CORROSION PROTECTION FOR METALLIC SUBSTRATES COMPRISING ONE OR MORE 2D MATERIAL PLATELETS

Abstract

A composition comprising a carrier medium, a first corrosion inhibitor, and a second corrosion inhibitor having a barrier mechanism. The first corrosion inhibitor comprises at least one of an ion exchanged pigment, a silica, a calcium exchanged silica, an oxyaminophosphate salt of magnesium, and/or a mixture of an organic amine, a phosphoric acid and/or an inorganic phosphate and a metal oxide and/or a metal hydroxide, and the second corrosion inhibitor comprises one or more 2D material platelets in which the 2D material platelets comprise: nanoplates of one or more 2D materials and or nanoplates of one or more layered 2D materials and or graphite flakes in which the graphite flakes have one nanoscale dimension and 35 or less layers of atoms.

Claims

1. A composition comprising a carrier medium, a first corrosion inhibitor having a passivation mechanism, and a second corrosion inhibitor having a barrier mechanism in which the first corrosion inhibitor comprises at least one of an ion exchanged pigment, a silica, a calcium exchanged silica, an oxyaminophosphate salt of magnesium, and/or a mixture of an organic amine, a phosphoric acid and/or an inorganic phosphate and a metal oxide and/or a metal hydroxide, and the second corrosion inhibitor comprises one or more 2D material platelets in which the 2D material platelets comprise; nanoplates of one or more 2D materials and or nanoplates of one or more layered 2D materials and or graphite flakes in which the graphite flakes have one nanoscale dimension and 35 or less layers of atoms, wherein the second corrosion inhibitor has a D50 particle size of less than 45 m, less than 30 m, or less than 15 m.

2. A composition according to claim 1 in which the 2D materials are one or more of graphene (C), hexagonal boron nitride (hBN), molybdenum disulphide (MoS2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), Graphyne (C), borophene (B), phosphorene (P), or a 2D in-plane heterostructure of two or more of the aforesaid materials.

3. A composition according to claim 1 in which the layered 2D materials may be layers of graphene (C), hexagonal boron nitride (hBN), molybdenum disulphide (MoS2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), Graphyne (C), borophene (B), phosphorene (P), or a 2D vertical heterostructure of two or more of the aforesaid materials.

4. A composition according to claim 1 in which the 2D material platelets have an electrical conductivity of around or less than 2.010.sup.5/m at 20 C.

5. A composition according to claim 1 in which the first corrosion inhibitor comprises one or more of zinc chromate, zinc molybdate, zinc tungstate, zinc vanadate, zinc phosphite, zinc polyphosphate, zinc borate, zinc metaborate, magnesium chromate, magnesium molybdate, magnesium tungstate, magnesium vanadate, magnesium phosphate, magnesium phosphite, magnesium polyphosphate, magnesium borate, magnesium metaborate, calcium chromate, calcium molybdate, calcium tungstate, calcium vanadate, calcium phosphate, calcium phosphite, calcium polyphosphate, calcium borate, calcium metaborate, strontium chromate, strontium molybdate, strontium tungstate, strontium vanadate, strontium phosphate, strontium phosphite, strontium polyphosphate, borate, strontium metaborate, barium chromate, barium molybdate, barium tungstate, barium vanadate, barium phosphate, barium phosphite, barium polyphosphate, barium borate, barium metaborate, aluminium chromate, aluminium molybdate, aluminium tungstate, aluminium vanadate, aluminium phosphite, aluminium borate, and/or aluminium metaborate.

6. A composition according to claim 1 in which the second corrosion inhibitor is present in the range of 0.05 wt % to 1.0 wt %, 0.05 wt % to 0.8 wt %, 0.05 wt % to 0.6 wt %, or 0.1 wt % to 0.5 wt %, 0.1 wt % or 0.5 wt %.

7. (canceled)

8. A composition according to claim 1 in which the first corrosion inhibitor is present in the range of 1 wt % to 15 wt %, 2 wt % to 10 wt %, 4 wt % to 8 wt %, 4 wt % or 8 wt %.

9. A composition according to claim 1 in which the first corrosion inhibitor is comprised of a calcium exchanged silica, and the second corrosion inhibitor is or is comprised of graphite flakes having one nanoscale dimension and 25 to 35 layers of carbon atoms.

10. A composition according to claim 1 in which the carrier medium is selected from crosslinkable resins, non-crosslinkable resins, thermosetting acrylics, aminoplasts, urethanes, carbamates, polyesters, alkyds epoxies, silicones, polyureas, silicates, polydimethyl siloxanes, vinyl esters, unsaturated polyesters and mixtures and combinations thereof.

11. A coating comprising a composition according to claim 1.

12. A method of manufacture of a composition according to claim 1 in which the manufacture comprises a grind stage and a let down stage, and the 2D material platelets are added at the grind stage, at the let down stage, or as a stir in additive after the let down stage.

13. A method of manufacture of a composition according to claim 12 in which the 2D material platelets are added at the let down stage

14. A method of manufacture of a composition according to claim 12 in which the grind stage comprises mixing the carrier medium and the first corrosion inhibitor.

15. A coating according to claim 11, wherein the coating has a dry film thickness of from 60 m to 75 m.

16. A coating according to claim 11, wherein the coating comprises multiple layers of 2D material platelets providing a labyrinthine path for the penetration of water, any dissolved oxygen it carries, and any aggressive ions such as Cl.sup. or H.sup.+.

Description

EXAMPLE

[0054] A composition according to the present invention is manufactured with the constituents shown in Table 2.

[0055] Constituents 1 to 5 are charged into a high speed overhead mixer and mixed at 2000 rpm for 10 minutes. The resultant gel is checked to see if it is homogenous and free of bits. If not, mixing is continued until the gel is homogenous and free of bits.

[0056] Constituents 6 to 8 are added to the mixer and mixed at 2000 rpm for 15 minutes. The mixture is checked to see if the grind (maximum particle size) is less than 25 m. This is known as the grind stage of the manufacture.

[0057] Constituent 9 is pre-dispersed into Constituent 10. The subsequent dispersion is then added alongside constituent 11 and are mixed at 1000 rpm for 15 minutes. This is known as the let down stage of the manufacture. If constituent 9 were added after this mixing step, such an addition would be at the post addition stage of manufacture.

[0058] A polyamide curing agent 12 was added at 10 wt % (85% stoichiometry) and the composition was then ready for application to a substrate to form an anti-corrosive coating.

[0059] To perform comparative testing on compositions according to the present invention, such compositions were manufactured as above. Further compositions were manufactured using the same method but not including constituent 7 and/or 9 and including constituent 10.

[0060] For constituent 7, different compositions were made using one of four commercially available anti-corrosion pigments. They were zinc phosphate (Delaphos 2M commercially available from DelaphosPart of JPE Holdings Ltd), Pigmentan E with a loading range of 0.5-2.4 wt % available from Banner Chemicals, part of 2M Holdings Limited, Inhibisil 75 with a loading range of 1.0-10.0 wt % available from PPG Industries, Inc., and Shieldex AC5 with a loading range of 1.2-2.4 wt % available from W.R. Grace & Co. Pigmentan E has an active ingredient of an oxyaminophosphate salt of magnesium. Inhibisil 75 and Shieldex AC5 have as an active ingredient ion exchange pigments in the form of silica or calcium exchanged silica.

[0061] The graphene/graphitic platelets used were commercially available from Applied Graphene Plc as A-GNP10 or A-GNP35 grades (A-GNP35 which has 6 to 14 layers of carbon atoms and A-GNP10 which has 25 to 35 layers of carbon atoms, both available from Applied Graphene Materials Plc).

[0062] Samples for testing were prepared in the following fashion:

[0063] Substrates of cold rolled steel were prepared by grit blasting to SA2-1/2, using irregularly shaped chrome/nickel steel shot followed by degreasing with acetone. Each of composition numbers 1 to 18 were applied by spray application to a substrate using a gravity-fed gun with a 1.2 mm tip to give a coating thickness of DFT 60-75 m. The substrates were cured for 7 days.

[0064] A substrate coated with each composition was subject to cyclic salt spray testing (ASTM G85 annex 5) and assessed at intervals of 1, 2, 3 and 4 thousand hours. The results of the assessments are as shown in Tables 3, 4, 5, and 6.

[0065] A substrate coated with each composition was subject to assessment in connection with the mechanical performance of the coatings. Specifically, the coatings were assessed in connection with impact resistance (using the Elcometer Impact test), abrasion resistance (using a Taber abrader and 100 Cycles, 1 Kg Weight, CS-10 Discs), adhesion (using a PAT device), and flexibility (using a Conical mandrel). The results of that assessment are shown in Tables 7, 8, 9, and 10 the following test methods being used

[0066] Abrasion resistance: Taber abrasionASTM 5144

[0067] Flexibility: Conical MandrelISO6860:2006

[0068] Impact resistance:ISO6272

[0069] AdhesionISO4624

[0070] The assessment reveals that compositions according to the present invention provide better corrosion resistance than known coating compositions, are better for the environment than known compositions, and have longer service lives than known coating compositions.

[0071] In the formulation of the compositions 1 to 18, the graphene platelets can be incorporated into the composition at the grind stage, the let down stage, or after all the other constituents have been combined. It has been found that the time of incorporation of the graphene platelets has an effect on the anti-corrosive properties of coatings resultant from the composition. The best properties were achieved when the incorporation of the graphene platelets occurred at the let down stage of manufacture.

[0072] To test the theory that the graphene/graphitic platelets in the composition of the present invention have a barrier effect only, and without wishing to be bound by theory, AC Electrochemical Impedance Spectroscopy (AC EIS) and Corrosion Potential (E.sub.corr) measurements have been taken in connection with some of the samples for testing that were prepared as discussed above. AC EIS and E.sub.corr, measurements allow the quantitative determination of several properties related to corrosion resistance of a sample without the prolonged testing required of artificial weathering.

[0073] E.sub.corrElectrochemical corrosion potential (ECP) is the voltage difference between a metal immersed in a given environment and an appropriate standard reference electrode (SRE), or an electrode which has a stable and well-known electrode potential. Electrochemical corrosion potential is also known as rest potential, open circuit potential or freely corroding potential, and in equations it is represented by E.sub.corr. Higher values of E.sub.corr indicate lower corrosion rates, and lower values higher corrosion rates.

[0074] The barrier properties of organic coatings, for a coating where the carrier medium is an epoxy resin or other suitable organic composition, are such that they exhibit a high impedance across the coating thickness. Traditionally it is understood that as a coating ages the interconnecting network of pores within the coating become saturated with water and salts exposing the metal substrate to a corrosive environment while also lowering the electrical resistance of the coating. Aged organic coatings also possess other electric properties which cause the coating to behave as capacitors to electric current. When corrosion occurs at the metal surface a polarisation resistance can be related to the corrosion rate while the electrical double layer behaves as a capacitor. The measurements made below were used to explain the performance of coatings of various of the samples prepared as described above.

[0075] In order to demonstrate the mechanism of the graphene/graphitic platelets in a coating of a composition of the present invention, and the relationship with active inhibitors in providing corrosion prevention, the samples were evaluated with and without a scribe through the coating. The scribe provides direct access of the salt solution to the metal surface and demonstrates through the electrochemical reaction the nature of any resistance to corrosion on damage to the coating. In evaluating coatings in this manner it is possible to demonstrate the mechanisms of action operating in intact films.

[0076] All electrochemical measurements were recorded using a Gamry 1000E potentionstat in conjunction with a Gamry ECM8 multiplexer to permit the concurrent testing of up to 8 samples per experiment. Each individual channel was connected to a Gamry PCT-1 paint test cell with an exposed paint surface of 14.6 cm.sup.2, specially designed for the electrochemical testing of coated samples. One panel for each Formulation and Control was scribed with a 25 mm scribe using a knife. Care was taken that the scribes were as consistent as possible throughout due to relatively small surface area of study. The panels for each Formulation and Control were tested in duplicate in both scribed and unscribed forms.

[0077] Within each paint test cell, a conventional three-electrode system was formed, the bare steel, epoxy coated steel, and scribed epoxy coated steel panels were the working electrode, a graphite rod served as a counter electrode and a saturated calomel electrode (SCE) served as the reference electrode. All tests were run using a 3.5 wt % NaCl electrolyte. All corrosion potential (E.sub.corr) measurements were recorded against the SCE reference electrode. EIS analysis was carried out using reference to a modified Randle cell incorporating pore resistance.

[0078] The AC EIS data shown in Tables 11 to 23 was obtained by fitting of equivalent circuits to EIS data.

[0079] Pore resistance or R.sub.pore is the electrical resistance to current travelling through the pore network in the coating. As the pore network fills with electrolyte R.sub.pore changes. Higher values indicate lower rates of corrosion, and lower values a higher rate of corrosion.

[0080] C.sub.DL is the capacitance produced by the electric double layer at the water/substrate interface. A measurable C.sub.DL indicates that water is present at the substrate. Higher values indicate a greater wetted area of substrate.

[0081] C.sub.c is the capacitance produced by the dielectric properties of the coating. The C.sub.c is related to the dielectric strength of the coating and water absorption by the coating with higher values indicating higher water content

[0082] Tabular representations of the data measured are as shown in Tables 11 to 23. Each Table shows in the title the composition used to coat the sample being tested.

[0083] Commentary on Tables 11 to 23:

[0084] Corrosion Potential:

[0085] Tables 11 to 15 demonstrate the behaviour of E.sub.corr with time over the period of test. It can be seen in the Composition 1 that without scribing there is a steady reduction of the corrosion potential with time indicating slow moisture diffusion and onset of corrosion. With the scribe there is no difference in the E.sub.corr determined from that of uncoated steel which was to be expected.

[0086] Table 12 demonstrates the impact of inclusion of graphitic platelets (A-GNP10) in Composition 2 on unscribed panels. The graphene containing panel holds a higher corrosion potential and therefore resistance to corrosion compared to Composition 1. Table 13 however shows that when scribed there is no difference between the graphitic platelets containing Composition 2 and the Composition 1 or indeed uncoated steel suggesting that the behaviour of graphitic platelets is solely based on barrier performance and has no additional electrochemical activity on steel surfaces.

[0087] Tables 14 and 15 show the behaviour of Compositions 4 and 12. The unscribed Composition 12 indicates a higher E.sub.corr than Composition 4 suggesting higher corrosion protection. The results for scribed Composition 12 indicates that the activity of both Compositions 4 and 12 is close to that of uncoated steel with Composition 12 being slightly worse. This is not reflected in the results of the artificial weathering (salt spray tests) and is possibly a reflection of the short time period of the test and activity of the active component in that time frame.

[0088] Pore Resistance R.sub.pore and Coating Capacitance C.sub.c:

[0089] Tables 16 to 19 demonstrate the behaviour of the Pore resistance and Coating Capacitance. Comparison of the unscribed Compositions 1 and 2 are as expected. The graphitic platelets in Composition 2 enhance the pore resistance with a resulting lower coating capacitance indicating that there is less water at the coating/metal interface. Scribing of the sample panels results in there being no difference in performance.

[0090] Comparison of unscribed Compositions 4 and 12 demonstrates the greater performance of Composition 12. The scribed panels however do not reveal significant differences.

[0091] Double Layer Capacitance C.sub.DL:

[0092] Tables 20 to 23 show the double layer capacitance of the coatings and the water at the surface of the coating/metal interface. In both scribed and unscribed panels the compositions including graphene/graphitic platelets show enhanced barrier performance of the coating with less moisture being present at the coating/metal interface. This confirms the barrier properties of graphene. This is also reflected in the tests on Compositions 4 and 12 where the double layer capacitance of Composition 12 appears to be lower. This is reflected in the accelerated corrosion testing (salt spray) tests.

[0093] Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, and/or in the claims, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.