镁合金化学转化膜的制备及其性能研究

在磷酸钠-磷酸二氢铵-高锰酸钾体系中对镁合金进行化学转化处理.研究了磷酸钠、磷酸二氢铵、高锰酸钾、温度、时间和添加剂对转化膜性能的影响.通过对转化膜结构、成分及性能的测试评价,得到了性能较好的化学转化溶液配方:Na3PO4为5g·L-1,NH4H2PO4为15 g· L-1,KMnO4为1g· L-1,添加剂(NH4)6 Mo7O24为0.5g·L-1.由SEM可观察到转化膜的表面成“干枯河床”状.XRD和EDS检测表明,膜层的主要成分是Mg,Al12 Mg17和无定形相,膜层表面主要有Mn,Mg,K,O和Al等元素组成.腐蚀实验和电化学测试表明,添加剂能够降低转化膜的腐蚀率,转化膜较基体的腐蚀电位正移了0.73 V,提高了镁合金的耐蚀性.     

Characterization and release behaviors of porous PCL/Eudragit RS microcapsules containing tulobuterol

In this work, porous poly(ɛ-caprolactone) (PCL)/Eudragit RS 100 (ERS-100) microcapsules containing tulobuterol base as a model drug were prepared by a solvent evaporation method and the effect of the quaternary ammonium groups of ERS-100 on the release behaviors of the microcapsules was investigated. The microcapsules prepared with PCL alone showed a stable and smooth surface, whereas porous microcapsules were formed with the addition of ERS-100. Drug loading and encapsulation efficiency of the microcapsules were slightly decreased with an increase of ERS-100 content, resulting from an increase in the porosity of the microcapsules. In an acidic release medium, PCL microcapsules showed slow drug release, whereas PCL/ERS-100 microcapsules showed a faster release rate with an increasing ERS-100 content. These behaviors are likely due to an increase in the diffusion rate of the drugs stemming from an increased hydration of the microcapsules, which results from the interaction between the carboxyl group of the release medium and the quaternary ammonium group of ERS-100.     

Surface evaluation and electrochemical behavior of cerium conversion coating modified with silane on magnesium alloy

A new cerium conversion coating modified with the hydrolysis silane is designed for AZ31 magnesium alloy, which aims at assessing the surface characterizations and electrochemical behaviors between the cerium conversion coating with and without the silane modified. The effect of the silane addictive is studied by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The adhesion of the coatings is undertaken according to the American Society for Testing and Materials (ASTM) standard D3359‐08 cross tape test. The electrochemical behavior is evacuated by polarization experiment and electrochemical impedance spectroscopy (EIS) in NaCl electrolyte. The results show that the addition of bis‐[triethoxysilylpropyl] tetrasulfide (BTESPT) to loosen and porous cerium conversion coating leads to the formation of a more compact and homogenous film, higher resistance to water uptake and better adhesion to substrate. Electrochemical measurements show that, compared with the non‐modified cerium conversion coating, the coating modified with the silane exhibits better anticorrosion properties. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface characterization of growth process for cerium conversion coating on magnesium alloy and its anticorrosion mechanism

Cerium conversion coating is successfully deposited on magnesium alloy AZ31 for corrosion protection. Deposition time on the influence of cerium conversion coating morphology, composition, and electrochemical properties has been investigated in detail. Morphological observation reveals that the cerium conversion coating is a porous agglomerate nanostructure. XPS indicates that the coating exhibits a time‐dependent ingredient. Moreover, the coating is considered as a combination of magnesium oxide/hydroxide and cerium (III) and (IV) oxides/hydroxides. The results of electrochemical impedance spectroscopy indicate that the anticorrosion coating exhibits the best properties during deposition of 5 min. In view of the analysis, the anticorrosion mechanism is pioneered proposed because of the formation of H‐bonding layer, which forms a reasonable barrier to Cl^? ions. Copyright © 2014 John Wiley & Sons, Ltd.     

Microstructural analysis of a carbon fibre reinforced AZ91D magnesium alloy composite

Interfacial regions in metal matrix composites are important in controlling the mechanical and thermal properties of these materials. An ultrahigh modulus fibre‐reinforced magnesium alloy matrix composite has been studied, with particular attention paid to the interfacial and precipitate microstructures. Fibres were surface treated but uncoated prior to composite manufacture. Observations revealed that an interface consisting of polycrystalline magnesium oxide with occasional Mg₁₇Al₁₂ (β) precipitate particles predominates. Discontinuous β particles formed at fibre surfaces, and continuous spherical and lamellar β precipitates nucleated at grain boundaries and fibre surfaces. High dislocation densities exist at the interface indicating matrix‐yielding subsequent to manufacture and that a high mean residual compressive stress acts on fibres. The effect that the observed microstructural features has on composite properties and on interfacial bonding is discussed and compared to examples in the literature. Copyright © 2005 John Wiley & Sons, Ltd.     

Vertical phase separation and liquid-liquid dewetting of thin PS/PCL blend films during spin coating

Thin films of an amorphous polymer, polystyrene (PS), and a crystalline polymer, poly(ε-caprolactone) (PCL), blend were prepared by spin coating a toluene solution. Surface chemical compositions of the blend films were measured by X-ray photoelectron spectroscopy (XPS), and the surface and interface topographical changes were followed by atomic force microscopy (AFM). By changing the PS concentration and keeping the PCL concentration of the solution at 1 wt %, a great variety of morphologies were constructed. The results show that the morphology of the blend films can be divided into three regions with increasing PS concentration. In region I, PS island domains are embedded in PCL crystals when the PS concentration is lower than 0.3 wt % and the size of the PS island increases with increasing PS concentration. In region II, holes with different sizes surrounded by a low rim are obtained when the concentration of PS is between 0.35 and 0.5 wt %. After selectively washing the PS domains, we studied the interface morphology of PS/PCL and found that the upper PS-rich layer extended into the bottom PCL layer, forming a trench surrounding the holes. In region III, an enriched two-layer structure with the PS-rich layer on top of the blend films and the PCL-rich crystal layer underneath is obtained when the concentration of PS is higher than 0.5 wt %. Last, the formation mechanism of the different surface and interface morphologies is further discussed in terms of the vertical phase separation to a layered structure, followed by liquid-liquid dewetting and crystallization processes during spin coating.     

Degradation behaviour of PCL/PEO/PCL and PCL/PEO block copolymers under controlled hydrolytic,enzymatic and composting conditions

Short-term hydrolytic and enzymatic degradation of poly(ε-caprolactone) (PCL), one series of triblock (PCL/PEO/PCL) and the other of diblock (PCL/PEO) copolymers, with a low content of hydrophilic PEO segments is presented. The effect of the introduction of PEO as the central or lateral segment in the PCL chain on copolymer hydrolysis and biodegradation properties was investigated. FTIR results revealed higher hydrolytic degradation susceptibility of diblock copolymers due to a higher hydrophilicity compared to PCL and triblock copolymers. Enzymatic degradation was tested using cell-free extracts of Pseudomonas aeruginosa PAO1, for two weeks by following the weight loss, changes in surface roughness, and changes in carbonyl and crystallinity index. The results confirmed that all samples underwent enzymatic degradation through surface erosion which was accompanied with a decrease in molecular weights. Diblock copolymers showed significantly higher weight loss and decrease in molecular weight in comparison to PCL itself and triblock copolymers. AFM analysis confirmed significant surface erosion and increase in RMS values. In addition, biodegradation of polymer films was tested in compost model system at 37 °C, where an effective degradation of block copolymers was observed.     

纳米晶Ni-Mo合金复合镀层中钼含量对析氢反应的影响

本文利用复合电镀的方法, 将用高能机械球磨制备的纳米晶Ni-Mo合金粉制成对析氢反应有高催化性的电极。用X射线衍射仪、X射线光电子能谱仪测试了这些纳米晶的大小及复合镀层的组成, 用稳态极化曲线及交流阻抗技术测试了这些电极析氢的电化学特性。实验结果表明: 在本文研究的范围内镀层中钼含量的增加可以提高电极析氢的催化活性, 电化学脱附是这些电极上析氢反应速度的决定步骤。     

Effective properties of suspensions/emulsions, porous and composite materials

A new method (a version of a mean field method) is suggested to calculate effective properties of suspensions/emulsions, porous and dispersed materials. The aim is to demonstrate a wide range of applicability of the new method. To show the idea of the new method the dependence of the effective diffusion coefficient in the porous medium on the porosity is deduced. Based on the same method the following dependences are deduced: the effective viscosity of suspensions and emulsions as functions of volume fraction of suspended particles or droplets, elastic modules of rubber/polymer sheets with cracks and elastic modules of composite materials on the volume fraction of inclusions in the case of an arbitrary number of different types of inclusions. In all cases the calculated dependences are compared with available experimental data and published theoretical models.     

Surface chemistry of porous magnesium fluoride

Porous preparations of magnesium fluoride were obtained from magnesium sulphate and magnesium carbonate and their surface properties have been studied. It has been shown that pure magnesium fluoride has a weak surface acidity of the Lewis type and no protonic sites stronger than H_R?0.82. Base properties of MgF₂ surfaces are more pronounced than acid ones, but the base strength is low. Surfaces of MgF₂ also bear oxidizing and reducing centres capable of forming ion radicals with adsorbed perylene and tetracyanoethylene. The low catalytic activity of magnesium fluoride for acid catalysed reactions suggests the application of MgF₂ as a catalyst support rather than as a catalyst.     

Preparation of a palladium alloy composite membrane supported in a porous stainless steel by vacuum electrodeposition

Pinhole-free palladium/nickel (Pd/Ni) alloy membranes deposited on a porous stainless steel (SUS) support have been fabricated. The deposition was made by vacuum electrodeposition technique which could produce the alloy film less than 1 μm thick. This technique allows for the Pd/Ni alloy by employing Pd/Ni complex reagent, and typical Pd/Ni plating had compositions of 78% Pd and 22% Ni. In order to make the surface smooth and enhance the adhesive bond between the top layer and the substrate, a nascent porous SUS disk was treated sequently with submicron nickel powder and CuCN solution. The important parameters that can affect deposition were pore size, defects, and surface roughness of substrate. The membranes were characterized by permeation experiments with hydrogen and nitrogen at temperatures ranging from 623 to 823 K and pressures from 10.3 to 51.7 cmHg. The composite membranes prepared in this technique yielded excellent separation performance for hydrogen: hydrogen permeance of 5.79×10⁻² cm³/cm² cmHg s and hydrogen/nitrogen (H₂/N₂) selectivity was 4700 at 823 K.     

Preparation and characterization of porous TiO_2/ZnO composite nanofibers via electrospinning

<正>Porous TiO_2/ZnO composite nanofibers have been successfully prepared by electrospinning technique for the first time.It was generated by calcining TiO_2/ZnCl_2/PVP[PVP:polyvinyl pyrrolidone)]nanofibers,which were electrospun from a mixture solution of TiO_2,ZnCl_2 and PVP.Transmission electron microscopy(TEM) and X-ray diffraction(XRD) analyses were used to identify the morphology of the TiO_2/ZnO nanofibers and a formation of inorganic TiO_2/ZnO fibers.The porous structure of the TiO_2/ZnO fibers was characterized by N_2 adsoption/desorption isotherm.Surface photovoltage spectroscopy(SPS) and photocatalytic activity measurements revealed advance properties of the porous TiO_2/ZnO composite nanofibers and the results were compared with pure TiO_2 nanofibers,pure ZnO nanofibers and TiO_2/ZnO nanoparticles.     

Processing and characterization of LDPE/starch/PCL blends

Low-density polyethylene/plasticized starch/polycaprolactone blends were processed by conventional extrusion, injection molding, and film blowing techniques. The glass transition temperatures of plasticized starch were determined using differential scanning calorimetry. The blends were characterized by mechanical property measurements and scanning electron microscopy. The blend properties were found to depend not only on composition but also on the generated morphology. In films the fine dispersion of polycaprolactone phase in the polyethylene/starch matrix resulted in mechanical property increase, while in injection specimens there was property decrease due to phase coalescence. It appears that the different conditions existing at the two different shaping processes i.e. film blowing and injection molding could account for the final obtained morphology.     

Preparation of chitosan–silica/PCL composite membrane as wound dressing with enhanced cell attachment

In the present study, the asymmetrical polycaprolactone membranes were synthesized using phase inversion method and modified by addition of Pluronic (F‐127) and sodium hydroxide treatment to improve the cell attachment. The chemical structure, physical properties and mechanical behavior of the membranes as well as cell attachment and proliferation on them were characterized and compared to determine the appropriate membrane used in wound dressing fabrication. Then, a composite membrane as wound dressing capable of drug controlled‐release was prepared composed of two merged layers: an asymmetrical poly(ε‐caprolactone) layer coated with a drug‐loaded chitosan – silica matrix. Drug release behavior and biocompatibility of the final system were evaluated. The results showed that the polycaprolactone modified membrane provides appropriate properties to expand fibroblast cell adhesion and proliferation. This in‐vitro study also showed that the controlled‐release composite wound dressing was developed with approximately 70% cumulative release rate, which provided a porous substrate to support skin cells. Copyright © 2017 John Wiley & Sons, Ltd.     

Hydrophilicity/porous structure-tuned, SiO2/polyetherimide-coated polyimide nonwoven porous substrates for reinforced composite proton exchange membranes

Porous substrate-reinforced composite proton exchange membranes have drawn considerable attention due to their promising application to polymer electrolyte membrane fuel cells (PEMFCs). In the present study, we develop silica (SiO(2)) nanoparticles/polyetherimide (PEI) binders-coated polyimide (PI) nonwoven porous substrates (referred to as "S-PI substrates") for reinforced composite membranes. The properties of S-PI substrates, which crucially affect the performance of resulting reinforced composite membranes, are significantly improved by controlling the hygroscopic SiO(2) particle size. The 40 nm S-PI substrate (herein, 40 nm SiO(2) particles are employed) shows the stronger hydrophilicity and highly porous structure than the 530 nm S-PI substrate due to the larger specific surface area of 40 nm SiO(2) particles. Based on the comprehensive understanding of the S-PI substrates, the structures and performances of the S-PI substrates-reinforced composite membranes are elucidated. In comparison with the 530 nm S-PI substrate, the hydrophilicity/porous structure-tuned 40 nm S-PI substrate enables the impregnation of a large amount of a perfluorosulfonic acid ionomer (Nafion), which thus contributes to the improved proton conductivity of the reinforced Nafion composite membrane. Meanwhile, the reinforced Nafion composite membranes effectively mitigate the steep decline of proton conductivity with time at low humidity conditions, as compared to the pristine Nafion membrane. This intriguing finding is further discussed by considering the unusual features of the S-PI substrates and the state of water in the reinforced Nafion composite membranes.     

Calorimetric analysis of AM60 magnesium alloy

Calorimetric analysis is commonly used for the study of several solid state transformations, among which phase transformations. Information about enthalpy, kinetics and general features of transformations could be obtained with suitable configurations of the analysis equipment and arrangements of the tests procedures. An experimental analysis of the transformation occurring in a Mg-Al-Mn alloy, namely AM60, has been performed on samples cut from as die-cast components. The results obtained confirmed that calorimetric analysis is a suitable method for the study of transformations of such kind of alloys. Using the technique of multiple heating rate tests, an estimation of activation energy of dissolution of Mg₁₇Al₁₂ phase has been derived.     

Preparation, structure and properties of porous polyimide films via PAA/PU alloy

A new route to porous polyimide (PI) films with pore sizes in the nanometer regime was developed. A polyamic acid (PAA)/polyurethane (PU) blend with PU as the disperse phase was first prepared via in situ polymerization of pyromellitic dianhydride and 4,4-oxydianiline in PU solutions. Porous PI films were obtained from PAA/PU films by thermolysis of PU at 360°C and imidization of PAA at 300°C, respectively. Fourier transform infrared spectroscopy and thermal gravimetric analysis were used to detect the imidization and thermolysis processes of PAA/PU blends under thermal treatment. The microporous structure of the PI films was observed by transmission electron microscopy. It was found that the size and content of pores increased with an increase in the PU mass fraction in the PAA/PU blend up to 20%. Because of the existence of nanopores, the dielectric constant of PI films decreased by a wide margin and was less than 2.0 at a PU mass fraction of 20%. It implies that this is an effective means to reduce the dielectric constant of PI, but it also causes the decrease of tensile strength and the rise of water absorption. Translated from Chemistry Journal of Chinese Universities 2006, 27(1): (in Chinese)     

On the formation of the interlayer between Ni-P coating and AZ33 magnesium alloy substrate by means of in situ SEM observation

Pre-treatment process is the key step for electroless plating. Once a suitable pre-treatment film is in place, the desired metals can be plated. In this paper, Ni-P coating was successfully prepared on AZ33 magnesium alloy with Mg（OH）2 pre-treatment film by electroless plating. To investigate the role of MgF2 in Ni-P coating, the deposition procedures between Mg（OH）2 pre-treatment film and Mg（OH）2-MgF2 pre-treatment film （a traditional process） were compared. The surface morphology variations of coatings were observed with scanning electron microscopy and the compositions were analyzed by energy dispersive spectrometry. The results showed that during the plating, both MgF2 and Ni-P deposited at the initial stage, and MgF2 distributed in the bottom of the coating, forming a transitional interlayer with Ni- P. According to the heat quench test, a poor adhesion of the coating mainly occurred between the MgF2 and Ni-P coating.     

Fabrication of porous carbon/Si composite nanofibers as high-capacity battery electrodes

Carbon/Si composite nanofibers with porous structures are prepared by electrospinning and subsequent carbonization processes. It is found that these porous composite nanofibers can be used as anode materials for rechargeable lithium-ion batteries (LIBs) without adding any binding or conducting additive. The resultant anodes exhibit good electrochemical performance; for example, a large discharge capacity of 1100 mAh g^?1 at a high current density of 200 mA g^?1.     

Effect of gamma irradiation on linear low density polyethylene/magnesium hydroxide/sepiolite composite

Radiation crosslinking is generally used to improve the thermo-mechanical properties of the composites. A study has been carried out to investigate the effect of gamma radiation on the thermo-mechanical properties of linear low density polyethylene containing magnesium hydroxide (MH) and sepiolite (SP) as non-halogenated flame retardant additives. The developed composites are irradiated at different doses upto maximum of 150 kGy. Infrared spectra of the irradiated composites reveal the reduction in the intensity of O-H band with increase in the absorbed doses, thus indicates a distinct structural change in MH at higher doses. The thermogravimetric analysis results of unirradiated and composites irradiated at low doses (≤75 kGy) show two steps weight loss, which is changed to single step at higher doses with lower thermal stability. The melting temperature (T_m) and crystallization temperature (T_c) of irradiated composites are lowered with irradiation whereas Vicat softening temperature (VST) is increased. The increasing trend in gel content with increase in the absorbed dose confirms the presence of crosslinked network. The mechanical properties, results show significant improvement in the modulus of irradiated composites. The results also confirm that MH gradually loses its OH functionality with irradiation.