Acid-base concepts in AB cement chemistry

We now review the various concepts of acids and bases in order to see how appropriate and useful they are in the field of AB cements. 

This definition of acids and bases is of restricted application. The reaction between acids and bases is seen as the combination of hydrogen and hydroxyl ions in aqueous solution to form water. 

An acid is defined as a species that dissociates in aqueous solution to give hydrogen ions and anions, and a base as a species that dissociates in aqueous solution to give hydroxyl ions and cations. 

acids and bases are defined as aqueous solutions of substances and not as the substances themselves. It follows that ionization is a necessary characteristic of Arrhenius acids and bases. Another restriction of this definition is that acid-base behaviour is not recognized in non-aqueous solution. 

The Arrhenius definition is not suitable for AB cements for several reasons. It cannot be applied to zinc oxide eugenol cements, for these are non-aqueous, nor to the metal oxychloride and oxysulphate cements, where the acid component is not a protonic acid. Indeed, the theory is, strictly speaking, not applicable at all to AB cements where the base is not a water-soluble hydroxide but either an insoluble oxide or a silicate. 

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