Acid-base cements

Acid-base cements. Cement formation involves both acid-base and hydration reactions (Wilson, Paddon Crisp, 1979). These cements form the subject of this book. 

It is better than the Lewis theory for describing acid-base cements, for it avoids the awkwardness that the Lewis definition has with protonic acids. However, as Day Selbin (1969) have observed, the generality of the theory is such that it includes nearly all chemical reactions, so that acid-base reactions could simply be termed chemical reactions . 

The setting reaction for the great majority of acid-base cements takes place in water. (The exceptions based on o-phenols are described in Chapter 9.) This reaction does not usually proceed with formation of a precipitate but rather yields a substance which entrains all of the water used to prepare the original cement paste. Water thus acts as both solvent and component in the formation of these cements. It is also one of the reaction products, being formed in the acid-base reaction as the cements set. 

Water has three possible roles in acid-base cements. First, it acts as the medium for the setting reaction of these materials, and second, it is one of the components of the set cement, actually becoming incorporated into the cement as it hardens. Third, water may act as plasticizer in these cements. All of these roles are reviewed here. 

This chapter is devoted to a miscellaneous group of aqueous acid-base cements that do not fit into other categories. There are numerous cements in this group. Although many are of little practical interest, some are of theoretical interest, while others have considerable potential as sustained-release devices and biomedical materials. Deserving of special mention as biomedical materials of the future are the recently invented polyelectrolyte cements based on poly(vinylphosphonic adds), which are related both to the orthophosphoric acid and poly(alkenoic add) cements. 

Experimental techniques for the study of acid-base cements... 

The senior author first became interested in acid-base cements in 1964 when he undertook to examine the deficiencies of the dental silicate cement with a view to improving performance. At that time there was much concern by both dental surgeon and patient at the failure of this aesthetic material which was used to restore front teeth. Indeed, at the time, one correspondent commenting on this problem to a newspaper remarked that although mankind had solved the problem of nuclear energy the same could not be said of the restoration of front teeth. At the time it was supposed that the dental silicate cement was, as its name implied, a silicate cement which set by the formation of silica gel. Structural studies at the Laboratory of the Government Chemist (LGC) soon proved that this view was incorrect and that the cement set by formation of an amorphous aluminium phosphate salt. Thus we became aware of and intrigued by a class of materials that set by an acid-base reaction. It appeared that there was endless scope for the formulation of novel materials based on this concept. And so it proved. 

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