Influence of hydrodynamics and pulse plating parameters on the electrocodeposition of nickel-alumina nanocomposite films

Nickel-alumina nanocomposites were produced by electrocodeposition utilizing two electrode configurations, a parallel plate electrode (PPE) and impinging jet electrode (IJE), and various current modulations, i.e. direct current (DC), pulse plating (PP) and pulse reverse plating (PRP). Particle incorporation increased linearly with the particle loading of the electrolyte for all deposition conditions studied. A maximum incorporation of 12 vol.% of 50 nm γ-Al₂O₃ particles in a nickel matrix was achieved using an unsubmerged IJE system, while PP and PRP resulted in composites with particle contents up to 11 vol.% of 13 nm γ-Al₂O₃ particles. In general, nanocomposites showed higher hardness compared to the pure nickel coatings. The enhanced hardness of the composite films was associated with modifications in the microstructure of the nickel matrix as well as with the nanoparticle incorporation. The pure nickel deposits exhibited a strong (1 0 0) texture. With increasing plating current density and particle incorporation, a variation in the crystallite size and a loss of texture was observed.     

Electrocodeposition of nickel-alumina nanocomposite films under the influence of static magnetic fields

The influence of an external static magnetic field on the electrocodeposition of 13 nm alumina particles into a nickel matrix has been studied. Using the quartz crystal microbalance it was possible to determine the particle content of the layers in situ. The main factors controlling the codeposition are the flux density and the orientation of the magnetic field. The alumina particle content in electrodeposited nickel layer was substantially increased by the application of a perpendicular (with respect to the electric field) magnetic field. Magnetic functionalization of the particles by electroless coating with a thin nickel layer lead to bad reproducibility and did not significantly improve the particle content of the layer.     

Influence of clay on the vulcanization kinetics of fluoroelastomer nanocomposites

The vulcanization kinetics of gum and montmorillonite (Na-MMT) clay filled fluoroelatomer (FKM) nanocomposite was studied using both oscillating disc rheometer and differential scanning calorimetry under isothermal and dynamic conditions. The X-ray diffraction pattern of clay filled FKM showed a shift in d-spacing toward higher values indicating the formation of intercalated silicate layer. The cure characterization showed higher rate and state of vulcanization of modified clay filled compound than that of gum and unmodified clay filled FKM indicating the accelerating effect of quaternary ammonium salt modified clay. Although the unmodified clay slowed down the cure reaction, there was marked increase in cure rate at higher level of curative. Higher loading of clay decreased the cure rate with lowering of maximum torque values. The presence of organoclay increased the torque value through the formation of confined elastomer network within the silicate galleries. The experimental data obtained provided the evidence that the curing behavior illustrated autocatalytic characteristics. The kinetic parameters determined from the model equation had good agreement with the experimental results. The calculated activation energy of the gum and clay filled systems indicated the ease of cure process with respect to the type of clay. The cure kinetics measured by different methods was well correlated with each other.     

Polymer nanocomposites based on transition metal ion modified organoclays

A unique class of nanocomposites containing organoclays modified with catalytically active transition metal ions (TMI) and ethylene vinyl acetate (EVA) copolymers was prepared. The morphology, thermal and rheological properties of these nanocomposites were studied by thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS) spectroscopy, X-ray scattering/diffraction and oscillatory shear rheometry. TMI-modified organoclays were thought to possess pillaring of multivalent TMI in the interlayer silicate gallery, leading to a notable reduction of the interlayer d-spacing. The resulting nanocomposites exhibited significantly improved thermal stability and fire retardation properties, but similar morphology (i.e., an intercalated-exfoliated structure) and rheological properties comparable with EVA nanocomposites containing unmodified organoclays. It appears that the compressed organic component in the TMI-modified organoclay can still facilitate the intercalation/exfoliation processes of polymer molecules, especially under extensive shearing conditions. The improved fire retardation in nanocomposites with TMI-modified organoclays can be attributed to enhanced carbonaceous char formation during combustion, i.e., charring promoted by the presence of catalytically active TMI.     

Effect of surfactant BAS on MoS<Subscript>2</Subscript> codeposition behaviour

Ni–MoS₂ metal matrix composites were produced by electrodeposition in a Watts bath. The correlation of embedded particle ratio and operational parameters was studied. When surfactant BAS was adsorbed on the MoS₂ particle surface, the conductivity of the MoS₂ was significantly decreased. Thus, more Ni atoms may be deposited homogeneously over a wider area rather than on preferred conductive positions. This results in a smoother codeposition layer with lower porosity. Furthermore, strong adhesion between the codeposition layer and the substrate when using surfactant BAS may result from lower porosity of the codeposition layer.     

Effect of additives and pulse plating on copper nucleation onto Ru

The impact of organic additives and pulse-plating parameters on the initial stages of copper electrodeposition on Ru is characterized. Microscopy is used to observe 7-15 nm thick Cu deposits, prior to complete coverage of the substrate. Because the nucleus density is very high for the conditions studied here, the counting of individual Cu islands is difficult and an alternative method to analyze the images is presented. Results are compared for different additives for continuous plating and pulse-plating conditions. Pulse plating has a significant impact on the nucleus density. Replacement of Cl⁻ ions with Br⁻ ions of the same concentration yields an increase in the nucleus density at the same current density. A PEG-PPG-PEG block copolymer, when used instead of PEG as a suppressor, appeared to result in high nonuniformity in particle size.     

Wear behavior of metal matrix nanocomposites

Metal matrix nanocomposites (MMNCs), a unique class of metallic materials having superior mechanical, chemical, thermal or tribological properties, are commonly used in critical applications Those light-weight aluminum and magnesium alloys usually working in harsh wear conditions are susceptible to surface attacks. Although a lot of investigations have already been performed on those conventional composites reinforced by micro-particles, the wear behavior of the nanocomposites has not yet been fully understood. The surface properties associated with MMNCs are presented in this paper focusing mostly on manufacturing & processing routes, nano-particles as well as the dominant wear mechanisms. Studying wear behavior of MMNCs shows that no quantitative comparison of different existing studies is available as it is aimed to be done in the present review. To this end, wear reports have been categorized and discussed wherein the following results has been obtained: (i) it is found that ceramics reinforced composites usually exhibit a relatively better wear resistance behavior compared to those filled by carbon-based nanomaterials, (ii) hybrid MMNCs with two or more reinforcement types are promising materials to improve the surface resistance, particularly when the combination of ceramic and carbon-based particles are employed, (iii) solid-state processes like powder metallurgy usually provide superior wear resistance as compared to those liquid processing methods like casting, (iv) the use of smaller reinforcement size may almost always result in superior response, (v) abrasion is the most governing wear mechanism amongst the abrasion, adhesion and delamination mechanisms being frequently observed in MMNCs. A comprehensive review is made with particular attention on the composites reinforced by nano-sized reinforcing agents in order to evaluate the current research activities, discuss the pitfalls and provide a roadmap for future endeavors. It is believed that still countless research opportunities exist in order to fill the existing voids and fulfill the challenges with MMNCs.     

Fatgiue behavior of metal matrix nanocomposites

Light-weight high-strength composites (particularly with aluminum and magnesium base alloys) have principal applications in a wide variety of fields ranging from automotive and aerospace structures to medical and energy applications wherein the materials undergo both static and dynamic (fatigue) loading conditions. Conventional metal matrix composites (MMCs), i.e. those filled by micro-sized reinforcements, have usually poor ductility and insufficient mechanical performance made them, therefore, unreliable to be used in some critical applications. Instead, those composites strengthened by nano-sized reinforcing agents, namely metal matrix nano-composites (MMNCs), have newly been developed in order to boost the mechanical properties. The current paper aims to study the fatigue behavior of the MMCs with a particular attention on recent investigations made on MMNCs. It is believed that the materials selection, microstructural features, manufacturing and processing parameters, etc. have a dominant influence on the fatigue response of MMNCs.     

Analysis of the modulus of polyamide-6 silicate nanocomposites using moisture controlled variation of the matrix properties

The stiffness of PA6 silicate nanocomposites has been measured for a number of silicate fractions and moisture levels. The matrix modulus was varied experimentally by moisture conditioning, resulting in three different moisture levels. The moduli have been analysed with a Halpin-Tsai composite model. This model was used to calculate the matrix modulus in the nanocomposites based on the crystallinity, the amount of surfactant and the moisture content. The measured modulus of the nanocomposites with different moisture content was used to calculate the effective aspect ratios of the reinforcing particles with the Halpin-Tsai model. The calculated aspect ratio for each nanocomposite is independent on the moisture concentration. This indicates the validity of this composite model to describe nanocomposites, despite the small particle size. The results suggest that changes on the molecular level due to the presence of the silicate layers only have a small influence on the modulus, because the modulus can be explained with a composite model. The reduced efficiency of reinforcement at increasing filler levels can be partially explained by the reduction of the matrix modulus due to surfactant and reduced crystallinity, and partially by the occurrence of small stacks of platelets.     

脉冲电镀中脉冲参数对镍镀层显微硬度的影响

采用传统的瓦特镀液通过脉冲电镀制得纯镍镀层。研究了脉冲参数对镀层微观形貌与显微硬度的影 响。结果表明:镀层表面形貌为胞状结构;随着脉冲峰值电流密度的增加,胞状结构的尺寸逐渐变小,镀层显微硬度先增 加后减小;随着占空比的减小,最大显微硬度值对应的峰值电流密度增大,占空比减小到一定值后,峰值电流密度的改变 对显微硬度影响不再明显。     

Influence of pulse plating parameters on the synthesis and preferred orientation of nanocrystalline zinc from zinc sulfate electrolytes

The influence of pulse electrodeposition parameters (current on-time T_on, current off-time T_off, and pulse current density J_p) was investigated on the surface morphology and grain size of zinc electrodeposited from a sulfate bath containing polyacrylamide and thiourea additives. The grain size and surface morphology of zinc deposits were studied by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM), and the preferred orientation of the deposits was studied by X-ray diffraction. At constant current off-time and pulse current density, the grain size decreased asymptotically with increasing current on-time. In contrast, increase in the current off-time at constant current on-time and pulse current density resulted in grain growth. A progressive decrease of the grain size was observed with increasing pulse current density at constant current on-time and off-time. Nanocrystalline zinc with an average grain size of 38 nm was obtained at a pulse current density of 1200 mA/cm². The crystallographic orientations developed were correlated with the change in the cathodic overpotential, the angle between the preferred oriented plane and the lowest energy of formation plane (0 0 0 2), and the pulse electrodeposition parameters.     

Influence of polymer matrix crystallinity on nanocomposite morphology and properties

In order to understand more fully how polymer matrix attributes influence polymer nanocomposite properties, nanocomposites containing hydroxyapatite nanoparticles and a poly(3-hydroxybutyrate) matrix were prepared and compared to results for a chemically-similar nanocomposite system with a lesser degree of matrix crystallinity. Experimental results indicated that the higher degree of matrix crystallinity hinders nanoparticle dispersion at loadings above 0.5 wt.% and together these structural factors, high matrix crystallinity and nanoparticle aggregation, produced different mechanical reinforcement behavior below and above the glass transition temperature than has been seen previously in amorphous matrices or matrices with moderate crystallinity levels. Overall, these results suggested that the amorphous character of the polymer does not govern the properties at all crystallinity levels in polymer nanocomposite matrices.     

Influence of thermal processing on the perfection of crystals in polyamide 66 and polyamide 66/clay nanocomposites

A study of the changes in crystal perfection of polyamide 66 (PA66) and polyamide 66/clay nanocomposites (PA66CN) due to different thermal processing was carried out. We designed three series of thermal processing including melt-quench (MQ), post-annealing MQ sample (MQA), and melt–slow cooling–annealing (MSA). The annealing temperature was set as 180 or 210 °C, which is within Brill temperature range of PA66. Fourier transform infrared (FT-IR) spectroscopy and wide angle X-ray diffraction (WAXD) were employed to characterize the perfection in short-range order and long-range order structures, respectively. The results showed that the crystal perfection of PA66 and PA66CN with different thermal processing is quite different, and the changing fashions with thermal processing for different ordered structures are not similar. In this work, MSA is optimal thermal processing for high crystallinity and crystal perfection. Exfoliated nanoclay layers exert considerable impact on the perfection of long-range ordered structures, but little on that of short-range ordered ones.     

Heavy metals adsorption on some iminodiacetate chelating resins as a function of the adsorption parameters

The adsorption properties of some novel chelating resins (CRs) bearing iminodiacetate groups for removal of heavy metal ions like: Cu(II), Co(II) and Ni(II) from aqueous solutions comparative with the commercial resin Amberlite IRC-748 have been studied in this work by a batch equilibrium technique. Quantitative analysis for adsorption was conducted using UV–vis spectroscopy to investigate the kinetics, adsorption isotherm and thermodynamics of the removal process considering equilibration time, pH, metal ion concentration and temperature as controlling parameters. The metal adsorption capacities, at pH 5, were in the order Cu(II) > Ni(II) > Co(II), for both the CR with 10 wt.% DVB (CR-10) and the commercial resin Amberlite IRC-748. The adsorption capacities on CR-10 were higher for Ni(II) and Co(II) ions, but lower for Cu(II) ions compared with Amberlite IRC-748. Both Freundlich and Langmuir isotherms well fitted on the adsorption results of Cu(II), Ni(II) and Co(II) ions on all iminodiacetate resins.     

Crystallization behavior of polymer/montmorillonite nanocomposites. Part III. Polyamide-6/montmorillonite nanocomposites, influence of matrix molecular weight, and of montmorillonite type and concentration

Several series of polyamide-6 (PA-6) nanocomposites, differing in montmorillonite (MMT) type and content and PA-6 matrix molecular weight, were prepared by melt-extrusion and the associated PA-6 crystallization behavior and morphology was evaluated using (synchrotron) X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The nucleating ability of silicate layers is poor in PA-6 nanocomposites made by melt-extrusion because highly active, stable PA-6 crystallization precursors are generated during melt-extrusion. In most of the studied PA-6/MMT nanocomposites the dispersed silicate layers act as impurities and decrease rather than increase the overall crystallization kinetics of PA-6, especially at high MMT contents. Furthermore, at a given MMT concentration, the crystal growth retardation inflates with increasing degree of exfoliation, which dependents on the MMT type and which increases with increasing PA-6 molecular weight. One of the considered MMT types leads to a poorly exfoliated nanomorphology and as a result no retardation of crystal growth is observed. Furthermore, the disturbed crystal growth does not alter the PA-6 semicrystalline stack morphology. Moderate nucleation effects due to the presence of MMT can be observed when the particle load is low (low amount of MMT and/or poor degree of exfoliation) and provided the supercooling is sufficiently large.     

Flame retardancy and thermal stability of ethylene-vinyl acetate copolymer nanocomposites with alumina trihydrate and montmorillonite

The development of fire retardant for wire and cable sheathing materials has oriented toward low smoke and halogen-free flame retardant technology to achieve better safety for electrical equipment and devices and to satisfy standards. However, many polymer flame resistance materials require a very high proportion of metal hydrate filler within the polymer matrix (60 wt%) to achieve a suitable level of flame resistance, which may lead to inflexibility, poor mechanical properties and problems during compounding and processing. In this study, the alumina trihydrate (ATH) was added to montmorillonite (MMT) as the halogen-free flame retardant of ethylene-vinyl acetate (EVA) copolymer, with various ratios of EVA/ATH/MMT. The prepared nanocomposites were characterized through various techniques of XRD, tensile test, DSC analysis, TGA, LOI evaluation, and FE-SEM to explore the effects of organic modified clay (OMMT) and the layer distance on the mechanical, thermal, and flame resistance properties. In the XRD examinations, the layer-distance of MMT increased from 1.27 to 1.96 nm when polymer was added to the octadecylamine modified MMT. The best tensile strength was obtained at 3 wt% MMT. In addition, the halogen-free flame resistance grade of EVA containing 3 wt% OMMT and 47 wt% ATH revealed the best elongation and fire resistance (LOI = 28). The tensile and flame resistance properties of the nanocomposites were also significantly improved.     

以Guglielmi模型研究脉冲电流下Ni-SiC复合电沉积

在Guglielmi模型的基础上,推导了采用方形、上三角形、下三角形和锲形四类脉冲波形复合电沉积时,电流与镀层中惰性微粒体积分数的数学关系,并以Ni–SiC复合电沉积为例,进行了试验验证。结果表明,在相同峰值电流密度下,方波脉冲电流下SiC的沉积量是其他三类脉冲电流波形的1.51倍;而当平均电流密度相同时,方波脉冲电流下SiC的沉积量是其他三类电流波形的1.06倍。分析了电流密度对镍基体上SiC沉积量的影响。     

Influence of processing parameters on the surface quality of electrophoretically deposited alumina coatings on foam ceramics

Previous work showed that the electrophoretic deposition of coatings with aligned pore channels is technically feasible on Al₂O₃-C foams. In the next step, the amount and size of cracks in the sintered coatings should be reduced. The study revealed the drying conditions, alumina raw materials used, the chemistry of the foam skeleton and the sintering conditions as significant influences. The best drying procedure was freeze drying after sudden freezing in liquid nitrogen. Three alumina raw materials with different particle size distributions were tested with regard to linear shrinkage, number of cracks and number of channel-like pores. The CT 9 and CL 370 showed a low number of cracks, however CT 9 possessed almost no pores. The Al₂O₃-C foam skeletons electrophoretically coated with CL 370 and sintered at 1600 °C in air showed the best results with a low number of small cracks and high number of channel-like pores.     

Influence of spinning parameters on synthesis of alumina fibres by centrifugal spinning

The present study investigates the synthesis of alumina fibres of 5–15?µm dia. by sol-gel process through centrifugal spinning. Among various spinning parameters such as rpm, viscosity, humidity, chamber temperature etc., effect of rpm and viscosity on quality of spun fibres was examined in order to spin less defective (less shots) fibres. From the rpm vs viscosity experiments, it was concluded that viscosity between 13 and 42?Pa.s with 3000?rpm was favourable for obtaining fibres containing less shots. It was shown that besides viscosity, refractive index and percent weight loss of the aged sol can be used as indicator for determining spinnability of alumina precursor sols. Influence of only preheating and continuous heating of the chamber during spinning were also investigated and it was found that only preheating did not help in producing fibres. Besides this, influence of hot air blower (HAB) aligned in different directions with respect to the spinnerette, on fibre quality was tested. It was observed that the quality of fibres did not change due to change in HAB direction.     

The effects of intragallery polymerization on the structure of PMMA-clay nanocomposites

In situ bulk polymerization of polymethylmethacrylate (PMMA)-clay nanocomposites was initiated with a benzoyl peroxide/amine redox couple at room temperature. This was accomplished with a newly synthesized cationic molecule—containing an aliphatic chain and an aromatic tertiary amine—that was ion exchanged onto the clay surface in order to control the rate of intragallery polymerization relative to that of extragallery polymerization. The rate and location of initiation significantly affected the degree of dispersion of the silicate layers. Accelerating intragallery polymerization of clay with low cation exchange capacity was found to produce the maximum interlayer distance as evident from transmission electron microscope images.