Protection of silver surfaces against tarnishing by means of alumina/titania-nanolayers

Tarnishing of Ag is due to the fact that the surface layer containing sulfides is not protective at all as, for instance, the oxide layers which are formed on stainless steel.Transparent ceramic coatings obtained by physical vapor deposition (PVD) intended as corrosion barriers, were studied in the past but their intrinsic defectiveness (residual porosity of the order of 1%) has been the major obstacle in order to guarantee a long-lasting protection. Therefore, organic varnishes are currently employed as protection.Recent nanotechnologies like Atomic Layer Deposition (ALD) are suitable to deposit single molecular layers which, by growing sequentially, turn out to be almost free of defects, displaying therefore a remarkable corrosion protection.In this work, Ag surfaces were coated with ALD alumina/titania nanolayers. Their microstructure and composition were studied with scanning electron microscopy (SEM) and glow discharge optical emission spectroscopy (GDOES) depth profiling. An evaluation of the corrosion behavior of the coatings was made through tarnishing tests and it was shown that the protection given by the ALD layers is at least 10 times superior to conventional organic varnishes. Such result is supported by electrochemical impedance spectroscopy (EIS), which indicates that the initial porosity of the ALD layers is of the order of 0.003%. It was also possible to follow as a function of time, the evolution of the electrical parameters characteristic of the protection system without damaging seriously the structure of the protecting layer.     

Effect of thermal annealing on the corrosion protection of stainless steel by poly(3-octyl thiophene)

Poly(3-octyl thiophene) (P3OT) coatings have been chemically deposited by drop casting onto 304-type stainless steel. P3OT films were thermally annealed at 55, 80 and 100 °C in air during 30 h and their corrosion resistance was estimated by using polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy measurements, EIS. P3OT films decreased the corrosion rate of the substrate by at least one order of magnitude, although the best corrosion protection was given by annealing it at 100 °C whereas the worst corrosion protection was given by annealing the coating at 80 °C.     

Poly(ortho-ethoxyaniline) in corrosion protection of stainless steel

Corrosion protection of stainless steel (13% Cr) coated with poly(ortho-ethoxyaniline) (POEA) has been investigated. The layers of POEA were synthesised from sulphuric and phosphoric acid solutions by means of cyclic voltammetry. The protecting properties of the layers in supporting electrolytes were investigated by monitoring the open circuit potential (E_oc) vs. time, and by electrochemical impedance spectroscopy (EIS). It was found that polymer layers provide corrosion protection, i.e. they help to stabilise the potential of the metal in the passive potential region. The protective properties of POEA layers have shown to be superior to polyaniline (PANI) layers, which is explained by a denser morphology of POEA. The behaviour of POEA obtained on stainless steel, examined by EIS, is different from the one obtained for POEA on Pt electrode. The registered resistance in the case of POEA on stainless steel represents the charge transfer resistance at polymer/solution interface, i.e. the polymer resistance. These measurements show that a part of the layer is reduced, i.e. that there is an interaction between polymer layer and stainless steel. EIS measurements prove the influence of monomer on stainless steel oxide formation and suggest that polymer is partly incorporated into the oxide film.     

制镁还原罐的研制

从含镁的矿石中提炼金属镁的方法已不仅仅是电解法 ,还有目前广泛采用的真空还原法 (皮江法 ) ,但其所用的还原罐寿命短、价格高一直是困扰着国内、国外生产的难题。用研制出新的材料和改革后的铸造工艺生产出的还原罐 ,较好地解决了上述问题 ;并达到国内、国外先进水平。     

Optimization of corrosion protection potential for stress corrosion cracking and hydrogen embrittlement of 5083-H112 alloy in seawater

We report on the optimum corrosion protection potential range for stress corrosion cracking and hydrogen embrittlement of 5083-H112 Al alloy specimens using electrochemical methods and slow strain rate testing (SSRT) in seawater. In the results of the cathodic polarization curve, the concentration polarization due to dissolved oxygen reduction reaction correspondeds to a protection potential of OCP≈ −1.55 V. However, a potential of −1.2 V in the SSRT showed little effect of atomic hydrogen evolution. Potentials less than −1.6 V are affected by atomic and molecular hydrogen. We thus concluded that the effect of atomic hydrogen predominates. Overall, the optimum corrosion protection range for SCC and hydrogen embrittlement of 5083-H112 seems to be between −0.9 V and −0.7 V.     

Polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene) as additives of organic coatings to prevent corrosion

The aim of this work is to compare the protection against corrosion imparted by different conducting polymers when these materials are used as anticorrosive additives in the formulation of conventional epoxy paints. Specifically, the polymers employed as anticorrosive additives are polyaniline emeraldine salt, polyaniline emeraldine base, polyaniline emeraldine salt composite with carbon black, polypyrrole composite with carbon black and poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonate). Initially, the structural, thermal and mechanical properties of the unmodified epoxy paint as well as the modified coatings, obtained by the addition of 0.3 wt.% of conducting polymers, have been characterized. After this, controlled accelerated corrosion assays in an aggressive solution medium were developed using coated steel panels. Results indicate that the protection against corrosion imparted by the formulations modified by the addition of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonate), polyaniline emeraldine salt and, especially, polyaniline emeraldine base is significantly higher than that of the unmodified paint. In contrast, the use of conducting polymer composite with carbon black reduces the efficacy of the coating. Results indicate that some conducting polymer compositions should be considered as a suitable alternative to replace inorganic anticorrosive pigments currently used in paint formulations.     

Synthesis and corrosion protection study of poly(o-ethylaniline) coatings on copper

Poly(o-ethylaniline) coatings were synthesized on copper (Cu) by electrochemical polymerization of o-ethylaniline in an aqueous salicylate solution by using cyclic voltammetry. The characterization of these coatings was carried out by cyclic voltammetry, UV-visible absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results of these characterizations indicate that the aqueous salicylate solution is a suitable medium for the electrochemical polymerization of o-ethylaniline to generate strongly adherent and smooth poly(o-ethylaniline) coatings on Cu substrates. The performance of poly(o-ethylaniline) as protective coating against corrosion of Cu in aqueous 3% NaCl was assessed by the potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results of these studies demonstrate that the poly(o-ethylaniline) coating has ability to protect the Cu against corrosion. The corrosion potential was about 0.078 V versus SCE more positive in aqueous 3% NaCl for the poly(o-ethylaniline) coated Cu (∼ 15 μm thick) than that of uncoated Cu and reduces the corrosion rate of Cu almost by a factor of 70.     

Organic films for protection of copper and bronze against acid rain corrosion

In this paper, the anticorrosive effects of surface films formed on copper and bronzes by different organic inhibitors (mainly benzotriazole derivatives) are evaluated. Several alloys, nominally similar in composition to ancient artistic bronzes, were studied in comparison with copper. The protective efficiency of the organic coatings was tested by electrochemical ac and dc measurements performed both in acid and neutral rain. The experimental data show that benzotriazole derivatives with a long aliphatic chain form thin and very protective films on copper. The presence of the alloying elements (e.g. Sn, Zn, Pb) and multiphasic structures decrease the organic film performances. Nevertheless, among the compounds used, the most efficient, 5-octyl-1,2,3-benzotriazole (C8), seems to be a promising coating in the bronze conservation field.     

Study of electrolyte effects on electrochemical synthesis and p-doping of poly(thienyl biphenyl) films

The electrochemical synthesis and charging–discharging process of a copolymer consisting of 3-octylthiophene (3-OT) and biphenyl units have been studied in different electrolytic media. The polymer material has been characterized by electrochemical and spectroscopic methods: cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), chronopotentiometry, chronoamperometry and FTIR spectroscopy. The diffusion coefficients of different ions in poly(thienyl biphenyl) (PTB) films have been determined by chronoamperometry and compared with corresponding values in poly(3-octylthiophene) (POT) and poly(paraphenylene) (PPP). The best electrolytic conditions for synthesis of poly(thienyl biphenyl) concerning the copolymer structure was found to be in 0.1 M lithium hexafluoro arsenate (LiAsF₆) in acetonitrile. In this electrolyte solution, the content of phenylene segments compared to thienylene segments is highest resulting in a higher degree of cross-linking compared with films made in the presence of the other electrolyte salts studied.     

Two‐step electrosynthesis of polypyrrole for corrosion protection of stainless steel

Smooth polypyrrole (PPy) films were successfully electrosynthesized on a stainless steel (SS, 1Cr18Ni9) surface by a self‐catalytic two‐step process. SS substrate dissolution during PPy electrosynthesis was effectively depressed. The redox properties and corrosion behavior of PPy film coated SS electrodes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization. The reduction of PPy was found to include two reaction processes: an anion dedoping process and a cation insertion process. The PPy film was found to lose its electroactivity when polarized at high potentials due to peroxidation. EIS of SS/PPy mainly corresponds to PPy film response and charge transfer resistance decreases as film thickness increases, indicating that SS corrosion can be inhibited effectively by the PPy film.     

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.     

真空-还原精炼法制备低氧高钛铁合金

针对铝热还原法制备的高钛铁中O含量高、夹杂多等缺点,提出了以铝热法高钛铁为原料进行真空还原精炼制备低O高钛铁的新思路。研究了精炼温度、精炼渣等因素对精炼效果的影响,采用XRD、SEM及化学元素分析等手段对高钛铁合金进行了研究。结果表明,合适的精炼渣和较高的精炼温度对保证精炼效果十分重要;还原精炼后合金的微观结构均匀致密,夹杂物得到有效去除,O含量显著降低;2000℃时以CaO-Al2O3为精炼渣制备的高钛铁合金中钛含量为69.80%,铁含量为22.55%,铝含量为2.58%,硅含量为2.02%,O含量为2.60%,符合优质高钛铁合金的技术要求。     

微弧氧化-溶胶凝胶复合表面技术改善铝合金的耐腐蚀性能

通过微弧氧化-溶胶凝胶复合表面处理技术来提高铝合金的耐腐蚀性能,分析了多层凝胶层对6061铝合金耐腐蚀性能的影响。采用扫描电镜（SEM）、X射线衍射仪（XRD）和电化学分析等方法对膜层的表面形貌、化学组成、结构以及耐腐蚀性能进行了表征。研究表明：TiO2溶胶渗入微弧氧化陶瓷膜的微孔以及裂纹中,能有效阻挡腐蚀介质的扩散和渗透;复合处理后的试样较仅微弧氧化处理更平滑、致密;膜层除了γ-Al2O3相外,经高温退火处理后出现TiO2锐钛矿,并形成较好的晶相结构;在3.5%NaCl溶液中的室温电化学行为中,复合处理较微弧氧化处理后的试样自腐蚀电位上升最高约400 mV,自腐蚀电流密度最高减小约3个数量级,极化电阻明显增大;随着凝胶层厚度的增加耐腐蚀性能逐渐增强,但当凝胶层数大于4时,膜层龟裂现象严重,并导致耐腐蚀性能开始下滑。     

Electrochemical characteristics of poly(3-methyl thiophene)/sulfonated-SEBS composite electrode for polymer battery

We, in this study, focus on the effect of sulfonated poly(styrene-ethylene-butylene-styene) (SSEBS) as a binder to enhance electrochemical property of poly(3-methyl thiophene) (P3MT) as a active material of cathode in redox system. P3MT was polymerized using FeCl₃ as both a dopant and an initiator. The cathode was prepared to cast on Al mesh the slurry mixed P3MT, carbon black and binder (8:1:1 wt.%). The specific discharge capacity of P3MT–SSEBS electrode is high as 80 mAh/g, while that of P3MT–SEBS and P3MT–PVDF electrodes have lower values as 50 and 25 mAh/g, respectively. The reason for this is that SSEBS acts as a binder as well as a dopant. In an advance, the effect of sulfonation promotes the miscibility, contact area and affinity.     

Formation and immobilization of silver nanoparticles onto chromia surface by novel preparation route involving polyol process

Silver nanoparticles were formed and immobilized onto the chromia surface by novel preparation route involving polyol process for the first time. (3-Mercaptopropyl) trimethoxy silane (MPTMS) was employed as a chemical protocol to make a binding between silver nanoparticle and chromia surface. UV-vis absorption spectroscopy, TEM observation and EDS analysis revealed that silver nanoparticles with a size of ∼ 50 nm in diameter were formed and immobilized onto the surface of chromia particles with an average size of 210 nm. It is thought that this novel preparation route can be extended to the preparation of various metal-inorganic heterogeneous composite particles.     

The role of rusts in corrosion and corrosion protection of iron and steel

The processes of atmospheric corrosion of iron and steel and the properties of corrosion products (rusts) are modeled based on a quantitative evaluation of the chemical reactions pertaining to corrosion to elucidate the conditions with which corrosion-protective rust films form. Based on the model, it is suggested that in the initial stage of corrosion, in the rusts, the pH of the aquatic system is maintained at 9.31 owing to an equilibrium with iron(II) hydroxide and the rate of air-oxidation at this pH is very fast, and that dense, self-repairing rust films form, protecting the underlying iron and steel. However, after corrosion stops, the rust film deteriorates due to the dissolution and shrinkage by aging, and the deteriorated rust film separates the anode and cathode reaction products (Fe²⁺ and OH⁻ ions) to cause crevice corrosion. The air-oxidation of iron(II) in anode channels without the presence of OH⁻ ions results in strongly acidic solutions (pH 1.41), causing acid-corrosion. It is proposed that good catalysts (e.g. copper(II) and phosphate ions) accelerate the air-oxidation at low pH, delaying the crevice- and acid-corrosion stages. Further, it is argued that iron compounds with negative charges due to the non-stoichiometric proportions of the lattice oxide ions and metal ions (solid oxoanions of iron) exhibit stable cation-selective permeability even with a drop in pH. Rust films including such compounds would stop the passage of aggressive anions and act to protect iron and steel.     

An efficient protection of stainless steel against corrosion: Combination of a conversion layer and titanium dioxide deposit

In the present work, a novel process has been developed to improve the corrosion properties of ferritic stainless steels. Titanium oxide coatings have been deposited onto stainless steel by sol-gel process after a pre-functionalization of the substrate in a conversion bath. Gel titania was prepared by hydrolysis of a titanium butoxide through a sol-gel process. Duplex systems “conversion layer/uniform TiO₂ coating” have been prepared on stainless steels using a dipping technique and thermal post-treatments at 450 °C. The preparation of sol-gel coatings with specific chemical functions offers tailoring of their structure, texture and thickness and allows the fabrication of large coatings. The morphology and structure of the coatings were analysed using scanning electron microscopy with field effect gun (SEM-FEG), Mass spectroscopy of secondary ions (SIMS) and X-ray diffraction (XRD). The anticorrosion performances and the ageing effects of the coatings have been evaluated in neutral and aggressive media by using several normalized tests.The results show that the conversion layer was not sufficient to protect steel but sol-gel TiO₂ coatings, anchored on the metal substrate via the conversion layer, show good adhesion with the substrate and act as a very efficient protective barrier against corrosion. So, duplex layers with TiO₂ nanoparticle coatings on steels exhibit an excellent corrosion resistance due to a ceramic protective barrier on metal surface. Analysis of the data indicates that the films act as geometric blocking layers against exposure to the corrosive media and increase drastically the lifetime of the substrate.     

Investigation of preparation and characteristics of Sn-Bi eutectic powders derived from a high shear mechanical approach

Fusible Sn-Bi eutectic alloy particles were synthesized from bulk Sn-Bi alloy via a high-shear mechanical approach. The morphology, composition, and structure of the as-prepared Sn-Bi alloy particles were characterized by XRD, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, thermogravimetry, and Fourier-transform infrared spectroscopy. The particles were found to be spherical and consist of the tetragonal phase of tin as well as the rhombohedral phase of bismuth. In addition, there were large amounts of poly(N-vinylpyrrolidone) coated on the particles.