Rapid Laser In-situ Growth Of Graphene And Its Anti-corrosion Performance

Graphene, composed of a single layer or a few layers of carbon atoms, has attracted a tremendous amount of attention and research focus. The exceptional properties of graphene, such as ultra-high electrical conductivity, excellent thermal stability, and outstanding mechanical properties make graphene a promising material for many potential applications, including micro-electro-mechanical devices, flexible screen displays, sensors, solar cells, and so forth. Besides, graphene is highly inert, and so can also act as a corrosion barrier against water and oxygen diffusion. The merit of graphene as anti-corrosion coating is that graphene can serve as an ultrathin physical barrier, preventing direct interaction between m etals and ambient environment. However, the studies of graphene as a protective coating are far from sufficient, especially about protecting carbon steel, a most widely-used engineering material. The greatest obstacle is lack of a comprehensive approach to grow graphene. In this thesis, we have succeeded in developing a unique approach for large-area and patterned graphene growth by laser irradiation at room temperature. The graphene films has been in-situ grown on the surfaces of pure Ni, 45# steel and Ni-Cu alloy rapidly without any gas emission. All the merits make this novel approach be a cost- and time-efficient and eco-friendly method to produce high-quality graphene films.Direct in-situ growth of graphene on solid carbon coated nickel surface was realized by laser irradiation. Large-area graphene was obtained rapidly by diode laser with the beam size of 16 mm×1 mm. The graphene can be grown with a very high rate of 28.8 cm2/min. Arbitrary graphene patterns designed by computer aided design(CAD) software were fabricated directly on Ni substrates by focused fibre laser, without any additional mask or setup. The influences on graphene growth, including laser power density, scanning rate, energy distribution, cooling rate and carbon coating, were studied systematically. With the help of thermography and solidification theory, we understood the graphene formation mechanism during rapid solidification, caused by laser processing.Ni atoms were introduced into 45# steel surface to form a Ni/Fe catalyst by laser alloying. Graphene then grew on this alloy catalyst. Varying the powder feeding rate, different Ni/Fe coatings were obtained with different surface composition. With increasing of Ni, the quality of graphene became better and the layer number of graphen e increased. Besides, the Ni/Cu alloy catalysts by laser clading were also used for graphene growth. High power density fiber laser was employed to melt Ni and Cu mixed powders. The Ni/Cu alloy catalysts were formed with a high rate. Then the graphene with controllable layers was rapidly and locally grown on the Ni/Cu catalysts by laser irradiation.The anti-corrosion capacity of graphene has been investigated by immersion tests and electrochemical measurements. The results demonstrated that after graphene growth on Ni, the corrosion rate was 1000 times lower than that of the bare Ni. After graphene growth on 45# steel, the corrosion resistance had been improved to the same level as stainless steel has. The degradation of graphene has been quantitatively analyzed by potentiodynamic polarization analyses and electrochemical impedance spectroscopy(EIS) and equivalent electric circuit(EEC). The mechanism of graphene as a high anti-corrosion coating was attributable to the excellent impermeability and extremely high conductivity of graphene.