Corrosive Effect of Plastics,Rubber and Wood on Metals in Confined Spaces

Abstract

The corrosion of metals enclosed in equipment or packages is influenced by vapours arising from other materials which may also be present. Plastics, wood and rubber are the principal sources of such vapours. Even when no vapours are evolved, corrosion of a metal may result from contact with some non-metallic materials.

Samples of iron, zinc, copper, aluminium and cadmium either in contact with or in a sealed space with various types of non-metallic material, were exposed to corrosion. The extent of corrosion was observed and analyses were made of products and of the surrounding atmosphere. Formic and acetic acid are the most aggressive volatile products from wood and the same compounds, together with formaldehyde, ammonia and halogen acids, may be evolved from plastics and sulphur compounds from rubber. Of the plastics, phenolic resins, especially as mouldings filled with wood flour, and, of the woods, oak, chestnut and beech are the most likely to produce acetic and formic acid vapours, but other materials have appreciable specific vapour or contact effects.     

The effect of mechanical polishing and finishing on the corrosion resistance of AISI 304 stainless steel

The aim of the present work was to study the influence of surface finishing on the corrosion resistance of AISI 304 stainless steel samples. Samples were submitted to lathe-turning, milling, lapping and grinding. Roughness parameters were determined by confocal laser scanning microscopy (CLSM). The corrosion resistance was evaluated using potentiodynamic polarisation curves and the corrosion morphology was assessed using CLSM and scanning electron microscopy. The results showed that the surface state had a remarkable influence on the corrosion behaviour of the samples, especially surface imperfections, whereas the roughness parameters did not directly correlate with the corrosion resistance.     

Effect of small additions of ruthenium on pitting corrosion resistance of LDX2101 duplex stainless steel

Four stainless steel alloys with ruthenium compositions of 0·16, 0·24, 0·32 and 0·64 wt-% were produced from pieces cut from commercial LDX2101 duplex stainless steel plate with the manufacturer’s composition of 0·03C–21·5Cr–1·5Ni–0·3Mo–5·0Mn plus pressed ruthenium powder with purity of 99·8%. After solution annealing the samples, the actual chemical composition was analysed using X-ray fluorescence analysis, and then, ASTM A923 (01·03) test method A – sodium hydroxide etch test for classification of etch structures of duplex stainless steel was used to analyse their microstructure. Corrosion potential and pitting potential of these samples were evaluated using a potentiodynamic polarisation technique, and the results were compared to corrosion and pitting potentials of the control alloy LDX2101. The tests for both produced and control alloys were performed in naturally aerated 3·56%NaCl aqueous solution at 25±2°C. The results indicated that small additions of ruthenium significantly improved the pitting potentials of the resulting alloys. The results also indicated that ruthenium additions have no detrimental effect to the microstructure of the resulting alloys. In addition, if such small additions of ruthenium will not improve the general corrosion of the resulting alloy, it will at least not have any detrimental effect on the resulting alloy. Ruthenium will also lower the current required to maintain the passive state of LDX2101 stainless steel. In addition to reduced current to maintain the passivity of LDX2101 stainless steel, ruthenium also increased the passive range of LDX2101 stainless steel.     

Effect of surface mechanical attrition treatment (SMAT) on zinc phosphating of steel

The effects of surface mechanical attrition treatment (SMAT) of EN8 steel on the growth of phosphate coatings, morphological features and corrosion resistance of the resultant coatings have been studied. SMAT enabled the formation of a uniform surface profile although the average surface roughness is increased after treatment. SMAT increased the extent of metal dissolution and the rate of growth of phosphate coating. In spite of the similarity in phase composition, the phosphate crystallite size is relatively high for samples treated by SMAT. Compared to the untreated one, a cathodic shift in E_corr with a corresponding decrease in i_corr is observed for SMAT treated EN8 steel after phosphating. For all tested samples, zinc phosphate coatings deposited on EN8 steel after SMAT using 8 mm Ø balls for 30 min offers the highest corrosion resistance. The increase in surface roughness by SMAT is partly compensated by the expected improvement in corrosion resistance.     

Environmental influences on linear polarisation corrosion rate measurement in reinforced concrete

The linear polarisation resistance (LPR) method can be used to measure the active rate of corrosion of steel reinforcement in concrete structures. However a single measurement may be sensitive to the ambient environmental conditions and thus may not be representative of the mean annual rate of corrosion. The LPR measurement may be dependent upon the temperature at the time of sampling and on any wetting/drying effects resulting from rainfall and wind or sunshine.Recent studies have examined the behaviour of a series of reinforced concrete specimens subject to chloride contamination or carbonation induced corrosion in a controlled laboratory environment. LPR measurements taken at frequent intervals have been related to a wet/dry cycle imposed upon the specimens to promote corrosion activity. In addition, similar studies have been carried out, of an in situ reinforced concrete specimen exposed to the ambient weather conditions. The study is only partly completed, but interim results show the variability of LPR measurements and the influences the environment may exert on single spot measurements.     

Studies on the effect of pyranocoumarin derivatives on the corrosion of iron in 0.5 M HCl

The effect of some new synthesized pyranocoumarins on the corrosion of iron in 0.5 M HCl was investigated. The investigation involved electrochemical polarization methods (potentiodynamic, Tafel extrapolation and the determination of the polarization resistance) as well as weight loss measurements. The results show that these compounds act as mixed type inhibitors, but the cathode is more preferentially polarized. The inhibition efficiency depends on both the nature and concentrations of the investigated compounds. Compounds are found to adsorb on the iron surface according to the Langmuir adsorption isotherm. Fourier transform infrared spectrophotometry was used to obtain information on bonding mechanism between the metallic surface and the inhibitors.     

Effects of pH and chloride concentration on pitting corrosion of AA6061 aluminum alloy

Effects of pH solution and chloride (Cl⁻) ion concentration on the corrosion behaviour of alloy AA6061 immersed in aqueous solutions of NaCl have been investigated using measurements of weight loss, potentiodynamic polarisation, linear polarisation, cyclic polarisation experiment combined with open circuit potential transient technique and optical or scanning electron microscopy.The corrosion behaviour of the AA6061 aluminum alloy was found to be dependant on the pH and chloride concentration [NaCl] of solution. In acidic or slightly neutral solutions, general and pitting corrosion occurred simultaneously. In contrast, exposure to alkaline solutions results in general corrosion. Experience revealed that the alloy AA6061 was susceptible to pitting corrosion in all chloride solution of concentration ranging between 0.003 wt% and 5.5 wt% NaCl and an increase in the chloride concentration slightly shifted both the pitting E_pit and corrosion E_cor potentials to more active values. In function of the conditions of treatment, the sheets of the alloy AA6061 undergo two types of localised corrosion process, leading to the formation of hemispherical and crystallographic pits.Polarisation resistance measurements in acidic (pH = 2) and alkaline chloride solutions (pH = 12) which are in good agreement with those of weight loss, show that the corrosion kinetic is minimised in slightly neutral solutions (pH = 6).     

Effect of ecofriendly sealing coat against corrosion protection of steel rebars in concrete

Phosphating is one of the most important chemical conversion treatments for steel, mainly to improve corrosion resistance and paint adhesion and as an absorbing layer for waxes, oils, lacquers, etc. However, phosphate coating are crystalline and porous and need a sealing treatment after phosphating. Chromate sealing is a well known practice, and due to its toxicity, development of an ecofriendly sealing treatment is very essential. This paper focuses on the effect of zinc phosphate chemical conversion coating with the addition of nano-SiO₂ to protect the mild steel rebars against corrosion in chloride contaminated concrete. The coated surfaces were characterised by scanning electron microscopy and X-ray diffraction. Corrosion resistances of coated and uncoated rebars were evaluated by anodic polarisation, linear polarisation resistance, Tafel and alternating current impedance spectroscopy and cyclic polarisation technique. The results indicated that the coated rebars have considerably reduced the corrosion rate even in the presence of 3% chloride environments.     

Corrosion behaviour of NiTi endodontic instruments

Abstract

The present study investigates the influence of the sterilisation treatment conducted at 50°C in 5% sodium hypochlorite solution (NaClO) on the corrosion behaviour of endodontic instruments made of NiTi (GT Rotary and K3) and stainless steel (K file) by measuring potentiodynamic polarisation curves in the same environment at 37°C. For comparison, the electrochemical characterisation was also carried out on endodontic instruments that were not sterilised. The characterisation of the sample surface after the electrochemical tests were carried out by means of scanning electron microscopy coupled with X-ray energy dispersive spectroscopy. There was no significant influence of the sterilisation treatment on the corrosion behaviour of K file and GT Rotary endodontic instruments. However, a negative influence of the sterilisation treatment on the corrosion resistance of K3 endodontic instruments was observed, and the effect appears to be more dramatic for longer sterlisation treatment periods.     

Effect of cerium addition on the corrosion behaviour of carbon-alloyed iron aluminides

The effect of Ce addition on the microstructure and corrosion behavior of carbon-alloyed iron aluminides Fe-20.0Al-2.0C, Fe-18.5Al-3.6C and Fe-19.2Al-3.3C-0.07Ce (in at.%) has been studied. The potentiodynamic polarization behaviour of the alloys was evaluated in freely aerated 0.25 mol/l H₂SO₄. A 0.05% C steel was used for comparison purposes. All the alloys exhibited active-passive behaviour in the acidic solution. The addition of Ce destroyed passivity as indicated by lower breakdown potentials in polarization studies. This has been related to the finer distribution of the carbides in the microstructure. Corrosion rates were evaluated by immersion testing. The iron aluminide with Ce addition exhibited a lower corrosion rate compared to the aluminides without Ce addition. This has been attributed to modifications in surface film with Ce addition. Scanning electron microscopy of corroded surfaces indicated that the carbon-alloyed intermetallics were susceptible to localized galvanic corrosion due to the presence of carbides in the microstructure.     

Enhanced corrosion resistance of WC-Co with an ion beam mixed silicon carbide coating

Strong adhesion of a silicon carbide (SiC) coating to a WC-Co substrate was achieved through an ion beam mixing technique and the corrosion resistance of the SiC coated WC-Co was investigated by means of a potentiodynamic electrochemical test. In a 1 M NaOH solution, the corrosion current density of SiC-coated WC-Co after heat treatment at 500 °C was about 50 times lower than that for the as-received WC-Co. In addition, the corrosion resistance systematically increases with increasing the SiC coating thickness. On the other hand, for a 0.5 M H₂SO₄ solution, the corrosion current density for SiC-coated WC-Co was about 3 times lower than that for the as-received WC-Co. We discuss the physical reasons for the changes in the corrosion current density with the different electrolytes.     

Improved corrosion behavior of nanocrystalline zinc produced by pulse-current electrodeposition

Pulse electrodeposition was used to produce nanocrystalline (nc) zinc from zinc chloride electrolyte with polyacrylamide and thiourea as additives. Field emission scanning electron microscopy (FESEM) was used to study the grain size and surface morphology of the deposits and X-ray diffraction was used to examine their preferred orientation. Corrosion behavior of the electrodeposited nc zinc in comparison with electrogalvanized (EG) steel in de-aerated 0.5 N NaOH solution was studied using potentiodynamic polarization and impedance measurements. A scanning electron microscope (SEM) was used to characterize the surface morphology of the EG steel before corrosion testing. Surface morphologies of nc zinc deposits and EG steel were also studied after potentiondynamic polarization by SEM. Nanocrystalline zinc (56 nm) with random orientation was produced. The estimated corrosion rate of nc zinc was found to be about 60% lower than that of EG steel, 90 and 229 μA/cm², respectively. The surface morphology of corroded nc zinc was characterized by discrete etch pits, however, uniform corrosion was obtained after potentiodynamic polarization of EG steel. The passive film formed on the nc zinc surface seems to be a dominating factor for the corrosion behavior observed.     

Oxidation resistance and corrosion behavior of hot-dip aluminized coatings on commercial-purity titanium

Aluminizing is an effective method to protect alloys from oxidation and corrosion. In this article, the microstructure, morphology, phase composition of the aluminized layers and the oxide films were investigated by SEM, EDS and X-ray diffraction. The high temperature oxidation resistance and electrochemical behavior of hot dip aluminizing coatings on commercial-purity titanium had been studied by cyclic oxidation test and potentiodynamic polarization technique. The results show that the reaction between the titanium and the molten aluminum leads to form an aluminum coating which almost has the composition of the aluminum bath. After diffusion annealing at 950 °C for 6 h, the aluminum coating transformed into a composite layer, which was composed of an inner layer and an outer layer. The inner layer was identified as Ti₃Al or Ti₂Al phase, and the outer layer was TiAl₃ and Al₂O₃ phase. The cyclic oxidation treatment at 1000 °C for 51 h shows that the oxidation resistance of the diffused titanium is 13 times more than the bare titanium. And the formation of TiAl₃, θ-Al₂O₃ and compact α-Al₂O₃ at the outer layer was thought to account for the improvement of the oxidation resistance at high temperature. However, the corrosion resistance of the aluminized titanium and the diffused titanium were reduced in 3.5 wt.% NaCl solution. The corrosion resistance of the aluminized titanium was only one third of bare titanium. Moreover, the corrosion resistance of the diffused titanium was far less than bare titanium.     

Effect of potassium fluoride on structure and corrosion resistance of plasma electrolytic oxidation films formed on AZ31 magnesium alloy

Plasma electrolytic oxidation films on AZ31 magnesium alloy were prepared in silicate–KOH–glycol (base electrolyte) electrolyte with the addition of different KF concentration. The effect of KF on the characteristic of discharge in electrolytes was studied. The compositions, structures and morphologies of the oxide films formed in different KF concentration were determined by energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Corrosion behavior of the oxide films was evaluated in 3.5 wt.% NaCl solution using potentiodynamic polarization tests, electrochemical impedance spectroscopy and potentiodynamic scanning tests. The films were mainly composed of Mg, Al, O, C, Si as well as a trace of Na and K. Major phases were MgSiO₃ and forsterite Mg₂SiO₄. The appearance of KF in the base electrolyte resulted in the decrease of the equilibrium current density and the appearance of MgF₂ in the films. Corrosion resistance depends on the amount of MgF₂ composition in the films. The films formed in the electrolyte containing 8.0 g/L KF exhibit the highest uniform corrosion resistance and the lowest pitting-corrosion tendency in NaCl solution.     

Effect of heat treatment on corrosion properties of CuAlNi shape memory alloy

The effect of heat treatment on corrosion properties of CuAlNi shape memory alloy was investigated in 0.9% NaCl solution at pH 7.4 and 37 °C by open circuit potential measurements, polarisation techniques, and electrochemical impedance spectroscopy. Investigations were performed on CuAlNi alloy samples in as-cast state and after heat treatment procedure containing annealing at 850, 885 and 920 °C followed by water quenching. Electrochemical impedance measurement results indicate that heat treatment of CuAlNi alloy leads to the increase in charge transfer resistance and surface layer resistance and the decrease in values of capacitance of the double and surface layers, indicating higher corrosion resistance compared with the as-cast CuAlNi alloy. The increase in polarisation resistance and the decrease in corrosion current density of heat-treated CuAlNi alloy also suggest beneficial influence of heat treatment on corrosion resistance of CuAlNi alloy. Optical microscopy, SEM/EDX and XRD analysis of samples surface after polarisation measurements show the occurrence of pitting corrosion on the electrode surfaces, with the existence of CuCl₂, AlCl₃ and Cu₂Cl(OH)₃ compounds as the surface corrosion products.     

Selected corrosion behaviors of a Cu0.5NiAlCoCrFeSi bulk glassy alloy in 288 °C high-purity water

Selected corrosion behaviors of a Cu_0.5NiAlCoCrFeSi bulk glassy alloy like electrochemical corrosion potential (ECP), potentiodynamic polarization, and weight loss were investigated in 288 °C high-purity water. The change of ECP with dissolved oxygen showed a sigmoid curve. The Cu_0.5NiAlCoCrFeSi alloy exhibited a wide passive region and the passive current density was 2 × 10⁻⁴ A/cm² in deaerated 288 °C water containing 0.01 N sodium sulfate. A low weight loss of 4.5 μg/mm² was found for the Cu_0.5NiAlCoCrFeSi alloy after immersion in deaerated 288 °C water for 12 weeks.     

Development of chromate-free coated steel sheet with high corrosion resistance and conductivity

The ideal coating structure, which can achieve both high corrosion resistance and high conductivity, was examined by SEM analysis of conventional chromate-free coated steel sheets. Based on the results of SEM analysis, it was found that high conductivity was achieved by maintaining the convex parts of zinc plating crystals at the coating surface. High corrosion resistance was also achieved by combining a novel silicate binder and metal salt. The results of electrochemical analysis revealed that the silicate binder contributed to suppressing the anodic reaction, while a composite coating involving epoxy resin and phosphoric acid was effective for suppressing the cathodic reaction and maintaining a high barrier property for an extended time.     

镁合金表面聚苯胺膜层防腐性能的研究

用循环伏安法在镁合金表面制备了聚苯胺膜层,并用扫描电子显微镜(SEM)和电极电位研究了聚苯胺膜的表面形貌和腐蚀防护性能.研究表明:聚苯胺膜层并不是均匀覆盖在基体表面,而且膜层表面存在很多的微孔;聚苯胺改变了膜层的电极电位;在腐蚀介质中聚苯胺膜以点蚀或剥离的方式进行腐蚀.     

The effect of alloying element gallium on the polarization characteristics of Pb-free Sn-Zn-Ag-Al-XGa solders in NaCl solution

The polarization characteristics of Sn-8.5Zn-0.5Ag-0.1Al-XGa lead-free solders were investigated in 3.5% NaCl solution where X ranges from 0.05-1.5 wt%. The results show that Ga affects the anodic polarization behaviour of the solders. Passivation behaviour is observed for all the investigated Sn-8.5Zn-0.5Ag-0.1Al-XGa solders. Increase in the Ga content from 0.05 to 0.25 wt% increases the ability for passivation but the oxide film formed due to passivity is not so protective. However Ga content > 0.25 wt% enhances corrosion and decreases the protective power of the passive film. The magnitude of the passivation current densities depend on the composition of the solders and the potentials applied. Layers of oxides of tin and zinc are responsible for the passivation behaviour. XRD and SEM results revealed the formation of corrosion products like SnO, ZnO, SnO₂ at different potentials during the polarization study.     

Effect of calcium ions on CO_2 corrosion of 3Cr low-alloy steel

The effect of calcium ions on the corrosion behavior of 3Cr low-alloy steel in CO 2 containing sodium chloride solution was investigated by immersion test and electrochemical measurements. It is found that with the addition of Ca 2+ to CO 2-containing solution,the crazing level of the corrosion scale on the specimen is much slighter than that of the specimen immersed in solution without Ca 2+ . The pitting on the surface of the specimens immersed in the solution with Ca 2+ is relatively small and distribute...