Ferrite apphcations

Ferrites can be classified according to crystal stmcture, ie, cubic vs hexagonal, or magnetic behavior, ie, soft vs hard ferrites. A systematic classification as well as some appHcations ate given in Table 1 (see also Magnetic materials, bulk Magnetic materials, thin film). 

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). 

Ferroxplana offer unique high frequency properties, being appHcable where other high frequency materials such as NiZn ferrites fail (0.1—1 GHz). Some representatives are (17) and (1 )- spite of numerous investigations, appHcation has always remained limited because of the difficult... 

It is possible to systematically alter the net magnetic moment of ferrites by chemical substitutions. A very important industrial appHcation is the increase of the magnetic moment in mixed MnZn-ferrites and NiZn-ferrites. When Zn ions are introduced in Mn-ferrite or Ni-ferrite, these ions prefer to occupy A-sites. Because is nonmagnetic, the A-sublattice magnetization is reduced and consequendy the total net magnetic moment is increased. 

Since the 1960s, the quaUty of M-ferrite manufactured has improved continuously, while the price has decreased considerably. Decisive progress in quahty was obtained by the appHcation of sinter additives (90), the introduction of pressing in a magnetic field (23), and the use of Sr instead of Ba, in combination with a sophisticated appHcation of Si02 (91,92). Important contributions to price reduction came from the development of fast multiple-die... 

Ferrites aHowing for operation at frequencies well above 1 MH2 have also become available, eg, 3F4 and 4F1 (Table 6). Other newer industrial power ferrites are the Siemens-Matsushita N-series (28,97) the TDK PC-series (28,100), and the Thomson B-series (28,103). While moving to higher frequencies, the ferrites have been optimized for different loss contributions, eg, hysteresis losses, eddy current losses, and resonance losses. Loss levels are specified at 100°C because ambient temperature in power appHcations is about 60°C plus an increase caused by internal heat dissipation of about 40°C. 

Duplex stainless steels (ca 4% nickel, 23% chrome) have been identified as having potential appHcation to nitric acid service (75). Because they have a lower nickel and higher chromium content than typical austenitic steels, they provide the ductabdity of austenitic SS and the stress—corrosion cracking resistance of ferritic SS. The higher strength and corrosion resistance of duplex steel offer potential cost advantages as a material of constmction for absorption columns (see CORROSION AND CORROSION CONTROL). 

The most commonly used ferrites, the so-called soft ferrites, are used ia soft magnet and low field telecommunication appHcations, low power... 

Other Metals. Metals such as the austenitic series. Types 301—347, and the ferritic series. Types 409—446, of stainless steels may be enameled, as well as a number of other alloys (17). The metal preparation usually consists of degreasiag and grit blasting. Copper, gold, and silver are also enameled. These metals are usually prepared for appHcation by degreasiag. Copper is pickled usiag either a nitric acid [7697-37-2] or a sulfuric acid [7664-93-9] solution, followed by a dilute nitric acid dip. Silver may be pickled in hot dilute sulfuric acid followed by a dip in a nitric acid solution (18). 

Encinas-BachUlerP, Tascon-GarciaML, Vazquez-Barbado MD, Sanchez-Batanero P (1994) Electroanalytical study of copper and iron compounds in the solid state apphcation to copper ferrite characterization. J Electroanal Chem 367 99-108. 

Barium ferrites do not affect the mechanical properties of natural rubber and hence are useful in magnetic apphcations. Cure rates are increased considerably but ferrites may cause reversion problem. " The magnetic properties increase almost linearly with the amount of ferrite added. 

Iron oxide nanoparticles are undoubtedly one of the most investigated nanoparticles owing to their importance in industrial and medical appUcations. Hematite nanoparticles are comparatively more stable and therefore have wider applications as well. While several methods are available for the synthesis of nanoparticles, the green synthesis routes are preferred, more so iu biological apphcations. It has beeu demoustrated that natural products such as polysaccharides can be employed as effective templates, both through sacrillcial and otherwise routes to generate mono-dispersed nanoparticles of below 20 run. Such methods are easy to adopt for other ferrite nauoparticles as well. Incidentally, some of the polysaccharide methods are facile and possibly simple for rephcation at industrial scales. 

In the majority of apphcations, plasticizers are added in modest quantities most likely because larger additions affect surface properties of products and cause problems related to the hydrophilic nature of plasticizers used. Larger quantities of plasticizers have been added to products such as controlled-release of pharmaceutical tablets, sintered materials produced from ferrites, and water soluble films. 

Gangwal eta . [25] investigated zinc ferrite and zinc ferrite/copper oxide adsorbents for the removal of H2S from coal gas for molten carbonate fuel cell (MCFC) appHcations at 540-800 °C. H2S concentrations are much higher, that is, 13 400 ppmv, and must be below 10 ppmv in the product gas. A typical breakthrough performance was achieved at 600 °C for 3 ppmv, leading to a capacity of 11.8 g of S per 100 g of sorbent Further investigations on improved adsorbents have been reported [26-28]. 

The ferritic-austenitic steels are passive in seawater due to their high chromium content and do not suffer from general corrosion. Their resistance to pitting and crevice corrosion is raised by the molybdenum and nitrogen components. The duplex steels have therefore proved their worth well in a wide range of marine engineering apphcations [131-134]. 

The use of different types of MnZn and NiZn ferrite materials varies with the operating frequency in the apphcation concerned. Figure 4.3-73 and Table 4.3-52 indicate the typical ranges of use and the magnetic properties of characteristic materials. Typically, MnZn ferrites are used in the range of several MHz. Table 4.3-53 hsts the major applications with the perti-... 

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