Ferrite system

Fig. 8. Composition regions of optimal magnetic properties ia the MnZn ferrite system (33). Values of ia units of Pq.

Figure 5.22 Lattice image of MYMYg intergrowth in the barium ferrite system. (From Anderson Hutchison, 1975.)...

A major use of high-quality pot-core inductors is in combination with capacitors in filter circuits. They were once extensively used in telephone systems but solid state switched systems have replaced them. The soft MnZn and NiZn ferrite systems are dominant for pot-core manufacture, although metal dust cores are used for certain applications. The important design principles can be understood by reference to a simple series LCR circuit to which a sinusoidal voltage U of angular frequency co is applied (Fig. 9.46). The circuit impedance Z = R+](coL - 1/coC) is a minimum when ojZ, = /<<>C. Thus the resonant frequency o0 is given by... 

As expected, the NiZn ferrite system is available for the higher frequencies (up to approximately 5 MHz), whereas for frequencies up to about 100 kHz the MnZn ferrites are favoured because of their higher permeabilities. 

The pellets are then fed onto the sinter strand and are heated by burning blast furnace gas. This ignites the coke and raises the temperature of the solids to about 1280 °C. The limestone is calcined and reacts with silica and alumina in the ore to produce a molten calcium silicate-aluminate-ferrite system, which bonds the iron ore particles and produces strong pellets. 

Fig. 4.27. Temperature dependence of the magnetocrystalline anisotropy constant in the Ni-Zn ferrite system for various compositions. (Adapted from Broese van Groenou, Schulkes Artrtis, 1967.)...

Sek] Sekine, K., Yamaguchi, T., Thermodynamics of Ferrite Systems (in Japanese), Yogyo Kyokai Shi, 87(1009), 443-452 (1979) (Review, Phase Diagram, Phase Relations, Thenno-dyn., 60)... 

Bi-Fe-O ferrite systems, and possibly to layered double hydroxides. 

In actual practice the markers in the spinel phase are found somewhere between the extreme values that correspond to these idealized cases, and several mechanisms can be operative simultaneously. Experiments with diffusion couples of ferrite systems indicated that mechanisms 1 and 4 both actually occur to some degree. In a vacuum, there cannot be oxygen transport through the gas phase, and any oxygen that does form is removed. 

Isothermal transformation map of the austenitic-ferritic system with various cooling curves. (From Boyer, H., Ed. Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, p. 28. Reprinted with permission of ASM International. All rights reserved.)... 

Some power tubes can be operated without the need for a protective ferrite isolator. One example is the cooker magnetron (700 W) used in modern microwave ovens (57). At higher power levels, such as 25 kW, it is more common to employ a protective ferrite device, particularly in the form of a circulator (58), as shown in Figure 3. This results in a power loss equivalent to a few percentage points in system efficiency. The ferrite circulator prevents reflected power from returning to the power tube and instead directs it into an auxiHary dummy load. The pulling of tube frequency is thus minimised. 

This chapter presents detailed and thorough studies of chemical synthesis in three quite different chemical systems zinc ferrite, intermetallic, and metal oxide. In addition to different reaction types (oxide-oxide, metal-metal, and metal oxide), the systems have quite different heats of reaction. The oxide-oxide system has no heat of reaction, while the intermetallic has a significant, but modest, heat of reaction. The metal oxide system has a very large heat of reaction. The various observations appear to be consistent with the proposed conceptual models involving configuration, activation, mixing, and heating required to describe the mechanisms of shock-induced solid state chemistry. 

---