THE CHEMICAL CHARACTERIZATION OF ZIRCONIUM MOLYBDATE GELS

The stability of zirconium molybdate gel is pH dependent and related to its point of zero charge (p.z.c.). The p.z.c. (in log [H+] units) increases with decreasing ionic radius of the alkali metal cation associated with the gel. The stability and p.z.c. of zirconium molybdate gels are determined by potentiometric titration and pH-stat techniques. Incorporation of cerium(IV) in the gel matrix improves the elution properties of the gel. This improvement is due to the interaction between the molybdate moieties and the higher Lewis acidity of the cerium-zirconium oxide substrate compared with the standard hydrous zirconium substrate. Zirconium molybdate gels are used in a new type of technetium-99m generator. Evidence for the proposed mechanism of elution of technetium-99m from the gels is provided by structural information generated from thermogravimetric (TG) and differential thermal analysis (DTA), combined with Fourier transform-infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) spectrometry.