The research progress on the corrosion of key heat transfer components of boilers in domestic waste incineration power plants was reviewed. The corrosion characteristics and mechanism of three common corrosion types including chlorine corrosion, sulfur corrosion and alkali metal salt corrosion have been discussed respectively. Factors affecting corrosion were analyzed，such as metal materials, temperature, corrosive medium content, water vapor and heavy metal elements. The main achievements and shortcomings of the current research were summarized, and on this basis, further research directions were also proposed.
Corrosion survey on alternative current (AC) interference associated corrosion cases showed that the traditional criteria for cathodic protection (CP) is not applicable in the presence of AC interference. It is known about that in the presence of AC interference, the corrosion rate of buried pipeline even under CP of high quality is not negligible. Therefore, it was urgent to know how to evaluate the corrosion risk for the cathodically protected buried-pipelines in the presence of AC interference and how to choose the applicable CP parameter to protect pipelines. Base on that, the present criteria related with AC corrosion were analyzed and several corrosion theories have been proposed about the mechanism by which AC induces and enhances the corrosion of carbon steel in CP condition. After summarizing the AC corrosion mechanisms, the key problems are indicated and the development trend of this research field is predicted.
The development of electrochemical noise signal processing methods for investigation of corrosion mechanisms was introduced. The measurement and interpretation of the electrochemical noise occurred during stress corrosion cracking were reviewed. The applicability and existing problems related with the electrochemical noise technique for in situ monitoring of stress corrosion cracking in high-temperature and high-pressure water were also discussed.
The corrosion behavior of X65 pipeline steel at oil-water interface region in hyperbaric CO2 environment was studied by means of weight loss method, polarization curve, electrochemical impedance spectroscopy and other electrochemical analysis techniques, as well as corrosion morphology observation and corrosion products analysis. The results revealed that the X65 steel had little corrosion in the oil phase, local corrosion occurred at the interface region between oil and water, severe corrosion occurred in the aqueous region, where the oil-water stratified medium was under stationary state with CO2 partial pressure of 0.9 MPa at 60 ℃. The addition of seventeen alkenyl amide ethyl imidazoline quaternary ammonium salt, which is water soluble rust inhibitor, could reduced the corrosion rate of X65 steel under this condition, while the addition of the decyl mercaptan, which is oil soluble rust inhibitor, could aggravated the local corrosion of X65 steel at the oil-water interface, whilst, groove corrosion was observed at the oil-water interface.
The synergistic inhibition effect of imidazoline ammonium salt (IAS) coupled respectively with three cationic surfactants in H2S/CO2 brine solution was predicted by molecular dynamic simulation technology. The predicted results were verified for Q235 steel in 3.5%NaCl solution by means of mass loss method, potentiodynamic polarization measurement and XPS analysis. Results show that the combination of IAS with dodecyl trimethyl ammonium bromide (DTAB) or tetradecyl trimethyl ammonium bromide (TTAB) all presents good synergistic inhibition effect. The complex corrosion inhibitors are mixed-type inhibitor. From XPS results, it follows that during the corrosion process, the IAS might mainly play the role in the formation of inhibition film on the Q235 steel surface, while the surfactant could mainly fill in the defects of the forming corrosion inhibition film. Possibly, the difference in synergistic inhibition effect for different complex inhibitors may be related to the steric hindrance of inhibitor molecules.
A new type of urotropine quaternary ammonium salt as corrosion inhibitor was synthesized through nucleophilic reaction with urotropine and bromohexane as raw materials, while methanol as solvent. Then, the corrosion inhibition effect of quaternary ammonium salt for QT-800 steel in 15% (mass fraction) HCl solution was assessed by mass loss measurements, IR spectrometer and SEM. The mechanism of corrosion inhibition was studied by quantum chemical density functional theory. The results indicated that the quaternary ammonium salt has good corrosion inhibition performance, when urotropine quaternary ammonium salt of 0.5% (mass fraction) was added into 15%HCl solution at 90 ℃, the inhibition efficiency for QT-800 steel could reach up to 98.41%. The complexes of the urotropine quaternary ammonium salt with polyethylene glycol, potassium iodide and propynol were prepared respectively, and they all showed good performance in corrosion inhibition. Quantum chemical parameters indicates that the chemical activity of the urotropine quaternary ammonium salt is mainly distributed on the molecular ring, which has a smaller energy gap than the urotropine, and a larger adsorption energy on the iron surface. Therefore, the reactivity of urotropine quaternary ammonium salt is higher than that of urotropine. The results of IR spectrum and SEM analysis reveal that the urotropine quaternary ammonium salt molecules could adsorb on the surface of QT-800 steel during the corrosion test in HCl solution.
Marine Al-alloy 5083 owns low density, good weldability and high hardness, but it is easily suffered from pitting corrosion in sea water due to the effect of Cl-. Micro-arc oxidation (MAO) is an effective way to improve the corrosion resistance of Al-alloy. In the present study the electrolyte formula was optimized via response surface methodology so that to acquire a novel MAO coating on Al-alloy 5083, which composed of merely a dense layer. The prepare MAO coating was then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-hardness meter and dynamic polarization technology in terms of microstructure, micro-hardness and corrosion resistance. Results showed that in comparison with the coating prepared with the ordinary electrolyte, the thickness of the MAO coating increases from 30 μm to 90 μm, size of the sintered particles on MAO coating grown from 10 μm to 50 μm, and the thickness of the dense layer increased from 20 μm to 70 μm, accompanied by the increase of the percentage of α-Al2O3 in the MAO coating as well. The hardness of the polished MAO coating increased from 900 HV to 1500 HV. Polarization curve and salt frog test results also found that with the increasing of micro-arc oxidation time, the corrosion current density of MAO coating was gradually decreased, while its passivation ability was enhanced. Therefore, corrosion resistance of Al-alloy 5083 was increased substantially in the presence of the MAO coating composed merely of a thick dense layer.
In recent years, many accidents caused by alternating current (AC) corrosion have been reported. AC corrosion had become a serious potential damage to buried steel pipelines. X100 pipeline steel is very promising material for long distance gas pipeline, and the soil at Korla district is a kind of typical saline-alkali soil in the western China. The effects of AC current density (0~500 A/m2) on the corrosion behavior of X100 steel in an artificial solution, which simulated the soil medium at Korla district of the Xinjiang Uygur Autonomous Region was investigated by electrochemical test, immersion tests and surface analysis techniques. Results show that the average corrosion rate of X100 steel increases with the increasing AC current density. When the AC current density is below 100 A/m2, the corrosion is uniform corrosion, while local corrosion occurred under a larger AC current density. The corrosion product of X100 steel under AC interference may be differentiated as two layers. The outer layer is a loose yellow product mainly composed of FeOOH, and the inner layer is a relatively dense and black product with cracks mainly composed of Fe3O4, which has almost no protectiveness to the substrate. At the beginning of AC interference, the corrosion potential of X100 steel in the simulated solution shifts negatively and the higher the AC density is, the potential shifts more significant, but as the AC density higher than 200 A/m2, the corrosion potential shifts positively and then tends to be stable. The potentiodynamic polarization curve shows that X100 steel is actively dissolved in the test solution under AC interference, and the corrosion current density increases as the AC current density increases.
The oxidation behavior of austenitic stainless steel C-HRA-5 was studied in 650 ℃/25 MPa and 700 ℃/25 MPa supercritical water. Then its oxidation products were characterized by means of SEM, EDS, XRD and Raman spectroscopy in terms of the morphology and composition. Results show that a double layered oxide scale rich in Fe and Cr was formed on C-HRA-5 steel after oxidation test in the supercritical water, while a thin internal oxidation transition zone was also formed between the outer oxide scale and the matrix. As the temperature increases, the oxidation weight gain rate of C-HRA-5 increases gradually, and the oxidation weight gain rate at 700 ℃ is greater than the that at 650 ℃. The oxidation kinetics follows approximately parabolic and cubic law at 650 and 700 ℃, respectively.
Ni-Cr-P alloy coatings on Q235 steel were prepared by electroless plating. The effect of CrCl3, C3H6O3, C2H5NO2 and K2C2O4 on the structure, composition and corrosion resistance of the prepared coatings was investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that with the increase of concentration of lactic acid, glycine, and potassium oxalate, the deposition rate was decreased continuously. In the contrast, the deposition rate was increased continuously with the increase of concentration of chromium chloride. The Ni-Cr-P coatings presented a surface morphology of cauliflower-like microstructures composed of a mixture of polycrystalline and amorphous. Notably, the anticorrosion performance of the Ni-Cr-P coatings were found to be much better than that of the Ni-P coatings.
The self-assembly process of hexadecanethiol on the surface of Ag-plating on Cu-plate has been studied by means of charge and discharge capacitance method, contact angle measurement, and electrochemical impedance spectroscopy. The theoretical fitting to the capacitance data acquired from tests in 10 and 100 μmol·L-1 solution gives the adsorption rate constants of (1.3±0.2)×106 and (2.8±0.5)×104 mol-1·L·s-1 respectively, which are closed to those of (9.3±0.7)×105 and (3.4±0.6)×104 mol-1·L·s-1 obtained by using contact angle measurements. The results indicate that the adsorption rate constant of hexadecanethiol in the dilute solution is higher than that in the concentrated one. Tafel polarization curves reveal that both anodic and cathodic currents are significantly reduced while the silver plating was immersed in 5 mmol·L-1 hexadecanethiol solution for 15 min, correspondingly the corrosion inhibition rate reaches 98.6%. Furthermore, when the Ag-plating was firstly covered with a self-assembled film through immersion in 5 mmol·L-1 hexadecanethiol solution and then subjected to post heat treatment at 80 ℃ for 12 h, as expected, the treated Ag-plating exhibits excellent corrosion resistance to Na2S solution and H2S containing atmosphere. Therefore, the application of hexadecanethiol solution is effective and feasible in practice.
Graphene-modified mixed metal oxide anodes of Ti/IrTaSnSb-G were prepared by thermal decomposition, and then the electrochemical performance of the anodes in NaCl solutions was examined via electrochemical workshop type PAR2273 and SEM equipped with EDS in terms of the effect of graphene on the performance of anodes. The results show that the graphene promotes the segregation of IrO2, which then resulted in the formation of dendritic structure on the surface of the anodes, in the meanwhile, secondary crystallization phenomenon could induce the formation of nano-needle structure of IrO2, which increases the active surface areas and improves subsequently the electrocatalytic activity of the anodes. Besides, the electrolysis current efficiency of the electrode with 0.6 g/L graphene increases 9% in 3.5%NaCl solution at 5 ℃ and 13% in 1.5%NaCl solution at 15 ℃ respectively.
