JP2004043960A - Method for reducing copper solubility on inner surface of copper tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent provide copper ions dissolved from copper by coating an inner surface of copper tube with tin from being infiltrated into drinking water when the copper tube is used as components for drinking water pipe. <P>SOLUTION: In the method of reducing the solubility of copper in water on the inner surface of copper tube, in order to accomplish uniformly oriented crystal growth, in a process of tin plating and copper/tin-phase formation, process parameters of a surface treatment (degreasing and pickling), flow conditions (flow rate <1 m/s), temperature (50°C-80°C), and time (1 min-10 min) are intentionally and mutually harmonized. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for reducing the solubility of copper on the inner surface of a copper tube.
[0002]
[Prior art]
The interior surface of the copper tubing is coated with tin, and the copper ions dissolved from the copper by such tin coating flood the drinking water when such copper tubing is used as a component in drinking water conduits. It is known to prevent exit. In this connection, European standards for drinking water requirements should also be noted.
[0003]
In the case of the conventionally known method for applying a tin layer to the inner surface of a copper tube, only disordered crystals are formed. Therefore, the packing density of tin crystals is not satisfactory. Therefore, copper ions can enter the drinking water beyond the tin layer.
[0004]
[Problems to be solved by the invention]
It is an object of the present invention to provide a method, starting from the prior art, which ensures that copper dissolution on the inner surface of a copper tube is distinctly reduced.
[0005]
[Means for Solving the Problems]
This problem is solved by the characteristic features described in claim 1.
[0006]
The present invention has shown that a high packing density of tin crystals can be achieved when there is oriented crystal growth during the tin coating. The high packing density of the tin layer results in a copper / tin phase which is very uniform and uniformly formed and is very stable. For this purpose, the tin layer is uniform and coated with a small thickness, on the order of about 0.1 μm to 3 μm, with a small number of pores. This oriented crystal growth is intended for the process parameters of surface pretreatment (degreasing and pickling), flow conditions (flow rate <1 m / s), temperature (50-80 ° C) and time (1-10 minutes). Is achieved by a typical preparation.
[0007]
Despite the situation in which metallic tin can no longer be fixed to the tube surface after a relatively short operating time, the copper solubility remains low due to the external stable Cu / Sn-phase. Is obtained. Tube surfaces treated according to the invention are characterized by very low copper solubility and high durability.
[0008]
Confirmation of the crystal structure of tin is advantageously performed by the results of X-ray diffraction experiments. Upon interaction between the X-rays and the single crystal, the incident wave is diffracted in separate spatial directions due to the lattice-like structure of the tin crystal. The orientation of the crystal lattice with respect to the initial light, the dimensions of the lattice and the wavelength used determine the state of the diffraction direction, but the intensity of the diffracted light depends on the distribution of tin atoms in the unit cell.
[0009]
For this purpose, long sections are separated as samples from tin-coated copper tubes according to the invention. The sample is then slit longitudinally and the cut sample is then bent into a flat material. This flat material with a tin coating on top is then irradiated with X-rays at λ (FeKα) = 1.3733 °, with the X-rays being directed at various diffraction angles onto a flat sample. The results show that high X-ray diffraction intensity can be confirmed under various angles, thereby demonstrating that almost 100% of the X-rays are reflected. Thus, tin atoms have a very high packing density. A satisfactory barrier to the entry of copper ions into the drinking water is formed.
[0010]
In an advantageous embodiment of the basic idea of the invention, the plane of the tin crystal (101) is oriented parallel to the inner surface of the copper tube according to claim 2.
[0011]
In this connection, it is advantageous according to claim 3 if the tin crystal plane (101) is oriented parallel to the copper crystal plane (101).
[0012]
Furthermore, according to claim 4, a further improvement is achieved by orienting the copper and tin crystal planes (101) parallel to each other and the directions (101) perpendicular to each other.
[0013]
Advantageous tin coatings have been confirmed by the following internal comparative experiments:
The coated copper tube of the present invention is brought into contact with drinking water for 15 months. This contact results in a tin dioxide layer (Sn ₃ O ₂ (OH) ₂ ) on the inner surface. Similarly long sections are separated from the copper tube, cut longitudinally, bent flat and then irradiated with X-rays at λ (FeKα) = 1.9373 °. In this case, it was confirmed that the X-ray reflection (X-ray diffraction intensity) was clearly 100% or less. It is believed that the object of the present invention was not achieved.
[0014]
The tin hydroxide layer is then completely removed, and the original coating state is restored. That is, the copper / tin on a copper - layer _(Cu 6 Sn ₅₎ is present.
[0015]
Then, when X-ray irradiation was performed, almost 100% reflection was confirmed. Thus, the advantages of the method of the present invention are fully confirmed.

Claims (4)

In a method of reducing the copper solubility of the inner surface of the copper tube, surface treatment (degreasing and pickling) of process parameters in the course of tin coating and copper / tin-phase formation to achieve uniformly oriented crystal growth; The above method characterized in that the flow conditions (flow velocity <1 m / s), the temperature (50 ° C. to 80 ° C.) and the time (1 min to 10 min) are intentionally matched to one another. The method according to claim 1, wherein the tin crystal plane (101) is oriented parallel to the inner surface of the copper tube. 3. The method according to claim 1, wherein the tin crystal plane (101) is oriented parallel to the copper crystal plane (101). 4. The method according to claim 1, wherein the copper and tin crystal faces are oriented parallel to one another and the directions are oriented perpendicular to one another.