EP0631637B1 - Verfahren und vorrichtung zum verhindern von verkrustung und/oder korrosion von strukturen in seewasser, brackwasser und/oder frischwasser - Google Patents

Verfahren und vorrichtung zum verhindern von verkrustung und/oder korrosion von strukturen in seewasser, brackwasser und/oder frischwasser Download PDF

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Publication number
EP0631637B1
EP0631637B1 EP91905906A EP91905906A EP0631637B1 EP 0631637 B1 EP0631637 B1 EP 0631637B1 EP 91905906 A EP91905906 A EP 91905906A EP 91905906 A EP91905906 A EP 91905906A EP 0631637 B1 EP0631637 B1 EP 0631637B1
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Prior art keywords
water
zinc
inducing
fouling
maintaining
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EP91905906A
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English (en)
French (fr)
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EP0631637A1 (de
EP0631637A4 (de
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William J. Riffe
Jack D. Carter
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Marine Environmental Research Inc
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Marine Environmental Research Inc
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Priority claimed from US07/523,418 external-priority patent/US5055165A/en
Priority claimed from US07/658,582 external-priority patent/US5346598A/en
Application filed by Marine Environmental Research Inc filed Critical Marine Environmental Research Inc
Publication of EP0631637A4 publication Critical patent/EP0631637A4/de
Publication of EP0631637A1 publication Critical patent/EP0631637A1/de
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B59/00—Hull protection specially adapted for vessels; Cleaning devices specially adapted for vessels
    • B63B59/04—Preventing hull fouling

Definitions

  • the present invention relates generally to methods and apparatus for preventing fouling and/or corrosion of structures, and more particularly to methods and apparatus for preventing fouling and/or corrosion of marine vessels, buoys, piping systems, filters, oil rigs, and other structures fully or partially submerged in seawater, brackish water, fresh water, or a combination of these.
  • Marine organisms which become attached to the hull must periodically be removed, thereby usually taking the ship out of operation for extended periods of time for dry dock maintenance. Also, if fouling is not prevented, aquatic organisms will continue to attach to the hull and will cause ever increasing operating costs associated with additional fuel requirements and decreased speeds.
  • the pleasure boat market faces similar problems.
  • U.S. Patent No. 3,817,759 discloses the use of an antifouling coating comprising a polymeric titanium ester of an aliphatic alcohol. Titanium has good corrosion resistance and low water solubility which prevents premature leaching and exhaustion of the coating.
  • Another known antifouling method involves coating the hull of a ship with a metallic paint whose ions are toxic to marine life, i.e., copper, mercury, silver, tin, arsenic, and cadmium, and then to periodically apply a voltage to the hull to anodically dissolve the toxic ions into seawater thereby inhibiting marine life growth.
  • a metallic paint whose ions are toxic to marine life, i.e., copper, mercury, silver, tin, arsenic, and cadmium
  • Antifouling systems which rely on dissolution of toxic substances into seawater have limited utility since the coating applied to the hull is depleted and the hull must be periodically repainted. The problem is made more severe in those systems which make the hull anodic to force dissolution since it increases the rate of dissolution. This poses a potentially serious problem since once the hull is exposed it too will be dissolved, resulting in pitting or puncturing of the hull.
  • zebra mussels Another aquatic animal, zebra mussels ( Dreissena polymorpha ), is posing major problems to electric utilities, and municipal and industrial facilities, that are dependent on raw waters, e.g., from the Great Lakes.
  • the morphological, behavioral and physiological characteristics of zebra mussels promote rapid spread of the mussel within and between water bodies, colonization of natural and artificial structures, fouling of intakes, conduits, condensers, and piping systems, and resistant to on-line procedures typically used to maintain system reliability at fresh water power plants.
  • Power plants offer prime habitats for zebra mussels.
  • the plants contain a plethora of hard, relatively clean surfaces for mussels to colonize. This colonization is enhanced by the source and flow rate of water drawn into the plant. For example, most plants draw near-surface water where the larvae are found in the highest concentrations.
  • flow rates specified at many intakes to prevent fish impingement are not high enough to prevent larval settlement. In fact, flowing water is advantageous for the settled mussels because it maintains food and dissolves oxygen concentrations necessary for sustenance. All power plant systems circulating raw water are vulnerable to zebra mussel fouling.
  • Corrosion normally occurs to underwater portions of a ship's hull because the seawater acts as an electrolyte and current will consequently flow, as in a battery, between surface areas of differing electrical potential. The flow of current takes with it metal ions thereby gradually corroding anodic portions of the hull.
  • Sacrificial anodes of active metals such as zinc or magnesium have been fastened to the hull. Such anodes, through galvanic action, themselves corrode away instead of the hull.
  • One known cathodic protection system utilizes a titanium anode plated with platinum.
  • the platinum acts as the electrical discharge surface for the anode into the electrolytic seawater. No current is discharged from any surface portions of the electrode comprising titanium.
  • This particular system impresses high current densities on the anode on the order of 5929 amps/m 2 [550 amps per square foot]. Since there is a high current flow from the platinum on other non-soluble anode metal, there is a very low potential and essentially no current flow from the surface of the titanium.
  • An example of such a system is disclosed in U.S. Patent No. 3,313,721.
  • a final problem faced by those desiring to develop a successful antifouling system is hydrogen embrittlement of the ship's hull.
  • electrolytic action takes place close to the surface of the ship's hull, such as in some of those systems described above, hydrolysis of the seawater may occur.
  • Such hydrolysis releases hydrogen ions which cause embrittlement of the ship's hull. Consequently, it is important in any antifouling system which is installed that the system not be operated at such high current as to cause hydrolysis of the water thereby releasing hydrogen.
  • an object of the present invention to provide a system, e.g., an electrochemical system, which prevents fouling in seawater or brackish water or fresh water ("water” hereinafter), of the exposed surfaces of metallic or nonmetallic, conductive structures exposed to the water.
  • a system e.g., an electrochemical system, which prevents fouling in seawater or brackish water or fresh water ("water” hereinafter), of the exposed surfaces of metallic or nonmetallic, conductive structures exposed to the water.
  • Another object of the present invention is to provide an electrochemical system which applies a net negative potential to the exposed surfaces of such structures to avoid dissolution of a conductive zinc coating thereon thereby obviating the need for repainting the hull at periodic intervals.
  • Another object of the present invention is to provide an electrochemical system for preventing fouling and/or corroding, which eliminates the requirement of external anodes which are susceptible to damage.
  • Another object of the present invention is to provide an electrochemical system which utilizes low-current densities on the structure so as to avoid hydrogen embrittlement and reduce costs.
  • the present invention provides a method, and a corresponding apparatus, for preventing fouling and/or corrosion of the surface of a metallic or non-metallic structure (e.g., the hull of a ship, a buoy, a piping system, a filter, an oil rig, etc.) comprising a zinc-containing surface in contact with (e.g., partially or fully submerged) seawater, brackish water, or fresh water.
  • a metallic or non-metallic structure e.g., the hull of a ship, a buoy, a piping system, a filter, an oil rig, etc.
  • Such fouling includes fouling with barnacles and other marine organisms. This result is achieved by impressing and maintaining a net negative electrostatic charge or by inducing and maintaining an asymmetric alternating electrostatic potential on the surface and permitting only a small periodic current flow, as defined in independent claims 1 and 6. Specific embodiments are defined in dependent claims 2 to 5 and 7 to 10.
  • the surface(s) in contact with the water environment must comprise zinc.
  • the structure may be made of zinc or of zinc alloy, or the surface(s) of the structure in contact with the water environment may be equipped with a zinc or zinc alloy layer forming an interface between the structure and the water, or the surface(s) of the structure in contact with the water may be equipped with a zinc-containing coating in conductive contact with the surface(s) in contact with the water.
  • This zinc-containing surface of the structure has a resistance in the order of less than 1 ohm.
  • the present invention relates to an antifouling and anticorrosion system which applies either a net negative electrostatic charge or a faradic potential on the surface(s) of the structure to protect the structure from fouling and/or corrosion.
  • the present invention prevents attachment of aquatic organisms such as barnacles, tubeworms and/or zebra mussels on the exposed surface(s) of aquatic structures, including the hulls of ships.
  • the structure which is protected in accordance with the present invention may be a ship, a pipe, a screen, a sheet, a bar, an expanded mesh, a perforated sheet, an expanded sheet, or a wire, or any other structure having any given form and which is exposed to a water environment.
  • Such structures in contact with an aqueous environment include buoys, piping systems, filters, oil riggs, and any other structure fully or partially submerged in sea water, brackish water, fresh water, or a combination of these, including power plant systems circulating raw water.
  • ship used herein includes all and every known type of water crafts, including both submarines and surface vessels. In one preferred embodiment the present invention is advantageously applied to the hulls of ships.
  • the present invention is used to prevent attachment of zebra mussels to the exposed surfaces of structures susceptible to zebra mussel fouling.
  • the present invention provides a solution to zebra mussel fouling of any system dependent on raw waters, such as power plant equipment, including any and all power plant systems circulating raw water.
  • a net negative capacitive charge is induced and maintained on the zinc-containing conductive surface(s) of the structure in contact with the water environment.
  • the net negative capacitive charge may be induced by using a means comprising a power supply having a terminal of a first polarity conductively connected to the surface(s) of the structure in contact with the water environment and a terminal of opposite polarity capacitively connected to the surface(s).
  • the power supply and the capacitative connection means are both protected from contact by the water environment.
  • the net negative capacitive charge may be in the form of a self-induced charge upon the surface(s) of the structure in contact with the water environment.
  • a self-induced charge at least one bare metal surface which is galvanically exposed to the water medium is used, with the zinc-comprising surface being positive in relation to the bare metal surface.
  • the bare metal surface(s) may be small blocks of copper, brass, iron, etc., attached to the external surface(s) of the structure. Any metal or metal alloy can be used for the bare metal surface(s) so long as the zinc-containing surface, when in the aqueous medium, is positive in relation to the bare metal surface.
  • an induced periodic potential is used, providing an electrostatic charge on the zinc-containing surface providing an oscillating Helmholtz plane thereon.
  • the resulting asymmetric potentials and small periodic currents in the submerged conductive surface(s) prevent adherence of marine organisms to the surface(s) while simultaneously preventing corrosion of the submerged conductive structure more effectively than if a non-faradic negative electrostatic charge is applied.
  • the invention is also illustrated below with reference being made to the Figures. These Figures are illustrative of the invention and are not provided to limit the same in any way.
  • the figures illustrate the application of the present invention to the hull of a ship equipped with a zinc-containing coating.
  • the examples provided below illustrate the application of the present invention to buoys equipped with a zinc-containing coating forming an interfacial layer between the buoys' outer surface and the water.
  • the present invention is not limited to ships or buoys, or to structures equipped with zinc-containing coatings, but can be applied to any structure made of zinc or of a zinc alloy, or to any structure having a surface(s) equipped with a layer of zinc or of a zinc alloy, as well as structures equipped with zinc-containing coatings.
  • the minimum requirement is that the surface of the structure in contact with the aqueous environment contain zinc and that it be conductive.
  • the structure itself when it is not made of zinc or of a zinc alloy, can be made of any conductive or non-conductive material(s) suitable for the intended use of the structure.
  • the structure can be made of both metallic or non-metallic, e.g., polymeric or composite, material.
  • the present invention can be used with metallic structures, various methods of rendering non-metallic structures conductive are currently available and utilization of the present invention with such structures is equally effective as when used with metallic structures, and thus within the scope of this invention.
  • a zinc-containing surface is distinguished from a zinc-containing coating as follows.
  • a zinc-containing surface is zinc-containing metallic layer applied to the surface of the structure.
  • such a surface could be a zinc-containing sheet or sheet attached onto (e.g., rivetted) the surface of the structure.
  • a zinc-containing coating is obtained by applying a zinc-containing composition, e.g., an inorganic zinc coating of the alkyl silicate or alkali hydrolyzed type, onto the surface structure.
  • galvanized is a coating.
  • the zinc-containing surface can be advantageously equipped with an additive or a mixture of additives which improve performance.
  • the zinc-containing surfaces used in accordance with the present invention may further contain a silicate, i.e., Na 2 O:SiO 2 of varying ratios, including sodium orthosilicate with a ratio of 2:1 and sodium metasilicate with a ratio of 1:1, and solid or liquid "water glasses” having ratios of 1:2 to 1:3.2 or ethyl silicate, to protect the zinc from dissolving into the aqueous media.
  • This material may be present in the zinc-containing surface in an amount of up to 5 wt.%.
  • the zinc-containing surface may also advantageously contain iron oxide in an amount of up to 5 wt.% to passivate the zinc-containing surface and retard the release of zinc ions into the aqueous media. This prolongs the life of the zinc-containing surface.
  • the zinc-containing surface may also advantageously contain di-iron phosphide in an amount of up to 2 wt.%. This enhances the conductivity of the surface.
  • the zinc-containing surface(s) used in accordance with the present invention may contain a combination of two or more of a silicate, iron oxide and di-iron phosphide.
  • the present invention prevents corrosion and/or fouling of the conductive surface of a structure in contact with water by barnacles and/or other aquatic organisms, including zebra mussels, by impressing and maintaining a net negative electrostatic charge on the conductive surface of the structure (e.g., on the hull of a ship), which surface is rendered conductive and comprises zinc and is at least partially submerged in water, permitting only a small current flow. Because of the presence of charge on the zinc-containing surface, a Helmholtz double layer forms at the zinc/water interface. The innermost Helmholtz plane contains a high concentration of positively charged ions, most notably zinc and sodium.
  • the outer Helmholtz plane consists of negatively charged ions, a relatively high concentration of which are hydroxyl ions.
  • the negative hydroxyl ions in the outer Helmholtz plane are attracted to the positively charged zinc and sodium ions in the inner Helmholtz plane to form a caustic solution which destroys and/or repels the lower organisms of the fouling community. This prevents succession and attachment of higher organisms such as barnacles, tubeworms, and zebra mussels.
  • the antifouling system described herein has many advantages over prior systems, including the following.
  • the present invention incorporates an internal electrode which was not previously thought to be practical, and does not require an external anode (i.e., an anode in contact with the water).
  • prior devices using current to prevent fouling have typically involved high current densities so they cause hydrogen embrittlement of the hull and are expensive to operate.
  • the present invention avoids these problems since it utilizes extremely low current densities with relatively high potential difference between the surface and a titanium electrode.
  • This preferred embodiment of the present invention is illustrated hereinbelow in terms of its application to a ship's hull.
  • This application to a ship's hull is provided for purposes of illustrating the present invention without intending to limit the application of the present invention to any other structure which, in use, is in contact with (e.g., fully or partially submerged in) seawater, brackish water or fresh water.
  • the present invention is readily applied to marine vessels, buoys, oil rigs, and any other metallic or non-metallic structure which is fully or partially submerged in seawater, brackish water, or fresh water, including piping systems, filter systems, cooling systems, desalination systems, etc.
  • Figure 1 provides a view of the ship's hull [10] which is at least partially submerged in seawater, brackish water, and/or fresh water [12].
  • the exposed surface of the ship's hull [10] below the water line [14] is susceptible to fouling and/or corrosion.
  • Fouling appears to occur as a succession.
  • Bacteria in the aquatic environment are chemotypically attracted to the adsorbed nutrients and form a bacterial slime layer of discernible thickness.
  • the bacterial slime layer is then infiltrated by diatoms, algae, and other single celled organisms. Sessile organisms, such as barnacles, tubeworms and zebra mussels, feed upon the diatoms, algae, etc., and attach permanently to the nutrient-rich surface.
  • Sessile organisms such as barnacles, tubeworms and zebra mussels
  • the present invention appears to prevent fouling by breaking the chain from dissolved nutrients to higher plants and animals.
  • the exposed surface of the ship's hull [10] is coated with a conductive zinc-containing coating [16] upon which is impressed a small negative current.
  • a Helmholtz double layer forms at the surface/water interface which would appear to preclude the lower organisms of the fouling community from adhering to the exposed surfaces.
  • the ship's hull [10] is first sandblasted to white steel to remove oxides and produce a reactive surface. While in a reactive state, a conductive zinc rich paint, which may be a zinc rich inorganic paint, is applied to the steel hull [10] to form a predominantly zinc coating [16], which may be from 0.7112 mm [2.8 mils] to [4.1 mils] 1.0414 mm thick.
  • Inorganic zinc coatings suitable for use with the present invention are of the alkyl silicate or the alkali hydrolyzed type which are commercially readily available.
  • One such commercially available paint is "carbozinc 118TM" manufactured by Carboline, Inc., 1401 South Hanley Road, St. Louis, MO (USA) 63144.
  • dry film coat having a zinc content of 82 to 97 weight percent is preferred, but zinc contents outside of this range, i.e., 70 to 99 weight percent, are also useful as long as a conductive zinc coating is obtained.
  • a galvanized zinc coating can be used.
  • the zinc coating [16] forms an interfacial layer between the water [12] and the ship's hull [10] and is bonded to the iron in the ship's hull [10].
  • one or more titanium electrodes [18] are disposed within the ship's hull [10], and capacitatively coupled to form a large electrolytic capacitor in which the ship's hull [10] functions as a negative plate.
  • the titanium electrodes [18] are mounted on insulators [32] within a conductive hollow body [20] filled with a liquid electrolyte [22].
  • the electrolyte may be, e.g., a mixture of ethylene glycol and water containing Na 3 PO 4 borax, and sodium mercaptobenzo-thiazole.
  • the electrolyte may contain 1 to 10 wt.%, preferably 5 wt.% H 2 O, 0.1 to 10 wt., preferably about 0.3 wt.%, Na 3 PO 4 , 2 to 10 wt.%, preferably about 4 wt.% borax, 0.1 to 1 wt.%, preferably 0.5 wt.%, mercaptobenzothiazole, the balance being ethylene glycol.
  • the hollow body [20] is secured to the ship's hull [10] by a conductive mount [24].
  • An insulated through-hull fitting [26] penetrates the hollow body [20] and forms a water tight seal.
  • the fitting [26] provides an insulated conduit through the hollow body [20].
  • a titanium rod [28] of similar alloy as the titanium electrode [18] extends through the fitting [26] and is connected to the electrode [18].
  • a power supply means [30] is connected to the titanium rod [28] and the conductive surface of the ship's hull [10].
  • power supply means [30] preferably provides a potential difference of eight or more volts DC.
  • the positive terminal of the power supply is connected to the titanium rod [28] externally of the hollow body [20] and the negative terminal is connected to the ship's hull [10].
  • a plurality of contacts from the negative terminal of the power supply [30] to spaced apart points on the hull [10] may be required to assure a proper potential gradient across the entire surface.
  • titanium oxide film forms on the surface of titanium electrode [18], which film is only several tenths millionths of millimeters [angstroms] thick and in intimate contact with the titanium electrodes [18].
  • This oxide film can have a dielectric constant of up to 100.
  • the entire system acts as a large electrolytic capacitor.
  • the titanium electrode [18] functions as the positive plate with an impressed positive charge.
  • the ship's hull [10] and the electrolyte [22] act as the negative plate with an impressed negative charge.
  • the electrolyte [22] effectively moves the ship's hull [10] into close proximity to the titanium oxide dielectric creating a capacitative relationship between the electrode [28] and the ship's hull [10].
  • the oxide film which is formed on the titanium electrode [18] functions as the dielectric of the capacitor. Because of the dielectric effect of the oxide film, a relatively high potential difference can be applied between the ship's hull [10] and the titanium electrode [18] while permitting only a small controllable current leakage.
  • the potential difference between the titanium electrode and the ship's hull [10] is approximately 8 to 10 volts.
  • a half-cell voltage of approximately 0.9 to 1.2 negative volts DC measured from the ship's hull [10] to a silver-silver chloride reference cell is achieved.
  • Current densities in the range of 43.12 to 86.24 mA/m 2 [4 to 8 mA ft -2 ] are preferred. At these levels, there is sufficient energy to ionize water without evolving sufficient free hydrogen at the zinc/water interface to cause hydrogen embrittlement of the hull.
  • the negative charge impressed upon the ship's hull [10] and the conductively coupled zinc coating [16] causes limited electrolytic disassociation of water into hydrogen ions and hydroxyl ions.
  • the hydroxyl ions combine with zinc ions oxided from the zinc coating [16] but are prevented from escaping by the pH level and the impressed charge.
  • the resultant, zinc hydroxide raises the pH level of the water from 7 to somewhere between 8 and 11 which is in the passivity range of zinc as shown in the Pourbaix diagram of Figure 3. This effectively prevents dissolution of the zinc coating [16] into the water.
  • a Helmholtz double layer illustrated in Figure 4.
  • Within the innermost Helmholtz plane is a concentration of positively charged metallic ions disassociated from the adjacent water, i.e., calcium, magnesium, sodium, and zinc.
  • Within the outermost Helmholtz plane there is a concentration of negatively charged ions which are also disassociated from the water including hydroxyls in chloride.
  • the hydroxyl ions in the outermost Helmholtz plane are chemically attracted to the zinc and sodium ions in the innermost Helmholtz plane and appear to form a caustic solution that prevents adherence of fouling organisms.
  • the present invention appears to prevent the development of the bacterial slime in two ways; one chemically oriented and one tropism oriented. It has been demonstrated that most bacterial cells possess a negative surface charge which, when placed in an electrical field, causes them to migrate away from the negative end. In the system embodied herein, the negative surface charge of the outer Helmholtz plane repels not only bacteria but many higher organisms in the food chain. Such organisms are not harmed by the negative charge, but are simply repelled and avoid the area in which they sense the effects.
  • the chemical effect upon fouling organisms has three major facets: saponaceous, osmotic, and poisonous.
  • saponaceous osmotic
  • poisonous the surface of the zinc is maintained at a pH level approaching 11.
  • the lipid content of the bacterial cell reacts with sodium hydroxide, thus, destroying the bacterial capsule and killing the bacteria and other similar one-celled organisms.
  • concentration of positive ions tightly bound to the zinc coating [16] as a result of the negative attraction of the coating [16]. This results in higher concentrations of metallic ion salts.
  • the salts When a microorganism enters the inner Helmholtz plane, the salts have a negative osmotic effect and withdraw cellular fluid, thus, "salting out” the cell proteins and causing death of the organism. While some organisms in seawater can tolerate high osmotic pressures, they are not usually in the fouling community. Lastly, as salts of a heavy metal, zinc salts are capable of combining with and poisoning cellular protein. The toxic effect of zinc, however, is somewhat speculative since zinc has never been proven to be toxic as a coating in seawater.
  • At least one bare metal surface(s) which is galvanically exposed to the surrounding aqueous medium, with the zinc-containing surface(s) exposed to the water being positive to the bare metal surface(s), is used.
  • This embodiment of the invention is to be distinguished from a possible accidental scratch through a zinc-containing coating painted onto a metal structure which would result in a self-induced charge upon the zinc interface because the zinc surface happens to be positive in relation to the bare metal surface galvanically exposed to the surrounding aqueous medium as a result of the scratch.
  • the bare metal surface(s) are situated on the surface of the structure exposed to the water environment.
  • the bare metal surface may be made of a single metal or of an alloy of metals, with the only requirements being that the zinc-containing surface be positive in relation to the bare metal surface.
  • the bare metal surface(s) may be made of copper, brass, iron, etc..
  • the bare metal surface may be in the form of a noble metal cathode situated externally to the structure with a capacitor couple being placed between the noble metal cathode and the zinc-containing surface, thereby providing a galvanic system providing the advantageous effects of the present invention.
  • the bare metal surface made of a metal more noble than zinc is deliberately exposed and galvanically coupled to the zinc-containing surface.
  • the bare metal surface used in accordance with the invention has a single geometry.
  • the bare metal surface may be in the form of small blocks or strips of metal which are susceptible to easy replacement.
  • the antifouling system described in this embodiment which is quite similar to the above-described system and primarily distinguished therefrom by its use of an asymmetric alternating electrostatic potential instead of simply using a net negative capacitive charge, also has many advantages over currently available devices, including the following.
  • First, the faradic potential applied to the conductive structure is skewed sufficiently negative so that there is negligible dissolution of the zinc-containing surface. This eliminates the necessity for periodically repainting and/or repairing surface structure.
  • cathodic protection system for preventing corrosion are known, they always employ external anodes in contact with the water.
  • the present invention incorporates an induced electrostatic charge which was not previously thought to be practical, advantageously not requiring external anodes (i.e., anodes in contact with the water).
  • Third, currently available devices using current to prevent fouling of ship hulls have typically involved high current densities which cause hydrogen embrittlement of the hull and are expensive to operate.
  • the present invention avoids these problems since it utilizes extremely low current densities with relatively high potential differences between the conductive structure and the water.
  • the antifouling system comprises (a) a structure which is capable of being in contact with water and is equipped with a conductive zinc-containing surface corresponding to the submersible portion of the structure, with the zinc-containing surface forming an interfacial layer between the water and the structure, and (b) means for inducing and maintaining an asymmetric alternating electrostatic potential on the zinc--containing surface, sufficient to prevent fouling and/or corrosion of the surface.
  • an oscillating Helmholtz double layer is created and maintained at the interface between the zinc-containing surface and the water.
  • the means for inducing the asymmetric alternating electrostatic potential on the zinc-containing surface may comprise:
  • the first conductor means is mounted internally-, within the structure where it is protected from contact by the water.
  • the system may also further include a faradic inductor system to convert an equipotential galvanic current source to an asymmetric alternating electrostatic potential mounted within the structure.
  • the first conductor means may be a power source of asymmetric alternating current attached conductively to a condenser bank so arranged, with alternately directed diodes, that the supplied current is converted to an asymmetric alternating electrostatic potential.
  • the means for impressing the net negative electrostatic charge may include means for maintaining a current density on the structure sufficient to cause limited dissociation of the water and form zinc hydroxide, sodium hydroxide, and hydrogen peroxide at the oscillating Helmholtz double layer, without evolution of free hydrogen.
  • the antifouling system may be used on a structure which is at least partially submerged in water, with the zinc-containing surface being forming an interfacial layer between the water and the structure.
  • the means for impressing the asymmetric electrostatic potentials comprises a faradic, electrostatic conductor mounted. internally within the water structure and means for creating an electrostatic potential between the water and the structure, while having a net negative charge with respect to the water.
  • the means for impressing the net negative electrostatic charge can further comprise a means for maintaining a current density sufficient to dissociate water into its basic components and form zinc hydroxide, sodium hydroxide, and hydrogen peroxide at the helmholtz double layer without evolution of free hydrogen.
  • the means for impressing the net negative electrostatic charge can further comprise an inductor apparatus for generating an asymmetric alternating electrostatic potential, with the apparatus being insulatively mounted within the structure to which it is conductively coupled.
  • the conversion from galvanic to faradic potentials may be achieved by diode switching of current to condenser banks.
  • a power supply generator producing an asymmetric alternating polarity galvanic current may be used, connected conductively to a diode, condenser couple such that the galvanic current is converted to faradic electrostatic potential.
  • Figure 1 provides a view of a ship's hull [10] on which the antifouling coating of the present invention is at least partially submerged in water [12].
  • the exposed surface of the ship's hull [10] below the water line [14] is susceptible to fouling by various marine organisms, including bacteria (which form a bacterial slime layer of discernible thickness), diatoms, algae, or other single-celled organisms, and more sessile organisms, such as barnacles, tubeworms, and zebra mussels.
  • the exposed surface of the ship's hull [10] is also coated with a conductive zinc-containing coating [16] upon which is induced a faradically oscillating Helmholtz double layer at the surface/seawater interface which precludes the lower organisms of the fouling community from adhering to the exposed surface.
  • the ship's hull [10] is first sandblasted to white metal to remove oxides and produce a reactive surface.
  • a surface coating termed inorganic zinc-rich paint, comprised of zinc powder or zinc oxide, and a "vehicle”, e.g., a silicate-based "vehicle”, which may be from 0.7112 mm to 1.0414 millimeters [2.8 mils to 4.1 mils] thick is applied by spray or brush.
  • the resultant dry film coating which is chemically covalently bonded to the metallic hull [10], can contain from 70 to 99, preferably 85 to 97, percent by weight zinc.
  • Inorganic zinc coatings suitable for practicing the present invention are the alkyl silicate or the alkaline hydrolyzed type which are commercially available.
  • One such available paint is Carbozinc 11® manufactured by Carboline, Inc.
  • one or more power supply means [30] and condenser bank means [18] are disposed within the ship's hull [10]. It is one important aspect of the invention that the one or more condenser bank means [18] are disposed in a manner preventing contact with the water [12].
  • the one or more power supply means [30] and condenser bank means [18] are attached to the hull in such a manner that the hull [10] becomes a faradic conductor for the induced charges of the condenser banks.
  • the power supply mean [30] is connected between the condenser banks and the ship's hull providing an asymmetric alternating potential to each at a potential of from 1.0 to 10.0 volts.
  • a half-cell voltage of approximately 0.9 to 1.2 negative volts DC measured from the ship's hull [10] to a silver-silver chloride reference cell in the water is achieved.
  • Current densities of no more than 43.12 to 86.24 mA/m 2 [4 to 8 mA ft -2 ] are preferred. At these levels, there is sufficient energy to protect the hull.
  • a plurality of contacts from the negative terminal of power supply [30] to spaced apart-points on the hull [10] may be advantageously used to assure a proper potential gradient for the full length of the hull.
  • the entire system appears to act as a large Faradic Cage with the hull as the external screen from which induced charges may go to ground. In use, this effectively prevents dissolution of the zinc coating [16] into the seawater.
  • Example 1 A buoy was constructed from a section of black, rolled steel covered with zinc-rich paint. A titanium electrode similar to that shown in Figures 2 and 5 was housed within. An eight-volt potential difference between the titanium electrode and the external pipe was impressed upon the assembly which was placed in the water in Bogue Sound at Morehead City. Extensive fouling was noted on cables used to secure the buoys; however, no appreciable fouling was found on the zinc-coated surfaces.
  • Example 2 A control buoy was installed, which, although zinc coated, had no titanium electrode and no impressed potential.
  • the control buoy was placed in the water at the same location as the assembly described in Example 1 and was left for the same period of time.
  • the control buoy was extensively fouled when placed in the water at the same period of time.
  • the control buoy was extensively fouled proving that inorganic zinc-rich paint itself is not an antifoulant.
  • Example 3 In this experiment a test buoy was constructed identical to that described in Example 1 except the buoy was not coated. The test buoy was placed in the water at the same location as the previous two assemblies and was left for the same period of time. Although a negative potential between the electrode and the surface of the buoy was impressed, the buoy was extensively fouled indicating that a charge on a metal surface alone will not prevent fouling.

Claims (10)

  1. System umfassend:
    (a) - eine Struktur, die eine leitfähige, Zink enthaltende Oberfläche aufweist, die dazu geeignet ist, während des Gebrauchs in Kontakt mit Seewasser, Brackwasser, Frischwasser oder einer Kombination davon zu geraten, wobei die Struktur aus Zink oder einer Zink enthaltenden Legierung hergestellt ist, oder die Struktur aus einem leitfähigen oder nicht-leitfähigen Material besteht und mit einer leitfähigen, Zink enthaltenden Oberflächenlage oder einer leitfähigen, Zink enthaltenden Beschichtung versehen ist, die zumindest auf einen Teil der Struktur aufgebracht ist, wobei die Zink enthaltende Oberflächenlage und Beschichtung eine Grenzflächenlage zwischen der Struktur und dem Wasser bilden, wenn beim Gebrauch die Struktur mit dem Wasser in Kontakt gebracht wird, dadurch gekennzeichnet, daß das System weiterhin umfaßt:
    (b) - eine Einrichtung zum (b1) Induzieren und Aufrechterhalten einer negativen Netto-Kapazitivladung an der Oberfläche der Struktur oder (b2) Induzieren und Aufrechterhalten eines asymmetrischen wechselnden elektrostatischen Potentials an der Oberfläche der Struktur, was ausreichend ist, um eine Korrosion oder Verkrustung der Struktur zu verhindern, wobei die Einrichtung (b1) zum Induzieren und Aufrechterhalten einer negativen Netto-Kapzitivladung an der Oberfläche der Struktur umfaßt:
    (i) - zumindest eine an der Struktur angebrachte Kondensatorbank, wobei, wenn die Struktur im Gebrauch mit dem Wasser in Kontakt gebracht wird, die zumindest eine Kondensatorbank vor Kontakt mit dem Wasser geschützt ist; und eine Stromversorgung, die einen leitend mit der Außenfläche verbundenen Anschluß einer ersten Polarität und einen Anschluß der entgegengesetzten Polarität aufweist, der kapazitiv mit der Außenfläche verbunden ist, wobei die Stromversorgung und die kapazitive Verbindungseinrichtung beide in Gebrauch vor Kontakt mit der Wasserumgebung geschützt sind; oder
    (ii) - zumindest eine blanke Metallfläche, die galvanisch dem Wasser ausgesetzt ist, wenn die Struktur im Gebrauch in Kontakt mit dem Wasser gebracht wird, wobei die Zink enthaltende Oberfläche galvanisch positiv bezüglich der blanken Metalloberfläche ist, und wobei
    (iii) - die Einrichtung (b2) zum Induzieren und Aufrechterhalten eines asymmetrischen, wechselnden elektrostatischen Potentials auf der Oberfläche der Struktur umfaßt:
    - die zumindest eine an der Struktur angebrachte Kondensatorbank, wobei, wenn die Struktur im Gebrauch mit dem Wasser in Kontakt gerät, die zumindest eine Kondensatorbank vor Kontakt mit dem Wasser geschützt ist;
    - eine Einrichtung zum Zwischenlegen eines Dielektrikums zwischen einer ersten und zweiten Leitereinrichtung, wobei die erste Leitereinrichtung eine Stromquelle für asymmetrischen Wechselstrom ist, die leitend an der Kondensatorbank angebracht, die mit alternierend gerichteten Dioden so angeordnet ist, daß der zugeführte Strom in ein asymmetrischer, wechselndes, elektrostatisches Potential umgewandelt wird, wobei der zweite Leiter die Struktur ist; und
    - eine Einrichtung zum Erzeugen einer Potentialdifferenz zwischen der ersten Leitereinrichtung und der zweiten Leitereinrichtung, wobei die zweite Leitereinrichtung negativ bezüglich der ersten Leitereinrichtung ist.
  2. System nach Anspruch 1, das die Einrichtung zum Induzieren und Aufrechterhalten eine negative Kapazitvladung umfaßt.
  3. System nach Anspruch 1, das die Einrichtung zum Induzieren eines asymmetrischen, alternierenden, elektrostatischen Potentials umfaßt.
  4. System nach Anspruch 1, wobei die Struktur einen Schiffsrumpf, eine Röhre, eine Blende, einen Stab, ein ausgedehntes Gitter, eine perforierte Platte, eine ausgedehnte Platte, eine Platte oder einen Draht umfaßt.
  5. System nach Anspruch 1, wobei die Zink enthaltende Oberfläche weiterhin ein Silikat, Eisenoxid, Di-Eisenphosphid oder einer Mischung davon enthält.
  6. Verfahren zum Verhindern des Verkrustens oder der Korrosion einer Struktur, die im Gebrauch eine Oberfläche mit Kontakt zu Seewasser, Brackwasser, Frischwasser oder einer Kombination davon aufweist, wobei das Verfahren die Verwendung einer Struktur mit einer leitfähigen, Zink enthaltenden Oberfläche umfaßt, wobei die Struktur aus Zink oder aus einer Zink enthaltenden Legierung hergestellt ist oder die Struktur aus einem leitfähigen oder nicht-leitfähigen Material hergestellt ist und mit einer Zink enthaltenden Oberflächenlage oder mit einer darauf aufgebrachten, Zink enthaltenden Beschichtung versehen ist, wobei die leitfähige, Zink enthaltende Oberflächenlage und Beschichtung eine Grenzflächenlage zwischen der leitfähigen Struktur und dem Wasser bilden, wobei das Verfahren dadurch gekennzeichnet ist, daß es weiterhin folgende Verfahrensschritte umfaßt:
    (a) - Induzieren und Aufrechterhalten einer negativen Kapazitivladung an der Oberfläche der in Kontakt mit dem Wasser befindlichen Struktur in ausreichender Weise, um das Verkrusten oder Korrodieren zu verhindern, oder
    (b) - Induzieren und Aufrechterhalten eines asymmetrischen, alternierenden elektrostatischen Potentials auf der leitfähigen, Zink enthaltenden Beschichtung in ausreichender Weise, um das Verkrusten oder Korrodieren zu verhindern;
    wobei im Schritt (a) eine Einrichtung (b1) zum Induzieren der negativen Kapazitivladung verwendet wird, welche Einrichtung (b1) umfaßt:
    (i) - eine Einrichtung zum Induzieren und Aufrechterhalten einer negativen Netto-Kapazitivladung an der Oberfläche der Struktur mit:
    - zumindest einer an der Struktur angebrachten Kondensatorbank, wobei die zumindest eine Kondensatorbank vor Kontakt mit dem Wasser geschützt ist, und
    - einer Stromversorgung mit einem leitend mit der Außenfläche verbundenen Anschluß einer ersten Polarität und mit einem Anschluß entgegengesetzter Polarität, der kapazitv mit der Außenfläche verbunden ist, wobei die Stromversorgung und die kapazitiven Verbindungseinrichtungen beide im Gebrauch vor Kontakt mit der Wasserumgebung geschützt sind; oder
    (ii) - eine Einrichtung zum Induzieren und Aufrechterhalten einer negativen Netto-Kapazitivladung auf der Oberfläche der Struktur, die zumindest eine blanke Metallfläche umfaßt, die galvanisch dem Wasser ausgesetzt ist, wenn die Struktur im Gebrauch in Kontakt mit dem Wasser gerät, wobei die Zink enthaltende Oberfläche galvanisch positiv bezüglich der blanken Metallfläche ist;
    bei dem Schritt (b) wird eine Einrichtung (b2) für das Induzieren und Aufrechterhalten eines asymmetrischen, alternierenden elektrostatischen Potentials auf der Oberfläche der Struktur verwendet,
    (iii) - wobei die Einrichtung (b2) umfaßt:
    - zumindest eine an der Struktur angebrachte Kondensatorbank, wobei die zumindest eine Kondensatorbank vor Kontakt mit dem Wasser geschützt ist;
    - eine Einrichtung zum Zwischensetzen eines Dielektrikums zwischen einer ersten und einer zweiten Leitereinrichtung, wobei die erste Leitereinrichtung eine Stromquelle für asymmetrischen Wechselstrom ist, die leitend mit der Kondensatorbank verbunden und so mit alternierend gerichteten Dioden angeordnet ist, daß der zugeführte Strom in ein asymmetrisches, alternierendes elektrostatisches Potential umgewandelt wird, wobei der zweite Leiter die Struktur ist, und
    - eine Einrichtung zur Erzeugung einer Potentialdifferenz zwischen der ersten Leitereinrichtung und der zweiten Leitereinrichtung, wobei die zweite Leitereinrichtung negativ bezüglich der ersten Leitereinrichtung ist.
  7. Verfahren nach Anspruch 6, zur Verhinderung der Verkrustung der Struktur durch Zebramuscheln.
  8. Verfahren nach Anspruch 6, umfassend das Induzieren und Aufrechterhalten der negativen Kapazitivladung.
  9. Verfahren nach Anspruch 6, umfassend das Induzieren des asymmetrischen, alternierenden elektrostatischen Potentials.
  10. Verfahren nach Anspruch 6, wobei die Zink enthaltende Oberfläche weiterhin ein Silikat, Eisenoxid, Di-Eisenphosphid oder einer Mischung davon enthält.
EP91905906A 1990-05-15 1991-03-01 Verfahren und vorrichtung zum verhindern von verkrustung und/oder korrosion von strukturen in seewasser, brackwasser und/oder frischwasser Expired - Lifetime EP0631637B1 (de)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US07/523,418 US5055165A (en) 1988-01-19 1990-05-15 Method and apparatus for the prevention of fouling and/or corrosion of structures in seawater, brackish water and fresh water
US523418 1990-05-15
US658582 1991-02-21
US07/658,582 US5346598A (en) 1988-01-19 1991-02-21 Method for the prevention of fouling and/or corrosion of structures in seawater, brackish water and/or fresh water
PCT/US1991/001202 WO1991018130A1 (en) 1990-05-15 1991-03-01 Method and apparatus for the prevention of fouling and/or corrosion of structures in seawater, brackish water and/or fresh water

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EP0631637A4 EP0631637A4 (de) 1993-05-28
EP0631637A1 EP0631637A1 (de) 1995-01-04
EP0631637B1 true EP0631637B1 (de) 1997-08-06

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JP (1) JPH05507116A (de)
KR (1) KR100246555B1 (de)
CN (1) CN1056537A (de)
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AU (1) AU649246B2 (de)
BR (1) BR9106460A (de)
CA (1) CA2083263A1 (de)
DE (1) DE69127209D1 (de)
FI (1) FI925197A (de)
IL (1) IL97490A (de)
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CN1035881C (zh) * 1993-05-21 1997-09-17 北京化工学院 采用牺牲型涂料的防腐蚀方法
CN102336256A (zh) * 2011-05-27 2012-02-01 中国船舶重工集团公司第七二五研究所 一种防止船舶螺旋桨腐蚀和海生物污损的方法
US10227243B2 (en) * 2012-08-28 2019-03-12 Ecospec Global Technology Pte. Ltd System and method for prevention of adhesion of organisms in water to a substrate in contact with water
CN117209007A (zh) * 2014-06-30 2023-12-12 皇家飞利浦有限公司 防生物结垢的系统
CN105965122B (zh) * 2016-06-25 2018-12-28 天津泊荣石油科技发展有限公司 一种海洋工程钢表面防污耐蚀合金及钎涂方法
EP3481151A1 (de) * 2017-11-01 2019-05-08 Koninklijke Philips N.V. Elektrisches stromversorgungssystem zum zumindest teilweisen eintauchen in eine elektrisch leitende flüssigkeit während des betriebs davon
CN108088785B (zh) * 2017-11-30 2020-04-10 厦门双瑞船舶涂料有限公司 防污涂层体系耐淡海水/淡水浸泡性能的评价方法
CN108795267B (zh) * 2018-06-21 2020-07-31 北方工业大学 一种石墨烯改性静电防污涂料及其制备方法与应用
CN113631476A (zh) * 2018-11-22 2021-11-09 罗伯特·凯塞尔 防止海洋环境中生物积垢的方法
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CA2083263A1 (en) 1991-11-16
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NZ237326A (en) 1993-07-27
AU7486191A (en) 1991-12-10
FI925197A0 (fi) 1992-11-16
CN1056537A (zh) 1991-11-27
BR9106460A (pt) 1993-05-18
JPH05507116A (ja) 1993-10-14
EP0631637A1 (de) 1995-01-04
NO308010B1 (no) 2000-07-03
NO924419D0 (no) 1992-11-16
EP0631637A4 (de) 1993-05-28
DE69127209D1 (de) 1997-09-11
NO924419L (no) 1993-01-05
KR100246555B1 (ko) 2000-04-01
IL97490A0 (en) 1992-06-21
FI925197A (fi) 1992-11-16
AU649246B2 (en) 1994-05-19

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