The influence of the marine aerobic Pseudomonas strain on the corrosion of 70/30 Cu–Ni alloy

A comparative study of the corrosion behavior of the 70/30 Cu–Ni alloy in a nutrient-rich simulated seawater-based nutrient-rich medium in the presence and the absence of a marine aerobic Pseudomonas bacterium was carried out by electrochemical experiments, microscopic methods and X-ray photoelectron spectroscopy (XPS). The results of Tafel plot measurements showed the noticeable increase in the corrosion rate of the alloy in the presence of the Pseudomonas bacteria as compared to the corresponding control samples. The E1S data demonstrated that the charge transfer resistance, R_ct, and the resistance of oxide film, R_f, gradually increased with time in the abiotic medium; whereas, both of them dramatically decreased with time in the biotic medium inoculated with the Pseudomonas, indicative of the acceleration of corrosion rates of the alloy. The bacterial cells preferentially attached themselves to the alloy surface to form patchy or blotchy biofilms, as observed by fluorescent microscopy (FM). Scanning electron microscopy (SEM) images revealed the occurrence of micro-pitting corrosion underneath the biofilms on the alloy surface after the biofilm removal. XPS studies presented the evolution of the passive film on the alloy surface with time in the presence and the absence of the Pseudomonas bacteria under experimental conditions, and further revealed that the presence of the Pseudomonas cells and its extra-cellular polymers (EPS) on the alloy surface retarded the formation process or impaired the protective nature of the oxide film. Furthermore, XPS results verified the difference in the chelating functional groups between the conditioning layers and the bacterial cells and the EPS in the biofilms, which was believed to connect with the loss of the passivity of the protective oxide film.     

Localised corrosion of mild steel in presence of Pseudomonas aeruginosa biofilm

Microbially influenced corrosion (MIC) is a destructive type of corrosion, which is initiated, facilitated or accelerated by the presence of bacteria. The objective of this study is to determine the MIC behaviour of mild steel exposed to Pseudomonas aeruginosa inoculated nutrient rich simulated sea water medium. The formation of the biofilm layer, corrosion products and pitting areas on the steel substrate are characterised by field emission scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy and atomic force microscopy. The overall results showed the aggressive role of P. aeruginosa biofilm in inducing the corrosion process and generating significant pits on steel. This study may provide a new understanding of the MIC behaviour of steel caused by bacterial colonisation and biofilm formation.     

Corrosion behavior of 3C magnesium alloys in simulated sweat solution

AZ series Mg alloys AZ31, AZ61, and AZ80 are widely applied in 3C (computer, communication, and consumer electronic) industry. Their corrosion characters in simulated sweat solution have been investigated by electrochemical technology, surface analysis, and pH measurements. Electrochemical test results showed that the three magnesium alloys revealed different corrosion resistance (R_t) in simulated sweat solution, R_t(AZ31) < R_t(AZ61) < R_t(AZ80). Three major components of simulated sweat solution played different roles during corrosion processes. Lactic acid was a kind of strong erosive medium for the magnesium alloys, and NaCl can induce pitting corrosion on alloys surface, while urea acted as a corrosion inhibitor. The corroded surface morphology of the three magnesium alloys was observed using scanning electron microscopy (SEM) and corrosion products were analyzed by X‐ray diffraction (XRD). Result of pH measurement tests showed that there were differences in climbing speed and final values of pH for the three magnesium alloys in simulated sweat solution.     

N-Aminorhodanine as an effective corrosion inhibitor for mild steel in 0.5 M H2SO4

The corrosion inhibition effect of N-aminorhodanine (N-AR) on mild steel (MS) in 0.5 M H₂SO₄ was studied in both short and long immersion duration using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), chronoamperometry and hydrogen gas evolution. The surface morphology of MS was examined with scanning electron microscopy (SEM) in absence and presence inhibitor. The inhibitor adsorption process on MS surfaces obeys the Langmuir adsorption isotherm. The results show that NAR is a good inhibitor for MS in the acidic medium. The inhibition efficiency obtained from potentiodynamic polarization, EIS and LPR up to 98% is determined.     

Study on effects of alternating current field to pack boriding of medium carbon steel

Abstract

A plain medium carbon steel was borided by alternating current field enhanced pack boriding (ACFEPB). Diffusion kinetics and case characteristics of the borided steel were investigated to understand effects of an alternating current field (ACF) on pack boriding. Conventional pack boriding (CPB) was also employed for comparison. A series of boriding were conducted at temperatures of 873, 973, 1073 and 1173 K for 1, 2, 4 and 6 h, respectively, with a fixed current of 4 A. The morphology and types of borides formed in the steel were investigated by optical microscopy and X-ray diffraction, respectively. Boride growth kinetics was analysed by measuring the average thickness of the boriding case as a function of time and temperature. The growth rate of the ACFEPB case versus time showed the same parabolic character as CPB. The parameters of the boron diffusion kinetics, D?=?D₀exp(?QR^?1T^??1), have been determined. The results showed that the ACF enhanced inter-diffusion of boron in the substrate. The value of D, diffusion coefficient, in ACFEPB was more than 4 times of that in the CPB. The activation energy Q (44·45 kJ mol^?1) of the borided steel in the ACFEPB was less than 1/4 of that (180·6 kJ mol^?1) in the CPB.     

Characterization of Microplasma Sprayed Hydroxyapatite Coating

Microplasma sprayed (MIPS) HAP coatings on SS316L substrates were characterized by x-ray diffraction, Fourier transformed infrared spectroscopy, optical microscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), atomic force microscopy and image analysis. The coating showed a high degree of crystallinity ~92%, a high porosity level of 20 vol.% and a moderate bonding strength of about 13 MPa. The displacement controlled three-point bend tests and associated results of optical microscopy indicated that crack deflection, crack branching, and also local crack bridging occurred during crack propagation in the coating. The nano-hardness (H) and Young’s modulus (E) of the MIPS-HAP coatings as measured by nanoindentation technique were about 6 and 92 GPa, respectively. The fracture toughness (K _ic) of the coating was ~0.6 MPa·m^0.5. From the nano-scratch experiments, the critical normal load at which localized microcracking led to delamination was measured to be ~400 mN.     

Electrochemical corrosion behaviour and surface morphology of electrodeposited zinc,zinc–cobalt and their composite coatings

Abstract

The electrochemical behaviour as well as the surface morphology characteristics of electrodeposited Zn and Zn-Co (≈3 wt-%) alloy coatings on low carbon steel samples, with and without included nanoparticles of organic co-polymers in their structure, are discussed. Their corrosion resistance and protective properties were studied in a model corrosion medium, 5 wt-% NaCl, using electrochemical methods such as polarisation resistance (R _p) measurements and potentiodynamic (PD) polarisation curves. Scanning electron microscopy (SEM) was performed to examine the surface morphology changes of the samples before and after the corrosion treatment. Some conclusions are drawn about the influence and importance of the organic nanoparticles on the corrosion behaviour of the coatings presented.     

An insight into the influence of morphological and compositional heterogeneity of an individual intermetallic particle on aluminium alloy corrosion initiation

In this work, a multi‐analytical in situ and ex situ approach was used to provide information needed to identify the role of an individual heterogeneous intermetallic particle (IMP) in localized corrosion initiation of aluminium alloys. The heterogeneity of the IMP was studied by combining atomic force microscopy (AFM), scanning electron microscopy and energy dispersive spectroscopy (SEM–EDS) and scanning electrochemical microscopy (SECM). A complex Al–Mn–Fe–Si IMP phase with different chemical composition in its inner and outer parts was characterized by SEM–EDS analysis. AFM results uniquely revealed a brain‐like feature of an IMP with 20 nm height variations. Submicron sized galvanic cell induced by morphological and compositional heterogeneity resulted in a localized corrosion attack inside the individual IMP. Various collected current levels measured by SECM were associated to the morphological and compositional heterogeneity of IMPs.     

Calcium phosphate forming ability of thermally oxidized titanium implant

Commercially pure titanium disks as-received and heat treated at 600°C in air for 10 min were used to investigate differences in calcium phosphate forming ability. Crystallinity and surface morphology were analyzed by X-ray diffraction and field emission scanning electron microscopy. Energy dispersive X-ray spectrometry and Fourier transform infrared reflection spectroscopy were used to collect information on chemical composition and chemical surface structure. TiO₂ layers with a heterogeneous structure produced by heat treatment showed highin vitro calcium phosphate forming ability in contact with Eagle’s minimum essential medium.     

Electrodeposition of NiFe/Cu multilayers from a single bath

NiFe/Cu multilayers were deposited from a single bath in the potentiostatic mode using two different solutions. In solution A, the ionic concentration ratios were Fe²⁺: Ni²⁺: Cu²⁺ 9: 60: 10 and in solution B they were 1: 103: 1. To characterize the layers, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and atomic force microscopy (AFM) were used. SEM results revealed the layered structure of the deposits for relatively thick bilayers. While HRTEM provided direct evidence for the composition modulation across successive layers in the NiFe/Cu nanometer-multilayered structure prepared from solution B. Therefore, the layers prepared from solution B seemed to be more appropriate for giant magnetoresistance (GMR) applications. The effect of stirring during the electrodeposition process of the multilayers was also investigated.     

N-methyl-2-hydroxyethylammonium oleate ionic liquid performance as corrosion inhibitor for mild steel in hydrochloric acid medium

The aim of the present study is to evaluate the performance of N-methyl-2-hydroxyethylammonium oleate ([m-2HEA][Ol]) as a corrosion inhibitor for mild steel in a 0.1-mol/L hydrochloric acid solution and also investigate the role of chloride in the inhibition mechanism. This protic ionic liquid (PIL) has formerly shown a high efficiency as a corrosion inhibitor in a neutral chloride medium. Electrochemical and weight loss measurements, surface contact angle determination, scanning electron microscopy, and Raman spectroscopy were used to understand the factors that influence the response of the studied inhibitor. Results revealed that [m-2HEA][Ol] behaves as a mixed-type adsorption inhibitor, by blocking cathodic sites and by modifying the activation energy of the anodic reaction, and it can reach up to 94–97% of inhibition efficiency. PIL adsorption was enhanced by the excess of positive charge of the mild steel. The effect of inhibitor molecule has been discussed to propose a mechanism that explains the inhibitory action of the corrosion inhibitor, pointing out the role of chloride in the inhibition mechanism.     

Improvement of optical properties of nanocrystalline Fe-doped ZnO powders through precipitation method from citrate-modified zinc nitrate solution

Nanocrystalline Zn_1−xFe_xO (where x = 0, 0.01 and 0.02) powders were successfully synthesized by a precipitation method from citrate-modified zinc nitrate solution. X-ray powder diffraction, Fourier transformed infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy were used to study the structural properties. The optical properties were determined by UV–vis spectrophotometer and luminescent spectrometer. In this study, the optical band gap of nanocrystalline ZnO powder increased from 3.170 eV to 3.214 eV when the Fe concentration in the solution was increased up to 2 mol. %.     

Electrochemical characterization of the different surface states formed in the corrosion of carbon steel in alkaline sour medium

In this study the different surface states that manifest in the corrosion process of 1018 carbon steel in alkaline sour environment, solution prepared specifically to mimic the sour waters occurring in the catalytic oil refinery plants of the Mexican Oil Company (PEMEX) (0.1 M (NH₄)₂S and 10 ppm NaCN at pH 9.2) were prepared and characterized. The surface states of the carbon steel were formed by treating the surface with cyclic voltammetry at different switching potentials (E_λ+), commencing at the corrosion potential (E_corr=−0.890 V vs sulfate saturated electrode, SSE). The surface states thus obtained were characterized using electrochemical impedance spectroscopy and scanning electron microscopy techniques. It was found that for E_λ+=−0.7 and −0.6 V vs SSE a first product of corrosion formed, characterized by a high passivity. Moreover, it was very compact (with a thickness of 0.047 μm). However, at more anodic potentials (E_λ+>−0.5 V vs SSE) a second corrosion product with non-protective properties (porous with a thickness of 0.4 μm and very active) was observed. The diffusion of atomic hydrogen (H⁰) was identified as the slowest step in the carbon steel corrosion process in the alkaline sour media. The H⁰ diffusion coefficients in the first and second products that formed at the carbon steel–sour medium interface were of the order of 10⁻¹⁵ and 10⁻¹² cm²/s respectively.     

Electrochemical behavior of microbiologically influenced corrosion on Fe3Al in marine environment

In this article, microbiologically influenced corrosion behavior of Fe₃Al intermetallic compound in microorganism culture medium has been investigated by using weight loss methods, electrochemical techniques, and electron microscopy. Polarization curves showed that a sharp electrical current peak caused by surface pitting could be observed after Fe₃Al electrodes were immersed in culture medium for 15 days when the polarization potential was about -790 mV vs SCE. Based on the electrochemical impedance spectroscopy (EIS) and the equivalent circuit parameters of the associated system, the corrosion products were found to exhibit a two-layer structured feature and the microorganisms could induce pitting and erosion corrosion of the inner layer. In addition, the passivating film of the inner layer was absolutely destroyed by microbial metabolic products.     

Deformation behaviour of an advanced nickel-based superalloy studied by neutron diffraction and electron microscopy

Deformation mechanisms under tensile loading at room temperature have been studied in a polycrystalline nickel-based superalloy containing close to 50 vol.% γ′. In order to identify the effect of γ′ particle size on deformation mechanisms, model microstructures with unimodal γ′ size distributions were developed. The investigations were carried out by combining in situ loading experiments using neutron diffraction and two-site elasto-plastic self-consistent plasticity modelling with detailed post-mortem electron microscopy. The microscopy work also includes results for samples strained at 500 °C. During early plastic deformation, the diffraction data demonstrate that γ and γ′ display the same elastic strain response, indicating that at this stage γ′ is cut by dislocations regardless of the γ′ particle size. Scanning electron microscopy studies showed an abundance of shearing processes in all three microstructures, hence supporting the conclusions drawn from the diffraction experiment. As the material is further deformed, elastic load transfer from γ to γ′ was observed in the medium (130 nm) and coarse (230 nm) γ′ microstructures but not in the fine (90 nm) γ′ microstructure. The load transfer can be explained by assuming that Orowan looping becomes an additional operative deformation mode. Transmission electron microscopy confirmed that in the fine γ′ microstructure deformation takes place by strongly coupled dislocations cutting the γ′, while the medium and coarse γ′ microstructures showed additional signs of Orowan looping.     

Influence of gas nitriding of Ti6Al4V alloy at high temperature on the adhesion of Staphylococcus aureus

In this in vitro study, we investigated the influence of titanium nitride (TiN) treatments on the Staphylococcus aureus colonisation and biofilm formation on Ti6Al4V alloy at different times. The development of biofilm in static tests was carried out in a TSB culture medium at 37 °C, for 12, 24, 48 and 72 h. Bacterial adhesion on nitrided titanium alloy was analysed by both epifluorescence microscopy and scanning electron microscopy. The results revealed that the number of attached bacteria, their viability, and distribution were different for nitrided alloys than for the control group (non-nitrided alloys).     

脱硫弧菌引起的铝的微生物腐蚀机理研究

目的揭示培养周期内脱硫弧菌(一种硫酸盐还原菌)引起的铝的微生物腐蚀机理。方法采用细胞计数、荧光显微镜、电子显微镜、X射线能谱仪以及电化学测试等技术,测试并分析铝在硫酸盐还原菌(SRB)培养基中的腐蚀行为和机理。结果培养初期,SRB没有引起铝的腐蚀速率加速。铝电极的线性极化电阻在SRB培养基中的值甚至高于无菌培养基。这是因为生物膜的累积阻碍了基体与溶液介质界面的电子传输。随着培养时间的延长,铝在SRB培养基中的腐蚀速率明显提高。培养7天时,铝电极在SRB培养基中的腐蚀电流比无菌培养基中高3个数量级。结论随着时间的延长,培养基中有机碳源等营养成分消耗过多,导致SRB无法从培养基中获得足够的营养源,进而转向从铝中获取自身呼吸作用所需的能量。同时,由于生物膜的覆盖导致膜下微环境的改变,局部酸性可能较大,进而加速了点蚀的形成。     

A novel fluorescent,conducting polymer: Poly[1-(thiophene-2-yl)benzothieno[3,2-b]benzothiophene] electrosynthesis,characterization and optical properties

Poly[1-(thiophene-2-yl)benzothieno[3,2-b]benzothiophene] (poly-TBTBT) was electrosynthesized on a Pt electrode by anodic oxidation of TBTBT in 0.1 M LiClO₄ acetonitrile solution and in a micellar medium (water/methanol, 9/91, v/v) containing 0.39 M perchloric acid and 0.1 M sodium dodecylsulfate (SDS). Films prepared in acetonitrile were thick and electroactive, whereas in micellar medium they were very thin. Poly-TBTBT was characterized by cyclic voltammetry, MALDI-TOF mass spectrometry, IR, and scanning electron microscopy (SEM). Poly-TBTBT films were essentially constituted of short-chain oligomers (dimer to octamer). The molecular orbital (MO) calculations, carried out on the basis of a radical–cation electropolymerization mechanism, confirmed the spectral results The optical properties, including the electronic absorption and fluorescence spectra, were also examined.     

Pitting corrosion of titanium by a freshwater strain of sulphate reducing bacteria (Desulfovibrio vulgaris)

Pitting corrosion of titanium (ASTM Grade 2) was investigated by exposing coupons (2.0 × 1.5 cm) to a semi-continuous culture of sulphate reducing bacteria (SRB) strain Desulfovibrio vulgaris. The coupons were exposed to the SRB culture for 90 days along with a control set in uninoculated medium. During the course of the experiment sulphide was estimated at intervals of 4 days and the concentrations ranged from 0.2 to 0.4 mM in the bulk medium. Epifluorescence microscopy revealed extensive colonization by the SRB and the cell count ranged from 10⁴ to 10⁵ cells cm⁻². Optical microscopy revealed the presence of two types of pits; large hemispherical pits of ∼2 mm diameter and many micropits. Pitting was not observed in control coupons exposed to SRB free medium. SEM and CSLM pictures showed the corroded titanium surface with several micropits, along with typical rod shaped SRB cells in the pitted regions. EDAX analysis revealed peaks for Ti, O, N, C, Fe and P in the pitted region. XPS data showed clear peaks for titanium sulphur (three states) and phosphorous. The study reveals that at room temperature and in the presence of 0.2-0.4 mM of sulphide, as well as the putative phosphine, SRB can promote pitting corrosion of titanium by formation of titanium sulphide.     

一种镍基高温合金熔敷金属的组织及性能

通过热力学计算、光学显微镜(OM)、扫描电镜(SEM)和透射电镜(TEM)等分析了一种镍基高温合金熔敷金属的组织结构和力学性能.结果表明,试验用镍基高温合金熔敷金属的组织主要由柱状NiCr奥氏体以及在其亚晶间分布的少量γ'相、MC型碳化物和Laves相组成.熔敷金属组织结构完好,无裂纹、孔洞等缺陷,但多数合金元素存在偏析行为,其中元素Fe在亚晶粒中心含量较高,元素Mo,Nb,Al和Si在亚晶间含量较高,而元素Cr不存在偏析行为.熔敷金属具有良好的强度和韧性,在拉伸试验及冲击试验中其断裂形式均为塑性断裂,断口形貌为典型的韧窝状.