I.B. Obot

Gum arabic as a potential corrosion inhibitor for aluminium in alkaline medium and its adsorption characteristics

Purpose – To investigate the inhibitive effect of gum arabic (GA) for the corrosion of aluminium in alkaline (NaOH) medium and determine its adsorption characteristics. The present work is another trial to find a cheap and environmentally safe inhibitor for aluminium corrosion.Design/methodology/approach – The inhibition efficiency (%I) has been evaluated using the hydrogen evolution (via the gasometric assembly) and the thermometric methods at 30 and 40°C. The concentrations of GA (inhibitor) used were 0.1‐0.5 g/l and the concentrations of NaOH (the corrodent) were 0.1‐2.5 M. The mechanism of adsorption inhibition and type of adsorption isotherms were proposed from the trend of inhibition efficiency with temperature, Ea, ΔGads and Qads values.Findings – GA inhibited the corrosion of aluminium in NaOH solutions. The inhibition efficiency increased with increase in GA concentration and with increase in temperature. Phenomenon of chemical adsorption is proposed for the inhibition and the process followed th...

Corrosion Inhibition of Aluminium Using Exudate Gum from Pachylobus edulis in the Presence of Halide Ions in HCl

The anti-corrosive effect of Pachylobus edulis exudate gum in combination with halides ions (Cl–, Br– and I–) for aluminium corrosion in HCl was studied at temperature range of 30-60°C using weight loss method. Results obtained showed that the naturally occurring exudate gum acts as an inhibitor for aluminium corrosion in acidic environment. Inhibition efficiency (%I) increases with increase in concentration of the exudate gum and synergistically increased to a considerable extent on the addition of the halide ions. The increase in inhibition efficiency (%I) and surface coverage (θ) in the presence of the halides was found to be in the order I– > Br– > Cl– which indicates that the radii as well as electronegativity of the halide ions play a significant role in the adsorption process. Pachylobus edulis exudate gum obeys Temkin adsorption isotherm. Phenomenon of physical adsorption is proposed from the values of kinetic and thermodynamic parameters obtained. The values of synergism parameter (S1) obtained for the halides are greater than unity suggesting that the enhanced inhibition efficiency of the P. edulis caused by the addition of the halide ions is only due to synergistic effect.

Performance evaluation of pectin as ecofriendly corrosion inhibitor for X60 pipeline steel in acid medium: experimental and theoretical approaches.

The corrosion inhibition effect of pectin (a biopolymer) for X60 pipeline steel in HCl medium was investigated using weight loss, electrochemical, water contact angle measurements, and scanning electron microscopy techniques. The results obtained show that pectin acts as a good corrosion inhibitor for X60 steel. Inhibition efficiency increased with increase in pectin concentration and temperature. Potentiodynamic polarization results reveal that pectin could be classified as a mixed-type corrosion inhibitor with predominant control of the cathodic reaction. The effective corrosion inhibition potential of pectin could be related to the adsorption of pectin molecules at the metal/solution interface which is found to accord with the Langmuir adsorption isotherm model and a protective film formation. Quantum chemical calculations provided insights into the active sites and reactivity parameters governing pectin activity as a good corrosion inhibitor for X60 steel.

POLYVINYLPYROLLIDONE AND POLYACRYLAMIDE AS CORROSION INHIBITORS FOR MILD STEEL IN ACIDIC MEDIUM

The corrosion inhibition of mild steel in 1 M H2SO4 in the presence of polyvinylpyrollidone (PVP) and polyacrylamide (PA) as inhibitors at 30–60°C was studied using gravimetric and gasometric techniques. The inhibition efficiency (1%) increased with increase in concentration of the inhibitors. Increase in temperature increased the corrosion rate in the absence and presence of inhibitors but decreased the inhibition efficiency. Both PVP and PA were found to obey Temkin adsorption isotherm and Kinetic-Thermodynamic Model of El-Awady at all the concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameters obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. PVP was found to be a better inhibitor than PA.

Inhibitory Effect And Adsorption Characteristics Of 2,3-Diaminonaphthalene At Aluminum/Hydrochloric Acid Interface: Experimental And Theoretical Study

The inhibitive effect of 2,3-diaminonaphthalene (2,3-DAN) for corrosion of aluminum in 1 M HCl was investigated using hydrogen evolution technique at 30 and 40°C. Quantum chemical calculation results showed that 2,3-DAN molecule possessed planar structure with a number of active centers, which aided the adsorption process. The Mulliken charge density, the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) were found mainly focused around nitrogen atoms and the cyclic of the benzene as well. The presence of 2,3-DAN molecules in the corrosive medium (1 M HCl solution) inhibits the corrosion process of aluminum and as the concentration of 2,3-DAN increases the inhibition efficiency also increases but decreases with rise in temperature. The corrosion inhibition of 2,3-DAN was discussed in terms of blocking of the Al surface by adsorption of the molecules of the inhibitor at the active centers. It was found that the adsorption of 2,3-DAN onto the Al surface followed the Langmuir adsorption isotherm and 2,3-DAN adsorbed on Al surface probably by physisorption. The proposed physisorption mechanism was supported by the calculated values of Ea, Qads, and ΔGads.

Fabrication of nitrogen doped graphene oxide coatings: experimental and theoretical approach for surface protection

In this work, we present a simple strategy of fabricating an N-doped graphene oxide (N-GO) coating on stainless steel (SS) for protective applications. Electrochemical, surface analytical and quantum chemical techniques were employed to characterize the synthesized coatings on the SS surface. Graphene oxide (GO) and reduced graphene oxide (rGO) coatings on SS were adopted for comparison. The downshift of the G band in the Raman spectra of N-GO corroborated the incorporation of N atoms and the deconvoluted spectra of N1s revealed that N-GO coatings retain three types of nitrogen. The influence of N doping on the surface roughness and hydrophobicity of GO was investigated using surface topographic and contact angle measurements. An electrochemical corrosion study on the coatings indicated that N doping of GO enhances the corrosion resistance of SS in 3.5% NaCl solution more than GO and rGO. In order to describe the underlying mechanism, the adsorption energies of GO coatings with SS were computed using molecular dynamics simulation (MDS). The MDS results revealed that all the coating systems adsorbed in a parallel orientation on the Fe surface. N-GO coating exhibited the strongest and the most stable chemisorbed interaction on SS when compared to GO and rGO.

5-Arylpyrimido-[4,5-b]quinoline-diones as new and sustainable corrosion inhibitors for mild steel in 1 M HCl: a combined experimental and theoretical approach

The inhibition of mild steel corrosion in 1 M HCl by four 5-arylpyrimido-[4,5-b]quinoline-diones (APQDs), namely 5-(4-nitrophenyl)-5,10-dihydropyrimido [4,5-b]quinoline-2,4(1H,3H)-dione (APQD-1), 5-phenyl-5,10-dihydropyrimido[4,5-b]quinoline-2,4(1H,3H)-dione (APQD-2), 5-(4-hydroxyphenyl)-5,10-dihydropyrimido[4,5-b]quinoline-2,4(1H,3H)-dione (APQD-3) and 5-(2,4-dihydroxyphenyl)-5,10-dihydropyrimido[4,5-b]quinoline-2,4(1H,3H)-dione (APQD-4) has been investigated using weight loss, electrochemical, surface, and quantum chemical calculations and molecular dynamics simulation methods. The results showed that the inhibition efficiency (η%) increased with increasing concentration of the inhibitors. Among the studied compounds, APQD-4 exhibited the highest inhibition efficiency of 98.30% at 20 mg l−1 concentration. The studied compounds effectively retarded the corrosion of mild steel in 1 M HCl by adsorbing onto the steel surface, and the adsorption data conformed to the Langmuir adsorption isotherm. The results of potentiodynamic polarization measurements revealed that the studied compounds are cathodic-type inhibitors. Scanning electron microscopy (SEM) study confirmed the formation of adsorbed films of the inhibitor molecules on the steel surface. Quantum chemical calculations and molecular dynamics simulations were undertaken to corroborate experimental findings and provide adequate insight into the corrosion inhibition mechanisms and adsorption characteristics of the studied compounds.

2,4-Diamino-5-(phenylthio)-5H-chromeno [2,3-b] pyridine-3-carbonitriles as green and effective corrosion inhibitors: gravimetric, electrochemical, surface morphology and theoretical studies

The inhibition of mild steel corrosion in 1 M HCl by three newly synthesized 2,4-diamino-5-(phenylthio)-5H-chromeno[2,3-b]pyridine-3-carbonitriles (DHPCs) namely, 2,4-diamino-7-nitro-5-(phenylthio)-5H-chromeno[2,3-b]pyridine-3-carbonitrile (DHPC-1), 2,4-diamino-5-(phenylthio)-5H-chromeno[2,3-b]pyridine-3-carbonitrile (DHPC-2) and 2,4-diamino-7-hydroxy-5-(phenylthio)-5H-chromeno[2,3-b]pyridine-3-carbonitrile (DHPC-3) was studied using weight loss method, electrochemical techniques, surface morphology (SEM, AFM) studies and theoretical (quantum chemical calculations and molecular dynamic simulation) methods. The weight loss and electrochemical measurements showed that the inhibition efficiency increases with increasing inhibitor concentration and the relative trend of inhibition performance is DHPC-3 > DHPC-2 > DHPC-1. A potentiodynamic polarization study reveals that the investigated DHPCs act as mixed type inhibitors. The adsorption of the DHPCs on the mild steel surface obeys the Langmuir adsorption isotherm and involves both physisorption and chemisorption modes. The presence of the electron releasing –OH group at position seven on the chromenopyridine ring is considered to be responsible for the highest inhibition efficiency of DHPC-3 among the studied compounds. Whereas the presence of the electron withdrawing nitro (–NO2) group at position seven on the chromenopyridine ring is responsible for the lowest inhibitive strength of DHPC-1. Quantum chemical calculations and molecular dynamic simulation studies were undertaken to provide mechanistic insight into the roles of the different substituents (–OH and –NO2) on the corrosion inhibition behavior of the studied inhibitors.

Multi-functional ceramic hybrid coatings on biodegradable AZ31 Mg implants: electrochemical, tribological and quantum chemical aspects for orthopaedic applications

Application of biodegradable implants has received increasing attention for the treatment of bone damage due to their low adverse effects. To achieve better biocompatibility and enhanced corrosion resistance of biodegradable implants with improved wear resistance, multifunctional coatings need to be developed. Herein, a ceramic hybrid coating has been fabricated by a plasma electrolytic oxidation (PEO) technique using Ta2O5 nanoparticle inclusion on AZ31 Mg alloy in order to attain superior corrosion, wear behavior, and surface porosity that enable improved bioactivity. X-ray diffraction analysis of PEO coatings showed that the surface coating is mainly composed of Mg3(PO4)2, MgO and Ta2O5 in different quantities based on PEO processing. Furthermore, scanning electron microscopy (SEM) analysis was employed to observe the surface of the resultant PEO hybrid coatings after and before wear tests. With Ta2O5 nanoparticles, PEO coatings showed excellent wear compared with pure PEO coatings. The efficiency of the hybrid coatings in corrosion protection was verified by the Tafel plot and electrochemical impedance spectroscopy measurements in simulated body fluid. Furthermore, in vitro cell culture studies were performed on MG-63 human cells to evaluate the biocompatibility of PEO coatings. A quantum chemical approach and force-field molecular dynamics simulation were employed to evaluate the interaction between the AZ31 Mg surface and PEO hybrid coatings. All of the observations evidently showed that the ceramic hybrid PEO coating provides improved wear and corrosion protection performance with superior biocompatibility with Ta2O5 nanoparticles, when compared to pure PEO coatings, due to its synergistic beneficial effect.

Adsorption and corrosive inhibitive properties of Vigna unguiculata in alkaline and acidic media

Purpose – To investigate the adsorption behaviour and inhibitive effect of Vigna unguiculata (VU) extract (agricultural waste material) for aluminium corrosion in 0.5 M NaOH and H2SO4.Design/methodology/approach – The inhibitive effect of the plant extract was assessed using weight loss method at 30 and 60oC. The trend of inhibition efficiency with temperature was used to propose the mechanism of inhibition and type of adsorption.Findings – VU extract effectively inhibited aluminium corrosion in both alkaline and acidic media. Inhibition efficiency (I %) of the extract increased with increase in concentration of the extract and temperature. Inhibitor adsorption characteristics were approximated by Freunlich and Temkin adsorption isotherms at all the concentrations and temperatures studied. The phenomenon of chemical adsorption is proposed from the activation parameters obtained.Research limitations/implications – The mechanistic aspect of the corrosion inhibition can be better understood using electrochem...