Magnetic ceramics applications

Many ceramic applications are high value and small volume, so energy expenditure is high. Ferroelectric magnets, electronic substrates, electrooptics, abrasives such as silicon carbide and diamond, are examples. Diamond is found naturally, and made synthetically by the General Electric Company at high pressure and temperature. Synthetic diamonds for abrasives require less energy to make than the value in Table 4 nevertheless, the market is carefully divided between natural and synthetic diamonds. 

Finally, the combination of dendrimers and organometallic entities as fundamental building blocks affords an opportunity to construct an infinite variety of organometallic starburst polymeric superstructures of nanoscopic, microscopic, and even macroscopic dimensions. These may represent a promising class of organometallic materials due to their specific properties, and potential applications as magnetic ceramic precursors, nonlinear optical materials, and liquid crystal devices in nanoscale technology. 

Magnetic ceramics, or ferrites, are a very well-established group of magnetic materials. Research activity on ferrites, especially intense in the last 50 years, has led to the establishment of many theories and models additional to or complementing those obtained from research on metallic materials. Magnetic ceramics participate in virtually every application area in some cases, there are no other practical alternative materials. 

Magnetic ceramics are well established, but improvements and innovations continue to take place many new and exciting applications, theories and preparation technologies are currently under development. For instance, at the last scientific meeting devoted entirely to ferrites (held every four years), the 6th International Conference on Ferrites, Japan, October 1992, more than 550 research papers were presented by some 1159 authors. 

In this book, an attempt is made to provide an overview of the science of magnetic ceramics. Chemical aspects are covered in terms of synthetic methods and crystallography. Physics is introduced to provide a theoretical basis to magnetism, which is necessary to interpret the property measurements. Materials science links together physics and chemistry and, in addition, provides the framework for a scientific understanding of fabrication and testing, leading to applications. 

Magnetic ceramics represent an important fraction of the magnetic industry in the US, an estimated 40% of the total hard magnetic materials market value is dominated by ferrites, and in spite of the continuous development of new materials, ferrite consumption is still growing. In soft material applications, ferrites participate with an estimated 20% of the market value. In 1990, the estimated world production was 159 500 metric tons of soft ferrites, and 431 100 metric tons of hard ferrites (Ruthner, 1989). In addition to the versatility of ferrites, there are two essential factors which explain this success the low electrical conductivity, and the low production cost. The market value of ferrites ( 3/kg) is very low compared with other electroceramics 33/kg for varistors, 330/kg for thermistors and 1100/kg for ceramic capacitors (Cantagrel, 1986). 

Magnetic ceramics are used in a number of applications such as radar-signal absorbers, magnetic printers, magnetic levitation, lithiated materials for ionic conductivity, etc. A brief description of these applications is given... 

The book corresponds to a final-year undergraduate or graduate level in solid-state chemistry, solid-state physics, or materials science, but is expected to be useful also for the researcher specialising in other areas who is interested in a basic overview of magnetic ceramics. It is hoped, additionally, that it will be helpful for the development engineer concerned with the science of ferrites which underpins their applications. 

In the context of magnetic ceramics, Ni-Zn ferrite awakens much interest of scientific community for its high permeability and high resistivity. This fact constitutes a reason for the application of this material in microwave devices. This absorption capacity may be generated or potentiated by changing material magnetic and dielectric properties. 

The major ceramic applications for spinels are the magnetic ferrospinels (ferrites), chromite brick and spinel colors (see table). Magnetic recording tape coated with a-CrjOj is a relatively recent development. Also used as a porous protective coating in oxygen sensors for automotive emission controls. 

XPS has been used in almost every area in which the properties of surfaces are important. The most prominent areas can be deduced from conferences on surface analysis, especially from ECASIA, which is held every two years. These areas are adhesion, biomaterials, catalysis, ceramics and glasses, corrosion, environmental problems, magnetic materials, metals, micro- and optoelectronics, nanomaterials, polymers and composite materials, superconductors, thin films and coatings, and tribology and wear. The contributions to these conferences are also representative of actual surface-analytical problems and studies [2.33 a,b]. A few examples from the areas mentioned above are given below more comprehensive discussions of the applications of XPS are given elsewhere [1.1,1.3-1.9, 2.34—2.39]. 

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