Anodic behaviour of aluminium and its alloys in alkaline media in the presence of inhibitive and complexing substances

Abstract

In order to find out the suitability of four different grades of aluminium, namely 2S, 3S, 57S, and unalloyed aluminium for use as a galvanic anode in 1M-sodium hydroxide solution containing calcium oxide and sodium citrate, the potential-time variation, the anodic polarisation, the anode efficiency and corrosion/behaviour of these grades have been investigated. It has been found that all the above mentioned grades of aluminium behave in a similar manner, and self-corrosion can be reduced by more than 75% by the joint addition of calcium oxide and sodium citrate. However, on the basis of anode efficiency in inhibited 1M-sodium hydroxide solution, 28 grade and unalloyed aluminium seem to be the materials of choice since maximum efficienciesof 93–94% can be obtained by the use of appropriate current densities. Even in these cases, high anode efficienciesof the order of 80–94% are attained only at current densities of 9–12 mA/cm² but the results are less encouraging at lower current densities, and at 3 mA/cm² the anode efficiencieswere between 20% and 40% for alloyed and unalloyed aluminium.     

The effect of some B-diketo compounds on the retardation of aluminium dissolution in HCl

The inhibitive action of some B-diketo compounds on the dissolution of aluminium in 2M HCl has been investigated by hydrogen evolution, thermometric and weight loss techniques. The adsorbability of inhibitors is dependent on the basicity of the oxygen and nitrogen sites involved. The dissolution reaction of aluminium in hydrochloric acid solutions is zero order and remains so when B-diketo compounds are present. The rate constant decreases as the inhibition efficiency increases. The activation energy of the dissolution reaction increases with decreasing acid concentration and increasing inhibitor concentration. Values of the Arrhenius activation energies agree with those obtained for an activation controlled process.     

Inhibitoren der Korrosion 22 (1) — Einfluß von pH,Sauerstoff, Fremdionen,Art und Konzentration von Säuren auf den Korrosionsverlauf von Aluminium

Corrosion inhibitors 22 (1) – Influence of pH, oxygen, added ions, type and concentration of acids on the corrosion of aluminium Corrosion of aluminium in the presence of oxygen is practically independent from the pH and proceeds with oxygen consumption and hydrogen evolution. This behaviour is found in a solution of acetate buffer with sodium chloride as well as in inorganic (nitric, sulfuric, phosphoric, hydrochloric) acids as in organic acids. In the case of the latter the results are not as clear; in acetic acid the corrosion rate is not influenced by sodium chloride and the same applies to formic acid. While oxalic acid gives rise to hydrogen evolution in the presence of sodium chloride only and citric acid does not give rise to any hydrogen evolution. The solution which appears to be optimum for testing organic inhibitors of aluminium corrosion is unaqueous 1 N hydrochloric acid solution with 2.5% sodium chloride under nitrogen.     

Behaviour of Aluminium in Alkaline and Neutral Tartrate and Citrate Solutions

Abstract

The anodic polarisation of aluminium (2S) in a solution containing 1 M-sodium hydroxide, 0·3/ sodium chloride and 1–10% sodium tartrate and saturated with calcium hydroxide has been studied. The anode utilisation efficiency has been determined at various current densities starting from 2 mA cm^?2. It has been found that the corrosion of aluminium in a solution containing 10% tartrate, alkali and chloride is reduced by addition of calcium hydroxide. It has, however, been observed that under similar conditions, tartrate causes a greater degree of polarisation than citrate, indicating that tartrate may not be as effectiveas citrate in complexingaluminium and may even favour anodic oxidation.     

Serum effect on the electrochemical behaviour of titanium, Ti6Al4V and Ti6Al7Nb alloys in sulphuric acid and sodium hydroxide

The corrosion behaviour of cp titanium Ti6Al4V and Ti6Al7Nb alloys is investigated in 2 M sulphuric acid and 2 M sodium hydroxide with and without additions of bovine serum in order to get an insight into the effect of a biological electrolyte on the active corrosion of widely used metallic implants. Ti6Al7Nb alloy shows the highest corrosion resistance in 2 M sulphuric acid, whereas it is the least corrosion-resistant in 2 M sodium hydroxide. Bovine serum inhibits the hydrogen evolution as well as the anodic dissolution reactions in both sulphuric acid and sodium hydroxide. However, the cathodic efficiency of serum in sodium hydroxide is significantly higher than in sulphuric acid. Besides, the results suggest that serum forms a 2-D adsorption layer on the implant materials. Additionally, the surface coverage in sodium hydroxide is ca. 90%, while in acidic solutions only ca. 40%.     

Citric acid as natural corrosion inhibitor for aluminium protection

Abstract

The inhibition effect of citric acid on the corrosion behaviour of aluminium in 2M NaCl solution (pH 2) was studied with the help of potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS) and linear polarisation resistance (LPR) techniques. The experimental results showed that citric acid inhibits the corrosion of aluminium in NaCl solution and the inhibition efficiency depends on its concentration. The protection efficiency increases with citric acid concentration up to a critical value of 1·0 × 10^?5M. At higher concentrations, the inhibition efficiency reduced again with increasing concentration. The mechanism of inhibition was attributed to the adsorption of citric acid onto the metal surface.     

Thioamidines as novel class of corrosion inhibitors

Abstract

Four nitrogen substituted thiobisformamidines – phenyl thiobisformamidines (PTBF), tolyl thiobisformamidines (TTBF), anisidyl thiobisformamidines (ATBF), and 4-chlorophenyl thiobisformamidines (CPTBF) – were synthesised and their corrosion inhibiting behaviour for mild steel in 1M, 3M, and 5M HCl was studied. The optimum concentration of these compounds for maximum inhibition efficiency was determined by weight loss methods. All the investigated thiobisformamidines gave more than 95% inhibition in the presence of 1M HCl, and CPTBF showed the best inhibition efficiency (98% in 5M HCl). Potentiodynamic polarisation studies revealed that all the tested compounds are of mixed inhibitor type. The adsorption of these compounds from the acid solution obeyed Temkin's adsorption isotherm. All the inhibitors were able to reduce hydrogen permeation through the steel surface and their performance was enhanced by the addition of iodide ions. Electron impedance spectroscopic studies were also carried out in order to understand the mechanism of inhibition. Auger electron spectroscopic analysis confirmed that the adsorption of these compounds on the surface of the mild steel occurs through nitrogen and sulphur atoms.     

A study of the inhibiting properties of some derivatives of thiourea

Polarization of mild steel in 0·1 and 1·0 M hydrochloric acid in the presence of derivatives of thiourea has been studied at various inhibitor concentrations. The inhibition efficiency of the compounds was related to the properties of the polar groups and the size of the N-substituted groups. A mechanism for high adsorption and inhibition of S-containing compounds based on the principle of hard and soft acids and bases is suggested.     

Anodic behaviour of a model second phase: Al-20at.%Mg-20at.%Cu

The anodic behaviour of sputtering-deposited Al-20at.%Mg-20at.%Cu alloy is investigated during anodizing and potentiodynamic polarization treatments using transmission electron microscopy, X-ray photoelectron spectroscopy and medium energy ion scattering. The composition of the alloy is close to that of the S-phase in 2024 aluminium alloy. The anodizing behaviour in both 0.1 M ammonium pentaborate and 0.1 M sodium hydroxide electrolytes follows the behaviour of more dilute, solid-solution, aluminium alloys, with enrichment of copper developing in the alloy during the growth of an alumina-based initial oxide containing incorporated magnesium species. Oxygen gas is generated following sufficient enrichment of copper for its oxidation to proceed and hence, for copper species to enter the oxide film. The generation of oxygen gas causes extensive damage to the film, which limits the voltage to relatively low values. Potentiodynamic polarization in 0.1 M sodium hydroxide electrolyte revealed mainly passive behaviour following an initial period of corrosion during which the passive film is developed. In this initial period, copper enriches in the alloy, beneath an oxide film containing aluminium and magnesium species. The magnesium species migrate faster through the film than the aluminium species and form a surface layer of MgO/Mg(OH)₂, which protects against losses of aluminium species to solution and permits the establishment of the passive film. The steady open-circuit potential of the passivated alloy in the hydroxide solution is about −550 mV (SCE), compared with about −1940 mV (SCE) for aluminium.     

Dicyandiamide—an inhibitor for acid corrosion of pure aluminium

Inhibition efficiency of dicyandiamide on the acid corrosion of pure aluminium in 0·5N, 1·0N, 1·5N and 2·0N hydrochloric acid have been studied. A relation between inhibition efficiency and inhibitor concentrations have been thoroughly investigated. The inhibition efficiency increases with the increased concentration of the inhibitor but reaches a maximum at certain inhibitor concentration beyond which it remains practically constant. In a particular solution corrosion rate is found to have rectilinear relation with dipping time.     

Evaluation of the corrosion inhibition of salts of organic acids in alkaline solutions and chloride contaminated concrete

This paper summarizes the results of testing on salts of organic acids for evaluating their use as inhibitors of rebar corrosion in chloride‐contaminated concrete. Initially a screening based on electrochemical tests in alkalinized calcium hydroxide solutions was performed on a number of carboxylic acid salts with different number of carbon atoms in the chain and carboxylic groups, also covering substances with hydroxyl and amine group substituents. The screening was completed by testing on carbon steel rebars in concretes with chlorides and substances added at 1:1 molar ratio, focused on sodium lactate, sodium oxalate and sodium borate for comparison. The monitoring of free corrosion potential and linear polarization resistance of steel bars have confirmed significant inhibition only for lactate. Corrosion was only restricted to occluded zones where the access of substance was limited by disadvantageous geometry, producing shallow attacks. Results of further tests in saturated calcium hydroxide solution are reported in order to assess the inhibition ability of lactate as a function of its content, chloride content and pH.     

氢氧化钠溶液中丙炔醇对铝的缓蚀作用及吸附热力学研究

采用失重法研究了氢氧化钠溶液中丙炔醇在不同温度和浓度下对铝的缓蚀作用,发现丙炔醇在铝表面上的吸附是产生缓蚀作用的重要原因,且吸附规律服从Langmuir吸附等温式.用Sekine方法处理实验数据,获得了吸附过程相关的重要热力学参数.吸附过程是吸热过程,且熵值增大.随温度升高,吉布斯自由能减少,缓蚀率增大.     

Amino acids as corrosion inhibitors in hydrochloric acid solutions

Inhibition of the corrosion of iron in hydrochloric acid solutions by amino acids was studied. Twenty-two different common amino acids and four related compounds were used. Potentiodynamic polarization curves were obtained for iron wire in deaerated 1 M hydrochloric acid solution. Intersection of the linear Tafel lines at the corrosion potential gave values of the corrosion current. At 10 mM concentration of the inhibitors, the best results were obtained with 3,5-diiodotyrosine, with an inhibition efficiency of 87%. The best common amino acid was tryptophan with an inhibition efficiency of 80%. Hydroxyproline, cystine, and cysteine acted as corrosion accelerators. Definite trends were observed which were related to the molecular structure. In general, amino acids with longer hydrocarbon chains showed greater inhibition. Additional amino groups or groups which increased electron density on the alpha amino group also increased the inhibition efficiency.     

N-heterocyclic compounds as corrosion inhibitors for aluminium-copper alloy in hydrochloric acid

The inhibition of the corrosion of Al---4Cu alloy (B26S) in solutions of hydrochloric acid by some N-heterocyclic compounds has been studied in relation to the concentration of the acid and of inhibitor as well as the temperature. In general, at constant acid concentration, inhibitor efficiency increases with concentration of inhibitor and also with a rise in temperature. Except for the three picolines the efficiency also increases with increase in acid concentration. In general, at an inhibitor concentration of 0.05-1.0% in 0.1–1.0 M HCl, the efficiency increases in the order: 4-picoline < 3-picoline < 2-picoline > pyridine < piperidine < acridine.The inhibitors appear to function through general adsorption following the Langmuir adsorption isotherm. However galvanostatic polarisation data suggest that in the case of all the six inhibitors the cathode is preferentially polarised under the influence of an external current.     

Gossipium hirsutum L. extracts as green corrosion inhibitor for aluminum in NaOH solution

The corrosion inhibition properties of Gossypium hirsutum L. leave extracts (GLE) and seed extracts (GSE) in 2 M sodium hydroxide (NaOH) solutions were studied using chemical technique. Gossypium extracts inhibited the corrosion of aluminium in NaOH solution. The inhibition efficiency increased with increasing concentration of the extracts. The leave extract (GLE) was found to be more effective than the seed extract (GSE). The GLE gave 97% inhibition efficiency while the GSE gave 94% at the highest concentration.     

硅渣中金属离子的分离和利用

本实验研究了硅渣用盐酸处理后，加入动物胶，分离出硅，然后通过调节pH值，让溶液中的钙、钠、铝分离开。钙、铝的化合物，过滤后回到氧化铝流程，进行再利用，溶液通过浓缩结晶，回到生产硅产品的流程中去，氧化钠回收利用。本试验为探索出硅渣处理，促进氧化铝生产的发展，搞好环境保护和提高经济效益，提供重要方法。     

Effect of tantalum film on corrosion behaviour of AA6061 aluminium alloy in hydrochloric acid- and chloride-containing solutions

ABSTRACT

The present work is concerned with the corrosion resistance of AA6061 aluminium alloys with tantalum films in hydrochloric acid- and chloride-containing solutions. The tantalum films were produced by magnetron sputtering at different sputtering times (50 and 120 min). The films’ morphologies were observed by metallographic microscope and scanning electron microscope with energy dispersion spectrum. It is shown in this paper that with longer sputtering time, the film’s thickness increased, but it became less dense. The corrosion behaviour was characterised by potentiodynamic polarisation, scanning electrochemical microscopy analysis and an immersion experiment. These investigations revealed that the corrosion resistance of AA6061 aluminium alloy in chloride ions medium and hydrochloric acid was significantly improved after deposition of a tantalum film. Specifically, samples deposited for 50 min exhibited the best corrosion resistance in hydrochloric acid, while samples deposited for 120 min showed best corrosion resistance in sodium chloride solution.     

适用于带钢酸洗的盐酸缓蚀剂

提出了一种以乌洛托品、脂肪胺聚氧乙烯醚、十二烷基硫酸钠、0P-10乳化剂等为主要成份的盐酸缓蚀剂配方的一种高效复合型缓蚀剂，并研究了缓蚀剂添加量和温度对其缓蚀效果的影响，以及该缓蚀剂对废酸回收的影响.结果表明,该缓蚀剂的缓蚀率可以达到90%以上，控制合适的缓蚀剂添加量对废酸回收不会产生严重影响，适合大型钢板连续酸洗生产线使用.     

Antifungal drugs as corrosion inhibitors for aluminium in 0.1 M HCl

The inhibitive capabilities of Clotrimazole (CTM) and Fluconazole (FLC), two antifungal drugs, on the electrochemical corrosion of aluminium in 0.1 M HCl solution has been studied using weight loss measurements at 30 and 50 °C. The results indicate that both compound act as inhibitors in the acidic corrodent. At constant acid concentration, the inhibition efficiency (%I) increased with increase in the concentration of the inhibitors. Increase in temperature increased the corrosion rate in the absence and presence of the inhibitors but decreased the inhibition efficiency. CTM and FLC adsorbed on the surface of aluminium according to the Langmuir adsorption isotherm model at all the concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameter obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. The reactivity of these compounds was analyzed through theoretical calculations based on AM1 semi-empirical method to explain the different efficiencies of these compounds as corrosion inhibitors. CTM was found to be a better inhibitor than FLC.     

拜耳法赤泥凝胶法制备防腐颜料三聚磷酸铝

本文以拜耳法赤泥和工业磷酸为主要原料,用盐酸溶出拜耳法赤泥中的铝,来制备三聚磷酸铝。在制备工艺中,分别对拜耳法赤泥中铝的溶出和三聚磷酸铝的制备等相关参数进行了系统研究,得到了拜耳法赤泥制备三聚磷酸铝的最佳工艺参数。对产品进行测试分析,研究表明,按最佳工艺参数生产的三聚磷酸铝产品具有很好的防腐性能,且达到工业指标,并与工业氢氧化铝合成工艺进行比较表明,凝胶氢氧化铝合成工艺可以降低能耗、缩短周期。因此,该工艺具有非常好的环保意义和应用前景。