Uniform Composites Research Articles

Preparation and Thermal Shock Properties of Al2O3p/40Cr Functionally Graded Composites Materials

Al2O3p/40Cr graded composite was prepared by the squeeze casting method, and the as-cast structure, hardness, thermal shock properties of the composites were preliminary tested. The results show that the microstructure is compact and the grains of the matrix is small in the composite layer. Al2O3particles well-distributed in the 40Cr matrix in continuous trend. The Macro-interface of 40Cr substrate and composites layer transits naturally and has good continuity, moreover the micro-interface of Al2O3particles and the matrix is dense without any cavities. While the macrohardness decreases with the Al2O3content reduced gradually. At the 20°C~650°C condition of the cold and heat cycle, graded composites has superior thermal shock properties than uniform composite.

One-step thermal synthesis of graphene nanosheet-metal nanoparticle hybrids from graphite–liquid crystal–metal salt composite

A facile one-step thermal-assisted method is reported to synthesize graphene nanosheet-metal nanoparticle hybrids. For this purpose, graphite, ionic liquid crystal and the metal salt were mixed to form a uniform composite. After thermal treatment, graphene nanosheets were synthesized and simultaneously, the noble metal nanoparticles were uniformly anchored on the surface of graphene nanosheets. The method needs no functionalization of the graphene surface. This is an efficient method for high yield production of graphene nanosheet-metal nanoparticle hybrid that can be used for design and fabrication of nanocomposite electrodes. In this work, graphene nanosheet-Ag nanoparticle hybrid was used for the fabrication of graphene nanosheet-Ag nanoparticle/ionic liquid electrode and its electrocatalytic effect was investigated towards oxygen reduction.

Synthesis of conducting poly(5-carboxyindole)/Au nanocomposite: Investigation of structural and nanoscale electrical properties

We report, herein, redox chemical synthesis of processible nanocomposite of carboxylic acid functionalized conducting polymer, poly(5-carboxyindole) (5C-PIn) and gold metal nanoparticles. The method involves a reaction between aqueous dispersion of carboxyindole monomer and aqueous solution of HAuCl4. The progress of the reaction is monitored by UV–visible spectroscopy and further nanocomposite is studied for structural, morphological, electrochemical and thermal properties. The concentration ratio of monomer and HAuCl4 is crucial to get desired morphology and uniformity of nanocomposite. The effect of the increasing concentration of gold salt is demonstrated with change in morphology and homogeneity of the nanocomposite. A uniform composite is formed using 1:2 mole ratio of HAuCl4 to monomer. Nanoscale electrical characterization of 5CPIn/Au nanocomposite is performed using current-sensing atomic force microscopy which exhibited a nonlinear and rectifying diode behavior with Al metal junction. Fluorescent spectral studies indicate that photoluminescence for the nanocomposite can be tuned from violet blue to yellow spectral range. The composite proves enormous potential in fabrication of nanoscale organic devices and organic optoelectronics.

Synthesis and properties of polyvinylpyrrolidone films containing the photomagnetic chromium (tris)oxalate complex

Uniform composites of polyvinylpyrrolidone with the paramagnetic chromium (tris)oxalate complex (C23H23N2O+)3Cr(C2O4)3·11.56 H2O and cation of quinoline spiropyran of the indo-line series were obtained for the first time. Their photochemical properties and static and superhigh-frequency dynamic magnetic characteristics were studied. The change in the ESR spectra under UV irradiation in films of polyvinylpyrrolidone containing photochromic paramagnetic was observed.

Suppression of Segregation, Settling and Agglomeration in Mechanically Processed Composites Fabricated by a Semisolid Agitation Processes

The development of metal matrix composites is of great interest in industrial applications for lighter materials with high specific strength, stiffness and heat resistance. An attempt has been made in the present investigation to study and systematically record the effects of secondary mechanical processing with different reductions on the porosity, microstructure and mechanical properties of high strength and highly uniform Al matrix composites. In order to overcome some of the drawbacks associated with the conventional stir casting techniques, semisolid agitation processes was employed. It is observed that the fabrication of these composites via compocasting technique plus reduction (90 %) during cold rolling process lead to reasonably uniform distribution of particles in the matrix and minimum clustering or agglomeration of the reinforcing phase. The as-cast composite exhibited higher porosity content as compared with the composite in the rolled conditions.

Searching for a novel optimization strategy in tensile and fatigue properties of alumina particulates reinforced aluminum matrix composite

Development and application of metal matrix composite materials and increased application of calculations, simulations and modeling in the area of semi-solid solidification ask for the knowledge of compocasting for these materials. In this study, a self-organizing hierarchical particle swarm optimizer is implemented for computational modeling and optimization of the compocast high strength and highly uniform Al matrix composites. The matrix of the composite was a 6061 Al alloy and the reinforcement was alumina particle (Al2O3p). Experimental results were obtained for hardness, tensile and fatigue properties of the Al alloys with different vol.% of micro-particles. The tensile strength of the composites increased considerably by increasing the reduction ratio in the cold rolling process. It is observed that the presence of reinforcement in the Al alloy degrades the low-cycle fatigue property when the Al matrix composites are subject to strain-controlled cyclic loading. The method combines position update rules, the standard velocity and the strengths of particle swarm optimization with the ideas of selection, crossover and mutation from GA.

Fabrication of Al/Ni/Cu composite by accumulative roll bonding and electroplating processes and investigation of its microstructure and mechanical properties

Al–Ni–Cu composite was produced using accumulative roll bonding (ARB) and electroplating processes. Nickel was electroplated on copper substrate for a certain time and voltage. In this study, the microstructural evolution and mechanical properties of the Al–Ni–Cu composite during various ARB cycles were studied by optical and scanning electron microscopes, microhardness, tensile and bending tests. It was observed that at first, nickel layers and then copper layers, were necked, fractured and distributed in aluminum matrix as accumulative roll bonding cycles were increased. Finally, after 11 cycles of ARB process, a completely uniform composite was produced with a homogeneous distribution of copper and nickel particles in aluminum matrix. The results showed that by increasing the number of ARB cycles, the bending strength of produced composite was increased. Also, it was found that when the number of cycles was increased, not only elongation was increased but also the tensile strength of the composite was improved. Microhardness for different elements in different cycles was also evaluated. Finally, fracture surfaces of samples were studied, using scanning electron microscopy (SEM), to reveal the failure mechanism.

The synthesis of the particulates Al matrix composites by the compocasting method

Many scientific and engineering applications require optimization methods to find more than one solution to multimodal optimization problems. This paper presents an experimental and computational investigation on the influences of the secondary mechanical processing with different reductions on the porosity, microstructure and mechanical properties of compocast high strength and highly uniform Al matrix composites. Multiple solutions to the problems are located and refined using a new particle swarm optimization (PSO) technique. The technique, NichePSO, extends the inherent unimodal nature of the standard PSO approach by growing multiple swarms from an initial particle population. Each subswarm represents a different solution or niche; optimized individually. The outcome of the NichePSO algorithm is a set of particle swarms, each representing a unique solution. The as-cast composite exhibited higher porosity content as compared with the composite in the rolled conditions. Furthermore, the tensile strength of the composites increased considerably by increasing the reduction ratio in the cold rolling process.

Polymer Composites Containing Non-Covalently Functionalized Carbon Nanotubes: A Study of Their Dispersion Characteristics and Response to AC Electric Fields

Abstract Multi-wall carbon nanotubes (MWCNT) functionalized with a hyperbranched polyethylene (HBPE) and subsequently melt compounded with an ethylene-octene copolymer (EOC8100) matrix are examined in terms of their dispersion characteristics and electric field response. It was found that, when compared with their non-functionalized counterparts, HBPE-functionalized MWCNT produce substantially more uniform composites. On the other hand, MWCNT functionalization results in a higher electrical percolation threshold. Electrification of the composite melts showed that longer insulator-to-conductor transition times should be expected as a consequence of the improved dispersion quality. The functionalization, however, did not prevent MWCNT from forming highly electrically conducting networks in the melt, or exhibiting electric field-induced percolation thresholds of less than 1wt% filler.

Unit yarn-reduction technique and flexural properties of tapered composites based on four-step row and column braiding

Mechanisms of unit yarn-reduction braiding were investigated and preform microstructures were characterized by digital image photography and topological analysis. Flexural properties and failure mechanisms of the unit yarn-reduction composites, cut composites and uniform composites were compared. Results indicated that continuity of the braiding process must be ensured after yarn reduction and distribution of the reduction units should be uniform. A smoothly trapezoidal profile appeared near the unit yarn-reduction cross-section and braiding angles and yarn lengths in the surface or interior yarn-reduction control volumes all increased. Flexural properties of the unit yarn-reduction composites were significantly higher than those of the cut composites and slightly lower than the uniform composites. The damage process of the yarn-reduction composites can be divided into the initial, developing and serious damage stages with yarn breakage being the dominant failure mechanism, while the primary failure mechanisms of the cut composites were matrix microcracking and fiber pulling-out.

Structural Analysis of Ciprofloxacin-Carbopol Polymeric Composites by X-Ray Diffraction and Fourier Transform Infra-Red Spectroscopy

Purpose: To evaluate physicochemical changes in ciprofloxacin following incorporation in Carbopol polymeric composites. Methods: The ciprofloxacin and Carbopol were mixed in water in a drug:polymer ratio of 1:5 (w/w) and homogenized to produce uniform composites. X-ray powder diffraction analysis of the pure ciprofloxacin and the Carbopol polymeric composites of the drug were obtained using a powder diffractometer. Spectra for the materials were also generated by Fourier transform infrared (FTIR) spectroscope interfaced with an infrared (IR) microscope operated in reflectance mode. Results: Based on the Hanawalt system, three prominent x-ray diffractogram (XRD) peaks of the pure ciprofloxacin and the drug in the polymeric composites exhibited d-spacing at similar 2 � values, but the relative intensity of these peaks was higher in the polymeric composites. FTIR analysis indicates that there were intermolecular hydrogen bonding and esterification between the drug and polymer in the polymeric composites. Conclusion: The changes that occurred in ciprofloxacin indicate increase in stability, decrease in solubility and delayed release of the drug from polymeric composites which could facilitate the formulation of a sustained release form of the drug.

Fabrication of porous PCL/elastin composite scaffolds for tissue engineering applications

We present the development of a technique that enables the fabrication of three-dimensional (3D) porous poly(ɛ-caprolactone) (PCL)/elastin composites. High pressure CO 2 was used as a foaming agent to create large pores in a PCL matrix and impregnate elastin into the 3D structure of the scaffold. The effects of process variables such as temperature, pressure, processing time, depressurization rate, and salt concentration on the characteristics of PCL scaffolds were determined. Scaffolds with average pore sizes of 540 μm and porosity of 91% were produced using CO 2 at 65 bar, 70 °C, processing time of 1 h, depressurization rate of 15 bar/min, and addition of 30 wt% salt particles. The PCL/elastin composites were then prepared under different conditions: ambient pressure, vacuum, and high pressure CO 2. The fabrication of composites under vacuum resulted in the formation of nonhomogenous scaffolds. However, uniform 3D composites were formed when using high pressure CO 2 at 37 °C and 60 bar.

Enhanced capacitance and rate capability of graphene/polypyrrole composite as electrode material for supercapacitors

Graphene and polypyrrole composite (PPy/GNS) is synthesized via in situ polymerization of pyrrole monomer in the presence of graphene under acid conditions. The structure and morphology of the composite are characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectrometer (FTIR), X-rays photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). It is found that a uniform composite is formed with polypyrrole being homogeneously surrounded by graphene nanosheets (GNS). The composite is a promising candidate for supercapacitors to have higher specific capacitance, better rate capability and cycling stability than those of pure polypyrrole. The specific capacitance of PPy/GNS composite based on the three-electrode cell configuration is as high as 482 F g −1 at a current density of 0.5 A g −1. After 1000 cycles, the attenuation of the specific capacitance is less than 5%, indicating that composite has excellent cycling performance.

Shaping Gold Nanocomposites with Tunable Optical Properties

We report the synthesis of morphological uniform composites using miniemulsions of poly(tert-butyl acrylate) or poly(styrene) containing organically capped gold nanocrystals (NCs). The optical features of such hybrid structures are dominated by plasmonic effects and depend critically on the morphology of the resulting nanocomposite. In particular, we demonstrate the ability to tune the overall optical response in the visible spectral region by varying the Au NCs arrangement within the polymer matrix, and therefore the interparticle plasmon coupling, using Au NCs resulting from the same batch of synthesis. This is a consequence of two well-known effects on the optical properties of Au particles: the variation of the surrounding dielectric refractive index and interparticle plasmonic coupling. The research reported here shows a general strategy to produce optical responsive nanocomposites via control of the morphology of submicrometric polymer particles containing metal nanocrystals and thus is an alternative to the more common strategy of size tuning metal nanoparticles used as nanofillers.

Effects of Surface Modification of SiC Nanoparticles and Preparation Process on Microstructures of SiCp/A6061 Alloy Matrix Composites

SiC nanoparticles (40nm) reinforced metal matrix composites (MMCs) were made by a common stir casting technique in two different preparation processing routes. In the first route, the coated ceramic powder was prepared using electroless plating to coat SiC nanoparticles by Cu. In the second route, Cu and SiC nanoparticles were fully mixed by high energy ball milling, and then SiC nanoparticles were embedded in Cu to form a “jujube-cake” structure. In both cases the average particles size were 0.2μm. The SiC nanoparticles enhanced A6061 alloy matrix composites were made by stir casting, and as-cast microstructures were studied by means of optical microscopy (OM) and scanning electron microscopy (SEM). The results show that in the first route, the Cu off and the slagging reaction occurs to form a mixture at the upper part of the ingot by a vacuum melting and the ingot central also has a large number of pores, only the lower part of the ingot organization is uniform. The second route can make better uniform composites.

PREPARATION AND CHARACTERIZATION OF BIOACTIVE COMPOSITES OF PCL/BIOACTIVE FILLERS

A variety of bioactive composites have been invested over the last two decades as substitute materials for diseased or damaged tissues in the human body. In this paper, bioactive composites were prepared using polycaprolactone ( PCL ) and hydroxyapatite ( HA ). The influence of micro-sized and nano-sized HA on composite properties was investigated. The nano- HA was prepared by wet chemical co-precipitation reaction method. Studies of biocomposite specimen morphology were performed by Field-emission scanning electron microscopy (SEM). XRD (X-Ray Diffraction) and DSC (Differential scanning calorimetry) were used to assess the crystal structure of HA and thermal properties of the composites, respectively. The synthesized nano- HA is found to be of high purity HA structure. The relationship between composition, structure and properties was studied. Different methods to prepare uniform composites were tried, and the outcome of this work suggests that by proper manipulation of biodegradable polymers and bioactive ceramics through material design, bioactive composites with controlled properties might be achievable.

Fabrication and mechanical properties of high-dispersion-treated carbon nanofiber/alumina composites

High-dispersion-treated carbon nanofibers (CNFs) were used to fabricate uniformly-dispersed CNFs-alumina composites with enhanced mechanical properties. The treatment was effective in obtaining dense and uniform composites. The composites containing 0.4–0.8 wt % CNFs were densified to a relative density of more than 99% by vacuum sintering and subsequent hot isostatic pressing, and those containing 1.6–2.5 wt % CNFs were densified to full density by plasma activated sintering. The maximum bending strength of the composites (1050 MPa) was approximately the same as the bending strength of monolithic alumina (1079 MPa). The maximum fracture toughness of the composites was 5.9 MPa·m0.5, which was a 69% increase compared with the fracture toughness of monolithic alumina (3.5 MPa·m0.5). Fracture toughness (KIC) increased rapidly with a decrease in alumina grain size (G), and we found that the relationship could be expressed by the following equation: KIC = (k1/G2) + k2 (where k1 and k2 are constants).

High dispersion and electrochemical capacitive performance of NiO on benzenesulfonic functionalized carbon nanotubes

This work describes an effective method to synthesize structurally uniform composite of nickel oxide/benzenesulfonic functionalized multiwalled carbon nanotubes composite (NiO/f-MWCNTs) using benzenesulfonic MWCNTs as the substrate. Benzenesulfonic group here is bifunctional both for solubilizing MWCNTs into aqueous solution and for tethering Ni 2+ precursor onto MWCNTs surfaces to facilitate the follow-up chemical deposition of NiO by supplying surface binding and anchoring groups. The composite has a uniform surface dispersion and large coverage of NiO onto f-MWCNTs, which is characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscope, cyclic voltammetry and galvanostatic charge/discharge measurements. The NiO/f-MWCNTs composite improved the utilization of electrochemical capacitive materials and delivered capacity of 384 F/g at the constant current of 0.20 A/g due to f-MWCNTs as substrate.

Micro‐Scale Modeling of a Functionally Graded Ni‐YSZ Anode

AbstractA mathematical model was developed to investigate the coupled transport and electrochemical reactions in a nickel‐yttrial‐stablized zirconia (Ni‐YSZ) anode for use in solid oxide fuel cells (SOFCs). The modeling results were consistent with experimental data from the literature. Comparison between conventional non‐graded (uniform random composites) and two types of functionally graded electrodes (FGE), namely particle size graded and porosity graded SOFC anodes were conducted to evaluate the potential of FGE for SOFC. Improved performance of both types of FGE was observed due to reduced mass transport resistance and increased volumetric reactive surface area close to the electrode‐electrolyte interface. It was found that the particle size graded SOFC anode showed the best performance. This paper demonstrates that the SOFC performance could be enhanced by modifying the microstructures of the electrodes. The results presented in this paper provide a better understanding of the working mechanisms of SOFC electrodes and could serve as an important reference for design optimizations.

Micromechanics-based thermoelastic model for functionally graded particulate materials with particle interactions

Thermoelastic behavior of functionally graded particulate materials is investigated with a micromechanical approach. Based on a special representative volume element constructed to represent the graded microstructure of a macroscopic material point, the relation between the averaged strains of the particle and matrix phases is derived with pair-wise particle interactions, and a set of governing equations for the thermoelastic behavior of functionally graded materials is presented. The effective coefficient of thermal expansion at a material point is solved through the overall averaged strain of two phases induced by temperature change under the stress-free condition, and is shown to exhibit a weak anisotropy due to the particle interactions within the graded microstructure. When the material gradient is eliminated, the proposed model predicts the effective coefficient of thermal expansion for uniform composites as expected. If the particle interactions are disregarded, the proposed model recovers the Kerner model. The proposed semi-analytical scheme is consistent and general, and can handle any thermal loading variation. As examples, the thermal stress distributions of graded thermal barrier coatings are solved for two types of thermal loading: uniform temperature change and steady-state heat conduction in the gradation direction.