Compounds Ceramic Materials

Defining what the term ceramic means is not simple, as there is no single definition on which everyone agrees there are in fact various definitions depending on the point of view adopted. We can thus consider the points of view of a historian, a scientist (physicist, chemist, etc.), an engineer or a manufacturer. 

The concept of ceramics is historically related to the concept of terra cotta and pottery, from which the Greek term Kspapoo derives. This vision refers to the soils, the cmshed rocks, that is, the geological materials and it also highlights firing ceramic art is the art of fire, even if the ceramist has his feet in clay... 

The potter chooses suitable soils, primarily clay soils, which in the wet state offer the plasticity required to model them in the desired form cup, vase or statuette. Then the piece is dried and water loss makes it lose its plasticity, but rehydration wottld restore the clay s initial properties. In fact, dried clay is not yet a ceramic, although it is utihzed in the production of radimentary bricks used in very dry countries - like Saharan Africa. It is in fact the firing that causes the irreversible 

Chapter written by Philippe BOCH and Jean-Franpois BAUMARD. 

The identification between ceramic and terra cotta gathers together the basic concepts that we will continue to encounter throughout this book powdery mineral raw materials [RIN 96], the shaping which is made possible by the plasticity of wet clay, the heat treatments which start by drying (reversible dehydration) and continue with firing (irreversible dehydration and permanent physicochemical modifications). We have not yet mentioned in the description a major characteristic that conditions the preparation techniques as well as the uses of ceramics brittleness. The flower pot is hard (it can scratch a metal sheet) but is vulnerable to impact. This brittleness is a hydra with many heads, as it implies  

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S. Hori, Characterization and Processing of CVD Powders for Fabrication of Composite and Compound Ceramics. Materials Research Society of Symposium Proceedings, Vol.155, 1989, pp.3-12. 

Tetraethylene glycol may be used direcdy as a plasticizer or modified by esterification with fatty acids to produce plasticizers (qv). Tetraethylene glycol is used directly to plasticize separation membranes, such as siHcone mbber, poly(vinyl acetate), and ceUulose triacetate. Ceramic materials utilize tetraethylene glycol as plasticizing agents in resistant refractory plastics and molded ceramics. It is also employed to improve the physical properties of cyanoacrylate and polyacrylonitrile adhesives, and is chemically modified to form polyisocyanate, polymethacrylate, and to contain siHcone compounds used for adhesives. 

Beryllium is principally consumed in the metallic form, either as an alloy constituent or as the pure metal. Consequendy, there is no industry associated with beryllium compounds except for beryllium oxide, BeO, which is commercially important as a ceramic material. BeO powder is available at 154/kg in 1991. 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

The deposition of a binary compound can be achieved by a coreduction reaction. In this manner, ceramic materials such as oxides, carbides, nitrides, borides, and silicides can be produced readily and usually more readily than the parent metal. A common example is the deposition of titanium diboride ... 

The number of oxides is large since most metallic elements form stable compounds with oxygen, either as single or mixed oxides. However, the CVD of many of these materials has yet to be investigated and generally this area of CVD has lagged behind the CVD of other ceramic materials, such as metals, carbides, or nitrides. The CVD of oxides has been slower to develop than other thin-film processes, particularly in optical applications where evaporation. 

The CVD of Ceramic Materials Borides, SUicides, III—V Compounds and II—VI Compounds (Chalcogenides)... 

Organometallic polymer precursors offer the potential to manufacture shaped forms of advanced ceramic materials using low temperature processing. Polysilazanes, compounds containing Si-N bonds in the polymer backbone, can be used as precursors to silicon nitride containing ceramic materials. This chapter provides an overview of the general synthetic approaches to polysilazanes with particular emphasis on the synthesis of preceramic polysilazanes. 

This is one of the main purposes of inorganic polymer research —the search for new and useful compounds and materials that combine the properties of polymers with those of ceramics and/or metals. 

Di-t-butyl phosphate complexes of zinc were synthesized as precursors for ceramic material formation. A tetrameric zinc complex was characterized from the treatment of zinc acetate with the phosphate resulting in a compound with a bridging oxo at the center, [Zn4(/i4-0)(di-t-butyl phosphate)6]. In the presence of auxiliary donor ligands such as imidazole or ethylenediamine, monomeric complexes are formed, [Zn(di-t-butyl phosphate)2(imidazole)4]. It is also possible to convert the tetramer into the monomer by treating with a large excess of imidazole.41... 

Organic substances can be identified both as the main constituents of an artwork or a cultural heritage object, and as secondary components, mixed with inorganic compounds. Organic materials can be found in the finish or decoration of the surfaces, or as residues of commodities, such as in ceramic or glass vessels. Moreover, the majority of restoration products applied as consolidants, adhesives, restoration paints and varnishes are of an organic nature. 

Examples of martensitic transformation. This kind of transformation has been observed in a number of substances elements, compounds, alloys, minerals, metallic and ceramic materials. A few examples of systems showing a... 

In cold molding, the compound is compacted in a mold at around room temperature. The compressing operation is similar to that employed in the production of KBr pellets from powdered KBr. The compound generally contains a lot of filler and binder. The compacted material is removed from the mold and placed in an oven where it becomes cross-linked. Ceramic materials are often produced using cold molding. 

The quest for higher transition temperatures in superconductors took a strange turn when ceramic materials, possessing good, room-temperature metallic conductivity, were investigated. A study of simple binary compounds such as ZrN (Tc = 10.7 K), NbC (Tc =... 

In the system Ba(Pb1.xBix)Os, the compound with x = 0.25 must be considered the first discovered ceramic material showing high-temperature superconductivity (7). Structure determinations have been carried out over the entire range of composition (8)-(ll) and the refined parameters are presented in Table 2. Superconductivity in this system exists only for values of x between 0.05 and 0.35. The value of the critical temperature increases with x, reaches a maximum value Tc 13K for x = 0.25, and then decreases. For x > 0.35, the material becomes a semiconductor. 

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