Corrosion protection of magnesium AZ31 alloy using poly(ether imide) [PEI] coatings prepared by the dip coating method: Influence of solvent and substrate pre-treatment

In this study, investigations on the protectiveness of poly(ether imide) coatings against corrosion of magnesium AZ31 alloy sheets are performed. The coatings were prepared in different pre-treated substrates by the dip coating method using N′N′-dimethyl acetamide (DMAc) and N′-methyl pyrrolidone solutions. The optimal performance was obtained for hydrofluoric acid treated substrates coated using DMAc solution (coating thickness 13 μm) which showed impedances in the order of 10⁷ Ω cm² even after more than 3300 h of exposure to a 3.5 wt.% NaCl solution. This high performance is associated to an acid–base interaction at the interface as observed by X-ray photoelectron spectroscopy.     

OLEDs based on new oxadiazole derivatives

The absorption, photoluminescence and electroluminescence properties of systematically modified poly(1,3,4-oxadiazole)s are reported and compared with low molar mass compounds. Poly(1,3,4-oxadiazole)s are functionalised by introducing pendent alkyl side chains and tetraphenylsilane or hexafluoroisopropylidene group (6F) into the main chain, respectively. The photo-and electroluminescence of single layer devices was found to be in the blue and green spectral range. A further strategy was to start with the optimisation of the substituents of low molar mass compounds followed by bonding the optimised structure to a flexible PMMA main chain. It was demonstrated that it is possible to preserve the optical properties of the oxadiazole unit and at the same time to improve film forming properties of the final polymer.     

Synthesis of bicyclometalated iridium complex containing 1,3,4-oxadiazole-based picolinic acid derivative and its optoelectronic properties in polymer light-emitting devices

A picolinic acid derivative bearing an 1,3,4-oxadiazole unit and its bicyclometalated iridium complex (PhOXD)₂Ir(BuPhOXD-Pic) were synthesized and characterized, in which BuPhOXD-Pic is 5-(4′-(5″-(4-tert-butylphenyl)-1″,3″,4″-oxadiazol-2″-yl) phenyl) picolinic acid and PhOXD is 2,5-diphenyl-1,3,4-oxadiazole. The optoelectronic properties of this iridium complex were studied in the double-layer polymer light-emitting devices using a blend of poly (9,9-dioctylfluorene) and 5-biphenyl-2-(4-tert-butyl) phenyl-1,3,4-oxadiazole as a host matrix. This complex exhibited a maximum luminance efficiency of 7.7 cd/A at 5.6 mA/cm² and a peak brightness of 5288 cd/m² at 153.7 mA/cm² in the devices. Compared to the (PhOXD)₂Ir(Pic) complex, the (PhOXD)₂Ir(BuPhOXD-Pic) complex displays better optoelectronic properties in the devices. This study provides a convenient way to improve the optoelectronic properties of iridium complexes by modifying an ancillary ligand of picolinic acid (Pic) with an 1,3,4-oxadiazole unit.     

“点击”化学法聚合物包覆纳米二氧化硅的研究

目的为了提高纳米二氧化硅与树脂的相容性,采用"点击"化学法研究表面接枝聚合物。方法利用普通自由基聚合制备的聚(甲基丙烯酸甲酯-马来酸酐)和聚(甲基丙烯酸甲酯-甲基丙烯酸缩水甘油酯),分别与丙炔醇和叠氮钠反应从而在分子链上引入多个炔基和叠氮基,然后与叠氮基改性的纳米二氧化硅粒子进行"点击"化学反应实现纳米二氧化硅包覆改性,并通过热重分析、红外光谱分析以及扫描电镜进行结构表征。结果聚合物接枝到了纳米二氧化硅表面,包覆第一层聚合物后,二氧化硅分散性明显提高;包覆第二层聚合物后,分散性有所下降。结论通过在纳米二氧化硅表面包覆聚合物,可以明显提高其分散性能。     

Effect of anodic oxidation on fatigue performance of 7075-T6 alloy

Effect of anodic oxidation on fatigue performance of 7075-T6 alloy for pre-corroded and non-corroded specimens has been investigated by conducting a series of rotary bending fatigue tests at 95 Hz. The anodized specimens with different coating thickness (6, 12 and 23 μm) were exposed to 3.5 wt.% NaCl solution for 6, 48, 96 and 240 h. The results indicate that oxidation has a tendency to decrease the fatigue performance. Fatigue strength was reduced with increasing coating thickness; approximately 40% reduction for a 23 μm thick coating was obtained. It was observed that oxidation mitigated pitting corrosion. Superior corrosion resistance was obtained for the thickest coating layer. Fatigue tests with pre-corroded specimens showed that fatigue life of coated specimens was significantly affected by pre-corrosion, except for the specimen with the thickest coating layer. When the pre-corroded bare and coated specimens were compared, the coating improved the fatigue performance in high cycle fatigue (> 10⁵) only and it degraded the fatigue performance in low cycle regime.     

Poly(m‐phenylenediamine)‐coated 316L SS: A promising material for bipolar plates in PEMFC environment

The applicability of conducting polymer coatings to enhance corrosion resistance of bipolar plates in proton exchange membrane fuel cells (PEMFC) is gaining greater significance as electrical conductivity is as important as corrosion resistance. Metaphenylenediamine (mPD) monomer was electropolymerized to poly(m‐phenylenediamine) (PmPD) conducting polymer over 316L SS and characterized by attenuated total reflectance infrared spectroscopy to confirm the formation of P mPD polymer. Scanning electron microscopy was used to study the surface morphology of the polymer. Open‐circuit potential, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization studies were conducted to assess the corrosion protection performance of the PmPD polymer coating in PEMFC environment. The charge‐transfer resistance measured from EIS for the coated substrates was higher than the uncoated substrate. Potentiodynamic polarization studies showed lower corrosion current density for the PmPD‐coated substrates. All the results proved that the PmPD‐coated substrates could exhibit enhanced corrosion resistance in PEMFC environment.     

Combination of zinc alloy coating with thin plasma polymer films for novel corrosion protective systems on coated steel

Steel sheet used in automotive applications has to be corrosion protected effectively, which is usually realized by zinc or zinc alloy coatings with a thickness range of 5–10 μm. Steel sheet for areas of a car body which are exceptionally stressed by corrosion, e.g. cavity flanges or joints, may be protected additionally by a thin weldable organic coating with a thickness of 2–4 μm. A very promising approach to a significantly reduced use of resources is the combination of zinc alloy coatings with thin plasma polymer films deposited by means of plasma-enhanced chemical vapour deposition (PECVD). Such plasma polymer films of just a few 100 nm thickness show excellent barrier and adhesion properties as well as a high mechanical stability.Within this work thin plasma polymer films were deposited on zinc alloy coated steel substrates using the strip hollow cathode (SHC) method, which was modified for application on grounded substrates. A pulsed DC glow discharge in a mixture of argon and an organosilane precursor was used for the deposition of films with a thickness of 100–500 nm.The chemical compositions of the coatings were determined by means of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The morphologies of the coating systems were studied by means of scanning electron microscopy. The performance of the coating systems has been studied in different specific tests of corrosion and processing behaviour. The investigated coating systems show a corrosion resistance comparable to reference samples of electro-galvanised steel sheet with additional organic coating even with a coating thickness less of half of the reference samples.     

Electrodeposition of polypyrrole onto NiTi and the corrosion behaviour of the coated alloy

Polypyrrole (PPy) films were electrodeposited onto nickel--titanium alloy (NiTi) employing sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT or AOT) solutions. Polarizing anodically NiTi samples recovered by PPy in a monomer-free solution increases adhesion of the coating. Electrochemical techniques, scanning electron microscopy (SEM) and element analysis were used in determining the corrosion performance of the coated samples in chloride solution. The polymer improves the corrosion performance at the open circuit potential and at potentials where the bare substrate suffers pitting attack. The improvement in both, adhesion and corrosion performance, is discussed considering substrate/polymer interaction, overoxidation of PPy and the role played by AOT.     

Comparative study on corrosion protection properties of electroless Ni‐P‐ZrO2 and Ni‐P coatings on AZ91D magnesium alloy

Electroless Ni‐P‐ZrO₂ and Ni‐P coatings on AZ91D magnesium alloy were prepared, and their corrosion protection properties were compared in this paper. The potentiodynamic curves and electrochemical impedance spectroscopy (EIS) of the coated magnesium alloy in 3.5% NaCl solution showed that the corrosion performance of Ni‐P‐ZrO₂ composite coating was superior to that of Ni‐P coating. The same conclusion was obtained with salt spray and immersion tests. The corrosion morphologies of two kinds of coatings with various immersion time intervals in 3.5% NaCl solution indicated that most corrosion products concentrated on the nodules boundaries of Ni‐P coating and blocked corrosion pit was the main corrosion form. For the Ni‐P‐ZrO₂ coating, tortuous nodules boundaries were not the weak sites of the coating and corrosion initiated from the nickel phosphor alloy around the nanometer powders. Open corrosion pits occurred on the composite coating surface, and the coating was corroded gradually. Thus, the Ni‐P‐ZrO₂ coating exhibited better corrosion protection property to magnesium alloy substrate than Ni‐P coating.     

Biodegradation Behavior of Coated As-Extruded Mg–Sr Alloy in Simulated Body Fluid

As-extruded Mg–Sr alloy, a kind of promising biodegradable biomedical material, was coated using micro-arc oxidation and also using a phosphate conversion coating. The corrosion behaviors were investigated using Hanks' solution. The corrosion of the as-extruded Mg–Sr alloy became more serious with increasing immersion time; that is, the corrosion pits became more numerous, larger and deeper. The micro-arc oxidation coating and the phosphate conversion coating were effective in improving the corrosion resistance of the as-extruded Mg–Sr alloy. The micro-arc oxidation coating was much more effective. Moreover, the as-extruded Mg–Sr alloy and the coated as-extruded Mg–Sr alloy exhibited lower corrosion rates than the as-cast Mg–Sr alloy and the corresponding coated as-cast Mg–Sr alloy, indicating that the corrosion properties of the coated samples are dependent on their substrates. The finer microstructure of the substrate of the as-extruded condition corroded much slower. The corrosion resistance of the coated Mg–Sr alloy depended on the coating itself and on the microstructure of the substrate.     

Growth process and corrosion resistance of micro-arc oxidation coating on Mg-Zn-Gd magnesium alloys

A Mg-6Zn-3Gd (mass fraction, %) alloy, noted as ZG63, was coated by different micro-arc oxidation (MAO) processes, and the coating structure and corrosion resistance of the alloy were studied using scanning electron microscopy (SEM), glancing angle X-ray diffractometry (GAXRD) and various electrochemical methods. The micro-arc oxidation process consists of three stages and corresponds with different coating structures. In the initial stage, the coating thickness is linearly increased and is controlled by electrochemical polarization. In the second stage, the coating grows mainly inward and accords with parabolic regularity. In the third stage, the loose coating forms and is controlled by local arc light. The looser coating is mainly composed of MgSiO₃ and the compact coating is mainly composed of MgO. From micro-arc oxidation stage to local arc light stage, the corrosion resistance of the coated alloy firstly increases and then decreases. The satisfied corrosion resistance corresponds to the coating time ranging from 6 to10 min.     

Heterocycle-substituted poly(p-phenylene vinylene) for light-emitting devices

Results are presented which explore the synthesis, characterization and electroluminescence performance of a new type of conjugated polymer, poly(2,5-diphenyl-1,3,4-oxadiazolyl)-4,4′-vinylene (O-PPV). A light-emitting diode consisting of ITO/O-PPV/Al is driven at about 6 V and has a peak emission wavelength of 483 nm, and this is in agreement with the result determined by the X-ray photoelectron spectroscopy (XPS) technique.     

Corrosion evaluation of microarc oxidation coatings formed on 2024 aluminium alloy

Dense alumina ceramic coatings of 7 μm thickness were fabricated on 2024 aluminium alloy by microarc oxidation (MAO). The corrosion behaviour of the MAO coated alloys was evaluated using potentiodynamic polarisation and EIS measurements. The results show that the corrosion process of the coated alloy can be divided into three stages: (1) the initial stage (the first 2-6 h of immersion): penetration of corrosion medium into the aluminium alloy was inhibited by coating; (2) the second stage (after 24 h of immersion), corrosion medium penetrated to attack the interface between the substrate and the coating; (3) the final stage (after about 96 h): corrosion process was controlled by the diffusion of corrosion products.     

Corrosion electrochemical behaviors of silane coating coated magnesium alloy in NaCl solution containing cerium nitrate

Sol–gel coatings cannot provide adequate corrosion protection for metal/alloys in the corrosive environments due to their high crack‐forming potential. This paper demonstrates the possibility to employ cerium nitrate as inhibitor to decrease the corrosion development of sol–gel‐based silane coating on the magnesium alloy in NaCl solution. Cerium nitrate was added into the NaCl solution where the silane coating coated magnesium alloy was immersed. Scanning electron microcopy (SEM) was used to examine surface morphology of the silane coating coated magnesium alloy immersed in NaCl solutions doped and undoped with cerium nitrate. The corrosion electrochemical behaviors were investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. The results showed that the introduction of cerium nitrate into NaCl solution could effectively inhibit the corrosion of the silane coating coated magnesium alloy. Moreover, the influence of concentration of cerium nitrate on the corrosion inhibition and the possible inhibiting mechanism were also discussed in detail.     

Effect of fluxing chemical: An option for Zn-5wt.%Al alloy coating on wire surface by single hot dip process

The corrosion of wire is one of the primary causes for premature failure. The ideal way to overcome this problem is to provide corrosion protection right at the time of manufacturing. It is well established fact that Zn-5 wt.% Al alloy coating on steel surface provides much better protection against corrosion than the conventional pure Zn coating. Conventional fluxing operation is done on wire surface using zinc and ammonium chloride mixture before dipping in molten zinc bath. Galvanization bath temperature of about 415 °C for Zn-5 wt.% Al alloy coating on wire surface develops black spots of AlCl₃ when conventional flux is used. Double dip process is being followed for Zn alloy coating on wire surface due to non availability of suitable flux. An effort has been made to develop a suitable flux to obtain Zn-5 wt.% Al alloy coating on wire surface by single hot dip process. A salt mixture (containing zinc, ammonium, sodium, potassium, cobalt and lead chloride) was formulated based on the decomposition temperature of individual chloride salts. Differential thermal and thermo gravimetric analysis indicate the temperatures for complete decomposition of conventional and formulated flux are 445 and 410 °C, respectively. The lower decomposition temperature of formulated flux is ensured black spot free Zn-5 wt.% Al alloy coating. Alloy coated wire consists of alternative layers of zinc rich and aluminium rich phases. The performance of alloy coated wires has been evaluated by salt spray and Tafel tests. The alloy coated wire shows around 4 times improvement of corrosion performance against aggressive chloride environment compared to pure zinc coated wire. This can be attributed to the fact that aluminium rich phase prevents dissolution of zinc rich phase.     

耐海洋环境中霉菌腐蚀有机涂层的研究

为了提高铝合金耐海洋环境中霉菌腐蚀的性能,先在铝合金表面涂覆硅烷膜作为过渡层,然后在硅烷膜上涂覆成分配比不同的有机硅改性环氧树脂涂料.对比研究了涂层的表面形貌、相组成及霉菌腐蚀的性能.并探讨了涂层与基体的结合机理.结果表明:硅烷膜与铝合金基体、有机涂层之间发生了化学反应,使涂层与铝合金基体结合良好;按有机硅改性环氧树脂...     

Emeraldine base as corrosion protective layer on aluminium alloy AA5182, effect of the surface microstructure

AA5182 aluminium alloy cold rolled samples were coated by thin films of emeraldine base (EB) obtained from a 5% solution in N-methylpyrrolidinone. Accelerated corrosion tests prove this coating very effective for corrosion protection of aluminium alloys in neutral environment. This study underlines the prominent role of surface cathodic intermetallic particles in pit initiation and coating break down in enhanced corrosion conditions and suggest that, beside the EB barrier properties, the enhanced corrosion resistance observed on the EB coated samples could partly arise from two other mains factors:

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a weak redox activity of the polymer which passivate the metal,

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a proton involving self-healing process taking place at the polymer-metal interface, which contributes to delay local acidification in first steps of corrosion on EB coated aluminium surfaces.

     

Corrosion fatigue behavior of epoxy-coated Mg–3Al–1Zn alloy in NaCl solution

The corrosion fatigue behavior of epoxy-coated Mg–3Al–1Zn alloy was investigated in air and 3.5 wt%NaCl solution. Epoxy coating as a new method was used to improve the corrosion fatigue property of the material.Results show that the fatigue limit(FL) of the coated specimens is higher than that of the uncoated specimens in3.5 wt% NaCl solution because of the strengthening and blocking functions of the epoxy coating. The FL of the coated specimens in 3.5 wt% NaCl solution is as high as that in air. It implies that the coated specimens are not as sensitive to the environment as the magnesium alloy. The low tensile strength and the short elongation of the pure epoxy coating lead to that the fatigue crack of the coated specimen is always initiated from the epoxy-coating film Pores and pinholes accelerate the fatigue crack initiation process. Pinholes are caused by the corrosion reactions between the epoxy coating and the NaCl solution.     

Photo-, and electroluminescence studies of 2,5-bis[2′-(4″-(6-hexoxy benzyl))-1′-ethenyl]-3, 4-dibutyl thiophenes

We have synthesized a thiophene-based compound 2,5-bis[2′-(4″-(6-hexoxy benzyl))-1′-ethenyl]-3, 4-dibutyl thiophene (HBDT) and a copolymer poly(2,5-bis(2′-(4″-(6-hexoxy benzyl))-1′-ethenyl)-3,4-dibutyl thiophene-1,6-diisocyanatohexane) (HBDT-PU) consisting of alternating HBDT and urethane spacer units. Absorption and photoluminescence (PL) spectra of the compounds coincide indicating that emission in HBDT-PU occurs from the thiophene containing unit. PL is emitted in the blue–green region with a maximum at 460 nm. Concentration quenching occurs in pure materials: PL efficiency is strongly enhanced when the compounds are dispersed in a polymer matrix like poly(N-vinyl carbozole) (PVK) or poly(methyl metacrylate) (PMMA). Light emitting devices were fabricated using a PVK:2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) blend doped with HBDT as the emitter material. Efficient energy transfer from PVK:PBD to HBDT molecules takes place in blended films. The electroluminescence (EL) spectra coincided with the PL spectra of HBDT indicating that EL emission comes solely from HBDT molecules. The influence of the doping concentration on the EL efficiency was found to coincide with the concentration dependence of the PL quantum yield.     

Electric field assisted chemical conversion process of AZ91D magnesium alloy in HCO3−/CO32− solution

A new method for synthesizing Mg–Al hydrotalcite conversion coating on AZ91D Mg alloy was developed by the application of electric field (EF). By using EF technique, the formation time of the coating can be significantly reduced. The SEM results indicate that a continuous and compact Mg–Al hydrotalcite coating is formed on the surface of Mg alloy after short time EF treatment. However, a long time treatment would make the coating partially exfoliate. The corrosion current density (J_corr) of the coated sample (EF1+1 h) is approximately two orders of magnitude lower than that of Mg alloy substrate. The test of electrochemical impedance spectroscopy (EIS) and immersion corrosion also suggest that the coating can effectively protect Mg alloy against corrosion.