Corrosion evaluation of one dry desulfurization equipment – Circulating fluidized bed boiler

As a clean fuel combustion technology, circulating fluidized bed (CFB) possesses various advantages. Among them, flexibility in fuels and superiority in desulfurization are the two prominent ones and can hereby facilitate sufficient utilization of high-sulfur fuels. But unfortunately, these low-grade fuels always introduce harsh service environment within the CFB boilers and consequently result in severe degradation extent on relevant equipments, especially the high-temperature sulfur corrosion. In this event, by nearly ten characterization methods, comprehensive investigation was carried out on a whole CFB boiler during downtime, and special emphasis was particularly laid on the failure components including one perforated nozzle along with its fractured inlet tube for primary air, and one perforated manhole door of refeed valve. Finally, countermeasure and suggestion was put forward, which can provide instructive significance in corrosion prevention for the CFB boilers, even other desulfurization equipments, running under similar aggressive conditions in engineering practice.     

Synthesis and characterization of carbon/silica superhydrophobic multi-layer films

C/SiO₂ multi-layer films (3-layer films and 5-layer films) were obtained by sol-gel method and physical deposition on glass plates, and then heated at 500 °C for 1 h under a nitrogen atmosphere. The mechanical adhesive force with the substrate of the multi-layer films was sharply enhanced compared to the as-deposited amorphous carbon film. An absorption layer was formed on heat treated C/SiO₂ multi-layer films by modification of the surface with trimethylchlorosilane, and the wettability of the films changed from hydrophilic to super-hydrophobic. The structures of the physically deposited carbon and the multi-layer films were analyzed by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The experimental results showed that the 5-layer films had a concentric ring structure that caused the film to be superhydrophobic.     

Failure Analysis of a Steel Motorcycle Kickstand

A fractured steel motorcycle kickstand was metallurgically investigated using a range of failure analysis tools [visual examination, energy dispersive X-ray (EDX) analysis, electron microprobe analysis (EPMA), scanning electron microscopy (SEM), fractography, optical microscopy, hardness testing and non-destructive testing (NDT)]. The steel kickstand’s composition, its microstructure, electron fractographs, and mechanical test results have been critically interpreted. Some evidence of wear damage, in the failed kickstand, was observed. The microstructural and fractographic analyses showed pre-existing micro-cracks which were believed to have grown to result in ductile failure followed by acceleration of corrosion. Recommendations have been made to avoid the failure of the motorcycle kickstand.     

Self-ordering of anodic nanoporous alumina fabricated by accelerated mild anodization method

A processing method called “accelerated mild anodization” is developed for preparation of high density and uniform nanoporous by anodization of aluminum. The idea is to use two different temperatures for both sides of sample in order to maintain mid level of current density during the anodization process. Here we have used high temperature for the back side of the sample in order to increase the current density while the electrolyte is kept at low temperature in the level of mild anodization. It is shown that not only the film growth is considerably fast, almost ten times faster than mild anodization, but also the anodization voltage is constant and anodization current variation is much less compared to hard anodization technique. Using oxalic acid, interpore distances of 89, 104, 117 and 130 nm were obtained for 35, 40, 45 and 50 V anodization voltages, respectively. It is found that the interpore distances are proportional to the anodization potential, almost same as that for the mild anodization. The porosity obtained tended to obey the same rule as that in mild anodization. This method is promising for industrial application due to short fabrication time as well as high-speed pore ordering.     

Growth of highly textured aluminum films on LiTaO3 with optimized titanium intermediate layers

Ultra thin titanium films in the range of a few nanometers have been deposited on monocrystalline lithiumtantalate (LiTaO₃) followed by deposition of 400 nm pure aluminum (Al). Texture measurements by means of electron backscatter diffraction show that the thickness of the intermediate titanium (Ti) layer significantly influences texture and grain structure of the overlying Al film. Increasing the thickness of the Ti layer from 0 nm to 20 nm leads to a change of aluminums texture from unoriented polycrystalline over highly oriented in single direction to highly oriented in twin structure.     

On the ultraviolet light induced oxidation of amorphous As2S3 film

Illumination of amorphous As₂S₃ film by ultraviolet light with an overall light intensity on the sample surface of around 10 W cm^− 2 leads to extensive film oxidation. After 2 min of illumination most of As₂S₃ film of an original thickness at around 0.425 μm was converted into a cubic form of As₂O₃-arsenolite. A considerable amount of arsenolite microcrystals were found at a height of around 2 μm and more which indicated a growth of As₂O₃ microcrystalline particles from the vapor phase.     

Electrodeposition of gold thin films from 1-butyl-1-methylpyrrolidinium dicyanamide Au solutions

The electrodeposition of gold from a HAuCl₄.3H₂O solution in 1-butyl-1-methyl-pyrrolidinium dicyanamide is reported in the present paper. A cyclic voltammetry study of the electrochemical behaviour of the plating solution showed that the reduction of gold occurs by a two-step process. Gold thin films were obtained by electrodeposition on nickel substrates under potentiostatic control at a constant potential of − 1 V, for temperatures from 293 to 353 K and deposition times of 1500 and 4500 s. The films prepared at 293 and 333 K consist of 9-15 nm diameter polyhedral particles aggregated in clusters 50-250 nm in diameter. The films deposited at 353 K consist of a quasi-continuous film of nanoparticles covered by nanosized dendrites. This morphology evolves towards a globular structure with increasing deposition time.     

Premature Failure in Orthopedic Implants: Analysis of Three Different Cases

The increasing lifetime of the population on a world-wide scale over the last decades has led to a significant growth in the use of surgical implants for replacement of bones and teeth in affected patients. Other factors, such as scientific-technological development and more frequent exposure of individuals to trauma risk, have also contributed to this general trend. Metallic materials designed for applications in surgical implants, no matter whether orthopedic or dental, must show a group of properties in which biocompatibility, mechanical strength, and resistance to degradation (by wear or corrosion) are of primary importance. In order to reach these aims, orthopedic materials must fulfill certain requirements, usually specified in standards. These requirements include chemical composition, microstructure, and even macrographic appearances. In the present work, three cases of implant failure are presented. These cases demonstrate the most frequent causes of premature failure in orthopedic implants: inadequate surgical procedures and processing/design errors. Evaluation techniques, including optical and scanning electron microscopy (SEM), were used to evaluate macroscopic and microstructural aspects of the failed implants, and the chemical composition of each material was analyzed. These evaluations showed that design errors and improper surgical procedures of outright violation of standards were the cause of the failures.     

电子功函数在材料磨损及腐蚀方面的研究进展

本文简要叙述了电子功函数的基本概念及其基本原理,并概括了电子功函数作为一种基本的物理分析手段在材料磨损及腐蚀方面的应用。从电子结构出发将会更微观地反映材料的基本性能。具有电子结构的材料其磨损和腐蚀行为与其电子的结构存在必然的联系。通过电子功函数来反映材料的磨损和腐蚀行为将会更深层次揭示材料在磨损和腐蚀过程中的组织结构变化的特征和本质。     

Corrosion of polyaniline-coated steel in high pH electrolytes

Cyclic polarization measurements made on steel, iron oxalate-coated steel and polyaniline in a high pH solution and in the absence of chloride ions showed no tendency of the surface towards pitting corrosion. In all cases, the pitting potential was similar to the protection potential. Chlorides in the caustic solution caused significant pitting in the bare steel and slight pitting in the oxalate coated steel. The polyaniline coated-steel showed no pitting in the chloride-containing alkaline solution. Scratches through the polyaniline coating did not initiate pitting in the polyaniline coated steel surface when tested in the chloride-containing solutions.     

芦笋罐头容器材料内壁腐蚀失效分析

文章对马口铁芦笋罐头容器的腐蚀失效进行了分析和研究。     

Laser welding of Ti–6Al–4V to Nitinol

Formation of brittle intermetallic phases in addition to different thermal expansion coefficients associated with dissimilar welding leads to the formation of transverse cracks in weld metal and eventually restricts widespread applications of dissimilar joints. Therefore, joining technology should be expanded in field of dissimilar welding in order to solve its difficulties. In the present study, an experimental work with pulsed Nd:YAG laser was performed for dissimilar welding of Ti–6Al–4V and Nitinol. Autogenous welding of these two alloys resulted in joints with poor strength and ductility due to the formation of transverse cracks in the weld metal. Therefore, the chemical composition of the weld metal has to be modified in order to reduce the formation of brittle phases and eliminate subsequent cracking. In this work, this was done by insertion of a copper interlayer with a thickness of 75 μm between the base metals. The results indicated that insertion of copper interlayer has a great influence on the reduction of the amount of Ti₂Ni brittle intermetallic phase, elimination of transverse cracks through the weld metal and eventually improvement of mechanical properties of the joints. Insertion of copper interlayer was very useful since it altered the cracked autogenous joint to a joint which could withstand a tensile stress of 300 MPa.     

Effect of laser-arc hybrid welding on fracture and corrosion behaviour of AA6061-T6 alloy

The welding condition of the hybrid laser-gas metal arc (GMA) welding for AA6061-T6 alloy was optimized by tensile test. Formability performance was checked by the bend test. Fractographic analysis indicates a large number of fine ductile type voids in the fracture surface. The microstructure measurements exhibit a dendritic cellular structure in the weld fusion zone (WFZ) and a partially melted zone adjacent to the fusion boundaries. The corrosion behaviour of the weldment and the base alloy were investigated by weight-loss test in nitric acid solution. The WFZ suffers more severe pitting than the rest regions in the weldment. It shows that corrosion cracking is owing to the precipitation of intermetallic phases and the formation of galvanic corrosion couplings in the weldment of AA6061-T6 alloy.     

双卡簧片失效分析

采用光学金相、扫描电镜、电子探针成分分析和显微硬度测定等方法分析了双卡簧片非正常断裂的原因。在部分双卡簧片折弯处发现有尖锐凹角并有明显微裂纹,裂纹表面有镍和铜,说明裂纹是在成形加工过程中形成。双卡簧片盛开有时弯角较尖锐并有明显裂纹是导致失效的原因。     

Failure analysis of bursting on the inner pipe of a jacketed pipe in a tubular heat exchanger

In order to identify the causes of a bursting incident that occurred on the inner pipe of a jacketed pipe in a tubular heat exchanger for synthesis of high pressure polyethylene, series of characterization analysis were conducted. Metallurgical structure and chemical composition of the pipe’s metal matrix were inspected by metallographic microscope (MM) and photoelectric direct reading spectrometer; scanning electron microscope (SEM) and energy dispersive spectroscope (EDS) were applied to observe the microscopic morphology and micro-area composition on the ruptured surface; compositions of the coolant, i.e. the circulating cooling water were examined by inductively coupled plasma-atomic emission spectrometry (ICP-AES), ion chromatography (IC) and Fourier transform infrared spectroscopy (FTIR). In addition to these, finite element analysis (FEA) was employed to study the erosive effect of on the pipe. Analysis results revealed that interaction between corrosion and erosion both led by scaling, was the main cause that accelerated its thinning and eventually resulted in its premature failure. Finally countermeasures and suggestions were proposed.     

Inconel 625合金波纹管失效分析

采用化学分析,透射电子显微镜(TEM)、X射线光电子能谱仪(XPS)和扫描电子显微镜(SEM)等微观测试手段对失效波纹管化学成分、力学性能、断口腐蚀产物及断口微观形貌进行综合分析。研究结果表明,波纹管的失效是材料在腐蚀性环境下局部高应力处首先发生高温氧化、硫化腐蚀,产生疲劳裂纹源,在交变应力的作用下发生腐蚀疲劳而造成的。通过降低腐蚀和波纹管应力可以防止或减轻腐蚀疲劳发生,延长波纹管使用寿命。     

Synthesis and characterization of plasma assisted chemically vapor deposited tantalum

This study focuses on the synthesis of tantalum (Ta) coatings on high strength steel by plasma assisted chemical vapor deposition using tantalum pentachloride (TaCl₅) as a preferred precursor and hydrogen (H₂) as a reducing agent. The interrelationships governing the growth kinetics, compositions, and coating properties are discussed as a function of deposition temperature, total pressure, and gas composition. The synthesized tantalum coatings are shown to be essentially pure with trace amounts of oxygen, carbon, and chlorine. The coatings are found to be dense and to exhibit conformal coverage. Preferential formation of the α-Ta phase is noted to occur when coatings are grown sequentially and in-situ on a TaN_x seed layer.     

腐蚀失效分析方法及展望

概述了腐蚀失效分析的意义,根据实际腐蚀失效分析工作,从现场调查、实验室分析两个方面阐述了腐蚀失效分析的思路,并综合一些典型的腐蚀失效案例对常用的腐蚀失效分析方法进行了简单的归纳。对腐蚀失效分析工作进行了展望。