Non-silicate ceramics

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. 

Unlike silicate ceramics, raw materials used for the preparation of non-silicate ceramics are generally synthetic powders and not mixtures of crashed rocks. But these synthetic powders can result from natural products, which the English terminology makes easy to understand by distinguishing between starting materials (for example, alumina powders) and raw materials (bauxite rocks, in this case, whose treatment by the Bayer process yields the alumina powders) [CAS 90],... 

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. 

The bodies under consideration (silicate, oxide or non-oxide ceramic) all take the form of a heterogeneous substance mixture with water as fluid phase. As such they are subject to the following influencing factors during plastic deformation ... 

Another application with growing interest is the use of open-framework materials like zeolites or layered silicates as ceramic precursors. Certainly, silicon or phosphorus nitrides could be an approach to a similar precursor chemistry for non-oxidic ceramic materials. 

Ceramics can be elementary i.e., they may consist of only one element (carbon, for example, can exist in two different ceramic forms, as diamond or graphite), or they can be compounds of different elements. Of technical importance are silicate ceramics, containing silicon oxide (for example, porcelain or mullite), oxide ceramics i.e., compounds of metallic elements with oxygen (for example, aluminium oxide AI2O3, zirconium oxide Zr02, or magnesium oxide MgO), and non-oxide ceramics i. e., oxygen-free compounds like silicon carbide and silicon nitride. 

Though non-exhaustive, this list shows the variety of the products involved. As regards the composition on the one hand, and the raw materials brought into play on the other, a silicate ceramics can be located primarily in a ternary diagram ... 

These capillary effects contribute to the vitrification of silicate ceramics, because the viscous liquid formed by the molten components infiltrates into the interstices between the non-molten particles. 

A. Kioul and L. Mascia, Compatibility of polyimide-silicate ceramers induced by alkoxysilane silane couphng agents , J. Non-crystal Solids 1994, 175, 169. 

It is important for high performance ceramic applications that the ash content of the polymer blend should be low in silicates and alkali metals. For moulding of non-carbide ceramics it is desirable to have a low residual carbon content. 

Silicon-containing ceramics include the oxide materials, silica and the silicates the binary compounds of silicon with non-metals, principally silicon carbide and silicon nitride silicon oxynitride and the sialons main group and transition metal silicides, and, finally, elemental silicon itself. There is a vigorous research activity throughout the world on the preparation of all of these classes of solid silicon compounds by the newer preparative techniques. In this report, we will focus on silicon carbide and silicon nitride. 

Many raw materials for ceramic parts contain days. During densification, the lamellar shape of clay minerals results in a more-or-less defined texture because the foliated silicates tend to orient themselves vertically to the direction of force. Since lamellar particles shrink non-isotropically, such textures may result in high stresses in the sintered part, causing cracking during cooling. The orientation effect also plays a role in... 

---