Even if the heating temperature is excessively high, there is no great difference in the formation efficiency of the corrosion-resistant oxide film, and the heating cost is unnecessarily increased, and the copper member may be adversely affected. Therefore, the heating temperature is preferably in the range of 40 to 400 ° C.

The more preferable heating temperature varies depending on the heating time, the oxygen concentration in the atmosphere, the size and shape of the copper member to be treated, and the required degree of pitting corrosion resistance. When performing the surface treatment of a copper pipe used for a pipe such as or a heat transfer pipe such as an air conditioner or a heat exchanger, by heating in air at 150 to 350 ° C for about 0.2 to 60 minutes, 10 to 500 on the tube surface
It is preferable to form a corrosion resistant oxide film having a thickness of about 20 nm, preferably about 20 to 100 nm.

The surface treatment method for a copper member according to the present invention as described above can be effectively applied not only to copper pipes but also to other copper members.

[0013]

[Function] By heating and oxidizing a copper member such as a copper pipe in an oxygen-containing atmosphere, an oxide film having excellent corrosion resistance can be formed. This corrosion-resistant oxide film suppresses an increase in spontaneous potential, resulting in pitting corrosion. Can be prevented.

That is, the increase in the natural potential of a copper member such as a copper pipe that causes pitting corrosion occurs when a condition for accelerating the cathodic reaction represented by the following formula that occurs on the copper surface during the corrosion reaction is established. .

[0015] _{O 2 + 2H 2 O + 4e} - → 4OH - ... As the conditions for the cathode reaction is accelerated, and that the place where microorganisms active oxygen generated by adhering to the copper tube surface.

However, the thick oxide film serves as a barrier for electron conduction, and even if a field for generating active oxygen is formed, the cathode reaction in the above formula is not promoted and the spontaneous potential does not rise. Therefore, pitting corrosion is prevented.

[0017]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

The copper pipe test pieces used in the examples were Nos. 1 to 5 below, and the inner surface of the pipe was used as the test surface, and the other surfaces were coated with silicone resin.

No. 1: Conventional product (product subjected to bright annealing) No. 2: Heat-oxidized in air atmosphere at 275 ° C. for 1 minute No. 3: Heat-oxidized in air atmosphere at 275 ° C. for 2 minutes No .4: Heat-oxidized in air atmosphere at 275 ° C. for 5 minutes No. 5: Heat-oxidized in air atmosphere at 275 ° C. for 60 minutes In addition, in the above-mentioned heat oxidation of copper pipes No. 2 to No. The thickness of the oxide film formed is No. 2: 8 nm and No. 3:
It was 16 nm, No. 4:40 nm, and No. 5: 100 nm.

Example 1: Test for raising self-potential of copper tube in active oxygen system NBT (Nitro Blue Tetrazolium: redox dye:
_{C 40 H 30 N 10 O 6} Cl 2 = molecular weight 817.65) 50
The copper tube test pieces of Nos. 1 to 4 and the reference electrode (silver / silver chloride electrode) were immersed in 1 liter of a phosphate buffer (pH 8.1) containing μM and maintained at 37 ° C. Active oxygen was generated by adding 10 g (1% by weight) of xylose, and the change with time of the spontaneous potential was measured, and the results are shown in FIG.

From FIG. 1, it is clear that the conventional product of No. 1 has a rapid increase in the natural potential, but the increase in the natural potential is suppressed by the thermal oxidation.

Example 2: Self-potential rise test of copper pipe in fresh water system 100 liters of well water was added as test water 2 to tank 1 of the water flow test apparatus shown in FIG. The test water was circulated by the pump 4 by immersing each of Nos. 1, 4, and 5. A silver / silver chloride electrode is used as the reference electrode 5, and a change in spontaneous potential with time is measured by a potentiometer 6.
The results are shown in Fig. 3. In FIG. 2, 7 is a flow meter and 8 is a valve.

As shown in FIG. 3, in the conventional product of No. 1, the spontaneous potential rises above the critical value (190 mV) to cause pitting corrosion. However, the thermal oxidation suppresses the increase in spontaneous potential and causes pitting corrosion. Clearly not.

[0024]

As described above in detail, according to the surface treatment method for a copper member of the present invention, the corrosion resistance of a copper member such as a copper pipe is remarkably enhanced by the extremely simple treatment of heating in an oxygen-containing atmosphere, Food can be surely prevented.

[Brief description of drawings]

FIG. 1 is a graph showing the results of Example 1.

FIG. 2 is a system diagram showing a test apparatus used in Example 2.

FIG. 3 is a graph showing the results of Example 2.

[Explanation of symbols]

 1 Tank 3 Copper tube test piece 5 Reference electrode 6 Potentiometer

Claims (2)

[Claims] 1. A method for treating a surface of a copper member, which comprises forming a corrosion resistant oxide film on the surface of the copper member by heating the copper member in an oxygen-containing atmosphere. 2. The surface treatment method for a copper member according to claim 1, wherein the oxide film formed has a thickness of 10 to 500 nm.