K. Praveena

Development of nanocrystalline Mn–Zn ferrites for forward type DC–DC converter for switching mode power supplies

Abstract Nanocrystalline Mn–Zn ferrites have been successfully synthesised using the microwave–hydrothermal method for high frequency applications. The nanopowders were characterised using X-ray diffraction (XRD) and transmission electron microscopy (TEM). They were annealed using the microwave sintering method at 900°C for 20 min. The frequency dependence of the dielectric constant ϵ′ and and the initial permeability μ i were measured in the range 10 Hz to 1·3 GHz. The saturation magnetisation M s and coercive force H c were obtained using a vibration sample magnetometer (VSM) in the field of 20 kOe. The total power loss was measured in the range of 100 kHz to 1 MHz with a flux density of 50 mT on the annealed samples. Conductor-embedded ferrite transformers were fabricated and the output power P o and efficiency η were measured; 80% efficiency was obtained for a forward-type multilayered transformer.

Fabrication of dc–dc converter using nanocrystalline Mn–Zn ferrites

Abstract The microwave–hydrothermal method has been successfully used for synthesis of nanocrystalline Mn–Zn ferrites which are used for high frequency applications. The nanopowders were characterised using X-ray diffraction and TEM. The nanopowders were annealed using microwaves at 600°C/10 min. The frequency dependence of dielectric constant ϵ′ was measured in the range from 10 Hz to 1·3 GHz, and initial permeability μ i was measured in the range from 10 Hz to 1 MHz. The total power loss was measured at 100 kHz and 200 mT on the annealed samples. Conductor embedded ferrite transformers were fabricated, and output power P o, efficiency η and temperature increase ΔT were measured at sinusoidal voltage of 25 V with frequency 1 MHz. The transformer efficiency η was found to be high, and surface rise of temperature ΔT is very low.

DIELECTRIC AND MAGNETIC PROPERTIES OF BaTiO3+MgCuZnFe2O4 NANOCOMPOSITES

Nanocrystalline MgCuZnFe2O4 and BaTiO3 powders were synthesized using the microwave hydrothermal (M-H) method at 160°C for 45 min for the preparation of xBaTiO3+(1-x)MgCuZnFe2O4. The nanopowders were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The particle size of the powders was found to be ~30 and ~40 nm for MgCuZnFe2O4 and BaTiO3, respectively. The nanopowders were mixed at different weight percentages and densified at 910°C for 30 min using the microwave sintering method. The sintered composites were characterized using XRD and scanning electron microscopy (SEM). The density of the composites varies 93–96% of theoretical density. The density of the present composites increases as the weight percentage of BaTiO3 content increases. The frequency variation of dielectric constant (e), dissipation factor (D), initial permeability (μi) and quality factor (Q) were measured from 1 kHz to 1 MHz.

Structural and magnetic properties of nanocrystalline Y3Fe5O12 using co-precipitation method

The Y3Fe5O12 (YIG) nanopowders were synthesized using Co-precipitation method. The single phase YIG nano powders are synthesized at a low sintering temperature of 800°C and the grain size is found to be close to the critical diameter for the single domain to multidomain crossover. The values of Ms = 20emu/g and Hc= 76Oe were observed for the sample sintered at 800°C.

Microwave-Hydrothermal Synthesis of Ni0.53Cu0.12Zn0.35Fe2O4/SiO2 Nanocomposites for MLCI

The nanocomposites of NiCuZnFe2O4-SiO2 were prepared using Microwave-Hydrothermal method at 160°C/45 min.The as-synthesized powders were characterized using X-ray diffraction and Transmission Electron Microscope (TEM).The average particle size of the powders were found to be ∼20 nm.The powders were densified at 900°C/30 min using Microwave sintering method. The sintered composite samples were characterized using XRD and Scanning Electron Microscopy (SEM). Crystallite size of the ferrites decreases with an increase of SiO2 content. The density of the composites varies of 93–98% of theoretical density. The densities of the present composites were increasing with the addition of SiO2. The bulk densities of the present composites were increasing with the addition of SiO2. The structural changes in these samples were characterized using Fourier Transform Infrared Spectrometer (FTIR) in the 400–4000 cm−1. The bands in the range of 580–880 cm−1 show a slight increase in intensity, which could be ascribed to the enhanced interactions between the NiCuZnFe2O4 clusters and silica matrix. The resistivity of the sintered samples was increased with an addition of ferrite content. The real and imaginary parts of permittivity and permeability were measured in the frequency range of 1 MHz–1.8 GHz.The addition of SiO2 alters the values of dielectric constant and permeability which is useful to the Multilayer Chip Inductors (MLCI) fabrication.

Ultrasonic studies of zeolites during dehydration

Abstract The synthetic zeolites of the heulandite group were prepared using the microwave hydrothermal method at 120°C for 30 min. The powders were characterised using X‐ray diffraction. The zeolites were annealed at 60, 80 and 100°C for 1 h. Dehydration studies were conducted on prepared zelolite in the temperature range 300–800 K using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A conventional ultrasonic pulse transmission technique was used to measure the longitudinal ultrasonic velocity and attenuation at 1 MHz in the temperature range 300–500 K. The accuracy of ultrasonic velocities and attenuation measurements was 0·01 and 0·2% respectively. The observed ultrasonic velocity changes were compared with FTIR, DSC and TGA studies, and it was found that the one can study dehydration studies in zeolites by carrying out ultrasonic studies.