# Surface Coatings and Treatments for Controlled Hydrate Formation: A Mini Review
## 3 Hydrate-Public Surface Treatments and Coatings
### Other Surface Treatments  
Recently, [PERSON] et al. [51] demonstrated, as a proof of concept, that a ferrofluid can be used as a coating to create a liquid/liquid interface to reduce the hydrate adhesion on the pipeline walls. This strategy can be applied by pumping the fluid in high-risk areas, namely, a low spot of the tubing and pipeline. The magnets placed on the designated spots of the outer walls, therefore, will assist in the formation of a liquid/liquid interface on the inner wall. The magnetic, slippery surface in this work was prepared by dispersing magnetic particles within a hydrocarbon-based magnetic fluid. The particles were dispersed uniformly in the fluid irrespective of the introduction of a magnetic/force field. The fluid was applied on a metal surface and the adhesion strength of tetrahydrofuran hydrates at atmospheric pressure was measured under static and dynamic conditions. The results indicated that the ferrofluid coating gel did not prevent the ice/hydrate formation but reduced the adhesion strength of both ice/hydrates and reduced the torque values after hydrate formation. As a control, the neodymium magnet coated with diesel oil was used to ensure that the hydrocarbon in the ferrofluid was not responsible for antiadhesion characteristic  
Figure 3: The images obtained at 20-s intervals from the touch moment during the adhesion measurement for different treated substrates: (**a**) X80; (**b**) Coating without surface modification; (**c**) CeO2/pDA@X80 coating; (**d**) X80 after sand abrasion; (**e**) CeO2/pDA@X80 coating after sand abrasion; (**f**) X80 with a water drop deposited on the surface. Reprinted with permission from ref. [54]. © 2021 Elsevier. of hydrates. The diesel-coated magnet allowed the formation of ice/hydrate. On tilting the magnet at 90\({}^{\circ}\), the ice/hydrate remained stuck to the magnet surface, indicating that the iron particles dispersed in the fluid were mainly responsible for the antiadhesion properties of this formulation. Other mechanical tests were performed on the THF hydrates where the neodymium magnets need to be detached from the hydrate mold by applying some force. In the absence of coating, a significant force was needed, whereas in presence of ferrofluid, a minimum force was needed to overcome the adhesion between magnet and mold. Hydrocarbon-based ferrofluids can be crucial in lowering the production costs because of their low evaporation rate and, therefore, long life. In order to prevent/overcome the depletion of the coating issue over time, a ferrofluid gel was also used. Further tests in realistic, high-pressure conditions are required to fully assess the potential of this strategy. The presence of produced hydrocarbons might dilute the gel/liquid. [PERSON] et al. [52] pointed out that the surface coatings can significantly reduce the hydrate adhesion strength, which can further be reduced by the application of microscale/nanoscale textures on the surfaces. They chose four different substrates, namely, X70 steel, X80 steel, Zirconia (ZrO2), and tinplate, which were treated following a rigorous procedure with three different coatings, namely, a fluoro-coating reagent (F-coating), polydimethylsiloxane (PDMS), and hexagonal boron nitride (HBN). Hydrophobic fuming SiO2 in different proportions was also added in each system to prepare various types of coatings. The sample with 96% PDMS + 4% SiO2 applied on a bare X70 substrate showed the maximum water contact angle of 158\({}^{\circ}\). A micromechanical force apparatus was used to measure the adhesion forces between the coated surfaces and model hydrate former THF. The results indicated that the combination of coating materials with a specific surface structure applied on an appropriate substrate can lead to reduced adhesion and growth of hydrates.