Pre-treatment coating composition and a method for producing the same
The invention relates to a method for producing a pre-treatment coating composition for a metal substrate, the method comprising the steps of: i. mining graphite ore from a graphite ore body; ii. subjecting the graphite ore to an electrolytic treatment to obtain an expanded graphitic material; iii. subjecting the expanded graphitic material to an exfoliation treatment to obtain single-layer graphene and few-layer graphene, and iv. functionalising the graphene with a coupling agent for coupling graphene to the metal substrate.
1. A method for producing a pre-treatment coating composition for a metal substrate, the method comprising the steps of:
i. subjecting a graphite ore to an electrolytic treatment to obtain an expanded graphitic material;
ii. subjecting the expanded graphitic material to an exfoliation treatment to obtain single-layer graphene and few-layer graphene, wherein the exfoliation treatment is a combined chemical and high-pressure treatment comprising intercalating the graphitic material with an intercalating agent and a surfactant in an intercalation step and subjecting the intercalated graphitic material to a high-pressure homogenisation treatment;
iii. separating graphene obtained from the exfoliation treatment from any residual graphitic material; and
iv. functionalising the graphene with a coupling agent for coupling graphene to the metal substrate;
wherein the electrolytic treatment is carried out in the presence of an electrolyte that comprises ammonium ions and sulphur-containing ions and the sulphur-containing ions are separated from the expanded graphitic material by mixing the expanded graphitic material with a liquid that is immiscible with water.
2. Method according to claim 1 , wherein the electrolyte has a pH between 6.0 and 8.5.
3. Method according to claim 1 , wherein the immiscible liquid comprises kerosene.
4. Method according to claim 1 , wherein the intercalation step comprises mixing the graphitic material with a solution containing 0.5-7 wt. % of the intercalation agent.
5. Method according to claim 4 , wherein the intercalation agent comprises a quaternary ammonium salt or an ammonium persulfate salt.
6. Method according to claim 4 , wherein the solution comprising the intercalation agent comprises up to 10 wt. % of the surfactant.
7. Method according to claim 1 , wherein the high pressure homogenisation treatment is between 200 bar and 5000 bar.
8. Method according to claim 1 , wherein the coupling agent comprises an organosiloxane.
9. Method according to claim 8 , wherein the coupling agent comprises an amino siloxane or an amino alkyl siloxane.
10. Method according to claim 8 , wherein the coupling agent comprises at least a first organosiloxane oligomer and a second organosiloxane oligomer.
11. Method according to claim 10 , wherein the ratio of the first organosiloxane oligomer to the second organosiloxane oligomer is 1.2:1 to 1.8:1.
12. Method according to claim 8 , wherein prior to the step of functionalising graphene, the organosiloxane is (i) hydrolysed at an acidic pH when the pre-treatment coating composition is for application onto mild steel or galvanised steel, or (ii) hydrolysed at a pH of 5.5 to 9.0 when the pre-treatment coating composition is for application onto aluminium, or (iii) hydrolysed at a pH of 7.0 to 12.0 when the pre-treatment coating composition is for application onto copper, or (iv) hydrolysed at a pH of 11.5 to 14.0 when the pre-treatment coating composition is for application onto magnesium, or (v) hydrolysed at neutral pH when the pre-treatment coating composition is for application onto stainless steel.