Sulfuric acid dew point corrosion is a common and troublesome issue for thermal power plants. Therefore, it is of great significance to clearly understand the relevant mechanism, influencing factors and protection methods. The main obstacle currently encountered for the matter is how to reliably obtain the sulfuric acid gas to simulate the real sulfuric acid dew point corrosion environment. By analyzing the insufficiency of the existed methods for preparation of such gas at home and abroad, a method of introducing the simulated gas into the reaction chamber by inert gas carrier is proposed, namely, with help of a nitrogen steam, the sulfuric acid vapor is brought into the dew point corrosion simulation device. Based on the monitored index of conductivity and SO42-, the effect of sulfuric acid volume, sulfuric acid concentration, heating temperature and N2 flow rate on the production efficiency of sulfuric acid vapor were discussed. The results show that the new method can rightly provide for dew point corrosion of sulfuric acid vapor. At the same time, the feasibility of the method is verified by taking the exhaust gas of the waste heat boiler of the actual gas turbine power station.
To provide guideline for storage period and hot roll process, field corrosion behavior of hot-rolled AH36 steel with two typical oxide scales, namely the black and red ones respectively, were investigated in storage environment. Corrosion loss was calculated and corrosion morphologies and environmental conditions were continuously monitored. Results revealed that the oxide scale of AH36 steel could increase the corrosion potential and greatly decrease the corrosion current density. Moreover, corrosion resistance of the black oxide scale is superior to that of the red one due to its thicker and more compact scale. The black scale started to blister while the red one exhibited apparent rust staining after exposure for 119 d in storage environment with relative humidity of 72% at c.a. 23.4 ℃. Corrosion area was enlarged rapidly after 119 d exposure for both samples. Cross-sectional morphologies revealed that corrosion has already occurred and a thickness of 2~3 μm of corrosion products has been formed at the interface of oxide scale and substrate. Meanwhile, apparent voids and microcracks appeared in oxide scale, especially for the red one. Moreover, corrosion depth approximately obeyed exponential growth within the first stage of 119 d and hereafter increased almost linearly.
With a home-made facility, the corrosion behavior of 316L and HR-2 stainless steels at 60~90 ℃ beneath thin films of condensate HCl steam of 1, 0.5 and 0.1 mol/L HCl solutions was assessed by means of mass loss method, resistance probe, Tafel polarization measurement, electrochemical impedance spectroscopy, metallographic microscope and XRD. Results show that the corrosion rate of the two stainless steels accelerates with time in the initial stage, then slows down and finally stabilizes. The corrosion rate of 316L is faster. Both stainless steels can form stable passivation zone with more or less the same maintaining passivity current densities. The passivation interval of the HR-2 steel is higher than that of 316L steel, indicating that former is more resistant to corrosion. In addition, the corrosion products of the two stainless steel surfaces are basically the same, however, the corrosion product on the 316L steel is much dense. Due to the fact that the oxygen in the corrosion product scale is replaced by the competition of Cl-, correspondingly, the passivation film on the surface of the steel may tend to crack and be difficult to be healed, therefore, pitting corrosion may be initiated of the stainless steels.
The effect of Ru addition on the corrosion behavior of Ti-6Al-4V (TC4) alloy in HCl solution were studied by means of electrochemical method, energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The corrosion products and concentration variation of elements along surface depth were analyzed. The results showed that, the addition of Ru increased the corrosion potential of TC4 alloy in 10% (mass fraction) HCl solution from -0.585 V to -0.529 V, and the corrosion current density decreased from 6.193×10-5 A/cm2 to 2.750×10-5 A/cm2. The passive current densities changed a little, from 2.335×10-5 A/cm2 to 2.608×10-5 A/cm2. The addition of Ru reduced the corrosion rate of TC4 alloy in 15% (mass fraction) HCl solution from 1.48 mm/a to 0.94 mm/a as well. According to XPS results, the main corrosion products of TC4 alloy after corrosion in HCl solution were TiO2, Al2O3 and V2O5. During the corrosion, Ru played an effective role in cathodic modification, promoted the deposition of TiO2 passive film on the surface and thickened the passive film by one time. Therefore, Ru increased the denseness of the passive film, thereby improved the corrosion resistance of TC4 alloy effectively.
Two Mannich base corrosion inhibitors, ZJ-1 and ZJ-2, were synthesized by Mannich reaction. The products were characterized by infrared spectroscopy. Corrosion inhibition effect of these two inhibitors on P110 steel were studied by means of polarization curve measurement, electrochemical impedance spectroscopy and molecular dynamics simulation. While the relevant corrosion inhibition mechanism and adsorption behavior were also discussed. Results showed that the two synthesized corrosion inhibitors presented obvious corrosion inhibition effect on P110 steel in 1 mol/L NaCl+CO2 environment, however, ZJ-1 had better corrosion inhibition effect with a corrosion inhibition efficiency up to 92.06%. These two corrosion inhibitors were belonged to mixed corrosion inhibitors based on anode control. Both the anode reaction and the cathode reaction were restrained in the corrosion process due to the adsorption film formed on the metal surface by corrosion inhibitors. Furthermore, ZJ-1 and ZJ-2 can displace water molecules and adsorb on the metal surface, the lone pair electrons provided by the active atoms N and O could form coordination bonds with the vacant orbital of Fe. Therefore, corrosion inhibitor molecules can be adsorbed on the metal surface and the corrosion inhibition effect is enhanced due to strong chemical forces of the bonds. Compared with ZJ-2 inhibitor, ZJ-1 inhibitor molecule has higher adsorption energy and better corrosion inhibition performance to the surface of Fe-based alloys.
The submicron-sheet zinc phosphate (SZP) was modified with silane coupling agent (KH560), and then the modified zinc phosphate (KH560-SZP) was characterized by FT-IR, SEM and EDS. Dispersion statuses of SZP and KH560-SZP, as pigments in epoxy coating were comparatively analyzed by SEM. Then, corrosion resistance of epoxy coatings with SZP and KH560-SZP respectively were assessed via EIS, adhesion test and surface morphology observation. The results showed that KH560-SZP, as a pigment coated with cross-linking silane polymer could be dispersed effectively into the epoxy resins. Thus, the barrier performances and adhesion of the coatings were significantly improved. Consequentially, the anti-corrosion performance of the coating was comprehensively improved because due to the addition of the silane coupling agent modified zinc phosphate.
A new Ni-free white copper alloy was designed by alloying with Sn and Al. The microstructure of the alloy was observed by optical microscopy and scanning electron microscopy (SEM). The corrosion resistance of the alloy was evaluated by dezincification corrosion test and electrochemical corrosion test. The mechanical properties were examined by tensile test and hardness test. The results show that the addition of trace Sn and Al can significantly improve the corrosion resistance and slightly improve the mechanical properties of the alloy.
The microstructure and corrosion resistance of SAF2304 duplex stainless steel after aging treatment for 2 h at 600, 650, 700, 750 and 800 ℃, as well as at 700 ℃ for 0.25, 0.5,1, 2, 3, 4 and 5 h respectively were characterized by means of optical microscopy (OM), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurement. The results showed that with the increasing aging temperature, the amount of secondary phase precipitated at grain-boundaries of ferrite/austenite increased and the maximum value of which emerged at 700 ℃ sharply, correspondingly the steel after solution treated at 1050 ℃ for 1 h and aged at 700 ℃ for 2 h showed the worst corrosion resistance. Therefore, the SAF2304 duplex stainless steel is sensitive to the aging treatment at 700 ℃ in terms of the secondary phase precipitation and corrosion resistance. For the steel aged at 800 ℃, the precipitated phase was rarely observed, and its corrosion resistance was enhanced. Furthermore, with the increasing time for the aging at 700 ℃, precipitates of secondary phase increased sharply, while the formed passivation film became poor and poor in compactness and uniformity, so as the corrosion resistance of the steel.
Ni-P-BN(h)-Al2O3 composite coating was prepared on the surface of 45 steel parts by spray electrodeposition technology. The surface morphology of thecomposite coating was characterized by scanning electron microscopy (SEM). The corrosion resistance of the composite coating was studied by electrochemical workstation. Results showed that with the increase of the applied voltage within arrange of 22~28 V, the corrosion resistance of the composite coating was enhanced at first and then decreased. Among others, the composite coating deposited at voltage of 25 V presented the best corrosion resistance. While the corrosion resistance of the composite coating was enhanced gradually with the increase of the gap from 1.6 mm to 2.0 mm between injection nozzle to the workpiece, and the composite coating had the best corrosion resistance when prepared with the gap of 2.0 mm.
In order to solve the problem of serious environmental pollution caused by traditional chemical sterilization methods, the bactericidal enhancement effect and relevant mechanism of D-tyrosine in inhibiting and dispersing corrosive iron bacteria biofilm were studied by means of molecular biology, electrochemical detection and surface morphology observation. The results showed that D-tyrosine can successfully disperse the biofilm on the surface of the sample, turn which from adherent state to planktonic state entering the water system, thus inhibit the occurrence of microbial corrosion, while the bacteria of the planktonic iron bacteria film can be quickly killed by bactericide in the water. The bactericidal effect of the combined D-tyrosine and bactericide is very remarkable, the bactericidal rate can reach 98.73%, which is better than that of single bactericide, therefore, the dosage of bactericide can be decreased by 50%~70%. The results of surface analysis showed that the corrosion products were mainly iron oxides when bactericides and D-tyrosine were added to the solution, and the product film formed on the sample surface was loose and easy to fall off, which effectively slowed down the corrosion. The impedance spectroscopy showed that the polarization resistance of the sample increased and the corrosion rate decreased after adding D-tyrosine acids and bactericides. The above analysis showed that D-tyrosine had obvious enhancement effect on bactericides, played a very good role in inhibiting the microbial corrosion, and effectively alleviated the problems of microbial drug resistance and environmental pollution caused by the application of excessive microbicides.
The corrosion behavior of 50% (volume fraction) W particles/Zr41.2Ti13.8Cu12.5Ni10Be22.5 metallic glass matrix composite in 3% (mass fraction) NaCl solution was studied by electrochemical test, immersion test and surface analysis. The result showed that: in 3%NaCl solution, local corrosion microcells were formed on the surface of the composite due to the coupling effect of W particles and metallic glass matrix, the corrosion dissolution on the surface of metallic glass matrix is intensified as a local anodic zone, the corrosion current density of the composite increased, and the corrosion resistance of the composite is significantly lower than that of Zr41.2Ti13.8Cu12.5Ni10Be22.5 metallic glass. The incorporation of 50%W particles have no effect on the pitting resistance of the composite, the uniform corrosion dissolution occurs in the metallic glass site of the composite in 3%NaCl solution, and the composite has better pitting resistance.
The iso-thermal oxidation behavior of Co-20Re-25Cr-1Si alloy in 0.1 MPa pure oxygen at 1000~1100 ℃ for 24 h was investigated. The oxidation kinetics is irregular at both temperatures. The alloys show obvious mass loss due to the evaporation of Re element in the form of ReO3. However, at 1100 ℃ continuous mass gain occurred during the initial 15 min of oxidation, while at 1000 ℃ the alloys remained in a mass loss state during the whole oxidation process. The scales formed at both temperatures are very similar. The outermost layer is composed of CoO, while the subsequent layer is composed of CoO and CoCr2O4. The innermost layer is a thin and protective layer of Cr2O3 with a certain degree of continuity. Moreover, there is an inner oxidation zone of Si beneath the outer scales. Since the Cr2O3 layer formed at 1000 ℃ is more continuous and denser, the alloy exhibits a better oxidation resistance at 1000 ℃.