Investigation of Graphene

Abstract
This research work focuses on the synthesis, characterization and processing of potassium silicate/zinc/graphene composites to improve the corrosion performance of zinc-rich coatings. A stable high-modulus potassium silicate composite material was prepared with silica sol and potassium silicate and then, different percentages of graphene were added and ultrasonication process was used to prepare potassium silicate/zinc/graphene composites. Coatings were applied on carbon steel panels with composition of zinc and 0.5 wt.%, 1 wt.%, 1.5 wt.%, and 2 wt.% graphene. SEM was utilized to analyze the structural characteristics of the samples. The coating can be divided into two pieces: the upper layer with high modulus potassium silicate as binder and graphene as filler; the lower layer with high modulus potassium silicate, graphene and zinc particles. The anticorrosive properties of the nanocomposites were investigated by DC polarization technique and electrochemical impedance spectroscopy (EIS). The results of electrochemical tests showed that there exist three stages: the activated stage, the cathodic protection stage and the barrier protection stage. The addition of graphene improves the corrosion resistance of coatings and the best corrosion performance obtained for the nanocomposite sample with 2 wt.% graphene. 
Key words: coating, potassium silicate, waterborne, graphene, corrosion


1 Introduction
Shop primer, which is also called maintenance primer and known as metal pretreatment primer, is utilized for the temporary protection of carbon steel from cutting, welding, rust or corrosion. So far, using zinc-rich coatings is a very efficient method for protecting steel structures against corrosion in some aspects of the steel industry[1, 2]. At the beginning of immersion, zinc particles provide a cathodic protection of the steel substrate, causing electrical conductivity of dry film by binding to the surface of the base metal and protects the substrate with sacrificial galvanic protection[3]. Then, the corrosion products of zinc powder will gradually deposit to form a layer of protective film on the steel, which may seal the pores in the primer and improve barrier properties[4-7].
Many works are being done to improve the properties of zinc-rich coatings. Jagtap et al. found that a specific amount of zinc oxide in zinc-rich coatings could improve the corrosion resistance of zinc-rich coating due to the barrier properties[8, 9]. Y. Cubides[10] found that carbon nanotube can improve the corrosion protection and N. Arianpouya[11] found that PU/Zn/OMMT nanocomposite coatings exhibit superior corrosion protection effect and enhance coating adhesion to the substrate and obviously increase the barrier properties of the coating. At present, the effect of waterborne zinc rich coating has almost been comparable with the performance of solvent coatings[2, 12]. Inorganic zinc-rich coatings has many features, including low VOC, fast drying, good rust resistance, weld ability, high mechanical performances[13] low maintenance cost and safety[14-17].
To ensure good electrical contacts between zinc pigments and the cathodic protection of the carbon steel substrate, a high pigment concentration with 92 wt.% to 95 wt.% zinc is required in dry film [18]. However, the high amount of zinc in coating weaken the adhesion properties of the film and zinc oxide dust produced in welding is harmful to the health of workers. It is also important to point out the need of decrease of zinc in coatings, which help to save materials and energy[11].
So, in this paper graphene was used to reduce the amount of required zinc. and it seems that the addition of lamellar pigments to the coating has positive effect on the performance of zinc-rich coatings.[10, 11]
Graphene has gained relevance in many applications[19], for its good mechanical and thermal stability [20, 21], low chemical reactivity[22], gas impermeability[23], and good barrier property [23-25]. Because of these properties, graphene is gaining scientists’ attention for preparing anti-corrosion coatings. Several groups have demonstrated the effectiveness of graphene as oxidation resistive[26, 27] and corrosion inhibitive coatings[28, 29]. However, there’s little research of graphene on the waterborne inorganic zinc-rich coating.
In our work, we show that the composite coating has much better corrosion protection properties than only zinc-rich coatings and reduces the percentage of zinc dust. 


2 Experimental
2.1. The preparation of samples and materials
The tinplate sheets used as metallic substrates were sandblasted to Sa 21/2 according to ASTM D609 and were cut into 2×5×0.4 cm3 dimensions for EIS measurements. 
Aqueous solution of potassium silicate (30wt%, the modulus is 3.7) was provided by Xingtai Ocean Chemical Company. 30wt% colloidal solution of nano-silica AJN-830 with a particle size of 5-10nm were purchased from Dali Zhongfa Company. Zinc dust (1#) with an average particle size of 5-10 μm was offered by Changsha Resucerial New Material Company. Graphene nanoplatelets (8-10 layers) were supplied by the Suzhou Geruifeng Nanotechnology limited company (China).


2.2. Preparation of nanocomposites
The potassium silicate was slowly heated to 55 °C in a water bath and then colloidal solution of nano-silica was added until SiO2/K2O molar ratio is 5:1 and the mixture was stirred for 2 h followed by sonication for 1 h. Paints were made up of the modified potassium silicate (the solid matter is about 25%.), zinc dust and graphene. The modified potassium silicate serves as the binder while zinc dusts and graphene serve as antirust filler. The coatings were applied by mayer bar rod on steel panels and cured at room temperature in 5 minutes. The final thickness (dry thickness) of coating on the panels was between 40 and 50 μm. The prepared samples were mentioned with G1 to G5 corresponding to different percentages of graphene (Table 1). 
Table 1 shows the characteristics of zinc-rich coating. 
Table 1 Characteristics of coatings
Sample Zinc dust/g Graphene/g Modified potassium silicate /g Graphene/zinc
G1 30 0 30 0
G2 30 0.15 30 0.005
G3 30 0.3 30 0.01
G4 30 0.45 30 0.015
G5 30 0.6 30 0.02


2.3. Electrochemical measurements
Electrochemical measurements were conducted in CHI760E electrochemical workstation. Samples were embedded with epoxy resin in order to obtain a well-defined surface of 1 cm2. A three-electrode system: the coated sample as the working electrodes, a saturated calomel electrode (SCE) as the reference electrode, and the Pt electrode with a diameter of 2 cm as the counter electrode was used for the measurements of open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and DC polarization technique. Impedance spectra were collected at the open circuit potential. A 10-mV perturbation signal was applied to the electrochemical cell to measure electrochemical impedance. Electrochemical impedance was measured by applying a 10-mV perturbation signal to the electrochemical cell with the frequency ranging from 105Hz to 0.01Hz.
All electrochemical measurements were performed in the 3.5 wt% NaCl electrolyte on carbon steel panels coated with different coatings (exposed area of 1 cm2) at different exposure times. In this experiment, the corrosion potential (Ecorr) and the corrosion current (Icorr) were obtained from the Tafel plots. The Tafel plots facilitated a direct measure of corrosion current to calculate the corrosion rate.


3 Results and discussion
3.1 Morphology and structure of the coatings
Fig 1 shows the surface and the connection of the carbon steel SEM images for G5. The surface of the sample G5 is very smooth and there’s no spherical zinc particles can be seen on the surface (Fig 1A). However, the other side of the coating shows a rough surface which increase the contact area between the coating and the carbon steel (Fig 1B). This shows that the zinc powder disperses unevenly. The sedimentation rate of the zinc powder which is much higher than that of the graphene. can be estimated by Stockes settlement formula:
ω=(g*d^2*(ρ_d-ρ))/(18*μ)
where ω is sedimentation rate; g is acceleration of gravity; d is the particle size of zinc powder; ρ_d is the density of zinc; ρ is the density of solution and μ is the viscosity of solution. The sedimentation rate of graphene is so slow that settlement of graphene is considered not to occur before the coating solidification. Fig 2 shows the double layer structure of the coating. The coating can be divided into two pieces: the upper layer with high modulus potassium silicate as binder and graphene as filler; the lower layer with high modulus potassium silicate, graphene and zinc particles. The upper layer prevents water from penetration and corrosion products from dissolution while the lower layer contributes to the conductive network between zinc powder. 
  Fig 1 SEM micrographs of surface of the sample G5
 (A) the front surface (B)the opposite surface


 
Fig 2 Sketch map of coating structure
3.2 Corrosion rate of the coatings
Fig3 A shows the Tafel plots of G1, G2, G3, G4 and G5 when the samples have just been immersed in 3.5% NaCl solution, while the Fig3 B, Fig3 C and Fig3 D show the Tafel plots after 1, 3 and 8 days immersion, respectively. A marked change of Tafel plot has taken place when the addition of graphene reaches 1.5% (Fig3 A). The corrosion potential of the coating shifts negatively, while the corrosion current increases obviously. Especially, the corrosion current of the sample G5 is ten times higher than the sample G1, G2 and G3. This means that only 30phr of zinc powder begin to react under the action of graphene. However, the mixed corrosion potential of the coating is still at -0.3-0V (Vs SCE), revealing there’s no cathodic protection. Tafel plots change a lot after 1-day immersion in NaCl solution (Fig3 B). Compared with the blank sample G1, the addition of graphene greatly decreases the corrosion potential of the coating after a period. The corrosion potential of the sample G4 and G5 are stay at -1.0--1.2V (Vs SCE) while the electrode of Fe oxidation equals -0.76V (Vs SCE), so that the conditions of the sacrificial anode cathodic protection are satisfied. What’s more, there exists a period of activation. Only when the coating has passed through a period of activation, and water penetrates the coating will graphene maximize its value. The corrosion current density, I_corr of coatings increase with the amount of graphene. I_corr of the sample G4 is probably 100 times as the blank sample G1. This means that the addition of 1.5% graphene improves the conductive network between zinc powders and the cathodic protection performance of the coatings. Fig 3 C shows the Tafel plots after 3 days’ immersion. The OCP of all the samples shift positively after 3 days’ immersion. The OCP of G4 moves to -0.28V while that of G5 moves to -0.69V, both of which exceed the threshold -0.76V[10, 30], so that the coatings provide physical shielding instead of cathodic protection. Fig 3 D shows the Tafel plots after 8 days’ immersion. The OCP of all the samples shift positively after 3 days’ immersion. Except G5, graphene in all the other samples has already lost its electronic function. It is also because the coating no longer provides cathodic protection, the corrosion current drops to the previous level, which is the same as the blank sample.
 
Fig3 Tafel plots of the samples with different coatings measured in 3.5wt% NaCl solution. (A) after 0-day immersion (B) after 1-day immersion (C) after 3-days immersion (D) after 8-days immersion 


Table2 Electrochemical parameters obtained from potential dynamic polarization measurements after 0 days immersion of samples.
Samples Electrochemical corrosion measurements
E_corr
(V/SCE) R_P
(MΩ∙〖cm〗^2) β_a
(V/dec) β_c
(V/dec) I_corr
(μA/〖cm〗^2) Corrosion rate
(mm/year)
1 -0.063 0.077 0.27 0.10 0.43 0.0062
2 -0.059 0.064 0.28 0.14 0.56 0.0080
3 -0.064 0.064 0.32 0.11 0.57 0.0081
4 -0.22 0.014 0.52 0.21 4.68 0.067
5 -0.33 0.0050 0.74 0.22 14.85 0.21
 
Fig 4 Sketch map of the coating in activated stage
As to the polarization curve, graphene changes the cathodic and anodic polarization slope. When the coating is just in the early activated stage (Fig 4), the polarization resistance R_p of coatings declined with the increase of graphene (Table 2), decreasing from 0.077 V/dec to 0.0050 V/dec. This indicates that the more graphene, the shorter the duration of activation period. and zinc powder can more quickly produce the cathodic protection effect. For G1, G2 and G3, there’s little difference on the OCP and the cathodic polarization slope although the slope of anodic polarization increases from 0.27 V/dec (G1) to 0.74 V/dec (G5). The OCP of G5 is -0.33V, which has not yet reached the standard of cathodic protection, however, zinc powder has started to react for the I_corr reaches 14.85 μA/〖cm〗^2. 
In neutral solution, the corrosion potential is the mixed potential of oxygen reduction and zinc oxidation:
cathode O_2+2H_2 O+4e^-→4OH^- E_(c.e)=0.16V (vs SCE)
anode Zn-2e^-→〖Zn〗^(2+) E_(a.e)=-1.1V (vs SCE)


 
Fig 5 Corrosion polarization diagrams of alloys of the coating under activated polarization control
Table 2 shows the increase of β_a and I_corr and the decrease of E_corr with the addition of graphene. There’re two theories to explain this phenomenon. One is the increase of anodic reaction current I_a and the other is the decrease of anodic equilibrium potential E_(a.e).according to the corrosion polarization diagrams (Fig. 5). No matter which theory fit the reality, it is obvious that graphene changes the anodic reaction of the system and zinc particles participate in the reaction. 


Table3 Electrochemical parameters obtained from potential dynamic polarization measurements after 1 day’s immersion of samples.
Samples Electrochemical corrosion measurements
E_corr
(V/SCE) R_P
(MΩ∙〖cm〗^2) β_a
(V/dec) β_c
(V/dec) I_corr
(μA/〖cm〗^2) Corrosion rate
(mm/year)
1 -0.033 0.072 0.21 0.11 0.46 0.0066
2 -0.094 0.030 0.22 0.21 1.52 0.022
3 -0.64 0.012 0.22 0.17 3.56 0.051
4 -1.08 0.00048 0.44 0.19 118.07 1.70
5 -1.01 0.0056 0.46 0.24 12.17 0.18


Table 3 shows that the OCP of G4 and G5 are lower than the threshold -0.76V (Vs SCE). At this stage, water has penetrated the coating, forming a conductive network in which zinc powder contact with each other and graphene makes more zinc powder possible to join in the conductive network. The effect of cathodic protection and the utilization rate of zinc are improved by graphene. In G2, 0.5% graphene dispersed in the whole system is not enough so that there’s little difference between G2 and G1 in providing barrier protection. 
  
Fig 6 Tafel plots of G4 and G5 after 1days’ immersion
What’s more, there exists a passivation phenomenon of anode polarization curve of G4 and G5 after 1-day immersion (Fig 6): the current density decreases with the increase of potential. The curves are similar to passivation curve of metal. Table 4 lists the possible equations in Zn-Si-H2O while Figure 7 shows the E-pH pattern of Zn-Si-H2O. At the first beginning of immersion in the 3.5 wt% NaCl electrolyte, pH equals 7 and c[Zn^(2+)] is very low so the whole system locates in A Corrosion Area (Fig. 7). However, c[Zn^(2+)] increases with the development of corrosion and when it reaches 〖10〗^(-4)  mol/L, zinc in local region transfers to B Passivation Area. Thus, as shown in anode polarization curve, the current density decreases. Nevertheless, because of the discontinuity of zinc powder particles. the whole systems are still in active dissolution zone and also for their corrosion potentials are not in passivation area, this phenomenon doesn’t last long. 
Table 4 E-pH equations of Zn-Si-H2O
No. Equation E-pH
1 HSiO_3^-+H^+→ H_2 SiO_3 pH=10.3+log⁡〖([H_2 SiO_3])/([HSiO_3^-])〗
2 SiO_3^(2-)+H^+→ HSiO_3^- pH=11.7+log⁡〖([HSiO_3^-])/([SiO_3^(2-)])〗
3 ZnSiO_3+2H^++2e→Zn+H_2 SiO_3 E=-0.86-0.0296 log⁡[H_2 SiO_3 ]-0.0296pH
4 ZnSiO_3+H^++2e→Zn+HSiO_3^- E=-1.17-0.0296 log⁡[HSiO_3^- ]-0.0296pH
5 ZnSiO_3+2e→Zn+SiO_3^(2-) E=-1.55-0.0296 log⁡[SiO_3^(2-) ]
6 〖Zn〗^(2+)+SiO_2+H_2 O+2e→Zn+H_2 SiO_3 E=-1.18-0.0296 log⁡〖([H_2 SiO_3])/([〖Zn〗^(2+)])〗
7 ZnSiO_3+2H^+→〖Zn〗^(2+)+SiO_2+H_2 O pH=5.37-1/2  log⁡〖[〖Zn〗^(2+)]〗
8 〖Zn〗^(2+)+O_2+2H^++4e→ZnO+H_2 O E=1.06-0.0148 log⁡〖1/([〖Zn〗^(2+)])〗-0.0296pH
9 ZnSiO_3+O_2+4H^++4e→ZnO+H_2 O+SiO_2 E_0=1.22-0.0591pH
10 2H^++2e→H_2 E=-0.0591pH-0.0296 log⁡〖P_(H_2 ) 〗
11 O_2+4H^++4e→2H_2 O E=1.23-0.0591pH-0.0148 log⁡〖P_(O_2 ) 〗


 
Fig 7 E-pH parttern of Zn-Si-H2O
(T=25℃, c[H_2 SiO_3]= c[HSiO_3^- ]=c[SiO_3^(2-)]=0.1 mol/L)
Table 5 shows the parameters of polarization curves after 8 days’ immersion. The OCP of all the samples are shifted positively. Along with graphene content increases from 0% to 1.5%, the corrosion currents reduce from 0.44 μA/〖cm〗^2 to 0.15μA/〖cm〗^2, and the polarization resistance of coatings increase from 0.083 MΩ∙〖cm〗^2 to 0.19 MΩ∙〖cm〗^2. This means that in this stage, despite there still exists a lot of zinc powder unreacted, the coatings only provide normal physical shielding and all the zinc lose its function, serving as filler. As shown in Fig.8, there’s no difference between the two curves which means that all the zinc particles of G1 didn’t participate in the reaction. However, the addition of graphene changes the situation. The corrosion products of G5 with 2% graphene after 15-days immersion is simonkolleite (Z_n5 〖(OH)〗_8 〖Cl〗_2∙H_2 O)(Fig 9) according to XRD analysis. It means that zinc particles participate in the reaction with the help of 2% graphene and the utilization of zinc has been greatly improved.
Table5 Electrochemical parameters obtained from potential dynamic polarization measurements after 8 days’ immersion of samples.
Samples Electrochemical corrosion measurements
E_corr
(V/SCE) R_P
(MΩ∙〖cm〗^2) β_a
(V/dec) β_c
(V/dec) I_corr
(μA/〖cm〗^2) Corrosion rate
(mm/year)
1 -0.063 0.085 0.30 0.12 0.44 0.0064
2 -0.058 0.10 0.26 0.10 0.32 0.0046
3 -0.036 0.14 0.21 0.10 0.21 0.0030
4 -0.018 0.19 0.18 0.10 0.15 0.0021
5 -0.19 0.0089 0.80 0.26 9.60 0.14




  
Fig 8 XRD parttern of G1 before and after corrosion
 
Fig 9 XRD parttern of G5 before and after corrosion
What’s more, the outer layer of graphene can also play a role in blocking the electrolyte, leading to the decrease of the corrosion rate. In the other side, the corrosion rate decreased from 0.0064 mm/year to 0.0021 mm/year also because of the corrosion products, including the oxidation products of zinc, which accumulate in the coating and fill in the gap and result in a tortuous percolation path of the electrolyte. Even all the five samples have the same content of zinc powder, the higher concentration of graphene, the more zinc powder connect with each other by two-dimension structure of graphene. Therefore, G5 still shows the corrosion rate of 9.60 μA/〖cm〗^2.


3.3 EIS of the coatings
The |Z| Bode plot of G1 gives a straight line which corresponds to a capacity (Fig 10). Impedance magnitude measured at 0.01Hz reaches 105, which means that good barrier protection was provided by the coating system and there’s no charge transfer processes on the carbon steel substrate. This behavior results from the low content of zinc particles, all of which are well wetted by potassium silicate. Water can penetrate straight towards the carbon steel substrate through micropores for the long distance between zinc particles. The phase Bode plots show little difference after different days immersion and only one-time constant can be observed at 1-10Hz in the low frequency region.
  Fig 10 EIS of carbon steel coated with G1 at different immersion times in the NaCl solution a) Nyquist diagram b) Bode diagram
  Fig 11 EIS of carbon steel coated with G5 at different immersion times in the NaCl solution a) Nyquist diagram b) Bode diagram


 
Fig 12 Sketch map of the coating in cathodic protection stage


The |Z| Bode plot of G5 shows only 104 compared with that of G1 and there’s resistive behavior at the initial time, following capacitive behavior which is the same as G1 (Fig 11). The peak of phase Bode plot shifts from 100Hz (after 1 day) to 1Hz (after 15 days). In addition, there’s a noticeable change between G1 and G5 in the Nyquist representation. Impedance diagram of G1 shows a straight line with high impedance at 0.01Hz, while that of G5 shows an obvious capacity arc. This means that potassium silicate surrounding zinc particles has been dissolved by water and zinc particles in contact with water form a double layer capacitance. Water penetrates along with the surface of graphene instead of straight toward substrate, which can win more time for zinc particles to take effect (Fig 12 permeation pathway). At the same time, curvature radius of capacitive arc increases with immersion time. This is probably because many corrosion products adsorbed on the surface of the sample, filling in the coating pores, blocking the other anions involved in the reaction, and graphene blocking the diffusion of dissolved oxygen (Fig 13).
 
Fig 13 Sketch map of the coating in barrier protection stage


4 Conclusions
In this study, a series of PS/Zn/Graphene coatings were synthesized under various graphene loadings by using mechanical agitation and sonication process. SEM was used to observe the structure of the zinc/graphene coatings. It shows that the coating can be divided into two pieces: the upper layer provides barrier protection and the lower layer provides both cathodic protection and barrier protection. It is found that coating corrosion resistance is improved as the amounts of graphene are increased to 2 wt.%. These results show that graphene improves the utilization ratio of zinc powder and the cathodic protection of the coatings at the beginning of immersion and then acts as filler to fill the voids, crevices and pinholes of the polymer in the coating and increases the corrosion resistance of the coatings. So, it was observed that the corrosion protection of zinc-rich coatings is improved as the graphene loading is increased up to 2 wt.% and the best performance was for 2 wt.% graphene that corresponded with electrochemical test results




References
[1] A. Gergely, É. Pfeifer, I. Bertóti, T. Török, E. Kálmán, Corrosion protection of cold-rolled steel by zinc-rich epoxy paint coatings loaded with nano-size alumina supported polypyrrole, Corrosion Science, 53 (2011) 3486-3499.
[2] G. Canosa, P.V. Alfieri, C.A. Giudice, Environmentally friendly, nano lithium silicate anticorrosive coatings, Progress in Organic Coatings, 73 (2012) 178-185.
[3] H. Marchebois, M. Keddam, C. Savall, J. Bernard, S. Touzain, Zinc-rich powder coatings characterisation in artificial sea water, Electrochimica Acta, 49 (2004) 1719-1729.
[4] D.D.N. Singh, S. Yadav, Role of tannic acid based rust converter on formation of passive film on zinc rich coating exposed in simulated concrete pore solution, Surface and Coatings Technology, 202 (2008) 1526-1542.
[5] O.Ø. Knudsen, U. Steinsmo, M. Bjordal, Zinc-rich primers—Test performance and electrochemical properties, Progress in Organic Coatings, 54 (2005) 224-229.
[6] K. Schaefer, A. Miszczyk, Improvement of electrochemical action of zinc-rich paints by addition of nanoparticulate zinc, Corrosion Science, 66 (2013) 380-391.
[7] S.Y. Arman, B. Ramezanzadeh, S. Farghadani, M. Mehdipour, A. Rajabi, Application of the electrochemical noise to investigate the corrosion resistance of an epoxy zinc-rich coating loaded with lamellar aluminum and micaceous iron oxide particles, Corrosion Science, 77 (2013) 118-127.
[8] R.N. Jagtap, P.P. Patil, S.Z. Hassan, Effect of zinc oxide in combating corrosion in zinc-rich primer, Progress in Organic Coatings, 63 (2008) 389-394.
[9] S. Fujita, H. Kajiyama, Perforation of coated steel panels on automobiles and its corrosion mechanism, Zairyo to Kankyo/ Corrosion Engineering, (2001) 115-123.
[10] Y. Cubides, H. Castaneda, Corrosion protection mechanisms of carbon nanotube and zinc-rich epoxy primers on carbon steel in simulated concrete pore solutions in the presence of chloride ions, Corrosion Science, 109 (2016) 145-161.
[11] N. Arianpouya, M. Shishesaz, M. Arianpouya, M. Nematollahi, Evaluation of synergistic effect of nanozinc/nanoclay additives on the corrosion performance of zinc-rich polyurethane nanocomposite coatings using electrochemical properties and salt spray testing, Surface and Coatings Technology, 216 (2013) 199-206.
[12] G. Parashar, M. Bajpayee, P.K. Kamani, Water-borne non-toxic high-performance inorganic silicate coatings, Surface Coatings International Part B: Coatings Transactions, 86 (2003) 209-216.
[13] M.N. Kakaei, I. Danaee, D. Zaarei, Evaluation of cathodic protection behavior of waterborne inorganic zinc-rich silicates containing various contents of MIO pigments, Anti-Corrosion Methods and Materials, Vol.60 (2013) 37-44.
[14] M.N. Kakaei, I. Danaee, D. Zaarei, Investigation of corrosion protection afforded by inorganic anticorrosive coatings comprising micaceous iron oxide and zinc dust, Corrosion Engineering, Science and Technology, Vol.48 (2013) 194-198.
[15] M. Selvaraj, S. Guruviah, The electrochemical aspects of the influence of different binders on tne corrosion protection afforded by zinc-rich paints, Surface Coatings International, 80 (1997) 12-17.
[16] S. Shreepathi, P. Bajaj, B.P. Mallik, Electrochemical impedance spectroscopy investigations of epoxy zinc rich coatings: Role of Zn content on corrosion protection mechanism, Electrochimica Acta, 55 (2010) 5129-5134.
[17] A. Meroufel, S. Touzain, EIS characterisation of new zinc-rich powder coatings, Progress in Organic Coatings, 59 (2007) 197-205.
[18] T.K. Ross, J. Wolstenholme, Anti-corrosion properties of zinc dust paints, Corrosion Science, 17 (1977) 341-351.
[19] A.C. Ferrari, F. Bonaccorso, V. Fal'ko, K.S. Novoselov, S. Roche, P. Boggild, S. Borini, F.H.L. Koppens, V. Palermo, N. Pugno, J.A. Garrido, R. Sordan, A. Bianco, L. Ballerini, M. Prato, E. Lidorikis, J. Kivioja, C. Marinelli, T. Ryhanen, A. Morpurgo, J.N. Coleman, V. Nicolosi, L. Colombo, A. Fert, M. Garcia-Hernandez, A. Bachtold, G.F. Schneider, F. Guinea, C. Dekker, M. Barbone, Z. Sun, C. Galiotis, A.N. Grigorenko, G. Konstantatos, A. Kis, M. Katsnelson, L. Vandersypen, A. Loiseau, V. Morandi, D. Neumaier, E. Treossi, V. Pellegrini, M. Polini, A. Tredicucci, G.M. Williams, B. Hee Hong, J.-H. Ahn, J. Min Kim, H. Zirath, B.J. van Wees, H. van der Zant, L. Occhipinti, A. Di Matteo, I.A. Kinloch, T. Seyller, E. Quesnel, X. Feng, K. Teo, N. Rupesinghe, P. Hakonen, S.R.T. Neil, Q. Tannock, T. Lofwander, J. Kinaret, Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, Nanoscale, 7 (2015) 4598-4810.
[20] H. Chen, M.B. Müller, K.J. Gilmore, G.G. Wallace, D. Li, Mechanically Strong, Electrically Conductive, and Biocompatible Graphene Paper, Advanced Materials, 20 (2008) 3557-3561.
[21] S. Vadukumpully, J. Paul, N. Mahanta, S. Valiyaveettil, Flexible conductive graphene/poly(vinyl chloride) composite thin films with high mechanical strength and thermal stability, Carbon, 49 (2011) 198-205.
[22] C. Mattevi, G. Eda, S. Agnoli, S. Miller, K.A. Mkhoyan, O. Celik, D. Mastrogiovanni, G. Granozzi, E. Garfunkel, M. Chhowalla, Evolution of Electrical, Chemical, and Structural Properties of Transparent and Conducting Chemically Derived Graphene Thin Films, Advanced Functional Materials, 19 (2009) 2577-2583.
[23] J.S. Bunch, S.S. Verbridge, J.S. Alden, A.M. van der Zande, J.M. Parpia, H.G. Craighead, P.L. McEuen, Impermeable Atomic Membranes from Graphene Sheets, Nano Letters, 8 (2008) 2458-2462.
[24] O.C. Compton, S. Kim, C. Pierre, J.M. Torkelson, S.T. Nguyen, Crumpled Graphene Nanosheets as Highly Effective Barrier Property Enhancers, Advanced Materials, 22 (2010) 4759-4763.
[25] B.M. Yoo, H.J. Shin, H.W. Yoon, H.B. Park, Graphene and graphene oxide and their uses in barrier polymers, Journal of Applied Polymer Science, 131 (2014) n/a-n/a.
[26] A.S. Kousalya, A. Kumar, R. Paul, D. Zemlyanov, T.S. Fisher, Graphene: An effective oxidation barrier coating for liquid and two-phase cooling systems, Corrosion Science, 69 (2013) 5-10.
[27] D. Kang, J.Y. Kwon, H. Cho, J.-H. Sim, H.S. Hwang, C.S. Kim, Y.J. Kim, R.S. Ruoff, H.S. Shin, Oxidation Resistance of Iron and Copper Foils Coated with Reduced Graphene Oxide Multilayers, ACS Nano, 6 (2012) 7763-7769.
[28] D. Prasai, J.C. Tuberquia, R.R. Harl, G.K. Jennings, K.I. Bolotin, Graphene: Corrosion-Inhibiting Coating, ACS Nano, 6 (2012) 1102-1108.
[29] M. Merisalu, T. Kahro, J. Kozlova, A. Niilisk, A. Nikolajev, M. Marandi, A. Floren, H. Alles, V. Sammelselg, Graphene–polypyrrole thin hybrid corrosion resistant coatings for copper, Synthetic Metals, 200 (2015) 16-23.
[30] K. Davies, J. Broomfield, Cathodic protection mechanism and a review of criteria, in:  Cathodic Protection of Steel in Concrete and Masonry, Second Edition, CRC Press, 2013, pp. 41-56.