Ceramic magnets

Over the past 60 years ceramic magnets have become firmly established as electrical and electronic engineering materials most contain iron as a major constituent and are known collectively as ferrites . 

Fig. 3. Device B is a powerful permanent ceramic magnet (obtained from Texas Magnetics Corp., Garland, Texas) the outer dimensions are the same as those of device A. ...

The sintered magnets are hard and brittle. They can only he machined by the techniques developed for Alnicos, ceramic magnets or semiconductors. They can he sliced with diamond impregnated blades, surface ground with carborundum or diamond grinding wheels, or cut on electric spark-erosion machines (EDM). This must he done in a demagnetized state. 

Table 15.4 Magnetic properties of a number of magnetic ceramics. Magnetic moments are given in Bohr magnetons per formula unit at 0 K...

The two mineral sources for strontium are the sulfate (celes-tite) and carbonate (strontianite). The main use of strontium is as a component in colour television faceplate glass ( 8% SrO is incorporated into the glass) where its function is to stop X-ray emissions from the cathode ray tube (CRT). However, the increasing market for CRT-free flat-screen televisions is having a dramatic effect on the demand for strontium. Other uses of strontium include ferrite ceramic magnets and pyrotechnics (see Flame tests in Section 12.3). 

Like small amphiphile nanotubes [14], block copolymer nanotubes should have potential applications in controlled deUvery and release [97,98], in encapsulation [99], and in nanoelectronics [100] etc. Although there have been reports on laboratory use of block copolymer nanofibers as vehicles for drug delivery [101], as scaffolds for cell growth [88,102], as precursors for ceramic magnetic nanowires [103,104], and as precursors for carbon nanofibers [105,106[, practical applications of block copolymer nanotubes have not been reported. This is probably due to the difficulty in making such structures. Their preparation from the self-assembly of block copolymers and interests from industry will likely change the scenery of nanotube appUca-tions in the futme. 

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