Research progress on corrosion of carbon steels induced by SRB is reviewed in terms of the formation mechanism of biofilm, the traditional corrosion mechanism of SRB, mechanism of biocatalysis cathodic sulfate reduction, and the corrosion of carbon steels under the deposit scale induced by SRB biomineralization. In addition, the paper focused on the key role of the theory of bioenergetics and bioelectrochemistry in understanding the mechanism of MIC induced by SRB. The novel technologies and methods for control of SRB biofilm which provide reference for control of SRB corrosion are introduced.
Galvanic corrosion performance of 5383 Al alloy coupled with 907 steel and aluminum bronze respectively in the early stage was studied by galvanic current test and scanning electron microscopy (SEM). The results showed that the 5383 Al alloy acted as anodes for the two galvanic couples, while 907 steel and aluminum bronze were cathode. The corrosion morphology of 5383 Al alloy could be metastable pitting, irregular stable pitting and filiform-like corrosion. The galvanic current density Ig of two couples varied similarly with immersion time, they decreased at the beginning and then became stable. The galvanic current density decreased with the increase of distance from the couple joint, and it became uniform in the far end. Compared with the couple 5383 Al alloy/aluminum bronze, the galvanic corrosion for couple 5383 Al alloy/907 steel was less severe, but it was more concentrated with in an area of 2 mm nearby the joint line.
研究了Al-0.5Mg-0.1Sn-0.1Si-0.02In合金作为铝空气电池的阳极材料,在2 mol/L NaCl,4 mol/L NaOH乙醇-10%水,4 mol/L NaOH溶液中的腐蚀行为及电化学性能。结果表明,该合金在4 mol/L NaOH乙醇-10%水溶液中性能优良,具有较高的阳极利用率及较低的自腐蚀速率。腐蚀形貌及电化学阻抗谱测试结果与合金腐蚀特性一致。通过对比Zn在4 mol/L NaOH溶液中的电化学性能,Al-0.5Mg-0.1Sn-0.1Si-0.02In合金在4 mol/L NaOH乙醇-10%水介质中作为铝空气电池的阳极材料具有可行性。
As anode material for aluminum-air battery, Al-0.5Mg-0.1Sn-0.1Si-0.02In alloy was prepared, and then its corrosion behavior and electrochemical performance were investigated in several solutions such as 2 mol/L NaCl, 4 mol/L NaOH and 4 mol/L NaOH ethanol+10%water. The results show that the alloy exhibited the optimal electrochemical performance in 4 mol/L NaOH ethanol-10% water solutions i.e. the alloy has higher anodic utilization and lower free-corrosion rate. Results of SEM observation and EIS measurements of the alloy all coincide well with the above corrosion performance for the alloy. Therefore, the Al-0.5Mg-0.1Sn-0.1Si-0.02In alloy has good feasibility as anode material for aluminum-air battery in 4 mol/L NaOH ethanol+10% water solution.
Electrochemical performance of sacrificial anode of Zn-Al-Cd alloy and pure Zn, which coupled with 20# steel, in underground water and artificial seawater respectively at different temperature was studied by means of polarization technology and self-discharge method. It has been proved that when coupled with 20# steel, the potential polarity reversal of Zn-Al-Cd alloy and pure Zn was not appeared in the two media by measurements of open circuit potential, working potential and polarization curves at temperature range 30~80 ℃. The sacrificial anode of the Zn-Al-Cd alloy coupled with 20# steel has a good electrochemical performance under the test conditions. The oxide scale formed on Zn-Al-Cd alloy in the underground water is more stable than that in the artificial seawater; the potential reversal between anode and cathode in cathodic protection can be prevented effectively by rationalizing the composition of the sacrificial anode alloy.
通过电火花数控线性切割机将弯头沿轴向剖开的实验方法,研究了SiO2颗粒对弯头冲蚀后的壁厚损失及微观形态,并分析了弯头磨损的分布与强度。结果表明,管流状态下颗粒对弯头的冲蚀主要集中于弯头外半圈,弯头外半圈质量损失与弯头内半圈质量损失比 (定义为α) 随着颗粒粒径增大而增大；小粒径颗粒对弯头冲蚀区域的影响较大而对壁厚损失影响相对较小,弯头 (R=1.5D) 最大冲蚀角为55°,此时颗粒对壁面的冲蚀作用最大,最容易造成磨损刺穿而导致弯头失效；冲蚀坑随着颗粒粒径增大而变大,但数量相对减少,颗粒对弯头的主要磨蚀机理是变形磨损,次要机理是低角度的微削磨损,它们的综合影响造成了弯头的穿孔刺漏。
Local erosion behavior of a square bend of 304SS steel induced by SiO2 sand blast was studied in terms of wall thickness loss along the band periphery and micro-morphology on the inner wall surface of the longitudinal section of a band after erosion test. The result shows that the erosion of the bend caused by sand particles is mainly concentrated on the outer half of the band and the ratio of the mass loss of the outer half to that of the inner half of a band, namely index α, increases with the increase of the particle size of the sand. Particles with small mean diameter have a greater effect on the dimension of eroded area, but less influence on the wall thickness loss. The maximum impact angle is 55° for a band with R=1.5D, where is apt to be suffered from perforation,leading to failure of the band. The size of pits induced by erosion increases but their quantity decreases with the increase of the sand particles size. The abrasion mechanism for particle impacting on the bend may mainly be ascribed to deformation wear,as well as to low angle microcutting wear, moreover, their comprehensive effect results in perforation and cut damage of the bend.
Galvanostatic pulse measurement (GPM) was introduced as a new non-destructive technique to monitor corrosion of X80 pipeline steel in a red soil environment. Corrosion rate and double layer capacitance of the metal/soil interface for X80 pipeline steel in red soil were measured by GPM, and then the acquired data were compared with those measured by polarization method. Results show that the galvanostatic pulse method is applicable for monitoring soil corrosion of the steel and it can provide a nondestructive analytical probe into double layer characteristics at soil/steel interface. The polarization resistance measurement indicated that corrosion rate of the steel decreased with time in the water saturated red soil.
A weld ring with rim of 90/10 cupronickel for marine pipe combination was corroded after 3 years operation. The failure of the ring was analyzed by means of chemical composition analysis, visual examination, metallographic observation of the alloy, as well as characterization of corrosion morphology and corrosion product by SEM/EDS. Results showed that intergranular corrosion was prevalent on the bottom of corrosion pits, in the erosion-corrosion zones and in the thinned region around corrosion perforations. De-nickelification and dissolution occurred in grains which were surrounded by the preferentially attacked boundaries. It was supposed that selective dealloying and dissolution was related with the types of grain boundary and the grain orientations. Sulfide was detected on the surface of the corrosion product and on the facet of emerged grains on the erosion-corrosion zone. Therefore, the failure of the cupronickel ring was the result from the synergistic effect of intergranular corrosion, dealloying corrosion and erosion-corrosion in the sulfide-containing environment.
Corrosion behaviour of four cast magnesium alloys (ZK60, AM60, AZ31 and AZ91D) was investigated in a simulated body fluid (SBF) for 72 h by weight-loss method, as well as electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. Their surface morphology after immersion tests was observed by scanning electron microscopy (SEM). The results show that among the four alloys, AZ91D exhibits uniform corrosion with the lowest corrosion rate; AZ31 suffers serious pitting corrosion with the highest corrosion rate; while AM60 and ZK60 alloys exhibit similar corrosion behavior.
通过循环极化确定纯Al和Al-7Zn-0.1Sn-0.015Ga (质量分数,%) 合金在3.5%NaCl溶液中的自腐蚀电位Ecorr、点蚀电位Epit、点蚀转变电位Eptp和保护电位Erp,并通过Al和铝合金在这些特征电位的点蚀形貌研究了它们的点蚀行为及点蚀扩展机理。结果表明：在点蚀电位时开始出现点蚀坑,随着电位升高点蚀坑迅速向横向和纵向扩展直至保护电位；纯Al的点蚀坑为窄而深的方形点蚀形貌,蚀坑内部为粗糙的结晶状结构,且表面出现明显的丝状腐蚀。Al-7Zn-0.1Sn-0.015Ga合金的点蚀形貌为宽而浅的圆形腐蚀坑,蚀坑内部比较光滑,且丝状腐蚀消失。合金元素能明显活化合金,降低点蚀坑深度,改善其腐蚀形貌。
Pitting corrosion behavior of pure Al and Al-7Zn-0.1Sn-0.015Ga (mass fraction, %) alloy in 3.5%NaCl solution was studied by cyclic polarization technique in terms of characteristics of corrosion potential Ecorr, pitting potential Epit, pitting transition potential Eptp and repassivation potential Erp. While the corrosion morphology of them was investigated by scanning electron microscopy (SEM). The results showed that pits initiate at the pitting potential, they grow quickly both in depth and diameter with the increasing potential until the protective potential. Pits formed on pure Al are narrow and deep square pits, the inner wall of which exhibits rough crystalline structure with a filament corrosion like surface. While pits on Al-7Zn-0.1Sn-0.015Ga alloy are wide and shallow circular pits, with relatively smooth wall but without the filament corrosion like feature. Alloying elements can significantly activate the alloy, reduce its pitting depth, and thus alter the corrosion morphology.
To improve the over sedimentation of fillers, the poor adhesive strength and wear resistance of ceramic/epoxy (EP) composite coating, SiO2 powder with particle size of 5~50 μm was sprayed on the surface of liquid epoxy coating to let the particles settling naturally in the coating. The graded SiO2/EP composite coating was prepared by controlling the curing temperature and time and thereby the sedimentation depth of the SiO2 particles of different sizes. It follows that the adhesive strength and wear resistance of the SiO2/EP composite coating prepared by the new process is higher than that prepared by the traditional blending method.
The tap water corrosion of ductile cast iron for water-supply pipe (DCIWP) is studied by means of electrochemical method and mass loss method. Taking into account the effects of initial corrosion on the correctness of the experimental results, a mass loss test including a period of pre-corrosion is conducted to study the main influence factors for the corrosion process through the orthogonal test design. The result turns out that at first the corrosion rate of the iron fluctuates significantly, then declines gradually over time and becomes stable in 48 h finally. The influence of pH of the water and test temperature is roughly equal and far more than the impact of total hardness and total residual chlorine of the water. The main influence factors affecting the corrosion of the ductile cast iron can be ranked as follows: temperature>pH>total residual chlorine>total hardness.
通过人工合成铁铝氧化物,并采用电化学阻抗谱 (EIS)、极化曲线、扫描电镜 (SEM)、能谱分析 (EDS) 和X射线衍射 (XRD) 等技术,考察了接地极铜材料在添加不同浓度铁铝氧化物的饱和红壤溶液中的腐蚀行为。结果表明,铁铝氧化物对铜腐蚀具有先促进后抑制作用。在添加不同浓度铁铝氧化物的红壤条件下Cu的阻抗随着浸泡时间的延长先升高后降低并趋于平稳。Cu的腐蚀速率随添加的铁铝氧化物含量的增大出现先增大后减小的趋势。Cu的腐蚀主要以全面腐蚀为主,腐蚀产物膜主要由Cu2O组成。
As test materials acidic red soil i.e. ferrallitic soil was taken from Yichun area of Jiangxi province and an Fe-Al double oxide was synthesized in laboratory. The corrosion behavior of copper for grounding grids in saturated solutions of mixtures of red soil with different amount of the Fe-Al double oxide was studied by EIS, polarization curve measurement, SEM, EDS and XRD. The results show that the Fe-Al double oxide can promote and then inhibit the copper corrosion process in the red soil. The corrosion impedance of copper increases and then tends to be stable in the saturated solutions of mixtures of red soil with different amount of the Fe-Al double oxide. The corrosion rates of copper increase and then decrease with the increase amount of the Fe-Al double oxide. Corrosion of copper is mainly uniform corrosion, accompanied by microbial corrosion phenomena, corrosion products formed are consisted mainly of Cu2O.