METALLIC COATED SUBSTRATES

Abstract

The invention relates to metallic substrates surface coated with a coating layer comprising a metal and an additive.

Claims

1. A metallic substrate, wherein the surface of the substrate is coated with a coating layer comprising a metal having dispersed therein a plurality of sealed nanotubes loaded with an anti-corrosion agent.

2. The metallic substrate according to claim 1, wherein said metal of the metallic coating layer is selected from the group consisting of transition metals, post transition metals and any combination thereof.

3. The metallic substrate according to claim 1, wherein said metal of the metallic coating layer is not, or does not include, chromium or cadmium.

4. The metallic substrate according to claim 1, wherein said metal of the metallic coating layer is selected from the group consisting of copper, zinc, silver, tin, gold, nickel or an alloy comprising one or more thereof.

5. The metallic substrate according to claim 1, wherein said nanotubes are halloysites of formula (Al2Si2)5(OH)4.nH2O) where n is 0-2.

6. The metallic substrate according to claim 1, wherein said anti-corrosion agent is selected from the group consisting of phosphate salts, organophosphates, organosulfur compounds; poly(3-ammoniumpropylethoxysiloxane) dodecanoate, (NH4)2TiF6, sodium poly(methacrylate), salicylaldoxime, triazole derivatives, benzotriazole (BTA) or a derivative thereof, syanate compounds, and any combination thereof.

7. The metallic substrate according to claim 6, wherein said anti-corrosion agent is: (i) BTA or a BTA derivative, wherein said BTA derivative is optionally selected from the group consisting of 4-methyl-1H-benzotriazole, 5-methyl-1H-benzotriazole, 6-methyl-1H-benzotriazole and 5,6-dimethyl-1H-benzotriazole, 1-(2-pyrrolecarbonyl)benzotriazole (PBTA) and 1(2-thienylcarbonyl)benzotriazole (TBTA), 1-hydroxymethyl benzotriazole and N,N-dibenzotriazol-1-ylmethylamine; (ii) a phosphate salt; or (iii) a cynate compound.

8. The metallic substrate according to claim 1, wherein said nanotubes are sealed with a material comprising metal ions, wherein said metal ions are preferably ions of a transition metal or an alkaline earth metal.

9. The metallic substrate according to claim 8, wherein said nanotubes are sealed with a material comprising transition metal ions selected from the group consisting or ions of zinc, silver, gold, nickel and any combination thereof, or wherein said nanotubes are sealed with a material comprising alkaline earth metal ions selected from magnesium, calcium and any combination thereof.

10. The metallic substrate according to claim 5, wherein: (i) said anti-corrosion agent comprises BTA and said nanotubes are sealed with zinc ions; (ii) said anti-corrosion agent comprises BTA and said nanotubes are sealed with calcium ions; (iii) said anti-corrosion agent comprises a phosphate salt, and said nanotubes are sealed with zinc ions; (iv) said anti-corrosion agent comprises a phosphate salt, and said nanotubes are sealed with calcium ions; (v) said anti-corrosion agent comprises a cyanate compound, and said nanotubes are sealed with zinc ions; or (vi) said anti-corrosion agent comprises a cyanate compound, and said nanotubes are sealed with calcium ions.

11. The metallic substrate according to claim 1, wherein said sealed nanotubes comprise from about 1 to 25 wt % and preferably from about 1 to 6 wt % of said anti-corrosion agent with respect to the total weight of the unloaded nanotubes.

12. The metallic substrate according to claim 1, wherein said nanotubes are present in the coating layer in an amount from about 0.5 to 8% by weight with respect of the total weight of the coating layer.

13. The metallic substrate according to claim 1, wherein said substrate is selected from the group consisting of iron, steel, mild steel, aluminium and aluminium alloys, wherein said alloys further comprise one or more metal selected from copper, magnesium, manganese, silicon, tin, nickel, silver, gold and zinc.

14. The metallic substrate according to claim 1, wherein said substrate is steel or mild steel.

15. The metallic substrate according to claim 1, wherein: (i) said coating layer is from about 1 to 100 μm thick; and/or (ii) said coating layer has a tensile strength of from about 200 to 1000 MPa.

16. An electroplating solution wherein said electroplating solution comprises transition metal and/or post transition metal ions and a plurality of sealed nanotubes loaded with an anti-corrosion agent.

17. The electroplating solution according to claim 16, wherein: (i) said transition metal and/or post transition metal ions are selected from the group consisting of copper ions, zinc ions, silver ions, tin ions, gold ions, nickel ions and any combination thereof, (ii) said nanotubes are halloysites of formula (Al2Si2)5(OH)4.nH2O) where n is 0-2; (iii) said anti-corrosion agent is selected from the group consisting of phosphate salts, organophosphates, organosulfur compounds, poly(3-ammoniumproplethoxysiloxane) dodecanoate, (NH4)2TiF6, sodium poly(methacrylate), salicylaldoxime, triazole derivatives, benzotriazole (BTA) or a derivative thereof, cyanate compounds, and any combination thereof, and/or (iv) said nanotubes are sealed with a material comprising metal ions, wherein said metal ions are preferably ions or a transition metal or an alkaline earth metal.

18. The electroplating solution according to claim 16, wherein said solution comprises transition metal and/or post transition metal ions at a concentration of from about 0.1M to 5M.

19. The electroplating solution according to claim 16, wherein: (i) said electroplating solution has a pH of from about 0.5 to 6.5; or (ii) said electroplating solution has a pH of from about 7.5 to 10.5.

20. The electroplating solution according to claim 16, wherein said solution comprises said sealed nanotubes at a concentration of from about 1 to 100 g/L and more suitably from about 1 to 10 g/L.

21. An electroplating apparatus comprising a power source, an electroplating solution according to claim 16, an anode and a cathode, wherein the anode and the cathode are connected to the power source and are immersed in the electroplating solution and wherein a substrate to be plated may be placed at or in contact with the cathode.

22. An electroless plating solution wherein said electroless plating solution comprises a reducing agent; transition metal and/or post transition metal ions; and a plurality of sealed nanotubes loaded with an anti-corrosion agent.

23. The electroless plating solution according to claim 22, wherein: (i) said transition metal and/or post transition metals are selected from the group consisting of copper ions, zinc ions, silver ions, tin ions, gold ions, nickel ions and any combination thereof, (ii) said nanotubes are halloysites of formula (Al2Si2)5(OH)4.nH2O) where n is 0-2; (iii) said anti-corrosion agent is selected from the group consisting of phosphate salts; organophosphates; organosulfur compounds; poly(3-ammoniumpropylethoxysiloxane) dodecanoate; (NH4)2TiF6; sodium poly(methacrylate); salicylaldoxime; triazole; benzotriazole (BTA) or a derivative thereof, and any combination thereof, (iv) said nanotubes are sealed with a material comprising metal ions, wherein said metal ions are preferably ions of a transition metal or an alkaline earth metal; and/or (v) said reducing agent is selected from hypophosphite, alkali metal borohydrides, soluble borane compounds, hydrazine, aldehyde reducing agents or a mixture thereof;

24. An electroless plating solution according to claim 22, wherein said solution comprises: (i) said reducing agent at a concentration of from about 0.01 g/L and 200 g/L; (ii) said transition metal and/or post transition metal ions in the form of a salt, wherein the concentration of said salt is from about 2-10 g/l; and/or (iii) said nanotubes at a concentration of from about 1 to 100 g/L, more suitably from about 1 to 10 g/L.

25. An electroless plating apparatus comprising an electroless plating solution according to claim 22 disposed within a temperature controlled bath and a cathode material, wherein said cathode material is immersed in said electroless plating solution and wherein a substrate to be plated may be placed at or in contact with said cathode.

26. A process for the preparation of a coated metallic substrate according to a claim 1, wherein: (A) said process is an electroplating process, said process comprising the steps of: i) providing the electroplating solution according to claim 16 a vessel to contain said electroplating solution, an anode immersed in the electroplating solution a metallic substrate immersed in the plating solution and which is in electric contact with a cathode and a power source in electric contact with the anode and the cathode; ii) applying an electric current from the power source for a time such that the surface of the substrate is coated with a metallic layer, and iii) removing the coated metallic substrate from the electroplating solution; or (B) said process in an electroless plating process, said process comprising the steps of: i) providing the electroless plating solution according claim 22 in a vessel to contain said plating solution; ii) immersing a metallic substrate in said plating solution for a time such that the surface of the metallic substrate is coated with a metallic layer, and iii) removing the coated metallic substrate according to the invention from the electroless plating solution.

27. The process according to claim 26, wherein said metallic substrate is selected from the group consisting of iron, steel, mild steel, aluminium and aluminium alloys comprising copper, magnesium, manganese, silicon, tin, nickel, silver, gold and zinc.

28. The process for preparing the electroplating solution according to claim 16 or the electroless plating solution according to claim 22, wherein said process further comprises the preliminary steps of: la) loading empty nanotubes with a corrosion inhibitor to form loaded nanotubes; lia) sealing said loaded nanotubes with a metal to form sealed nanotubes; and liia) dispersing said sealed nanotubes in said electroplating or electroless plating solution.

29. The process according to claim 26, wherein said process is an electroplating process and wherein said anode comprises a metal selected from the group consisting of copper, zinc, silver, tin, gold, nickel, or an alloy comprising one or more thereof.

30. The metallic substrate according to claim 6, wherein: (i) said anti-corrosion agent comprises BTA and said nanotubes are sealed with zinc ions; (ii) said anti-corrosion agent comprises BTA and said nanotubes are sealed with calcium ions; (iii) said anti-corrosion agent comprises a phosphate salt, and said nanotubes are sealed with zinc ions; (iv) said anti-corrosion agent comprises a phosphate salt, and said nanotubes are sealed with calcium ions; (v) said anti-corrosion agent comprises a cyanate compound, and said nanotubes are sealed with zinc ions; or (vi) said anti-corrosion agent comprises a cyanate compound, and said nanotubes are sealed with calcium ions.

31. The metallic substrate according to claim 8, wherein: (i) said anti-corrosion agent comprises BTA and said nanotubes are sealed with zinc ions; (ii) said anti-corrosion agent comprises BTA and said nanotubes are sealed with calcium ions; (iii) said anti-corrosion agent comprises a phosphate salt, and said nanotubes are sealed with zinc ions; (iv) said anti-corrosion agent comprises a phosphate salt, and said nanotubes are sealed with calcium ions; (v) said anti-corrosion agent comprises a cyanate compound, and said nanotubes are sealed with zinc ions; or (vi) said anti-corrosion agent comprises a cyanate compound, and said nanotubes are sealed with calcium ions.

Description

FIGURES

[0167] FIG. 1: Schematic representation of the barrel electroplating process.

[0168] FIG. 2: shows an exemplary nanotube loading procedure and cap formation:

[0169] (a) nanotube in BTA containing solution; (b) vacuum removes air from inner lumen of nanotube; (c) application of pressure forces solution into the inner lumen of the nanotube; (d) nanotubes are washed and centrifuged; (e) nanotubes are dried; (f) dried loaded nanotubes are placed in solution containing transition metal ions; (g) BTA at the exposed ends of the nanotube lumen forms complex with transition mental ions from the solution; (h) the complex forms caps at the ends of the nanotubes; (i) the nanotubes are dried and ball milled.

[0170] FIG. 3: plot showing zeta potential as a function of pH (3-10) in water for i) raw halloysites, ii) BTA loaded halloysites and iii) BTA loaded halloysites with caps.

[0171] FIG. 4: plot showing average particle size distribution as a function of time for raw halloysites under high shear in electroplating solution

[0172] FIG. 5: Images of electroplated mild steel specimens: (A) Images of the copper electroplated specimens with the following coating additive: 1) No additive control, 2) BTA (10 g/L), 3) raw halloysites (10 g/L), 4) BTA-loaded halloysites (10 g/L), 5) BTA-loaded halloysites (10 g/L) with Cu tube caps, 6) BTA-loaded halloysites (10 g/L) with Zn tube caps, and 7) BTA-loaded halloysites (50 g/L) with Zn tube caps; (B) Images of zinc electroplated specimens with the following coating additive: 8) No additive control, 9) Raw halloysite (10 g/L) control, 10) BTA-loaded halloysites (10 g/L), 11) BTA-loaded halloysites (10 g/L) with Zn tube cap, and 12); BTA-loaded halloysites (50 g/L) with Zn tube cap; (C) Images of nickel electroplated specimens with the following coating additive: 13) No additive control, 14) Raw halloysite (10 g/L) control, 15) SHMP loaded halloysite (10 g/L), 16) SHMP-loaded halloysites (10 g/L) with Ca tube caps, and 17) SHMP-loaded halloysites (50 g/L) with Ca tube caps.

[0173] FIG. 6: OCP measurements recorded over 15 minutes for i) Zn capped BTA-loaded halloysite, ii) control and iii) Raw halloysite electroplate additions

[0174] FIG. 7: Potentiodynamic polarisation of −0.5V from the OCP for i) Zn capped BTA-loaded halloysite, ii) control and iii) Raw halloysite electroplate additions

[0175] FIG. 8: —Potentiodynamic polarisation of +0.8V from the OCP for i) Zn capped BTA-loaded halloysite, ii) control and iii) Raw halloysite electroplate additions

[0176] FIG. 9: Images of copper electroplated mild steel specimens with the following coating additive: C1) No additive control, C2) BTA-loaded halloysites (0.02 wt %) with Zn tube caps; 18) BTA-loaded halloysites (1 wt %) with Ca tube caps; and 19) phosphate-loaded halloysites (1 wt %) with Zn tube caps.

[0177] FIG. 10: Images of silver electroplated mild steel specimens with the following coating additive: S1) No additive control, S2) cyanate-loaded halloysites (0.2 wt %) with Ca tube caps; and 20) cyanate-loaded halloysites (0.2 wt %) with Zn tube caps.

[0178] FIG. 11: Images of copper electroplated mild steel specimens with the following coating additive following completion of 12 month tarnish test: 1) No additive control, 6) BTA-loaded halloysites (10 g/L) with Zn tube caps.

[0179] FIG. 12: Images of zinc electroplated mild steel specimens with the following coating additive following completion of 80 day natural weathering test: 8) No additive control, 11) BTA-loaded halloysites (10 g/L) with Zn tube caps.

[0180] FIG. 13: Images of nickel electroplated mild steel specimens with the following coating additive following completion of 250 day natural weathering test: 13) No additive control, 14) unloaded (raw) halloysites (10 g/L), 16) phosphate-loaded halloysites (10 g/L) with Ca tube caps.

[0181] FIG. 14: Images of silver electroplated mild steel specimens with the following coating additive following completion of 168 hour humidity and splash tarnish test: S1) No additive control, S2) cyanate-loaded halloysites (0.2 wt %) with Ca tube caps.

EXAMPLES

[0182] Materials and Methods

Example 1—Preparation of Electroplated Samples

[0183] Materials

[0184] The halloysite nanotube material, BTA, SHMP, salts (CuSO.sub.4.5H.sub.2O, ZnSO.sub.4.7H.sub.2O, NiSO.sub.4.6H.sub.2O, NaCl) were purchased from Sigma Aldrich Ltd. The loaded nanotubes were manufactured at Swansea University. The copper, zinc and nickel electroplating solutions were made up at The Royal Mint electroplating foundry, comprising 1 mol/L CuSO.sub.4, ZnSO.sub.4 or NiSO.sub.4 and 60 g/l H.sub.2SO.sub.4. Pure Cu, Zn or Ni bulk anode and mild steel cathodes (100×50×0.5 mm) were used as plating electrodes.

[0185] Methods

[0186] Surface charge measurements for loaded halloysite derivatives were recorded using a Malvern Zetasizer Nano™. The average effective diameter of raw halloysites following exposure to high shear mixing in the electroplating solution was taken using a Malvern Mastersizer 3000™, which provides particle size measurements on a volume average basis using a laser diffraction method.

[0187] Nanotube Packing

[0188] The halloysite loading method has been slightly adapted from that described by Abdullayev et al (18) and is depicted in FIG. 2: 2 litres of acetone was saturated with BTA at 20° C. (FIG. 2a). The solution was poured into in a vacuum chamber that was attached to a vacuum pump. 50 g/L of raw halloysite dry power was added to the chamber and constantly agitated using a magnetic stirrer. The chamber was then evacuated, and fizzing was observed immediately as air is forced from the nanotubes (FIG. 2b). The solution was left under vacuum for approximately 3 hours before being cycled back to atmospheric pressure. BTA containing solution is forced inside the nanotube cavity as pressure is reintroduced (FIG. 2c). This process was repeated 3 times to maximise halloysite loading. Loaded halloysite was separated from residual solution and centrifuged (FIG. 2d), and the remaining paste is washed with water and left to air dry (FIG. 2e). An analogous process was used to prepare SHMP loaded halloysites. The formation of ‘caps’ at the ends of the nanotubes occurs through the reaction of BTA inside the halloysite and transition metal ion in solution (Cu.sup.2+ or Zn.sup.2+) (FIGS. 2f, 2g, 2h). The metal-BTA complexes at the nanotube ends, effectively sealing BTA inside the halloysite (18). This ensures that BTA remains inside the carrier during electroplating and is released only when corrosive conditions cause metal-BTA bonds to break. Again, an analogous process was used to cap SHMP loaded halloysites. Specifically, the ‘caps’ were formed at the end of the nanotubes through the reaction of SHMP inside the halloysite and calcium ions in solution.

[0189] The anode and cathode materials were submerged in 250 mL of plating solution and electrically connected to the power supply. 1 g/L to 50 g/L of additive was included in the solution under high shear for 15 minutes before the power supply was turned on. A current density of 1.71 A/m.sup.2 was applied for 24 minutes in each case achieving ca. 25 μm plate thickness in each case. Table 1 outlines the specimens produced.

TABLE-US-00001 TABLE 1 Electroplate Additive Nanotube Specimen Substrate (25 μm) (1% wt./vol) cap 1 Mild steel Cu None N/a 2 Mild steel Cu BTA N/a 3 Mild steel Cu Raw halloysite N/a 4 Mild steel Cu BTA loaded None halloysite 5 Mild steel Cu BTA loaded Cu halloysite 6 Mild steel Cu BTA loaded Zn halloysite 7 Mild steel Cu BTA loaded Zn halloysite* 8 Mild steel Zn None N/a 9 Mild steel Zn Raw halloysite N/a 10 Mild steel Zn BTA loaded None halloysite 11 Mild steel Zn BTA loaded Zn halloysite 12 Mild steel Zn BTA loaded Zn halloysite* 13 Mild steel Ni None N/a 14 Mild steel Ni Raw halloysite N/a 15 Mild steel Ni phosphate loaded None halloysite 16 Mild steel Ni Phosphate loaded Ca halloysite 17 Mild steel Ni Phosphate loaded Ca halloysite* *5% wt./vol

[0190] Photography

[0191] Following electroplating, all samples were imaged using a Canon 600D digital SLR camera.

[0192] Results

[0193] Raw halloysites in water exhibit negative 4 potentials: −13.07, −46.7 and −50.87 mV, at pH 3.7 and 10 respectively—i) in FIG. 3. Loading the halloysites with BTA causes a positive ζ shift over the same pH range as shown in ii) of FIG. 3. The cap formation at the tube ends does not appear to influence the ζ potential as shown in FIG. 3, where ii) and iii) exhibit very similar trends. The electroplating solution used has a pH of 4.5; it is expected that raw halloysites, BTA-loaded halloysites and BTA-loaded halloysites with metal caps, will exhibit ζ potential values of ca. −30, −10 and −10 mV respectively during plating. The surface charge is therefore on the incorrect side of the isoelectric point (a positive charge is desirable for electrical attraction to a negatively charged cathode). However, ζ potentials at pH4.5 are close to the isoelectric point. This, combined with the physical diffusion associated with the solution adjacent to the cathode (with the power supply on) proved sufficient in plating out Cu.sup.2+ and additive in situ.

[0194] The change in average halloysite particle size distribution is shown per unit time under high shear in FIG. 4. This indicates the extent of initial aggregation, and how this is reduced over time under high shear mixing. Individual halloysite nanotubes have diameter ranging from 10-150 nm and length ranging from 1-15 μm. FIG. 4 shows a sharp decrease in agglomeration in the first 5 minutes under mixing—90% of the sample has a size of 30.4 μm or less at 4.2 minutes. Halloysites additions are therefore exposed to high shear mixing no less than 15 minutes prior to electroplating, to assist in producing a fine, well-dispersed additive throughout the plated layer.

[0195] The images in FIG. 5 show the finished specimens following electroplating. Pure Cu plate with no additive produces a bright, uniform and well-adhered coating. Introducing 1 wt % (10 g/L) of BTA to the electroplating solution results in a dark and extremely blistered coating (a poor anti-corrosion electroplating additive in this case). Raw halloysite powder additions led to a uniform and bright Cu plate, much like that of the control specimen. The poor plate associated with uncapped and Cu-capped BTA-loaded halloysite additions is likely a consequence of BTA leaching out of the nanotubes in the electroplating solution and interfering with the Cu deposition causing blistering and discolouration. Using Zn as nanotube capping agent appears to have sealed the BTA inside the halloysite successfully during transit. The coating is bright, uniform and well-adhered. This specimen appears brighter than the control as a result of the additive, included at 10 g/L or 50 g/L. Raw and Zn-capped BTA-loaded halloysite electroplating additives have successfully been included in a Cu plate for further corrosion testing. It appears that BTA is extremely detrimental to the electroplating of Cu on mild steel under these experimental conditions, as it is seriously detrimental to Cu lamination and plate brightness. Raw halloysites do not interfere with the Cu plate quality. Sealed with Zn caps, halloysites can deliver BTA into a Cu plate without negatively influencing the quality of the coating as shown by images 6 and 7 in FIG. 5.

[0196] Images 8 to 12 in FIG. 5 also demonstrate that BTA is detrimental to the electroplating of zinc on mild steel, but BTA loaded halloysites sealed with Zn caps can deliver BTA into a zinc plate without negatively influencing the quality of the coating.

[0197] Images 13 to 17 in FIG. 5 demonstrate not only that phosphate is detrimental to the electroplating of nickel on mild steel, but also that a bright, uniform and well-adhered nickel coating can be achieved using corrosion inhibitor (SHMP) loaded halloysites sealed with calcium.

Example 2—Corrosion Testing

[0198] Corrosion Testing Method

[0199] The specimens were cut into ca. 1 cm.sup.2 squares and polished by lightly abrading the plate surface with an alumina suspension. Samples were subsequently washed with DI water and dried. A 0.95 cm.sup.2 area of the plate was exposed by screwing the sample into a nylon working electrode (WE) casing. The WE was immersed in a 1% w/v NaCl(aq) electrolyte (pH7) adjacent to a saturated calomel electrode (SCE) reference electrode (RE). Time dependent open-circuit potential (OCP) measurements were recorded using a Solartron SI 1280B Electrochemical Workstation. Potentiodynamic data was obtained by polarising the WE +0.8V and −0.5V about the free corrosion potential to measure the anodic and cathodic current densities respectively. A platinum counter electrode (CE) was included in the setup (distanced from the WE and RE) in order to do this. Potentiodynamic data was obtained immediately after OCP experiments in the same solution to allow the sample surface to equilibrate.

[0200] Results

[0201] The variation in OCP over time in the presence of an inhibitor is often a good indication of whether anodic or cathodic processes are being affected. OCP measurements are recorded over 15 minutes in a corrosive electrolyte of 1% w/v NaCl(aq) (pH7) and displayed in FIG. 6. Cu plated specimens containing no additive and raw halloysites are shown to exhibit very similar OCP signals over time, where the initial OCP gradually decreases to equilibrium from ca. −200 to −220 mV vs SCE. Cu plate with raw halloysite additives exhibits neither anodic nor cathodic inhibition, referring to the control specimen in FIG. 6. The Zn-capped BTA-loaded halloysite Cu plate gradually decreases from ca. −200 to −370 mV vs SCE. The negative shift of 170 mV vs SCE indicates that the cathodic process is being retarded by the adsorption of BTA onto active cathode sites, delaying the oxygen reduction reaction. When the WE is polarised under the same experimental condition the variation in OCP is better defined as shown in FIG. 7. This further supports that BTA has successfully released from the halloysite nanotubes and is acting preferentially at the cathodic sites on the Cu plate surface. FIG. 8 demonstrates the anodic Tafel trend, for which a depression is observed for the Zn-capped BTA loaded halloysite Cu plate specimen. This indicates passivation of the metal surface by the action of BTA.

[0202] Halloysite nanotubes have been successfully electroplated throughout a 25 μm Cu plated layer. The surface charge character of loaded and unloaded halloysite has been measured over a pH ranging 3-10. A decrease in ζ potential is shown as solution basicity is raised, with an isoelectric condition identified at ca. pH4 for unloaded and loaded/capped halloysites. The effects of solution diffusion adjacent to the cathode-solution interface were sufficient enough to overcome the weak electrical repulsion (in a pH4.5 electroplating solution) between the pigment and mild steel cathode, such that additive was included in the Cu plated coating. The average particle size distribution of raw halloysite showed that 90% of the sample exhibited a size of 30.4 μm in less than 4.2 minutes in the electroplating solution under high shear mixing (this condition was therefore applied for 15 minutes before electroplating commenced) to limit aggregation and agglomeration during plating, ensuring a finer distribution of additive throughout the Cu plate. The loading procedure closely resembles that carried out by Abdullayev et al (18), and by successfully sealing BTA inside the halloysite during electroplating (using a Zn capping agent), active corrosion inhibitor (BTA) has been included throughout the Cu plate without disrupting the plate adherence or colour. It was found that BTA, either as a raw additive, or loaded into halloysite with subsequent leaching into the electroplating solution, caused severe Cu plate blistering and discolouration. Cu plate with Zn capped BTA-loaded halloysite additions show OCP potential measurements over 15 minutes that are significantly lower than that of a control. This indicates that the BTA is releasing from encapsulation in a corrosive environment and acting preferentially on cathodic sites at the Cu plate surface. A depression in the anodic branch of the Tafel relationship is also observed, indicating the formation of a passivation film, as the additive loaded sample is positively polarised. This study has shown that environmentally friendly and cost-effective, anti-corrosion pigments can be added to a Cu-plate electroplating setup to further, and successfully respond to a corrosive environment.

Example 3—Preparation of Electroless Plated Samples

[0203] To demonstrate that acceptable (bright, uniform and well-adhered) metallic coatings can also be achieved via electroless plating in the presence of sealed, corrosion inhibitor loaded halloysites, a commercially available electroless nickel plating kit (https://www.caswelleurope.co.uk/electroless-nickel-plating-kit/) was modified by the addition of calcium capped, SHMP loaded halloysites (5 g/L) to the electroless plating solution under high shear for 15 minutes before a mild steel substrate was submerged for plating. During plating, the pH of the plating solution was maintained between 6.8 and 6.9, and heating was applied to maintain a temperature of about 80° C. Similar to the results observed via electroplating, bright, uniform and well adhered coatings of ca. 25 μm plate thickness can be achieved.

Example 4—Preparation of Additional Copper Electroplated Samples

[0204] To further demonstrate the utility of various sealed, corrosion inhibitor loaded halloysites, additional Copper electroplated samples were prepared using sealed nanotube additives formed using different corrosion inhibitor and metal cap combinations and/or different nanotube additive levels.

[0205] Materials

[0206] The halloysite nanotube material, BTA, SHMP, salts (CuSO.sub.4.5H.sub.2O, NaCl) were purchased from Sigma Aldrich Ltd. The loaded nanotubes were manufactured at Swansea University. The copper electroplating solutions were made up at Swansea University, comprising 1 mol/L CuSO.sub.4 and 60 g/l H.sub.2SO.sub.4. Pure Cu bulk anode and mild steel cathodes (100×50×0.5 mm) were used as plating electrodes.

[0207] Methods

[0208] The halloysite loading method was adapted as necessary from that described in Example 1 above and depicted in FIG. 2 to prepare BTA or SHMP loaded halloysites. Nanotube end caps were then formed through a metal complexation reaction between BTA and Zn.sup.2+ ions, BTA and Ca.sup.2+ ions or SHMP and Zn.sup.2+ ions.

[0209] The anode and cathode materials were submerged in 500 mL of copper plating solution and electrically connected to the power supply. 0 to 100 g/L (0 to 10 wt %) of additive was included in the solution under high shear for 15 minutes before the power supply was turned on. A current density of 1.71 A/m.sup.2 was applied for 24 minutes in each case achieving ca. 20 μm plate thickness. Table 2 outlines the copper plated specimens produced.

TABLE-US-00002 TABLE 2 Electroplate Nanotube Specimen Substrate (20 μm) Additive cap C1 Mild steel Cu None N/a C2 Mild steel Cu BTA loaded Zn halloysite (0.2 g/L) C3 Mild steel Cu BTA loaded Zn halloysite (0.4 g/L) C4 Mild steel Cu BTA loaded Zn halloysite (0.6 g/L) C5 Mild steel Cu BTA loaded Zn halloysite (0.8 g/L) C6 Mild steel Cu BTA loaded Zn halloysite (1 g/L) C7 Mild steel Cu BTA loaded Zn halloysite (10 g/L) C8 Mild steel Cu BTA loaded Zn halloysite (20 g/L) C9 Mild steel Cu BTA loaded Zn halloysite (50 g/L)  C10 Mild steel Cu BTA loaded Zn halloysite (100 g/L) 18 Mild steel Cu BTA loaded Ca halloysite (10 g/L) 19 Mild steel Cu Phosphate loaded Zn halloysite (10 g/L)

[0210] Results

[0211] In all cases, a bright, uniform and well-adhered coating was produced. Images for plated specimens C1, C2, 18 and 19 are provided in FIG. 9, demonstrating that BTA or phosphate loaded halloysites can be sealed with zinc or Calcium ion derived caps to deliver such corrosion inhibitors into a cupper plate without negatively influencing the quality of the coating.

Example 5—Preparation of Silver Electroplated Samples

[0212] Silver electroplated mild steel samples were also prepared using cyanate corrosion inhibitor-containing halloysites sealed via complexation with calcium or zinc ions.

[0213] Materials

[0214] The halloysite nanotube material and NaOCN were purchased from Sigma Aldrich Ltd. The loaded nanotubes were manufactured at Swansea University. A silver electroplating solution was purchased from Gateros Plating Ltd. and contains C.sub.2, 4-Imidazolidinedione, 5,5-dimethyl-, Ag.sup.+, salt (2:1). Pure Ag bulk anode and mild steel cathodes (100×50×0.5 mm) were used as plating electrodes.

[0215] Methods

[0216] The halloysite loading method was adapted as necessary from that described in Example 1 above and depicted in FIG. 2 to prepare cyanate loaded halloysites. Nanotube end caps were then formed through a metal complexation reaction between cyanate and Zn.sup.2+ or Ca.sup.2+ ions.

[0217] The anode and cathode materials were submerged in 500 mL of silver plating solution at 50-55 Deg C. and electrically connected to the power supply. 0 to 100 g/L (0 to 10 wt %) of additive was included in the solution under high shear for 15 minutes before the power supply was turned on. A current density of 0.5 A/m.sup.2 was applied for 40 minutes in each case achieving 15-20 μm plate thickness. Table 3 outlines the silver plated specimens produced.

TABLE-US-00003 TABLE 3 Electroplate Nanotube Specimen Substrate (20 μm) Additive cap S1 Mild steel Ag None N/a S2 Mild steel Ag Cyanate loaded Ca halloysite (2 g/L) S3 Mild steel Ag Cyanate loaded Ca halloysite (4 g/L) S4 Mild steel Ag Cyanate loaded Ca halloysite (6 g/L) S5 Mild steel Ag Cyanate loaded Ca halloysite (8 g/L) S6 Mild steel Ag Cyanate loaded Ca halloysite (10 g/L) 20 Mild steel Ag Cyanate loaded Zn halloysite (2 g/L)

[0218] Results

[0219] In all cases, a bright, uniform and well-adhered coating was produced. Images for plated specimens S1, S2 and 20 are provided in FIG. 10, demonstrating that cyanate corrosion inhibitors can be delivered into a silver plate without negatively influencing the quality of the coating.

Example 6—Further Corrosion Testing

[0220] Corrosion Testing Methods

[0221] Two copper electroplated mild steel specimens, corresponding to specimen 1 (additive free) and specimen 6 (BTA loaded halloysites (10 g/L) with Zn cap) were subjected to a 12 month tarnish test which involved exposing the specimens to indoor environmental conditions (50% humid air at 25° C.).

[0222] Two zinc electroplated mild steel specimens, corresponding to specimen 8 (additive free) and specimen 11 (BTA loaded halloysites (10 g/L) with Zn cap) were subjected to an 80 day natural weathering test which involved exposing the specimens to outdoor conditions (in Cheshire, UK) with a weekly spray of 3.5% NaCl solution to accelerate corrosion.

[0223] Three nickel electroplated mild steel specimens, corresponding to specimen 13 (additive free), specimen 14 (10 g/L unloaded halloysite) and specimen 16 (phosphate loaded halloysites (10 g/L) with Ca cap) were subjected to a 250 day natural weathering test which involved exposing the specimens to outdoor conditions (in Swansea UK) with a weekly spray of 3.5% NaCl solution to accelerate corrosion.

[0224] Two silver electroplated mild steel specimens, corresponding to specimen S1 (additive free) and specimen S2 (cyanate loaded halloysites (2 g/L) with Ca cap) were subjected to a 168 hour humidity and splash tarnish test which involved enclosing the specimens in a holding space with relative humidity of 80-90% and spraying 3.5% NaCl solution over the specimens daily.

[0225] Results

[0226] As shown in FIG. 11, significant tarnishing was observed on additive free specimen 1 upon completion of the 12 month tarnish test, whereas specimen 6 retained a bright, uniform and well-adhered coating. This indicates that the BTA was released from encapsulation in an aggressive, corrosive environment over time, thus protecting the copper plate from tarnish/corrosion. As the plating additive is present throughout the entire plating layer, corrosion protection can be maintained in abrasive and high wear service environments.

[0227] Similarly, as shown in FIG. 12, corrosion of the underlying steel, following breakdown of the zinc coating, was observed for additive free specimen 8 upon completion of the 80 day natural weathering test, whereas the integrity of the zinc coating was retained in specimen 11. This indicates that the BTA was released from encapsulation in an aggressive, corrosive environment over time, thus protecting the zinc plate from corrosion.

[0228] Further, as shown in FIG. 13, significant corrosion of the nickel plate was observed upon completion of the 250 day natural weathering test for both additive free specimen 13 and the empty halloysite containing specimen 14. In contrast, specimen 16 retained a bright, uniform and well-adhered coating. This indicates that the phosphate was released from encapsulation in an aggressive, corrosive environment over time, thus protecting the nickel plate from corrosion.

[0229] Further still, as shown in FIG. 14, significant tarnishing of the silver plate was observed on additive free specimen S1 upon completion of the 168 hour humidity and splash tarnish test, whereas specimen S2 retained a bright, uniform and well-adhered coating. This indicates that the cyanate corrosion inhibitor was released from encapsulation in an aggressive, corrosive environment over time, thus protecting the silver plate from tarnish/corrosion.

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