Microelectrochemical sensor has been widely applied in various fields involving redox reactions, including experimental research and industrial applications. This paper briefly introduces the recent advances of microelectrochemical pH sensor. The microelectrochemical pH sensor associated with potentiometric mode of different scanning probe microscope is also described for monitoring the local pH distribution of interfaces. Research work of microelectrochemical pH sensor in the measurement of micro-area pH at interfaces by our group is also introduced. Future applications of microelectrochemical pH sensor in corrosion are highlighted.
Marine biofouling is one of the important issues encountered by marine engineering materials in the service process. Therefore, it is of great significance to develop new and effective antifouling materials with high efficiency and environmental-friendly. Bi-based semiconductor materials are a new class of photocatalysts that have been studied with great concern in recent years. Because of their unique structure and suitable band gap, they exhibit good visible light catalytic performance and have great application prospects in marine antifouling field. From the perspective of visible light photocatalytic antifouling materials and the antifouling mechanism, this article describes the recent research progress in Bi-based semiconductor material systems. As a new type of antifouling material, the Bi-based semiconductor material related visible light photocatalytic antifouling technology is expected to provide a new strategy in the field of marine antifouling.
Sulfate-reducing bacteria (SRB) are the most corrosive and the most extensively studied corrosion related microorganisms, they are widely distributed in various marine environments. Although it has been clearly known that the status of SRB is closely related with their roles in relevant corrosion processes, however the determination of the population concentration and metabolic activity of SRB is still a big problem in the present. The development of quick and accurate detection approach could provide theoretical basis and guidance for revealing the mechanism of SRB action in the corrosion process and monitoring of microbial influenced corrosion status. This paper briefly introduces the research progress of our research group in detection of the population concentration and metabolic activity of SRB, and elaborates their advantages and disadvantages, applicable conditions and detection performance, which may provide reference for the development and practical application of detection methods for the actual situation of SRB in marine environments in the future.
Thermal barrier coatings (TBCs) are widely used in hot section of gas turbine engines, holding excellent protection properties at high temperature, with the goal of improving engine efficiency and reducing the operation cost. Generally, a typical TBC is composed of a ceramic topcoat and an oxidation-resistant bond coat, while, the oxidation performance of the bond coat directly determines the overall performance and lifetime of the whole TBC. Thus, the challenge of TBCs operating at higher temperature and harsher environments has attracted the relevant researchers to develop advanced bond coats. Pt-modified aluminide coatings, possessing excellent oxidation resistance, are capable of forming a continuously dense Al2O3 scale with low tendency of spallation during exposure at elevated temperature. In the present paper, special attention is devoted to review the development and status of Pt- modified bond coats, including MCrAlY and nickel aluminides, as well as the merits and deficiency of such coatings have been elucidated. At last, the perspectives of manufacturing an advanced bond coat and the development trend are summarized.
The interaction of mechanical friction-wear and electrochemical corrosion in biological environments is named as bio-tribocorrosion. Due to large bio molecules in the surrounding environment, the adsorption of such molecules has great influence on the tribocorrosion behaviour of implant materials. In terms of the influence of bio-tribocorrosion, both the artificial joint implants and dental implants encounters obviously issues of bio-tribocorrosion. In this paper, we summarized the current status of research on bio-tribocorrosion with the emphasis on the mechanisms of relevant processes and the effect of bio-tribocorrosion on the surface microstructure of implants. It is noted that to choose proper testing methods is a very important matter for assessing the bio-tribocorrosion process. Besides, the future trend and directions of research in this area are also put forward.
A metal-enamel composite high temperature protective coating was prepared by using borosilicate enamel with low softening point as bonding phase. Its thermal shock behavior was investigated via cyclically heating at 900 ℃ and quenching into room-temperature water. The higher the proportion of silica, the higher the softening point of the borosilicate enamel. When the ratio (mass fraction) of boron oxide to silica reaches 0.6, the softening point of the borosilicate enamel is higher than 750 ℃. Thermal shock test indicated that the metal-enamel composite coating containing 20% nickel particles had high thermal shock resistance, and the coating surface was intact after 30 thermal shock cycles. The enamel coating is easy to crack and peel under thermal shock condition when no metal particles are incorporated or the metal content is as high as 40%.
The oxide scale formed on FeCr15Ni15 single crystal alloy at 600 ℃ for 20 h was characterized by means of transmission electron microscope. Results showed that the oxide scale of 4~6 μm in thickness was differentiated into two layers. The inner layer of the scale was spinel oxide rich in Fe and Cr, while the outer layer was spinel oxide rich in Fe and Ni. The region I of inner layer was anisotropy, of which oxides present epitaxial growth along a large amount of (111) plane of the matrix, i.e. [110]matrix//[110]ox, (111)matrix//(111)ox, however the region II and region III compose completely of oxides, while there exist a large number of surface defects and holes left by the kirkendall effect, which become the most porous area of the oxide scale, therefore, as a result, cracking and spalling off may certainly occur there. In the contrast, the outer layer of the oxide scale is dense one composed of polycrystalline spinel oxides.
CrN films on 304 stainless steel were prepared by magnetron sputtering. The effect of N2 partial pressure, sputtering power and inclusion quantity of the steel on the structure, composition and corrosion resistance of the prepared films was investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the increase of nitrogen partial pressure is beneficial to the increment of CrN-phase content for the CrN film, while which presents obviously the preferential orientations of the crystal planes (111) and (200) of CrN-phase. Reducing the sputtering power is beneficial to generate the increased amount of Cr to participate in the reaction with nitrogen and thus generate more CrN. The amount of inclusions on the steel surface has significant influence on the quality of films, and the inclusions sites are not conducive to the integrity of the prepared CrN films, which, correspondingly, results in significant degradation of corrosion resistance for the prepared CrN films.
The effect of sulfuric acid concentration, applied voltage and oxidation time on the corrosion resistance of anodizing film of 2195 Al-Li alloy was studied. The surface morphology, thickness and corrosion resistance of the oxide film were characterized by scanning electron microscopy (SEM) and electrochemical workstation. The results show that as the concentration of sulfuric acid increases, the formation rate of the oxide film increases first and then decreases. With the increasing of applied voltage, the oxide film thickness increases in turn, but when the voltage is too high, the phenomenon of "ashing" will occur. As the oxidation time increases, the thickness of the oxide film increases sequentially. When the oxidation time reaches 30 min, the film formation rate increases. The anodizing film presents the best corrosion resistance, when anodizing process was performed with the following parameters: the sulfuric acid concentration is 180~200 g/L, the temperature is 14 ℃, the applied voltage is 14 V and the oxidation time is 50 min.
The effect of tensile load on pitting corrosion behavior of 2297 Al-Li alloy in 3.5% (mass fraction) NaCl solution was studied by short time immersion test and in-situ electrochemical test under different loading conditions within the range of 0%, 30%, 60%, 90% and 103% of the σ0.2 of the alloy, while the microstructure of the initial and plastically deformed 2297 Al-Li alloy was characterized. After plastic deformation, AlCuMnFe intermetallic particles of 2297 Al-Li alloy become fine and uniformly dispersed, and dislocation walls are formed inside the grains due to dislocation accumulation. Pitting corrosion mainly occurs around the AlCuMnFe intermetallic particles, and crystal defects such as crystal plane slip and dislocation entanglement also become corrosion nucleation sites. The increase of the applied load within the range of 0%σ0.2~103%σ0.2 leads to negative shift of the corrosion potential, increase of the corrosion current density and the charge transfer resistance, which will become more obvious when the stress level reaches the plastic stress range.
Surface re-melted layer was obtained on super 13Cr stainless steel via laser surface melting (LSM) treatment, then, of which the microstructure, micro-hardness and corrosion performance were characterized by means of optical microscope, scanning electron microscope, X-ray diffractometer, micro-hardness tester, immersion test and scanning micro-zone electrochemical workstation. It is found that with a laser beam of 200 W and 5 mm/s of laser scanning speed, the LSM treatment could produce a remelting surface composed of 200 μm thick LSM layer and a 600 μm thick transition layer on the steel surface. The above two layers all show martensite microstructure, while the steel matrix is comprised of martensite and austenite. The micro-hardness of the LSM layer is 410 HV, which is 25% higher than the hardness of steel matrix, while that of the transition layer is 360~400 HV. Moreover, comparing with the LSM layer and steel matrix, the transition layer shows the widest passive range, lowest passive current density, and highest pitting potential and Kelvin potential. In addition, the inter-pass interface of the LSM layer is sensitive to localized corrosion. It is concluded that LSM treatment can significantly enhance the surface hardness of super 13Cr stainless steel, and the corrosion resistance of super 13Cr lies in the order of transition layer＞steel matrix＞LSM layer, indicating that a highly corrosion-resistant transition layer can be obtained on the steel surface via laser surface modification.
MgAl-layered double hydroxide (MgAl-LDH) coatings were prepared on AZ31 magnesium alloy by electrochemical deposition. The surface morphology and corrosion resistance of the coatings were characterized by X-ray diffraction (XRD), Fourier infrared spectrometer (FT-IR), scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS) and Tafel polarization curves. The results show that the coating prepared with the optimal processing parameters has good corrosion resistance in 3.5%(mass fraction) NaCl solution and can effectively protect the magnesium alloy from corrosion. In comparison to those of the bare My-alloy substrate, the impedance modulus of the coating is increased by two orders of magnitude , the free-corrosion potential is increased by 0.96 V, and the corrosion current density is reduced by three orders of magnitude. These findings demonstrate that the MgAl-LDH coatings with good corrosion resistance can be obtained by a simple electrochemical deposition method.
Ni-based alloy coating was prepared on the Q235 carbon steel substrate via laser cladding with a high power diode laser. The microstructure, composition and erosion-corrosion behavior of the coating were characterized by means of SEM+EDS and a home-made pipe flow erosion-corrosion tester. The effect of erosion angle and solid particles on the erosion-corrosion behavior of the coating were investigated. Results show that the laser-clad Ni-based alloy coating had uniform microstructure and fewer defects. The erosion-corrosion behavior of the coating was greatly affected by the synergistic effect of the normal stress and shear stress in flow. In addition, the addition of solid particles further reduced the corrosion resistance of the coating.
