聚苯胺防腐蚀电化学方法研究

本文综述了国内外在聚苯胺 (PANI)防腐研究中一些常用和新颖的电化学方法 ,指出其测试原理、过程和结果 ,表明PANI有良好的防腐效果。     

Aluminium nitride: review of synthesis methods

Abstract

Several technologies have been reported for the synthesis of AlN. These are reviewed and described in detail. The processes are classified according to the principle of synthesis, and the AlN product characteristics for each method of synthesis are identified. Only two of the methods reported, direct nitridation and carbothermal reduction, are currently used industrially. Due to the requirement for higher quality AlN powders, several other methods are being developed. The level of development, the principle of synthesis, the raw materials used, the reaction products, and the powder characteristics of the synthesis methods are discussed. Where appropriate, environmental or safety concerns are identified. Process flowcharts for each of the technologies were developed on the basis of information available.

MST/1794     

Tarnish and corrosion behaviour of palladium-silver alloys

Binary and commercial palladium-silver dental alloys show a greatest resistance to both tarnish and corrosion at compositions of between 50 and 75% Ag, most probably due to saturation of the d-electron shell in this composition range. The commercial Pd-Ag alloys have more corrosion resistance, but a lower tarnish resistance than the binary Pd-Ag alloys, due in part to the minor alloying with indium or zinc. The addition of copper increases the segregtion of silver, which adversely affects both tarnish and corrosion resistance. A solutionization heat treatment degrades tarnish resistance, but does not affect corrosion resistance.     

High-temperature chlorine corrosion of metals and alloys

High-temperature (> 200° C) corrosion of metals and alloys in atmospheres containing Cl₂ and/or HCl, which are widely encountered in many industrial environments, is reviewed. Topics include high-temperature corrosion mechanism and kinetics, thermodynamic considerations, and effects of gaseous components in the atmosphere (oxygen, air, water vapour, sulphur dioxide, and nitrogen) on the corrosion.     

Low-noble metal alloys: in vitro corrosion evaluation

The electrochemical behaviour and the resistance to corrosion and tarnishing of seven commercial low-noble metal alloys were investigated, in artificial saliva at two different pH values (3 and 6.7) and in 2% Na₂S solution. The alloys were tested as-received and after a hardening treatment suggested by the manufacturers: ageing 15 min in a temperature range between 360 and 450 °C. Scanning electron microscopy (SEM) examination of the alloys evidenced some slight microstructural modifications. The electrochemical characterization was performed by means of anodic polarization curves. Alloys with noble metal content > 30% show a good electrochemical behaviour and a satisfactory corrosion resistance against tarnishing, and the hardening treatment had no influence on the corrosion resistance.     

Blood triggered corrosion of magnesium alloys

Intravascular stents manufactured out of bioabsorbable magnesium (Mg) or Mg-alloys are considered as auspicious candidates for the next stent generation. However, before clinical application numerous physical and biological tests, especially to predict the clinically highly important degradation kinetics in vivo, have to be performed. In a Chandler-Loop model, the initial degradation of eight different magnesium alloys during 6 h in contact with human whole blood was investigated. The magnesium release varied between 0.91 ± 0.33 mg/cm² (MgAl9Zn1) and 2.57 ± 0.38 mg/cm² (MgZn1). No correlation could be found with Mg release data obtained after immersion in simulated body fluid (SBF). This pilot study showed that Mg corrosion is highly influenced by the biological test environment (SBF or blood, etc.) and that a modified Chandler-Loop model with human whole blood may be superior to predict corrosion of Mg alloys under clinical conditions than the SBF models presently used.     

Mechanism of corrosion resistance of nickel-molybdenum alloys

Conclusions With the use of a combination of electrochemical and -ray spectrometric methods and also of photoelectronic spectroscopy the rules of partial processes of dissolution of the components of nickel-molybdenum alloys and of the change in composition of their surface as a result of dissolution were investigated.The existence of two basic areas of potentials having the greatest value for industrial use of the alloys was established. Considerations were given on the probably mechanisms of corrosion resistance of the alloys according to which the high retarding action of molybdenum and the investigated inhibitors (I^– ions and propargylic alcohol) are caused by blocking of active centers of the surface being dissolved. Together with this, with sufficiently negative potentials it is possible to have an additional retarding effect from the passivating film formed here, which is enriched with molybdenum oxides.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 16, No. 1, pp. 7–13, January–February, 1980.     

Trends in corrosion protection of materials

The rapid advances in technologies in various fields have also recorded significant progresses in the field of newer materials as the reliability and effective performance of industrial equipment as well as the associated components mostly depend upon their integrity over specified period. Though the basic methods of protection of materials like use of corrosion-resistant alloys, application of surface coatings, modification of the environment and application of cathodic protection have largely remained the same, the approaches and techniques adopted in each of these fields have been so advanced that one could today advocate appropriate protection systems with high reliability and performance. The author presents some of his contributions along with his colleagues in the fields of cathodic protection of vital structures, development of newer coatings for specific applications and new approaches to corrosion monitoring techniques, besides highlighting the corrosion behaviour of some of the heat-treated alloys which are specifically used in such strategic areas as space and defence. The presentation would also cover briefly some of the techniques that have been employed by the author for better understanding of corrosion and passivation of metals and alloys.     

Evaluation of mechanical and corrosion biocompatibility of TiTa alloys

As-received and heat-treated Ti40Ta and Ti50Ta alloys were evaluated to determine their corrosion as well as mechanical performances and compared to Ti6A14V, a common material utilized for orthopedic (surgical) implants. Anodic potentiodynamic tests performed in Plasmalyte^TM showed that all samples, except for the Ti50Ta specimen aged at 400 °C for 3 h gave a curve similar to that of Ti6A14V. Optical and TEM microscopy was performed to determine as-received and heat-treated microstructures. As-received materials showed an precipitate in an + and martensite matrix. Samples that were aged at 400 °C increased in the density and the length of the precipitate. Vickers hardness measurements were performed to get an approximation of the tensile strengths. Aged Ti40Ta and Ti50Ta specimens produced the highest tensile values when compared to the Ti6A14V material, representing a 31% and 56% increase for the 3 h samples and an 18% and 58% increase for the 10 h samples. Of all the materials studied the Ti50Ta specimen aged for 10 h exhibited the best biocompatibility showing excellent corrosion resistance combined with the highest tensile strength (1089 MPa and 58% harder/stronger than Ti6A14V). © 2001 Kluwer Academic Publishers     

Microstructure and corrosion behaviour of FeCoNiCuSnx high entropy alloys

Abstract

The FeCoNiCuSn_x alloys with different Sn contents are prepared, the microstructure and the corrosion behaviour of the alloys are investigated. When Sn content is lower than 0.09, FeCoNiCuSn_x alloys consist of a single FCC phase. While Sn content of the alloy is 0.09, a small quantity of BCC structure is present. The FeCoNiCuSn_x alloys have a wider passive region in the NaOH solution. FeCoNiCuSn_x alloys exhibit a better corrosion resistance in NaCl solution than 304 stainless steel, the corrosion resistance of FeCoNiCuSn_0.04 alloy is best among all the alloys. The corrosion resistance of FeCoNiCuSn_x alloys in NaOH solution is lower than that of 304 stainless steel, the corrosion resistance of FeCoNiCuSn_0.03 alloy is best among all FeCoNiCuSn_x alloys.     

Coal-ash deposit corrosion of some steels and nimonic alloys

The corrosion behaviour of some commercial austenitic steels and nimonic aalloys has been studied at 650, 800, 900 and 1000°C in air and in the presence of ash residues obtained from coals of Indian origin. The ash is non-aggressive at temperature s where formation of corrosion-producing alkali iron trisulphates is normally expected; on the contrary, the silicates present in the ash provide protection against corrosron. A.t higher temperatures the ash is corrosive due to onset of sulphidation and molten alhali sulphate attack. In general, the corrosion rates of high-ash coated alloys are much higher than those coated with low ash. The higher corrosion rates in the former have been attributed to a higher level of free silica in the ash which undergoes slag-type reactions. Both types of ash exhibit two different and distinct scale morphologies.     

Fabrication of superhydrophobic surfaces for corrosion protection: a review

ABSTRACT

Steel, aluminium and magnesium are important engineering materials owing to their excellent mechanical properties. However, their applications are limited due to inadequate corrosion resistance. Various coatings and improvement technologies are used to enhance the corrosion resistance in industry and consumer products. Fabrication of hydrophobic surfaces is a very interesting approach to anticorrosion in that it is derived from the superhydrophobicity found in nature. This paper is a general review of the methods to construct a superhydrophobic surface, i.e. a thin coating layer, on various metallic materials surfaces to enhance their anticorrosion property, providing an introduction of the superhydrophobicity, including theory, properties and fabricating methods. Different methods including spray technique, laser ablation, electrochemical deposition, micro-arc oxidation and etching routes were discussed.     

Stress corrosion cracking of Al-Mg-Zn-Cu alloys after precompression

Stress corrosion cracking (SCC) experiments have been carried out on double-cantilever-beam (DCB) specimens of 7017-T651 aluminium alloy. The specimens were first subjected to a known compressive load which caused plastic deformation at the notch tip. On unloading, this region developed a residual tensile stress field and on subsequent exposure to moist air at 40° C (95% relative humidity, r.h.), intergranular cracks formed. These cracks grew at a decelerating rate until they stopped. The final crack length increased with the value of the initial compressive preload, provided this was below the value for general yielding of the alloy. Electron fractography has been used to correlate changes in surface morphology with crack growth rate. It was found that ductile tearing of the notch tip may occur during unloading when the compression exceeds — 30kN. The practical importance of these results is outlined.     

Correlation between corrosion pits and stresses in Al alloys

Pitting corrosion is commonly observed in a wide range of aluminum alloys that are being used for aerospace applications. There is a need to study the stress environment around pits in order to predict the nucleation of cracks. The objective of this study is to investigate the correlation between pits and stresses in aluminum alloys. Corrosion experiments were carried out on aluminum 2024-T3 alloy samples and imaged through Atomic Force Microscopy (AFM) to obtain the pit profiles. An analysis procedure was developed using CAD and finite element analysis to predict stresses resulting from corrosion pits. Based on the analysis, it was observed that the stress distribution and levels on the corroded surface varied due to irregularity in the corrosion process. The results obtained indicate that the stress initially increases and reaches a plateau with increasing corrosion time. From these stresses it is possible to estimate the initiation of cracks, from which the life can be estimated for failure in the material.     

Properties of ordered intermetallic alloys: first-principles and approximate methods

Intermetallic alloys which can be made ductile at low temperatures and strong at high temperatures are of great value as materials for current and future high technology applications. Computational physics is a useful tool for locating candidate materials. The current generation of first-principles techniques can be used to study ordered phases of candidate materials. The results of these calculations may be used to construct highly accurate model potentials which can then be used to study systems containing thousands of atoms, including impurities, voids, defects and cracks. First-principles calculations are used to compute the elastic constants of a wide range of monatomic metals and ordered binary intermetallic alloys. The results are usually within 10% of the experimentally determined values. We also examine some of the high melting temperature A15 compounds. Total energy calculations for a simplified model of an antiphase boundary are presented. These results can be used to calibrate model potentials for use in studying the energy of isolated defects. Finally, we study the possibility of using the Harris functional to speed total energy calculations.