People realized that microbes can cause serious microbiologically influenced corrosion (MIC) attack on metals since a century ago. In the past 20 years, the research relevant to MIC became more and more important due to severe damages and huge economic losses caused by microorganisms. Due to a lack of understanding, MIC has even been considered to be a "myth" in the field of corrosion, therefore, a theory which can cogently explain MIC phenomena is needed. The latest research result indicated that MIC is a bioelectrochemical process in essence. When the organic carbon is not available or fully consumed, metal such as iron would replace organic carbons as an electron donor for microorganisms, resulting in the occurrence of MIC. In addition, another theory related with the mechanism of MIC is that microbes could secrete corrosive metabolites such as organic acids. It is well known that corrosion is an exergonic process, and the microorganisms would utilize the energy released by the corrosion of metal to obtain their maintenance energy. Currently, electrochemical methods are widely used in MIC research, and the classical cathodic depolarization theory (CDT) was proposed based on electrochemistry. However, if only from the perspective of the electrochemistry, many phenomena of MIC can not be cogently explained. Researchers realized that the knowledge of bioenergetics and bioelectrochemistry may be the key to better understand the interactions between microorganisms and metals and then the process of MIC. This review is to summarize the recent works, and introduce the latest theories concerning the mechanism of MIC emphatically, such as biocatalytic cathodic sulfate reduction (BCSR) and electrical microbial influenced corrosion (EMIC). The introduction of the novel perspective to study MIC from bioenergetics and bioelectrochemistry is also provided in this review. Based on bioenergetics and bioelectrochemistry, the BCSR theory can cogently explain how and why MIC happens, which has been a long-term unsolved research problem.
The cold rolling with different reduction degrees for a new type high-nitrogen nickel-free stainless steel was conducted, then the cold deformation performance and its effect on the friction wear property for the steel were studied. The results showed that the microstructure of the steel was stable and there was no strain-induced martensite even by the maximum deformation of 60%. As the cold deformation increased, the strength and hardness of the steel increased rapidly while the elongation and work-hardening exponent decreased gradually. There existed a trend that the wear rate of the steel decreased firstly and then increased with the increasing cold deformation, whilst, the best wear resistance can be achieved by 20% cold deformation for the loads of 2 N and 5 N, and by 40% cold deformation for 10 N, respectively. Moreover, the main wear mechanism of the high-nitrogen nickel-free stainless steel changed from abrasive wear, oxidation wear and brittle flaking to abrasive wear and brittle flaking with the increasing cold deformation and load.
Fracture toughness of X80 pipeline steel in a simulated petrochemical environment is studied in this paper. Original specimens and saturated H2S pre-corroded specimens were tested respectively and δ-Δa resistance curves were obtained, while the influence of hydrogen sulfide corrosive environment on the resistance curve, fracture toughness and plastic work of X80 pipeline steel was analyzed. It follows that the lower limit of KIC of the pre-corroded X80 steel is 75.43 MPam½, and the hydrogen sulfide corrosion affect significantly on the fracture toughness of X80 steel: the crack growth resistance curve obtained from original specimens is much higher than that of the pre-corroded specimens; the fracture toughness of stable crack propagation δ0.2BL is 0.740 mm and 0.365 mm respectively, and the former is 2.02 times of the latter. In case for a given amount of crack propagation Δa, the plastic work of the original specimen is about 2.29 times of the pre-corroded specimen. Hydrogen sulfide corrosion reduced the fracture toughness of the X80 steel remarkablely. Thus, in the course of natural gas pipeline, hydrogen sulfide corrosive environment should be avoided to keep the steel a proper high toughness to prevent damage.
Composites of polyaniline/carbon microcoils (PANI/CMCs) were prepared by microemulsion-polymerization method. The observation by scanning electron microscopy (SEM) showed that the surface of the CMCs became rough due to the coverage of PANI on the surface after the synthesis process. The infrared spectroscopy measurement proved the presence of chemical bonding between PANI and CMCs. When the volume ratio of chloroform, as co-emulsifier, to the total reaction matters was 1: 24, the maximum amount of PANI coverage can be acquired, which well grafted on the surface of CMCs. Results of constant current charge-discharge and cyclic voltammetry tests show that in comparison with the single PANI or CMCs, the composites possess superior capacitive performance with a specific capacitance 134.8 F·g-1 and an excellent cycling stability with a remaining capacitance 63.3% after 750 cycles.
Nano-flake barium phosphate was prepared by hydrothermal synthesis, and then the effect of which as pigment on the corrosion behavior of epoxy coating was investigated by means of electrochemical impedance spectroscopy (EIS) and salt spray tests. The results show that the nano-flake barium phosphate in the epoxy coating can react with iron oxide, the corrosion product of metal substraste, to generate an insoluble FePO4 as a barrier on the corrosion spot, thereby to enhance the corrosion resistance of the coating; Among others, an epoxy coating with 5 mass% nano flake barium phosphate shows the highest corrosion resistance.
Carbon nanotubes (CNTs) and ammonium polyphosphate (APP) were applied to improve the flame retardancy of nylon6 (PA6). The results showed that PA6/APP/CNTs exhibited excellent flame retardancy with 1% CNTs and 20% APP (in mass fraction). While for a PA6/APP/CNTs blended with the flammable acrylonitrile-butadiene-styrene (ABS) it needed to add only 0.25% CNTs to meet the flame retardancy equal to that of the above mentioned PA6/APP/CNTs with 1% CNTs. TEM observation showed that CNTs were exclusively dispersed in the PA6 phase of PA6/ABS/APP. Rheological tests showed that the selective dispersion of CNTs facilitated the formation of the network structure of CNTs, thus the needed CNTs content could be lowered from 1% to 0.25% to meet the required flame retardancy. The morphology observation of the residue char revealed that the network structure was benefitial to the formation of compact residue char thus enhanced the flame retardancy for the 1% CNTs filled PA6/APP or 0.25% CNTs filled PA6/ABS/APP, respectively. When the CNTs content in PA6/ABS/APP was 1%, the formed network structure was so dense that the swell of the char layer was inhibited, thereby resulting in poor flame retardancy.
Hollow glass microspheres (HGM) are modified with different types of coupling agents.Phenolic syntactic foams are prepared by introducing the modified hollow glass microspheres into phenolic matrix. The interaction between HGM and phenolic matrix, as well as the flexural strength, fracture toughness, and dynamic mechanical properties of phenolic syntactic foams were then studied. Results showed that the graft of coupling agent onto the surface of HGM could reduce the agglomeration of HGM in the phenolic matrix, enhance the compatibility of HGM with phenolic matrix and the hydrophobicityof HGM, resulting in a good comprehensive property of phenolic syntactic foams. Among various types of coupling agents of γ-aminopropyltriethoxysilane(APTES), di(dioctylpyrophosphato) ethylene titanate(NDZ-311), and glutaraldehyde(GA), the long chains on the surface of NDZ311grafted HGM may interact with polymer chains of PF matrix through Vander Waals forces and physical entanglement of molecular chains; For the case of APTES-HGM, when the particles are immersed in resol phenolic, a few hydroxymethylgroup could react with amino group to form chemical bonding, the physicalentanglement of molecular chains dominates the linkage between filler and matrix; In syntactic foams containing GA modified HGM, the aldehyde group could react with phenolic resinmonomers and form acetal linkage with resin matrix.
The in vitro biocompatibility of a novel magnesium phosphate whisker (M-PW) was evaluated by real-time cellular analysis (RTCA) and Annexin-V/PI double marking methods, and its antibacterial property was evaluated by co-culture method. Results show that the in vitro biocompatibility of the M-PW decreased with the increase of M-PW in the suspensions. It possessed excellent in vitro biocompatibility for the suspensions containing 500 μg/mL or lower amount of the M-PW. It had no toxic effect on osteoblast cells for the suspension with 50 and 200 μg/mL of M-PW respectively. The antibacterial efficacy of the suspensions increased with the increasing amount of M-PW. The antibacterial efficacy against Escherichia coli and Staphylococcus aureus achieved 96.84% and 99.93% respectively for the suspension with 500 μg/mL of M-PW, demonstrating that the novel phosphorous-magnesium whisker possesses excellent antibacterial property.
A kind of carbon fiber / graphene oxide multi-scale reinforcement was prepared by "grafting to" method, with raw materials of the graphene oxide fabricated by a modified Hummers method and the carbon fiber treated with silane coupling agent Kh550.The prepared product was characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), Ramanspectroscopy (Raman), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The mechanical properties and the conductivity of the reinforced carbon fiber were measured by electronic tensile strength tester for fiber and resistivity instrument. The results showthatafter grafting, the graphene oxide can be grafted onto grooves and defects of the carbon fiber surface; the number of unsaturated carbon atom increases andthe size of microcrystalline decreases on the surface of the carbon fiber; andthe tensile strength andthe fractureelongation of single carbon fiber may be increased up to 9.8% and 13.1%, respectively andhowever the conductivity of carbon fiber is reduced by 11.6%.
A series of micro-arc oxidation (MAO) films were prepared on Mg-Mn-RE alloy by an alternating current with symmetric voltage in different alkaline solutions containing aluminate, phosphate or silicate and then the MAO films were characterized by SEM and XRD. The corrosion resistance of MAO films was evaluated by EIS potentiodynamic polarization. The results indicated that the MAO films prepared in phosphate or silicate systems have low thickness with obvious cracks, leading to poor corrosion resistance. In the contrast, the MAO films prepared in aluminate system exhibit the better corrosion resistance due to the compactness and higher surface quality, which shows a good prospect for the application.
