Introduction and Definitions

Because many mono- and oligosaccharides have a sweet taste, carbohydrates of low Mr are often called sugars. 

Of the compounds shown, (1) and (2) are not carbohydrates because they have only one hydroxyl group each (3), (4), and (5) are carbohydrates because they have the general formula (CH20) . and are polyhydroxylic. 

The classification of each of the following monosaccharides is given below the structure. 

Phanes are compounds with at least one aromatic nucleus and at least one bridge 28 Such structures can incorporate a great number of arenes — carbophanes contain carbocycles such as benzene or naphthalene, heterophanes heteroaromatic rings including metallocenes — and a wide variety of bridges spanning the ring (s) in different positions from one to several simple alkylidene residues (e.g. hexamethylene or 

3 If however the Q-tetrahedron (ABYZ) were treated in the usual way for specifying the chirality (by viewing towards the comer with lowest priority and determining the (R) or (S) sequence of the three comers left according to the sequence rule 2)) this might reverse several assignments (as have been deduced so far) and would result in much confusion. 

The term catalyst is often used to encompass both the catalyst precursor and the catalytically active species. A catalyst precursor is the substance added to the reaction, but it may undergo loss of a ligand such as CO or PPh3 before it is available as the catalytically active species. 

Although one tends to associate a catalyst with increasing the rate of a reactirMi, a negative catalyst slows down a reaction. Some reactions are internally catalysed autocatalysis) once the reaction is under way, e.g. in the reaction of [C204] with [Mn04] , the Mn ions formed catalyse the forward reaction. 

In an autocatalytic reaction, one of the products is able to catalyse the reaction. 

Catalysts fall into two categories, homogeneous and heterogeneous, depending on their relationship to the phase of the reaction in which they are involved. 

A catalyst is a substance that alters the rate of a reaction without appearing in any of the products of that reaction it may speed up or slow down a reaction. For a reversible reaction, a catalyst alters the rate at which equilibrium is attained it does not alter the position of equilibrium. 

Consider first the deformation of a perfect elastic solid. The work done on it is stored as energy of deformation and the energy is released completely when the stresses are removed and the original shape is restored. A metal spring approximates to this ideal. In contrast, when a viscous liquid flows, the work done on it by shearing stresses is dissipated as heat. When the stresses causing the flow are removed, the flow ceases and there is no tendency for the liquid to return to its original state. Viscoelastic properties lie somewhere between these two extremes. 

An isotropic perfectly elastic solid obeys equation (6.5) or 

This is essentially the result obtained for one of the simple models for viscoelasticity to be considered below. 

The models will assume linearity, as expressed in equations (7.1) and (7.2). These equations apply only at small strains and considerations in this chapter are restricted to such small strains. It should, however, be noted that real polymers are often non-linear even at small strains. The subject of non-linear viscoelasticity lies outside the scope of this book but is considered in the books referred to as (1) in section 7.7. 

The word ceramics is derived from the Greek keramos, meaning solid materials obtained from the firing of clays. According to a broader modern definition, ceramics are either crystalline or amorphous solid materials involving only ionic, covalent, or iono-covalent chemical bonds between metallic and nonmetallic elements. Well-known examples are silica and silicates, alumina, magnesia, calcia, titania, and zirconia. Despite the fact that, historically, oxides and silicates have been of prominent importance among ceramic materials, modern ceramics also include borides, carbides, silicides, nitrides, phosphides, and sulfides. 

As a general rule ceramic materials can be grouped into three main groups traditional ceramics, refractories and castables, and advanced or engineered ceramics. 

Before describing each class, a description of the most common raw materials used in the manufacture of traditional and advanced ceramics, refractories, and glasses is presented below. 

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