Acoustic emission (AE) signals during corrosion fatigue of a rolled AZ31B magnesium alloy were studied. There were mainly four types of signals found in the corrosion fatigue process. Two types of AE signals corresponded respectively to anodic dissolution and cathodic hydrogen evolution appeared in a whole loading cycle. The signals of anodic dissolution belonged to the sources in plate produced extensive waveform, while the signals of cathodic hydrogen evolution belonged to the sources out of plate produced flexural waveform.Another two types of AE signals were corresponded to mechanical signals. One was the signals of plastic deformation which were continuous signal and appeared at the certain stress stage in a loading cycle. At the stage of crack propagation, crack propagation signals appeared at high stress loading part of each cycle.
The effects of aluminum powders with different shapes and sizes on the surface morphology, corrosion resistance and electrochemical behavior of the coating were studied by means of scanning electron microscope （SEM）, X-ray diffraction（XRD）, neutral salt spray test and electrochemical impedance spectroscopy. The results show that aluminum powders can improve the appearance of the coatings, and can also increase the corrosion resistance of the coatings by extending the electrochemical protection term of zinc powders, with a better effectiveness for the small-size and well-dispersed Al powders.
The API-RP38 medium was used to culture the thermophile sulfate-reducing bacteria (SRB) isolated from Bohai oilfield，and the bacteria was preliminarily identified according to its growth characteristics. Additionally, electrochemical means were taken to study the effect of the bacteria on carbon steel. The results show that the growth cycle of the bacteria is shorter than that cultured under normal temperature. The optimum growth temperature of the bacteria is at 60℃ within the growth temperature range from 40℃ to 80℃. The growth pH ranges from 6.0 to 7.6, and the optimum is about 7.0. The mass loss measurement at 60 ℃ in the culture medium indicates that the corrosion on carbon steel in thermophile SRB solution is 2.6 times more serious than that in the blank medium. As an uneven biofilm occurs on the carbon steel surface，energy dispersive spectrometer (EDS) analysis indicates that the corrosion products have various FeSx structures in the uneven biofilm. The free corrosion potential increases in the first few days, and later decreases. The electrochemical impedance spectroscopy (EIS) shows that the structure changes in accordance with the growth of the bacteria. Therefore, high temperature microbial corrosion occurs on the matrix materials.
A nickel coating with high density nano--scale twins has been synthesized on Q235 steel by using pulsed electrodeposition technique. The potentiodynamic polarization measurements were performed on nano--scale twin nickel coating and cast nickel in 0.1mol/L H3BO3 + 0.025 mol/L Na2B4O7 buffer solution with pH= 8.4. The results indicated that both samples showed auto--passivated behavior, while nano-scale twin nickel coating possessed higher corrosion resistance and better passive property than cast nickel. The effect of nano-scale twin structure on the properties of passive film was investigated in terms of thermodynamics and kinetics by using Mott-Schottky relationship and point defect model (PDM). It demonstrated that nano--scale twin structure has little effect on the defect density, but has great effect on the diffusion coefficient (Dm). It is the main cause to the formation of a thinner, more compact and higher corrosion resistant film on the nano-scale twin nickel coating.
Soft lithography and anodic process were combined to prepare the pattern porous alumina successfully. The experiments showed that the spacing after monomer volatilizing during polymerization and the cavity produced by thermal motion of segment were the key factors to weaken the protection of film. In addition, the thickness of which should be thinner than the max height of polymer spread by the capillary force.
A new type of optical fiber grating sensor for monitoring corrosion of reinforcement steel was presented--optical fiber grating corrosion sensor with two steel bars. In the sensor, Bragg grating is stick on the top surface of two bars against each other, for which the principle is that the steel volume will be expanded due to corrosion. The monitoring will be carried out by transforming the volume increase to the fiber strain. While Bragg gratings is tensioned, the reflected spectrum will have a single distinct peak shift in center wavelength, as a result the loss and rate of steel corrosion can be obtained. By the designed sensor, corrosion is recorded with the shift in center wavelength through the fiber, and the degree of corrosion of reinforcement steel will be measured indirectly, which is not affected by corrosion factors. Therefore the sensor proposed in the paper could be used in the early corrosion monitoring of reinforcement steel in concrete structures.
Using light color conductive mica, titanium oxides and environmentally friendly anticorrosive pigments in the two-component epoxy paint system, a new kind of environmentally friendly waterborne paint with good antistatic property, excellent anticorrosion performance and good ornamental behavior was prepared. The antistatic property and anticorrosive performance of the paint were analyzed by use of scanning electron microscopy, laser particle diameter analyzer and surface resistivity tester. The results indicated that the particle size and the amount of conductive mica, its dispersing speed, the amount of titanium oxides, and the type of anti-settlement agent have great influence on the antistatic property of the paint. Combined with 30 mass % conductive mica (of volume average diameter as 16.96μm) under its dispersing speed of 1000 r/min and fumed SiO2 as anti-settlement agent, the surface resistivity of the paint can reach to 106Ω. The optimal addition of titanium oxides is 2.7 mass%. The integrated properties of paint were decided by the ratio of epoxy resin to its curing agent, the pigment volume concentration (PVC) and the type of anticorrosive pigments. As the PVC range from 30% to 35% and the ratio of epoxy resin to its curing agent reach to 4:1, the optimal integrated property of the paint can be obtained.
Hot-dip galvanized steel samples have been treated in a solution containing molybdate, phosphate and silane. The distribution of the elements in the coating layers has been determined using Auger electron spectroscopy (AES). The corrosion resistance of the treated samples has been compared to that of bare samples after exposure to 5% NaCl solution using polarization curves and electrochemical impedance spectra (EIS) data. The samples have also been exposed to the salt spray test. The results of these tests suggest that the modified silane coating layer is composed of an outer C-Si-O rich layer and an inner Mo-P-O-Zn rich layer and it is a promising candidate for replacing conventional chromate treatments.
The corrosion electrochemical behavior of anti-sulfur carbon steel in 3% NaCl solution containing CO2/H2S was investigated by mass loss test, potentiodynamic polarization curves, electrochemical impedance spectrum. The results showed that more quickly sulfuration film dissolved, more less was there sediment on the exterior of electrode with pH reduction at 30℃. In addition, reduction of pH makes product film turn into rich--sulfur from rich-iron and contents of Cr(OH)3 and Cr2O3 reduce，all which weaken protection of product film and then corrosion rate at pH=2 was more rapid than that when at pH=4. H2S could not accelerate to anode process of anti--sulfur carbon steel when pH=4 and H2S concentration was bigger than 100 mg/L，moreover electrode reactions still were self--catalyzed reaction of acid with increase of concentration of H2S.
Several low-carbon steels and low-alloy steels with representative metallurgical factors were selected. Their susceptibility to pitting initiation was compared by means of polarization test in 3% NaCl solution with pH=10. Characteristic of pitting initiated by inclusions in steels was analyzed with the EPMA. The results showed that the resistance of susceptibility to pitting in boiling steel was obviously better than that of killed steel, the resistance of susceptibility to pitting in killed steel treated by rare earth was improved, between boiling and killed steel. The resistance of susceptibility of Ni-Cr steel to pit was higher than that of Mn steel, which indicated the susceptibility to pitting initiation was significantly affected by alloy elements. The inclusions were the most primary sites of pitting initiation. Passivation film of boundary between steel matrix and inclusions was the weakest and pitting was firstly initiated there.
Fatigue crack initiation of rolled AZ31B magnesium alloy in air and NaCl solution was investigated. In air, the cracked second phases were responsible for crack initiation. While in NaCl solution, crack initiated from surface damage which was produced by pit corrosion or filiform corrosion. Increasing Cl- concentration, the crack initiation and propagation in NaCl solutions were enhanced and the fatigue lifetime was decreased.
Monolayer of n-tetradecanoic acid (CH3(CH2)12COOH) salt is self-assembled on the native oxide surfaces of Fe3Al, and characterized by contact angle measurement and scanning electron microscope (SEM). The structure of the adsorbed film is similar to that of the lotus leaf, and the contact angle is larger than 150° for seawater. The corrosion behavior of Fe3Al with and without super-hydrophobic film, in seawater (pH 8.02), has been investigated by electrochemical impedance spectroscopy (EIS) and mass loss measurements. Both results reveal that corrosion rate of modified Fe3Al decreases dramatically. It is believed that the super-hydrophobic film can inhibit the corrosion process of Fe3Al in the seawater in a certain degree.
Ni-Co alloys were deposited by applying current pulses from a sulfate electrolyte. The effect of the ionic concentration of cobalt in the electrolyte and pulse parameters on the cobalt content in the deposits and the microhardness of the deposits were studied. The morphologies and metallic phases of the alloys were analysed by scanning electron microscope(SEM) and X-ray diffraction(XRD). The results indicated that the cobalt content in alloy deposits had a strong effect on its hardness, and the increase of cobalt content resulted in increasing of the hardness of the deposits. At low cobalt content, pure face centered cubic (fcc) structure was identified.
The corrosion inhibition effect of the uric acid self-assembled film on nickel in 3% NaCl solution was studied by electrochemical methods. The experimental results showed that uric acid mainly suppressed the anodic reaction and its inhibition efficiency was different with the variation of uric acid concentration, self-assembled time as well as the pH value of uric acid solution. When the nickel electrode was modified with 0.8 mmol/L uric acid for 12 h at pH 9.0, the corrosion current density of the electrode was the lowest and the inhibition efficiency reached the highest value of 95.7%.
Phytic acid was abstracted from the rice bran by hydrochloric acid leaching method and used as main component of corrosion inhibitor for hydrochloric acid pickling. Its inhibiting behavior on carbon steel in hydrochloric acid was investigated by means of mass loss, polarization curves and electrochemical impedance spectroscopy (EIS) methods. The results show that the corrosion inhibitor exhibits good inhibition effect for carbon steel in 1mol/L hydrochloric acid and inhibition efficiency is less affected by temperature. The results of polarization curves indicate that the corrosion inhibitor mainly prohibits the cathodic process.
This article has reviewed the present application of bactericide for sulfate reducing bacteria (SRB) and its research progress，illustrated the major problems of those bactericides，such as the destruction to environment，controlling the drug-resistance SRB， inhibiting SRB growth in the biofilm etc. New bactericide which should meet the practical needs take the microorganisms growth and the corresponding bactericidal mechanism as research guiding，find out the relationship between sterilization mechanism，the molecule structures and properties. Moreover，inhibiting microbiologically influenced corrosion must consider the environment protecting，and researching and developing new sterilizing method must have high efficient of bactericide and at the same time，which should be low toxic to the environment.
