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History of copper antifouling
In 1882 four Royal Navy copper bottomed ships were lost off Newfound with great loss of life. Copper bottoming of ships was about to be abandoned when a method of making hard drawn copper bolts was invented which solved the corrosion problem.
Plating the bottoms of wooden ships with copper sheet became the standard method of protection and antifouling and is still popular in many areas today.
COPPER NICKEL VESSELS
This alloy with small amounts of iron and manganese were used because unlike pure copper it has a low corrosion rate, is weldable, ductile and has excellent resistance to fracture under impact.
The most notable of these vessels was the Copper Mariner, a 22 metre prawn trawler built in Mexico 1971 and operated off the Pacific coast of Nicaragua. (2) She was built to evaluate whether the inherent resistance of 90-10 copper-nickel to bio-fouling would generate sufficient fuel and maintenance savings to justify the cost premium. Although the hull remained free of fouling for 16 years in a high fouling area of tropical water, the advent of TBT antifouling meant that most of the vessels financial advantages were lost.
COPPER-NICKEL CLAD STEEL HULLS
Copper-nickel can be metallurgically bonded to steel by hot rolling to provide corrosion and bio-fouling protection. The idea being to produce thicker, stronger plate at lower cost. The Copper Mariner 11, a 25 metre prawn trawler was the first vessel to be constructed with copper-nickel clad steel in 1977. (3) The hull was easy to fabricate and it was reported that the copper-nickel had always remained free of fouling and corrosion. Seven other craft are known to have been built with copper-nickel clad steel the last one being the Cupro in 1991 in Japan.
SELF ADHESIVE COPPER-NICKEL FOIL
There have been several producers of self adhesive copper and copper-nickel foil antifoul systems. All have performed well in service but have not found commercial success due to the labour intensive application process.
A commercial product is currently made in the UK by the Foil Specialist Company.
HOT SPRAYED COPPER
A hot spray applied copper coating named Copperlok has been developed. It electrically insulated from the substrate by an epoxy coating containing glass microspheres. When cured the surface is abraded to expose and fracture the glass microspheres thereby creating micro cavities that the hot metal fills creating a mechanical bond.
BIOFOULING RESISTANCE (4)
A considerable amount of research has been conducted into the bio-fouling resistance of 90-10 and 70-30 copper-nickel. It was generally thought that the 70-30 grade has less bio-fouling resistance than 90-10 but 14 year tests under quiet, tidal and flowing conditions at LaQue Corrosion Services, Wrightsville Beach, North Carolina site showed negligible fouling on 70-30 copper-nickel panels. Five year exposure tests at the same site under quiet conditions showed that the response to fouling was the same whether the metal was 70-30, 90-10 or pure copper. Also yachts built of 70-30 copper-nickel have given excellent results. The most important requirement for good bio-fouling resistance is that the metal should be insulated from less noble metals and be free of cathodic protection.
REASONS FOR BIOFOULING RESISTANCE
It was originally thought that it was copper ions being released from the surface that provided that antifouling effect. However 70-30 copper-nickel corrodes as a much lower rate than pure copper but it provides similar antifouling performance in most areas. It is now considered that it is the surface film that forms on the surface of copper and copper-nickel soon after immersion in sea water that is responsible for its antifouling properties.
The surface film is very thin and predominantly comprises cuprous oxide and often contains iron and nickel oxides, cuprous hydroxychloride and cupric oxide. The film can be brown, greenish brown or brownish black.
EASE OF BIOFOULING REMOVAL
Under continuous exposure to sea water the film of cuprous oxide slowly converts to cuprous hydroxychloride by reaction with sodium chloride in the water. The cuprous hydroxychloride has less bio-fouling resistance than the cuprous oxide and some fouling will occur. The cuprous hydroxychloride film has poor adhesion to the underlying cuprous oxide and washes off together with any fouling to expose a fresh surface.
RESIN BOUND METALLIC COPPER COATINGS
The first record of the use of copper powder as an antifouling agent in a liquid resin is in US patent number 19610111872 dated 22.05.1961. This patent described the use of copper powder in a water impermeable, thermosetting resin that could be used as a laminating or coating system.
Nearly 20 years later Scott Bader filed patent application number GB 8026663 dated 15.08.1980 which described a low acid value polyester resin that would cure in the presence of copper. (Copper is a cure inhibitor for most polyester resins) This application was followed by GB 2084488 dated 3.10.80 which described a polyester resin coating containing copper powder that could be used for protecting marine craft and structures from fouling.
The result of these patent applications was launched by Scott Bader onto the marine market under the name of Copperclad in the early 1980's. It was used as a gel coat that could be applied into a boat mould before a hull was laminated. The product was received enthusiastically by the industry but it soon became apparent that the requirement to abrade the surface of the coating to reveal the copper powder was not practical and the product was withdrawn after a few years due to the number of complaints.
Later (in the mid -late 80's) Copperbot was introduced to the UK market by Sea Defence Limited. It was a water born epoxy bound copper powder antifouling that also contained a soluble resin that was intended to dissolve and wash out of the cured coating when immersed, to leave it porous and thus allow the copper to leach to the surface.
Adding a water soluble resin to the binder of an antifouling was not a new idea, it has been patented earlier in relation to conventional leaching type antifouling.
Since the introduction of Copperbot several other epoxy bound copper powder antifoulings have been introduced all containing soluble components intended to render the coating porous.
The successor of Copperbot is now marketed as Coppercoat.
1 C. A. Powell. Corrosion and bio fouling protection of ships hulls using copper-nickel. 1994 The Royal Institution of Naval Architects, London.
2 Manzolillo, Thiele and Tuthill CA-706 Copper-nickel alloy hulls. The Copper Mariner’s experience and economics. The Society of Naval Architects and Marine Engineers. November 1976
3 Nickel Topics No 63, 1998, Copper Development Association.
4 C. A. Powell, H. T. Mitchels. Copper-nickel alloys for sea water corrosion resistance and antifouling – a state of the art review. Corrosion 2000 NACE Houston.
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