Fig. 3 shows the XRD patterns of the Zn(OH)2 precipitated
at pH 7 and calcined at various temperatures for 10 min.
Fig. 3(a) indicates that the crystalline phases of the calcined
powders comprise the major phase of Zn(OH)2 and the minor
phase of ZnO. Moreover, Fig. 3(a) also indicates that the
precipitates also contain ZnO as the minor phase. This is
because as part of the coprecipitation process, Zn(OH)2
precipitates dissolve in the supersaturated solution, Zn2+
complex with OH ions, and form Zn(OH)4
2.