Corrosion Protection Polybutadiene-Coated Mild Steel in Marine Water by Nanocoating and Filler Compounds

Mild steel is economical metal so it is used in different appliances of industries, railways, bridges, construction works and marine water. Marine water produces corrosive environment for this metal. Marine water is saline in character so it corrodes mild steel. Polybutadiene is coated on the surface of mild steel for corrosion protection. But this coating does not provide sufficient protection of base metal. Marine water is major absorber of CO 2 . It converts CO 2 into H 2 CO 3 . Saline water and H 2 CO 3 interacts with polybutadiene-coated mild steel and they exhibit chemical and electrochemical reactions. This chemical reaction produces swelling and dissolving corrosion and produce disbonding between carbon and carbon of polybutadiene. These corrosive agents show osmosis or diffusion process and inter inside the base metal and develop corrosion cell. Metal generates corrosion reaction which produces several forms of corrosion like galvanic, pitting, crevice, stress, intergranular, blistering and embrittlement. For the protection from such types of corrosions synthesized organic compounds octahydrodibenzo[a,d][8]annulene-5,12-dioxime nanocoated on surface of developed mild they


Introduction
Research & Development in Material Science 2/7 Res Dev Material Sci dioxime and immersed into sea water and corrosion rate recorded at above mentioned temperatures and days. Nanocoated samples were coated by ZnS filler and dipped into sea water to calculate the corrosion rate given temperatures and days. The corrosion potential, corrosion current and corrosion current densities were calculated by potentiostat technique. For these results pt electrode used as reference electrode, calomel as auxiliary electrode and polybutaine-coated mild steel sample electrode. Nanocoated compound octahydrodibenzo[a,d] [8]annulene-5,12-dioxime was synthesized by given methods as:   When 3, 4-dihydronaphthalen-1(2H)-one (25gm) is added into cold solution of benzene (50gm) containing PCl 5 (30gm), the reaction mixture was stirred for one hour. The reaction mixture was quenched with NaHCO 3 and did workup with diethyl ether. The solvent evaporated with rotator vapour. The product was purified by silica gel column chromatography and produced 89% 4-chloro-1, 2-dihydonaphthalene (Figure 1-4).

Synthesis of octahydrodibenzo[a,d][8]annulene-5,12dioxime
Octahydrodibenzo[a,d] [8]annulene-5,12-dione (30g), hydroxylamine hydrochloride (50g) and 135ml of dry ethanol were taken and adding 70ml of pyridine and refluxing reaction mixture for two hours. Solvent was removed by use of rotator vapour and water was added in reaction mixture and after cooling the reaction by ice, solution was stirred until oxime crystallized. Solid was filtered and washed with a little water and then dried. The product was recrystallized with ethanol and 71% yield of octahydrodibenzo[a,d] [8]annulene-5,12-dioxime was obtained Figure 13

Results and Discussion
Marine water generates hostile environment for polybutadienecoated mild steel. Corrosion is control in such hostile environment by the use of nanocoating and filler materials. Polybutadienecoated mild steel corrosion rates were studied in marine water environment at 283, 293, 303, 313 and 323 0K temperatures after interval of 2, 5, 8, 11 and 14days with the help of gravimetric method equation K(mmpy) = 13.56 X(W/DAt) (where W=weight loss of test coupon expressed in kg, A=area of test coupon in square meter, D=Density of the material in kg. m -3 ) and their values recorded in Table 1. Similarly, the samples of polybutadiene-coated mild steel nanocoated with octahydrodibenzo[a,d] [8]annulene-5,12-dioxime and ZnS filler were immersed into marine water and corrosion rate was calculated on above mentioned temperatures and days and their values were mentioned in Table 1, Figure 15 plotted between corrosion rate K(mmpy) versus times (t) in days which produced straight line and it indicated that corrosion rate of polybutadiene-coated mild steel increased without coating and their values were reduced after nanocoating and filler compounds. The results of Table 1 were shown that the corrosion rate of material is reduced by the action of nanocoating and filler compounds. The octahydrodibenzo[a,d] [8]annulene-5,12-dioxime is an electronic rich compound and large molecular weight so it is suitable for nanocoating materials. Nanocoating compound is coordinated its electron to ZnS filler thus they can form strong barrier on the surface of polybutadiene-coated mild steel. This barrier stops osmosis or diffusion process of saline water.   Studied the effect of temperature on the polybutadiene-coated mild steel at mentioned above temperatures and their results were written in Table 1, it observed that corrosion rate of material increased without nanocoating but its values were reduced with nanocoating and filler compounds such types trends clearly noticed in Figure 16 which plotted between log K versus 1/T found to be a straight line. Nanocoating and filler compounds were formed a stable barrier with on the surface of polybutadiene-coated mild steel. This barrier has thermal stability and suppressed the attack of Cl-ions. Nanocoating and filler materials were developed composite barrier i.e. stable in saline water as temperature increased. The plot of log (θ/1-θ) versus 1/T depicted a linear graph as shown in Figure 17. The plot of Figure 17 & Table 1 results confirmed that nanocoating compound octahydrodibenzo [a,d] [8]annluene-5,12-dioxime and ZnS filler increased log (θ/1-θ) as temperature enhanced. The values of log (θ/1-θ) increased with octahydrodibenzo[a,d] [8]annluene-5,12-dioxime but its values more increased with ZnS filler in marine water system. The surface coverage area (θ) of nanocoating compound octahydrodibenzo[a,d] [8]annluene-5,12-dioxime and ZnS filler was calculated by equation θ=(1-K/K o ) (where K is the corrosion rate before coating and Ko is the corrosion rate after coating) and their values were mentioned in Table 1. Figure 18 plotted between surface coverage (θ) versus temperature (T) which indicated that filler compound covered more surface area with respect of nanocoating compound octahydrodibenzo[a,d] [8]annluene-5,12-dioxime. The low dose of nanocoating and filler compounds were occupied more surface coverage area as temperatures were increased. These results were given information that as temperatures were risen nanocoating and filler compounds were accommodated more surface areas.  Table 1. Figure 19 plotted between %CE (percentage coating efficiency) versus T (temperature) indicated that filler compound enhanced percentage coating efficiency with respect of nanocoating compound. Nanocating and filler compounds were electron rich compound so they have more binding capacities. Activation energy of polybutadiene-coated mild steel, nanocoating compound octahydrodibenzo[a,d] [8]annulene-5,12-dioxime and ZnS filler were determined by Arrhenius equation, d/dt (log K)=E a /RT 2 (where T is temperature in Kelvin, R is universal gas constant and E a is the activation energy of the reaction) and Figure 16 which plotted between log K versus 1/T. The calculated values of activation energies were mentioned in Table 2. Polybutadiene-coated mild steel produced high activation energies at different temperatures in marine water whereas nanocoating and filler compounds exhibited lower activation energy. The results of activation energies were shown that nanocoating and filler compounds adhered on the surface of polybutadiene-coated mild steel by chemical bonding Table 2. Thermal parameters of nanocoating compound octahydrodibenzo [a,d] [8]annulene-5,12dioxime and ZnS filler coated on polybutadiene-coated mild steel in marine water heat of adsorption of nanocoating compound octahydrodibenzo[a,d] [8]annulene-5,12-dioxime and ZnS filler were calculated by Langmuir equation, log (θ/1-θ) = log (A .C) -(q ads / 2.303 RT) (where T is temperature in Kelvin and q ads heat of adsorption) and Figure 17 plotted against log(θ/1-θ) versus 1/T which produced straight lines. Heat adsorption values found to be negative with nanocoating and filler compounds so the formation of composite barrier is a chemical process. These compounds were adhered with base material by chemical bonding.

Research & Development in Material Science
Free energies of both compounds give information that coating is an exothermic process. It is clear by data calculated for octahydrodibenzo[a,d] [8]annulene-5,12-dioxime and ZnS filler with the help of equation, ΔG =-2.303RT log (33.3K) (where R is universal gas constant, T be temperature and K corrosion rate) and their values were written in Table 2 and plotted in Figure 20. Both compounds were produced a negative heat of adsorption which indicated that they formed chemical bonding during nanocoating process.   Figure 21 and their values were recorded in Table 2. The results of enthalpy and entropy were shown that both compounds were adsorbed with the base materials by chemical bonding. Such coating is an exothermic process. The negative entropy indicated that nanocoating and filler compounds accommodated on the surface of polybutadienecoated mild steel in an ordered matrix. Figure 21 plotted between free energy (∆G) and temperatures for surface coverage area (θ) occupied by octahydrodibenzo[a,d] [8]annulene-5,12-dioxime and ZnS filler that confined free energy decreased when temperatures increased but at this moment surface coverage area was enhanced. The corrosion potential, corrosion current and corrosion current density of polybutadiene-coated mild steel, nanocoated octahydrodibenzo[a,d] [8]annulene and ZnS filler were calculated by equation, ∆E/∆I = β a β c /2.303 Icorr (β a +β c ) (where ∆E/∆I is the slope which linear polarization resistance (R p , β a and β c are anodic and cathodic Tafel slope respectively and I corr is the corrosion current density in mA/cm 2 ) and Tafel plot between electrode potential (∆E) versus current density (I) and their values were mentioned in (Table 3). It was observed that electrode potential and corrosion current density were high with polybutadiene whereas anodic current density increased and cathodic density current reduced. But octahydrodibenzo[a,d] [8]annulene-5,12dioxime and ZnS filler reduced electrode potential and corrosion current density. Tafel plot of Figure 22 and the results of Table 3 indicated that nanocoating and filler compounds minimized anodic current and maximized cathodic current. These results confirmed that nanocoaing and filler compounds developed a strong barrier on the polybutadiene-coated mild steel which neutralized the attack of saline water and carbonic acid.  The corrosion current was obtained by above equation and Tafel graph of Figure 22 for polybutadiene-coated mild steel, nanocoated octahydrodibenzo [a,d] [8]annulene and ZnS filler and these values were put in equation, C. R (mmpy) = 0.1288 I (mA/ cm 2 ) × Eq .Wt (g) / ρ (g/cm 3 ) (where I is the corrosion current density ρ is specimen density and Eq. Wt is specimen equivalent weight) and their values were recorded in Table 3. It was noticed that corrosion rate increased with polybutadiene-coated mild steel and these values were reduced with nanocoating and filler compounds. The results of corrosion rate measured by weight loss experiment are confirmed the results of potentiostat. Potentiostat polarization of octahydrodibenzo[a,d] [8]annulene-5,12-dioxime and ZnS nanocoated on polybutadiene-coated mild steel in marine water (Table 3).

Conclusion
It is very difficult to control corrosion of marine water. Polybutadiene-coated mild steel uses in marine water for different works but this material is face corrosion problem. In this research, it is tried to check corrosion of polybutadiene mild steel by the application of nanocoating compound octahydrodibenzo[a,d] [8] annulene-5,12-dioxime and filler ZnS. The corrosion activities of polybutadiene was studied at 283 0K, 293 0 K, 303 0 K, 313 0 K and 323 0 K temperatures and the concentration of nanocoating and filler compounds were taken in 50mM and 10mM. The results of surface coverage areas and coating efficiencies of nanocoating and filler compounds were indicated these compounds had more coverage capability. Nanocoating and filler compounds results of activation energy, heat of adsorption, free energy, enthalpy and entropy were shown that these compounds were attached with base material by chemical bonding. They can form composite thin film barrier which is passive in corrosive environment. Filler material blocks the porosities of nanocoating compounds and stop osmosis or diffusion process of corrosive agents.