Solubility Characteristics of Zinc Oxide

Like calcium oxide, zinc oxide readily forms zinc hydroxide in water. Thus, the solubility of zinc hydroxide is more relevant with regard to the formation of zinc ceramics that are formed in an aqueous solution. 

Five different phases of zinc hydroxides have been identified [21]. Amorphous Zn(OH)2 is the most soluble species, while less soluble phases are denoted by Greek letters a, (3, 7 and e with e-Zn(OH)2 being the least soluble phase. The corresponding solubility equations may be derived from first principles, as discussed in Chapter 5, or may simply be reproduced from Ref. [21]  

Corresponding to these three solubility equations, the dissolved ionic concentrations are 

In the equations given above, a stands for the most stable phase e-Zn(OH)2, while b stands for the amorphous phase that is most soluble. 

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As mentioned in Chapter 2, zinc phosphate dental cements were discovered over a century ago, and their development has continued since then [1-9]. A brief history of this development is given in that chapter. For a detailed history of these cements and properties of contemporary formulations, the reader is referred to the book by Wilson and Nicholson [10]. Because, the kinetics of formation of these cements has not been discussed in these earlier publications, we will emphasize it in this chapter and present the earlier work in light of the solubility characteristics of zinc oxide and its products in an acid phosphate solution. 

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