Carbon Based Coating on Steel with Improved Electrical Conductivity

Research Article

Austin J Nanomed Nanotechnol. 2015; 3(1): 1041.

Carbon Based Coating on Steel with Improved Electrical Conductivity

Tong Y¹, Bohm S² and Song M¹*

¹Department of Materials, University of Loughborough, UK

²Tata Steel Research & Development, Surface Engineering Department, Advanced coating knowledge group, 9, Sir William Lyon Road, The University of Warwick Science Park, Coventry, CV4 7EZ, UK

*Corresponding author: Song M, Department of Materials, Loughborough University, Loughborough LE11 3TU, UK

Received: September 01, 2015; Accepted: October 29, 2015; Published: November 06, 2015


Graphene and graphite were coated on steel plates by means of Electro Phoresis Deposition (EPD) for electrical conductivity improvement. Thermal treatment was used after EPD to improve the adhesion between the coating layer and the steel substrate. The highest value of the electrical conductivity achieved was 20 times higher than that of the steel substrate. The optimized EPD and thermal treatment conditions were identified. The coating-steel interface and surface structure suggested that good bonding between the coating and the steel substrate was achieved.

Keywords: Graphene; Nano-graphite; Conductive coating; Steel; EPD


Steel, an alloy of iron and other elements, is a very important and widely applied material in industry. Various in composition and forms, steel have been applied in many different applications such as automotive shell, supporting column and tableware [1]. It is also an important material that is widely utilized in energy storage applications such as interconnect for Solid-Oxide Fuel Cells (SOFC) [2] and bipolar plate for proton exchange membrane fuel cells [3]. For energy storage applications, the electrical conductivity and corrosion resistance of the working environment of the major components are the essential properties. Although some types of steel have good electrical conductivity, their electrical conductivities are still not high enough and they do not possess excellent anti-corrosion properties for the long-term durability of the energy storage device. Hence, different coating systems have been adopted to improve the performance of the steel based components in energy storage applications. For example, polymer based coatings [4-7], multilayer coatings [8,9] and ceramic based coatings [2,10,11] were used as electrical conductivity and corrosion resistant enhancers on steel surface for energy storage applications. However, there is still a long way to go from small scale lab production to large scale commercialization although the improvement was promising. Therefore, seeking of new materials and new technologies are still crucial for the future development.

Graphene, a new era material, has many extraordinary properties such as high tensile strength [12], high electrical conductivity [12- 14] and barrier properties [15]. It is a very promising material to be utilized as coating to improve a wide range of properties no matter applied as composite or pristine form [16]. Electrophoresis Deposition (EPD) has been received increasing interest due to its simplicity and cost effectiveness. The graphene EPD based materials on steel have been adopted by researchers for various applications such as biocompatible materials [17] and transparent conductive materials [18]. Although all the reported results in the electrical conductivity were promising, only few papers mentioned the adhesion between graphene based materials and the substrates in the literature [19]. Pristine graphene is a pure carbon material and it does not form interactions with steel. Hence, the adhesion between steel and graphene is poor and the coated pristine graphene sheets on steel can be easily starched off after EPD. Without improved adhesion between pristine graphene and steel substrates, the graphene coating layer will not able to satisfy the requirements for long-term durable coating in energy storage applications.

In this paper, graphene and graphite were applied onto steel as conductive coating by means of Electrophoresis deposition (EPD). A simple method, thermal treatment was initially used to improve the adhesion between pristine graphene or graphite and steel substrates. The effects of EPD conditions and thermal treatment on the electrical conductivity were investigated. The composition and the morphology of the coating surface and the coating-steel interface were also assessed.



Acetone (99.5% purity) and iodine were purchased from Sigma Aldrich. TIMREX PP10 natural graphite (PP10) was purchased from TIMCAL Ltd. Graphene was produced by mechanochemical method from expandable graphite in the lab [20]. The expandable graphite was purchased from China Qing Dao Graphite Company. The cold rolled steel ‘Black Plate’, which was used as substrates, was provided by TATA Steel R&D. The BP steel was a 0.2mm thick steel sheet initially and it was cut into 20mm by 50mm steel sheets.

Sample preparation

Expandable graphite was mixed with melamine in a volume ratio of 1:1. The mixture was dispensed into de-ionised water to make solution with a concentration of 1g/100ml. The solution was then heated up to and kept at 80oC for 1 hour with constant stirring, to allow the melamine to fully penetrate and expand the graphite layers. Thereafter, the solution was filtrated and dried at 80oC for 5 hours. The dried mixture then underwent ball-milling to exfoliate the graphite layers initially. The resulted mixture was dispersed in de-ionised water and ultrasonicated for further exfoliation for 1 hour (Fisher Scientific Sonic Dismembrator Model 500, 300 W). At last, hot water was used to repeatedly wash the mixture to remove the melamine. The obtained graphene was shown in Figures 1c & 1e.

Graphene or graphite was mixed with acetone to form a suspension. Iodine was then added into the suspension and stirred until fully dissolved. The resulted mixture was ultrasonicated for 30 minutes by using Fisher Scientific Sonic Dismembrator Model 500 at room temperature. The BP substrates were cleaned by acetone and then it was degreased in 5% alkaline solution at 70°C for 3 minutes. The distance between two electrodes was 10mm and a voltage of 40V was applied for 30 seconds initially. The DC source used in EPD was Consort EV265. EPD coated samples were thermal treated in a furnace (Carbolite RHF 16/8) with different temperatures for different length of times. Different EPD conditions were used as well to investigate the optimized EPD conditions for the best conductivity.


Carl Zeis (Leo) 1530VP Field Emission Gun Scanning Electron Microscope (FEG-SEM) and Thermo Scientific K-Alpha X-Ray Photoelectron Spectroscopy (XPS) were used to characterize the surface morphology and surface composition of the coated samples respectively. Transmission Electron Microscope (TEM), JEM- 2000FX electron microscopy manufactured by JEOL, was used to characterize the natural graphite PP10 and the graphene produced from expandable graphite. The graphite and graphene were ultrasonicated for 30 minutes in water before TEM characterization.

The electrical conductivity of the coated samples was measured by using a FLUKE PM6306 programmable automatic RCL meter with a four point probe. Relative electrical conductivity Cc/Cs was used show the electrical conductivity enhancement, where Cc represents the measured electrical conductivity of the coated samples and Cs represents the measured electrical conductivity of bare steel.

Results and Discussion

TEM images and diffraction pattern of PP10 graphite and the graphene fabricated from expandable Graphite (G) are shown in Figure 3.1. The sampling area of the x-ray diffraction of this TEM is in nano scale. Comparing Figures 3.1(a) and (c), PP10 has smaller amount of graphene sheets than G and the size of the graphene sheets are smaller as well. Figure 1(e) can further confirm that G has larger amount of graphene sheets with various layers and folding and their size are bigger. In addition, graphite nano flakes also present in the figure. In the literature, only electron diffraction patterns of graphene sheets with different layers were discussed [21,22]. However, x-ray diffraction pattern and electron diffraction pattern of a substance is similar. The schemes of the electron diffraction pattern of single layer and two layer graphene in literature were redrawn and shown in Figure 2. In a diffraction pattern, a triangle is formed around the centre bright spot. For the diffraction pattern of single layer graphene, the two spots in the middle of one side of the triangle have higher intensity than other two spots as indicated by the arrows in Figure 2a. For two layer graphene, the spots in the vertices of the triangle have higher intensity Figure 2b. The x-ray patterns shown in Figure 1 for single layer graphene are similar to the electron diffraction pattern in the literature. As a result, the existence of single layer graphene sheets in PP10 and G can be confirmed. Although G has more graphene sheets, the phenomenon of bigger graphene sheets cover smaller graphene sheets is more serious and this will lead to a ring x-ray diffraction pattern at the stacking site [21,22]. Figure 1f indicates that a couple of graphene sheets are stacking at the site. The x-ray pattern will start to grow to be a ring shape if more graphene sheets are stacking in an area.