Ayhan Mergen

Dielectric Properties of Polymer Composites Filled with Different Metals

Electrically conductive composite systems based on polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) filled with metal powders of Al and Cu have been studied. The composite preparation conditions allow the formation of a random distribution of metallic particles in the polymer matrix. Dependence of the dielectric and conductivity properties of the PVC and PMMA/fillers was studied over a broad range of frequency and volume fraction of metal fillers. The experimental results could be explained by means of the conductivity of fillers and the interface polarization between polymers and fillers. Percolation was also seen in this study when the volume fraction of conducting fillers was close to critical value, in which the composites undergo an insulator‐conductor transition. The relation among the dielectric property and the fillers with different conductivity was proposed.

Hydrothermal and thermal treatment of natural clinoptilolite zeolite from Bigadiç, Turkey: An experimental study

The clinoptilolite rich zeolite from Bigadiç which was formed from alteration of volcanic glass were treated with acidic (HCl, H3BO3, H3PO4), alkaline (KOH, NaOH) solutions. Hydrothermally treated and untreated samples were heat treated at 400, 550 and 700°C. XRD, ICP-MS and N2 gas adsorption were used for physicochemical characterization of zeolites. Considering the Si/Al > 4 and Na+K/Ca+Mg < 1 ratios, zeolite sample is included to earth alkali clinoptilolite class (Heu II) which is also revealed by thermal treatments. Since zeolite structure contains low alkalies it was at collapsed 550°C.The removal of oxide elements efficiency of acids and alkalies were in the order of HCl > H3PO4 > HBO3 > KOH > NaOH. XRD analysis indicated that the structure of zeolite was not altered with acids and alkali treatments. The structure of zeolite treated with HCl and other acids started to deform at 400 and 550°C respectively. In treatment with HCl, Si/Al ratio increases with significant a decrease in K content which resulted in a decrease in the heat stability of zeolite. No change was observed in the structure and thermal stability of clinoptilolite after alkali treatments. The fact that although significant amount of Na is removed with H3BO3 acid and Na is increased with NaOH but the thermal stability remains the same indicates that Na cation is not an important parameter as much as K. HCl and H3PO4 acid treatments increased the surface area depending on the dissolution of amorphous material and H3PO4 was found to be more effective. However, the total pore size decreased due to formation of new micropores.

Structural, optical, electrical and dielectric properties of Bi1·5Zn0·92Nb1·5−xNixO6·92−3x/2 solid solution

Abstract The effects of Ni content on the structural, optical, dielectric and electrical properties of Bi1·5Zn0·92Nb1·5O6·92 pyrochlore ceramics have been investigated. Nickel atoms were inserted into pure samples in accordance to the composition Bi1·5Zn0·92Nb1·5−xNixO6·92−3x/2, with x varying from 0·07 to 0·40. The structural analysis revealed that a single phase of the pyrochlore compound can be obtained for x values of 0·07 and 0·10 only. Further increase in Ni caused the appearance of multiple phases. The optical energy band gaps are determined as 3·30, 3·35 and 3·52 eV for Ni content of 0·00, 0·07 and 0·10 respectively. The temperature dependent electrical resistivity and the frequency dependent capacitance are observed to increase with increasing Ni content. The resonance frequency, which was determined from the capacitance–frequency dependence, was observed to shift from 12·14 to 10·47 kHz as the x values increase from 0·00 to 0·10 respectively.

Production of Anorthite from Kaolinite and CaCO3 via Colemanite

Boron oxide has been found to be useful flux for the preparation of dense anorthite ceramics (CaO.Al 2O3.2SiO 2). Inexpensive starting materials of kaolinite, calcium carbonate and silica were used for anorthite ceramic production. Colemanite (2CaO.3B 2O3.5H 2O) was added into the mixtures and the effects of colemanite upon the transformation towards anorthite and on the densification were investigated between 900-1400 °C. Single phase anorthite ceramic formed at lower temperatures in boron containing mixtures. Boron containing powder compacts were sintered above 90% theoretical density at 1350 °C.

Electrical conductivity and capacitance spectra of Bi1.37Sm0.13Zn0.92Nb1.50O6.92 pyrochlore ceramic in the range of 0–3 GHz

In this work, the electrical properties of samarium-doped bismuth niobium zinc oxide (Sm-doped BZN) pyrochlore ceramics are investigated by means of temperature dependent electrical conductivity and capacitance spectroscopy in the frequency range of 0–3 GHz. It was observed that the novel dielectric Sm-BZN ceramic exhibits a temperature and electric field dependent dielectric breakdown. When measured at 300 K, the breakdown electric field is 1.12 kV/cm and when heated the breakdown temperature is ~ 420 K. The pyrochlore is thermally active above 440 K with conductivity activation energy of 1.37 eV. In addition, the room temperature capacitance spectra reflected a resonance–antiresonance switching property at 53 MHz when subjected to an AC signal of low power of 5 dBm. Furthermore, when the Sm-BZN ceramics are used as microwave cavity and tested in the frequency range of 1.0–3.0 GHz, the cavity behaves as low pass filter with wide tunability up to a frequency of 1.91 GHz. At this frequency it behaves as a band rejection filter that blocks waves of 1.91 GHz and 2.57 GHz frequencies. These properties of the Sm-doped BZN are promising as they indicate the usability of the ceramics in digital electronic circuits as resonant microwave cavities suitable for the production of low pass/rejection band filters.

Electrical characterization of Bi1.50-xYxZn0.92Nb1.5O6.92 varactors

The electrical properties of yttrium doped bismuth zinc niobium oxide (BZN) pyrochlore ceramics are explored by means of temperature dependent electrical conductivity dielectric constant and capacitance spectra in the frequency range of 0–3 GHz. It is observed that the doped BZN exhibit a conductivity type conversion from intrinsic to extrinsic as the doping content increased from 0.04 to 0.06. The thermal energy bandgap of the intrinsic type is 3.45 eV. The pyrochlore is observed to exhibit a dielectric breakdown at 395 K. In addition, a negative capacitance (NC) spectrum with main resonance peak position of 23.2 MHz is detected. The NC effect is ascribed to the increased polarization and the availability of more free carriers in the device. When the NC signal amplitude is attenuated in the range of 0–20 dBm at 50 MHz and 150 MHz, wide tunability is monitored. Such characteristics of the Y-doped BZN are attractive for using them to cancel the positive parasitic capacitance of electronic circuits. The canceling of parasitic capacitance improves the high frequency performance of filter inductors and reduces the common mode noise of the resonance signal.

Dielectric and magnetic properties of YIG/PMMA nanocomposites

Yittrium iron garnet, Y3Fe5O12 (YIG), is a material used widely in electronic devices for the microwave region as well as the magnetic bubble domain-type memories. Yittrium iron garnet (Y3Fe5O12) was produced by mechanochemical synthesis from Y2O3 and Fe2O3 with particle size of around 150 nm. PMMA/YIG composite films were prepared by solution casting method at diffferent concentration (i.e. 10%, 20% and 40%) of YIG filler. Dielectric permitivity of composite materials were studied over a wide a range of frequency and temperature as a function of filler concentration. The electrical properties of composites were explained by in terms of molecular mobility and interfacial polarization.

Infiltration of Al Alloys into MgAl2O4 under Different Atmospheres

The reactions between spinel (MgAl2O4) and Al alloys of different compositions were investigated at temperatures of between 800-1250°C for different times under different atmospheres of air and nitrogen. Although Al metal did not infiltrate into the spinel in ambient atmosphere, oxide growth on the metal surface took place at temperatures of 1250°C depending on the alloy composition and firing time. Spontaneous infiltration of the Al metal into the spinel occured under nitrogen at 900°C. X-ray diffraction analysis revealed that the composite consisted of MgAl2O4, Al, MgO and Al2O3. The resultant microstructure was also investigated by scanning electron microscopy.

Physical properties of neodymium tin oxide pyrochlore ceramics

Abstract In this work, physical properties of neodymium tin oxide pyrochlore ceramics prepared by solid state reaction technique are investigated by means of X-ray diffraction, scanning electron microscopy, ultraviolet-visible light (UV-Vis) spectrophotometry and temperature dependent electrical resistivity measurements. The pyrochlore is observed to have a cubic FCC crystal lattice with lattice parameter of 10.578 Å. The planes of the cubic cell are best oriented in the [2 2 2] direction. From the X-ray, the UV-Vis spectrophotometry and the electrical resistivity data analysis, the grain size, strain, dislocation density, optical and thermal energy band gaps, localized energy band tail states and resistivity activation energies are determined and discussed. The pyrochlore is observed to have an optical energy band gap of ~3.40 eV. This value corresponds to 365 nm UV light spectra which nominates the neodymium tin oxide pyrochlore ceramics for the use as UV sensors.

Production of the novel fibrous structure of poly(ε-caprolactone)/tri-calcium phosphate/hexagonal boron nitride composites for bone tissue engineering

Nanofibrous composites of the poly(ε-caprolactone) (PCL), tricalcium phosphate (TCP), and hexagonal boron nitride (h-BN) with different compositions were manufactured by using an economical and non-complicated method called electrospinning. Produced fibrous structures showed no bead formation and had a clean surface. Characterization of the composites showed that particles were successfully mixed with polymer phase. High cell activity of SaOS-2 cells on the composites was observed with SEM images. In addition, fibrous scaffolds are biocompatible with human bone tissue and are highly degradable.