METHOD FOR PRODUCING A CORROSION-INHIBITING OR ADHESION-PROMOTING COATING

Abstract

A method of treating a substrate, the method comprising: delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to a surface of the substrate, to impregnate the surface of the substrate with the dopant; wherein the dopant comprises a corrosion-inhibiting or adhesion-promoting species, such as to form a corrosion-inhibiting or adhesion-promoting coating at or on the surface of the substrate. Also provided is an article comprising a substrate having a corrosion-inhibiting or adhesion-promoting coating, the said coating comprising particles of a corrosion-inhibiting or adhesion-promoting species that impregnate the surface of the substrate (e.g. as produced by the above method).

Claims

1. A method of treating a metal substrate, the method comprising: delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to a surface of the metal substrate, to impregnate the surface of the metal substrate with the dopant; wherein the dopant comprises a corrosion-inhibiting species such as to form a corrosion-inhibiting conversion coating at the surface of the metal substrate.

2. A method as claimed in claim 1, wherein the corrosion-inhibiting species is chemically bonded to the substrate.

3. A method of treating a metal substrate, the method comprising: delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to a surface of the metal substrate, to impregnate the surface of the metal substrate with the dopant; wherein the dopant comprises a corrosion-inhibiting species that forms a mechanically-bonded corrosion-inhibiting coating on the surface of the metal substrate.

4. A method as claimed in claim 1, wherein the nature of the corrosion-inhibiting coating is such that no laminate layer of the dopant results.

5. A method as claimed in claim 1, wherein the method further comprises removing a metal oxide from the surface of the metal substrate to expose a metal surface, by abrasively blasting the metal oxide with the second set of particles substantially simultaneously with the delivery of the first set of particles.

6. A method as claimed in claim 1, wherein no pre-treatment process is performed before delivering the first and second sets of particles.

7. A method as claimed in claim 1, wherein the corrosion-inhibiting coating forms a first layer, and the method further comprises applying a second layer to the first layer.

8. A method as claimed in claim 7, wherein the first layer acts as a primer to enhance adhesion of the second layer.

9. A method as claimed in claim 7, wherein the second layer is a scratch-inhibiting layer.

10. A method as claimed in claim 9, wherein the second layer is a further corrosion-inhibiting layer.

11. A method as claimed in claim 1, wherein the corrosion-inhibiting species comprises a chromate, phosphate, polymer, oxide or a nitride.

12. A method as claimed in claim 11, wherein the corrosion-inhibiting species comprises a transition metal phosphate.

13. A method as claimed in claim 12, wherein the corrosion-inhibiting species comprises iron phosphate, manganese phosphate or zinc phosphate, or a combination thereof.

14. A method as claimed in claim 11, wherein the corrosion-inhibiting species comprises cerium oxide.

15. A method of treating a substrate, the method comprising: delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to a surface of the substrate, to impregnate the surface of the substrate with the dopant; wherein the dopant comprises an adhesion-promoting species such as to form an adhesion-promoting coating at or on the surface of the substrate.

16. A method as claimed in claim 15, wherein the adhesion-promoting species forms a conversion coating at the surface of the substrate.

17. A method as claimed in claim 16, wherein the adhesion-promoting species is chemically bonded to the substrate.

18. A method as claimed in claim 15, wherein the adhesion-promoting species forms a mechanically-bonded adhesion-promoting coating on the surface of the substrate.

19. A method as claimed in claim 15, wherein no pre-treatment process is performed before delivering the first and second sets of particles.

20. A method as claimed in claim 15, wherein the adhesion-promoting species forms a primer layer on the substrate.

21-73. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Embodiments of the invention will now be described, by way of example only, and with reference to the drawings in which:

[0073] FIGS. 1a, 1b and 1c schematically illustrate a process for treating a metal substrate;

[0074] FIGS. 2a, 2b and 2c are schematic diagrams of three different nozzle configurations to deliver abrasive particles and dopant particles to a surface;

[0075] FIG. 3 is a schematic cross-sectional representation of a metal substrate having a corrosion-inhibiting conversion coating;

[0076] FIG. 4 is a schematic cross-sectional representation of a metal substrate having a corrosion-inhibiting conversion coating on which a second layer has been formed;

[0077] FIG. 5 is a schematic cross-sectional representation of a substrate having an adhesion-promoting coating;

[0078] FIG. 6 is a schematic cross-sectional representation of a substrate having an adhesion-promoting coating serving as a primer layer, onto which a subsequent coating has been formed; and

[0079] FIG. 7 presents the results of lap-shear strength testing following various surface treatments on titanium (in respect of Example 5 discussed below).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0080] The present embodiments represent the best ways known to the applicants of putting the invention into practice. However, they are not the only ways in which this can be achieved.

Overview of Variants

[0081] The present embodiments provide a method of treating a substrate, the method comprising: delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to a surface of the substrate, to impregnate the surface of the substrate with the dopant; wherein the dopant comprises a corrosion-inhibiting or adhesion-promoting species, such as to form a corrosion-inhibiting or adhesion-promoting coating at or on the surface of the substrate.

[0082] The action of the abrasive particles on the substrate causes a rough interface to be formed between the substrate material and the coating formed thereon. Furthermore, the degree of intermixing between the substrate and dopant species is such that no laminate layer of the dopant results.

[0083] The present embodiments may be subdivided into three main variants.

[0084] In accordance with a first variant, certain embodiments provide a method of treating a metal substrate, the method comprising: delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to a surface of the metal substrate, to impregnate the surface of the metal substrate with the dopant; wherein the dopant comprises a corrosion-inhibiting species such as to form a corrosion-inhibiting conversion coating at the surface of the metal substrate.

[0085] In accordance with a second variant, other embodiments provide a method of treating a metal substrate, the method comprising: delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to a surface of the metal substrate, to impregnate the surface of the metal substrate with the dopant; wherein the dopant comprises a corrosion-inhibiting species that forms a mechanically-bonded corrosion-inhibiting coating on the surface of the metal substrate.

[0086] In accordance with a third variant, further embodiments provide a method of treating a substrate (which need not be a metal), the method comprising: delivering substantially simultaneously a first set of particles comprising a dopant and a second set of particles comprising an abrasive from at least one fluid jet to a surface of the substrate, to impregnate the surface of the substrate with the dopant; wherein the dopant comprises an adhesion-promoting species such as to form (e.g. by conversion coating or mechanical bonding) an adhesion-promoting coating at or on the surface of the substrate.

Substantially Simultaneous Particle Delivery Method

[0087] For the details of carrying the method of each of the first, second and third variants, the reader is initially referred to WO 2008/033867, which describes techniques for the substantially simultaneous deposition of first and second sets of particles. However, it should be noted that WO 2008/033867 does not describe the dopant comprising a corrosion-inhibiting species such as to form a corrosion-inhibiting conversion coating or a mechanically-bonded corrosion-inhibiting coating at or on the surface of the metal substrate (as per the present first and second variants). WO 2008/033867 also does not describe forming an adhesion-promoting coating at or on the surface of the substrate (as per the present third variant).

[0088] Naturally, as those skilled in the art will appreciate, the first and second sets of particles are different from one another (i.e. the dopant species is different from the abrasive).

Embodiments which Form a Corrosion-Inhibiting Coating at or on the Surface of the Substrate (First and Second Variants)

[0089] Embodiments of the present method are encompassed in but not limited to the schematic representation shown in FIGS. 1a, 1b and 1c.

[0090] FIG. 1a schematically shows a fluid jet (nozzle) 2 that delivers a stream 3 comprising a set of abrasive particles 4 substantially simultaneously with a set of dopant particles 6. The dopant particles 6 comprise a corrosion-inhibiting species. Particle sets 4 and 6 bombard a surface 10 of a metal substrate 8, to impregnate the surface of the metal substrate with the corrosion-inhibiting dopant.

[0091] In accordance with the first variant, a chemical or electro-chemical reaction may take place between the dopant species and the substrate material, resulting in the formation of a corrosion-inhibiting conversion coating at the surface of the metal substrate 8. The energy required to initiate these reactions may be provided by the impact of both sets of particles on the surface. The abrasive particles may not necessarily partake directly in the chemical reaction, but their impact on the surface may provide the activation energy to initiate the conversion reaction.

[0092] Alternatively, in accordance with the second variant, a mechanically-bonded corrosion-inhibiting coating may be formed on the surface of the metal substrate, with some of the corrosion-inhibiting dopant particles mechanically interlocking with the surface of the substrate, the surface having been roughened by the action of the abrasive particles.

[0093] The formation of the corrosion-inhibiting coating may also involve a combination of both conversion coating and mechanical bonding of the dopant particles to the surface of the substrate.

[0094] With both the first and second variants, during the deposition process the dopant particles that have been deposited are subjected to ongoing bombardment by the abrasive particles, repeatedly hammering the dopant particles onto and into the surface of the substrate, resulting in an intimate mixing of the substrate and dopant species and a high level of bonding and interlocking between the two, such that, at the corrosion-inhibiting coating, no laminate layer of the dopant results.

[0095] In the embodiment illustrated in FIGS. 1a, 1b and 1c, the surface 10 is a metal oxide layer. As a result of bombardment by the abrasive particles 4, the surface oxide layer is disrupted, and breaches in the oxide layer 10 result to expose a new surface 10a of substrate 8 (FIG. 1b). In the case of a metal substrate, the newly exposed surface is a metal surface. As the particle stream 3 continues to impinge the substrate 8, the dopant particles 6 are integrated into the surface 10 of the substrate 8 (FIG. 1c). Such disruption of the oxide layer, to produce a newly exposed surface of metal, is particularly applicable if a chemical or electro-chemical reaction is to take place between the dopant and substrate species, enabling the dopant species to react with the substrate metal (rather than the surface oxide layer). However, disruption of the oxide layer is also beneficial if the coating is to be mechanically bonded to the substrate 8.

[0096] In some embodiments, the blasting equipment can be used in conjunction with controlled motion such as CNC (computer numerical control) or robotic control. The blasting can be performed in an inert environment.

[0097] In one embodiment, the dopants and abrasives are contained in the same reservoir and are delivered to a surface from the same jet (nozzle). In another embodiment, the dopant is contained in one reservoir and abrasive contained in a separate reservoir, and multiple nozzles deliver the dopants and abrasives. The multiple nozzles can take the form of a jet within a jet, i.e., the particles from each jet bombard the surface at the same incident angle. In another embodiment, the multiple nozzles are spatially separated so as to bombard the surface at different incident angles yet hit the same spot on the surface simultaneously.

[0098] FIGS. 2a, 2b and 2c are schematic diagrams of three different nozzle configurations to deliver the dopants and abrasive to a surface: single nozzle (FIG. 2a); multiple nozzles with dopants and abrasives delivered from separate reservoirs where one nozzle is situated within another nozzle (FIG. 2b); and multiple, separate nozzles with dopants and abrasives delivered from separate reservoirs (FIG. 2c). More specifically, FIG. 2a shows a single nozzle 20 for delivering a single stream 23 of abrasive particles 24 and corrosion-inhibiting dopant particles 26 to a substrate 28. FIG. 2b shows that multiple nozzles with dopants and abrasives delivered from separate reservoirs can be used, with FIG. 2b illustrating one nozzle 30 for delivering a stream 33 of abrasive particles 24 situated within another nozzle 40 for delivering a stream 43 of corrosion-inhibiting dopant particles 26, where streams 33 and 43 are coaxial. Multiple, separate nozzles with dopants and abrasives delivered from separate reservoirs can also be used, as indicated in FIG. 2c, which shows nozzles 30 and 40, for delivering streams 33 and 43 of abrasive particles 24 and corrosion-inhibiting dopant particles 26, respectively.

[0099] The distance D between the nozzle(s) and the substrate surface can be in the range of 0.1 mm to 100 mm, such as a range of 0.1 mm to 50 mm, or a range of 0.1 mm to 20 mm. The angle of the nozzle to the surface can range from 10 degrees to 90 degrees, such as a range of 30 degrees to 90 degrees, or a range of 70 to 90 degrees.

[0100] More than one type of dopant species can be used. It will readily be appreciated that where more than one type of dopant is used, the dopants may be delivered from a single nozzle, or each type may respectively be delivered from a separate nozzle.

[0101] As illustrated in FIG. 3, the layer of corrosion-inhibiting material 52 may be used as a final surface finish which acts as a corrosion resistant layer for the substrate 8. As discussed above, such a corrosion resistant layer 52 may be formed as a conversion coating at the surface of the substrate 8, or as a layer that is mechanically bonded to the substrate 8.

[0102] Alternatively, as shown in FIG. 4, the corrosion-inhibiting layer 52 may be further covered with one or more additional coating layer(s) 54 to enhance the corrosion resistance (and/or scratch resistance) of the surface. These one or more layer(s) may be applied by spraying, painting, dipping, vapor deposition or any suitable method to apply the subsequent layer(s). The corrosion-inhibiting material 52 may act as a primer onto which these additional layer(s) 54 are able to adhere, thereby enhancing the adhesion strength of the subsequent layer(s) 54 to the substrate metal 8. Adjusting the abrasive properties, dopant properties or blast conditions can alter the surface topography and chemistry of the deposited layer of corrosion resistant material 52, thereby optimising the primer surface to deliver improved primer performance.

[0103] Applications of the above technique for forming a corrosion-inhibiting coating include (but are in no way limited to) providing corrosion protection for: [0104] large-scale engineering components such as pipeline sections [0105] wind turbine components [0106] civil engineering structures [0107] external walls [0108] marine components [0109] automotive body parts [0110] oil and gas industry components [0111] aerospace components
Embodiments which Form an Adhesion-Promoting Coating at or on the Surface of the Substrate (Third Variant)

[0112] As with the above-described method for the formation of a corrosion-inhibiting coating, embodiments which form an adhesion-promoting coating are also encompassed in but not limited to the schematic representation shown in FIGS. 1a, 1b and 1c, in this case with the dopant particles 6 comprising an adhesion-promoting species. Particle sets 4 and 6 bombard a surface 10 of a substrate 8, which in some embodiments may be metal, but in others may be a non-metal (e.g. a polymer or ceramic) or a composite material, so as to impregnate the surface of the substrate 8 with the adhesion-promoting species.

[0113] If the substrate 8 is metal then the surface 10 may again comprise a metal oxide layer. As a result of bombardment by the abrasive particles 4, the surface oxide layer is disrupted, and breaches in the oxide layer 10 result to expose a new surface 10a of substrate 8 (FIG. 1b). For a metal substrate, the newly exposed surface is a metal surface. As the particle stream 3 continues to impinge the substrate 8, the adhesion-promoting dopant particles 6 are integrated into the surface 10 of the substrate 8 (FIG. 1c). Such disruption of the oxide layer, to produce a newly exposed surface of metal, is particularly applicable if a chemical or electro-chemical reaction is to take place between the dopant and substrate species, enabling the dopant species to react with the substrate metal (rather than the surface oxide layer). However, disruption of the oxide layer is also beneficial if the adhesion-promoting coating is to be mechanically bonded to the substrate 8.

[0114] As with the above-described method, three different possible nozzle configurations are illustrated schematically in FIGS. 2a, 2b and 2c.

[0115] A chemical or electro-chemical reaction may take place between the adhesion-promoting species and the substrate material, resulting in the formation of an adhesion-promoting conversion coating at the surface of the substrate 8.

[0116] Alternatively, a mechanically-bonded adhesion-promoting coating may be formed on the surface of the substrate, with some of the adhesion-promoting dopant particles mechanically interlocking with the surface of the substrate, the surface having been roughened by the action of the abrasive particles.

[0117] The formation of the adhesion-promoting coating may also involve a combination of both conversion coating and mechanical bonding of the dopant particles to the surface of the substrate.

[0118] With the third variant, during the deposition process the dopant particles that have been deposited are subjected to ongoing bombardment by the abrasive particles, repeatedly hammering the dopant particles onto and into the surface of the substrate, resulting in an intimate mixing of the substrate and dopant species and a high level of bonding and interlocking between the two, such that, at the adhesion-promoting coating, no laminate layer of the dopant results.

[0119] FIG. 5 shows a schematic cross-sectional representation of a substrate 8 having an adhesion-promoting coating 56, formed either as a conversion coating at the surface of the substrate, or as a mechanically-bonded coating on the surface of the substrate.

[0120] Optionally, in certain embodiments, the adhesion-promoting coating 56 may be deposited in an uncured or semi-cured form, for curing in a separate step using heat, radiation, moisture, etc., prior to the application of any subsequent coating. Such curing may be performed in a localised manner (e.g. using localised infra-red curing).

[0121] The adhesion-promoting coating 56 may be provided so as to improve the adhesion of the substrate 8 to another material or article with which the coated substrate subsequently comes into contact. That is to say, the production of the adhesion-promoting coating 56 may be the only surface treatment process carried out on the substrate.

[0122] However, as shown in FIG. 6, the adhesion-promoting coating 56 may alternatively serve as a primer layer, onto which a further coating 58 (or a plurality of subsequent coatings) may subsequently be applied. The coating 58 may be, for example, a scratch-inhibiting coating, or a corrosion-inhibiting coating (to inhibit corrosion of the underlying substrate 8), or a solid low-friction or non-stick coating such as polytetrafluoroethylene (PTFE), or an adhesive layer to enable the underlying substrate 8 to be adhesively bonded to another article. In other embodiments the coating 58 may comprise some other kind of fluoropolymer layer, a paint layer (e.g. epoxy paint), or a ceramic coating, etc. Subsequent fluoropolymer layers can also be applied to minimise the accumulation and deposition of unwanted scale, debris, asphaltenes, paraffins or debris which can impair the operation of the underlying substrate. For such fluoropolymer coatings, a fluoropolymer primer such as PTFE has been found to be especially beneficial as it allows the thick fluoropolymer coating to be effectively adhered to the substrate underneath. This was unexpected, as the first layer of fluoropolymer which impregnated the substrate would be expected to act as a release layer that would minimise the adhesion of subsequent layers. In contrast, it has been found that the subsequent fluoropolymer coatings adhere to the primer layer of fluoropolymer and the adhesion of the subsequent layer is enhanced by the presence of the primer layer. This process can be further enhanced by heating the multi-layered structure such that the fluoropolymer layers are thermally coalesced. Such coatings have been found to be highly beneficial when applied to the inner surfaces of pipes where they decrease corrosion and reduce maintenance requirements.

[0123] Optionally, in certain embodiments, the subsequently-applied coating 58 may be deposited in an uncured or semi-cured form, for curing in a separate step using heat, radiation, moisture, etc. Such curing may be performed in a localised manner (e.g. using localised infra-red curing).

[0124] Applications of the above techniques for forming an adhesion-promoting coating or a primer layer include (but are in no way limited to): [0125] Improving the adhesion of protective coatings on inner and outer surfaces of pipes to minimise build up of scale or to minimise corrosion. [0126] Enhanced adhesion of glues, silicones and other adhesives to metal components for improved bonding strength. [0127] Improved adhesion of protective paints for use in marine, aerospace or industrial applications. [0128] Improved adhesion of anti-scratch coatings. [0129] Formation of non-stick coatingsfor example on articles such as utensils, saucepans or other items (both domestic and industrial) used in the cooking of foodstuffs, to inhibit foodstuffs from sticking during cooking. For all such purposes the non-stick coating would be bonded to the substrate using a primer layer, and may comprise a fluoropolymer such as PTFE. [0130] Mould-release applicationsi.e. to form a non-stick coating on the inner surface of a mould (the mould typically being made of metal), to facilitate, in use of the mould, the removal of a moulded article from the mould. The non-stick coating would be bonded to the mould surface using a primer layer, and may comprise a fluoropolymer such as PTFE. Moulds coated in such a manner have many possible applications, including for the manufacture of vehicle tyres, engineering components, consumer products, and so on. [0131] The treatment of surfaces of engineering components where a low coefficient of friction is required, by bonding a low-friction coating (comprising, for example, a fluoropolymer such as PTFE) to the surface of the engineering component using a primer layer. [0132] Bonding applicationsi.e. to form an adhesive coating on a substrate to enhance the degree of bonding between the substrate and another material or article with which the coated substrate subsequently comes into contact. For example, metal wires may be treated with a bonding agent (the wire being the substrate in such a case) to promote the degree to which they will bond to rubber. Such wires may then used, for example, in the manufacture of vehicle tyres, the wires being encased within the rubber to provide reinforcement to the tyre. [0133] Improved bonding of metals to composites and plastics, more generally.

Examples of Abrasive Species

[0134] Abrasive species that may be used in any of the above variants of the present method (as a second set of particles, delivered substantially simultaneously with a first, different, set of particles comprising a dopant) include but are not limited to shot or grit made from silica, sand, alumina, zirconia, barium titanate, calcium titanate, sodium titanate, titanium oxide, glass, biocompatible glass, diamond, silicon carbide, boron carbide, dry ice, boron nitride, calcium phosphate, calcium carbonate, metallic powders, carbon fibre composites, polymeric composites, titanium, stainless steel, hardened steel, carbon steel chromium alloys or any combination thereof.

[0135] The abrasive particles preferably have a hardness of at least 7 on the Mohs scale.

[0136] The abrasive particles preferably have an average particle size (diameter) in the range of 1 m to 150 m, more preferably in the range of 10 m to 150 m, and particularly preferably in the range of 50 m to 150 m. The use of small abrasive particles of such dimensions gives rise to enhanced disruption of the surface of the substrate, thereby promoting penetration of the dopant particles into the substrate surface and intermixing of the dopant particles with the substrate surface. Thus, the dopant species is impregnated into the substrate such that no laminate layer of the dopant results.

Examples of Corrosion-Inhibiting Dopant Species

[0137] With regard to the first and second variants described above, corrosion-inhibiting dopant species that may be used in the present method (as a first set of particles, different from the second) include but are not limited to a chromate, phosphate, polymer (e.g. a thermoset or a thermoplastic), oxide or a nitride. For example, the dopant may be ceria. In a preferred method, the coating is derived from a phosphate compound. The phosphate may comprise iron phosphate, manganese phosphate, zinc phosphate or combinations thereof. As the phosphate is not deposited by an electrochemical process, a range of materials can be incorporated into the surface by modifying the starting dopant powder.

[0138] It is particularly noteworthy that the corrosion-inhibiting dopant species need not be a metal or a metal salt, which are inherently sacrificial in nature. Polymer based dopants may be deposited which form a stable deposit on the substrate surface and prevent corrosion by inhibiting the build-up of corrosive materials on the surface or by physically isolating the corrosive species from the underlying substrate. Fluoropolymer, acrylate, acetate and epoxy based layers may all perform this function.

[0139] The dopant particles preferably have an average particle size (diameter) in the range of 1 m to 100 m.

[0140] Preferably the ratio of the dopant particles to the abrasive particles is between 20:80 and 80:20 by weight, and particularly preferably is between 40:60 and 60:40 by weight.

Examples of Adhesion-Promoting Dopant Species

[0141] With regard to the third variant described above, adhesion-promoting dopant species that may be used in the present method (as a first set of particles, different from the second) include but are not limited to fluoropolymers such as PTFE, perfluoroalkoxy materials such as Teflon, polyvinylidene fluoride, perfluoropolyethers, perfluorinated elastomers, polyvinylfluoride. They may also include silanes, siloxanes, acrylates, epoxys, hydrogen bonded silicon compounds or materials which contain one or more vinyl, peroxyester, peroxide, acetate or carboxylate functional group.

[0142] In particular examples, when forming an adhesion-promoting coating to serve as a primer layer for a polymer-based subsequent layer, the primer layer may be composed of the same materials as present within the subsequent layer. PTFE or other fluoropolymers may be used as primer-forming dopant species for the improved adhesion of subsequent fluoropolymer layers.

[0143] The dopant particles preferably have an average particle size (diameter) in the range of 1 m to 100 m.

[0144] Preferably the ratio of the dopant particles to the abrasive particles is between 20:80 and 80:20 by weight, and particularly preferably is between 40:60 and 60:40 by weight.

EXAMPLES

[0145] The following examples demonstrate the use and efficacy of the above method in forming corrosion-inhibiting coatings and adhesion-promoting coatings, including as primer layers.

Example 1Deposition of Zinc Phosphate on a Range of Metal Substrates (Aluminium, Copper, Grade 2 and 5 Titanium, Hastelloy, Inconel, Magnesium, Mild Steel, Stainless Steel (316))

[0146] A series of metal substrates were obtained, made respectively of Aluminium, Copper, Grade 2 and 5 Titanium, Hastelloy, Inconel, Magnesium, Mild Steel and Stainless Steel (316). Zinc phosphate powder (<5 microns average particle size) was mixed in equal volumetric proportions with alumina grit (100 micron average particle size) and then loaded into an Accuflow powder feeder. The powder was fed from there to a grit blast nozzle which was moved over the surface of the metal substrates and the powder was blasted at the surface at a pressure of 75 psi. Following blasting, the substrates were cleaned with compressed air to remove loose powder. All treated samples were visibly noted to have significant levels of zinc phosphate deposited on the surface. Surface characterisation was carried out using SEM and EDX analysis. EDX was used to determine the concentration of the coating by measuring and summing the Zn and P concentrations. There appeared to be a moderate coverage of zinc phosphate (>30%) on all of the surfaces tested, confirming that the abrasive blasting process could effectively deposit a corrosion-inhibiting material. Examination of the deposited corrosion-inhibiting material suggested that it was formed by a combination of both a conversion process and mechanical bonding. Surface oxide is removed and so the zinc phosphate bonded to the surface as per conversion coatings, but some mechanical interlock is also seen, as a result of the bombardment process.

Example 2Corrosion Protection of Mild Steel

[0147] Mild steel coupons and buttons were blasted with a mixture of zinc phosphate powder and alumina grit. Following deposition, the samples were analysed using EDX and both types of treated samples were found to have approximately 40% zinc phosphate present on the surface. The coated samples were then immersed in a 3.5% w/w NaCl solution. Untreated mild steel coupons and buttons were used as controls. After 72 hours, the untreated steel samples were visibly discoloured and the sample containers had a significant deposit of brown sediment which had settled to the bottom of the jar. The zinc phosphate treated samples showed no visible changes from their initial condition. There was no evidence of any deposit, any discolouration or any other visible signs of corrosion. The test was continued until day 7, with the untreated samples continuing to degrade while the zinc phosphate blasted samples remained largely unchanged, thereby confirming the protective corrosion-inhibiting properties of the abrasive blasting treatment.

Example 3Primer for Epoxy Paint

[0148] Mild Steel (Grade SAE 1008) was used for all samples. The following surface treatments were then applied to a number of samples: [0149] Untreated Blank sample (i.e. as-received) [0150] Grit Blasted (to Sa 2 standard as per ISO 8501-1) [0151] Iron Phosphate (from Q-PanelHenkel Bonderite M-FE 1000) [0152] Zinc Plated (Tri-eco Zinc procured from Meath Metal, Ireland) [0153] Commercial dry Zinc Phosphate Primer (manufactured by Johnstones) [0154] A Zinc Phosphate produced by blasting the metal with dry zinc phosphate powder (supplied by Delaphos) and 100 micron alumina. The two powers were premixed and then blasted at the surface through a De Laval nozzle at a pressure of 75 psi.

[0155] Each component was then coated with a SP320 two-part epoxy laminating paint procured from www.UnionChandlery.ie. This particular paint gave a clear coat to allow observation of the rust/corrosion growth from the introduced scratch.

[0156] Corrosion testing was carried out using a neutral salt fog cabinet as per ISO 9227. A T scribe was introduced to each sample using a carbide tip as per ISO 18782. Throughout the course of the experiment, each sample was removed periodically and photographed to log the growth of corrosion from the scratch. The samples were cleaned in deionised water to remove excess rust/corrosion on top of the sample prior to taking the photograph. The width/growth of the corrosion from the scratch was measured using the freely available imageJ software. Each coupon was removed from the salt fog cabinet at set intervals over a period of 56 days.

[0157] The width of the corrosion was measured using the imageJ software. A steel ruler was used to calibrate the scale.

[0158] Somewhat surprisingly, the Iron Phosphate and Zinc Plated samples performed quite poorly. In particular, the Zinc Plated sample exhibited significant delamination of the epoxy paint after 28 days and almost complete catastrophic failure after 56 days.

[0159] The Blank & Grit-Blasted coupons initially appeared to perform quite well and produced results that appeared superficially identical to the zinc phosphate coatings. However, when sectioned and examined in detail, it was evident that the depth of corrosion was much greater for these samples than for either of the zinc phosphate treatments. Both zinc phosphate treatments were noticeably better than the other commercial treatments. The blasted zinc phosphate tie-layer was very close in performance to that of the commercial Dry Zinc Phosphate primer (which utilised a noticeably thicker coating).

Example 4Primer for Fluoropolymer Adhesion

[0160] Four 35 mild steel Q-panels were pre-treated with an abrasive blasting process as follows: [0161] (i) Two were blasted with a mixture of 100 micron alumina and PTFE (Zonyl MP 1300) using a 80:20 mix by weight and a blasting pressure of 40 psi and a stand-off distance of 30 mm. [0162] (ii) The other two were blasted with alumina only using the same conditions.

[0163] All samples were then washed in deionised water, dried with compressed air and then given a subsequent coating of PTFE fluoropolymer. The PTFE was sprayed at 2 psi and from 150 mm stand-off. To get a thick coating, three passes over the surface were required. All samples were then heated to 400 C. in a carbolite furnace and then air cooled.

[0164] Adhesion testing was then carried out using a modified version of ISO 2409.

[0165] This aggressive version of ISO 2409 used a higher tack tape (tesa 4613) and repeated tape pulls due to the poor adhesion between standard scotch tape and the PTFE coating. Prior to cutting, samples were boiled in DIW for 20 mins and then thoroughly dried and cooled. Cutting was carried out as per ISO 2409 with a multi-blade cutter with 2 mm spacing. Four separate areas were tested for each coating, and the tape pull was repeated 4 times at each test area. The ISO classification was followed, whereby samples that were undamaged by the tape test were rated 0, surfaces with less than 5% detachment were rated 1, surfaces with between 5 and 15% detachment were rated 2 and so on up until level 5.

[0166] After one tape test, samples prepared using the abrasively blasted pre-treatment yielded a value of 1, while the samples that were blasted with both abrasive and PTFE showed no effects and were therefore classified as 0. After four tape tests on the same area, the abrasively blasted samples were classified at level 2 to level 4, while the samples blasted with both abrasive and PTFE remained at classification 0 or 1, indicating significantly enhanced adhesion due to the PTFE primer.

[0167] Following this, samples were sectioned, mounted and polished, and viewed with a light microscope. Coating thickness was measured at 5 points on each sample at 10 magnification, and was consistent between the two coatings with both producing a thickness of 43 microns. No interface was visible between the PTFE primer layer and the top-coat, indicating they were completely fused.

Example 5Improved Bonding of Adhesive to Metal Components

[0168] The substrate in this case was grade V titanium. Five different surface treatments were then subjected to adhesion testing. These consisted of [0169] (i) Untreated titanium, henceforth called Blank. [0170] (ii) A grit blasted titanium surface produced by abrasively blasting the titanium with 50 micron alumina. [0171] (iii) A commercial Aerospace Primer. This consisted of Chromic Acid Anodized (CAA) surface followed by Cytec BR127 sol-gel primer. This will be referred to as CAA+Primer. [0172] (iv) A surface produced by blasting titanium with a mixture of alumina and a Thermoset epoxy LT3366 from Huntsman (referred to as Epoxy) [0173] (v) A surface produced by blasting titanium with a mixture of alumina and Zinc Phosphate powder (Heubach ZP10)

[0174] All samples were then bonded to a carbon fibre reinforced plastic (CFRP). The CFRP was Hexcel 8552/5H which was prepared for bonding using a wet peel ply (Henkel Hysol EA9895). The adhesive was Cytec FM300 epoxy film adhesive (0.03 gsm weight) which was cured at 177 C for 1 hour at a pressure of 45 psi.

[0175] Once the adhesive had fully cured, the samples were cooled to room temperature and then subjected to lap-shear testing, which was conducted in accordance with ISO 2243-1. The specimens were 25 mm wide with a 12.5 mm adhesive overlap. The lap-shear strength was calculated by dividing the force at failure by the overlap area. Four repetitions were performed for each surface treatment.

[0176] The results of these tests are shown in FIG. 7. All of the surface treatments out-performed the untreated blank. Simple roughening with alumina abrasive was sufficient to increase the adhesion significantly, but both the untreated and grit-blasted joint systems resulted in interfacial failure. However, the deposition of a chemical primer was far more successful and all three chemical primers exhibited cohesive failure modes. Both the zinc phosphate and epoxy dopants significantly enhanced the adhesion of the joint and matched the performance of the commercial aerospace primer. It should be noted that the abrasive blasting methods were able to achieve this level of performance without the use of toxic chromate conversion coatings or the use of aggressive wet chemical primers.

Example Areas of Industrial Application

[0177] The present method has potential application across a wide range of industries, including but not limited to: large-scale engineering components such as pipeline sections; wind turbine components; civil engineering structures; external walls; marine components; automotive body parts; oil and gas industry components; and aerospace components.