Fawad Inam

THE CONTRIBUTION OF ELECTRICAL CONDUCTIVITY, DIELECTRIC PERMITTIVITY AND DOMAIN SWITCHING IN FERROELECTRIC HYSTERESIS LOOPS

Triangular voltage waveform was employed to distinguish the contributions of dielectric permittivity, electric conductivity and domain switching in current-electric field curves. At the same time, it is shown how those contributions can affect the shape of the electric displacement — electric field loops (D–E loops). The effects of frequency, temperature and microstructure (point defects, grain size and texture) on the ferroelectric properties of several ferroelectric compositions is reported, including: BaTiO3; lead zirconate titanate (PZT); lead-free Na0.5K0.5NbO3; perovskite-like layer structured A2B2O7 with super high Curie point (Tc); Aurivillius phase ferroelectric Bi3.15Nd0.5Ti3O12; and multiferroic Bi0.89La0.05Tb0.06FeO3. This systematic study provides an instructive outline in the measurement of ferroelectric properties and the analysis and interpretation of experimental data.

Multiscale hybrid micro-nanocomposites based on carbon nanotubes and carbon fibers

Amino-modified double wall carbon nanotube (DWCNT-NH2)/carbon fiber (CF)/epoxy hybrid micro-nanocomposite laminates were prepared by a resin infusion technique. DWCNT-NH2/epoxy nanocomposites and carbon fiber/epoxy microcomposites were made for comparison. Morphological analysis of the hybrid composites was performed using field emission scanning electron microscope. A good dispersion at low loadings of carbon nanotubes (CNTs) in epoxymatrix was achieved by a bath ultrasonication method. Mechanical characterization of the hybrid micro-nanocomposites manufactured by a resin infusion process included three-point bending, mode I interlaminar toughness, dynamic mechanical analysis, and drop-weight impact testing. The addition of small amounts of CNTs (0.025, 0.05, and 0.1 wt%) to epoxy resins for the fabrication of multiscale carbon fiber composites resulted in a maximum enhancement in flexural modulus by 35%, a 5% improvement in flexural strength, a 6% improvement in absorbed impact energy, and 23% decrease in the mode I interlaminar toughness. Hybridization of carbon fiber-reinforced epoxy using CNTs resulted in a reduction in Tg and dampening characteristics, presumably as a result of the presence of micron-sized agglomerates.

Epoxy/graphene nanocomposites – processing and properties: a review

Graphene has recently attracted significant academic and industrial interest because of its excellent performance in mechanical, electrical and thermal applications. Graphene can significantly improve physical properties of epoxy at extremely small loading when incorporated appropriately. Herein, the structure, preparation and properties of epoxy/graphene nanocomposites are reviewed in general, along with detailed examples drawn from the key scientific literature. The modification of graphene and the utilization of these materials in the fabrication of nanocomposites with different processing methods have been explored. This review has been focused on the processing methods and mechanical, electrical, thermal, and fire retardant properties of the nanocomposites. The synergic effects of graphene and other fillers in epoxy matrix have been summarised as well.

Structural and chemical stability of multiwall carbon nanotubes in sintered ceramic nanocomposite

Abstract Abstract The structural and chemical stability of multiwall carbon nanotubes (MWNTs) in ceramic nanocomposites prepared by spark plasma sintering was studied. High resolution electron microscopy, X-ray diffraction and Raman spectroscopy were used to evaluate any degradation of the MWNTs. They were found to be well preserved in alumina after sintering up to 1900°C/100 MPa/3 min. In boron carbide, structural degradation of MWNTs started from ∼1600°C when sintered for 20 min. Multiwall carbon nanotubes maintained their high aspect ratio and fibrous nature even after being sintered in boron carbide at 2000°C for 20 min. However, no Raman vibrations of MWNTs were observed for nanocomposites processed at temperatures <2000°C, which indicates that they were severely degraded. Structural preservation of MWNTs in ceramic nanocomposites depends on the ceramic matrix, sintering temperature and dwell time. Multiwall carbon nanotubes were not preserved for matrices that require high sintering temperatures (>1600°C) and longer processing times (>13 min).

High-strength nanograined and translucent hydroxyapatite monoliths via continuous hydrothermal synthesis and optimized spark plasma sintering

The synthesis of high-strength, completely dense nanograined hydroxyapatite (bioceramic) monoliths is a challenge as high temperatures or long sintering times are often required. In this study, nanorods of hydroxyapatite (HA) and calcium-deficient HA (made using a novel continuous hydrothermal flow synthesis method) were consolidated using spark plasma sintering (SPS) up to full theoretical density in ∼5 min at temperatures up to 1000°C. After significant optimization of the SPS heating and loading cycles, fully dense HA discs were obtained which were translucent, suggesting very high densities. Significantly high three-point flexural strength values for such materials (up to 158 MPa) were measured. Freeze-fracturing of disks followed by scanning electron microscopy investigation revealed selected samples possessed sub-200 nm sized grains and no visible pores, suggesting they were fully dense.

Mechanical, Thermal, and Electrical Properties of Graphene-Epoxy Nanocomposites—A Review

Monolithic epoxy, because of its brittleness, cannot prevent crack propagation and is vulnerable to fracture. However, it is well established that when reinforced—especially by nano-fillers, such as metallic oxides, clays, carbon nanotubes, and other carbonaceous materials—its ability to withstand crack propagation is propitiously improved. Among various nano-fillers, graphene has recently been employed as reinforcement in epoxy to enhance the fracture related properties of the produced epoxy–graphene nanocomposites. In this review, mechanical, thermal, and electrical properties of graphene reinforced epoxy nanocomposites will be correlated with the topographical features, morphology, weight fraction, dispersion state, and surface functionalization of graphene. The factors in which contrasting results were reported in the literature are highlighted, such as the influence of graphene on the mechanical properties of epoxy nanocomposites. Furthermore, the challenges to achieving the desired performance of polymer nanocomposites are also suggested throughout the article.

Graphene nanoplatelets in epoxy system: dispersion, reaggregation, and mechanical properties of nanocomposites

The use of graphene nanocomposites in advanced applications has attracted much attention in recent years. However, in order to substitute traditional epoxy reinforcements with graphene, there are still some issues like dispersion, homogenization, and reaggregation. In this paper, graphene bundles dispersed in two-component epoxy system by bath sonication, dispersion state, and reaggregation behavior of graphene in this system have been studied. Light transmittance in ultraviolet-visible spectroscopy has been used to quantify the reaggregation by a series of controlled experiments. After 18 mins sonication of 0.005 wt% graphene dispersion at 20°C, the light transmittance decreased from 68.92% to 54.88% in liquid epoxy and decreased from 72.80% to 46.42% in hardener; while increasing the temperature from 20°C to 60°C, the light transmittance in liquid epoxy decreased from 65.96% to 53.21% after 6 mins sonication. With the incorporation of 0.3 wt% graphene, the tensile strength of nanocomposites increased from 57.2MPa to 64.4MPa and the storage modulus increased from 1.66GPa to 2.16GPa. The results showed that the dispersion state depends on the function of sonication time and temperature, and graphene has a significant reinforcement effect on epoxy.

Reasons and remedies for the agglomeration of multilayered graphene and carbon nanotubes in polymers

Summary One of the main issues in the production of polymer nanocomposites is the dispersion state of filler as multilayered graphene (MLG) and carbon nanotubes (CNTs) tend to agglomerate due to van der Waals forces. The agglomeration can be avoided by using organic solvents, selecting suitable dispersion and production methods, and functionalizing the fillers. Another proposed method is the use of hybrid fillers as synergistic effects can cause an improvement in the dispersion state of the fillers. In this review article, various aspects of each process that can help avoid filler agglomeration and improve dispersion state are discussed in detail. This review article would be helpful for both current and prospective researchers in the field of MLG- and CNT-based polymer nanocomposites to achieve maximum enhancement in mechanical, thermal, and electrical properties of produced polymer nanocomposites.

Nickel Hydroxide/Cobalt–Ferrite Magnetic Nanocatalyst for Alcohol Oxidation

A magnetically separable, active nickel hydroxide (Brønsted base) coated nanocobalt ferrite catalyst has been developed for oxidation of alcohols. High surface area was achieved by tuning the particle size with surfactant. The surface area of 120.94 m2 g(-1) has been achieved for the coated nanocobalt ferrite. Improved catalytic activity and selectivity were obtained by synergistic effect of transition metal hydroxide (basic hydroxide) on nanocobalt ferrite. The nanocatalyst oxidizes primary and secondary alcohols efficiently (87%) to corresponding carbonyls in good yields.

Use of morphological features of carbonaceous materials for improved mechanical properties of epoxy nanocomposites

The influence of reinforcement morphology on damage tolerance and fracture toughness of epoxy based nanocomposites has been studied. Two different forms of carbonaceous reinforcements were used: multi-layered graphene (MLG) and nanostructured graphite (NSG). The maximum increase in Youngs modulus was observed from 609.6 MPa to 766 MPa (25.7% increase) in the case of 0.1 wt% NSG. The NSG showed a maximum increase in hardness up to 7.9% while MLG showed up to 18.3%. The MLG and NSG increased the storage modulus and Tg while loss modulus and tan δ decreased with MLG and NSG. SEM images of the fractured surfaces of tensile specimens showed that the fracture mode was significantly altered by MLG and NSG.