Papers by Keyword: Hexaferrites

Abstract: Sintering aids play a crucial role in enhancing the properties of various ceramics, offering benefits such as increased density, lowered sintering temperatures, and changes in material electrical characteristics. This study focuses on investigating the impact of 3 wt.% additions of Bi₂O₃, B₂O₃, and V₂O₅ on the structural, morphological, and electrical properties of hexaferrite SrAlFe₁₁O₁₉ ceramics, known for their significance in microwave applications. Obtained by conventional solid-state synthesis, ceramic samples were subjected to X-ray diffraction (XRD) analysis, Raman spectroscopy, scanning electron microscopy (SEM), and resistivity measurements. Results revealed that the addition of Bi₂O₃ and V₂O₅ effectively reduced porosity in hexaferrite ceramics, which can potentially increase the magnetization values of ferrite material. Notably, the sample with 3 wt.% of B₂O₃ exhibited the highest resistivity, reaching 1.9·10⁷ Ω·cm. These findings suggest that incorporating specific sintering aids can help in achieving controlled conductivity and magnetization in hexaferrite ceramics, which is particularly beneficial for microwave components like inductors, antenna substrates, and circulators.

Abstract: Two-layered microwave absorbers are designed for the achievement of low reflection coefficient for wide angles of oblique incidence at the frequency of intelligent transport system (5.9 GHz). Magnetic composite sheets were fabricated with carbonyl iron (CI) and Co₂Z hexaferrite particles in rubber matrix. On the basis of transmission line theory, reflection loss has been calculated with variation of incident angles for both transverse electric (TE) and transverse magnetic (TM) polarization. The minimum reflection loss (less than-20 dB) is predicted at 5.9 GHz for the laminated composites of Co₂Z/CI. At the optimum thickness of the composite layers, a low value of reflection loss (less than-10 dB) is predicted for wide incidence angles up to 60°. The two-layer composites laminate can be proposed as the high potential microwave absorbers for improvement of electromagnetic environment in ITS operation.

Abstract: The Co2Z ferrites noise suppression sheet was prepared by tape casting. Its microstructural characterization was performed by electron microscopy and noise suppression effect was measured by a microstrip line method. Results indicate that as the sinter temperature increases, the imaginary permeability increases leading to the enhancement of the suppression capability, and the thickness of noise suppression sheets also contribute to the noise suppression capability.

Abstract: Since the introduction of Electroless (EL) coating in 1946 by Brenner and Riddle, the process has been the subject of steady growth. It is one of the most elegant methods available for the production of alloy coatings on surface. The technique involves the autocatalytic reduction, at the substrate/solution interface, of cations by EL bath released from suitable chemical reducing agents. EL coating technique is simple one, as can be manifested just by controlling pH and temperature of the coating bath. Such coatings are reported to provide excellent physical and mechanical properties. The electroless coatings are being studied at Indian Institute of Technology Roorkee since 1985. The structural and morphological behavior of Ni-P coatings for different phosphorous contents has been extensively studied. Sub-micron size coating islands and their transformations have been deduced. The metallography studies using hot stage within TEM to follow the phase transformations occurring at various temperatures have been studied for Ni-B EL coatings. The realization of mechanical bonding along with chemical bonding between EL coating and the substrate has been explained by coated copper on ceramic powder. As a forward step towards composite coatings, Ni-P-C, Ni-P-Al₂O₃, Ni-P-ZrO₂ has been developed by EL co-deposition technique. Ag-graphite coatings produced by EL technique exhibits nearly five times higher wear resistance and nearly two times better corrosion resistance apart from a good electrical conductor. The tribological behavior of electroless Ni-P-X and Ni-P coatings on steel and aluminium substrates in different conditions i.e., as coated, heat treated at various temperatures at different extents of time with different normal loads, have been studied in terms of dry sliding friction and wear against counter face of case hardened steel. In Ni-P-X nanocoating (X= ZrO₂-Al₂O₃-Al₃Zr), X has been produced in-situ and are of nanosize particles. Such coating could be done on carbon fibre of 7µ diameter uniformly. Ni-P-ferrite nanocoatings with thickness less than nearly 1mm thick, is exhibiting good absorption of microwave in the range of 12-18 GHz which can be exploited for radar applications. Micro-thickness coatings are paying ways to nanocoatings. Nanocoatings are the coatings in which either the thickness of the coating is in nanolevel or second phase that dispersed in the coat matrix is of nanosize. To further explore the field of EL nanocomposite coatings, now days, a work on EL Ni-P-ZnO, TiO₂, Al₂O₃, ZrO₂ and Ni-B-ZrO₂ for its mechanical properties has been carried out.

Abstract: This paper attempts to provide a historical survey of structure of various types of hexaferrites. It provides information about synthesis, characterization, structural, magnetic and dielectric properties of Y-type hexagonal ferrites using various chemical routes. We have prepared a series of cobalt doped Sr₂Cu_2-xCo_xFe₁₂O₂₂ (x = 0.0 to 1.0) hexaferrites using a wet chemical co-precipitation technique. The prepared hexaferrite precursors were calcined at 950 °C for 4 hours in a furnace and slowly cooled to room temperature. The crystal structure of Y-type hexaferrites is rather complicated. The chemical and structural changes were examined in detail by X-ray diffraction (XRD), Differential scanning calorimetry (DSC), Scanning electron microscopy (SEM), and Fourier transform infra-red (FTIR) spectroscopy. X-ray diffraction studies showed that sintering temperature as low as 950°C was sufficient to produce a single-phase Y-type hexaferrite material. The dielectric measurements were carried out over the frequency range of 100 Hz to 2 MHz at room temperature using an LCR meter to study the variation of dielectric constant and loss tangent with frequency. The magnetic properties of hexaferrite samples were investigated using a vibration sample magnetometer (VSM), and a superconducting quantum interference device (SQUID) magnetometer in the temperature range 30K to 200K. A change from ferromagnetic state to super paramagnetic state has been observed in Co doped Sr₂Cu_2-xCo_xFe₁₂O₂₂ (x= 0.6 to 1.0) hexaferrite. The novel applications of all types of hexaferrite materials have been described.