Electrochemical Comparison of SAN/PANI/FLG and ZnO/GO Coated Cast Iron Subject to Corrosive Environments

ZnO/GO (Graphene Oxide) and SAN (Styrene Acrylonitrile)/PANI (Polyaniline)/FLG (Few Layers Graphene) nanocomposite coatings were produced by solution casting and sol-gel methods, respectively, to enhance corrosion resistance of ferrous based materials. Corrosive seawater and ‘produced crude oil water’ environments were selected as electrolytes for this study. Impedance and coating capacitance values obtained from Electrochemical Impedance Spectroscopy (EIS) Alternating Current (AC technique) showed enhanced corrosion resistance of nanocomposites coatings in the corrosive environments. Tafel scan Direct Current (DC technique) was used to find the corrosion rate of nanocomposite coating. SAN/PANI/FLG coating reduced the corrosion of bare metal up to 90% in seawater whereas ZnO/GO suppressed the corrosion up to 75% having the impedance value of 100 Ω. In produced water of crude oil, SAN/PANI/FLG reduced the corrosion up to 95% while ZnO/GO suppressed the corrosion up to 10%. Hybrid composites of SAN/PANI/FLG coatings have demonstrated better performances compared to ZnO/GO in the corrosive environments under investigation. This study provides fabrication of state-of-the-art novel anti corrosive nanocomposite coatings for a wide range of industrial applications. Reduced corrosion will result in increased service lifetime, durability and reliability of components and system and will in turn lead to significant cost savings.


Introduction
Corrosion is an electrochemical phenomenon which leads to severe component, system and structural deteriorations. Various operational conditions lead to corresponding corrosion failure mechanisms such as pitting, crevice, uniform, galvanic and microbial corrosion. Combined with static or dynamic stresses corrosion often leads to corrosion fatigue, fretting and stress corrosion cracking. These damages cause replacement, unscheduled maintenance, reduced capacity, idle time

Sample Preparation
Ductile cast iron industrial pipeline samples were used as substrates. Samples were prepared iñ 4 × 4 cm 2 squared sections. Samples were ground with abrasive paper of 120-320 grades in order to develop a texture for adhesion of nanocomposites coating. Table 1 shows composition of the pipeline cast iron used for study.

Preparation of Polyaniline
Chemical oxidation polymerization technique was used to prepare conductive Polyaniline (PANI). 6 g of aniline monomer was mixed in 100 mL deionized water using a vessel fixed with a stirrer and equipped with ice bath for low temperature arrangement. Conductivity of the solution was improved by adding 1 M solution of HCl to obtain aniline hydrochloride; a continuous stirring was ensured during addition. As a surfactant, 1 M solution of Sodium Dodecyl Sulfate (SDS) was added. To start polymerization, 1.2 g APS (Ammonium per sulfate) was dissolved as initiator in a 20 g of deionized water. Gradual addition of the above solution was facilitated using a stirring mechanism while the low temperature (0 • C) was maintained with the help of an ice bath; the mixing continued for one hour. The stirring continued for one a half hour at room temperature. Methanol was used to facilitate precipitation followed by washing using deionized water for multiple times. Final drying was performed in an oven at 50 • C. A green colored PANI powder was the final product. Initially, methanol precipitation was performed. The polymer was then washed by using distilled water, this process of conditioning with distilled was repeated several times. After washing the precipitate, it was dried in an oven at 50 • C. A green colored PANI powder was produced as the final product from the above process.

Preparation of SAN/PANI/FLG Nano Composite
Thin film of nanocomposite coating was prepared through solution casting method. SAN polymer was added to 1,2-dichloroethane and then continuously stirred for 40 min in order to completely dissolve the constituents of the solution. Then PANI was slowly added; and the solution color turned dark green. Solution was probe sonicated and stirred overnight for proper dispersion of PANI. Once the SAN and PANI was completely dissolved, then an appropriate quantity of FLG was added. The solution was then subjected to probe sonication for 45 min to disperse the PANI and FLG. The acquired solution was kept on overnight stirring after which the nanocomposite was ready to coat on the substrate. Mechanical properties of the SAN/PANI/FLG thin film are shown in Table 3. (a) Synthesis of ZnO Nanoparticle Sol Gel Zinc Acetate Dehydrate (ZnAcDH) was used as a precursor in the synthesis. Isopropanol alcohol was used as the solvent. Ethanol amine was used as stabilizer in a specific amount for the preparation of 0.4 M ZnO sol. It was then stirred until opaque solution turned into transparent one i.e., ZnAcDH was completely dissolved. The resultant solution was left for 24 h for aging. The ingredients are given in the Table 4. A solution containing 0.5 mg/1 mL of graphene oxide in 2-methoxyethanol was formulated and prepared. For proper dispersion of graphene oxide, sonication was performed for 45 min in ultrasonic water bath. Both graphene oxide and ZnO solutions were mixed together. The obtained ZnO nanoparticles had 13 nm to 22 nm size range.

Dip Coating
Dip coating is a time efficient and most commercially adapted technique for coating purposes. Dip coating process involves five steps: (i) Immersion; (ii) Dwell time; (iii) Deposition; (iv) Drainage; and (v) Evaporation. Samples were dipped in the solution for 3 min. Dwell time was kept 0.5 min to achieve desired thickness. When the solution was properly deposited on the metal samples, the coated samples were then placed in an oven to drive off the solvent from the solution resulting in a meaningful deposition of thin films. Coating thicknesses were kept in a range from 5 to 7 µm, by controlling the process parameter e.g., dwell time etc. using the Landau-Levich equation. Coating thickness was measured by surface profilometry and further manually confirmed by micrometer screw gauge and Landau-Levich equation.

Electrochemical Testing
Gamry ® framework (Series G-750, Gamry Instruments, Inc., Warminster, PA, USA) equipped with DC corrosion testing as (Gamry Instruments, Inc.) EIS, was employed for all electrochemical measurements. EIS and Tafel scans were conducted by using three-electrode cell. The reference and counter electrodes in the cell were a Saturated Calomel Electrode (SCE) and a graphite rod respectfully. Metal samples of 4 cm × 4 cm dimensions were used. The surfaces were masked using epoxy leaving an exposed area of 3 cm × 3 cm. Two types of corrosive environments were used as electrolytes for investigation: (i) simulated seawater (pH slightly basic (7.9) and conductivity between ≥50 mS/cm); and (ii) a sample of produced water obtained from a local petroleum sector (pH 7.6) and bulk conductivity~150 µS/cm).

Equivalent Circuit Modeling
Equivalent circuit model of the cell system with input parameters is shown in Figure 1. It was used for fitting the curves to obtain pore resistance and coating capacitance values of two nanocomposites systems using Reap2cpe model. The determined values are shown in the Table 5. ` Gamry ® framework (Series G-750, Gamry Instruments, Inc., Warminster, PA, USA) equipped with DC corrosion testing as (Gamry Instruments, Inc.) EIS, was employed for all electrochemical measurements. EIS and Tafel scans were conducted by using three-electrode cell. The reference and counter electrodes in the cell were a Saturated Calomel Electrode (SCE) and a graphite rod respectfully. Metal samples of 4 cm × 4 cm dimensions were used. The surfaces were masked using epoxy leaving an exposed area of 3 cm × 3 cm. Two types of corrosive environments were used as electrolytes for investigation: (i) simulated seawater (pH slightly basic (7.9) and conductivity between ≥50 mS/cm); and (ii) a sample of produced water obtained from a local petroleum sector (pH 7.6) and bulk conductivity ~150 μS/cm).

Equivalent Circuit Modeling
Equivalent circuit model of the cell system with input parameters is shown in Figure 1. It was used for fitting the curves to obtain pore resistance and coating capacitance values of two nanocomposites systems using Reap2cpe model. The determined values are shown in the Table 5.

Surface Morphology
The surface morphology of the samples was studied before and after the corrosion test to observe the damage and deterioration caused by the corrosive environments. This morphological study was conducted by using Scanning Electron Microscope (JOEL JSM-6490A, JEOL USA, INC., Peabody, MA, USA).

Electrochemical Impedance Spectroscopy (EIS) in Seawater
Seawater was used as a corrosive medium to test the coated samples by using EIS and Tafel scan and compared their corrosion resistance with bare metal sample. It is shown in the Figure 2 that the impedance value of bare metal approached 50 Ω which was the indication of the low resistance of the metal sample against corrosion. Among the coating systems, SAN/PANI/FLG coating has shown higher impedance value of 250 Ω whereas impedance of ZnO/GO coating was approximately 100 Ω indicating the higher protection capability of SAN/PANI/FLG coating in seawater compared with ZnO/GO system.

Surface Morphology
The surface morphology of the samples was studied before and after the corrosion test to observe the damage and deterioration caused by the corrosive environments. This morphological study was conducted by using Scanning Electron Microscope (JOEL JSM-6490A, JEOL USA, INC., Peabody, MA, USA).

Electrochemical Impedance Spectroscopy (EIS) in Seawater
Seawater was used as a corrosive medium to test the coated samples by using EIS and Tafel scan and compared their corrosion resistance with bare metal sample. It is shown in the Figure 2 that the impedance value of bare metal approached 50 Ω which was the indication of the low resistance of the metal sample against corrosion. Among the coating systems, SAN/PANI/FLG coating has shown higher impedance value of 250 Ω whereas impedance of ZnO/GO coating was approximately 100 Ω indicating the higher protection capability of SAN/PANI/FLG coating in seawater compared with ZnO/GO system.

DC Corrosion Testing: Tafel Scan in Seawater
Corrosion rate data from DC corrosion testing is given in Table 6 and the 'E-log i' curves are shown in Figure 4. It was revealed that the corrosion of bare metal was reduced up to 85% by SAN/PANI/FLG nanocomposite coating on the metal, whereas ZnO/GO coating suppressed the corrosion rate up to 75% of the bare metal as shown in the Table 6. As mentioned corrosion potential was also shifted to more positive directions for coated metal indicating improvement in corrosion resistance due to coatings [23][24][25]. The phase shift difference in bare metal and the coated metal is also superimposed in Figure 2. The phase shift of ZnO/GO was found higher than SAN/PANI/FLG coating revealing a better capacitive behavior of ZnO/GO. It could be aligned to the greater surface activity of nano-ZnO that improved the absorption of water on its surface that increased the density of coating and blocked the passages of electrolyte through the coating, thereby improving the barrier protection against corrosion [21][22][23]. Mostafaei [23] reported similar work and studied the effect of Polyaniline and ZnO on corrosion protection. It was reported that the barrier against the corrosion of Epoxy/PANI/ZnO was 3 times higher by magnitude than Epoxy/PANI coating, and was 4 times higher than Epoxy coating [23]. Figure 3 displays Nyquist plots which appeared to agree with the Bode plots. SAN/PANI/FLG coated samples exhibited higher impedance value and thus higher corrosion resistance than ZnO/GO coated samples. Values of EIS parameters i.e., pore resistance (R pore ), coating capacitance (C c ), uncompensated/solution resistance (R u or R soln ), polarization resistance (R p or R corr ) and double layer capacitance (C dl or C corr ) obtained by fitting the respective curves through Reap2cpe (Rapid Electrochemical Assessment of Paint (REAP), Constant Phase Element (CPE)) model are shown as below in Table 5.

DC Corrosion Testing: Tafel Scan in Seawater
Corrosion rate data from DC corrosion testing is given in Table 6 and the 'E-log i' curves are shown in Figure 4. It was revealed that the corrosion of bare metal was reduced up to 85% by SAN/PANI/FLG nanocomposite coating on the metal, whereas ZnO/GO coating suppressed the corrosion rate up to 75% of the bare metal as shown in the Table 6. As mentioned corrosion potential was also shifted to more positive directions for coated metal indicating improvement in corrosion resistance due to coatings [23][24][25].
Polyaniline shifts the potential to the noble directions which is presumed to generation of passive oxide layer providing an alternative conducting path for the electron flow. PANI passivates The EIS data given in Table 5 was found helpful in determining the performance of coatings in corrosive environment. As shown in Table 5, SAN/PANI/FLG had higher pore resistance (R pore ) than ZnO/GO coating indicating better electrochemical stability and corrosion resistance of the polymeric nanocomposite in seawater environment as compared to ceramic base nanocomposite system. The higher value of pore resistance can be attributed to reduced formation of pores in the coating, restricting the ability of the electrolyte to reach the metal's surface, thereby decreasing the corrosion [15][16][17][18][19][20]; pore resistance parameters are also important for defining the chemical stability of coating in corrosive environment.
Coating capacitance of SAN/PANI/FLG system was found higher compared to ZnO/GO coating in seawater. It shows that the SAN/PANI/FLG has better water uptake and dielectric properties than ZnO/GO. The diffusion of electrolyte leads to diffusion of corrosive ions through thin film that expectedly affects the coating capacitance. Coating capacitance usually increases significantly with the increase of defects in the coating, when exposed to corrosive environment. This behavior was noticed in a few cases after immersion for short durations in aggressive environment, the value of C c initially increased and then decreased gradually, presumably, a deposition of corrosion residues in pinholes and defects takes place, resulting in blocking the diffusion of corrosive species and H 2 O molecules into the coating [8].

DC Corrosion Testing: Tafel Scan in Seawater
Corrosion rate data from DC corrosion testing is given in Table 6 and the 'E-log i' curves are shown in Figure 4. It was revealed that the corrosion of bare metal was reduced up to 85% by SAN/PANI/FLG nanocomposite coating on the metal, whereas ZnO/GO coating suppressed the corrosion rate up to 75% of the bare metal as shown in the Table 6. As mentioned corrosion potential was also shifted to more positive directions for coated metal indicating improvement in corrosion resistance due to coatings [23][24][25]. ` create the passive layer on the interface of metal and coating [25][26][27]. PANI functions as self-healing coating and this cyclic process helps in effective corrosion protection [25][26][27]. Wei-Kang Lu [11] reported the effect of polyaniline in protecting mild steel and shifting the corrosion potential to positive direction. This protection capability of Polyaniline to generate a passive oxide layer on the surface of the substrate has been discussed [11]. Corrosion protection of graphene is linked to several facts. It is hydrophobic due to which it resists hydrogen bonding with water while in parallel it has ability to prevent oxidation of metal. Its nano-sized structural defects lead to limited passivation. Moreover, it suppresses ion conduction preventing the formation of galvanic cells resulting in better protection properties [2,5].
The obtained value of the desired parameters confirmed better protection ability of SAN/PANI/FLG system due to lower value of corrosion rate as compared to that of ZnO/GO system.   Polyaniline shifts the potential to the noble directions which is presumed to generation of passive oxide layer providing an alternative conducting path for the electron flow. PANI passivates the pinholes through iron oxide on metal substrate surface. Polyaniline transfers the electron transport from metal surface to the outer surface of primer. Generally, in the process of corrosion protection, the release of acid dopant (camphorsulphonic acid) results in polyaniline leucosalt (PANI-LS) due to the reduction of polyaniline-emeraldine salt. The formation of a passive iron ions film within the defect sites is facilitated by these sulphonic ions. PANI-LS are re-oxidized by dissolved oxygen to PANI-ES. In other words, it can be assumed that at first PANI gets the ions that are released in the corrosion process of iron and gets doped. Once it gets doped, it releases the dopant ions which create the passive layer on the interface of metal and coating [25][26][27]. PANI functions as self-healing coating and this cyclic process helps in effective corrosion protection [25][26][27]. Wei-Kang Lu [11] reported the effect of polyaniline in protecting mild steel and shifting the corrosion potential to positive direction. This protection capability of Polyaniline to generate a passive oxide layer on the surface of the substrate has been discussed [11].

Surface Morphology in Seawater
Corrosion protection of graphene is linked to several facts. It is hydrophobic due to which it resists hydrogen bonding with water while in parallel it has ability to prevent oxidation of metal. Its nano-sized structural defects lead to limited passivation. Moreover, it suppresses ion conduction preventing the formation of galvanic cells resulting in better protection properties [2,5].
The obtained value of the desired parameters confirmed better protection ability of SAN/PANI/FLG system due to lower value of corrosion rate as compared to that of ZnO/GO system. Figure 5 shows that the surface morphology of the coating as observed under Scanning Electron Microscopy (SEM); the surface was altered by corrosion, but no significant cracks were developed in the coating indicating that the polymeric based coating afforded better protection properties. Figure 6 displays damage to ZnO/GO coating after the tests in which morphology was significantly changed by the cracks which are produced in the process of protection.

Surface Morphology in Seawater
Materials 2018, 11, x FOR PEER REVIEW 9 of 15 ` Figure 5 shows that the surface morphology of the coating as observed under Scanning Electron Microscopy (SEM); the surface was altered by corrosion, but no significant cracks were developed in the coating indicating that the polymeric based coating afforded better protection properties. Figure  6 displays damage to ZnO/GO coating after the tests in which morphology was significantly changed by the cracks which are produced in the process of protection.

EIS Measurements in Crude Oil Produced Water
Crude oil produced water holds various types of compounds and hydrocarbons along with impurities, which are aggressive and potentially harmful towards corrosion. EIS and DC corrosion tests were performed for bare metal and, SAN/PANI/FLG and ZnO/GO coated samples. Figure 7 displays Bode plots for bare metal, SAN/PANI/FLG coating and ZnO/GO coating. The graphs exhibit variation in impedance values of various systems and highlights phase shifts. SAN/PANI/FLG performed much better in this environment and offered better protection as compared to that of ZnO/GO and bare metal.
Relatively higher value of impedance approaching to 1000 Ω of SAN/PANI/FLG in produced water was noticed, whereas, the impedance of ZnO/GO was approximately 90 Ω. Likewise, the behavior in seawater environment, ZnO/GO also demonstrated a higher value of phase shift compared to SAN/PANI/FLG coating when exposed to produced water. This indicated its better capacitive and dielectric properties. However, being chemically unstable in this environment, it could not offer any significant resistance against corrosion [28,29]. ` Figure 5 shows that the surface morphology of the coating as observed under Scanning Electron Microscopy (SEM); the surface was altered by corrosion, but no significant cracks were developed in the coating indicating that the polymeric based coating afforded better protection properties. Figure  6 displays damage to ZnO/GO coating after the tests in which morphology was significantly changed by the cracks which are produced in the process of protection.

EIS Measurements in Crude Oil Produced Water
Crude oil produced water holds various types of compounds and hydrocarbons along with impurities, which are aggressive and potentially harmful towards corrosion. EIS and DC corrosion tests were performed for bare metal and, SAN/PANI/FLG and ZnO/GO coated samples. Figure 7 displays Bode plots for bare metal, SAN/PANI/FLG coating and ZnO/GO coating. The graphs exhibit variation in impedance values of various systems and highlights phase shifts. SAN/PANI/FLG performed much better in this environment and offered better protection as compared to that of ZnO/GO and bare metal.
Relatively higher value of impedance approaching to 1000 Ω of SAN/PANI/FLG in produced water was noticed, whereas, the impedance of ZnO/GO was approximately 90 Ω. Likewise, the behavior in seawater environment, ZnO/GO also demonstrated a higher value of phase shift compared to SAN/PANI/FLG coating when exposed to produced water. This indicated its better capacitive and dielectric properties. However, being chemically unstable in this environment, it could not offer any significant resistance against corrosion [28,29].

EIS Measurements in Crude Oil Produced Water
Crude oil produced water holds various types of compounds and hydrocarbons along with impurities, which are aggressive and potentially harmful towards corrosion. EIS and DC corrosion tests were performed for bare metal and, SAN/PANI/FLG and ZnO/GO coated samples. Figure 7 displays Bode plots for bare metal, SAN/PANI/FLG coating and ZnO/GO coating. The graphs exhibit variation in impedance values of various systems and highlights phase shifts. SAN/PANI/FLG performed much better in this environment and offered better protection as compared to that of ZnO/GO and bare metal.

`
Rpore values for SAN/PANI/FLG and ZnO/GO coatings. This indicates a better electrochemical stability and corrosion resistance capability of the polymeric nanocomposite system in produced water as compared to ceramic nanocomposite coating.
Coating capacitance of ZnO/GO was observed to be slightly higher than SAN/PANI/FLG coating indicating larger water absorption and dielectric nature of ceramic nanocomposite than the polymeric nanocomposite [8].  Relatively higher value of impedance approaching to 1000 Ω of SAN/PANI/FLG in produced water was noticed, whereas, the impedance of ZnO/GO was approximately 90 Ω. Likewise, the behavior in seawater environment, ZnO/GO also demonstrated a higher value of phase shift compared to SAN/PANI/FLG coating when exposed to produced water. This indicated its better capacitive and dielectric properties. However, being chemically unstable in this environment, it could not offer any significant resistance against corrosion [28,29].
As evident from Figure 8, Nyquist plots verified relatively higher corrosion resistance of SAN/PANI/FLG system in crude oil produced water compared with its ceramic counterpart.
Significantly higher values of impedance for SAN/PANI/FLG system were observed skewing the other two systems. The Nyquist plots showed a few suppressed semicircles representing a capacitance which is slightly deviating from ideal behavior [30]. Generally, the Nyquist plots of all coatings appeared to be semicircles with their centers on the x-axis (impedance), it would appear that the characteristics of the system influences the suppressed semicircles. It can also be attributed to few inhomogeneous features of the system such as non-uniform distribution of various surface properties at various locations over the electrode surface [26,31,32].
Values of R pore and C c are mentioned in Table 7, which displays a significant difference in the R pore values for SAN/PANI/FLG and ZnO/GO coatings. This indicates a better electrochemical stability and corrosion resistance capability of the polymeric nanocomposite system in produced water as compared to ceramic nanocomposite coating. ` Figure 8. Comparison of Nyquist Plot (crude oil produced water).

DC Corrosion Testing-Tafel Scan in Crude Oil Produced Water
Tafel scan results validate EIS data regarding the performance of the nanocomposites coatings in produced water. Both coatings exhibited improved corrosion resistance compared to uncoated metal. Corrosion resistance of SAN/PANI/FLG coating was observed to be significantly better compared to ZnO/GO coating, as displayed in Figure 9, the data is summarized in Table 8. As evident from Table 8 and Figure 9, ZnO/GO system did not prove to be protecting and the corrosion rate was found to be very close to bare metal. The SAN/PANI/FLG system, however, exhibited about 27 times reduction in the rate of corrosion compared with bare iron metal. Both the nanocomposites coatings, however, shifted the Ecorr value towards positive direction. The potential values display a qualitative check for aggressiveness of the electrolyte towards the working electrode, whereas, the quantitative data is based on the current values. In Figure 9, the potentials of the two coated samples although were in close vicinity, however, there position in terms of current were quite distant, presumably due to breakdown of the coating in the electrolyte used. Coating capacitance of ZnO/GO was observed to be slightly higher than SAN/PANI/FLG coating indicating larger water absorption and dielectric nature of ceramic nanocomposite than the polymeric nanocomposite [8].

DC Corrosion Testing-Tafel Scan in Crude Oil Produced Water
Tafel scan results validate EIS data regarding the performance of the nanocomposites coatings in produced water. Both coatings exhibited improved corrosion resistance compared to uncoated metal. Corrosion resistance of SAN/PANI/FLG coating was observed to be significantly better compared to ZnO/GO coating, as displayed in Figure 9, the data is summarized in Table 8.
As evident from Table 8 and Figure 9, ZnO/GO system did not prove to be protecting and the corrosion rate was found to be very close to bare metal. The SAN/PANI/FLG system, however, exhibited about 27 times reduction in the rate of corrosion compared with bare iron metal. Both the nanocomposites coatings, however, shifted the E corr value towards positive direction. The potential values display a qualitative check for aggressiveness of the electrolyte towards the working electrode, whereas, the quantitative data is based on the current values. In Figure 9, the potentials of the two coated samples although were in close vicinity, however, there position in terms of current were quite distant, presumably due to breakdown of the coating in the electrolyte used. ` Figure 9. 'E-log i' curves-bare and coated samples in (crude oil produced water). Figure 10 displays SAN/PANI/FLG coated surface before and after corrosion testing in produced water the micrographs exhibit a partial degradation appearing in the form of micro-cracks in the coating after corrosion testing. The surface, however, did not appear to be damaged thoroughly, indicating relatively better resistance against corrosive attack by produced water. Figure 11 shows morphology of ceramic nanocomposite coated surface. It was evident that the ceramic coating appeared to be significantly damaged after corrosion testing, indicating its weak resistance against corrosive attack of produced water.   Figure 10 displays SAN/PANI/FLG coated surface before and after corrosion testing in produced water the micrographs exhibit a partial degradation appearing in the form of micro-cracks in the coating after corrosion testing. The surface, however, did not appear to be damaged thoroughly, indicating relatively better resistance against corrosive attack by produced water.

Surface Morphology in Crude Oil Produced Water
Materials 2018, 11, x FOR PEER REVIEW 12 of 15 ` Figure 9. 'E-log i' curves-bare and coated samples in (crude oil produced water). Figure 10 displays SAN/PANI/FLG coated surface before and after corrosion testing in produced water the micrographs exhibit a partial degradation appearing in the form of micro-cracks in the coating after corrosion testing. The surface, however, did not appear to be damaged thoroughly, indicating relatively better resistance against corrosive attack by produced water. Figure 11 shows morphology of ceramic nanocomposite coated surface. It was evident that the ceramic coating appeared to be significantly damaged after corrosion testing, indicating its weak resistance against corrosive attack of produced water.   Figure 11 shows morphology of ceramic nanocomposite coated surface. It was evident that the ceramic coating appeared to be significantly damaged after corrosion testing, indicating its weak resistance against corrosive attack of produced water.