GB2196991A

GB2196991A - Patina remover, process for its preparation, and method for removing patina

Info

Publication number: GB2196991A
Application number: GB08724359A
Authority: GB
Inventors: Youichi Ohoya; Akihide Hirano
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 1985-05-28
Filing date: 1986-05-20
Publication date: 1988-05-11
Anticipated expiration: 2006-05-20
Also published as: JPS61272392A; BR8607125A; KR930004559B1; JPS6345474B2; KR880700102A; WO1986007099A1; GB8724359D0; GB2196991B

Abstract

A patina remover containing hydrazine, a method for removing patina by using the same, and a process for preparing a patina remover by mixing hydrazine with an anticorrosive agent for copper.

Description

SPECIFICATION Patina remover, method for manufacture thereof, and method for removal of patina FIELD OF THE INVENTION This invention relates to a patina remover, a method for the manufacture of the patina remover, and a method for the removal of patina and more particularly relates to a patina remover which is capable of selectively and effectively removing patina from the substrate of copper or a copper alloy without corroding the substrate and also capable of protecting the copper substrate against corrosion, a method for the manufacture of the patina remover, and a method for the removal of patina.

BACKGROUND OF THE INVENTION Devices using copper materials in a system such as a heat exchanger, during the course of a protracted use, sustain corrosion as in the form of pitting. The corrosion is aggravated with elapse of time eventually to jeopardize the performance of the equipment and impede safe operation thereof.

Heretofore, as means of removing products of corrosion including copper oxide which occur on the surface of the substrate, the practice of pickling the affected surface of the substrate with hydrochloric acid or sulfamic acid has been followed.

Since the effluent from the pickling plant is a strongly acidic solution of pH 1 to 4, however, the method resorting to the pickling entails various problems: (1) Since the pickling solution is capable of corroding the copper substrate, it has the possibility of inflicting damage by corrosion upon the copper substrate under treatment and does not permit the copper substrate to stand long therein.

(2) The copper ions eluted by the pickling adheres to the surface of an ion substrate by electrode position and induces secondary corrosion.

(3) The pickled substrate must be thoroughly rinsed with water to remove the adhering pickling solution. If the pickling solution escapes being rinsed, the surviving pickling solution has the possibility of starting new pitting.

None of the methods heretofore tried has been fully effective in removing products of corrosion from the copper substrates.

Incidentally, any idea of removing patina for the purpose of preventing corrosion has never been conceived. An agent developed exclusively for the removal of patina has never been proposed.

In the specification of Japanese Patent Publication SHO 47(1972)-41,230, use of hydrazine in the cleaning of the surface of a copper article is mentioned. The invention disclosed in this specification, however, relates to removal of copper or copper oxide from the surface of the copper article. Moreover, for the detegent used for the cleaning, an acid is claimed to be an essential component. The method taught therein dissolves copper with an acid and consequently forms thiourea and a chelate compound and, during the course of this dissolution, adds hydrazine to the acid for the purpose of enhancing the solubility of copper in the acid.Since this method removes not only the copper oxide occurring as scale but also the copper oxide layer formed on the surface of the copper substrate for the prevention of corrosion, the treated surface of the copper substrate is activated to a great extent. This method also has the possibility that the acid suffered to remain on the treated surface will cause corrosion of the copper substrate. The detergent disclosed in the specification of Japanese Patent Publication SHO 47(1972)-41,230, therefore, is not suitable for the selective removal of patina.

DISCLOSURE OF THE INVENTION An object of this invention is to solve the various problems suffered by the prior art as described above and provide a highly effective patina remover, a method for the manufacture- of the patina remover, and method for the removal of the patina remover, and a method for the removal of patina.

Another object of this invention is to provide -a patina remover incapable of corroding a substrate under treatment and exerting any adverse effect on the operation of a system incorpo rating therein the substrate, a method. for the manufacture of the patina remover, and a method for the removal of patina.

Yet another object of this invention is to provide a patina remover permitting the treatment for removal of patina to be carried out with ease, a method for the manufacture of the patina remover, and a method for the removal of patina.

These objects are accomplished by a patina remover characterized by containing hydrazine, a method for the manufacture of a patina remover characterized by mixing hydrazine with a corrosion inhibitor for copper, and a method for the removal of patina from a copper substrate, characterized by contacting the copper substrate with a water containing hydrazine.

Now, the present invention will be described in detail below.

This invention has originated in the finding that patina and pitting are in an indissociable relation such that when patina is present on a copper substrate, pitting proceeds in the portion of copper underlying the patina. It, therefore, aims to remove the patina from the copper substrate by cleansing and prevent occurrence and progress of the pitting. The term "patina" as used in the present invention refers to green products of corrosion of copper such as, for example, basic copper carbonate (CuC03.Cu(HO)2), copper hydroxide (Cu(OH)2), copper nitrate (Cu(NO3)2), basic copper nitrate (Cu(NO3)2.(Cu(OH2), copper pyrophosphate (CuP2O7), cupric phosphate (Cu3(PO4)2), hydrogen copper phosphate (CuHPO4), and basic copper sulfate (CuSO4.3Cu( OH)2).

The patina remover of the present invention contains hydrazine. Although the present invention does not discriminate the patina remover by its hydrazine content, the hydrazine content generally falls in the range of 10 to 50% by weight, preferably 20 to 40% by weight.

In the present invention, for the purpose of protecting the corrosionproofing copper oxide coating formed on the surface of a copper substrate under treatment and improving the patina remover's effect in selective removal of patina, the patina remover is desired to contain a corrosion inhibitor for copper in combination with hydrazine.

As examples of the corrosion inhibitor for copper, there can be cited benzothiazole, mercaptobenzothiazole, benzotriazole, tollyltriazole, and other similar azoles. Desirably the content of this corrosion inhibitor in the patina remover is approximately in the range of 0.05 to 20% by weight based on the amount of hydrazine.

The patina remover of this invention formulated as described above can be effectively used in portions affected by patina. It is also used highly effectively in cleansing copper heat exchangers in general cooling water plants, turborefrigerators, copper heat exchangers in suction type refrigerators, airconditioning devices such as air-handling units and fan coil units, and other building materials of copper.

Now, the method of this invention for the manufacture of the patina remover will be described.

The method of this invention for the manufacture of the patina remover comprises mixing hydrazine with a corrosion inhibitor for copper.

Desirably, this mixture of hydrazine with the corrosion inhibitor for copper is effected by preparing a base water, when necessary, and stirring the components of the mixture in the base water. In this case, the amount of hydrazine is such that the hydrazine content of the produced patina remover will fall in the range of 10 to 50% by weight and the amount of the corrosion inhibitor for copper is cush that the corrosion inhibitor content of the patina remover will fall in the range of 0.05 to 20% by weight based on the amount of hydrazine. As the corrosion inhibitor for copper, one member or a mixture of two or more members selected from the group of azole compounds cited above can be used.

The conditions under which the treatment of mixture of hydrazine with the corrosion inhibitor for copper is carried out are not specifically defined. Generally, this treatment is carried out at a temperature approximately in the range of 5" to 50"C. This mixture can be carried out speedily by the use of a rotary stirrer or a line mixer.

Now, the method of this invention for the removal of patina by the use of the patina remover of the present invention formulated as described above will be explained below.

The method of the present invention for the removal of patina comprises adding the aforementioned patina remover of the present invention to water and cleansing the copper substrate thereby ridding the copper substrate of the patina.

Concrete examples of the procedure adapted for effecting the cleansing include: (1) A procedure which comprises diluting the patina remover of this invention as with water, when necessary, thereby preparing a solution, placing this solution in a container, and immersing a copper substrate under treatment as it is or in a disassembled state (batchwise method). In this case, the solution may be kept stirred as occasion demands.

(2) A procedure which comprises suspending the operation of a copper substrate under treatment and circulating the prepared solution through the affected part of the copper substrate (batchwise method).

(3) A procedure which comprises intermiddently adding a prescribed amount of the patina remover of the present invention to the liquid being circulated through the copper substrate under treatment while the copper substrate is kept in continued operation [OSRR (On Stream Rust Remover) method; which method is suitable for the treatment of a heat exchanger, for example, and is capable of ridding the heat exchanger while in operation of patina and enabling the removed patina to be discharged out of the system as entrained by the blow water.] Suitably, any of the treatments described above is carried out invariably at a temperature falling approximately in the range of 0 to 100"C.

In the methods cited above, the OSRR method of (3) proves particularly desirable because it can be effected simply by adding the patina remover in a prescribed amount to the liquid in circulation during the course of the continued operation. Thus, the treatment can be given at any desired frequency and the patina remover to be consumed therein is relatively small, and number of cleansing treatments can be increased as desired.

In the method of this invention for the removal of patina, without reference to the choice between either of the batchwise methods and the OSRR method to be adopted for the treatment, the patina remoer of the present invention is desired to be added in such a manner that the initial hydrazine concentration in the system of treatment will be not less than 50 ppm. If the initial hydrazine concentration in the system at the time that the cleansing treatment is started is less than 50 ppm, the effect of the treatment in the removal of patina is insufficient. A desirable cleansing effect is manifested so long as the initial hydrazine concentration is not less than 50 ppm. If the hydrazine concentration is excessively high, however, there is the possibility of the cleansing solution exerting adverse effects upon the copper substrate under treatment.Desirably, the hydrazine concentration in the system is kept from exceeding the level of about 3%.

Preferably, the hydrazine concentration in the system of treatment falls in the range of 80 to 200 ppm.

In the present invention, owing to the action of hydrazine, the patina can be removed very efficiently by dissolving the patina through reduction or chelation. Further, since hydrazine has no ability to corrode copper or iron, this invention solves the problems such as secondary corrosion.

In accordance with the present invention which provides the patina recover containing hydrazine, a substance of such an outstanding performance as described above, and which provides a method for the removal of patina by the use of the patina remover, therefore, there are brought about numerous advantages as follows.

(1) The patina can be selectively and effectively removed.

(2) Owing to the action of hydrazine, the removed patina is not allowed to adhere to the surface of an iron substrate by electrode position. The otherwise inevitable secondary corrsion causable by the removed patina can be precluded.

(3) The solution containing the patina remover of this invention cannot remove the corrosionproofing coating of copper oxide. Unlike the treatment of pickling, the treatment by the use of the patina remover of the present invention does not activate the copper substrate under treatment, enabling the copper substrate to be retained in a highly desirable state in the solution.

(4) The patina remover of this invention is incapable of corroding copper or iron. Thus, the treatment with this patina remover can be continued long without entailing any serious problem.

If the solution remains on the treated surface, it does not cause corrosion of the copper substrate. Thus the burden of the work of rinsing performed on the treated copper substrate can be alleviated.

(5) In the treatment of a heat exchanger, for example, since the patina remover of this invention cannot exert any adverse effect upon the operation of the system under treatment, it can be used as added to the water circulated through the heat exchanged kept in operation.

Thus, the procedure involved in the treatment is easy to perform.

The use of the patina remover of the present invention and the adoption of the method of this invention for the removal of patina by the use of the patina remover, therefore, enable the desired removal of patina to be effected very efficiently in a short span of time and consequently protect the treated copper substrate against corrosion in the form of pitting, for example.

The patina remover of this invention enjoying such an outstanding performance can be manufactured easily by the method of this invention for the manufacture of patina remover.

PREFERRED EMBODIMENT OF THE INVENTION Now, the present invention will be described more specifically below with reference to working examples and a referential experiment. Of course, the present invention can be practiced otherwise without departing from the spirit of the invention.

Example 1: Solutions prepared by adding varying amounts of hydrazine to tap water were each placed in a beaker having an inner volume of 1 liter and left standing in a constant temperature bath at 20"C. The solutions in the beakers were constantly kept stirred slowly with stirrers plunged in the beakers. In the solutions, test copper tubes 9.5 mm in diameter and 75 mm in length having patina formed thereon were suspended for one hour to be cleansed. After the treatment, the test copper tubes were withdrawn from the solutions. The solutions were tested for total copper content. The treated copper tubes were examined with respect to their appearance and possible residue of the solution on their surface. The results are shown in Table 1.

Table 1 Amount of hydrazine 10 30 50 100 200 added (ppm) Total copper content in used 0.3 0.9 1.7 6.8 7.2 cleansing solution (ppm) Degree of residue of patina C B A A A Rating of visual observation: A Perfect removal B-Partial residue C Full residue Example 2: A cleansing treatment was performed by following the procedure of Example 1, excepting a solution containing 80 ppm of hydrazine and 10 ppm of mercaptobenzothiazole was used instead. The solution remaining after the treatment was tested for total copper content and the test copper tube was examined with respect to its appearance. Consequently, the total copper content of the used solution was found to be 4.6 ppm and absolutely no patina was detected on the treated copper tube, indicating that the treatment manifested a highly desirable cleansing effect.

Example 3: A copper tube used in an absorber of a suction type refrigerator and suffered to collect patina partially thereon was cleansed by the use of the patina remover of the present invention.

To be specific, the cleansing treatment was effected by adding 84 ppm of hydrazine to the water being circulated to the absorber with the refrigerator kept in continued operation. The inlet temperature of the absorber 27"C and the outlet temperature thereof was 32"C. After 24 hours' continued treatment, the hydrazine concentration in the circulating water fell to 0.8 ppm.

After completion of the treatment, the absorber was opened and the copper tube was cut half for inspection of the inner wall thereof. The inner wall was thoroughly deprived of patina and was emitting the gloss of copper oxide.

Example 4: A copper tube used in an evaporator of a turbo-refrigerator and was covered with patina substantially throughout the entire inner wall was cleansed by the use of the patina remover of this invention. To be specific, this cleansing treatment was effected by stopping the operation of the refrigerator, providing the evaporator temporarily with a bypass line, and adding 1.8% of N2H4 thereby giving the affected inner wall a batchwise cleansing.

After 2 hours' cleansing treatment, the coppe tube was cut half for inspection of the inner wall thereof. The inner was thoroughly deprived of the patina and was emitting the gloss of copper oxide.

Referential Experiment: A test copper tube was cleansed by following the procedure of Example 1, excepting a cleansing solution containing 80 ppm of hydrazine and 5% of hydrochloric acid was used insted.

After completion of the cleansing treatment, the cleansing solution was tested for total copper content and the copper tube was examined with respect to its appearance. The total copper content in the used cleansing solution was found to be 500 ppm and the copper tube did not show the color of copper oxide but emitted the gloss of pure copper.

From the results of this experiment, it is noted that when an acid is used in the cleansing solution, this cleansing solution has the possibility of eluting not only the patina but also the matenal of the substrate itself and exerting adverse effects upon the substrate.

INDUSTRIAL UTILITY OF THE INVENTION As described above, by the use of the patina remover of this invention and the adoption of the method of this invention for the removal of patina by the use of the patina remover, the desired removal of patina can be carried out very satisfactorily in a short span of time and, as the result, the treated copper substrate is protected against corrosion such as pitting, for example.

Claims

1. A patina remover, characterized by containing hydrazine.

2. A patina remover according to Claim 1, wherein said patina remover contains a corrosion inhibitor for copper.

3. A patina remover according to Claim 1, wherein the content of hydrazine is in the range of 10 to 50% by weight.

4. A patina remover according to Claim 2, wherein the content of said corrosion inhibitor for copper is in the range of 0.05 to 20% by weight based on the amount of hydrazine.

5. A patina remover according to Claim 1, wherein said corrosion inhibitor for copper is at least one azole selected from the group consisting of benzothiazole, mercaptobenzothiazole, benzotriazole, and tollyltriazole.

6. A method for the manufacture of a patina remover, characterized by mixing hydrazine with a corrosion inhibitor for copper.

7. A method according to Claim 6, wherein the mixing ratio of said corrosion inhibitor for copper to hydrazine is in the range of 0.05 to 20% by weight.

8. A method according to Claim 6, wherein said corrosion inhibitor for copper is at least one azole selected form the group consisting of benzothiazole, mercaptobenzothiazole, benzotriazole, and tollyltriazole.

9. A method according to Claim 6, wherein the mixing temperature is in the range of 5 to 50"C.

10. A method for the removal of patina from a copper substrate, characterized by contacting the copper substrate with a water containing hydrazine.

11. A method according to Claim 10, wherein hydrazine is added so that the concentration of hydrazine in the system under treatment will fall in the range of 50 ppm to 3% by weight.

12. A method according to Claim 11, wherein hydrazine is added so that the concentration of hydrazine in the system under treatment will fall in the range of 50 to 200 ppm.

13. A method according to Claim 10, wherein a corrosion inhibitor for copper is added to said water.

14. A method according to Claim 13, wherein the amount of said corrosion inhibitor for copper is in the range of 0.05 to 20% by weight based on the amount of hydrazine.

15. A method according to Claim 13, wherein said corrosion inhibotor for copper is at least one azole selected from the group consisting of benzothiazole, mercaptobenzothiazole, benzotriazole, and tollyltriazole.

16. A method according to Claim 10, wherein the temperature of treatment is n the range of 0 to 100"C.

17. A method according to Claim 10, wherein a copper substrate for treatment is immersed in said water.

18. A method according to Claim 10, wherein said water is circulated to the surface of said copper substrate.

19. A method according to Claim 10, wherein hydrazine is added to the circulating water.