Synthesis of core–shell microspheres of poly(methyl methacrylate)–CuO by solution deposition method

Poly(methyl methacrylate)–CuO microspheric particles with core–shell structure were synthesized by a chemical solution process within Cu(NO₃)₂/NH₃·H₂O reaction system. The composition and microstructure of the samples were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It showed that the shell was constructed by leaf-like CuO grains with the length of 500–800 nm. UV–vis absorbance spectra of the samples exhibited novel wide adsorption band in ultraviolet region.     

The influence of SiC particles on the corrosion resistance of electroless,Cu–P composite coating in 1 M HCl

The present paper aims to compare the corrosion resistance of the electroless Cu–P–SiC with Cu–P composite coating on carbon steel in 1 M HCl solution by the weight loss, potentiodynamic polarisation and electrochemical impedance spectroscopic (EIS) techniques. The study reveals that, the corrosion current density (I_corr) and the double layer capacitance (C_dl) values decrease, the charge transfer resistance (R_ct) and inhibition of efficiencies (IE %) increase with the incorporation of SiC particles in the Cu–P matrix indicating the improvement in corrosion resistance.     

Electrodeposition PbO2-TiO2 and PbO2-ZrO2 and its physicochemical properties

Composite materials based on PbO₂ containing TiO₂ or ZrO₂ were prepared from electrolytes containing a suspension of TiO₂ or ZrO₂. The contents of foreign oxides in the composite depend on the electrolyte composition and conditions of deposition. When a dispersed phase is incorporated into the composite coating, the dimensions of lead dioxide crystals decrease to submicro- and nano-size. Physico-chemical properties of composite materials are mainly determined by their chemical composition.     

Microstructure and orientation relationships of Mg alloy matrix composite reinforced with SiC whiskers and B4C particles

The microstructure and orientation relationships of ZK60A magnesium alloy matrix composite reinforced with SiC whiskers and B₄C particles have been studied by means of transmission electron microscopy and high-resolution electron microscopy. MgO nanocrystalline particles are formed at SiC/Mg interfaces with a cube-on-cube orientation relationship with SiC whiskers. MgB₂ nanorods are formed near the B₄C particles. Two types of orientation relationships between the SiC whisker and Mg are observed, which are [1¯11]_SiC|| [0001]_Mg and (022¯)_SiC|| (112¯0)_Mg, and [1¯11]_SiC|| [112¯0]_Mg and (022¯)_SiC|| (011¯2)_Mg. Geometrically, [1¯11]_SiC|| [0001]_Mg and (022¯)_SiC|| (112¯0)_Mg is more favorable than [1¯11]_SiC|| [112¯0]_Mg and (022¯)_SiC|| (011¯2)_Mg.     

Al/SiC composite coatings of steels by thermal spraying

Thermal spraying has been used to coat carbon steels (F112) and austenitic stainless steels (AISI 304) with aluminium matrix composites. Mixtures of aluminium powder and SiC particles were used as spraying material. A sol-gel silica coating was laid on SiC particles to reduce the porosity of the composite coatings and to inhibit the formation of aluminium carbide. The sol-gel silica coating acts as an active barrier enhancing the wettability of the reinforcement by molten aluminium. Coatings with a reinforcement volume fraction up to 30 vol.% were obtained with porosities of about 1.0 vol.%. The incorporation of sol-gel silica coated SiC particles reduces the coefficient of thermal expansion of the composite coating and enhances its adhesion to the substrates more than when uncoated SiC particles were used.     

A comparison of crystallization behaviors of laser spot welded Zr–Cu–Ag–Al and Zr–Cu–Ni–Al bulk metallic glasses

A novel Ni-free Zr–Cu–Ag–Al ((Zr₄₈Cu₃₆Ag₈Al₈)Si_0.75) and a Zr–Cu–Ni–Al ((Zr₅₃Cu₃₀Ni₉Al₈)Si_0.5) bulk metallic glass (BMG), for comparison, were employed for Nd:YAG laser spot welding with three pre-selected energy inputs, including a low (6.2 J), a medium (8.0 J) and a high (9.2 J) energy input. After the welding process, the microstructure evolution, glass-forming ability (GFA) and mechanical properties of the welded samples were determined by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and the Vicker's microhardness test.     

Corrosion behaviour of sediment electro-codeposited Ni–Al2O3 composite coatings

Ni–Al₂O₃ composite coatings were produced by the sediment electro-codeposition (SECD) technique at various particle loadings and current densities. The submicron Al₂O₃ particles were found to distribute uniformly in the coating, and 12–18 vol.% particles can be incorporated in the coating depending on deposition current density and particle loading in the plating bath. Electrochemical corrosion testing was conducted in 0.9 wt.% NaCl solution. The results show that the incorporation of Al₂O₃ particles in the coating did not affect the general corrosion behaviour of the Ni coating. However, at higher anodic potentials approaching the breakdown potential and with prolonged polarization, the composite coatings showed deteriorated corrosion resistance in terms of increased anodic current density, reduced pitting potential and quicker breakdown of the passive film. The detrimental effects of Al₂O₃ particle incorporation could be explained by the existence of numerous boundaries between the particles and the matrix, which would serve as active sites for anodic dissolution and micro-pit formation.     

Effect of Nd content on microstructure and mechanical properties of Grf/Al composite

M40 graphite fibre reinforced Al-17Mg matrix composites with different neodymium (Nd) content (Al-17Mg, Al-17Mg-0.2Nd, Al-17Mg-0.5Nd and Al-17Mg-2Nd) were fabricated by pressure infiltration method. Microstructure of Gr_f/Al composites was investigated by XRD, SEM, TEM and HRTEM. Effect of Nd on microstructure and mechanical properties of Gr_f/Al composites were deeply discussed. Al₃Mg₂ and Al₁₁Nd₃ phases followed by segregation of Nd and Mg at carbon-aluminum interface were detected in composites containing Nd. The size and amount of Al₄C₃ phase were increased with Nd content. Bending strength of Gr_f/Al composites were decreased sharply from 1463 MPa (Gr_f/Al-17Mg) to 791 MPa (Gr_f/Al-17Mg-2Nd) after the addition of Nd. The increased Nd content decreased the pull-out of single fibre and bundles, which was due to the high interfacial bonding strength with formation of Al₄C₃, Al₃Mg₂, Al₁₁Nd₃ phases and the transition layer.     

Preparation of HA/chitosan composite coatings on alkali treated titanium surfaces through sol-gel techniques

In this paper we demonstrated for the first time the feasibility to generate well crystallized hydroxyapatite/chitosan (HA/CS) composite coatings on alkali treated titanium surfaces through combining the in situ hydrothermal precipitation and sol-gel dip coating technique without introducing any other coupling agent. Alkali treatment converting hydrophobic Ti surfaces into super-hydrophilic surfaces was the pre-requirement of uniform coatings. Preliminary cell culturing results revealed that the coatings were biocompatible and supported osteoblasts attachment.     

Electromagnetic wave absorption properties of multi-walled carbon nanotubes decorated with La-doped BaTiO3 nanocrystals synthesized by a solvothermal method

Ba_1−xLa_xTiO₃/multi-walled carbon nanotube (MWCNT) nanocomposites with different concentrations of La³⁺ doping, were synthesized by a solvothermal process. The prepared nanocomposites had a hybrid microstructure in which Ba_1−xLa_xTiO₃ nanocrystals with diameter of 10–30 nm were firmly immobilized on the MWCNTs sidewalls. Electromagnetic (EM) wave absorption properties of La-doped BaTiO₃/MWCNT nanocomposites were investigated in the 7.5–18 GHz frequency range for an absorber thickness of 1 mm. The reflection loss (RL) calculated from the EM parameters of the samples, moved to low frequencies with increasing La³⁺ doping. The widest absorption bandwidth, with the lowest frequency range, was observed in a nanocomposite doped with 1.5 at% La³⁺. An RL exceeding −5 dB for this sample was obtained in the frequencies ranging from 9.6 to 16.3 GHz, with the optimal RL of −17.4 dB at 10.9 GHz, due to enhanced interfacial polarization resulting in developed ε^″r${{\epsilon }^{″}}_{\text{r}}$. In addition, the RL for the sample shifted to the low frequency region and the peaks became sharper in the 2–18 GHz frequency range with increasing absorber thickness. For BaTiO₃/MWCNT nanocomposites, La³⁺ doping can greatly improve the EM wave absorbing ability in a thin absorber thickness and the donor-doped nanocomposites show promise for application in EM wave shielding materials with broad absorption bandwidths.     

Fabrication of polystyrene hollow spheres in W/O/W multiple emulsions

One mild multiple emulsions was used for the fabrication of hollow polystyrene (PS) spheres. Polystyrene was dissolved in a volatile organic solvent to form the O phase, then an aqueous phase containing a surfactant was transferred into above phase to form an oil-in-water (W_in/O) emulsion, followed by addition of W_in/O emulsion in the external W_out phase, and solvent evaporation. Final product with diameter of 150 μm, surface roughness of 30 nm, and sphericity of 98.0% was obtained. The possible influences on the formation of PS hollow sphere were also discussed.     

Electrospun polymeric nanofibrous composites containing TiO2 short nanofibers

In this study, polymeric nanofibrous composites containing anatase TiO₂ short nanofibers (TiO₂-SNF) were successfully produced via electrospinning. The fabrication of the nanofibrous composite structure includes two steps. First, anatase TiO₂ nanofibers were obtained by calcination of electrospun PVP/TiO₂ nanofibers and then crushed into short nanofibers ranging from few microns in length. Second, these TiO₂-SNF were dispersed into polymer solutions and then electrospun into nanofibrous composites. We obtained nanofibers containing TiO₂-SNF from different polymer types including PMMA, PAN, PET and PC. The SEM and TEM imaging indicated that some of the TiO₂-SNF were fully covered by the polymeric matrix whereas some TiO₂-SNF were partially covered and/or stick on the surface of the fibers. The photocatalytic activity of nanofibrous composites containing TiO₂-SNF was evaluated by monitoring the photocatalytic decomposition of a model dye (rhodamine-6G) under UV irradiation.     

Cost-efficient high performance polyetheretherketone/expanded graphite nanocomposites with high conductivity for EMI shielding application

The cost efficient expanded graphite (EG) filled polyetheretherketone (PEEK) nanocomposites were prepared by hot pressing, which exhibited an electrical conductivity percolation threshold of 1.5 wt%. The electrical conductivity of the 1.5 wt% nanocomposite increased approximately eleven orders of magnitude than that of pure PEEK. The conductivities of 5 wt% and 10 wt% nanocomposites were increased to about 3.24 S cm⁻¹ and 12.3 S cm⁻¹, respectively. Scanning electron microscope showed 3-dimensional conductive network of EG across the PEEK matrix. The significant increase in electrical conductivity of the nanocomposites leads to the tremendous increase in electromagnetic interference shielding effectiveness.     

Thermally activated reactions of multi-walled carbon nanotubes reinforced aluminum matrix composite during the thermal spray consolidation

The interfacial phenomena of multi-walled carbon nanotubes (MWCNTs) embedded in an Al matrix during high-velocity oxygen fuel (HVOF) spraying were investigated. The high thermal energy supplied from the high temperature gas flow of HVOF spraying activated the interfacial reactions of MWCNTs with oxygen and Al, such as MWCNT oxidation and aluminum carbide formation. Interfacial reactions deteriorated the contribution of the MWCNTs to the coating properties by destroying the intrinsic structure of the MWCNTs. In this study, the interfacial reaction mechanisms of the MWCNTs are discussed based on microstructural and thermodynamic analysis.     

Statistical analysis of mechanical properties of pressureless sintered multiwalled carbon nanotube/alumina nanocomposites

Mechanical properties of pressureless sintered 0.15–1.2 vol.% multiwalled carbon nanotube reinforced alumina matrix nanocomposites have been analyzed using the 2-parameter Weibull statistics. Electron microscopy and phase analysis of nanocomposites sintered at 1700 °C for 2 h in Argon revealed existence of interpenetrating network of nanotubes in alumina, formation of thin interface resembling stoichiometric aluminum monoxycarbide and matrix grain refinement by nanotubes. Statistical analyses indicated that with increasing Vickers hardness testing load (4.9–19.6 N) and flexural strength measurement temperature (room temperature to 1100 °C), Weibull modulus of nanocomposites increased significantly suggesting improved consistency at higher load and temperature. The highest Weibull moduli were obtained for nanocomposites containing either 0.15 or 0.3 vol.% nanotube which were ∼40% and ∼15% higher than single phase alumina for hardness and strength, respectively, supporting the specimen size effect on reliability of present brittle ceramic matrix nanocomposites. Superior mechanical reliability of nanocomposites over pure alumina was primarily attributed to the presence of structurally intact nanotubes forming effective interface region to ensure proper load sharing, matrix grain refinement, and especially, at higher testing load and temperature, overall averaging effect of flaws to yield higher Weibull moduli.     

Corrosion behaviour and galvanic coupling with steel of Al-based coating alternatives to electroplated cadmium

The galvanic corrosion behaviour of bare steel coupled to steel with an Al–Zn flake inorganic spin coating, an Al-based slurry sprayed coating, an arc sprayed Al coating and electroplated cadmium has been investigated. The sacrificial and galvanic behaviour of the coatings was studied in 3.5 wt. % NaCl solution using open-circuit potential, potentiodynamic polarisation and electrochemical noise measurements. The coatings were characterised by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Experimental results showed that the Al-based slurry sprayed coating exhibited an open-circuit potential closer to the steel substrate than other coatings, as well as a low corrosion current density and a more positive corrosion potential. In terms of the galvanic suitability of the investigated coatings for the steel substrate, both the Al–Zn flake inorganic spin coating and the Al-based slurry sprayed coating show low galvanic current, in comparison with the arc sprayed Al coating and electroplated cadmium. This behaviour confirms their superior cathodic protection capability and galvanic compatibility over other coatings tested. Electrochemical noise measurements provide accurate information on the coatings' galvanic behaviour, which can be complimented by the data obtained from superposition of potentiodynamic corrosion scans of the coating and bare steel, provided that the corrosion potential difference between the two materials does not exceed 300 mV.     

Microstructural studies and wear assessments of Ti/TiC surface composite coatings on commercial pure Ti produced by titanium cored wires and TIG process

Tungsten Inert Gas (TIG) process and titanium cored wires filled with micro size TiC particles were employed to produce surface composite coatings on commercial pure Ti substrate for wear resistance improvement. Wire drawing process was utilized to produce several cored wires from titanium strips and titanium carbide powders. Subsequently, these cored wires were melted and coated on commercial pure Ti using TIG process. This procedure was repeated at different current intensities and welding travel speeds. Composite coating tracks were found to be affected by TIG heat input. The microstructural studies using optical and scanning electron microscopy supported by X-ray diffraction showed that the surface composite coatings consisted of α′-Ti, spherical and dendritic TiC particles. Also, greater volume fractions of TiC particles in the coatings were found at lower heat input. A maximum microhardness value of about 1100 HV was measured which is more than 7 times higher than the substrate material. Pin-on-disk wear tests exhibited a better performance of the surface composite coatings than the untreated material which was attributed to the presence of TiC particles in the microstructure.     

Corrosion resistance of electrodeposited Ni–Al composite coatings on the aluminum substrate

Ni matrix–Al particle composite coating was adopted via sediment co-deposition (SCD) method on the zincate coated aluminum substrate. Surface morphology was investigated by scanning electron microscopy (SEM). The electrochemical behavior of the coatings was studied by polarization potentiodynamic test in 3.5 wt.% sodium chloride using a three electrode open cell. The effect of the electroplating parameters on the Al co-deposition was studied. Maximum of 22 wt.% Al particles were deposited in the coating. It was found that the zincate coating plays an important role in improving the nickel layer adherent. Furthermore, incorporation of aluminum particles in Ni matrix refined the Ni crystal coatings. However, polarization curves shifted to negative potentials and corrosion rate is decreased.     

Mechanical properties of ABOw+MWNTs/Al hybrid composites made by squeeze cast technique

Multi-wall carbon nanotubes (MWNTs) have been considered a realistic kind of reinforcement for composite materials. In this paper, microstructure and mechanical properties of the aluminum borate whisker (ABOw) and MWNTs hybrid composites were investigated. The results show that MWNTs decrease the compressive deformation of the hybrid preforms and are kept intact in the matrix during squeeze cast processing. A small amount of MWNTs may effectively improve the modulus, strength and elongation of the hybrid composite. Decreasing micropores and strengthening the matrix, high strength MWNTs make the mechanical properties of the hybrid composite superior to the singularly reinforced ones. This makes MWNTs a promising material for novel micro/nanohybrid composite.