Corrosion inhibition studies of metals in acidic media

In this study the effect of acid rain on the geo technical properties of the soil was investigated. acidic environment was created to prepare the samples infiltrated with different pH level of acid rains. industrial advance in agriculture, chemical industries has led to release of pollutants in to the environment contaminating the soil. The soil is being contaminated by anthropogenic source such as leakage from waste contaminates facilities, accidental spills and industrial operations. This paper reports the effect sulphuric acid, oxalic acid and nitric acid on the
compaction characteristics of the soil at varying percentages. The acid contamination of soil adversely effects the geotechnical properties of soil. the geotechnical properties of the soil get altered when an acid compaction gets mixed with soil. Atterberg’s limits, compaction
characteristics and unconfined compressive strength test have been carried out. Result are indicative that the compaction characteristics and unconfined compressive strength are altered due to acid contamination.

Corrosion is an unavoidable but a controllable process. Due to the issues of toxicity of substances like chromate inhibitors, there is an increasing interest in exploration and utilization of eco-friendly inhibitors, which are also known as green inhibitors. This review briefly discusses some of the interesting features of the green inhibitors reported during the last decade.

The inhibitory potentials of ethanolic extracts and four fractions of the stem bark of Ficus asperifolia – Miq. for the corrosion of mild steel were assessed using weight loss method, Fourier atomic absorption spectroscopy, scanning electron microscopy (SEM). The effects of varying immersion period, concentration of the inhibitors and temperatures for mild steel corrosion in 5 M HCl acid solution were carried out. A detailed kinetic reaction, thermodynamic (Ea, ∆H, ∆S) and adsorption isotherm studies were obtained. The crude extract of F. asperifolia (EFA) has the highest inhibition efficiency of 55%. The inhibitory efficiency of the four fractions of F. asperifolia (EFA) compared with the crude extract was in the order ethyl acetate > n-hexane > butanol > EFA > Aqueous. The inhibition efficiency was found to increase with increase in the extracts concentration but decreased with temperature. Corrosion rate increases with time but decreases with extracts concentration. The kinetic studies of the data followed a first order reaction. Thermodynamic studies revealed that corrosion inhibition may be due to spontaneous mixed adsorption of the plant constituents on the metal surface. Experimental data were fitted to Langmuir, Freundlich and Temkin adsorption isotherms. The plant investigated showed a good potential for green corrosion inhibitors. Investigation of phytochemical constituents showed that the extracts contain alkaloids, flavonoids, saponins, tannins anthraquinones and reducing sugars.

In this work, new pyromellitic diimide linked to oxadiazole cycle was synthesized via multistep
processing. In the first step, pyromellitic diimide (1) was prepared by the reaction of its dianhydride
with urea by conventional and under microwave irradiation method. Treatment of compound (1)
with alcoholic KOH in the second step afforded the corresponding potassium salt (2). Compound (2)
was introduced in reaction with ethyl chloroacetate in the third step producing compound (3) ethyl-
2- (N-pyromellitic diimidyl) acetate. In the fourth step, compound (3) on treatment with hydrazine
hydrate afforded the corresponding acetohydrazide (4) and this in turn was subjected to the fifth
step in reaction with carbon disulfide in alcoholic KOH solution producing the target compound (5).
Corrosion inhibition efficiency of 50 ppm compound (5) was studied in 0.3 N HCl at different
temperatures. Also, antifungal and antibacterial activities of compound (5) was evaluated with
different microbial species and showed a good inhibition against all tested microorganisms.
The main goal of this research was directed to study the adsorption mechanism of this good
antibacterial oxadiazole –pyromellitic diimide (5) with carbon steel in acidic medium (0.3N HCl).
Calculated equilibrium constant (Kads.) values were increased with temperature raise reflecting the
excellent efficiency of adsorption at the studied conditions as a good antibacterial corrosion
inhibition derivative.

Purpose – The purpose of this paper is to describe the behavior of 2-mercaptobenzothiazole (MBT) on the corrosion of 316 stainless steel (SS) in acidic media and the mechanism of its action. Design/methodology/approach – The inhibitive effect of MBT towards the corrosion of 316 SS in acid solution is studied by means of weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy. The effect of inhibitor concentration and temperature against inhibitor action is investigated. Adsorption isotherm and adsorption mechanism are also discussed. Findings – MBT acts as inhibitor for this type of steel in acidic medium. This compound is mixed-type inhibitor and inhibition efficiency increased with increasing inhibitor concentration. MBT retards the rate of both anodic and cathodic corrosion reactions by adsorbing and forming a layer on the steel surface and the adsorption obeys Temkin adsorption isotherms. The inhibition efficiency is temperature dependence in the range from 25 to 658C and some thermodynamic parameters were calculated and analyzed. Originality/value – The results shown in this paper are an insight to the understanding of the corrosion resistance and electrochemical behavior of 316 SS in the presence of MBT for future industrial applications and development. It is the first time that corrosion inhibition effects of MBT on 316 SS have been evaluated.

This article reports the preparation of poly (methacrylic acid)/silver nanoparticles composite (PMAA/AgNPs) by in situ mixing of aqueous solutions of PMAA and 1 mM AgNO3 with natural honey as reducing and stabilizing agent. The prepared PMAA/AgNPs composite was characterized by UV–vis spectroscopy, Fourier transformed infrared, X-ray diffraction and energy dispersive spectroscopy (EDS) while the morphology of the AgNPs in the composite was obtained by transmission electron microscopy (TEM). TEM results revealed that the AgNPs were spherical in shape. The performance of PMAA/AgNPs composite as anticorrosion material for Al in acidic environment was examined by electrochemical, weight loss methods, complemented by surface analysis characterization with scanning electron microscopy (SEM), EDS and water contact angle measurements. Results obtained indicate that PMAA/AgNPs composite is effective corrosion inhibitor for Al in an acid-induced corrosive environment. Inhibition efficiency increased with increase in composite concentration but decreased with rise in temperature. From potentiodynamic polarization results, PMAA/AgNPs composite is found to function as a mixed-type corrosion inhibitor. The adsorption of the composite onto Al surface was found to follow El-Awady et al. adsorption isotherm model. SEM, EDS and water contact angle results confirmed the adsorption of the composite on Al surface.

Azadirachta indica (Neem) is one of the most versatile medicinal plants having wide spectrum of biological
activity. The Azadirachta indica fruit is rich nimbin, nimbinin, nimbidin, metiantriol (triterpenoid), azadirone,
epoxyazadiradione etc. The inhibitory efficacy of ethanolic extract of Azadirachta indica fruit (EEAiF) has been
investigated at room as well as elevated temperatures and the IE % has been observed significantly high (92.37 %) at
room temperature at concentration 1.052g/L. The experimentations has been carried out on acid corrosion of
Aluminium using weight loss measurement. The high inhibitive effect is attributed due to these photochemical present
in the extract. Efficiency of the inhibitor increases with the increasing concentration of inhibitor. The thermodynamic
parameters for Azadirachta indica fruit extract indicate that the process was spontaneous and the active constituents
have been physically adsorbed onto the metal surface. The adsorptive behavior of the inhibitor at room and higher
temperatures has been further endorsed by carrying out FT-IR spectroscopy.
Keywords: Aluminium, Azadirachta indica, Acid corrosion, FT-IR Spectroscopy, Kinetic and Thermodynamic
Parameters

Piper guineenseis a West African species of Piper known by the Igbos in the Southeastern Nigeria as Uziza. The spice obtained from its dried fruit is ambiguously known as Guinea pepper or West African black pepper. The leaves of this plant have been shown to be useful as spices and in traditional medicine. This study presents the proximate analysis as well as the qualitative and quantitative screening of the phytochemical constituents extracted from the leaves of this indigenous plant by solvent extraction using 95% ethanol. The results of the proximate analysis showed that on dry weight basis, the moisture content is 11.04% (22.08 mg/g), ash content 14.14% (28.28 mg/g), crude protein 17.15% (21.44 mg/g), carbohydrate 36.94% (369.4 mg/g), fats/lipids content 1.74% (3.48 mg/g), while fibre content is 18.99% (37.98 mg/g). The calorific value was estimated at 0.489 mg/g which is equivalent to 378.305 kcal/100g.The qualitative phytochemical analysis of the ethanolic leaf extracts showed strong or intense positivity (+++) for alkaloids, moderate positivity (++) for flavonoids, steroids, tannins, terpenoids, cardiac glycosides and total phenols, and weak positivity (+) for saponins. The quantitative phytochemistry of the leaves showed that the major phytochemicals present are flavonoids (7.86 mg/g), alkaloids (4.48 mg/g), saponins (3.38 mg/g) and tannins (3.20 mg/g) which have therapeutic, pharmacological, anti-oxidant and anti-inflammatory potentials. This study therefore reveals that the leaves of Piper guineense can be harnessed for medicinal purposes due to the presence in them of these phytochemicals.

The inhibition of low-carbon steel corrosion in 1 M HCl by extracts of Annona Muricata .L leaves was investigated using gravimetric and electrochemical techniques. The results show that the leaves extract functioned as effective corrosion inhibitor for low-carbon steel and its inhibition efficiency was concentration dependent. Weight loss method showed that the inhibition efficiency of the extracts increases with increase in its concentration and exposure time but decreases with increase in temperature. Potentiodynamic polarization results showed Annona Muricata .L leaves to be a mixed type inhibitor in 1 M HCl environment, whereas the electrochemical impedance spectroscopy results revealed adsorption of the extracts species on the steel surface. Fitting of the experimental data to the Arrhenius equation revealed that the constituents of the leaves extract were physically adsorbed on the corroding carbon steel surface. The experimental data complied with the Langmuir adsorption isotherm and the negative values of the Gibb's free energy of adsorption obtained suggested that inhibitor molecules have been spontaneously adsorbed onto the carbon steel.

The inhibition effect of Acacia nilotica P ethanolic extract on copper corrosion
in 0.5N hydrochloric acid has been studied by weight loss method between 303-353K
temperatures. The inhibition efficiency increased with increase in concentration of plant
extract. The corrosion rate increased with increase in temperature and decreased with
increase in concentration of inhibitor compared to blank. The adsorption of inhibitor on
Cu metal have been found to obey Langmuir adsorption isotherm. The values of
activation energy (Ea), free energy of adsorption (?G ), enthalpy of adsorption (?H), ads
and entropy of adsorption (? S) were calculated. The G values indicate that the
adsorption of EE P on copper metal surface is physical in nature. Surface analysis (FT- An
IR) was also carried out to establish the mechanism of corrosion inhibition on copper
corrosion in hydrochloric acid medium.
KEYWORDS:
Acacia nilotica, Copper, Acid corrosion, Adsorption isotherm, Kinetic parameters

The effect of glutaraldehyde as corrosion inhibitor for aluminum in phosphoric acid solution was studied by using weight loss method and characterized by fourier transform infrared spectroscopic and scanning electron microscopic analysis. The inhibition efficiency increases with increase in inhibitor concentration and decreases with increase in temperature while the corrosion rates increases with rise in temperature and decreases with increase in inhibitor concentration. The value of activation energy (ΔEa) was found to be 32.61 kJ/mol in uninhibited acid solution and increased to 47.33 kJ/mol in the presence of 0.1 M inhibitor concentration. The positive values of the enthalpy of activation (ΔHa) suggest an endothermic nature of the reaction and negative values of activation entropy (ΔSa) shows that the activation complexes in the rate determining step represent an association rather than dissociation. The values of free energies of adsorption were all negative which indicate spontaneity of the process. The phenomenon of physical adsorption is proposed from the values of activation energy and free energy of adsorption. The results also shows that the adsorption of inhibitor molecules on the surface of aluminum is accord with Langmuir adsorption isotherm as to the values of correlation coefficient (R 2) obtained were very close to unity. The result of the SEM analysis in the presence of inhibitor shows how the aluminium surface was protected against the aggressive effect of the acid. The new functional group in the FTIR analysis of the corrosion product is an indication of thin layer formation on the aluminium surface.

Piper guineenseis a West African species of Piper known by the Igbos in the Southeastern Nigeria as Uziza. The spice obtained from its dried fruit is ambiguously known as Guinea pepper or West African black pepper. The leaves of this plant have been shown to be useful as spices and in traditional medicine. This study presents the proximate analysis as well as the qualitative and quantitative screening of the phytochemical constituents extracted from the leaves of this indigenous plant by solvent extraction using 95% ethanol. The results of the proximate analysis showed that on dry weight basis, the moisture content is 11.04% (22.08 mg/g), ash content 14.14% (28.28 mg/g), crude protein 17.15% (21.44 mg/g), carbohydrate 36.94% (369.4 mg/g), fats/lipids content 1.74% (3.48 mg/g), while fibre content is 18.99% (37.98 mg/g). The calorific value was estimated at 0.489 mg/g which is equivalent to 378.305 kcal/100g.The qualitative phytochemical analysis of the ethanolic leaf extracts showed strong or intense positivity (+++) for alkaloids, moderate positivity (++) for flavonoids, steroids, tannins, terpenoids, cardiac glycosides and total phenols, and weak positivity (+) for saponins. The quantitative phytochemistry of the leaves showed that the major phytochemicals present are flavonoids (7.86 mg/g), alkaloids (4.48 mg/g), saponins (3.38 mg/g) and tannins (3.20 mg/g) which have therapeutic, pharmacological, anti-oxidant and anti-inflammatory potentials. This study therefore reveals that the leaves of Piper guineense can be harnessed for medicinal purposes due to the presence in them of these phytochemicals.

With the view of extracting gold out of waste, the ethanolic extract of weed (Bidens biternata) (EEBb) was explored for its inhibitory efficacy towards acid corrosion of AA6063 (aluminium alloy) in 0.5 M HCl. The experimentations were carried out employing chemical method at room and elevated temperatures and various corrosion parameters were calculated. The inhibitory efficacy was found to be 88.09 % at 1.04 g/L of EEBb. The adsorption of the inhibitor onto the metal surface was further endorsed by carrying out Quantum Chemical Analysis (QCA), spectroscopic (UV-Visible Spectroscopy) and surface morphological studies (SEM). The adsorptive nature of EEBb was investigated and found to best fitted in Langmuir adsorption isotherm. The high inhibition efficiency was attributed to the adsorption of active molecules leading to the formation of a protective layer on the AA6063 surface. The results were very promising and indicate that toxic weed Bidens biternata can be very effectively to combat acid corrosion of aluminium. Moreover, these can be a good replacement for most of the hazardous chemicals used to inhibit metal corrosion.

The Corrosion inhibition efficiency of Ketosulphide is investigated by AC-impedence method and Polarisation method. The parmaters such as corrosion potential (Ecorr), corrosion current density (icorr), cathodic Tafel slope (βc), anodic Tafel slope (βa) is computed by Tafel method. The Rp value and Cdl values are obtained by AC-impedance method. There is a good agreement between the AC- impedence method and polarization method. The percentage inhibition efficiency of ketosulfide is 75% in IM HCl solution at 303K. The decrease in the current density and the corrosion rate is decreased with the concentration of the ketosulfide and also the polarization method showed the mixed type inhibition characteristics of Ketosulphide. The increase in the Rp value with the increase in the concentration of inhibitor is calculated by the AC-Impedence method showed that the Ketosulphide is good inhibitor. There is a decrease in the Cdl value with the concentration which supports the electrochemical results.

The inhibitive mechanism, thermodynamics, and adsorptive properties of thiobarbituric acid (TBA) and thiourea (TU) on the corrosion of mild steel in 0.5 M HNO3 solution have been investigated using potentiodynamic, electrochemical impedance spectroscopy techniques, and quantum chemical calculations. Both inhibitors showed good inhibition efficiency in nitric acid solution. TU was the most effective inhibitor and its inhibition efficiency increases with increasing concentration to attain 99% at 6 × 10−3 mol · L−1 at 30°C. Theoretical fitting of different isotherms, Langmuir, Flory–Huggins, Temkin, and the kinetic-thermodynamic models were tested to clarify the nature of inhibitors adsorption on mild steel surface. The obtained experimental data fitted all the applied adsorption isotherms except Langmuir. The thermodynamic activation parameters were determined to provide evidence of the inhibitory effect of TBA and TU. To determine the surface charge at the steel surface in nitric acid solution the potential of zero charge was measured using AC measurements at different potentials. Quantum chemical parameters were calculated and explained. The data clarified that the inhibition of steel in nitric acid by TU or TBA takes place through physicochemical adsorption mechanism.

Corrosive effect of Seed extract of Lablab purpureus (LLP) was investigated using phytochemical screening, weight loss technique, surface morphological analysis and quantum chemical studies. Influence of bioactive compounds in LLP extract contributes for adsorption properties towards mild steel (MS). The maximum inhibition efficiency of LLP extract was 97.98 % in 1N HCl for immersion period of 5h at 2.5 % v/v. SEM analysis established formation of protective layer on mild steel surface. Inhibition efficiency was found to increase with increasing concentration of LLP extract at room temperature. Results from various studies show that LLP can serve as an efficient inhibitor for corrosion prevention of mild steel in 1N HCl medium. Inhibition action may be contributed by the products of hydrolysis of active constituents of seed extract.

The ravage Lovastatin drug was evaluated to screen its effectiveness to protect the copper corrosion in 3 M sulfuric acid solution. The weight loss, colorimetry and atomic absorption spectroscopy was employed to study the influence of ravage Lovastatin drug. The result showed that, ravage Lovastatin drug act as good copper corrosion inhibitor and remarkably reduces the copper corrosion density property. The utmost corrosion inhibition (protection) efficiency observed at 400 ppm. Further, electronic property of ravage Lovastatin drug was studied by using the Argus Lab software and surface studies was screened with the help of scanning electron microscopy (SEM) studies.

The effect of some ion-additives on the inhibitive effect of extract of Trigonella foenum graceums seeds (TfgS) on
acid corrosion of aluminium alloy (AA6063) was studied. The investigation was carried out for different immersion
periods in 0.5 N HCl at room temperature employing weight loss method. An optimum concentration (1.056 g/L) of
the inhibitor was used for the 0.05 g/L of various ion-additives (halide and Zn2+
ions). Various corrosion parameters
were evaluated using weight loss data. The inhibition efficiency was observed to increase synergistically on adding
the additives. The TfgS extract is a potential inhibitor for acid-induced corrosion of AA6063.
Keywords: Aluminium alloy (AA6063); Weight loss; Acid corrosion; Trigonella foenum graceums seeds (TfgS);
Additives; Synergism.

The influence of ethanolamine and ethylamine on the corrosion behaviour of mild steel in 1M H 2 SO 4 solution was investigated at room temperature (25 o C) by weight loss method. Results obtained show that the compounds are better inhibitors at low concentrations (<0.3M). From the decreasing weights of the metal over time, the concentrations of the metal was evaluated and plots of logarithm of the concentration of metal versus time as well as Erying-type equations facilitated the access of thermodynamic parameters such as equilibrium constant (k), enthalpy (∆H*) and entropy (∆S*) of the corrosion process. The entropy of the aggressive ions was found to have reduced on introduction of the inhibitors into the corrodent medium. Attempt to correlate the molecular structures of the inhibitors to the mechanism of inhibition was made.

The corrosive propensity of mild steel, aluminium
and copper in various concentrations of mineral acids viz. HCl
and H2SO4 has been studied by employing weight loss method.
The effect of acid strength on the metal corrosion has been
investigated at room temperature at different immersion
periods. In H2SO4 media, the corrosion rate of mild steel has
been observed to be higher than that of aluminium and copper;
while in HCl, aluminium has been observed to get corroded
fast. The thermodynamic as well as kinetic parameters have
also been evaluated. The surface morphological analysis has
been carried out by Optical micrographs.
Keywords: metal corrosion, mineral acids, corrosion parameters,
thermodynamic and kinetic parameters, optical micrograph