Ferrites high-density

For the practical use of ferrite it is necessary to get high-density material. In the firing process, the starting compound mixture has to be ferritized and densified by solid -solid and solid-gas reactions. In this process, the value of (5 and the grain size also have to be controlled. For this purpose, a heat-treatment, which was called atmosphere controlled two step firing by Tanaka, was devised, as shown schematically in Fig. 3.12 and in detail in Table 3.1. For reference, the usual heat-treatment for preparation of ferrites is shown in Fig. 3.12(b). The new heat treatment is composed of the following six processes. In process (1), the starting mixed compounds are heated to... 

The thus obtained high-density Mn-Zn ferrite was investigated in detail from the view of physical and mechanical properties, that is, the relationships between the composition of metals (a,) ) and <5 the magnetic properties such as temperature and frequency dependence of initial permeability, magnetic hysteresis loss and disaccommodation and the mechanical properties such as modulus of elasticity, hardness, strength, and workability. Figures 3.13(a) and (b) show the optical micrographs of the samples prepared by the processes depicted in Fig. 3.12(a) and (b), respectively. The density of the sample shown in Fig. 3.13(a) reached up to 99.8 per cent of the theoretical value, whereas the sample shown in Fig. 3.13(b) which was prepared without a densification process, has many voids. 

Kakizaki, K., and Hiratuka, N., Magnetic properties and crystal structures of acicular barium ferrite particles, J. Magn. Soc. Jpn., 22(suppl. SI), 129, 1998. Lemke, J.U., Ultra high density recording with new heads and tapes, IEEE Trans. Magn., 15, 1561, 1979. 

Ni-Zn ferrites have been obtained by freeze-drying a high density with... 

Srinivasan, T. T., Ravindranathan, P., Cross, L. E., Roy, R., Newnham, R., Sankar, S. G. Patil, K. C. (1988). Studies on high density nickel zinc ferrites and its magnetic properties using novel hydrazine precursors. Journal of Applied Physics, 63, 3789-91. 

Magnetic fluids can be used as a high-density solution for the sink-and-float separation of solids in suspension. This separation technique for non-ferrous metals is based on the anomalous viscosity increase of a magnetic suspension as a function of applied field. The magnetic fluid consists typically of magnetite particles with an average diameter of 100 A in water, with 15-25 wt% of ferrite. To prevent particle aggregation, a surfactant such as kerosene and oleic acid, or a polymer is usually... 

Figure 6.27 Density variation in a cross section of manganese ferrite powder compact produced by single-action die pressing from the top. High numbers correspond to low density while low numbers correspond to high density. The numbers are the optical density of the x-ray transmission photographs of the compact. (From Ref 31.)...

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