Influence of alloying additives on corrosion and hydrogen permeation through commercial aluminium in alkaline solution

The influence of alloying additives on the extent of corrosion and hydrogen permeation through aluminium of different grades such as 2S, 3S, 26S and 57S, in 0.01 M NaOH has been investigated using weight loss measurements and electropermeation. It is found that the extent of self corrosion and hydrogen permeated through different grades of commercial aluminium follow the order: 3S > 2S > 26S > 57S. The influence of incorporating zinc and indium either alone or in combination on self corrosion and permeation current has also been studied. It is found that ternary alloys of both 26S and 57S containing zinc and indium give considerably lesser values of self corrosion rate and permeation current.     

Influence of alloying additives on the performance of commercial grade aluminium as galvanic anode in alkaline zincate solution for use in primary alkaline batteries

The self-corrosion of different grades of commercial aluminium such as 2S, 3S, 26S and 57S in 4 M NaOH containing 0.6 M ZnO has been determined by weight loss measurements. It is found that 26S and 57S aluminium exhibit negligible corrosion rates in the range 0.05–0.06 mg cm^–2 min^–1, which can be attributed to the formation of a zincate coating on the aluminium surface. The influence of zincating on the performance of binary and ternary alloys of 26S and 57S aluminium obtained by incorporating alloying elements such as zinc, indium, thallium, gallium and tin as galvanic anode in 4 M NaOH containing 0.6 M ZnO has been examined by studying self corrosion, steady state open circuit potential, galvanostatic polarization and anode efficiency. It is found that zincated ternary alloys of 26S and 57S aluminium containing zinc and indium can serve as good galvanic anodes in alkaline medium. AC impedance measurements and X-ray diffraction studies have been carried out to understand the nature of the film formed on the aluminium surface.     

Different commercial grades of aluminium as galvanic anodes in alkaline zincate solutions

The self corrosion and electrochemical properties, such as open circuit potentials, polarisation characteristics and anode efficiencies, of different grades of aluminiumviz., 2S, 3S, 26S and 57S were examined in 4 M NaOH, containing 0.01 to 0.6 M zinc oxide. From these studies, 3S and 57S aluminiums were found to be the most suitable anode materials, among the different grades of aluminium and 4 M NaOH solution containing 0.6 M zinc oxide was found to be the best electrolyte.     

Self-discharge of the alkaline iron electrode

The self-discharge reaction, which is a hydrogen-evolving corrosion process, where the anode reaction is identical to the first discharge step, has been studied by three different methods: H₂-evolution, polarization curves and potentiodynamic discharge. The influence of 28 additives at 30, 50 and 70°C on both discharge and self-discharge is shown. Most additives decrease both the self-discharge and discharge rates but for K₂S and hydrazinesulphate added to the electroylte. These two additives have a positive influence on the discharge process of the iron electrode.     

Characterisation of different grades of commercially pure aluminium as prospective galvanic anodes in saline and alkaline battery electrolyte

The effect of calcium chloride and sodium chloride on the electrochemical properties of various grades of aluminium namely 2s, 3s, 26s and 57s in alkaline citrate solution has been examined by studying the self corrosion, open circuit potential, anodic polarization and anode efficiency. It has been found that among the different grades of aluminium the 57s grade is found to be the most promising galvanic anode material in the 4N NaOH containing 20% wt/vol. of sodium citrate and 2.5% wt/vol. of CaCl₂·2H₂O. Further, it has been found that the above alkaline citrate electrolyte required for aluminium air batteries can be prepared from tap water, saline water and even sea water. The presence of chloride ions in the electrolyte, even up to a concentration of 2.5% wt/vol. as CaCl₂·2H₂O, is not found to alter the electrochemical properties of the different grades of aluminium as anode materials, though 57s is found to be the best.     

Electrochemical noise analysis of corrosion of pure aluminium in alkaline solution in the presence of SO4 ion, NO3 ion and Na2S additives

The electrochemical noises obtained from pure aluminium in an alkaline solution have been analysed as a function of sulphate, nitrate or sodium sulphide concentration. A stochastic theory has been applied to the experimentally obtained electrochemical noises based upon the Weibull distribution function. From the occurrence of two linear regions on one Weibull probability plot, the present analysis method permitted us to distinguish between the dissolution of Al and the stochastic process concerning the series of nucleation, growth and detachment of hydrogen bubbles in an engineering sense. Moreover, the conditional event generation rate and the average charge in each event were quantitatively determined for the stochastic process of hydrogen bubbles as well as the dissolution of Al. Effects of sulphate, nitrate and sodium sulphide additives on the corrosion of pure aluminium in an alkaline solution have been discussed in terms of the conditional event generation rate and the average charge in each event.     

Electrochemical corrosion of solid and liquid phase sintered silicon carbide in acidic and alkaline environments

Solid and liquid phase sintered silicon carbide (SiC) ceramics are used in aggressive environments, e.g. as seals and linings in chemical plant equipments. There exist data concerning corrosion of solid phase sintered SiC (SSiC), but there are only few data concerning their electrochemical corrosion behaviour. The corrosion of liquid phase sintered SiC ceramics (LPS SiC) containing yttria aluminium oxide grain boundary phases has been investigated by standard methods that have shown the decisive influence of the oxide grain boundary on the corrosion stability of these materials. But no electrochemical investigations are known. In this study therefore, potentiodynamic polarisation measurements have been used to determine the corrosion mechanisms of SSiC and LPS SiC ceramics at room temperature in acidic and alkaline environments. The investigation has shown a pronounced electrochemical corrosion in acids and alkaline solutions for both types of materials. In HCl and HNO₃ pseudo-passivity features due to the formation of a thin layer of SiO₂ on the surface were observed, whereas in NaOH soluble silicate ions were observed resulting in more pronounced corrosion. Microstructural observations of initial and corroded samples revealed that the residual carbon found in the microstructure of SSiC did not dissolve preferentially. The corrosion current densities of the LPS SiC materials were caused by the dissolution of SiC and not by the corrosion of the oxide grain boundary phase. The corrosion current densities of the LPS SiC materials investigated were lower than those of the SSiC materials.     

铝阳极氧化碱蚀槽的维护

在铝合金阳极氧化生产工艺中，测定碱蚀槽液苛性钠、铝离子、添加剂的浓度。根据铝合金碱蚀工艺条件和铝材碱蚀后的表面状况，对碱蚀槽的槽液进行维护，提出了碱蚀常见故障和排除方法。本文还探讨了碱蚀机理。     

The corrosion and electrochemical behaviour of pure aluminium in alkaline methanol solutions

The corrosion and electrochemical behaviour of pure aluminium in alkaline methanol solutions has been investigated. The results of hydrogen collection experiments showed that aluminium has a lower corrosion rate in alkaline methanol solutions compared to water based solutions and that the corrosion rate increases with increasing water content of the solution. Polarization and galvanostatic discharge experiments showed that there is a wide potential window of electrochemical activity and a better discharge performance in the alkaline methanol solutions with a certain amount of water. Scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDAX) showed that the passivation in the later stages of discharge in alkaline methanol solutions at relatively high current densities is due to the formation of a dense Al(OH)₃ layer on the surface of the anode.     

新型铝系复合缓蚀剂的研究及应用

本文系统介绍铝离子与其它添加剂复配成的铝系复合缓蚀剂对水中碳钢腐蚀的缓蚀性能、特点及缓蚀协同机构,并进一步展望了它广阔的应用前景。     

Zinc-nickel coatings: Relationship between additives and deposit properties

The electroplating of zinc-nickel alloys from a chloride bath containing two brighteners (a phenolic derivative and an unsaturated aromatic compound) and a levelling agent (an aromatic carboxylate) has been studied under different plating conditions. The composition and morphology of the alloys depended on the concentration of all the additives and also on the temperature. As a general effect, these additives smooth the deposit and refine the grain size. By means of scanning electron microscopy, it was possible to classify the deposit morphologies according to the type and concentration of the additives. The resistance of the alloys to corrosion was studied by means of a neutral salt-spray test.Prema S. A. Company     

松香胺-铝盐缓蚀剂在冷却水中协同效应的研究

采用失重法,通过正交试验测定了氯化铝、松香胺、硫酸锌缓蚀剂在冷却水中对２０＃碳钢的缓蚀性能;并使用电化学方法测定其极化曲线,对其缓蚀机理进行初步研究。结果表明,松香胺与氯化铝、硫酸锌之间具有较强的协同效应,该配方缓蚀剂属混合型缓蚀剂,具有良好的缓蚀性能。     

Corrosion of nickel ferrite refractory by Na3AlF6–AlF3–CaF2–Al2O3 bath

Based on research on cermet inert anodes for aluminium production, it has been suggested that nickel ferrite spinel might be suitable for use as a sidewall refractory in Hall-Héroult cells. A corrosion resistant sidewall would allow elimination of the frozen bath ledge, and has potentially huge benefits in terms of energy savings and increased productivity. However, little work has been done to assess nickel ferrite's suitability as a refractory.Dense nickel ferrite samples were prepared and characterized, and corrosion tests in cryolite based baths were conducted. Results confirm that the spinel does have good corrosion resistance. The corrosion mechanism is complex, involving grain boundary attack and formation of a Ni–Fe alloy. This alloy could pose a risk in terms of contamination of the aluminium. The use of additives to restrict penetration of grain boundaries may be the key to development of a successful spinel based refractory.     

Effect of fluoride ions on the corrosion of aluminium in sulphuric acid and zinc electrolyte

The effect of fluoride ions on the corrosion of aluminium in sulphuric acid and zinc electrolyte has been investigated through thermodynamic analysis and corrosion experiments. The solution chemistry of aluminium, zinc, and iron in aqueous solution in the absence and in the presence of fluoride ions was studied with the construction of the Eh-pH diagrams for the Al–F–H₂O, Zn–F–H₂O and Fe–F–H₂O systems at 25°C. In the presence of fluoride ions, aluminium can form a series of aluminium-fluoride complexes depending on the fluoride concentration and pH whereas zinc and iron can form soluble or insoluble metal-fluoride complex species only at relatively high fluoride concentration and at higher pH values. Experimental results show that in the presence of fluoride ions, the corrosion of pure aluminium in sulphuric acid is due to uniform dissolution and the reaction rate depends on the fluoride concentration. In zinc electrolyte containing fluoride ions, zinc deposits onto the pure aluminium substrate spontaneously and the amount of deposited zinc also depends on the fluoride concentration. On the other hand, the presence of iron in the Al–Fe alloy accelerates the corrosion of aluminium in H₂SO₄ and zinc electrolyte significantly and prevents the deposition of zinc on the aluminium surface. The effect of fluoride ions on zinc adherence to the aluminium is also discussed.     

Corrosion of aluminium metal in OPC- and CAC-based cement matrices

Corrosion of aluminium metal in ordinary Portland cement (OPC) based pastes produces hydrogen gas and expansive reaction products causing problems for the encapsulation of aluminium containing nuclear wastes. Although corrosion of aluminium in cements has been long known, the extent of aluminium corrosion in the cement matrices and effects of such reaction on the cement phases are not well established. The present study investigates the corrosion reaction of aluminium in OPC, OPC-blast furnace slag (BFS) and calcium aluminate cement (CAC) based systems. The total amount of aluminium able to corrode in an OPC and 4:1 BFS:OPC system was determined, and the correlation between the amount of calcium hydroxide in the system and the reaction of aluminium obtained. It was also shown that a CAC-based system could offer a potential matrix to incorporate aluminium metal with a further reduction of pH by introduction of phosphate, producing a calcium phosphate cement.     

Electrochemical methods for the study of corrosionin lubricant additive systems

Potentiodynamic polarization has been used to study the corrosion behaviours of mild steel and copper in solutions containing some examples of common types of lubricant additives. A variety of conditions for performing of experiments were investigated. The best results were obtained in a background solution of 0.01m tetra-n-butylammonium perchlorate in 1:1 toluene/ethanol. The behaviour of the aforementioned metals was characterized and compared in solutions containing allyl amine, alkyl phosphite, and organic sulfides. For most solutions, corrosion and pitting potentials and corrosion rates of each metal were found to vary with the compound's concentration. Changes in the corrosivity of chemicals towards metals were monitored as a corrosion inhibitor was added to their solutions. The relative corrosion behaviour observed were consistent with the known performance of these metals in contact with lubricants containing these additives.     

Corrosion and passive behaviour of aluminium in weakly alkaline solution

The title subject has been studied by stationary and transient polarization measurements on high-purity aluminium electrodes in acetate solutions of pH 7–10 at 25°C and by Auger electron spectroscopic investigations of oxide films formed. In such deoxygenated solutions, aluminium corrodes under hydrogen evolution and is in some state of active/passive transition, or close to it. Oxygen (when added) acts as a passivator and mostly lowers the corrosion rate. The stationary passive current is potential independent, but varies with pH. It goes through a minimum at a pH of about 8. Oxide films formed have a thin inner barrier layer and an outer non-barrier layer whose thickness increases with increasing pH. Transients yield information on the barrier layer and on charge transfer reactions occurring.     

Inhibitive Behaviour of Zinc Gluconate on Aluminium Alloy in 3.5 % Nacl Solution

The present work investigates corrosion behaviour of aluminium alloy in 3.5 % sodium chloride medium at 28 °C in the absence and presence of 0.5, 1.0, 1.5 and 2.0 % g/v concentrations of zinc gluconate using gravimetric and electrochemical techniques. The aluminium alloy was cut to corrosion coupons, and immersed into 3.5 % sodium chloride solution containing different inhibitor concentrations (0.5, 1.0, 1.5 and 2.0 % g/v) within a period of twenty-eight days. The surface morphology of the metal was examined by high resolution scanning electron microscopy equipped with energy dispersive spectroscopy (HR-SEM/EDS). From the results, it was found that the adsorption of zinc gluconate reduced aluminium alloy corrosion in the sodium chloride medium. Experimental results also showed that inhibition efficiency increased with an increase in zinc gluconate concentration. Furthermore, potentiodynamic polarization results revealed decrease in corrosion rates (CR), corrosion current densities (Icorr), and increasing corrosion resistance (Rp) in the presence of zinc gluconate in 3.5 % NaCl solution. Tafel polarization analyses indicated that zinc gluconate is a mixed type inhibitor. The adsorption of zinc gluconate on the aluminium alloy surface followed Langmuir adsorption isotherm.     

Role of intermetallic phases in localized corrosion of AA5083

The presence of intermetallic inclusions very often plays a crucial role for the susceptibility of different aluminium alloys to localized corrosion attack. The intimate details of localized corrosion of 5083 aluminium alloy have been studied in the present work. Local techniques such as scanning Kelvin probe force microscopy, in situ atomic force microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy were used to investigate the mechanisms and the kinetics of localized corrosion attack. The importance of iron-rich and Mg₂Si intermetallic phases in the initiation of corrosion processes is demonstrated in the paper.The Mg₂Si phase has a potential lower relatively to the matrix. Moreover, the high reactivity of magnesium leads to the dissolution and consequently to the fast dealloying of these intermetallics. However, hydroxide (Mg(OH)₂ and SiO₂·nH₂O) deposits formed during corrosion act as an additional diffusion barrier hindering the deep propagation of pits.The iron containing intermetallics have the potential higher with respect to the aluminum matrix playing the role of effective cathodic centers for oxygen reduction causing anodic polarization and pitting in the surrounding alloy matrix. Dealloying of such intermetallics with subsequent iron enrichment was also revealed. Pitting initiation seems to be statistical and independent of the composition of Fe-rich intermetallics. However, the active growth of the pits prevents initiation of localized corrosion attack in nearby sites. A new pit can start to grow only when a neighbor one becomes passivated.     

Application of corrosion inhibitors in water-borne coatings

Modification of an acrylate-based model dispersion by different additives which should act as corrosion inhibitors during the flash-off time of the dispersion film on a mild steel surface has been investigated. It is shown that mercapto compounds with a second functional group are capable of interaction with both the substrate surface and the functional groups of the polyacrylate film. Such additives bring about sufficient corrosion inhibition without adversely affecting other properties of the acrylate dispersion. Thus coatings with pronounced barrier properties on steel sheets are built up. The corrosion protection properties of the additives in the liquid dispersion as well as in the coatings formed on steel sheets have been characterized by electrochemical impedance spectroscopy.