Study On Design And Preparation Of Superhydrophobic Composite Coatings And Their Anti-scaling And Anti-corrosion Performance

Scaling and corrosion on the inner wall of oil field pipes have always been the main obstacles to the development of the petroleum industry.Currently,most of the techniques used in oilfield production are to add anti-scale agent and anti-corrosion agent to the fluid in order to solve scale formation and corrosion.Furthermore,the chemical additives added to the fluid will be carried away by the fluid,it causes expensive costs,high energy use,environmental damage,as well as other issues.The superhydrophobic coating is an effective protective material,it has gained significant interest in several domains,including self-cleaning,scale prevention,corrosion prevention,and drag reduction in recently.However,the inherent problems of superhydrophobic coatings such as poor air film stability and long-term effectiveness restrict their use in scale prevention and corrosion prevention.On the one hand,superhydrophobic coatings can reduce the deposition of scale.Yet,once generated,heterogeneous nucleation scale can become the centre of subsequent scale crystal deposition and growth and eventually form visible scale.It can also be challenging to remove.On the other side,the air film of the superhydrophobic coating will still fail and the metal will be corroded under the long-term action of corrosive media.Thus,relying merely on the air film between the superhydrophobic coating and the medium is far from sufficient for scale prevention and corrosion prevention.Starting from enhancing the scale and corrosion resistance of superhydrophobic coatings,we have constructed a series of superhydrophobic coatings by adsorbing scale inhibitors,metal ion chelates,as well as polyalpha-olefin（PAO）in the coating’s micro and nanostructures.The impact of scale inhibitors,metal ion chelates,and PAO at the coating/medium interface on scale development and corrosion on the surface of superhydrophobic coating was examined in order to reinforce the surface and interface of superhydrophobic coating,and the mechanism of scale as well as corrosion prevention of superhydrophobic coating was revealed.The main research contents are as follows:（1）Based on the scale inhibition performance of ethylenediamine tetraacetic acid（EDTA）,the superhydrophobic polyvinylidene fluoride（PVDF）/carbon nanotubes（CNTs）-EDTA coating was fabricated.The findings indicate that the scale mass of the superhydrophobic PVDF/CNTs-EDTA coating is 49.4%as well as 38.4%lower than the PVDF coating and the superhydrophobic PVDF/CNTs coating respectively,demonstrating the coating’s effective scaling resistance.The crystal forms of CaCO₃on the coating surface are mainly thermodynamically unstable aragonite and aragonite.The contact between CaCO₃and the coating surface can be reduced by The air film between the superhydrophobic coating and the solution.Additionally,at the solution/coating interface,EDTA molecules adsorbed in the coating react with Ca²⁺to form EDTA-Ca²⁺chelates,which decreases the probability of Ca²⁺combining with CO₃^2-in order to form CaCO₃.The anti-scaling effectiveness of the superhydrophobic PVDF/CNTs-EDTA coating is improved by the physical barrier provided by the superhydrophobic coating air film and the interfacial contact with EDTA.（2）In order to further enhance the scale prevention and corrosion resistance of the superhydrophobic coating adsorbed by scale inhibitor,the diethylenetriamine pentamethylphosphonic acid（DTPMPA）,which has both anti-scale and anti-corrosion functions,was adsorbed into the micron-nano structure of the superhydrophobic PVDF/CNTs-DTPMPA coating,and the anti-scaling and anti-corrosion performance of the coating was explored.Comparing with the superhydrophobic PVDF/CNTs-EDTA coating,the surface scaling amount of the superhydrophobic PVDF/CNTs-DTPMPA coating decreased by 4.5%,and the corrosion resistance increased by 88.1%.This is due to the fact that,on the one hand,DTPMPA in coating and Ca²⁺in solution react at the interface to create DTPMPA-Ca²⁺,which prevents Ca²⁺from combining with CO₃^2-to form CaCO₃,realizing scale prevention.On the other hand,DTPMPA-Ca²⁺can further prevent the growth of CaCO₃crystals to achieve scale inhibition,resulting in lattice distortion of CaCO₃crystals.DTPMPA is also a type of cathodic corrosion inhibitor.In the electrochemical corrosion reaction,DTPMPA cations migrate to the cathodic region to block the cathodic process as well as play an anti-corrosion role.（3）Based on the idea that scale inhibitor and metal ion chelate(DTPMPA-Ca²⁺)can prevent scaling,we have developed a DTPMPA and Cu²⁺ion coupled superhydrophobic DTPMPA-Cu/anode copper oxide（ACO）coating on the surface of copper substrate.The results of the scale control test reveal that the scale formation amount of the superhydrophobic DTPMPA-Cu/ACO coating is 34.1%lower than that of the DTPMPA-Cu/ACO coating,which is mainly due to the positive contribution of the air film between the superhydrophobic coating and the medium to reduce the deposition of scale.Likewise,the chelating products of DTPMPA and Ca²⁺ions in the superhydrophobic DTPMPA-Cu/ACO coating will also impede the binding of Ca²⁺and CO₃^2-to prevent scaling.Additionally,the trace DTPMPA-Cu²⁺in the solution can be adsorbed on the surface of CaCO₃crystal and inhibit its further growth.DTPMPA and Cu²⁺ion chelate cooperate in order to enhance the scale resistance of super hydrophobic DTPMPA-Cu/ACO coating.（4）In order to further look into the scale prevention and corrosion resistance of chelate interface type superhydrophobic coatings,we fabricated a EDTA,Cu²⁺,and Zn²⁺ion coupled superhydrophobic EDTA-Cu-Zn/ACO coating on the surface of copper substrate.The scale formation of the superhydrophobic EDTA-Cu-Zn/ACO coating surface is 79.7%lower than that of the ACO surface,and the crystalline phase of CaCO₃is mainly aragonite.On the one hand,the air film on the surface of the superhydrophobic coating inhibits the nucleation and adhesion of CaCO₃scale on the coating surface.On the other hand,the dynamic release of EDTA and its chelates(EDTA-Cu²⁺and EDTA-Zn²⁺)to the coating/solution interface to inhibit the formation of CaCO₃scale.After soaking in 3.5%Na Cl solution for 7 days,the impedance value of the superhydrophobic EDTA-Cu-Zn/ACO coating remained above 10⁷Ω·cm²,demonstrating its high level of corrosion resistance.EDTA,Cu²⁺,and Zn²⁺ion chelates further enhance the scale and corrosion resistance of the superhydrophobic EDTA-Cu-Zn/ACO coating.（5）In order to improve the long-term protective properties of the superhydrophobic coating,polyalpha-olefin（PAO）was adsorbed into the the superhydrophobic PAO/PVDF/TiO₂coating,and the long-term anti-scaling and anti-corrosion performance of the coating was explored.After soaking in a supersaturated CaCO₃solution for 360 hours,the amount of scale on the surface of superhydrophobic PAO/PVDF/TiO₂coating is 52.2%lower than that of PVDF/TiO₂coating,and the crystalline type of CaCO₃is chiefly aragonite.The superhydrophobic PAO/PVDF/TiO₂coating exhibits excellent anti-scaling performance,which is due to the PAO on the coating surface making it difficult for CaCO₃crystal particles to remain and adhere.After soaking in a 3.5%Na Cl solution for 150 days,the electrochemical impedance value of the coating remains at 10¹⁰Ω·cm²,which is four orders of magnitude higher than that of hydrophobic PVDF/TiO₂coating,as well as the corrosion resistance of the coating is great.The formation of a PAO liquid barrier layer on the coating surface can successfully stop the entry of corrosive and scaling material.The superhydrophobic PAO/PVDF/TiO₂coating has excellent scale and corrosion resistance.