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Work has been performed to investigate the effect of inhibitor charge and pH, in the range 3.9 to 6.5, on the efficiency of various tertiary and quaternary amines. Results have revealed that for such adsorption type inhibitors performance at a given pH depends critically upon the charge of the adsorbing species. At pH 6.5 highest efficiencies were attained when the net charge on the inhibitor was negative, while at pH 3.9 positively charged species were discovered to give better results. Based on the data obtained it is suggested that at pH 6.5 the corrosion potential is more noble than the potential of zero charge causing the metal surface to be predominantly composed of positive charges. At the other end of the spectrum (pH 3.9), the situation is thought to be reversed thus aiding better the adsorption of positively charged inhibitors.

Application of rare earth (RE) salts as a corrosion inhibitor was first proposed by Goldie and McCarrol in 1984. They showed that, with the addition of 0.001 M of Ce(NO₃) or La(NO₃) to 3.5% NaCl solution, the inhibition efficiencies were 91 and 82% for carbon steel, respectively. The aim of this paper is to study the inhibition of a mixture of Ce and La cations on the corrosion prevention of St37 carbon steel in aerated NaCl solutions using weight loss, potentiodynamic polarization, open circuit potential and constant potential measurements.

In this study, St37 steel was used as an experimental sample. The applied inhibitor was a powder mixture of Ce and La oxides with the ratio of Ce/La = 2/1. Each gram of this powder was dissolved in 4 cc acetic acid because of their insolubility in water. Steel samples were polished with 120 to 800 grit SiC polishing papers, deoxidized in 15 per cent HCl, and then ultrasonically cleaned in ethanol. They were degreased in acetone and were dried in a flow of hot air.

It has been shown that a mixture of RE cations (Ce and La) can be used as a corrosion inhibitor for carbon steel in NaCl containing solutions. The optimum inhibitor concentration was found to be 500 ppm with a maximum inhibition efficiency of 76%. An increase in Cl⁻ ion concentration and a rise in temperature from room temperature to 70°C can have an adverse effect on corrosion inhibition efficiency.

The results obtained from various experiments indicated that the mixture of Ce and La cations could be considered as a suitable inhibitor for carbon steel in low to medium chloride‐containing solutions. Owing to their non‐toxic nature, they may be suitable to use in potable water pipelines.

The inhibition of corrosion of B26S aluminium by various colloidal substances in aqueous sodium hydroxide has been studied. The extent of corrosion decreased with increase in the concentration of the inhibition. At an inhibition concentration of 0.5% and above. The efficiency of the colloids in decimolar sodium hydroxide increased in the order: gelatin < dextrin < glue < agar agar < acacia < tragacanth (86%). The efficiency decreased with increase in the concentration of alkali, the P.I. at an inhibitor concentration of 1.5% in 1M sodium hydroxide being, glue (23%), gelatin (39%), dextrin (47%), agar agar (64%), acacia (71%) and tragacanth (86%). The inhibition appears to be due to the absorption of the inhibitor on the aluminium surface. An increase in temperature also decreased the extent of inhibition. The aver‐age energy of activation for corrosion of B26S aluminium in 0.1M sodium hydroxide appeared to be 12.5 KCal, the value in the presence of the inhibitor being somewhat higher.

This paper aims to evaluate the inhibition efficiency of thiadiazole derivatives, such as 2,5-dimercapto-1,3,4-thiadiazole (DMTD), 5-methly-2-mercapto-1,3,4-thiadiazole (MMTD) and 2,5-dithiododecyl-1,3,4-thiadiazole (DDTD), in 50 mg/L hydrogen sulfide for silver strip.

Evaluation was carried out by corrosion-inhibiting test, electrochemical measurement and surface analysis techniques. 3D surface profiler, atom force microscopy, scanning electron microscopy and energy-dispersive X-ray analysis were applied and finally confirmed the existence of the adsorbed film.

The electrochemical measurement showed that the inhibition efficiency increases with increasing inhibitor concentration in 50 mg/L hydrogen sulfide solution, while the corrosion rate and the corrosion current decrease. Weight-gained measurements also indicated that inhibitor decreases the corrosion rate in the studied solution. The adsorption of DMTD and MMTD on the silver surface obeys Temkin’s adsorption isotherm, but the adsorption of DDTD follows Langmuir’s adsorption isotherm. That means that the inhibition mechanism is different between DMTD, MMTD and DDTD. The ΔG0_ad values of DMTD, MMTD and DDTD were −37.47, −37.29 and −38.69 kJ/mol, respectively. It showed that there was an adsorption bond between silver surface and inhibitor, and the adsorption belongs to chemical adsorption.

The inhibitors have an excellent inhibition efficiency, and the best inhibition efficiency is 91.76 per cent. Inhibitors can effectively inhibit metal corrosion in the oil and gas.

The purpose of this paper is to investigate the inhibitive effect of azathiones, namely cyclopentyl‐tetrahydro‐azathione, cyclohexyl‐tetrahydro‐azathione and isobutyl‐methyl‐tetrahydro‐azathione on the corrosion of carbon steel in formic and acetic acid solution. The effect of inhibitor concentration, immersion time, acid concentration, and solution temperature on the inhibition efficiencies of the selected azathiones were studied systematically.

The synthesis of inhibitor was confirmed by methods such as Fourier transform infrared and nuclear magnetic resonance studies. All inhibition experiments were conducted on carbon steel in 20 percent formic acid and 20 percent acetic acid solution. Weight loss experiments were carried out according to the American Society for Testing and Materials standard procedure. Polarization studies were carried out in a three electrode cell assembly connected to an EG&G Princeton Applied Research potentiostat/galvanostat (model 173). The electrochemical impedance technique was carried out using Zahner IM‐6 electrochemical workstation at a frequency range of 5‐100 Hz. The scanning electron microscopy (SEM) study was carried out using a VP LEO model no. 435 microscope for the surface characterization of inhibited and uninhibited metal surfaces.

Various thermodynamic parameters were calculated using weight loss data in order to elaborate the mechanism of corrosion inhibition. Polarization measurements revealed that the studied azathiones acted predominantly as mixed inhibitors. Electrochemical impedance measurements revealed that the compounds were adsorbed onto the carbon steel surface and the adsorption obeyed the Langmuir adsorption isotherm. The SEM study showed that the inhibited metal surfaces were smoother than were uninhibited metal surfaces.

The presence of high efficiency and low cost inhibitors is essential for protection of carbon steel. In comparison with conventional carbon steel corrosion inhibitors, these findings would be considered as a step forward in development of new corrosion inhibitor.

This paper reveals that azathiones can be used successfully for the protection of carbon steel surfaces exposed in acid solution.

The purpose of this paper is to study the corrosion inhibition performance of an eco-friendly drug clozapine on the corrosion of copper in 1.0 M nitric acid and 0.5 M sulfuric acid solutions.

The corrosion inhibition nature of inhibitor molecule was evaluated by weight loss, electrochemical impedance spectroscopy and potentiodynamic polarization studies. An attempt was made to correlate the molecular properties of neutral and protonated forms of inhibitor molecule using quantum chemical calculations. The effect of temperature on the corrosion inhibition efficiency was also studied using electrochemical impedance spectroscopy. The potential of zero charge was determined to explain the mechanism of corrosion inhibition.

The studies on corrosion inhibition performance of clozapine showed that it has good corrosion inhibition efficiency on the corrosion of copper in 1.0 M nitric acid and 0.5 M sulfuric acid solutions. The adsorption of clozapine molecules onto the copper surface obeyed the Langmuir adsorption isotherm. The value of free energy of adsorption calculated is very close to −40 kJmol⁻¹, indicating that the adsorption is through electrostatic coulombic attraction and chemisorption. The decrease in the value of energy of activation with the addition of inhibitor also shows the chemisorption of the inhibitor on the metal surface. The potential of zero charge and quantum chemical studies confirmed that the protonated molecules also get involved in the corrosion inhibition process through physisorption.

The present work indicates that clozapine can act as a good corrosion inhibitor for the corrosion of copper in acid media.

Thioureas (TUs) have been studied extensively, but their inhibition mechanism is not fully understood. Experimental results and theoretical calculations were used to investigate the effect of TU and its derivatives on the corrosion reaction of mild steel in 1 M H₂SO₄ at 40°C. An attempt was made to correlate some molecular parameters of these compounds with their corrosion inhibitor efficiency.

The influence of the additives' N‐substituted derivatives of TU such as methylthiourea (MTU), phenylthiourea (PHTU), thiosemicarbazide (TSC) and thiocarbazide (TC) on the dissolution process of the specimen in sulphuric acid was monitored chemically by hydrogen evolution measurements.

The results show that inhibitor efficiency increased with increase in inhibitor concentration. The protonation process appeared to be the effective parameter with lowering of the inhibition efficiency. Alkyl N‐substituted TU with the least protonation and with the maximum adsorption was a better inhibitor than TU and aryl N‐substituted TU. The thiocarbazide molecule showed less efficiency with the highest protonation due to high charge density on the sulphur atom as well as lengthening and weakening of the C‐ S bond than the thiosemicarbazide.

The paper provides useful information relative to the corrosion inhibition efficiency of N‐substituted TU. It presents the experimental results and theoretical calculations that were used to investigate the effect of derivatives TU on their inhibition efficiency.

A survey of technical literature indicates that there is a shortage of excellent corrosion inhibitors for zinc in non‐oxidizing acids, particularly sulphuric acid. This paper aims to describe the behaviour of ethylenediamine‐N‐N′‐dibenzylidene, ethylenediamine‐N‐N′‐disalicylidene, ethylenediamine‐N‐N′‐dicinnamylidene, triethylenetetramine tribenzylidene and triethylenetetramine trisalicylidene as corrosion inhibitors for zinc in sulphuric acid solutions. The objective of this research work also is to have an insight into the action mechanism of these inhibitors.

The effect of the various parameters affecting the action of the above‐mentioned corrosion inhibitors has been studied using weight‐loss data and polarisation measurements. Adsorption data also were utilized.

The inhibitors showed excellent corrosion inhibition (>99 per cent) at effective inhibitor concentrations. The two salicylidenes were better corrosion inhibitors than were corresponding benzylidenes. It appeared from this study that an efficient inhibitor is characterised by a relatively greater decrease in free energy of adsorption, lower entropy of adsorption and relatively lower heat of adsorption. Basically, these inhibitors were cathodic, as was revealed by polarisation data, and the inhibitors followed Langmuir adsorption isotherm behaviour. In general, the conjoint action of the inhibitor and the cathodic current was synergistic.

Powerful Schiff bases still need to be synthesized so as to be effective at extremely low concentrations. The behaviour with other metals and alloys in diverse media also requires to be investigated.

Very few inhibitors demonstrate such excellent corrosion inhibition of zinc in aggressive corrosive media. Such detailed investigations on corrosion inhibitors are unusual.

The aim of this paper is to investigate peach juice as a cheap, raw, green and non‐toxic anti‐corrosion material for mild steel corrosion in hydrochloric acid at different temperatures.

The corrosion inhibition of mild steel in 1 M HCl solution in the presence of peach juice at temperature range of 30‐60°C and concentration range of 5‐50 cm³/l was studied using weight loss and polarization techniques. The inhibition effect, adsorption characteristics, mathematical and electrochemical modeling of peach juice were addressed.

Results show that inhibition efficiency rose with the increase of inhibitor concentration and temperature up to 50°C, while at temperatures above 50°C the values of efficiency decreased. The inhibitor adsorbed physically on metal surface and followed the Langmuir adsorption isotherm. Monolayer formed spontaneously on the metal surface. Maximum inhibition efficiency obtained was about 91 percent at 50°C in the 50 cm³/l inhibitor concentration.

This work is an attempt to find a new, safe to environment, non‐toxic corrosion inhibitor. Peach juice is a readily available material in Iraq and Middle East markets.

The evaluation of Schiff bases derived from o‐, m‐ and p‐aminophenols and salicylaldehyde as corrosion inhibitors of zinc in sulfuric acid and to study their action mechanism.

The effect of various parameters on the behaviour of these inhibitors has been studied using the weight loss and polarization measurements.

In general, the ortho isomer was highly effective as a corrosion inhibitor because it formed a chelate with a six‐membered ring and moreover the ortho isomer possessed pronounced electromeric effect. These inhibitors obey the Langmuir adsorption isotherm. The almost constant performance with temperature in the case of ortho and para isomers in 0.5 M sulfuric acid suggested strong adsorption bonds. The thermodynamic parameters suggested that this strong interaction of the inhibitor molecules with the metal surface resulted in spontaneous adsorption. It may be concluded that a good inhibitor is characterised by a relatively greater decrease in free energy of adsorption, lower entropy of adsorption and higher heat of adsorption. Polarization data indicated that all these isomers were predominantly cathodic inhibitors. The conjoint effect of external cathodic current and these inhibitors was either synergistic or additive.

Even more powerful Schiff bases need to be synthesised and evaluated as corrosion inhibitors with a number of metals and alloys in diverse media, which may be effective at low concentrations.

Very few inhibitors exhibit such excellent inhibitive effect on zinc in aggressive corrosive media. Rarely do we find such detailed studies.