Ferrous-ferric equilibrium in BaO-B2O3 melts

The ferrous-ferric equilibrium in different BaO-B₂O₃ melts containing iron oxides have been studied as functions of temperature and total iron concentration. On equilibrating the melts at 1200° C with air, 3 to 6% of the total iron was reduced to the ferrous state. The equilibrium ferric/ferrous ratio in the melt decreased with increasing temperature and with decreasing BaO content of the melt. Total iron content (in the concentration range of 0.6 to 11.5 wt% Fe) had no significant effect on the equilibrium ferric/ferrous ratio of the melts.     

Raman scattering for the size of CdSe and CdS nanocrystals and comparison with other techniques

The sizes of the ensembles of CdSe regular nanocrystals (RNCs), CdSe magic-sized nanocrystals (MSNCs), and CdS RNCs were investigated by Raman scattering. The nanocrystal ensembles were synthesized via wet-chemistry approaches. The size distribution increases from CdSe MSNCs (2.26 nm), to CdSe RNCs (3.52 nm), and to CdS RNCs (3-8 nm and 4-10 nm). The sizes derived from Raman spectra are compared with those from other characterization tools such as UV/vis spectroscopy and transmission electron microscopy (TEM). The present study suggests that Raman scattering is an alternative and reliable technique for the determination of nanocrystal size and size distribution.     

Preparation and characterisation of polyamide 11/montmorillonite (MMT) nanocomposites for use in angioplasty balloon applications

With increased demands on catheter balloon functionality, there is an emphasis to blend new materials which can improve mechanical performance. Polymer nanocomposites were prepared by melt blending polyamide 11 (PA 11) with organically modified montmorillonite nanoclay. The effects of incorporating the nanoclay on the short-term mechanical properties of PA 11 were assessed using a design of experiments (DoEs) approach. X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis techniques (DMA) were used to characterise the morphology of the nanocomposites. Design of experiments studies revealed that the optimum nanocomposites properties can be achieved by carefully controlling the melt compounding parameters. XRD and TEM data proved that exfoliated clay morphologies existed within the matrix at low clay loading (2%). Whereas the interaction between the polymer matrix and nanoclay was quantified in the DMA spectra, showed a significant increase in storage modulus (up to 80%). The reinforcing effect of nanoclay within the PA 11 was further investigated using mechanical testing, where significant increases in the ultimate tensile strength and strain at break of reinforced tri-layer balloon tubing were observed.     

Design of Wideband Rectangular-Shaped Coupler with Virtual Short Stubs for Wireless Communication Applications

This article presents the design of the sectional rectangular-shaped directional couplers with tight coupling of 3-dB over frequency of 2–6 GHz. The designed coupler consists of two substrates and one common ground plane between the substrate layers. It also formed by two conducting strips with virtual short stubs are placed to the middle section at the top and bottom layer, which coupled through three-section rectangular slots at the ground plane. The effect of these additional stubs in the design is studied and observed. The design and analysis are performed with the use of full-wave electromagnetic simulation software package, CST Microwave Studio. This designed coupler has been fabricated and its wideband performance is verified.     

Design and Development of Ferroelectric Tunable Coplanar Waveguide Components for Ku- and K-Band Applications

In the past several years, we have demonstrated electrically tunable microstrip components such as resonators, filters, diplexers, and couplers based on conductor/ferroelectrics/dielectric two-layered structure. Recently, we are focusing our efforts on tunable coplanar waveguide (CPW) components in collaboration with NASA Glenn Research Center, Cleveland, OH. The advantages of CPW components include higher dielectric tunability compared to microstrip structure, ease of shunt connections, and ease of testing. To date, we have modeled several CPW structures with ferroelectric thin-film to study the effect of inserting the ferroelectric thin-film on electric tunability, attenuation and dispersion. Also, we have designed and fabricated devices such as resonators, and filters. The ferroelectric tunable CPW filters were tunable by more than 3% at bias voltage levels of - 100V. The BSTO based CPW filters offer higher sensitivity parameter as well as lower loss parameter compared to BSTO tunable 2-pole microstrip filters.     

Ferroelectric tunable coplanar waveguide components for Ku- and K-band and applications

Abstract

The main objective of this research is to study the effect of inserting a Barium Strontium Titanate (BSTO) ferroelectric tuning layer in coplanar waveguide (CPW) and conductor-backed CPW (CBCPW) components. The modeled components include CPW and CBCPW transmission lines (with and without a dielectric filling between the center conductor and the ground planes). We have modeled the characteristic impedance (Z₀), effective dielectric constant (ε_eff), attenuation and dispersion as a function of circuit geometry and the ferroelectric thin-film's dielectric properties over the 10–20 GHz frequency range. We found that the presence of a ferroelectric layer between the transmission line and the ground planes improves the percentage change in ε_eff by almost two-fold with respect to a CPW deprived of this layer. This result is significant, as one could obtain larger frequency tunability with relatively lower applied fields compared to regular CPW or microstrip lines.     

Role of gamma radiation and EGDMA on the physico–mechanical properties of jute fabrics/polypropylene composites

Jute fabrics reinforced polypropylene (PP) composites (45 wt % fiber) were prepared by compression molding and their mechanical properties were investigated. Both jute fabrics and PP sheets were treated with gamma radiation (250–1,000 krad dose) at a rate of 350 krad/h. Irradiated jute fabrics were soaked into ethylene glycol dimethacrylate (EGDMA) solutions (5–40% by weight) and cured in an oven at different temperatures (40–100°C) for 60 min. The percentage of polymer loading (PL) was evaluated and found that 20% EGDMA‐treated jute fabrics contains the highest PL. Composites made of 20% EGDMA‐treated jute fabrics were studied further. It was found that the treatment using the EGDMA improved the mechanical properties of the composites significantly. Scanning electron microscopy and aging properties of untreated and treated composites were performed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Effect of nonionizing radiation on the physicomechanical properties of banana fiber/pp composites with HEMA

Banana fiber‐reinforced polypropylene (PP)‐based unidirectional composites (40% fiber by weight) was manufactured by compression molding. Banana fibers and PP sheets were treated with UV radiation at different intensities and then composites were fabricated. It was found that mechanical properties of irradiated banana fiber and irradiated PP‐based composites were found to increase significantly compared to that of untreated counterparts. Irradiated banana fibers were also treated with 2‐hydroxyethyl methacrylate (HEMA) mixed with methanol (MeOH) under thermal curing method at different temperatures (30–70°C) for different curing times (20–60 min). A series of solutions of different concentrations of HEMA in methanol along with 2% benzyl peroxide were prepared. Monomer concentration, curing temperature and curing time were optimized in terms of polymer loading and mechanical properties. Composites made of 15% HEMA, 50°C and 40 min curing time showed the best mechanical properties than those of untreated composite. Scanning electron microscopy (SEM), water uptake, and simulating weathering test of the composites were also investigated. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Comparative experimental measurements of jute fiber/polypropylene and coir fiber/polypropylene composites as ionizing radiation

Jute and coir fiber‐reinforced polypropylene (PP) composites (45 wt% fiber) were prepared by compression molding. Composites were fabricated with irradiated jute fiber/irradiated PP and irradiated coir fiber/irradiated PP at different doses (250–1,000 krad). It was revealed that jute‐based composites had better mechanical properties as compared to coir‐based composites. Interfacial shear strength of jute/PP and coir/PP systems was measured by using the single‐fiber fragmentation test. Scanning electron microscopy investigation shows poor fiber matrix adhesion for coir‐based composites than that of jute‐based composites. Water uptake and soil degradation tests of the composites were also performed. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Thermomechanical and Interfacial Properties of Calcium Alginate Fiber-Reinforced Polypropylene Composites

Polypropylene (PP) matrix calcium alginate fiber reinforced unidirectional composites (10% fiber by weight) were fabricated by compression molding. Tensile strength (TS), tensile modulus (TM), bending strength (BS), bending modulus (BM), and impact strength (IS) were found to be 26 MPa, 950 MPa, 38 MPa, 1320 MPa, and 20 kJ/m², respectively. Degradation tests of composites were performed for 6 weeks in soil and it was found that composites retained almost 75% of its original strength. The interfacial properties of the composite were investigated by using single fiber fragmentation test (SFFT) and by scanning electron microscope (SEM).