Traditional Ceramics and Cements

Glasses and ceramics based on the Al203-based systems have important applications as ceramic materials, optical materials, and biomedical materials. Aluminate materials include alkaline earth aluminates, such as those in the CaO-A Cf system, which are refractory cousins of hydrous Portland cement [1-3]. Calcium aluminates have a role as both traditional ceramic and cement materials and are used for example as refractory cements however, calcium aluminates are also important for more novel applications... 

Part 3 Classes of Materials starts with the selective treatment of metals that are applied as base and alloying elements of metallic materials. The next class of materials discussed are ceramics. Detailed groupings and definitions of technical ceramics are given and traditional ceramics and cements, silicate ceramics, refractory ceramics, oxide ceramics, and nonoxide ceramics are treated. The physical and physicochemical properties of those polymers, copolymers, and polymer blends which are widely used for scientific applications and in industry are described in the next chapter. The last chapter serves as a source of data and commercial product information on glasses as engineering materials of practical importance. 

A ceramic is an inorganic non-metallic solid prepared from powdered materials and can loosely be divided into cement, mortar and concrete, glass and glass ceramics, traditional ceramics, and what may be termed advanced (i.e. high performance, technical, engineering, or fine) ceramics. 

In addition, until the second half of the twentieth century, the term ceramic was related to the traditional clays, that is, pottery, bricks, tiles, and cements and glass however, during the last 50 years, the held of technical ceramics has been rapidly developed, and firmly established. 

Composites are combinations of more than one material or phase. Ceramics are used in many composites, often for reinforcement. For example, one of the reasons a B-2 stealth bomber is stealthy is that it contains over 22 tons of carbon/epoxy composite. In some composites the ceramic is acting as the matrix (ceramic matrix composites or CMCs). An early example of a CMC dating back over 9000 years is brick. These often consisted of a fired clay body reinforced with straw. Clay is an important ceramic and the backbone of the traditional ceramic industry. In concrete, both the matrix (cement) and the reinforcement (aggregate) are ceramics. 

If sufficient liquid is present (on the order of 25-30 vol%), rearrangement of the solid phase coupled with liquid flow can lead to a fully dense material. Such large volume fractions of liquid are commonly used in traditional, clay-based ceramics such as porcelains and in cemented carbides. In the traditional ceramics, the liquid phases are molten silicates that remain as a glassy phase after cooling, giving the fabricated materials a glassy appearance. The ceramics are referred to as vitrified, and the sintering process is referred to as vitrification. 

Traditional ceramics also include the concretes, which are composites consisting of rock, gravel, and sand, bonded together with some type of cement. Typical materials used are Portland cement or one of several polymers. Portland cement concrete and polymer concretes have been discussed in the previous chapter. 

This chapter deals with the preparation of ceramic materials such as pigments by sol-gel methods. Ceramics include a wide range of materials - from pottery to electronic materials. Accordingly, it can be classified into traditional ceramics - materials developed since the early civilizations until 1940 - and advanced ceramics - materials technically developed post-1940. Clay, refractories, glasses, cements, and concretes are considered traditional ceramics, whereas ceramics used in electrical, magnetic, electronic, and optical applications as well as in structural applications at elevated temperatures are called advanced ceramics. Traditional ceramics still constitute a major part of the ceramics industry [1]. 

Since the Earth s cmst is primarily made up of silicates, we can understand why all ceramics that come close, by near or by far, to terra cotta are silicate materials. Silicate ceramics form, in tormage, the majority of the world of ceramics. They are often described as traditional ceramics, a term which we do not endorse because it may be understood as opposed to progress and technical improvements - whereas many silicate ceramics are sophisticated materials - but which is justified by history it was only at the end of the 19 century that non-siUcate ceramics came to the scene, with specific uses that explain their other name, technical ceramics. Our choice here is to use silicate ceramics and non-silicate ceramics , rather than opposing tradition and advanced technology. We may note that almost all industrial glasses and cements are also sihcate compounds. 

In Chapter 1, we recalled the abundance of silicates on the Earth s crust and indicated that they were the basic components of non-metallic inorganic materials glasses, cements and ceramics. We restricted ourselves to ceramics and said that almost all traditional ceramics are sihcate materials. This is not necessarily the case with technical ceramics. For which it is alumina that constitutes the most useful compound and the most widespread. We can say that alumina is for a ceramist what iron is for a metallurgist and, to pursue the analogy further, that the alumina-silica diagram is as important for ceramics as the iron-carbon diagram is for metals. 

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