Classification of ceramic materials

WABS = ability to take up water Fig. 5.5 -1. Classification of Ceramic Materials. 

However, considering today s rapid developments in the field of ceramic materials, the question of what ceramics actually are calls for a very well-founded, fine-brush definition. I know of no one who would be better able to provide an answer to that complex question than Hubertus Reh, who, as editor-in-chief of major ceramic trade journals, author of numerous articles, and credentialed cognoscente of the industry, was able to draw on many years of relevant experience for his contribution entitled Current classification of ceramic materials . 

The first classification of ceramic materials was dated by Litzow [4] to around 1800. It was very rudimentary, simply dividing ceramic materials into col-oured/white and porous/dense variants (Fig. 2, page 41). It covered the materials coarse pottery, earthenware, stoneware and porcelain - refractories were not included. 

The past two decades have brought advances in many sectors and led to a much larger number of ceramic products as well as completely new applications, particularly in the technical field. On an initiative within the German Ceramic Society (DKG), professors and other experts reviewed the classification of ceramic materials at the end of 2004. They decided that the structure had been too detailed in some cases whereas it would be sensible make additions in other fields. This applies particularly to electrical ceramics, where the differences between products with active and passive functions are now so great that these are now divided into two main groups. 

Figui 13 1 Classification of ceramic materials on the basis of apphcation. 

A number of new ceramics do not necessarily use clay raw materials as plastic components. This function is met either by suitable organic substances (the so-called plasticizers) or use is made of other forming methods. With these materials, which include in particular the newer types of technical ceramics, the traditional classification of raw materials has lost its significance. 

This entry will be divided into sections covering the classification of ceramics, a brief history of ceramics, raw materials for ceramics, properties and applications of ceramics, processing of ceramics, and a brief commentary on future trends. The field of ceramics is very broad and encompasses not only well-known, conventionally used materials and technology but also much newer compositions, processing methods, and applications. More detailed information on all of these sections is available in printed format and on the web.[ °- "l... 

Refractories represent a broad classification of ceramics characterized by the ability of the materials to withstand high temperatures. These materials are used for steel making, glass melting, and in various chemical processing industries. They are used as containment materials, insulation, and heat and chemical barriers of all kinds. 

The first three sections of this chapter have described the three traditional primary classifications of materials metals, ceramics, and polymers. There is an increasing... 

Functionally graded materials (FGMs) are multifunctional materials, which contain a spatial variation in composition and/or microstructure for the specific purpose of controlling variations in thermal, structural or functional properties. Also in the ceramics composites field, a wide range of functionally graded (FG) ceramics are available. Hence, a possible classification of the different classes is made in this chapter. 

This review is intended to focus on ceramic matrix composite materials. However, the creep models which exist and which will be discussed are generic in the sense that they can apply to materials with polymer, metal or ceramic matrices. Only a case-by-case distinction between linear and nonlinear behavior separates the materials into classes of response. The temperature-dependent issue of whether the fibers creep or do not creep permits further classification. Therefore, in the review of the models, it is more attractive to use a classification scheme which accords with the nature of the material response rather than one which identifies the materials per se. Thus, this review could apply to polymer, metal or ceramic matrix materials equally well. 

The porous structure of ceramic supports and membranes can be first described using the lUPAC classification on porous materials. Thus, macroporous ceramic membranes (pore diameter >50 nm) deposited on ceramic, carbon, or metallic porous supports are used for cross-flow microfiltration. These membranes are obtained by two successive ceramic processing techniques extrusion of ceramic pastes to produce cylindrical-shaped macroporous supports and slip-casting of ceramic powder slurries to obtain the supported microfiltration layer [2]. For ultrafiltration membranes, an additional mesoporous ceramic layer (2 nm<pore diameter <50 nm) is deposited, most often by the solgel process [11]. Ceramic nanofilters are produced in the same way by depositing a very thin microporous membrane (pore diameter <2 nm) on the ultrafiltration layer [4]. Two categories of micropores are distinguished the supermicropores >0.7 nm and the ultramicropores <0.7 nm. 

Within industry and commerce, terms other than the mineral classifications are common. Ball clay is a type of kaolin particularly suited to the manufacture of ceramics in 2001, 35% of the ball clay produced in the US was used for tile manufactoe, 22% for sanitary ware, 14% for pottery and various ceramics, 6% for refractory materials, 7% for other uses, and the remainder was exported. Kaolinite (which is white and soft) is of great importance in the paper industry for coatings and as a filler of the 8.1 Mt produced in the US in 2001, 36% was consumed in... 

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