Ferrite, magnet cores

Barium carbonate of finely controlled particle size reacts in the soHd state when heated with iron oxide to form barium ferrites. Magnetically aligned barium ferrite [11138-11-7] powder can be pressed and sintered into a hard-core permanent magnet which is used in many types of small motors. Alternatively, ground up magnetic powder can be compounded into plastic strips which are used in a variety of appHances as part of the closure mechanism. 

Vestal, C.R. and Zhang, Z.J. (2003) Synthesis and magnetic characterization of Mn and Co spinel ferrite—silica nanopartides with tunable magnetic core. Nano Letters, 3 (12), 1739-1743. 

The combination of the above factors has rendered the nanocrystalline solution competitive, not only with amorphous Co-based alloys, but also with classical crystalline alloys and ferrites. The consequence is a steadily increasing level of applications in magnetic cores for ground fault interrupters, common mode chokes and high frequency transformers. Fig. 14 shows some typical examples. The worldwide production rate meanwhile approaches an estimated 1000 tons/year, and the trend is increasing. The only drawback of the nanocrystalline material appears to be the embrittlement that occurs upon crystallization, which requires final shape annealing and, thus, restricts application mainly to toroidally wound cores. 

Grasset, F., Labhsetwar, N., Li, D., Park, D.C., Saito, N., Haneda, H., Cador, O., Roisnel, T., Momet, S., Duguet, E., Portier, J., Etoumeau, J. Synthesis and magnetic characterization of zinc ferrite nanoparticles with different environments powder, colloidal solution, and zinc ferrite-silica core-shell nanoparticles. Langmuir 18, 8209-8212 (2002)... 

For precise absolute (not relative) measurements air-core eoil solutions are used, while for the relative measurements, using of eertain ferrite or other magnetic cores can be more efficient (SIGMASCOPE). 

Grasset F., Labhsetwar N., Li D., Park D C., Saito N., Haneda H., Cador O., Roisnel T., Mornet S., Duguet E., Portier J., Etoumeau J., Synthesis and Magnetic Characterization of Zinc Ferrite Nanoparticles with Different Environments Powder, Colloidal Solution and Zinc Ferrite-Silica Core-Shell Nanoparticles. Langmuir, 2002. 18 (21) p. 8209-8216. 

Spinel ferrites, isostmctural with the mineral spinel [1302-67-6] MgAl204, combine interesting soft magnetic properties with a relatively high electrical resistivity. The latter permits low eddy current losses in a-c appHcations, and based on this feature spinel ferrites have largely replaced the iron-based core materials in the r-f range. The main representatives are MnZn-ferrites (frequencies up to about 1 MH2) and NiZn-ferrites (frequencies 1 MHz). 

Soft magnetic materials are characterized by high permeabiUty and low coercivity. There are sis principal groups of commercially important soft magnetic materials iron and low carbon steels, iron—siUcon alloys, iron—aluminum and iron—aluminum—silicon alloys, nickel—iron alloys, iron-cobalt alloys, and ferrites. In addition, iron-boron-based amorphous soft magnetic alloys are commercially available. Some have properties similar to the best grades of the permalloys whereas others exhibit core losses substantially below those of the oriented siUcon steels. Table 1 summarizes the properties of some of these materials. 

In dc magnetic applications, an air-gap is usually required somewhere along the magnetic path of the core. In ferrite cores, the gap is placed in the center-leg of the core. The flux leaves one end of the core and flows towards the opposing end. The flux, though, repels itself and causes the flux lines to bulge out away from the centerline of the core. The presence of an air-gap creates an area... 

Gomes, J.D., Sousa, M.H., Tourinho, F.A. and Aquino, R. da Silva, G.J., Depeyrot, J., Dubois, E., Perzynski, R. (2008) Synthesis of core-shell ferrite nanopartides for ferrofluids chemical and magnetic analysis. Journal of Physical Chemistry C, 112 (16), 6220-6227. 

Magnetite is the ancient lodestone used as an early compass. More recently, ferrites have found use as memory devices in computers, as magnetic particles on recording tapes and as transformer cores. 

Soft ferriles have a slender S-shaped hysteresis loop with low rcntanencc and low ciicreivc force permitting easy magnetization and demagnetization with little magnetic loss. These ferrites are uniquely suited to low-ioss inductor and transformer cores for radio, television, and carrier telephony. 

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