Ferrites have widely been used in different electrical engineering applications including radio and TV sets as well as carrier telephony as cores of inductors, transformers and so forth, for their good electrical and mechanical properties. However, a substantial amount of foreign exchange is spent every year on the import of either finished ferrite products or raw materials for making these ferrites. The main aim of the present work was to produce different types of ferrites at comparatively low cost with improved electrical and mechanical properties using locally available raw materials.
Three types of ferrites, namely, Manganese-Zinc (Mnx Zn1-x Fe204), Nickel Zinc (Nix Znâ€“x Fe2 04) and Copper-Zinc (Cux Znl-x Fe2 04 ) ferrites with x = 0.66, 0.77, 0.88 and 0.99 were prepared by conventional double sintering method. A locally available low cost iron oxide (Fe2 03 ), containing small amount of Si (0.5%) as an impurity, was used to prepare the ferrites. The advantage of using locally available iron oxide was twofold: Firstly it reduced the process price markedly due to its low cost as compared with the price of commercially available pure ferrites. Secondly, the presence of Si, in the iron oxide, as an impurity was found to improve the properties of the ferrites produced.
Scanning Electron Microscopy (SEM) was used to characterize the microstructure of the ferrite samples. A homogenous and fine grain microstructure was found in all the ferrites studied. The chemical phase analysis carried out by X-Ray powder diffraction (XRD) method confirms the formation of the expected ferrite structure. Lattice parameters, X-ray density and bulk density along with porosity have been investigated to study the effect of composition on magnetic and electrical properties. Lattice parameters show a decreasing trend with increasing Ni and Cu in the composition, whereas an increase with increasing Mn content. Mass density of all the samples was found to increase by increasing x, which in turn decreases the porosity. However, the X-ray density of Ni-Zn and Cu-Zn ferrites was increased with increasing the x content whereas it was decreased in case of Mn-Zn ferrites.
Electrical resistivity of all the ferrite samples was measured and then used to calculate the activation energy and drift mobility. The room temperature resistivity shows an increasing trend with Ni and Mn concentrations while a decrease with increasing Cu content. The temperature dependent dc resistivity was found to decrease with increasing temperature from 303 to 453 K showing a semi conducting behaviour. The mobility showed a direct relation with temperature and inverse relation with resistivity in all the samples. It was observed that the samples having higher values of resistivity also possessed higher activation energies and vice versa.
The Dielectric constant (E') and the dielectric loss tangent (tan 8) were studied for all the ferrite system prepared at different temperatures (25-180 Â°C) and frequencies (100, 300, 500, 700 and 900 kHz). It was found that the values of E' and tan 8 decrease with increasing Ni, and Mn content x, and decreasing Cu content respectively.
The variation of the dielectric constant and dielectric loss tangent as a function of frequency for these series of ferrite system at different temperatures shows that both the dielectric constant and dielectric loss tangent decreases with increasing frequency. The decrease of dielectric constant and dielectric loss tangent with frequency is a normal dielectric behaviour of spinal ferrites
On increasing the temperature, electrical conductivity increases due to the increase in thermally activated drift mobility of electric charge carries according to hopping conduction mechanism. Therefore, the dielectric polarization Increases causing a marked increase in E' and tan 8 as the temperature increases.