Natural Ceramics

Man has been surrounded by ceramics from the very beginning. The natural tendency of humans is to put to use any and all available materials to satisfy their needs. Thus, the earliest humans used the natural ceramics around them—the boulders provided them shelter, and stones were used for defense and hunting. As time passed, man learned to chip rocks to make tools, leading to the evolution of hand-held axes. About 70,000 years ago. 

The Neanderthals disappeared about 35,000-30,000 years ago. Modern man appeared later on, and made advanced tools out of stone, bone, and ivory. A natural ceramic called red ochre was used to cover dead bodies. A later development was the use of pigments obtained by mixing colored soil with water. These were used to decorate the body and paint images. Prehistoric artisans used clay to mold animal images. They found that naturally occurring clay, when mixed with water, could be shaped. 

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Natural ceramic raw materials have the disadvantage that they are not soluble in water and consequently unsuitable for wet chemical analysis. That is why they are first destructed in the laboratory. Destruction means that a substance or a mixture of substances is heated together with a substance or a mixture of substances and as a result the component to be destructed is largely separated into ions and consequently dissolves in water. The destruction method and the substances are specific for the substance undergoing the destruction. Different methods applied to the same substance lead to different results. 

Although naturally occurring ceramic or mineral fibers are not as common as natural polymeric fibers, there are two important examples, asbestos and basalt fibers. Asbestos fiber has some health hazards associated with it which have curbed its use. We provide a summary of these two natural ceramic fibers before describing synthetic ceramic fibers in more detail. 

Since the Bronze Age both natural ceramic raw materials and synthetic raw materials have been used. Today synthetic raw materials are referred to as industrial minerals or specialty chemicals. Natural raw materials are those to which only physical separations are performed (e.g., clay soils from which organic raw materials are floated, feldspar rock ground to a particular size distribution). With this classification, a description of common ceramic raw materials will be given in the next part of this chapter. 

Ceramics have a very long history. Rocks, which are natural ceramic materials, served as the earliest tools. Later, clay vessels dried in the sun or baked in fires served as containers for food and water. These early vessels were crude and quite porous. With the discovery of glazing, which probably occurred about 3000 B.c. in Egypt, pottery became more serviceable as well as more beautiful. Prized porcelain is essentially the same material as crude earthenware, but specially selected clays and glazings are used for porcelain, which is also fired at a very high temperature. 

Ceramics have a very long history. Rcxrks, which are natural ceramic materials, served as the earliest tools. Later, clay vessels dried in the sun or baked... 

Most commercial and natural ceramics contain two or more phases and thus many PBs. 

Due to their chemical nature, ceramics and glasses (bioactive and nonbioactive) have been used in several biomedical applications, in particular for bone replacement, but their brittleness makes them unsuitable for load-bearing applications. 

Plastic natural ceramic raw materials, consisting predominately of kaolinite, illite and/or montmorUlonite, are accompanied by residual quartz, feldspar, mica, and calcite as well as organic residues. In particular, the hmestone content has been used to distinguish between clay (<4 mass% hme), marly day (4—10 mass% lime), clayey marl (10-40 mass% hme), marl (40-75 mass% hme), calcareous marl (75-90 mass% lime), marly hmestone (90-96 mass% hne), and hmestone (>96 mass% hme). Kaolinitic raw materials formed in situ (autochthoneous) are called kadine, while kaolinitic raw materials found in secondary deposits (aUochthone-ous) are called clays. Marl and marly hmestones are important raw materials for Portland cement production (see Section 5.2.1). 

Constructional ceramics (Porcelain/Stoneware/Earthenware) Ceramics—f Natural ceramics (Rocks)... 

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