超轻多孔金属的耐腐蚀性能

研究闭孔泡沫铝的孔结构、基体对耐蚀性能的影响,探讨提高耐腐蚀性能的途径。结果表明：其耐蚀性远低于实体金属,在孔径相近情况下,随孔隙率的增大,表面积增大,使耐腐蚀性能下降;Al-Mg-Re基防锈泡沫铝具有优异的耐腐蚀性能;添加适量稀土元素可以提高耐腐蚀性能。提高泡沫铝耐腐蚀性能的途径为：降低小孔径泡沫铝的孔隙率;采用防锈泡沫铝和添加适量稀土元素;对泡沫铝进行喷漆处理或阳极氧化、化学转化处理等。     

Anisotropy problems with synthetic metals

Because of their bond structure, most synthetic metals have 1D or 2D preferred directions of high electrical conductivity. Problems arising from their high anisotropy are considered with reference to electron band and chemical resonance bond models. Various electromagnetic properties can give relevant information provided perturbations from structural defects a re minimised.     

Corrosion resistance of zinc-coated structured sheet metals

The purpose of this study is to characterise the corrosion behaviour of zinc-coated sheet metals after a structuring process using the salt spray test. The investigated structured material is manufactured by hydroforming and has a periodic hexagonal geometry. The corrosion behaviour has been evaluated by estimating the development of the corrosion area and penetration depth. The results of the investigation show that the corrosion area is larger on the smooth sheet than on the structured sheet. The difference between the structured and smooth sheets is negligible with increasing exposure time. Furthermore, the reasons for the different corrosion behaviours are discussed.     

Non-dissipative transport in lamellar synthetic metals

The anisotropy of synthetic metals is generally high. For lamellar solids their electrical conductivity may be even roughly two dimensional. It is markedly enhanced by contriving charge transfer bonding between electron donor or electron acceptor molecules and the host framework which provides a layered skeleton of valence bonds in which delocalised electrons can transport electricity.Various aspects are discussed of systems of charge transfer bonds formed at the boundaries of each layered skeleton. Mass movement of the intercalated molecules often takes place with surprising ease, with only low activation energy for change of site. Constraints from the layered skeletons may favour “non-dissipative” diffusion of the intercalated molecules. Analogous instances are cited when constraints facilitate easy molecular movement in certain directions.Alternative ways in which the system of charge transfer bonds in a lamellar synthetic metal could enhance the electrical conductivity are considered. A primitive model assumes that the concentration of charge carriers is substabtially altered by the injection (or removal) of charges into a conduction band by the donor (or acceptor) molecules intercalated. As another contributory factor, charge carriers travelling within any layer at grazing incidence upon its boundaries may have their mean free paths notably extended through internal reflection and non-dissipitive forward scattering.Both factors may depend, in a sensitive way, on detailed characteristics of the system of charge transfer bonds set up at the boundaries of each layer.     

Corrosion prognosis for metals with oxygen depolarization

Based on the results of corrosion tests, the penetration coefficients of corrosion products and the steady-state corrosion rate of an CT-3 steel are statistically assessed as a function of the oxygen concentration distribution. Original Russian Text ? B.B. Chernov, O.P. Kovalev, A.V. Volkov, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 3, pp. 309–311.     

Corrosion inhibition of some metals using lawsonia extract

The aqueous extract of the leaves of henna (lawsonia) is tested as corrosion inhibitor of C-steel, nickel and zinc in acidic, neutral and alkaline solutions, using the polarization technique. It was found that the extract acts as a good corrosion inhibitor for the three tested electrodes in all tested media. The inhibition efficiency increases as the added concentration of extract is increased. The degree of inhibition depends on the nature of metal and the type of the medium. For C-steel and nickel, the inhibition efficiency increases in the order: alkaline < neutral < acid, while in the case of zinc it increases in the order: acid < alkaline < neutral. The extract acts as a mixed inhibitor. The inhibitive action of the extract is discussed in view of adsorption of lawsonia molecules on the metal surface. It was found that this adsorption follows Langmuir adsorption isotherm in all tested systems. The formation of complex between metal cations and lawsone is also proposed as additional inhibition mechanism of C-steel and nickel corrosion.     

Corrosion behavior of engineering alloys in synthetic wastewater

The corrosion behavior of 1018, 410, and 800 steels exposed to synthetic wastewater have been studied using linear polarization resistance, cyclic potentiodynamic curves (CPCs), electrochemical noise (EN), and electrochemical impedance spectroscopy (EIS) tests. The conditions were: a biochemical oxygen demand of 776 ppm; a chemical oxygen demand of 1293 ppm; a pH of 8; and a cell temperature of 25 °C. From the CPC and EN results, no localized corrosion was found for the stainless steels. However, small indications of a possible localized corrosion process were detected for the 1018 steel. The EIS results revealed that different corrosion mechanisms occurred in the carbon steel compared with the stainless steels. The results show that the corrosion mechanism strongly depends on the type of steel. Overall, the 1018 steel exhibited the highest corrosion rate, followed by the 410 alloy. The highest corrosion resistance was achieved by the 800 alloy. In addition, scanning electron microscopy analyses were carried out to explain the experimental findings.     

Search for C60-based synthetic metals

C₆₀ forms solvates with dimethylnaphthalenes (DMNAP) of either 1:1 or 1:2 molar ratio. All these solvates crystallize in the triclinic lattice with different lattice parameters. The C₆₀(DMNAP)₂ solvates decompose at approximately 80–120°C to the C₆₀DMNAP solvates. At higher temperatures the second solvent molecule is released and C₆₀ returns to the f.c.c. lattice. In our experiments we searched for C₆₀-based solvates where, in the solid form, the π-electron-rich fragments of the solvent molecules might be forced to a close contact with fullerenes, thus leading to a deformation of molecules and an overlap of the molecular orbitals. Molecular mechanical methods were used to optimize the structure of the molecules in the lattice determined by X-ray diffraction and semi-empirical quantum chemistry methods to calculate the electronic structure of the solvates.     

Ferroelectricity in synthetic metals: Reality and hypotheses

Ferroelectricity is one of the demanded effects in fundamental and applied solid state physics. Till now, the ferroelectrics were available mostly in the inorganic world. The breakthrough of 2000s was an unexpected discovery of the ferroelectricity related to the charge ordering in quasi-1D organic conductors (TMTTF)₂X, and in some layered compounds. The achieved understanding of underlying mechanisms allows to speculate on synthesis of a would-be ferroelectric polymer: it must possess a combination of dimerizations of sites and bonds, one of which must be build-in and another spontaneous. The theory of these “combined Peierls states” predicts an existence of solitons (dimerization kinks) with non-integer variable charges—they are the walls separating domains with opposite electric polarization. The physics of these exotic solitons will serve to describe transient processes in ferroelectric polymers, linking optical- and low-frequency properties. The promising example of such an (AB)_x conjugated polymer has already appeared but was not yet tested for ferroelectricity. A wide chemical search is necessary because of a problematic competition of an anti-ferroelectric phase, whose occurrence depends on complicated details of the interchain coupling.     

Corrosion and elution of harmful metals from metal buttons

Metals present in metal items may due to the corrosion processes that occur in sweat cause adverse health effects, such as allergic reactions, on direct and prolonged contact with the skin. For example, 20% of female population and about 6% of male population are allergic to nickel. Therefore, three different textile accessories were tested for metal leaching: the samples were kept at 30 °C in the artificial sweat solution for different time periods and quantified. The results have shown that the limits prescribed by international standards were much exceeded. Samples of such properties present a high risk for human health and should be used with special attention.     

Corrosion of Ferrous metals in Batch Cultures of Nitrate-Reducingu Bacteria

Abstract

The corrosion of an iron/carbon alloy has been investigated in short-term experiments in batch cultures of the bacterium Escherichia coli grown in media containing two concentrations of nitrate and in a nitrate-free medium. The growth of the organism was also investigated in the above media but in the absence of metal samples. The results show that growth is affected by the presence of the metal and that the principal cause of corrosion is the formation of metabolic organic acids. The nitrite produced by bacterial reduction of the nitrate reacts with the metal to form a protective film.     

铝基钎料真空钎焊接头的腐蚀性

采用NaCl的质量分数为3．5％的溶液对四种Al-Si-Cu钎料的真空钎焊接头进行全浸试验，对腐蚀后的钎焊接头进行观察，分析接头的腐蚀类型，研究接头的腐蚀机理，对Cu的晶界偏析及扩散进行了讨论。结果表明，铝基钎料真空钎焊后的接头仍然存在腐蚀问题，腐蚀产物为A1Cl3、Al(OH)3、Al(OH)2Cl，腐蚀类型有点蚀和晶间腐蚀；并且随着Cu含量的增加腐蚀加重，Cu的偏析与扩散对接头腐蚀行为产生重要的影响，在晶界形成他Cu，使晶界周围形成贫Cu区，与晶粒内部处于钝态的αAl存在较大电位差，构成局部腐蚀电池，形成晶间腐蚀。     

Corrosion resistance of nickel in artificial sweat and synthetic seawater

The corrosion resistance of nickel 200 has been determined in artificial sweats (perspiration) and in synthetic seawater by several electrochemical methods. Nickel 200 is not stable in the two electrolytes investigated and the attack occurs with the formation of pits. The electrochemical behaviour is characterized by a short passive region with a current density of about 0.1 mA/cm² then by a transpassive region. The corrosion rate has been measured in N₂-and O₂-saturated electroytes by the potentiostatic (10 mV potential step per min), polarization resistance in the vicinity of the corrosion potential and ac impedance methods. The three techniques gave comparable results. Corrosion rates were roughly 10 times larger in artificial sweat than in seawater. Nickel 200 cannot be used for application where it may be in direct contact with the skin because of its high corrosion rate in oxygenated sweat. The released nickel ion is responsible for contact dermatitis observed in some individuals.     

Corrosion behaviors of Al-Si-Cu-based filler metals and 6061-T6 brazements

The corrosion behaviors of a series of Al-Si-Cu-based filler metals and the 6061-T6 butt joints brazed with these filler metals are evaluated by polarization tests and immersion tests in a 3.5% NaCl aqueous solution. For comparison, a traditional Al-12Si filler metal is also employed. The results indicate that the Al-Si-Cu-based filler metals before brazing possess much higher corrosion current densities and pitting tendencies than the Al-12Si filler metal. However, brazing of the 6061-T6 alloy with an Al-12Si filler metal produces a wider butt joint, which, in this case, creates a more extensive corrosion region. Severe galvanic corrosion occurs at the 6061-T6 joints when brazed with Al-Si-Cu-based filler metals. However, in the case of the 6061-T6/Al-12Si brazements, selective corrosion of the Al-12Si eutectic phase can be observed. The bonding strengths of the 6061-T6 butt joints brazed with various filler metals are also measured before and after the immersion tests.     

The Corrosion of metals in an oxidizing-chloridizing environment at high temperature

An investigation has been undertaken into the behaviour of metals which form the basis of high-temperature alloys in an argon ?5.5% oxygen ?0.96% hydrogen chloride ?0.86% sulphur dioxide gas mixture at 900°C. The intention has been to ascertain the reaction products, with particular emphasis on the formation of volatile species which can cause considerable degradation of commercial alloys in this environment. From consideration of the thermodynamics of the gas system, the potentials of the reactive species can be determined and correlated with the possible reaction products. In this gas mixture, the oxides of nickel, iron, cobalt, chromium, molybdenum and tungsten are the stable phases with respect to the corresponding metals. Indeed, on exposure of the metals to the environment, the appropriate oxide scales are developed. However, the reactions are complicated by formation of volatile corrosion products, particularly for nickel, cobalt and molybdenum. Although a Cr₂O₃ scale is established on chromium, there is evidence for penetration of chlorine-containing species to the scale/alloy interface. The oxide scale on tungsten is not very protective and thickens rapidly while that on molybdenum is volatile, resulting in rapid consumption of the specimen.     

Corrosion of metals and alloys in sulfate melts at 750°C

The corrosion of Ni, Co, Ni-10Cr, Co-21Cr, and IN738 was studied at 750°C in the presence of molten sulfate mixtures (Na₂SO₄-Li₂SO₄ and Na₂SO₄-CoSO₄) and in an atmosphere consisting of O₂+0.12% SO₂-SO₃. The corrosion was observed to be similar for both Na₂SO₄-Li₂SO₄ and Na₂SO₄-CoSO₄ melts. The corrosion of Ni and Co tookplace by the formation of a mixed oxide plus sulfide scale, very similar to the corrosion in SO₂ or SO₃ alone. The initial stage for the corrosion of Ni-10Cr involved the formation of a thick NiO+Ni₃S₂ duplex scale, and Cr sulfide was formed during the later stages. A pitting type of morphology was observed for both Co-21 Cr and IN738. The pit was Cr sulfide at the beginning, and subsequently the sulfides oxidized to Cr₂O₃. A base-metal oxide layer was present above the pit, and this was observed to be formed very early in the corrosion process. A mechanism is proposed to explain this. In general, the formation of sulfides appears to be the primary mode of degradation in mixed sulfate melts.     

Corrosion of metals and alloys in mixed gas environments at elevated temperatures

The attack of nickel, cobalt, iron, and alloys of these metals containing chromium and aluminum, by gases containing sulfur-oxygen, carbon-oxygen, and nitrogen-oxygen has been studied at temperatures of 600 and 900°C. The degradation of these metals and alloys was characterized by using standard analytical techniques with emphasis on optical metallography. Three types of accelerated degradation were identified for the attack of alloys by gases containing another oxidant in addition to oxygen. One type of degradation occurred because of the formation of reaction products composed of mixtures of phases involving both of the oxidants. Another type resulted from the reaction of second oxidant phases with oxygen. The third form of degradation involved the development of less protective phases due to thermodynamic instabilities. Thermodynamic stability diagrams are used to help account for the effects produced by different elements in the alloys.