Dielectric properties of strontium titanate filled mullite composites in microwave region

This research was designed to form better dielectric composite material using one steady state dielectric with a good dielectric material. Distinct dielectric composite was successfully produced using locally sourced kaolinite clay. The samples were made using kaolinite as the base matrix and Strontium Titanate (ST) added in varying ratios. Strontium Titanate were synthesized via solid‐state reaction using Strontium Carbonate and rutile Titanium (IV) Oxide with sintering at 1300 °C. Local white kaolinite was used to fuse the barium titanate material in varying weight ratios. The powders were dry‐mixed and made into pellets for calcination at 1000 °C. The dielectric measurements were carried out using the HP 4291B Impedance Analyzer dielectric setup. Three samples were prepared, namely 10%ST, 20%ST and 30%ST. The dielectric measurements were carried out at room temperature. Microwave region measurements showed steady state and linear dielectric relaxation ranging from 7 in the control sample and dropping down to 5 in 30%ST. The responses indicate linear relation between ST addition and microwave region dielectric permittivity

Effect of AgI addition on elastic properties of quaternary tellurite glass systems

A series of quaternary tellurite glasses {[(TeO2)70(B2O3)30] 90[Ag2O]10}100-z{AgI}z with z=5, 8, 10, 13 and 15 mol% were fabricated by rapid quenching technique. Pulse echo technique was employed to detect the longitudinal and shear ultrasonic velocities generated by 5 MHz transducer room temperature. Elastic properties, Poisson’s ratio, micro hardness, softening temperature and Debye temperature calculated from the measured density and ultrasonic velocity were observed to decrease monotonously with the increase of AgI content. This shows that the presence of AgI inside the glass network creates a loose packing structure of the glass network and hence reduces the rigidity and the strength of the glass system

Sintering temperature dependence of room temperature magnetic and dielectric properties of Co0.5Zn0.5Fe2O4 prepared using mechanically alloyed nanoparticles

Co0.5Zn0.5Fe2O4 nanoparticles were prepared using mechanical alloying (MA) and sintering. The crystallite size, coercivity, retentivity and saturation magnetization were also measured. The frequency dependence of dielectric and the magnetic parameters, namely, real permittivity ε′, loss tanget tan δ, real permeability μ′ and loss factor μ″ were measured at room temperature for samples sintered from 600 to 1000 °C, in the frequency range 10 MHz to 1.0 GHz. The results show that the crystallite size of the resulting products ranges between 16 and 67 nm for as-milled sample and the sample sintered at 1000 °C, respectively. The sample sintered at 1000 °C, measured at room temperature exhibited a saturation magnetization of 37 emu g−1. The values of permittivity remain constant within the measured frequency, but vary with sintering temperature. The permeability values, on the other hand however vary with both the sintering temperature and the frequency, thus, the absolute value of the permeability decreased after the natural resonance frequency

X-ray diffraction studies on crystallite size evolution of CoFe2O4 nanoparticles prepared using mechanical alloying and sintering

Nanosized cobalt ferrite spinel particles have been prepared by using mechanically alloyed nanoparticles. The effects of various preparation parameters on the crystallite size of cobalt ferrite which includes milling time; ball-to powder weight ratio (BPR) and sintering temperature, were studied using X-ray diffractometer (XRD). Scherrer's equation was used to study the crystallite size evolution of the as-prepared materials. The results of the as-milled sample revealed that both milling time and BPR plays a role in determining the crystallite size of the milled powder. However, where sintering is involved, the sintering temperature results in grain growth, and thus plays a dominant role in determining the final crystallite size of the samples sintered at higher temperature (above 900 °C). From the vibrating-sample magnetometer (VSM) measurement it was observed that the coercivity of the as-milled samples without sintering is almost negligible, which is a type characteristic of superparamagnetic material. However, for the sintered samples, the saturation increases while coercivity decreases with increases sintering temperature

Effect of moisture content and grain direction on the dielectric properties of rubber wood at low frequencies

Dielectric constant and dielectric loss factor of rubber wood have been studied at different moisture content, grain direction and frequency. Different dielectric dispersion mechanisms are also observed at different ranges of moisture content. The moisture content above the fiber saturation point does not contribute much to the dielectric properties following a single dielectric mechanism. But the moisture content below the fiber saturation point shows considerable effect on the variations of dielectric properties having different dispersion processes at different moisture content ranges. Based on the shape of the curves, five different moisture content ranges have been identified such as 1) 25% and above, 2) 18-25%, 3) 11-17%, 4) 5-10% and 5) below 5%. It may be possible to explain all these dispersion processes by means of dielectric mechanism for dipole, quasi-dc and diffusive processes. Longitudinal direction shows a higher dielectric constant when compared to radial and tangential directions in ovendry condition. This dielectric anisotropy may be attributed to the microscopic, macroscopic and molecular structures of wood

Development of dielectric material with ceramic matrix composite (CMC) produced from kaolinite and CaCu3Ti4O12 (CCTO)

Ceramic matrix composites (CMC) combine reinforcing ceramic phases, CaCu3Ti4O12 (CCTO) with a ceramic matrix, kaolinite to create materials with new and superior properties. 10% and 20% CCTO were prepared by using a conventional solid state reaction method. CMC samples were pre‐sintered at 800 °C and sintered at 1000 °C. The dielectric properties of samples were measured using HP 4192A LF Impedance Analyzer. Microstructures of the samples were observed using an optical microscope. XRD was used to determine the crystalline structure of the samples. The AFM showed the morphology of the samples. The results showed that the dielectric constant and dielectric loss factor of both samples are frequency dependent. At 10 Hz, the dielectric constant is 1011 for both samples. The CMC samples were independent with temperature with low dielectric constant in the frequency range of 104–106 Hz. Since the CMC samples consist of different amount of kaolinite, so each sample exhibit different defect mechanism. Different reaction may occur for different composition of material. The effects of processing conditions on the microstructure and electrical properties of CMC are also discussed