SOJ Materials Science & Engineering

Epoxy coating uses for the corrosion protection of stainless steel. Epoxy-coated stainless steel surface has possessed lots of porosities so pollutants and particulates materials are entered inside by osmosis and diffusion process. Pollutants like oxides of carbon, oxides of nitrogen, and oxides of sulphur form acids and they make hostile environment for base metal and epoxy polymer. These acids develop chemical reaction with epoxy-coated stainless steel. They develop corrosion cell with metal and start corrosion reaction. They can produce several forms corrosion like galvanic, pitting, stress, crevice, blistering and embrittlement. Epoxy polymer is shown swelling corrosion. Such types of pollutants are disintegrated metal and polymer and change their physical, chemical and mechanical properties. Weather changes can affect the corrosion rate of materials because the compositions of corrosive substances increase or decrease temperatures of atmosphere, concentration of pollutants, moisture, humidity and acids. They initiate the corrosion of materials. The corrosion protection of epoxy-coated stainless steel was controlled by the application of synthesized decahydrobenzo [8] annulene-5, 10-disemicarbazone and this compound was nanocoated on the surface of epoxy-coated stainless steel. Nanocoating and filler materials were formed composite a thin barrier on the surface of epoxy-coated stainless steel and studied their action in corrosion in hostile environment. Nanocoating work can be completed by the use of nozzle spray and chemical vapor deposition. Thermal parameters like activation energy, heat of adsorption, free energy, enthalpy and entropy were used to study composite film formation. The corrosion rates of materials were calculated by gravimetric method. Surface coverage areas and coating efficiencies were obtained by the help of corrosion rate. Potentiostat used to determine corrosion potential, corrosion current and current density. Experimental observations indicated that composite film barrier was formed decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin which physical, chemical and mechanical properties did not change easily in ambient environment.

Keywords: Hostile environment; corrosion; nanocoating; filler; thermal parameters; composite film barrier;

The corrosion of materials is a spontaneously process. It is not fully control but it can be minimized by the application of corrosion protection technique. Epoxy paint is used by automobile industries for corrosion protection. The outer bodies of transport vehicles are made of stainless steel. This metal corrodes in contact of corrosive environment, hence for their protection epoxy-coating is applied on the surface of stainless steel. But this coating cannot protect stainless steel in H₂O, O₂ (moist), CO₂, NO₂ and SO₂ environment. In these environments for the corrosion protection of epoxy-coated stainless steel was used decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin. The synthesized organic compound decahydrobenzo [8] annulene-5, 10-disemicarbazone was nanocoated on the surface of epoxy-coated stainless steel and their porosities were blocked by Tin filler.

Abrasive blasting is a common method of preparing a metal surface for application of an organic coating [1]. The performance of an organic coating/metal [2] substrate system in a corrosive environment depends on the nature of the coating, substrate, and interface [3] between them. The properties of the interfacial region [4] are influenced by the abrasive blasting process. The corrosion behavior of coated stainless steel [5] is significantly affected by the choice of blasting abrasive and the parameters of the blasting process. They investigate the adhesion of polymer coating [6] systems of the following types: alkyd, acrylic, latex, vinyl, epoxy, coal tar epoxy [7] and a zinc-filled vinyl [8]. For every case zinc-filled vinyl, steel grit abrasive produced the lowest adhesion when compared with based abrasive. The resistance to blistering of both coal tar epoxy and urethane coatings [10] on underground steel storage tanks is more severe for tanks blasted with steel grit than for those blasted with silica sand. The effect of abrasive type on the corrosion rate and catholic delaminating performance of bare and coated pipeline steel. They found a reduction in the corrosion rate in distilled water and delamination rate of an epoxy powder coating [11] in Clions solution when the steel was abrasively blasted with alumina [12] compared to steel blasted with steel grit. They interpreted the results in terms of a reduction in catalytic efficiency [13] for the operative catholic reaction for the alumina-blasted surface, and hypothesized doping of the oxide layer on the steel with aluminum. Cathodic delamination of organic coatings [14] on steel has been widely studied. It is generally believed that the high pH generated by the oxygen reduction reaction at the delaminating front is responsible for the loss of coating adhesion [15]. There are several techniques like metallic and nonmetallic coating, inhibitors action, polymeric coating and paint coating [16] used to control the corrosion. Metallic coating did not provide good protection in presence of atmospheric pollutants. Polymeric coating [17] used in corrosive environment but this coating did not control attack pollutants. They penetrate polymeric barrier and corrode base metal. Its bonding and bond connective disintegrate in this environment. The nitrogen, oxygen and sulphur containing alkane, alkene, alkyne, aromatic and heterocyclic organic compounds [18] applied as inhibitors against pollutants but they are not protecting materials. These corrosion protection techniques did not shave material by attack of biological micro and macroorganism [19]. Particulates are also increasing corrosion of materials for their protection [20] above mention methods is used but they do not give suitable results. Effluents and biowastes corrode materials but their protection above mentioned protection techniques used which do not mitigate corrosion. Mixed types of organic inhibitors used which work as anodic and catholic protection in ambient environment but these inhibitors become passive in aggressive medium. The purpose of this study is to examine composite thin film formation on the surface epoxy-coated stainless steel by nanocoating compound decahydrobenzo [8] annulene-5, 10-disemicarbazone and filler Tin.

Coupons of epoxy-coated stainless steel kept in corrosive environment and their corrosion rate determined at different temperatures, times and weathers as mentioned 2780K, 2830K, 2880K, 2930K and 2980K temperature and time fixed 24, 48, 72, 96 and 120 hours. Epoxy-coated stainless steel was nanocoated with decahydrobenzo [8] annulene-5, 10- disemicarbazone and its corrosion rate calculated at above recorded temperatures and times. Tin filler used on the surface of decahydrobenzo [8] annulene-5, 10-diphenylhydrazone and corrosion rate of material determined above mentioned temperatures and times. These results were obtained by the help of weight loss experiment. Potentiostat 173 model EG & PG Princeton used to measured corrosion potential, corrosion current, current density, anodic and catholic polarization of epoxy-coated stainless steel, decahydrobenzo [8] annulene-5,10- disemicarbazone-epoxycoated stainless steel and Tin-decahydrobenzo [8] annulene-5, 10-diphenylhydrazone-epoxy-coated stainless steel. Plasma spray used for nanocoating purpose. The surface adherence properties studied by Arrhenius equation and Langmuir isotherm equation. The composite thin film barrier bonding formation studied by activation energy, heat of adsorption, free energy, enthalpy and entropy. The synthesis process of decahydrobenzo [8] annulene-5, 10- disemicarbazone was given as:

Cyclohexanone (80g) was added in dry benzene (150ml) and reaction mixture was poured drop wise into a cool solution of PCl5. The mixture was taken in two necks round bottle flask and stirred for further 3hours and during reaction temperature was maintained OC. The product was extracted from ethereal solution and was washed with 5% aqueous Na₂CO₃ then after dried with Na₂SO₄ and solvent removed by application of rotator vapor. The product was purified by column chromatograph by the use of silica gel in petroleum ether. After purification 87% of 1-chlorocyclohexane was obtained.

The corrosion rate of metal was calculated in the above mentioned environment in absence and presence of nanocoating and filler compounds at 2780K, 2830K, 2880K, 2930K and 2980K temperatures with help of equation K = 13.56 W/A D t (where, W = weight loss of sample in kg, A = surface area of coupon in square meter, D = density in kg M-3, t = exposure time in hour). The corrosion rate of epoxy-coated stainless steel, nanocoating and filler compounds were obtained at various 24, 48, 72, 96 and 120 hours and their values recorded in (Table1). (Figure1) indicated that corrosion rate of epoxy-coated stainless steel increased absence of coating as time enhanced but these values reduced in presence of nanocoating and filler compounds. They can be improved the quality of surface and minimized corrosion reaction. Nanocoating and filler materials were formed composite thin film barrier i.e. stopped osmosis or diffusion process of pollutants.

The corrosion of epoxy-coated stainless steel logK versus 1/T in absence and presence of nanocoating and filler compound were plotted in (Figure2). (Figure2) reflect that corrosion rate of epoxy-coated stainless steel was higher as temperatures rising from 278 to 2980K. But nanocoating of decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin reduced corrosion rate as temperatures increased. Such types of trends observed clearly in (Table1). Both compounds were formed stable barrier which suppressed the corrosion of material.

(Figure3) plotted between log (θ/1-θ) versus 1/T for nanocoated decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin filler. The values of both the compounds log (θ/1-θ) at 278 to 2980K were mentioned in (Table1). The results of (Table1) and (Figure 3,4,5) indicate that nanocoating and filler compounds increased the values of log (θ/1-θ) at different temperatures in H₂O, O₂ (moist), CO₂, NO₂ and SO₂ environment.

(Figure4) plotted between surface coverage area (θ) versus temperature (T) exhibited surface accommodation properties of nanocoating decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin filler. Both compounds enhanced surface coverage area at lower to higher temperature. The surface coverage area at different temperatures calculated by equation θ = (1-K/Ko) and their values were written in (Table1). Filler Tin increased more surface coverage area which blocked the porosities of nanocoating compound.

(Figure 5) plotted between percentages coating efficiency (%CE) versus temperature (T) at different temperatures for nanocoating and filler compounds. The nature of graph shows that nanocoating decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin filler rising % coating efficiency at different temperatures. The % coating efficiency at different intervals of temperatures were calculated by equation %CE = (1-K/Ko) X 100 and their values were mentioned in (Table1).

(Figure 2) is a straight line Arrhenius plot between logK versus 1/T with help of this figure and Arrhenius equation d/ dT(lnK) = A e-Ea/RT were calculated activation energy of epoxycoated stainless steel and nanocoating of decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin filler and their values were written in (Table 2,4,5) In all case activation energy found to be positive sign. It was observed that without coating activation energy increased but their values reduced after nanocoating and filler compounds. Both compounds occupied on the surface of epoxy-coated stainless steel by chemical bonding.

(Figure 3) indicated straight line plot between log (θ/1-θ) versus 1/T for nanocoating of decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin filler and it is a plot of Langmuir isotherm. Heat of adsorption of both nanocoating and filler compounds were determined by equation log (θ/1-θ) = log (AC) – (q/2.303 R T) and (Figure 3). The values of heat of adsorption are mentioned in (Table 2). Both compounds produced negative sign of energy which confirmed that nanocoating and filler compound formed thin film on the surface of epoxy-coated stainless steel by chemical bonding.

Free energy of nanocoating of decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin filler were calculated by equation -ΔG = 2.303 log RT and their results were expressed in (Table 2). The negative values of free energy express that nanocating and filler compounds were adhered with base material by chemical bonding. Free energy results show that coating is an exothermic process.

Enthalpy and entropy of nanocoating of decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin filler were calculated by transition state equation K = R T / N h log (ΔS# / R) X log (-ΔH #/ R T) and (Figure 6) and their values are recorded in (Table 2). These thermal parameters indicated that nanocoating and filler compounds were attached with base material by chemical bonding. Entropy of both the compounds show that nanocoating and filler compounds arranged on the surface of base material in ordered matrix. Thermal values of activation energy, heat of adsorption, free energy, enthalpy and entropy were confirmed

that decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin filler were adhered with epoxy-coated stainless steel by chemical bonding. These thermal parameters also noticed that nanocoating and filler compounds formed passive barrier which stable in higher temperature and corrosive medium.

(Figure 7) draws graph between enthalpy (ΔE), entropy (ΔS) and surface coverage area (θ) versus temperatures (T) for decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin in H₂O, O₂ (moist), CO₂ and SO₂ environment. The nature of plot indicate that the values of enthalpy and entropy decreased as temperatures rise which enhanced surface coverage area such results trend were observed in (Table 2).

(Figure 8) was a Tafel plot which was drawn between electrode potential (ΔE) versus current density (I) for nanocoating decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin filler. The corrosion current and corrosion rate of epoxy-coated stainless steel and after nanocoating with decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin were calculated by equation ΔE/ΔI = βa βc / 2.303 Icorr (βa + βc) and C. R (mmpy) = 0.1288 Icorr (mA /cm²) × Eq .Wt (g) / ρ (g/cm³) and their values were mentioned in (Table 3,4,5). The results of (Table 3) and (Figure 7) confirmed that epoxy-coated stainless steel exhibited more electrode potential and corrosion current when coated with decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin their values were decreased. It was also observed that anodic current increased with epoxy-coated stainless steel whereas catholic current decreased but nanocoating and filler compounds reduced anodic current and enhanced catholic current. Potentiostat results show that nanocoating and filler compounds minimized corrosion rate and increased surface coverage area and coating efficiency.

Nanocoating compound decahydrobenzo [8] annulene-5, 10-disemicarbazone and Tin filler were formed composite barrier on the surface of epoxy-coated stainless steel. The results of thermal parameters and coating efficiencies were indicated that composite barrier is stable in corrosive environment. All scientific observations indicate that these nanocoating and filler compounds mitigate corrosion rate. The values of thermal parameters show that they form stable barrier on the surface of base material. It is noticed that these compounds accommodate more surface coverage areas. Composite barrier stops osmosis or diffusion process of pollutants. Nanocoating and filler compounds improve the life of base material and durability.

Author is thankful to The UGC-New for providing financial grant for this work. Author holds deep sense of gratitude for Professor Sanjoy Misra. Author is grateful to Professor G Udhaybhanu, IIT-Dhanbad who provided laboratory facilities.

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