Clay ceramics

Glaze coatings (58) are appHed to dry or bisque-fired clay ceramics to form a strong, impermeable surface that is aesthetically pleasing. Protective ceramic coatings can also be deposited by CVD (68,90). Plasma activated CVD has been used extensively to produce diamond and diamondlike films. Diamond films can also be used to make optical coatings with a tailored refractive index. 

By linking both classifications it ought to be posssible to describe the technical developments in classical ceramics (clay ceramics) for each specific area. In this chapter I have confined myself to a brief description of the history of cultural and technical ceramics. 

In technical ceramics, also called non-clay ceramics, mainly synthetic raw materials are used. Sometimes these are complemented with clay or some naturally occurring silicates provided that these can be mined in an extremely pure form or can be purified simply and cheaply. Silicates can also be made synthetically by melting a mixture of oxides. 

Crushing is mainly applied for clay ceramics, e.g. in the case of chamotte, a baked clay which is sometimes added as a powder to unbaked clay in the manufacture of e.g. bricks. This is done to increase the dimensional stability during the baking process. 

A coating is applied to improve the surface properties. After sintering the surface of a clay ceramic object is dull, chemically instable, not very porous, nor wear resistant and it does not present an aesthetic... 

Westerwald, an area in Germany with lots of ceramics ( ) Ceramic screwdriver ( ) Musical instruments made of clay Ceramic chalk... 

It is very understandable that people know so little about ceramics. Ever since time immemorial, clay has been an important ceramic raw material. Not until approximately 1850 were other (synthetic) raw materials introduced in ceramics. The objects which are made of the latter often have specific properties which clearly differ from those of the clay ceramics and which meet the requirements of the sophisticated high-tech world of the nineties. So ceramics involve much more than simply clay ceramics and are, in my view, well worth writing a book about. 

Ceramics derives its name from the Greek word keramos (potter s clay). Ceramics or potter s clay has been used since prehistoric times to make a variety of objects. 

The Life Cycle of a Natural-Clay Ceramic Piece The Baby Is Born How and why is clay wedged ... 

National Emission Standards for Hazardous Air Pollutants for Clay Ceramics Manufacturing National Emission Standards for Hazardous Air Pollutants Asphalt Processing and Asphalt Roofing Manufacturing... 

Quantitywise clay ceramic products are the industrially more important. 

These process steps are illustrated below in the context of the manufacturing processes of industrially important clay ceramic products. 

The properties of the different clay ceramic products is critically influenced by the relative concentrations of the three main components in their pastes, these being clay (kaolin), quartz and feldspar. Fig. 5.5-2 shows a three component diagram of these ingredients for typical batches of clay ceramic pastes for the manufacture of a number of industrially important products. 

Clay materials impart to moist clay ceramic raw material batches the plasticity important for their processing. Quartz is used as a lean clay and reduces the shrinkage upon firing. The feldspar acts as a flux due to its alkali content. 

Kaolin and clay minerals belong to the large group of layer silicates. Their ability to form plastic pastes with water, endows the batches of clay ceramic products with the plasticity important for their processing. 

The properties of the clay ceramic products vary with the particle size distribution of the raw materials. 

Storage in moist atmospheres produces more plastic clay ceramic pastes... 

Plastic forming is based on the plasticity of water-containing clay ceramic pastes and, in the form of the potter s wheel, is the oldest known sort of forming. This turning of ceramic products can be automated on a large scale using the roller process. 

A new plastic forming process has been developed, injection casting, in which clay ceramic pastes are injected into the mold and further compressed by closing the slightly opened tool. This process can also be used for manufacturing nonrotationally symmetric articles. 

During the firing of clay ceramic products the following physicochemical processes take place ... 

During the firing of clay ceramic pastes a number of physicochemical processes take place, which are important for the mechanical and thermal properties of the final article ... 

Porous clay ceramic products can absorb more than 2% of their weight of water. This group of products includes colored earthenware (pottery) and the, generally white, fine earthenware (see Table 5.5-2). Due to its liquid and gas permeability, fine earthenware can be utilized in the manufacture of ceramic filters and diaphragms. Glazing renders it impermeable and suitable for the manufacture of household utensils, sanitary ware, wall panels and tiles (majolica, faience). 

So-called dental porcelains produced with particularly feldspar-rich mixtures (70 to 90% feldspar, 15 to 25% quartz, 2 to 8% calcite or kaolin) are not really clay ceramic products. Due to the high flux content, a glossy surface is formed upon firing and no glazing is necessary. 

Table 5.5-3. Produclion Statistics for Clay Ceramic Products in the Period 1991 to 1994.

In contrast with clay ceramic products, oxide ceramics consist essentially of a single crystalline phase of a pure high melting point metal oxide. Oxide ceramics are... 

The manufacture of such materials proceeds according to the process steps described in Section 5.5.3. However, in comparison with clay ceramic products a few characteristic chemically determined process modifications have to be taken into consideration ... 

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