Advanced Materials Research Vols. 79-82

Abstract: Element boron played an important role on magnetic properties and corrosion resistance of high energy density NdFeB products. The magnets were prepared by traditional powder metallurgy technique. It was found that with addition of 5.53 % B there was easy-plane phase formed. It owned not only lower remanence Br and coercivity iHc, but also poor corrosion resistance of magnet. As B content increase, the magnetic properties improved greatly, and obtained better properties at a content 5.7-5.87 % B. As increased B content further, superabundance B element formed too much B rich phase and led to Br decrease. Volume percent of phases calculated by theory formula, with the consumption of 0.1 % Nd oxided, it can be found that as B content increased from 5.53 %, the volume of main phase increased and easy-plane type Nd2Fe17 phase decreased in magnet, which resulted in Br, iHc increase. As B content increased higher than 5.82 %, more B rich phases formed which well isolated main phase grains and resulted in iHc increase. But too much B rich phase would decrease main phase proportion and lead to Br decrease. Examination of microstructure of magnets showed as B content increased from 5.53 % to 6.16 %, average matrix grain size was enlarged from 6.5µm to 8.2µm, and the proportion of sharp shape grains relatively increased as well. Abnormal grain growth was easily happened at higher B content. In addition, the decreased squareness Hk/iHc of magnets at higher B content also suggested inconsistent distribution of grain size and shape. Corrosion current density measured by polarization test for magnet with addition of 5.76 % B, near stoichiometric composition of Nd2Fe14B, owned lowest value and best corrosion resistance. Formation of Nd2Fe17 phase (lower B content) or B rich phase (higher B content) was not benefit for corrosion resistance improvement.

Abstract: The present work was focus on developing low driving voltage sacrificial anode for high strength steels. Taking the zinc and bismuth as main active elements, we designed and prepared several aluminum alloy anodes and investigated their electrochemical performance by galvanic test in natural seawater. The results showed that the anode exhibits high performance with 0.55wt.% Zn and 0.5wt.% Bi as the alloying elements. Its potential is varied from -800mV to -820mV, the current capacity is 2565 Ahr/kg, and the dissolution is homogeneous. We concluded that Al-0.55%Zn-0.5%Bi alloy anode can be used to high strength steel for corrosion protection. The microstructures of the anodes were observed by optical microscope, the result proposed that the uniform dissolution morphology of Al-0.55%Zn-0.5%Bi anode is due to its fine grain size.

Abstract: Hydrogen permeation current curve of galvanized steel with hot-dip zinc coating exposed to simulated marine atmosphere was measured using a modified Devanathan-Stachurski cell. Effect of temperature, humidity and coating defect on its hydrogen permeation behaviour was also investigated. The results indicated that hydrogen permeation current density and the amount of hydrogen accumulated increased evidently with temperature and humidity rising at moist environment; meanwhile, hydrogen absorption when coating defect occurred was accelerated by the cathodic protection of the exposed steel surface afforded by surrounding zinc coating.

Abstract: In this work, PDMS modified PU was synthesized using two-stage method to improve water resistance and weather resistance in the waterborne polyurethane was investigated. It was found that the absorbed water content decreased with increasing PDMS content in polyurethane. It was also found that PDMS modified polyurethane had better solvent resistance than unmodified polyurethane. The structure incorporated the PDMS into the soft segment of polyurethane chains was confirmed by FTIR. The phase separation increased by increasing PDMS content and was confirmed by DSC. The particle size of the dispersions increased and tensile strength and hardness decreased with the increase of PDMS content. Furthermore, with the improved water resistance and elongation, it was hoped that the modified polyurethane could be used as wood coatings superior to the solvent-borne systems.

Abstract: Urchin-like CuO, consisting of closely packed nanorods with a diameter of 10nm, have been successfully synthesized by a poly(ethylene glycol) (PEG)-assisted hydrothermal route at low temperature of 100°C. The as-obtained Urchin-like CuO were thoroughly characterized by X-ray diffraction (XRD) study, Field emission scanning electron microscope (FESEM), High-resolution transmission electron microscopy (HRTEM) and Gas sensor measurements. From the XRD pattern, all the peaks detected can be assigned to CuO in a monoclinic structure with lattice parameters a=4.662, b=3.416 and c=5.118 (JCPDS card no. 65-2309). The FESEM and TEM showed that the diameter of the urchin-like CuO sphere is about 1µm. Further investigation of the formation mechanism reveals that the PEG-assisted hydrothermal process is vital to the formation of 3D structures. Besides the template function, PEG often plays as a reductant while reacting with Cu(+2). In our case, no impurity peaks of Cu2O were observed in the XRD pattern, implying that PEG did not reduce Cu(+2) to Cu(+1). We attribute this to the high concentration of PEG. The sensor based on the urchin-like CuO nanostructures exhibit excellent ethanol-sensing properties at reduced working temperature (200°C), which shows a sensitivity two times higher than that of CuO particles(about 100nm, made from calcinations of Cu(NO3)2 at 400°C). The enhancement in sensitivity of the as-prepared CuO may be contributed to the fancy 3D nanostructures.

Abstract: Dissymmetric bis-quaternary ammonium with imidazoline ring was evaluated for corrosion inhibition efficiency against Q235 steel in 1.0mol•L-1hydrochloric acid solution at room temperature (298K) by gravimetric method, potentiodynamic polarization, electrochemical impedance spect- rum(EIS) and quantum chemical calculation. The results of mass loss and polarization data showed the compound acted as a very good mix-up inhibitor for Q235 steel in 1.0mol•L-1hydrochloric acid solution. EIS results showed that the associated values of the charge transfer resistance (Rct) increase by increasing the additive concentrations and immersing time whereas the associated values of double layer capacitance (Cdl) decrease. These changes in the impedance parameters (Rct and Cdl) are indicative of adsorption of the compound on Q235 steel surface leading to the formation of a protective film. The obtained correlations and Quantum chemical calculations conclusions agree well with the experimental results.

Abstract: Polystyrene sulfonic acid (PSSA) doped water-dispersible polyaniline (PANI) /montmorillonite (MMT) clay composites were firstly synthesized by intercalation polymerisation in aqueous medium and characterized by XRD and FT-IR. The results showed exfoliated silicate nanolayers of MMT clay dispersed in the PANI matrix and has interaction involving hydrogen bonding between the PSSA-PANI chain and the surface of the MMT clay layer. This composites is more thermal stable than that of without clay samples and results in good stable temperature-dependent dc conductivity [σdc(T)] as temperature changed. The composite anticorrosion coatings of PANI/MMT and waterborne epoxy resin emulsion (EP) were prepared by mixture in aqueous medium and used for corrosion protection of mild steel. Open circuit potential (OCP), Electrochemical impedance spectroscopy (EIS) and Tafel plot demonstrated that the PANI/MMT/EP composite coatings have better anticorrosion properties than PANI/EP, MMT/EP and PANI/MMT/EP mixture. It’s impedance and corrosion potential is higher and the corrosion current density is lower. The anticorrosion coatings are environmental friendly because of water dispersion medium. Introduction

Abstract: A dense ceramic coatings with a thickness of 95μm was fabricated on a SiCp/ZL101 aluminum composites by using a plasma electrolytic oxidation(PEO) method. The XRD analysis showed that the PEO coating was mainly composed of α-Al2O3 γ-Al2O3 and mullite.The corrosion resistance of the PEO coatings and SiCp/ZL101 aluminum composites was estimated by the immersion test, salt spray test and electrochemical test. All the test results showed that the corrosion resistance of the composite was improved by the existence of the ceramic coating.

Abstract: The rare earth (RE) modified chromizing coating was obtained on P110 oil casing tube steel (P110 steel) substrate by means of pack cementation technique to enhance the resistance against corrosion of P110 steel. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) were employed to research microstructure, composition distribution and phase constitution of the chromizing coating. The effect of minor addition of RE on the microstructure of chromizing was discussed. Corrosion resistance of chromizing coating was investigated and compared with that of bare P110 steel via electrochemical corrosion and immersion corrosion in simulated oilfield brine solution, respectively. The results showed that a uniform, continuous and compact coating was formed on P110 steel. The coating with RE addition was more compact than that of the coating added no RE, and a small amount of RE addition could promote the chromizing procedure notably. From SEM and EDX investigation, it had been confirmed that the coating was composed of two different layers, an out layer and an inner layer; the coating mainly contains Fe and Cr; the concentration of Cr decreased as the distance from the surface increased, yet Fe presented the inverse trend. XRD analysis indicated the coating was built up by (Cr, Fe)23C6 referring to the out layer, (Cr, Fe)7C3, Cr7C3 and α-(Cr, Fe) corresponding to the inner layer. Electrochemical corrosion consequence was obtained as follows: the self-corroding electric potential of chromizing coating was higher, and the corrosion current density was lower than that of bare P110 steel, which revealed that chromizing coating had better anti-corrosion performance; immersion corrosion results demonstrated the mass loss of chromized P110 steel was lower, and this meant that chromizing coating had a better corrosion resistance than that of bare P110 steel on the experimental condition. A compact (Cr, Fe)xCy coating can be fabricated by pack cementation technique. As a result of minor RE addition, microstructure and corrosion resistance of the chromizing coating are improved obviously.

Abstract: Marine biofouling on the surface of ship hull causes the hydrodynamic drag, fuel increase, and higher costs. In this case antifouling paint is often used to protect the submerged surface from marine organisms. In traditional antifouling paints, toxic biocides have been banned due to their severe environmental pollution. To develop novel environmental benign antifouling agents has been our pursuit, and among them, active substances from marine organism for antifouling application are our research focus. In the paper, a natural material in halobios was isolated from a kind of algae Ulva pertusa, which is the most common green alga. The antifouling activities of their extracts were screened by bioassays with two kinds of fouling organisms, diatom and mussel. The crude extract of ethyl acetate was found to be most active against diatom. Silica gel column chromatography (SGCC) and high performance liquid chromatography (HPLC) were used to further isolate the extract of ethyl acetate. In the SGCC extraction, four elution bands were collected, and minimum inhibitory concentrations (MIC) against diatom were determined. Among the four bands, the lowest MIC is 0.7 mg/mL, related to the band YC-EA. The YC-EA band was separated into four parts, and the second part (EE2) showed an inhibitive effect on the settlement of diatom and mussel. The natural product of EE2 can be characterized by a coupled liquid chromatography-mass spectrometry (LC-MS). Results demonstrated that there are antifouling active substances among extracts of Ulva pertusa. Compounds would be a potentially natural antifouling material, resulting in higher standards of environmental safety with outstanding antifouling performance.