Farid El-Tantawy

In situ network structure, electrical and thermal properties of conductive epoxy resin–carbon black composites for electrical heater applications

Abstract Epoxy composites at high carbon black (CB) concentration exhibited good electrical and thermal stability, which can make them attractive for consideration in heating devices and conducting composite applications. The effect of CB on the network structure of epoxy composites, like volume fraction of epoxy network ( V r ), the extent of CB reinforcing ( γ ), interparticle distance between conductive particles (IPD), epoxy–solvent interaction parameter ( χ ), average number molecular weight between cross-links ( M c ), number of elastically effective chains (NEC), cross-linking density (CLD) and scanning electron microscope (SEM), was investigated in details. The conductivity of an insulating epoxy matrix increases continuously with CB content and is well explained by percolation theory. The effects of different concentration of CB and sintering on the electrical conductivity of epoxy composite as a function of temperature during heating and cooling cycles were discussed. The conduction mechanism and negative temperature coefficient of conductivity (NTCC) of epoxy–CB composites were analyzed. The current–voltage–temperature and working power–temperature characteristics of these composites as a function of CB content were investigated. We attempt to contribute to a better understanding of the negative resistance phenomena in epoxy–CB composites. The nonlinear coefficient ( α ), the size of conductive particles (SCP) and hopping distance ( a h ) of charge carriers in epoxy–CB composites were evaluated. The thermal stability was tested by means of temperature–time curve at certain applied power, on and off, for one cycle. The characteristic thermal properties, like characteristic time growth τ g , decay τ d and current t i constants of epoxy as a function of CB content, were estimated. The specific heat ( C p ) and amount of heat transferred by radiation and convection ( h r ) were calculated based on energy balance concept as a function of CB content. The thermoelectric power (TEP) and thermal conductivity ( λ ) as a function of temperature of epoxy–CB composite were discussed. In conclusion, the epoxy–CB composites show good thermal stability and they can be used as heating devices for consumer products.

Joule heating treatments of conductive butyl rubber/ceramic superconductor composites : a new way for improving the stability and reproducibility?

The present paper describes the effect of superconductors on the sintering process, apparent cross-linking density, sintering factor, hardness and volume fraction of butyl rubber (IIR) composites. Electrical conductivity and I–V characteristics at various processing conditions of IIR with different concentrations of superconductor were measured. The stability and reproducibility of IIR composites were tested. Also, the conduction mechanism of electrical conductivity is discussed. Specific heat and the amount of heat transferred by radiation and convection were calculated via the proposed model and calorimetry as a function of superconductor content. It was found that superconductor accelerates the driving force during the sintering process and the characteristic time constant during sintering decreases while the sintering factor, the apparent cross-linking density, hardness and volume fraction of rubber increases as the content of superconductor increases. In addition, it was proved that the superconductor and Joule heating effect improves the electrical and thermal properties of IIR.

Semiconducting properties of Al doped ZnO thin films

Aluminum doped ZnO (AZO) thin films were successfully deposited via spin coating technique onto glass substrates. Structural properties of the films were analyzed by X-ray diffraction, atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy. X-ray diffraction results reveal that all the films are polycrystalline with a hexagonal wurtzite structure with a preferential orientation according to the direction (002) plane. The crystallite size of ZnO and AZO films was determined from Scherrers formula and Williamson-Hall analysis. The lattice parameters of the AZO films were found to decrease with increasing Al content. Energy dispersive spectroscopy (EDX) results indicate that Zn, Al and O elements are present in the AZO thin films. The electrical conductivity, mobility carriers and carrier concentration of the films are increased with increasing Al doping concentration. The optical band gap (Eg) of the films is increased with increasing Al concentration. The AZO thin films indicate a high transparency in the visible region with an average value of 86%. These transparent AZO films may be open a new avenue for optoelectronic and photonic devices applications in near future.

Microwave-assisted hydrothermal synthesis and characterization of ZnO nanorods.

For the purpose of this study, the nanorods of zinc oxide were synthesized by rapid microwave-assisted hydrothermal route. The microstructure and surface morphology of the sensitized nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). XRD results indicate that synthesized ZnO nanorods have wurtzite phase. The calculated value of the particle size using Debye Scherrer formula and Williamson Hall plot was found to be 20-28 nm and 35.3 nm, respectively. Low uniformity distribution of rod-like morphology (60-80 nm in diameter and average length about 250 nm) are seen in TEM micrographs. The optical parameters of the prepared ZnO nanorods have been calculated using Kubeleka-Munk approach for the UV-vis diffuse reflectance spectrum. It is found that the direct transition optical band gap of the studied sample is 3.17 eV. The direct current electrical conductivity (σ) was increased from 6.7×10(-8) to 3×10(-7) Ω(-1) cm(-1) with increasing the temperature (T) in the range (300-425 K). The obtained variation of σ with T refers that the conductivity mechanism is controlled by thermally activated process.

New double negative and positive temperature coefficients of conductive EPDM rubber TiC ceramic composites

Abstract In this paper, we have successfully prepared ethylene–propylene-diene monomer (EPDM)/TiC composites as thermistors, with new double negative and positive temperature coefficients of conductivity (NTCC/PTCC). EPDM composites loaded with 50 phr HAF carbon black and different concentrations of TiC were prepared. This study focuses on the effect of TiC content on the vulcanization process, the network structure and the electrical and thermal properties of EPDM/TiC composites. The effect of TiC on the network structure was evaluated e.g. the curing process, the characteristic time constant during vulcanization, the volume fraction of rubber, gel fraction, interparticle distance between conductive particles, the extent of TiC reinforcement in the rubber matrix and molecular weight between cross-linking through experimental and affine–phantom models. The effects of TiC content on the percolation theory, electrical conductivity, conducting mechanism of conductivity, conducting hysteresis and I–V characteristics were also studied, as well as its TiC on the (NTCC/PTCC), thermoelectric power, dielectric constant and thermal conductivity. Stability and reproducibility of the thermal cycles for heating element applications was tested. Specific heat and the amount of heat transfer by radiation and convection as a function of TiC content was calculated using both the calorimetric technique and a theoretical model. It was proved that TiC improves the network structure, electrical and thermal properties of EPDM composites for practical applications.

Novel rapid synthesis of zinc oxide nanotubes via hydrothermal technique and antibacterial properties.

ZnO nanotubes with the wurtzite structure have been successfully synthesized via simple hydrothermal solution route using zinc nitrate, urea and KOH for the first time. The structural, compositions and morphology architectures of the as synthesized ZnO nanotubes was performed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and high resolution transmission scanning electron microscopy (HRTEM). TEM showed that ZnO nanotubes exhibited a wall thickness of less than 2 nm, with an average diameter of 17 nm and the length is 2 μm. In addition, the antibacterial activity of ZnO nanotubes was carried out in vitro against two kinds of bacteria: gram - negative bacteria (G -ve) i.e. Escherichia coli (E. coli) and gram - positive bacteria (G +ve) i.e. Staphylococcus aureus. Therefore, this work demonstrates that simply synthesized ZnO nanotubes have excellent potencies, being ideal antibacterial agents for many biomedical applications.

Electrical properties and stability of epoxy reinforced carbon black composites

Abstract The conductivity of an insulating epoxy matrix increases continuously with carbon black (CB) content and is well explained by percolation theory. The effects of CB content and sintering on the electrical conductivity (σ) of epoxy composite as a function of temperature during heating and cooling cycles were discussed. The current–voltage–temperature (I–V–T) and working power–temperature (P–T) characteristics of these composites as a function of CB content were investigated. The thermal stability was tested by means of temperature–time (T–t) curve at certain applied power on and off for one cycle.

Influence of solvent transport on physico-chemical properties of crosslinked butyl rubber filled with TiC ceramic

Abstract Understanding the vulcanization and swelling behavior of polymers is potentially important for composite materials, since vulcanization and swelling may significantly influence the electrical and mechanical properties. This work investigates the effect of TiC content on vulcanization reaction and on network structures like the characteristic time constant of vulcanization, vulcanization factor, volume fraction of rubber, extent of filler and interparticle distance between conductive particles. The crosslinking density of the rubber was calculated by the Flory–Rehner equation. The affine and phantom models for physical crosslinks were used to predict the nature of crosslinks. The experimental results were compared with the theoretical predictions. Sorption and diffusion of kerosene were investigated through butyl rubber (IIR) composites reinforced with different concentration of TiC ceramic. Effect of TiC concentration and temperature on solvent uptake and mechanism of diffusion were studied in detail and the experimental diffusion data compared with theoretical predictions. Concentration profiles of the kerosene were calculated to predict the applicability of these composites under extreme service conditions. The apparent activation energy of diffusion and some useful thermodynamic parameters like enthalpy, entropy, Gibbs free energy and heat of sorption were calculated. An abrupt increase in electrical resistivity appears after a characteristic time of swelling. Mechanical properties increase with the addition of TiC reinforcing filler, and decrease after swelling with kerosene (compared with that before swelling with kerosene). In conclusion, it was found that TiC improves the network structure and slows the diffusion of kerosene into the polymer by acting as a barrier.

Effect of Bi-containing superconducting ceramic on the volume resistivity of butyl rubber composites

Abstract The present paper describes the effect of Bi-containing superconducting ceramic on the volume resistivity of butyl rubber (IIR) composites. The microstructure of butyl rubber filled with different concentrations of superconductor was examined by scanning electron microscopy (SEM). The influence of superconductor concentration, time, applied static pressure and temperature on the volume resistivity was investigated. The differences in volume resistivity–temperature dependencies with different filler levels under temperature increase and temperature decay were also measured. The effects observed are discussed from the viewpoint of ionic and electronic mechanisms of electrical conductivity in rubber-based composites.

A novel ultrasonic transducer backing from porous epoxy resin–titanium–silane coupling agent and plasticizer composites

Abstract In this paper, a new composite for ultrasonic attenuation backing has been successfully fabricated from porous epoxy resin containing titanium (Ti), silane coupling agent and plasticizer composites. The effect of Ti particles on the network structure and mechanical properties of epoxy resin has been analyzed in detail. The ultrasonic parameters in epoxy composites have been measured by a conventional pulse-echo-overlap technique at a frequency of 1–5 MHz. The effect of Ti content and temperature on the longitudinal sound velocity and attenuation of epoxy resin composites were investigated. Precise in situ observations of the acoustic properties such as attenuation and acoustic impedance of epoxy composites are expected to be useful for ultrasonic transducer systems for new as well as for backing application with high attenuation.