WO2000060138A1

WO2000060138A1 - An anode for use in a marine environment

Info

Publication number: WO2000060138A1
Application number: PCT/AU2000/000264
Authority: WO
Inventors: Ronald Kempin
Original assignee: Barnacle Guard System Pty Ltd; Ronald Kempin
Priority date: 1999-04-01
Filing date: 2000-03-30
Publication date: 2000-10-12
Also published as: AUPP958199A0; PE20010081A1; AR023252A1

Abstract

An anode for use in a marine environment includes a metallic surface on which is formed a basic metal chloride coating. It is preferred that the basic metal chloride coating is formed by applying a solution containing hypochlorite, a hypochlorite salt or a precursor thereof to the metallic surface and that the metallic surface is copper or contains copper and the coating is a basic cupric chloride. The present invention also provides a method for making an anode for use in a marine environment by applying a solution containing hypochlorite, a hypochlorite-containing material or a precursor thereof to a metallic surface of the anode. The present invention also provides for corrosion resistant system for use in a marine environment including an anode electrically connected to oxidation susceptible under water metal components, the anode having a surface exposed to water of the marine environment, the surface having a basic metal chloride coating.

Description

AN ANODE FOR USE IN A MARINE ENVIRONMENT

FIELD OF THE INVENTION

The present invention relates to an anode. In particular, the present invention relates to an anode for use in a marine environment.

BACKGROUND

It is well known that metallic structures, particularly those made from iron or steel are subject to corrosion in a marine environment. Corrosion is exasperated where an electric current is created at an interface between two different metals. The resulting stray current causes increased oxidation of the metal.

As a result, zinc anodes were introduced. Zinc is more prone to oxidation than iron and therefore it is sacrificially oxidised in order to save the iron. As marine vessel hulls evolved, recreational craft were constructed from fϊbreglass and timber epoxy technology. Tributal Tin based anti-fouling paint was used until its toxicity was realised, whereupon it was replaced with copper based anti-fouling paint.

This has created a problem with the traditional zinc anodes, particularly when a marine vessel is moored for a long period of time. The sacrificed zinc, in the form of zinc ions, becomes attracted to the copper in the anti-fouling paint and any other underwater metal components. As a result particles of zinc become deposited on the anti-fouling paint and/or underwater metal components causing the anti-fouling paint to fail. The underwater components then quickly become encrusted with marine life.

SUMMARY OF THE INVENTION

The present invention seeks to provide an anode which is suitable for use with copper based anti-fouling paint and/or copper components used in a marine environment.

According to a first aspect of the present invention, there is provided an anode for use in a marine environment, said anode includes a metallic surface on which is formed a basic metal chloride coating. Preferably, the basic metal chloride coating is formed by applying a solution containing hypochlorite, a hypochlorite salt or a precursor thereof to the metallic surface.

Preferably, the metallic surface is copper or contains copper and the coating is a basic cupric chloride. More preferably, the basic cupric chloride is a cupric oxy-chloride. More preferably still, the basic cupric chloride is cupric chloro hypo-chloride.

Alternatively, the metallic surface is silver or contains silver and the coating is a basic silver chloride.

Alternatively, the metallic surface is copper or contains copper and silver or contains silver and the metallic chloride is a composite of a basic copper chloride and a basic silver chloride.

According to a second aspect of the present invention there is provided a method of making an anode for use in a marine environment by applying a solution containing hypochlorite, a hypochlorite-containing material or a precursor thereof to a metallic surface of the anode.

Preferably, the metallic surface where the anode is made of copper, contains copper or the metallic surface is a copper surface or a surface containing copper. Preferably, the anode is made of silver, contains silver or the metallic surface is a silver surface or a surface containing silver. More preferably, the hypochlorite solution is a standard sodium hypochlorite solution containing sodium hypochlorite and sodium chloride with about 125g/L available active chlorine.

Preferably, the metallic surface is annealed before the hypochlorite solution is applied. Preferably, the metallic surface is oxidised as it is annealed.

According to a third aspect of the present invention there is provided a corrosion resistant system for use in a marine environment including an anode electrically connected to oxidation susceptible under water metal components, the anode having a surface exposed to water of the marine environment, the surface having a basic metal chloride coating.

Preferably, the surface is copper and the coating is a basic cupric chloride. Alternatively, the surface is silver and the coating is a basic silver chloride. In a further alternative, the surface is a combination of copper and silver and the coating is a combination of a basic cupric chloride and basic silver chloride.

DESCRIPTION OF PREFERRED EMBODIMENTS In order to provide a better understanding of the present invention, preferred embodiments will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic end view of a first type of anode in accordance with the present invention; Figure 2 is a schematic perspective view of a second type of anode in accordance with the present invention; Figure 3 is a schematic perspective view of a third type of anode in accordance with the present invention; Figure 4 is a schematic perspective view of a fourth type of anode in accordance with the present invention; and

Figure 5 is a schematic end view of a fifth type of anode in accordance with the present invention.

An anode is fabricated from a high grade copper bar or sheet copper. The anode is fabricated into a shape to suit the position at which the anode will be attached to a marine vessel or structure. The anode is prepared for fitting by, for example, drilling as necessary.

Figure 1 shows a simple anode 10A formed by pressing flat a piece of copper pipe.

Figure 2 shows another type of anode 10B used on the hull of a marine craft. An arc shaped piece of copper sheet is soldered to a base plate at 20. The solder preferably is silver solder. Figure 3 shows a further type of anode IOC. This anode IOC is formed by silver soldering 20 a copper sheet to form a cylinder which fits around, for example, a propeller shaft.

Figure 4 shows an anode 10D made of cast copper 12. This anode may be electroplated with silver 14. A hole 16 is drilled and tapped so that it may be screwed onto a threaded bolt.

Figure 5 shows the final example of an anode 10E. This anode is like that shown in Figure 1 , but also includes a length of silver 18 crimped in the flattened pipe.

Next, the anode is then annealed and the surface oxidised by an oxygen rich oxidising flame from an oxy-acetylene welding/blow torch. The surface turns black with copper oxide. It is believed this may assist in the formation of a basic cupric chloride coating. The anode is then sprayed with a sodium hypochlorite solution and then sealed in an air tight polyethylene container until a basic cupric chloride surface coating is established. It is believed the surface reactions are:

2Cu + O_{2 =>} 2CuO (oxidising by flame)

Cu + NaCIO => CuO + NaCl (application of hypochlorite) Cl

/ CuO + NaCl + NaCIO => Cu + 2 Na OH (further reaction with hypochlorite)

\ O-Cl

Silver plate has been found to be effective in place of copper. The silver plate anode is prepared as described above and sprayed with sodium hypochlorite to form a silver chloride coating on the silver plate anode. However, silver plate anodes are more expensive than the copper and therefore copper is preferred. It is envisaged that other metals may be suitable in the formation of a metallic chloride coating on the surface of an anode. A combination of copper and silver has been found to be very effective. In particular, copper with silver soldering or a length of silver embedded in the predominantly copper anode, for example, as shown in Figure 5. The anode acts as an electrode by which electrolytic energy can leave the vessel or structure via sea water. Other metallic components, in particular copper, bronze, iron or steel and to some extent copper based anti-fouling paint acts as a cathode. Thus any oxidation takes place at the anode. When oxidation of the anode takes place, minute particles of cupric chloride are formed which are compatible with copper base anti-fouling and serve to reinforce copper based anti-fouling systems. It is expected that an anode in accordance with the present invention will extend the life of copper based anti-fouling rather than shorten it that is the case with zinc anodes.

Example 1

A comparison was conducted between use of a zinc anode and a copper anode.

A first test was conducted in a shallow polyethylene tank with a unpainted bronze propeller connected to a zinc anode, a section of fibreglass panel painted with copper based anti-fouling paint, a section of stainless steel shafting and a small 12 volt lead acid battery. The tank was filled with sea water and the propeller submerged to a depth of 300 millimetres along the stainless steel shaft. The fibreglass anti-fouled panel was also submerged. The zinc anode was submerged in the tank and connected to the negative terminal of the battery. The propeller shaft was also connected to the negative terminal. The positive terminal of the battery was unconnected. This was to simulate a craft at idle with DC electric power turned off.

After three days, the water had become cloudy with spots of zinc showing on the propeller. After seven days, the water had become totally obscured. The propeller and panel were not visible at a depth of three hundred millimetres. After fourteen days, the propeller was removed and found to be firmly coated with zinc which needed to be removed with sand paper. The fibreglass panel was stained with zinc which would cause copper based anti-fouling to fail.

The same test was then conducted replacing the zinc anode with a copper chloride anode. In this case, after seven days minute blue-green particles of basic cupric chloride formed on the metal sections. After twenty-one days, additional cupric chloride formed on the propeller and to a lesser extent the adjacent copper based anti-fouling painted areas. The test was continued for 130 days. The fibre glass panel became completely coated in cupric chloride. Exposed copper turned blue green with the coating in this concentrated environment. The sea water in the tank remained clear. It is believed that the basic cupric chloride particles assist in the anti-fouling properties of the copper based anti-fouling paint.

Example 2

A similar test was conducted with a silver chloride anode with similar results to the copper chloride anode. This time a grey-white silver chloride particles formed. It is believed that the silver chloride coating also has anti-fouling properties. It is also believed that the basic metallic chloride coating on the anode is constantly replenished by chlorine from the sea water.

It will be apparent to the skilled addressee that the present invention has at least the following advantages:

1) a metallic chloride anode can co-exist with copper based anti-fouling; and,

2) sacrificial erosion of the anode can serve to extend the life of copper based anti-fouling.

It will be apparent to persons skilled in the relevant arts that modifications and variations can be made to the described invention without departing from the basic inventive concept, such as: a standard solution of sodium hypochlorite may be substituted with other hypochlorite salt solutions or the hypochlorite salt solution may be applied in various other ways to the metallic surface of the anode such as by painting or dipping.

All such modifications and variations as would be apparent to a skilled addressee are intended to be within the scope of the present invention, the nature of which is to be determined from the foregoing description and appendant claims.

Claims

CLAIMSThe claims defining the present invention are as follows:

1. An anode for use in a marine environment, including a metallic surface on which is formed a basic metal chloride coating.

2. An anode according to claim 1, wherein the basic metal chloride coating is formed by applying a solution containing hypochlorite, a hypochlorite salt or a precursor thereof to the metallic surface.

3. An anode according to claim 1, wherein the metallic surface is copper or contains copper and the coating is a basic cupric chloride.

4. An anode according to claim 3, wherein the basic cupric chloride is a cupric oxy- chloride.

5. An anode according to claim 3, wherein the basic cupric chloride is cupric chloro hypo-chloride.

6. An anode according to claim 1, wherein the metallic surface is silver or contains silver and the coating is a basic silver chloride.

7. An anode according to claim 1, wherein the metallic surface is copper or contains copper and silver or contains silver and the metallic chloride is a composite of basic copper chloride and basic silver chloride.

8. A method of making an anode for use in a marine environment by applying a solution containing hypochlorite, a hypochlorite-containing material or a precursor thereof to a metallic surface of the anode.

9. A method according to claim 8, wherein the anode is made of copper, contains copper or the metallic surface is a copper surface or a surface containing copper.

10. A method according to claim 8, wherein the anode is made of silver, contains silver or the metallic surface is a silver surface or a surface containing silver.

11. A method according to claim 8, wherein the hypochlorite solution is a standard sodium hypochlorite solution containing sodium hypochlorite and sodium chloride with about 125g/L available active chlorine.

12. A method according to claim 8, wherein the metallic surface is annealed before the hypochlorite solution is applied.

13. A method according to claim 12, wherein the metallic surface is oxidised as it is annealed.

14. A corrosion resistant system for use in a marine environment including an anode electrically connected to oxidation susceptible under water metal components, the anode having a surface exposed to water of the marine environment, the surface having a basic metal chloride coating.

15. A corrosion resistant system according to claim 14, wherein the surface is copper and the coating is a basic cupric chloride.

16. A corrosion resistant system according to claim 14, wherein the surface is silver and the coating is a basic silver chloride.

17. A corrosion resistant system according to claim 14, wherein the surface is a combination of copper and silver and the coating is a combination of a basic cupric chloride and a basic silver chloride.