Ubong Eduok

Application of carbohydrate polymers as corrosion inhibitors for metal substrates in different media: A review

Naturally occurring polysaccharides are biopolymers existing as products of biochemical processes in living systems. A wide variety of them have been employed for various material applications; as binders, coatings, drug delivery, corrosion inhibitors etc. This review describes the application of some green and benign carbohydrate biopolymers and their derivatives for inhibition of metal corrosion. Their modes and mechanisms of protection have also been described as directly related to their macromolecular weights, chemical composition and their unique molecular and electronic structures. For instance, cellulose and chitosan possess free amine and hydroxyl groups capable of metal ion chelation and their lone pairs of electrons are readily utilized for coordinate bonding at the metal/solution interface. Some of the carbohydrate polymers reviewed in this work are either pure or modified forms; their grafted systems and nanoparticle composites with multitude potentials for metal protection applications have also been highlighted. Few inhibitors grafted to introduce more compact structures with polar groups capable of increasing the total energy of the surface have also been mentioned. Exudate gums, carboxymethyl and hydroxyethyl cellulose, starch, pectin and pectates, substituted/modified chitosans, carrageenan, dextrin/cyclodextrins and alginates have been elaborately reviewed, including the effects of halide additives on their anticorrosion performances. Aspects of computational/theoretical approach to corrosion monitoring have been recommended for future studies. This non-experimental approach to corrosion could foster a better understanding of the corrosion inhibition processes by correlating actual inhibition mechanisms with molecular structures of these carbohydrate polymers.

Anticorrosion/antifouling properties of bacterial spore-loaded sol-gel type coating for mild steel in saline marine condition: a case of thermophilic strain of Bacillus licheniformis

This work reports the performance of a sol–gel type coating encapsulated with biofilm of inoculums of protective thermophilic strain of Bacillus licheniformis endospores isolated from the Gazan hot springs-Saudi Arabia for the inhibition of marine fouling and corrosion protection of S36-grade mild steel in 3.5 wt% NaCl medium. In order to improve its anticorrosion properties, the hybrid sol–gel coating is further doped with zinc molybdate (MOLY) and zinc aluminum polyphosphate (ZAPP) pigments. Marine fouling study was conducted at the Arabia Gulf water of Half Moon Bay, Al-Khobar, Saudi Arabia for 10 weeks on the coated samples with and without the bacterial endospores. The assessment of fouling results reveals that the bacterial endospores possess antifouling potentials since it performed better compared to its abiotic counterpart within the immersion period of study due to their foul-releasing effect. Improved corrosion and fouling resistant in the presence of the bacterial endospores could be attributed to their multi-layered hydrophobic and antibiotic coating surface after bacterial encapsulation. Spores accumulation in the sol–gel coating altered the surface wetness thereby preventing the diffusion of corrosion molecules and ions through the bulk of the coating to the metal surface; this is evident in the trend of electrochemical coating resistance and capacitance. Confocal laser scanning fluorescence and scanning electron microscopies were employed to probe bacterial viability and surface micro-cracks inherent in the coating, respectively. This is the first report of axenic thermophilic strain of Bacillus licheniformis isolated from the Arabian Gulf with inhibiting potentials against corrosion and fouling of industrial steel.

Comparative Study of the Corrosion Inhibition Efficacy of Polypropylene Glycol and Poly (Methacrylic Acid) for Mild Steel in Acid Solution

The performance of polypropylene glycol (PPG) and poly (methacrylic acid) (PMAA) as corrosion inhibitors for mild steel in acid solution was assessed by weight loss, electrochemical (electrochemical impedance spectroscopy, linear polarization resistance and potentiodynamic polarization), and surface analysis (water contact angles) techniques. Results obtained showed that both polymers inhibited mild steel corrosion but PPG was the best inhibitor. Inhibition efficiency increased with the increase in inhibitor concentration but decreased with temperature rise. Polarization results show that both PPG and PMAA behaved as a mixed-type inhibitors. The adsorption of the polymers onto the mild steel surface followed Temkin adsorption isotherm model. The variation of inhibition efficiency with temperature point toward physical adsorption which is supported by the kinetic and thermodynamic parameters derived from the experimental data. Water contact angle measurement results show that the polymers were adsorbed onto the mild steel surface. GRAPHICAL ABSTRACT

Probing the corrosion inhibiting role of a thermophilic Bacillus licheniformis biofilm on steel in a saline axenic culture

The growth of some bacterial biofilms has been widely reported to have defined consequences on industrial metals, and their related metabolic activities affect the overall electrochemical process of these metals in any given medium. This work seeks to unravel the role of a thermophilic Bacillus licheniformis biofilm (an isolate from the Jazan spring of Saudi Arabia) on corrosion reduction for stainless steel (316 L grade) in a saline culture medium. Grown on the steel substrate, this bacterial biofilm and the nature of its extracellular polymeric substances have been probed chemically and electrochemically for their influences on the metal dissolution within an incubation period. Corrosion inhibition in the presence of varying concentrations (in CFU ml−1) of this bacterium in the biotic-inoculate systems is explained in terms of corrosion resistance and capacitance of the biofilm. The corrosion rate of steel is found to reduce significantly in the saline culture medium within the range of concentrations of bacterium under study compared with the sterile control. This is attributed to the adhesion of a relatively compact and dense “beneficial” biofilm as well as the secretion of corrosion inhibiting substances from the bacterial biofilm as revealed during surface analysis.

Chemical and spectrophotometric studies of naphthol dye as an inhibitor for aluminium alloy corrosion in binary alkaline medium

The inhibition of a substituted naphthol compound, 4-(4-nitrophenylazo)-1-naphthol (44NIN), on the corrosion of aluminium (Al) in a basic medium was studied by classical chemical (gravimetric) and spectrophotometric (UV–Vis and FTIR) methods at 303–333 K. 44NIN demonstrated an excellent inhibiting property to Al corrosion in the aerated binary alkaline solution as shown from the results. The inhibition efficiency was found to increase with the azo dye concentration but not with temperature. Thermodynamic and adsorption evaluation for this inhibition process were accessed and thoroughly discussed. The UV–visible absorption spectra of the solution containing this dye after the immersion of Al specimen indicate the possible formation of a 44NIN–Fe type complex. The FTIR was carried out of the dye and protective film formed on the surface of the metal in the electrolyte containing the dye after a 72 h immersion period. These results show a correlation between the inhibitive effect and molecular structural information of 44NIN in this typical heterogeneous alkaline system.

Corrosion inhibition of X70 sheets by a film-forming imidazole derivative at acidic pH

The anticorrosion potential of a chemisorbed film formed from 3-imidazol-1-ylpropan-1-amine (IMPA) against the degradation of X70 steel in 1 M HCl has been investigated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. IMPA has been found to reduce the corrosion of X70 in the aqueous medium at pH 0 to a great extent; an inhibition efficiency (IE%) up to 90% has been achieved for 500 ppm IMPA concentration at room temperature. Corrosion inhibition by IMPA is concentration-dependent and becomes more stable by virtue of adsorption of IMPA film on the X70 substrate. This adsorption phenomenon has been probed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and infra-red (IR) spectroscopy. The formation of this film on the X70 surface fosters improved impedance against the flow of ionic currents of corrosive ions and molecules. IMPA acted as a mixed-type film-forming inhibitor as demonstrated from the results of potentiodynamic scans. The mechanism of X70 corrosion inhibition has been proposed using quantum structure/activity relations to explain the extent of influence of the molecular structure of IMPA on the corrosion inhibition of the IMPA film.

Retraction Note to: Corrosion protection of steel sheets by chitosan from shrimp shells at acid pH

The corrosion behavior of mild steel (MS) sheets in 0.5 M H2SO4 in the presence of chitosan extracted from shrimp shells (CSS) has been studied using electrochemical techniques. The optimum concentration (10 µM) of this carbohydrate polymer inhibited MS corrosion up to 85 % in the solution of the acid electrolyte. Results reveal that CSS reduced the dissolution of MS linearly with its concentration, and this reduction could be attributed to the interfacial formation of CSS film at the MS-electrolyte boundary. CSS is a mixed-type inhibitor and the shapes of Nyquist capacitive and inductive loops obtained from the impedance results could be associated with double layer reactions and relaxation of corrosive ions adsorption in the presence of CSS, respectively, at the MS/solution interface. Surface analytical studies with atomic force microscope, scanning electron microscope and Fourier transform infra-red also confirm the adsorption of CSS on MS.

Ultrasound-assisted synthesis of zinc molybdate nanocrystals and molybdate-doped epoxy/PDMS nanocomposite coatings for Mg alloy protection

Zinc molybdate (ZM) is a safer anticorrosive additive for cooling systems when compared with chromates and lead salts, due to its insolubility in aqueous media. For most molybdate pigments, their molybdate anion (MoO4-2) acts as an anionic inhibitor and its passivation capacity is comparable with chromate anion (CrO4-2). To alleviate the environmental concerns involving chromates-based industrial protective coatings, we have proposed new alternative in this work. We have synthesized ZM nanocrystals via ultrasound-assisted process and encapsulated them within an epoxy/PDMS coating towards corrosion protection. The surface morphology and mechanical properties of these ZM doped epoxy/PDMS nanocomposite coatings is exhaustively discussed to show the effect of ZM content on protective properties. The presence of ZM nanocrystals significantly contributed to the corrosion barrier performance of the coating while the amount of ZM nanocrystals needed to prepare an epoxy coating with optimum barrier performance was established. Beyond 2 wt% ZM concentration, the siloxane-structured epoxy coating network became saturated with ZM pigments. This further broadened inherent pores channels, leading to the percolation of corrosion chloride ions through the coating. SEM evidence has revealed proof of surface delamination on ZM3 coating. A model mechanism of corrosion resistance has been proposed for ZM doped epoxy/PDMS nanocomposite coatings from exhaustive surface morphological investigations and evidence. This coating matrix may have emerging applications in cooling systems as anticorrosive surface paints as well as create an avenue for environmental corrosion remediation.