With a series of factors such as time of immersion (TOI), temperature (Temp) and relative humidity (RH), the time of wetness (TOW) of Q235 steel covered by pure water thin film is investigated. The effect of the three factors on corrosion rate is also studied by Inductive Resistance Probe (IRP) measurement and Integration Filter Algorithm (IFA) previously implemented by the author. Standardization protocol (data mining technique) for multivariate analysis of variance is introduced in order to improve the accuracy of TOW linear regression model. The results prove the successful adoption of standardization protocol. Temperature plays a more important role than the humidity in shortening TOW for clean samples at elevated temperature. Around 20 ℃, a significant change of temperature effect on TOW is observed. IRP measurement plus IFA corrosion rate calculation confirms the judgment on temperature effect. Corrosion rate could be clustered into two groups( high and low zone) around the thresholds of 20 ℃ and RH 80% based on cluster analysis on corrosion rate. Quantitative evaluation on corrosion rate between high and low corrosion rate zones shows 4 times difference. Plateau in the very early stage of PLU movement over time of low corrosion rate zone is recorded at first time. However, no PLU plateau is observed for system at higher temperature than 20 ℃ and/or higher RH than 80%. A primary reasoning about this PLU plateau is assumed to be bounded with corrosion rate which is the function of temperature and humidity. This interesting and impressive PLU plateau could indicate the possible composition and/or structure transformation of corrosion product layer under thin liquid film and deserves more effort in future work.
The polarization curves of the Q345 were measured in NaHCO3 solution, and the concentration is 6 mmol/L, 3 mmol/L and 1.5 mmol/L respectively. The anodic polarization curves were amended by means of equidistance voltage. By this way, the influence of the solution resistance to the measurement was eliminated. By the modified results, the kinetic parameters, such as ba and Icorr could be got easily. Comparing with the results from EIS, under the effect of the polarization, because of the shifting of the iron concentration near the electrode surface and the movement speed of the ions is much fast under the effect of the electric field ,solution resistance is less than the resistance at the corrosion potential. Furthermore, the Rsol that calculated by the method of equidistance voltage is reasonable for the calculation range, but it can not be extended to the whole range of the measurement. Otherwise, a big error will be aroused. Being the effect of diffusion process, this method is not suitable for cathodal course.
Research on the corrosion properties of the specimens of auto galvanized steel sheet with various broken areas of the zinc coating prepared by dissolution with a dilute hydrochloric acid solution were carried out in 5 %NaCl solution in the present paper. The results show that in the initial period of time the corrosion mass-losses of the specimens with coating were higher than that of the specimen without coating, the loss of coating made the major part of contribution to the corrosion weigh-loss of specimen. The corrosion rates increased with the broken area of the coating and decreased with exposing time. In addition, the electrochemical characteristics of the duplex phase galvanic electrodes were studied by galvanic corrosion potential measuring, electrochemical impedance spectrum (EIS) and potentiodynamic polarization and compared with the corrosion results.
The effect of microbes on the early corrosion behavior of Q235 steel in fresh waters was studied using immersion tests, electrochemical measurements and surface analysis techniques. In the field immersion test at Dan Jiangkou reservoir in China, the corrosion weight loss of Q235 steel increased as the immersion water depth increased. The reason may be that the microbe amount (especially algae amount) decreased with water depth increasing, which resulted in the biofilm formed on the surface of coupons with weak density and reduced coverage area. Therefore, more surface of Q235 steel were exposed to water and the corrosion weight loss increased. This conclusion was also confirmed by the electrochemical measurements and immersion test in natural freshwater. The results of the scanning electron microscopy (SEM) and Fourier transform infra-red (FT-IR) spectra further confirmed that the surface film formed in eutrophic freshwater was thicker and with more complex corrosion products.
The weight loss method, electrochemical impedance spectroscopy and surface analysis methods (SEM) were employed to investigate the synergism effect of Thiobacillus ferrooxidans （T.f）and Thiobacillus thiooxidan （T.t）on the corrosion behavior of steel Q235. The results showed that the combined effect of Thiobacillus ferrooxidans and Thiobacillus thiooxidan obviously accelerated the general corrosion rate of steel Q235, weight loss in the mixed colonies system was greater than that caused by each single microorganism. The result of SEM indicated that there was no pitting occurred on the coupon immersed in the Thiobacillus Thiooxidan solution while pitting holes of steel Q235 in the mixed colonies system were smaller and lower than that in the Thiobacillus ferrooxidans system. The presence of Thiobacillus Thiooxidan decreased the pitting corrosion of Q235 steel.
The polarization curves, electrochemical noise, electrochemical impendence spectroscopy(EIS) and energy dispersive spectrometry(EDS) were employed to investigate the corrosion behaviors of 304 stainless steel (SS) in simulated low hardness cooling water containing Cl-, SO42-. The influence of RP-98H water treatment agent on the corrosion of 304 SS and the corresponding inhibition mechanism were also studied. The results showed that, corrosive ion Cl- increased the pitting susceptibility of 304 SS and SO42- reduced the effect of Cl-, while RP-98H rapidly produced a layer of film which is capable of improving the pitting potential of 304 SS and inhibiting the corrosion. RP-98H is a type of mixed water treatment agent with the inhibition efficiency over 84.8 %, and the excellent concentration for the system of 304 SS-low hardness cooling water is proved to be 100 mg/L.
The influence of the resistance to corrosion behavior was studied for industrial titanium in bittern solution under the different concentrations of CO32- and the different values of pH and the different temperatures by electrochemical method and electrochemical impedance spectra and the weight loss in coupon tests in this paper. Electrode process was discussed and impedance was analyzed. The corrosion images were observed by metallurgical microscope after the mass loss tests. The results showed that the resistance to corrosion enhanced obviously for the metal system decreased gradually with increasing the concentration of CO32- and increasing the pH value, and decreased with rising up temperature. The resistance to corrosion enhanced first and then decreased oppositely with increasing the immersion time and the value of Vp was the biggest after 7 days immersion for titanium in bittern solution. The electrode reaction was irreversible and controlled by both activation polarization and diffusiveness for titanium in bittern medium.
The surface of magnesium was pretreated in the W-78 or A-1200 silane solution by dip-coating process as a base coating，then the magnesium electrodes with silane coupling agents were followed, of which the electrochemical properties and others are compared with the one that without silane coupling agents. The two silane coupling agents could improve the performance of the magnesium electrode, which make the results of electrochemical test recur better, A-1200 is more superior to W-78. The affecting mechanism of W-78 and A-1200 silane solution is summarized in this paper.
Empirical mode decomposition technique is applied to noise removal of time-serial data obtained from coulostatically-induced transients(CITs).Different noises are added to the ideal CITs which is obtained by using randle equivalent circuit ,and then, the de-noising criterion in practice for CITs using the empirical mode decomposition is obtained. The result indicates that the most effective filtering under most cases should be that IMF1 and IMF2 together with 50 Hz component of the IMF4 were removed. In addition, such a de-noising criterion is also effective when it is applied to a real corrosion system.
ESPI were firstly used to monitor the real-time, in-situ corrosion behavior of 45 steel in 0.5 mol/L NaHCO3+0.05 mol/L NaCl solution during anodic polarization. By comparison between the ESPI image and the digital photo of the sample surface; it was found that at the same position where a speckle appeared, a pit appeared after the polarization experiment. It can be concluded that the bright speckles in the ESPI images were caused by the pitting corrosion products. Accordingly, the size, position and time of initial pitting corrosion could be deduced. The pitting potential (Eb) of 45 steel determined by the method under the condition is -0.15 V;\linebreak meanwhile, the polarization current is 12.2 μA. Information of the pitting growth could be obtained by changes of the speckles in ESPI results.
The corrosion behavior of LY12 aluminum alloy was studied with cyclic immersion test, associated with electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) equipped with energy dispersive analysis system of X-ray (EDAX) examination. The results showed that the corrosion of LY12 aluminum alloy started from pitting, and then to intergranular corrosion and exfoliation. EIS is comprised by three capacitive curves at high-mediate frequency and a shrinking inductive curve at low frequency. Some information about the corrosion mechanism, such as corrosion development rate, corrosion morphology，the variation of the interface and the protection of the corrosion product, can be obtained through the simulated EIS data combined with the analysis of the corrosion kinetics and the corrosion product.
Bis-1,2-[triethoxysilylpropyl]tetrasulfide (BTSPS) films have been successfully deposited at low cathodic potential in silane solution modified by surfactant, and a new critical cathodic potential (NCCP) (-1.6 V) has been found. The study indicated the surface morphology of silane films prepared at low cathodic potential were more compact and thicker than those prepared at conventional critical cathodic potential (-0.8 V),and BTSPS films prepared at low cathodic potentials in modified silane solution exhibited obviously higher corrosion resistances in comparison with silane films prepared by conventional electrodeposition method. Hydrogen evolution could be decreased as well as the electrodeposition of silane could be improved while adding the surfactant. Anti-corrosion of films is better as well as a negative shift of the critical cathodic potential.
Corrosion behavior and corrosion influencing factors(total pressure, temperature, corrosion time, Cl-, velocity of flow) of NT80SS casing steels were studied in simulating corrosion environment with high contents of H2S and CO2 in Luojiazhai Gas Field by loss weight corrosion, and corrosion scale was analyzed by potentiodynamically scan, electrochemical impedance spectroscope(EIS) and scanning electron microscope(SEM). The results show that 60 ℃ was the temperature at which corrosion rate of NT80SS steel was the lowest among temperatures tested in this paper. When the total pressure was 9 MPa or above it, corrosion rate at 120 ℃ was lower than that at 90 ℃. However, the total pressure was less than 9 MPa, the result is contrary. Corrosion rate was decreasing with time prolonging; Cl- promoted corrosion of steel. Corrosion rate increased with acce-\linebreak lerated velocity of flow. The electrochemical experiments show that: in the range of 30 ℃-120 ℃, Resistance performance and compact character of the corrosion scale formed at 60 ℃ was the most outstanding among those formed at others temperature, and the anodic polarization rate is high, so corrosion rate of the steel at 60 ℃ is the lowest.
The effects of four kinds of reductants, acrylic acid, succinic acid, glycerol, glucose, and their contents on the bonding strength and anticorrosion of zinc-based waterborne anticorrosive coatings were studied through adhesive tape test, ammonium nitrate solution accelerated corrosion method, electrochemical measurement, thermogravimetric and comparison with zinc plating. The experimental results indicate that variety and content of the reductants had markedly influenced on the bonding strength and corrosion resistance of coatings. Using acrylic acid as the reductant the coatings had high bonding strength in a large adding range, and it can hold high bonding strength when the other reductants had low content. The corrosion resistance time increases firstly, and then decreases with the increment of reductant content. The coatings with acrylic acid or glycerol as reductant had good comprehensive properties, optimal dosage were 60 g/L and 20 g/L respectively. The coatings are composed of multilayer flake zinc powder and cement substance, and the corrosion resistance performances are obviously superior to zinc plating under different environmental conditions. Moreover, the formation mechanism of coatings is analyzed, thermodynamical calculation shows that all the cure reactions using these reductants can proceed automatically at solidifying temperature.
To understand the arc erosion properties of carbon/carbon (C/C) composites with electric current, the experiments were carried out on the HST-100 tribo-tester with QCr0.5 disk under electric current, and compared with the materials of metal-impregnated carbon, which used in electric railway. Microstructure and phase composition of the friction surface were observed and analyzed by scanning electron microscope(SEM) and X-ray diffractometer(XRD), and macroscopic temperature of the fiction surface were measured. The results show that values of friction coefficients and wear rate of two kinds materials increased with increase of velocities. But both the friction coefficient and wear rate of C/C composites were lower than that of metal-impregnated, and the tendency of increment was poor. The C/C composites own an outstanding tribological characteristic and excellent current-carrying quality, and meets the performance requirements of the contact strip under high speed.
