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.     

Corrosion behavior of AZ91D magnesium alloy in distilled water

The corrosion of AZ91D magnesium alloy has received extensive attention due to the continuous expansion of its application field in recent years. However, the corrosion of AZ91D magnesium alloy in distilled water is relatively few. In this paper, the corrosion behavior of AZ91D magnesium alloy was studied in distilled water by electrochemical tests in combination with weight loss and surface analysis methods. The results indicated that the corrosion rate of AZ91D magnesium alloy increased with the increase of temperature and immersion time. The increase of the corrosion rate of AZ91D magnesium alloy with the increase of immersion time might be attributed to the damage of the structure of corrosion product film by hydrogen evolution, significantly accelerating the anodic process of AZ91D magnesium alloy. It was interesting that, in distilled water, the EIS of AZ91D magnesium alloy excluded an inductive arc in the low frequency region, which indicated that there was no the adsorption and desorption of aggressive ions or the damage and repair of film. The corrosion product film of AZ91D magnesium alloy in distilled water was composed of a compact inner corrosion product film and a loose outer corrosion product film.     

Film characteristics of anodic oxidized AZ91D magnesium alloy by applied power

This study examined the film characteristics of an anodized AZ91D magnesium alloy by varying the direct current and pulse frequency conditions. In order to evaluate the effect of the pulse frequency on film formation, anodic oxidation was carried out by applying direct current and pulse current at a current density of 300 mA/cm². Compared with the sample groups treated with the direct current, a large number of small arcs were generated continuously on the film treated with the pulse current and the film formation rate was found to increase. Homogeneous and compact pores were formed with increasing frequency, and the rate of formation was increased rapidly to the arrival voltage. The film thickness increased and the surface roughness decreased with increasing anodic oxidation time at a fixed frequency of 125 Hz. However, treatment for more than 3 min led to decomposition of the oxidized film onto the previously formed film, which caused an increase in the number of cracks and pores within the film. The most uniform and smallest pores were acquired when the surface was anodized for 3 min at a current density and frequency of 300 mA/cm² and 125 Hz, respectively. X‐ray diffraction revealed the formation of MgO and Mg₂SiO₄ peaks, with a relative decrease in peak intensity for the MgO and Mg substrate. The Vickers hardness value was higher on the treated groups than on the untreated group, and the potentiodynamic polarization test revealed satisfactory corrosion resistance through a decrease in corrosion density and a large improvement in the corrosion potential. Copyright © 2009 John Wiley & Sons, Ltd.     

ESEM observation of the process of hydrogen generation around the micro-droplets forming on AZ91 magnesium alloy

The process of hydrogen generation around micro-droplets on as-cast AZ91 magnesium alloy in an atmosphere of water vapor was in situ observed using an environmental scanning electron microscope (ESEM). The procedure for hydrogen generation was described. It indicated that the cathodic or anodic location gradually changed with the generation of hydrogen bubbles and the formation of corrosion products.     

Plasma electrolytic oxidation of AZ91D magnesium alloy in biosafety electrolyte for the surgical implant purpose

Plasma electrolytic oxidation (PEO) of AZ91D magnesium alloy in biosafety electrolyte was studied. The prepared PEO coating and its stability in the simulated body fluid (SBF) were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), potentio-dynamic polarization, electrochemical impedance spectroscopy (EIS) and immersion test. The SEM results show that a kind of smooth, compact and well adhesive PEO coating is prepared in the proposed biosafety electrolyte. The electric analytical results show that the corrosion resistance of the PEO coating is excellent even in harsh environment. Immersion test shows that the PEO coating is stable enough in the SBF solution. The weight loss, the average corrosion rate and the pH variation of the PEO treated magnesium alloy are far lower than the untreated ones. From these highly positive results, the proposed PEO process is promising in the treatment of the surgical magnesium alloy materials.     

Analytical characterization of coated carbon fibres

Summary Carbon fibres must be coated with a barrier layer in their application as reinforcement in metal matrix composites (MMC) to avoid reactions between the matrix and carbon. Materials frequently used are SiC, pyrolytical carbon or these materials in combination. The reactivity between the metallic matrix and the barrier layer depends on the stoichiometry and structure of the barrier material. XPS and AES are suitable methods for the investigation of the surface and of composition of the layer of the coated fibres. Additionally Raman-spectroscopy has been used to aid the distinction between the bonding states of carbon in the barrier layer and the fibre. The problems of the analysis of small, fibre-like materials are discussed.     

Surface characteristics of AZ91D alloy anodized with various conditions

Anodic oxidation of an AZ91D magnesium alloy was carried out in an attempt to increase the corrosion resistance. The alloy was placed in an electrolyte containing 0.1 M sodium silicate (Na₂SiO₃), 2.0 M sodium hydroxide (NaOH) and 0.1 M sodium phosphate (Na₃PO₄), and treated with a current density of 100–400 mA/cm² for 1 to 4 min. After the anodic oxidation treatment, the surface characteristics were analyzed by SEM, X‐ray diffraction (XRD) and a surface roughness tester. The corrosion resistance was determined by measuring the corrosion potential and corrosion current density using potentiodynamic polarization in a 3.5 wt% NaCl electrolyte solution. Although the anodic oxidation treatment with the base electrolyte resulted in an arrival voltage ranging from 60 to 70 V, the addition of silicate tended to reduce this arrival voltage by approximately 10–20 V and decrease the critical voltage required for the formation of a porous oxide film. The pore size and film thickness increased with increasing applied current and treatment time. The addition of silicate to the electrolyte resulted in films with a homogeneous pore size and a film thickness increasing with the increasing applied current and treatment time. XRD showed the formation of a new MgO and Mg₂SiO₄ phase. The formation of Mg₂SiO₄ was attributed to the presence of SiO₄^4? in the film. After the addition of silicate, the corrosion potential increased and corrosion current decreased, resulting in improved corrosion resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

Photoemission and absorption spectroscopy of carbon nanotube interfacial interaction

Element-specific techniques including near edge X-ray absorption fine structure, extended X-ray absorption fine structure and X-ray photoemission spectroscopy for the characterization of the carbon nanotube interfacial interactions are reviewed. These techniques involve soft and hard X-rays from the laboratory-based and synchrotron radiation facilities. The results provided information of how the nano-particles of catalysts are involved in the initial stage of nanotube growth, the nanotube chemical properties after purification, functionalization, doping and composite formation.     

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.     

Corrosion inhibition of magnesium alloy AZ31 in chloride-containing solutions by aqueous permanganate

In this work, corrosion of the AZ31 magnesium alloy was examined in 0.05 M NaCl solutions containing 0.01–0.150 mol/dm³ of potassium permanganate as a corrosion inhibitor. A set of electrochemical impedance spectroscopy, linear sweep voltammetry, and hydrogen evolution measurements revealed high inhibitor effectiveness at relatively high (0.150 mol/dm³) KMnO₄ concentrations. Based on data of energy-dispersive X-ray analysis, scanning electron microscopy, and Raman spectroscopy, a mechanism of the corrosion inhibition of AZ31 alloy by potassium permanganate in chloride-containing media was proposed.

     

CE-LIF analysis of mitochondria using uncoated and dynamically coated capillaries

This report is the first demonstration of the use of uncoated and dynamically coated capillaries for the separation of individual mitochondria via CE. Currently, the analysis of individual mitochondria relies upon fused-silica capillaries coated with a hydrophilic polymer (e.g. poly(acryloylaminopropanol)), which is used to minimize adsorption to the capillary surface. Both uncoated fused-silica capillaries and 0.2% w/w poly(vinyl alcohol) dynamic coating solutions are used to successfully analyze isolated individual mitochondrial particles using CE-LIF. While it was possible to separate mouse liver mitochondria on an uncoated capillary, rat liver mitochondria proved to have strong adsorption characteristics that only allowed them to be adequately separated with a PVA dynamic coating or a poly(acryloylaminopropanol) (AAP) capillary. The possible causes for this adsorption are analyzed and discussed. This study shows that uncoated and dynamically coated capillaries can be used in place of AAP-coated capillaries to analyze mitochondria and suggests the use of these capillaries for the analysis of other organelles, offering a greatly simplified method for the analysis of individual organelles.     

Carbon nanotube growth on high modulus carbon fibres: Morphological and interfacial characterization

Carbon nanotubes (CNTs) were grown directly on the surface of carbon fibres, using the catalytic chemical vapour deposition. FeCo bimetallic catalysts were deposited on carbon fibres using a simple wet impregnation method. CNTs were synthesized over the prepared catalysts by the catalytic decomposition of acetylene at 750^oC. The uniform CNT formation on the fibre surface was verified using scanning electron microscopy. Raman spectroscopy was employed to evaluate non‐destructively the CNT growth and the CNT quality. Thermo gravimetric analysis and differential thermal analysis were employed as destructive methods to confirm the spectroscopic data. Single CNT‐coated fibre fragmentation tests were performed to examine the interfacial shear strength (ISS) of the modified fibres. Acoustic emission was employed to monitor the fragmentation process in real time. Thus, the coated fibre structural integrity was assessed together with its stress transfer properties. Polarized optical microscopy was employed to cross validate the acoustic emission data. It was found that the ISS of the nanotube‐reinforced interphase was improved without affecting the fibre mechanical properties. Copyright © 2013 John Wiley & Sons, Ltd.     

XPS study of the effect of aluminium on the atmospheric corrosion of the AZ31 magnesium alloy

The surface characteristics and corrosion behaviour of the AZ31 magnesium alloy exposed to a high relative humidity (RH) atmosphere were investigated. During the first 15 days of humidity test at 98% RH and 50 °C, a significant increase of magnesium carbonate and a decrease of magnesium oxide were detected on the surface film by XPS; after this stage, increased exposure times did not produce substantial changes on the relative amounts of these compounds. The surface film of commercially pure magnesium, also examined for comparison purposes, revealed more magnesium carbonate and less magnesium oxide compared with the AZ31 alloy. Unlike the AZ31 alloy, the surface of pure Mg disclosed almost complete substitution of MgO by magnesium carbonate after 30 days of exposure time. Mass gain values of tested specimens and scanning electron microscope characterisation of corroded surfaces indicated lower corrosion susceptibility of the AZ31 alloy compared with the commercially pure Mg, suggesting superior chemical stability of the oxide/hydroxide film formed over the magnesium–aluminium alloy surface. XPS and energy dispersive X‐ray (EDX) analyses did not revealed any substantial enrichment of aluminium in the corrosion products film on the AZ31 alloy after 30 days of testing. Copyright © 2008 John Wiley & Sons, Ltd.     

Probing the interfacial interaction between monolayer molybdenum disulfide and Au nanoclusters

Coupling of plasmonic metal nanostructures on two‐dimensional materials represents one promising approach to improve their optoelectronic device performance. In this article, we systematically investigated the interfacial interactions between Au nanoclusters and monolayer molybdenum disulfide (MoS₂) and the effect of Au decoration on the electrical transport and optical properties of MoS₂, through the combination of in situ MoS₂ field‐effect transistor device evaluation and in situ ultraviolet photoelectron spectroscopy and X‐ray photoelectron spectroscopy measurements. The in situ X‐ray photoelectron spectroscopy/ultraviolet photoelectron spectroscopy experiments revealed a weak interfacial coupling between Au nanoclusters and monolayer MoS₂. The absence of strong charge transfer between Au nanoclusters and MoS₂ was further confirmed by the photoluminescence and Raman measurements. It was also found that the electron charge‐carrier concentration in monolayer MoS₂ weakly depended on the coverage of Au nanoclusters. Copyright © 2017 John Wiley & Sons, Ltd.     

Study on microarc oxidation of AZ31B magnesium alloy in alkaline metal silicate solution

The effects of pulsating current and voltage sources with different magnitudes on an oxide film formed by microarc oxidation (MAO) of AZ31B magnesium alloy in alkaline metal silicate solution were investigated. The thickness of an oxide film increased with increasing current source but the uniformity of the surface of an oxide film became worse. The unstable oxidation process represented by fluctuating voltage established across an oxide film was discussed and related to the surface roughness and the melting down of magnesium alloy. By comparing the surface of an oxide film a pulsating current source produced more uniform oxide film on magnesium alloy than a pulsating voltage source.     

Correlations between structure and some mechanical properties of carbon fibres

Three types of carbon materials were studied by X-ray analysis in order to get correlations between structure and some mechanical properties. Both X-ray and mechanical measurements were done in various conditions.     

Property characterization and formation mechanism of anticorrosion film coated on AZ31B Mg alloy by SNAP technology

Despite tremendous efforts in research and development after the discovery of high-temperature perovskite-type layered superconductors, and high expectations expressed in market projection potential electrical commercial applications of these materials, the popularity of these superconductors is taking off very slowly. One of the biggest hurdles facing the widespread application of the (RE)Ba₂Cu₃O₇ is developing a manufacturing process of flexible multifilamentary coated conductors, comprised of a buffered metallic substrate and a superconducting layer (Glowacki, in Frontiers in Superconducting Materials. Springer, New York, 2005), that will produce it in long lengths and at prices competitive with copper for applications such as motors, generators, transmission cables, and other power systems (Lectures on Superconductivity, University of Cambridge, Cambridge, 2008). The low-cost powder-in-tube or screen-printing processes, that are successful in the manufacturing of medium temperature superconductor MgB₂ and high-temperature Bi-family superconductors cannot be used for (RE)Ba₂Cu₃O₇ conductors due to their granularity and ceramic-like mechanical bulk properties. Deposition of a (RE)Ba₂Cu₃O₇ coating using physical deposition techniques is too expensive to provide low-cost highly textured coated conductor for AC applications (Lectures on Superconductivity, University of Cambridge, Cambridge, 2008). Therefore, the obvious choice is the chemical route and the sol gel deposited using ink-jet printing (Glowacki, in Frontiers in Superconducting Materials. Springer, New York, 2005; Lectures on Superconductivity, University of Cambridge, Cambridge, 2008) is currently recognised as potentially the best way to manufacture 3D multifilamentary high temperature superconductor (Glowacki, in Frontiers in Superconducting Materials. Springer, New York, 2005). In this paper the perspective of deposition of buffer layer and multifilamentary (RE)Ba₂Cu₃O₇ superconducting layer by sol gel ink-jet printing is discussed with respect to best conductor AC performance, and also addresses the future research that is required.     

Surface modification of carbon fiber for improving the interfacial adhesion between carbon fiber and polymer matrix

In this study, the reinforcing mechanism of amine functionalized on carbon fibers (CFs) has been precisely discussed, and the differences between aliphatic and aromatic compounds have been illustrated. Polyacrylonitrile‐based CFs were functionalized with ethylenediamine, 4,4‐diaminodiphenyl sulphone, and p‐aminobenzoic acid (PAB), and CF‐reinforced epoxy composites were prepared. The structural and surface characteristics of the functionalized CFs were investigated using X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT‐IR), and scanning electron microscopy (SEM). Mechanical properties in terms of tensile and flexural strengths and moduli were studied. The FT‐IR results confirm the success in bonding amines on the CF surface. After treatment of CFs, the oxygen and nitrogen contents as well as the N/C ratio showed an increase. XPS results provided evidence of the chemical reaction during functionalization, rather than being physically coated on the CF surface. Chemical modification of CF with diamines led to considerable enhancement in compatibility of CF filaments and epoxy resin, and remarkable improvements were seen in both tensile and flexural properties of the reinforced composites. SEM micrographs also confirmed the improvement of interface adhesion between the modified CFs and epoxy matrix. Finally, it can be concluded that PAB is a promising candidate to functionalize CF in order to improve interfacial properties of CF/epoxy composites. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrocatalysis and amperometric detection of aliphatic aldehydes at platinum-palladium alloy coated glassy carbon electrode

Aliphatic aldehydes undergo an electrocatalytic oxidation at a platinum-palladium (Pt-Pd) alloy coated glassy carbon electrode. The alloy modification offers a highly sensitive and stable, constant (+0.35 V) potential detection of simple aldehydes. The drastically enhanced catalytic response of the alloy deposit, compared to the single component metals, is attributed to synergistic effect associated with changes in the adsorption features of the surface. The influence of the alloy deposition conditions upon the amperometric response is assessed. Scanning electron microscopy, energy dispersive X-ray analysis and elemental distribution mapping offer useful insights into the microstructure and composition of the alloy deposit. Formaldehyde, acetaldehyde and propionaldehyde were detected in flow-injection analysis at levels as low as 0.9, 6.4 and 6.5 ng (30, 160 and 120 pmol), respectively. Such operation offers lower operating potentials and detection limits compared to the recently developed mixed-valent ruthenium coated detector for aldehydes [2].