1. Introduction

In all parts of the aircraft, as the main part of producing lift, wings are always influenced by ice. Icing will induce the changes on wings’ flatness, shape and aerodynamic layout, resulting in the aircraft of decreased lift resistance ratio, lift coefficient dropped, resistance increased and serious damage to flight safety. At present, the common method to avoid icing or frozen is using hot air to melt ice, which means that the hot air erupted from the engine can heat the wing’s leading edge to prevent freezing. However, the de-icing effect of this method is not satisfactory and complete. Therefore, many researchers are looking for a new way to improve the result. 

At the same time, two-dimensional materials were considered to make wings heating coating. Carbon coatings are the first one to be regarded and applied, but its property of heating is still unsatisfactory because of low heating rate and poor flexibility. Until the material ‘Graphene’ was discovered by Professor Andre Geim and Novoselov at the University of Manchester in 2004, the problem which material should be chosen had a bright prospect. Its various excellent properties, such as electronic, heating, radiating and flexible, were becoming more favoured by many scientists. According to a recent study of Lin zhang. Et al. (2017), graphene is the thinnest two-dimensional material in the world has high hardness, low friction, and high thermal conductivity and, hence, has attracted great attention. In addition, graphene’s good electrical and thermal conductivity which allowed it to be used as a flexible electro-thermal heating element in a rapid localized heating process (p. 1369). Nevertheless, Graphene has not been produced maturely and perfectly. This essay aims to enhance the processing of graphene to achieve high quality and large scale, and use graphene to make useful heating coating to de-ice wings.

2. Situation

When aircraft are flying under the condition of icy weather, the undercooling water droplets will impinge against the surface of the wings. The wings will become frozen. Notably, it is very easy to change of wings’ shape because of ice cover. These will influence aerodynamic performance, resulting in changes in aerodynamic performance of the wing. When the wings’ surface freeze, some bad conditions will happen, such as the increased resistance of the aircraft, the decreased lift, and the reductive critical angle of attack. As a result, the manoeuvrability and stability of the aircraft will be seriously affected. At present, although the anti-icing and de-icing system of the wings have been greatly enhanced, accidents due to icing on the wing still occur. According to the dissertation of Sam Lee (2001, p 1), from 1987 to 1996, in all major flight accidents in the United States, ice and snow accumulation accounted for 9% of the major causes. Therefore, the influence of wing surface icing on the aerodynamic performance of wing has been a hot topic in the field of aircraft anti-icing.

The basic principle of anti-icing system is de-icing. Obviously, the effect of heating can serve as an anti-icing action. Then, the heating coating becomes the object of this paper. At present, the materials which are used more and can be prepared are two-dimensional materials. Two-dimensional materials have many advantages, such as excellent optical, electronic and mechanical properties, its two-dimensional structure also lays the foundation for which excellent coating materials can be prepared. 

In 2004, after the discovery and preparation of a new type of two-dimensional graphene material, its extraordinary performance attracted researchers from all over the world. Graphene is the first two-dimensional atomic crystal to be prepared, its properties of stiffness, strength, elasticity, conductivity, and thermal conductivity are unmatched. In particular, graphene’s transparency, conductivity, impermeability, and elasticity make it available for flexible electronic devices. Graphene is, therefore, a very suitable two-dimensional material for the preparation of films or coatings. At present, the preparation methods of graphene can be divided into two categories, one is a physical method, and the other is a chemical method. The physical method, in the early period, was used of micro mechanical stripping method. Professor Geim who works in University of Manchester (2004) used the way of ion etching graphite surface, and then paste onto a glass substrate, using photoresist repeatedly tearing, eventually obtained graphene using ultrasound. After this is derived from the method of liquid phase and gas phase direct stripping, usually by graphite or graphite (EG) mixed with water or organic solvent, by heating, graphene solution ultrasonic or air flow obtained in a certain concentration. In addition to physical methods, oxidation reduction is the most common chemical method employed by researchers in the laboratory.

3. Problem

At present, the application of graphene has been a question, the most important reason is that it is still unable to achieve large scales and high-quality industrial production. Without high quality and large quantities of graphene in the process of graphene research. graphene also cannot be applied in civilian and military fields. Therefore, how to prepare large-scale and high-quality graphene is the primary problem to be solved in this paper.

Since the application of the de-icing coating is on the wing, this requires the coating to be resistant to complex environments and to have strong adhesion, high electrical conductivity, excellent flexibility, and long service life. Thus, how to use the prepared graphene to produce a feasible coating is another essential problem that needs to be solved in this paper.

4. Solution

As for the first problem, how to prepare large-scale and high-quality graphene, this paper shows a new idea which uses hydrogen peroxide to treat graphite intercalation compounds(GIC), and then receives graphene suspension water to produce the heating coating. The graphite intercalation compound is a layered, synthetic metal compound. It can be made by Inserting a charge transfer between the middle layer of metal atoms and the layer of carbon atoms, which will produce the electrical potential difference and the formation of compounds. In this paper, there are two methods to use different raw materials, respectively LiCl and FeCl3, to insert plane of carbon atoms and then forming GICs. Next, the GIC is processed, and the inserted compound reacts with the catalyst solution to produce a large number of bubbles that separate the intercalation layer from the carbon atom layer. In this way, the multilayered carbon layer is divided into layers of carbon atoms. If the reaction process is homogeneous and complete, there is a great chance of producing a single layer of carbon atoms, that is, perfect graphene layer. Due to the excellent adhesion properties of single-layer graphene, it is easy to mix graphene with another high-property composite material to make expected coating. By doing this, the second problem how to make practicable heating coating can be solved greatly. 

4.1 Preparation for GIC

In the process of preparing GIC, the compound powder (FeCl3) and graphite powder are heated by the heating system of CVD tube furnace at high temperature. When the environmental temperature reaches the melting point of the intercalation compound, the intercalation compound of the molten state enters the graphite interlayer in the form of molecules. Then, when intercalation molecules enter the layers of graphite, these molecules produce intermolecular forces (van Edward force) with the graphite molecules. Therefore, the intercalation compound molecules are left at the position where the intermolecular force is produced, thus forming a molecular bond and a stable structure. The intercalation compound with this stable structure is the graphite intercalation compound (GIC). 

4.2 Preparation for Graphene

The preparation of graphene, as for Ferric chloride intercalation graphite compound (FeCl3-GIC), can be catalyzed by ferric chloride and strong oxidizing agents, such as hydrogen peroxide, sulfuric acid and nitric acid, and produce large amounts of bubbles. These bubbles can produce a force perpendicular to the surface of the intercalation compound layer and the graphite layer, i.e., tension. When the tension reaches a certain extent, it will be greater than the intermolecular force between layers. At this point, the molecular bonds between the intercalation layer and the carbon layer will break. As a result, the intercalation layer separates from the carbon layer and produces a few layers or even a single layer of carbon atoms (Graphene).

According to a report of Geng et al (2013), The process is clearly illustrated in the schematic diagram (Fig. 1a). The preparation is accomplished by the interlayer catalytic reaction of the stage-1 FeCl3-intercalated graphite (FeCl3-GIC) with H2O2, in which interlayer FeCl3 serves as effective catalyst and H2O2 as both reductant and oxidant. FeCl3-GIC and highly expanded product after ICE show a striking contrast in volume and shape (Fig. 1b, c).

Figure 1 | Few-layer Graphene produced by interlayer catalytic exfoliation. (a) Schematic illustration of the process from stage-1 FeCl3-intercalated graphite (FeCl3-GIC) to Interlayer catalytic exfoliation graphene layers. (b, c) Photographs of the FeCl3-GIC powder and the greatly expanded products consisting of interconnected graphene layers access interlayer catalytic exfoliation. (Geng. Et al., 2013)

4.3 Preparation for Graphene coating

Graphene coating was prepared by mixing graphene with epoxy resin and adding acetone to mechanical agitation. This process allows graphene molecules to form molecular bonds with the organic chain ends of the epoxy resin and maintain a stable chemical state. Second, as the graphene needs to be painted on the wing, it is necessary to add curing agents to improve the viscosity of the coating. Finally, the graphene coating can be obtained by heating the above coating on the substrate, such as the wing’s surface.

4.4 Apply for wings of aircraft

To model the heating of the graphene coating, Allen Y. et al (2017), introduced a simplified structure of a strip-shaped Si substrate coated with a thin conductive film in an external alternating current (AC) magnetic field vertical to the plan. In this paper, wings serve as the substrate for coating. Usually, wings are made of composite materials, such as Fibre Reinforced Plastics, carbon fibre and glass fibre. This means Painting is a suitable method to ensure the coating cover on the whole part of wings. Specifically, painting to electric circuit is a very important step in this process. 

5. Evaluation

At present, there are many methods for preparing graphene, which can be divided into experimental and industrial methods. Because graphene has many excellent properties, since the graphene was discovered, people always hope to be able to use large-scale graphene in their daily life. However, there has been no mass production of high-quality graphene problem. In this paper, a method for the preparation of mass production graphene is proposed. The method is simple, easy to operate, environmentally friendly and capable of mass production. From raw materials, FeCl3 and graphite on the market are very common, cost-effective. From the product point of view, graphene prepared by this topic cannot be compared with the properties of graphene. Therefore, the preparation methods of this subject need to be improved in the future research process. We hope to prepare higher quality graphene and achieve mass production.

Wing icing problem is a prevalent topic in aircraft manufacturing. This essay is based on the two-dimensional material for the lead, selected the graphene of excellent properties as the basic raw materials, and made graphene heating coating to improve the plane’s wings icing. Specifically, using graphite intercalation compounds to prepare large-scale and high-quality graphene powder, then using this graphene powder to produce a heating film by silk screen, and putting forward a viable application product, such as coating covered on the wings of aircraft. It is expected to provide a method for mass production and application of high-quality graphene to solve the problem of aviation devices. 

6. Conclusion

To sum up, this paper has put a new method for preparation of graphene and graphene coatings and presented with the aim of de-icing wings. The method of interlayer catalytic exfoliation has shown world-shaking ability to prepare the pure and high-quality graphene with large-scale size. In the part of GICs, due to FeCl3-GIC has very specific thermal stability and water solubility, graphene has been produced perfectly. That means when the method of interlayer catalytic exfoliation (ICE) has been used, the intercalation layer and the graphite layer still maintain a complete structure. Because the FeCl3 molecule has a weak connection with the graphite layer. In addition, another advantage is that FeCl3 is an effective catalyst for catalytic oxidation. FeCl3 and H2O2 reacted to produce a mild and persistent gas to achieve the effect of the stripping layer. In particular, catalytic reactions yielded only environmentally benign products, water and oxygen. Obviously, the intercalation method is superior to thermal expansion, exfoliation and general chemical reactions in terms of the thickness and size of the product. Using the graphene suspension which produced by intercalation method has been able to paint the whole wings of the plane to form the heating coating, then made the coating work and melted ice covered on the wings. The result has expressed important breakthroughs in the research on the preparation of high-quality graphene and the aircraft safety system application of graphene heating coating. The solution, therefore, has already been concentrating our efforts on exploring the new idea to make perfect graphene and solving the problem of de-icing the wings. Of course, this job indeed is an essential area for further research because of the benefits to flying safety of aircraft.  

References

Geim, A. and Novoselov, K. (2007). The rise of graphene. Nature Materials, 6(3), pp.183-191.
Wissler, M. (2006). Graphite and carbon powders for electrochemical applications. Journal of Power Sources, 156(2), pp.142-150.
Geim, A. (2009). Graphene: Status and Prospects. Science, 324(5934), pp.1530-1534.
Zhang, L., Zhou, W. and Yi, A. (2017). Rapid localized heating of graphene coating on a silicon mold by induction for precision molding of polymer optics. Optics Letters, 42(7), pp.1369-1371.
Sam Lee (2001). Effects of Super-cooled Large-droplet Icing on Airfoil Aerodynamics. Ph.D. University of Illinois at Urbana-Champaign.
Novoselov, K. (2004). Electric Field Effect in Atomically Thin Carbon Films. Science, 306(5696), pp.666-669.
Geng, X. et al. (2013). Interlayer catalytic exfoliation realizing scalable production of large-size pristine few-layer graphene. Scientific Reports, 3(1).

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