The performance of commercial aluminium as a sacrificial anode for cathodic protection of mild steel in 0.3% sodium chloride has been studied in alkaline compositions for anolyte…
Abstract
The performance of commercial aluminium as a sacrificial anode for cathodic protection of mild steel in 0.3% sodium chloride has been studied in alkaline compositions for anolyte based on slaked lime. The influence of several addition agents has been investigated with a view to suppressing local cell action in the above‐mentioned environment.
K. Venu, N. Subramanyan and K.S.G. Doss
In a critical range of concentrations of chloride ions in sodium hydroxide solutions, mild steel can be anodically polarised, but the polarised state cannot be maintained. It is…
Abstract
In a critical range of concentrations of chloride ions in sodium hydroxide solutions, mild steel can be anodically polarised, but the polarised state cannot be maintained. It is, however, found that the polarised state can be restored by cutting off the current for a minimum amount of time or by substituting a purely inhibitive solution for the original corrosive solution. The anodic potential accelerates the depassivation caused by chloride ions. It has been observed that cathodic polarisation is only as effective as interruption of the anodic current in restoring the polarised state. The results are discussed in relation to the occurrence of depassivation at a few random spots, and the significance of the results is pointed out from the point of view of the technique for finding out the corrosive or inhibitive character of an environment.
A. Elango, V.M. Periasamy, M. Paramasivam and E. Rakesh
The purpose of this paper is to show how to develop inhibition 57S aluminium in 2M NaOH solution.
Abstract
Purpose
The purpose of this paper is to show how to develop inhibition 57S aluminium in 2M NaOH solution.
Design/methodology/approach
The approach is used to measure gravimetric and polarization measurements.
Findings
The results of the paper clearly reveal that the 0.2 M ZnO with 700 ppm polyaniline in N‐methyl‐2‐pyrrolidone solution is found to offer inhibition up to 71.2 per cent.
Originality/value
The paper deals with the development of newer inhibitor based on polyaniline. Gravimetric and galvanostatic methods were employed to evaluate inhibition efficiency.
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Keywords
M.N. Desai, J.D. Talati and N.K. Shah
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…
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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.
Research limitations/implications
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.
Originality/value
Very few inhibitors demonstrate such excellent corrosion inhibition of zinc in aggressive corrosive media. Such detailed investigations on corrosion inhibitors are unusual.
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Keywords
J.D. Talati, M.N. Desai and N.K. Shah
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.
Abstract
Purpose
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.
Design/methodology/approach
The effect of various parameters on the behaviour of these inhibitors has been studied using the weight loss and polarization measurements.
Findings
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.
Research limitations/implications
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.
Originality/value
Very few inhibitors exhibit such excellent inhibitive effect on zinc in aggressive corrosive media. Rarely do we find such detailed studies.
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Keywords
K. Madhavan, S. Muralidharan and S. Venkatakrishna Iyer
The influence of thiophenol on the corrosion and hydrogen permeation 1M HCl and 0.SM H2SO4 has weightloss measurements, gasometric studies and other electrochemical techniques…
Abstract
The influence of thiophenol on the corrosion and hydrogen permeation 1M HCl and 0.SM H2SO4 has weightloss measurements, gasometric studies and other electrochemical techniques. Thiophenol inhibits the corrosion of mild steel in both the acids, but it is found to be more effective in H2SO4. It behaves predominantly as a cathodic inhibitor. It brings down the permeation current in both the acids, but is more effective in H2SO4. The adsorption of thiophenol on the mild steel surface from both the acids obeys Temkin’s adsorption isotherm.
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GERMANY Preparing metal surfaces with liquid jets A comparative newcomer among the many conventional methods of surface treatment and finishing is the technique of using liquid…
Abstract
GERMANY Preparing metal surfaces with liquid jets A comparative newcomer among the many conventional methods of surface treatment and finishing is the technique of using liquid jets. A method designed to permit multi‐purpose surface treatment in a single series of operations has been developed in Switzerland and is described in Technisclie Zeitschrift für praktische Metalbearbeitung (No. 5, 1964) by O. Burnand, Lausanne.
M.N. Moussa, M.M. El‐Tagoury, A.A. Radi and S.M. Hassan
Inhibition of carboxylic acids of aluminium corrosion in hydrochloric acid and sodium hydroxide solutions has been studied using weight‐loss and hydrogen evolution methods. The…
Abstract
Inhibition of carboxylic acids of aluminium corrosion in hydrochloric acid and sodium hydroxide solutions has been studied using weight‐loss and hydrogen evolution methods. The order of inhibition action of aromatic acids depends on the number and position of the carboxylic groups and the other substituents in the benzene ring. Increase of the chain length increases the inhibiting power of aliphatic acids. The inhibition efficiency in NaOH is higher than that in HCI solutions. The action of inhibition was discussed in terms of the chemical structure of the inhibitors.
The dock gate cable seen in the photograph below is submerged in sea‐water for 12 hours out of every 24. Nine years ago an inspection showed the appearance of rust on the same…
Abstract
The dock gate cable seen in the photograph below is submerged in sea‐water for 12 hours out of every 24. Nine years ago an inspection showed the appearance of rust on the same cable and a replacement was considered. However, it was decided to try an application of the anti‐corrosive lubricant Voler V 200 R, a graphited compound made by Revol Ltd. The cable was ‘unlocked’ and impregnated with the compound. In the nine years since, no further trouble has been experienced. Another example of the protection afforded by V 200 R in the marine field is its use on the cables of Arctic survey ships. After treatment with the compound it is claimed that the life of these cables has been quadrupled.
G. Bereket, A. Pınarbaşı and C. Öğretir
The effect of benzimidazole‐2‐tione and benzoxazole‐2‐tione derivatives on the corrosion of aluminium in 0.1 M HCl has been investigated by a potentiostatic polarisation…
Abstract
The effect of benzimidazole‐2‐tione and benzoxazole‐2‐tione derivatives on the corrosion of aluminium in 0.1 M HCl has been investigated by a potentiostatic polarisation technique. Inhibition efficiencies were found to follow the order: benzimidazole‐2‐tione > 5‐methyl benzimidazole‐2‐tione > 5‐chloro benzimidazole‐2‐tione, while that of benzoxazole‐2‐tione derivatives were found to follow the order: 5‐methyl benzoxazole‐2‐tione > benzoxazole‐2‐tione > 5‐chloro benzoxazole‐2‐tione > 5‐nitro benzoxazole‐2‐tione. The inhibitive action of these heterocyclic compounds was mainly due to adsorption on the metal surfaces, which show parallelism with the calculated total negative charge of each of the molecules. Thermodynamic parameters, such as values of free energies of adsorption ΔGads and values of equilibrium constants Kads, were determined. Activation energies Ea, activation enthalpies ΔH* and activation entropies ΔS* were determined from the corrosion currents measured at different temperatures.