Xiaochen Hu, Pei Zhang, Yong Zhou and Fuan Yan
The purpose of this paper is to reveal the mechanism of nitrite (NO2−) for the surface passivation of carbon steels in acidic environments through investigating the influences of…
Abstract
Purpose
The purpose of this paper is to reveal the mechanism of nitrite (NO2−) for the surface passivation of carbon steels in acidic environments through investigating the influences of 0.01 mol/L NaNO2 addition on the corrosion and passivation behaviors of Q235 carbon steel in acidic phosphate buffer (APB) solutions (pH 2 to 6).
Design/methodology/approach
The electrochemical techniques including open circle potential evolution, potentiodynamic polarization, electrochemical impedance spectroscopy and cyclic voltammetry were applied.
Findings
In APB solutions without NO2−, the Q235 steel presented the electrochemical behaviors of activation (A), activation-passivation-transpassivation and self-passivation-transpassivation at pH 2 to 4, pH 5 and pH 6, respectively; the corrosion rate decreased with the up of pH value, and the surface passivation occurred in the pH 5 and pH 6 solutions only: the anodic passivation at pH 5 and the spontaneous passivation at pH 6.
Originality/value
In APB solutions without NO2−, the corrosion rate decreased with the up of pH value, and the surface passivation occurred in the pH 5 and pH 6 solutions only: the anodic passivation at pH 5 and the spontaneous passivation at pH 6. With the addition of 0.01 mol/L NaNO2, into APB solutions, the variation of corrosion rate showed the same rule, but the surface passivation occurred over the whole acidic pH range, including the anodic passivation at pH 2 to 4 and the spontaneous passivation at pH 5 to 6.
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Chunhui Kang, Decheng Kong, JiZheng Yao, Chunyun Guo, Li Wang, K. Xiao and C.F. Dong
This paper aims to investigate the corrosion behavior of zinc in a typical hot and dry atmosphere. It proposes the dynamic corrosion for different exposure periods. Results can…
Abstract
Purpose
This paper aims to investigate the corrosion behavior of zinc in a typical hot and dry atmosphere. It proposes the dynamic corrosion for different exposure periods. Results can provide the basic data and corrosion mechanism of zinc in such environment.
Design/methodology/approach
In this paper, the authors investigated the corrosion behavior of pure zinc exposed in the typical hot and dry environment in Turpan for one-four years, which has never been studied. Scanning electron microscopy, laser scanning confocal microscopy, electron probe micro-analyzer (EPMA), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were conducted to measure the corrosion morphology and products of zinc. Finally, combining electrochemical impedance spectroscopy and scanning Kelvin probe techniques, the corrosion mechanism of zinc in Turpan was examined.
Findings
The thickness loss of the zinc followed an exponential law with respect to exposure time: D = 3.17 t0.61, and both of the rust layer resistance and the charge transfer resistance increased with exposure time. The corrosion products mainly comprised ZnO, Zn(OH)2, Zn5(CO3)2(OH)6, Zn4SO4(OH)6·5H2O and Zn12(SO4)3Cl3(OH)15·5H2O. The Kelvin potentials shifted toward the positive direction from −0.380 to −0.262 V (vs saturated calomel electrode [SCE]) when the exposure time extended from one to four years and the distribution of the corrosion products became more and more uniform.
Originality/value
The corrosion behavior of pure zinc in the typical hot and dry environment in Turpan has not been studied. The dynamic corrosion for different exposure periods was obtained. The corrosion products were systemically investigated via energy-dispersive X-ray spectroscopy, EPMA, XPS and XRD.
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This bibliography is offered as a practical guide to published papers, conference proceedings papers and theses/dissertations on the finite element (FE) and boundary element (BE…
Abstract
This bibliography is offered as a practical guide to published papers, conference proceedings papers and theses/dissertations on the finite element (FE) and boundary element (BE) applications in different fields of biomechanics between 1976 and 1991. The aim of this paper is to help the users of FE and BE techniques to get better value from a large collection of papers on the subjects. Categories in biomechanics included in this survey are: orthopaedic mechanics, dental mechanics, cardiovascular mechanics, soft tissue mechanics, biological flow, impact injury, and other fields of applications. More than 900 references are listed.
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Minglei Hu, Kunjie Dai, Wei Zhang, Ke Xu, Jingkun Shi, Xiaoqian Fu, Yucheng Ji and Chaofang Dong
This study aims to investigate the crevice corrosion behavior of carbon steel in neutral/alkaline environments utilizing a transient multi-physics field model.
Abstract
Purpose
This study aims to investigate the crevice corrosion behavior of carbon steel in neutral/alkaline environments utilizing a transient multi-physics field model.
Design/methodology/approach
The crevice corrosion of carbon steel with different solution pH and crevice width was modeled, incorporating mass transfer, homogeneous phase and localized electrochemical reactions. The extent of crevice corrosion was evaluated by the geometric deformation of the model mesh. The hydro-chemical state inside the crevice was discussed through the Cl− concentration and potential distribution of the solution.
Findings
Results revealed that the formation of pitting corrosion near the crevice mouth was accelerated in a neutral solution. When pH = 8 and pH = 9, the carbon steel matrix was dissolved and the Cl− content within the solution was significantly reduced due to the higher concentration of hydroxide ions (OH−).
Originality/value
The crevice corrosion behavior of carbon steel in neutral/alkaline environments is closely associated with solution pH rather than the crevice width. The inhibition of crevice corrosion in alkaline environments was proved by finite element simulation. These findings provide valuable insights that can be applied in engineering applications to prevent and mitigate crevice corrosion in neutral/alkaline environments.
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Yijiang Chen, Pei Zhang, Yong Zhou and Fuan Yan
The purpose of this work is to reveal the mechanism of WO42− on surface passivation for Q235 carbon steel in tungstate solution.
Abstract
Purpose
The purpose of this work is to reveal the mechanism of WO42− on surface passivation for Q235 carbon steel in tungstate solution.
Design/methodology/approach
In Na2WO4 solutions with the different concentrations of WO42−, the spontaneous passivation occurred on the surface of Q235 carbon steel when the concentration of WO42− was up to 0.13 mmol/L, which was attributed to the formations of the inner deposition film and the outer adsorption film on the Q235 surface under the action of WO42−.
Findings
The inner deposition film presented a two-layer microstructure: the inside layer was composed of Fe2O3 mainly, and the outside layer comprised Fe(OH)2•nH2O, Fe(OH)3•nH2O, FeWO4 and Fe2(WO4)3.
Originality/value
Both FeWO4 and Fe2(WO4)3 repaired the defects in the outside layer of the inner deposition film; however, the outer adsorption film played a more important role in the surface passivation than the inner deposition film did.
Xiangyu Lu, Leyuan Zhang, Xingguo Feng, D. Chen and Yu Zuo
Aluminum tripolyphosphate was used as a corrosion inhibitor in a simulated concrete pore solution. For studies of the inhibition mechanism of aluminum tripolyphosphate on the…
Abstract
Purpose
Aluminum tripolyphosphate was used as a corrosion inhibitor in a simulated concrete pore solution. For studies of the inhibition mechanism of aluminum tripolyphosphate on the carbon steel, its influence on the pitting initiation on the carbon steel in a Cl− containing pore solution were investigated.
Design/methodology/approach
Potentiodynamic polarization curves, Mott–Schottky plots and potentiostatic polarization of the carbon steel in the pore solution with different content of aluminum tripolyphosphate were measured, as well as the optical micrographs of pitting on the carbon steel was observed.
Findings
The metastable pitting potential and the stable pitting potential increased, while the donor density and the flat band potential decreased with the concentration of aluminum tripolyphosphate in solution. Furthermore, the initiation of pitting was suppressed, as well as the transition from metastable to stable pitting was hindered by the aluminum tripolyphosphate. The scale parameter (a), in the extreme distribution of the maximum current peak, could be used to predict the transition from metastable to stable pitting.
Originality/value
The inhibition mechanism of aluminum tripolyphosphate on carbon steel in pore solution was revealed. It suppresses the initiation of pitting and hinders the transition from metastable to stable pitting. Furthermore, a parameter defined as the scale parameter (a) in the extreme distribution of the maximum current peak was introduced to predict the transition from metastable to stable pitting.
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Haoyue Zhang, Luqi Chang, Hongwei Zhang, Junyan Li, Zijiang Yang, Bingxuan Qiao, Zhenjiang Zhao, Chaofang Dong and Kai Zhang
The purpose of this paper is to study the mechanical and corrosion behaviors of selective laser melting (SLM) 30CrMnSiA steel.
Abstract
Purpose
The purpose of this paper is to study the mechanical and corrosion behaviors of selective laser melting (SLM) 30CrMnSiA steel.
Design/methodology/approach
The microstructure, mechanical behavior and corrosion resistance of SLM 30CrMnSiA steel were studied by electrochemical test and immersion experiment.
Findings
The results showed that the microstructure of SLM 30CrMnSiA steel contained equiaxed fine (25.0 µm) ferrite and lamellar pearlite. The tensile strength of SLM 30CrMnSiA steel under the process parameters is 1,447 MPa and the elongation is 7.5%. As the immersion/salt spray test time increased to 15 days/48 h, corrosion mainly occurred in the local position of the sample and corrosion resistance decreased. When the immersion/salt spray test time increased to 30 days/168 h, the corrosion production covered the surface of the samples and the corrosion resistance increased.
Originality/value
The paper can guide the application and in situ repair for low-alloy steel by additive manufacturing.
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Xiaoqing Ni, Liang Zhang, Wenheng Wu, Dexiang Zhu, Decheng Kong, Chaofang Dong and Guoliang Zhu
Laser melting deposition (LMD) is an advanced additive manufacturing (AM) technology without powder waste, and nickel-based alloys with different Nb contents were created one-time…
Abstract
Purpose
Laser melting deposition (LMD) is an advanced additive manufacturing (AM) technology without powder waste, and nickel-based alloys with different Nb contents were created one-time by adjusting the ratio of mixed powders via a dual-feed system. Here, the authors provide a systematic report on the effects of the Nb content on the microstructure, Laves phase segregation and mechanical properties of as-received LMD nickel-based alloys. The effects of the Nb content on the microstructure, precipitation evolution and mechanical properties of the subsequent heat-treated LMD samples are also discussed in this paper.
Design/methodology/approach
Thus, the present research aims to obtain a better understanding of the effect of Nb content on the microstructural and mechanical properties of the as-received LMD Inconel 718 alloys through high-throughput sample fabrication. The microstructures were characterized by scanning electron microscopy and energy-dispersive spectroscopy, electron back-scattered diffraction and transmission electron microscopy methods. The mechanical properties were obtained from compressive tests and nano-indentation tests. Electrochemical tests, including electrochemical impedance spectroscopy and potentiodynamic polarizations, were carried out to evaluate the durability of the Inconel 718 alloys. Results can provide a factual basis for future applications of the functionally graded by AM technology.
Findings
The grain size of the as-received LMD Inconel 718 alloys decreased with the Nb content. The Laves phase distribution at the macro level was relatively uniform and the Laves phase exhibited a 1.5-fold nano-hardness compared with the matrix. The strength improvement for the as-received LMD Inconel 718 alloys with Nb content was attributed to grain refinement and enhancement of the Laves phase in terms of both hardness and content. Meanwhile, the corrosion resistance increased with the increase of the Nb content, especially for the pitting potential, which was attributed to the optimization of carbide precipitates due to the strong affinity between niobium and carbon.
Originality/value
The results provide a factual basis for the Nb content effect in LMD nickel-based alloys, and this method can greatly promote the development of new materials. The authors believe that this study makes a significant contribution to the literature and is suitable for publication.
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Ali Akbar Abbasian Arani and Hamed Uosofvand
This paper aims to investigate the fluid flow and heat transfer of a laboratory shell and tube heat exchanger that are analyzed using computational fluid dynamic approach by…
Abstract
Purpose
This paper aims to investigate the fluid flow and heat transfer of a laboratory shell and tube heat exchanger that are analyzed using computational fluid dynamic approach by SOLIDWORKS flow simulation (ver. 2015) software.
Design/methodology/approach
In this study, several types of baffle including segmental baffle, butterfly baffle, helical baffle, combined helical-segmental baffle, combined helical-disk baffle and combined helical-butterfly baffle are examined. Two important parameters as the heat transfer and pressure drop are evaluated and analyzed. Based on obtained results, segmental baffle has the highest amount of heat transfer and pressure drop. To assess the integrative performance, performance coefficient defines as “Q/Δp” is used.
Findings
This investigation showed that among the presented baffle types, the heat exchangers equipped with disk baffle has the highest heat transfer. In addition, in the same mass flow rate, the performance coefficient of the shell and tube heat exchanger equipped with helical-butterfly baffle is the highest among the proposed models.
Originality/value
After combined helical-butterfly baffle the butterfly baffle, disk baffle, helical-segmental baffle and helical-disk baffle show their superiority of 35.12, 25, 22 and 12 per cent rather than the common segmental baffle, respectively. Furthermore, except for the combined helical-disk baffle, the other type of combined baffle have better performance compare to the basic configuration (butterfly and segmental baffle).
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Xuehui Hao, Changzheng Wang, Shuai Guo, Jie Ma, Hui Chen and Xingchuan Zhao
The poor corrosion resistance of the ferrite-pearlite steel limits its application in marine engineering because of the enhanced galvanic effect caused by continuously accumulated…
Abstract
Purpose
The poor corrosion resistance of the ferrite-pearlite steel limits its application in marine engineering because of the enhanced galvanic effect caused by continuously accumulated cementite. Cr as one principal alloying element is commonly used to improve the corrosion resistance of steels. This paper aims to study the effect of Cr on corrosion behaviors of ferrite-pearlite steels in an acidic environment.
Design/methodology/approach
The tested steels were immersed in a simulated solution of 10 Wt.% NaCl with pH 0.85 for 72 h to evaluate the corrosion rate. After the immersion test, the corrosion morphologies and products were tested by scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction. Meanwhile, an electrochemical workstation was used to study the electrochemical behaviors of samples.
Findings
At the initial corrosion stage, the corrosion rate increased in the sequence of Cr0, Cr0.5 and Cr1 steels, which was because of the competitive effect between the area ratio and the driving force caused by alloyed Cr. However, Cr1 steel exhibited the best corrosion resistance after a 72-h immersion test. This was because the alloyed Cr promoted the formation of protective Fe2O3 and FeCr2O4, which suppressed the preferential dissolution of ferrite and, thus, reduced the accumulation rate of carbides, resulting in the weakened galvanic corrosion.
Originality/value
This paper reports the role that Cr plays in the galvanic corrosion of ferrite-pearlite steels, which is important for the engineering application of ferrite-pearlite steels in marine environment.