Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
  • G01N17/006—Investigating resistance of materials to the weather, to corrosion, or to light of metals
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
  • G01N17/04—Corrosion probes
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
  • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
  • G01N21/64—Fluorescence; Phosphorescence
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
  • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
  • G01N21/64—Fluorescence; Phosphorescence
  • G01N21/6447—Fluorescence; Phosphorescence by visual observation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/91—Investigating the presence of flaws or contamination using penetration of dyes, e.g. fluorescent ink

Definitions

• the present invention relates to a non-destructive chemical probe for the detection of corrosion and a method of detecting corrosion at a metal substrate, and in particular although not exclusively, to the detection of metal ions generated at the metal substrate.
• One of the more primitive forms of corrosion detection is by visual inspection in which a person is required to visually inspect all parts of the metal structure.
• This type of detection method is disadvantageous for a number of reasons including for example the time taken to carefully inspect all parts of the metalwork including joints, welds and relatively inaccessible locations which make visual detection difficult. Additionally, it is extremely difficult to detect corrosion visually at a very early stage. Accordingly, a number of different types of inspection methods have been developed in an attempt to facilitate the ease of early corrosion detection.
• US 2003/0068824 discloses a method of detecting corrosion involving the application of a removable corrosion-detecting substance that changes appearance in response to corrosion occurring on the surface of the metal structure.
• the indication method disclosed is cathodic reaction based in that cathodic reactions, that are integral to the corrosion process, increase the local pH at the point of corrosion.
• the detection coating is pH sensitive whereby corrosion detection is indicated by an associated coating colour change in the region of pH change.
• US 4,278,508 also discloses a method of detecting a cathodic corrosion site on a metallic substrate in which a pH sensitive fluorescent dye is deposited onto the substrate and configured to fluoresce in response to the hydrogen generated from the cathodic corrosion reaction.
• Fluorescent probes including lumogallion and Phen GreenTM are used being responsive to aluminum, magnesium and copper ions in aqueous solution and corrosion processes.
• the fluorescent probes are doped into epoxy/polyamide primers deposited on aluminum alloy surfaces. Fluorescence microscopy is then used to reveal localised corrosion.
• US 4,044,253 discloses a method for detecting cracks or defects in a composite skin bonded to a metal substrate.
• the method comprises the steps of applying a solution of 8- hydroxyquinoline in a solvent to the composite coating and then exposing the coating to ultraviolet radiation. The presence of defects or cracks in the coating is indicated by a fluorescent glow.
• the 8-hydroxyquinoline reacts with the metal substrate forming a metal chelate which fluoresces in response to exposure to ultraviolet light.
• the inventors provide an inexpensive corrosion detection probe and convenient method of corrosion detection at both a bare metal substrate and a coated metal substrate.
• the detection formulation is capable of remaining in position at the substrate for a considerable period of time following the spray application. Therefore, once the substrate has been coated with the formulation of the present invention, the step of detecting corrosion using ultraviolet radiation may be carried out at some later stage that may be more practical and convenient whilst still enabling reliable corrosion identification.
• a method of detecting corrosion at a surface of a metal substrate comprising: spray coating a portion of said surface of said metal substrate with a solution comprising a binder and a metal ion chelating agent capable of fluorescence; and exposing the coated metal surface to ultraviolet radiation.
• the chelating agent may comprise any one or a combination of the following: alizarin; lumogalliol; morin; o.o'-dihydroxyazobenzene (dhab); 8- hydroxyquinoline; 8-hydroxyquinoline-5-sulphonic acid hydrate (8-HQS).
• the binder compound configured to provide adhesion of the detection solution to the metal substrate is preferably a polymer compound in particular polyvinylalcohol.
• the binder is configured to increase the viscosity of the corrosion detection solution, thereby inhibiting removal once applied to the substrate.
• the binder is selected to provide the required viscosity whilst permitting the solution to be applied to the substrate in the form of a particulate spray or mist.
• the binder may alternatively include a natural or synthetic gum.
• the solution comprises a composition of 0.5-1.5 weight % of the chelating agent and 3.5-5.5 weight % of the binder.
• the present method and apparatus for corrosion detection is particularly suitable for use with aluminum based substrates and for the chelation of trivalent aluminum ions.
• the solution of the present invention comprises a solvent suitable for solvating the chelating agent wherein the solvent is preferably dimethylsulphoxide.
• the solution is allowed to dry or partially dry after application on the substrate surface prior to exposing the coated metal surface to ultraviolet radiation.
• the present invention is equally suitable for the instantaneous detection of corrosion immediately after spray application and exposure to ultraviolet radiation.
• the formulation solution of the present invention is applied to the substrate in aerosol form according to conventional aerosol spray techniques.
• a corrosion indicator formulation configured to indicate the presence of metal ions generated at a surface of a metal substrate, said formulation comprising: a metal ion chelating agent configured to chelate with metal ions generated at said substrate and to fluoresce in response to exposure to ultraviolet radiation; and a binder configured to inhibit removal of said chelating agent from said substrate following a spray coating of said formulation onto said substrate.
• Figure 1 herein shows an aluminum test panel exposed to UV light indicating corrosion where a protective film has been scored by a scalpel.
• the present invention provides a corrosion detection probe suitable for investigating corrosion at metal substrates and in particular large metal structures particularly within the aviation and automotive industries.
• the detection probe in the form of a solution, is capable of being sprayed onto the metal substrate in the form of a temporary coating.
• the detection probe may be formed as a permanent or semipermanent coating, in the form of a paint.
• Both the rudimentary 'spray applied' coating and the corrosion detecting paint are configured to fluoresce when exposed to ultraviolet radiation and, in the presence of metal ions generated at the metal substrate resulting from the corrosion process.
• the corrosion detection formulation configured specifically for corrosion detection at aluminium based substrates comprises 8-hydroxyquinoline-5- sulphonic acid hydrate (8-HQS).
• 8-HQS is capable of chelating with trivalent aluminium ions to form a complex having a maximum excitation wavelength of 367 mn, an emission maximum at 395 nm and a stability constant pK of 20.3.
• Polyester samples were prepared from a polyester based resin in styrene with peroxide catalyst P2 in the ratio 197:3 by weight.
• Epoxy samples were prepared from an epoxy based resin cured with an amine hardener in the ratio 69:31 by weight.
• Polyurethane samples were prepared from a water based polyurethane allowed to dry in air. Films of each polymer were prepared by spreading the polymer on a PTFE base using a draw-bar, and removing the films when hardened. Light transmission was measured at various wavelengths in a UV/visible spectrophotometer. Ion transport was measured in a container fashioned from polycarbonate, with two wells joined by a tunnel and with the sample placed in the tunnel to form a barrier between the solutions in each well. One well was filled with the test solution and the other with de-ionised water. The increase in ion concentration of the de-ionised water was measured as a function of time as ions passed through the polymer film.
• a solution in dimethyl sulfoxide was prepared by dissolving 1% by weight of 8-HQS and 4% by weight of polyvinyl alcohol (Aldrich Chemicals) at 70 0 C.
• the solution was allowed to cool and kept in a stoppered bottle.
• a thin film was deposited on a standard aluminium test panel using a draw-bar set at 100 microns gap.
• the solution was allowed to dry in air for 48 hours and then further drying carried out at 60 0 C in an oven.
• the aluminium surface had an even, yellow colouration.
• the surface was then coated with epoxy resin to provide a protective coating for the bare aluminium substrate.
• the exposed edges were coated with beeswax and the film was scored with a scalpel to provide a corrosion site and the panel exposed to a salt spray.
• the test panel was visualised using a hand-held UV lamp with a maximum output centred at 373 nm.
• Table (1 ) gives the percentage transmission at wavelengths selected to represent excitation and emission wavelengths of fluorophores of interest.
• Polyurethane gave a similar result but polyester showed no distortion after 12 days exposure and chloride was not detected in the receiving chamber. This would infer that polyester coatings would be the most effective to inhibit corrosion.
• the polymer of choice is epoxy due to its good light transmission and ion transport characteristics.
• the fluorescent output of the aluminium complex of 8-HQS is shown in Table 2 below. In the absence of aluminium, 8-HQS is only weakly fluorescent at 0.01 M concentration.
• the semi-quantitative data in Table 2 show the detection limit and linear response range of the fluorescent probe in solution.
• Figure 1 herein shows an aluminium test panel prepared in accordance with the preparation procedure detailed above.
• the region of the test panel scored with a scalpel is identified by the lightly shaded horizontal line positioned just above centre of the test panel.
• the salt solution inducing corrosion at the scored region also induced corrosion at various regions of the test panel, being represented by circular light spots. These circular regions correspond to bubbles formed in the epoxy film that allow penetration of the corrosive species through the film in contact with the aluminium substrate.
• Figure 1 shows the test panel illuminated by UV light whereby corrosion is easily identified by the lightly shaded regions according to figure 1.

Applications Claiming Priority (2)

Publications (1)

Family

ID=34685245

Family Applications (1)

Country Status (3)

Families Citing this family (9)

Family Cites Families (5)

• 2005
  • 2005-05-07 GB GB0705948A patent/GB2434447B/en not_active Expired - Fee Related
  • 2005-05-07 GB GB0509358A patent/GB2425835B/en not_active Expired - Fee Related
• 2006
  • 2006-05-03 WO PCT/GB2006/001626 patent/WO2006120389A1/en not_active Application Discontinuation
  • 2006-05-03 EP EP06743874A patent/EP1886115A1/de not_active Withdrawn

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events