Sobia A. Rakha

Optimization of the Carbon Coating of Honeycomb Cores for Broadband Microwave Absorption

A simple and fast coating method of honeycomb cores for microwave absorption has been described. The honeycomb cores with two different thicknesses (5 and 20 mm) coated with thermoplastic resin filled with carbon powder as lossy filler in 5, 10, 15, and 20 wt% have been tested for microwave absorption in 2 - 18-GHz frequency range. The 5-mm-thick honeycomb has shown absorption bandwidth of 14 GHz for maximum absorption of -6 dB (75%) with 15 wt%. filler content. However, the percentage of the filler was decreased to 10 wt% in 20-mm-thick honeycomb absorber for maximum absorption over a wide frequency range. The honeycomb sample with 10 wt% filler has bandwidth of 18 GHz for -7 dB (80%) reflection loss. The reflection loss measurements of coated honeycomb cores have also shown that use of E-glass fiber/epoxy composite can enhance the performance of the honeycomb absorber. The combination of a microwave absorbing nanocomposite and the coated honeycombs has been resulted in inferior absorption properties in 2 - 18-GHz frequency range.

Correlation of electrical conductivity, dielectric properties, microwave absorption, and matrix properties of composites filled with graphene nanoplatelets and carbon nanotubes

The DC electrical conductivity, percolation threshold, and dielectric properties of Graphene Nanoplatelets (GNPs) filled epoxy composites are studied and correlated with microwave absorption. The properties of GNPs filled composites are also compared with multiwalled carbon nanotubes (MWCNTs) composites, and GNPs are observed to have superior conductivity than MWCNTs. In all batches, the nanofillers have 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 wt. %. All composites irrespective of the type of nanofiller and viscosity of the matrix have shown electrical percolation threshold at 3.0 wt. %. The dielectric properties, i.e., complex permittivity, tan loss, and AC conductivity, are studied in 100 Hz–5.5 MHz. The DC and AC electrical conductivities (at and below the percolation) measured in 100 Hz–5.5 MHz are correlated to the GNPs and MWCNTs epoxy composites in the microwave frequency range (11–17 GHz). The maximum return loss of −12 dB and −6 dB was determined for MWCNTs and GNPs, respectively. The effects of na...

Microwave Properties of Nanocomposites: Effect of Manufacturing Methods and Nanofiller Structure

Nanocomposite materials filled with multiwall carbon nanotubes (MWCNTs) having three types of structures, i.e., longer (200lm), shorter (20‐50lm), and aminated (20‐50lm), are manufactured for microwave absorption (MA) in 11‐17GHz frequency range. Microstructure, dielectric permittivity, direct current (DC) electrical conductivity, and MA properties of the MWCNTs‐epoxy nanocomposite were investigated. A correlation has been developed between the structure (aspect ratio and surface functionality) of MWCNTs, electrical conductivity of the composite, and MA (return loss (RL)). E-glass/epoxy composite filled with longer carbon nanotubes (CNTs) has shown higher RL as compared to that of other two nanocomposites. The measurements have shown that the magnitude of RL of microwaves depends strongly on the structure of MWCNTs used in the composite. Furthermore, the effect of synthesis route followed for the manufacturing of nanocomposite on its electrical conductivity and microwave absorbing properties is also investigated; three different approaches were followed to manufacture CNT/epoxy nanocomposites from longer CNTs (200lm). [DOI: 10.1115/1.4029916]

Optimization of the manufacturing parameters of honeycomb composite sandwich structures for aerospace application

Sandwich structures comprising para-aramid paper honeycomb core and carbon fiber epoxy matrix composite facesheets were fabricated for aerospace applications. For the adhesion of honeycomb core and composite facesheets, two different types of adhesive films were used. The curing parameters for adhesive films, including temperature and time, were optimized for maximum bonding strength.

Inducing the magnetic character in reduced graphene oxide through incorporation of Fe2O3 nanoparticles

A chemical two-step approach based on solvothermal technique has been adopted to synthesize the reduced graphene oxide (rGO)/Fe2O3 hybrid materials. The rGO was prepurified by acidic treatment, followed by sensitization to attach the desired functional groups. The structural, compositional, morphological and magnetic analyzes of the prepared samples were carried out using various characterization techniques. The fabricated rGO/Fe2O3 heterostructures were confirmed by X-ray diffraction analysis and Fourier transform infrared spectroscopy. Raman spectroscopy evidenced the fabrication of multilayer graphene and scanning electron microscopy was carried out to study the morphology of the prepared samples. The average particle size of Fe2O3 nanoparticles (NPs) loaded on rGO was found to be ∼20 nm, as was observed during transmission electron microscopy. Thermogravimetric analysis of rGO/Fe2O3 hybrid structures was performed to investigate their thermal behaviors. It was evidenced that the incorporation of Fe2O3 NPs into rGO enhanced its thermal stability. Vibrating sample magnetometry showed that ferromagnetic character was induced in rGO due to involvement of Fe2O3 NPs. The rGO/Fe2O3 hybrid structures can be considered as a competent material for fabrication of various magnetic devices.

Ion irradiation-induced modifications of diamond nanorods synthesised by microwave plasma chemical vapour deposition

Diamond nanorods (DNRs) synthesised by the high methane content in argon rich microwave plasma chemical vapour deposition (MPCVD) have been implanted with nitrogen ions. The nanorods were characterised by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The DNRs consist of single-crystalline diamond cores of 3–5 nm in diameter and several tens of nanometres in length. For purification from non-diamond contents, hydrogen plasma etching of DNRs was performed. Structural modifications of etched DNRs were studied after irradiating with 50 keV nitrogen ions under the fluence of 5 × 1014, 1 × 1015, 5 × 1015 and 1 × 1016 ions cm−2. Nitrogen-ion implantation changes the carbon–carbon bonding and structural state of the nanocrystalline diamond (NCD). Raman spectroscopy was used to study the structure before and after ion irradiation, indicating the coexistence of diamond and graphite in the samples. The results indicated the increase in graphitic and sp2-related content, at the expense of decrease in diamond crystallinity, for ion implantation dose of 5 × 1015 cm−2 and higher. The method proves valuable for the formation of hybrid nanostructures with controlled fractions of sp3–sp2 bonding.