Sol-gel preparation of transition metal, lanthanide, and actinide silicate glasses

Binary transition metal (Cr(III), (VI), Mn(II),(III) and Ni(II)), lanthanide (Pr(III), Tb(III), Dy(III) and Er(III)) and actinide (U(VI) and Th(IV)) silicated glasses have been obtained by sol-gel methods starting with various metal sources and TEOS (tetraethoxysilane). Metal carbonates were used for the transition metal and lanthanide silicate glasses, and metal oxide or hydroxide was used for the actinide silicate glasses. Expressed in the form xMaOb· (1 -x)SiO2, the glasses have compositions in the range x = 0.0012-0.0562 (Cr, Mn and Ni), x = 0.009-0.052 (Pr, Tb, Dy and Er) and x = 0.0017-0.0468 (U and Th) or up to about 23 weight percent rare earth oxide as determined by electron microprobe. The glasses were produced by densification at temperature of 600-800 degree C. Partial crystallization of uranium silicate occurs on heating at 700 degree C or above. The oxidative stabilities of lanthanide and actinide ions were high enough for them to withstand the drying and densifying stages of the gel to glass transformation without change in oxidation state, but the transition metal ions presented a more complicated situation, because of their accessible oxidation states, coordination numbers and geometries. The infrared and near infrared spectra were obtained to probe the OH content and the network formation. The ultraviolet - visible - near infrared spectra of gels and glasses were used to probe the oxidation states and coordination of the metal ion, and were interpreted in terms on ligand field theory. The magnetic susceptibilities supported the results of the absorption spectral studies. All glasses were amorphous by both x-ray diffraction and electron microprobe measurement, and free of chlorine to within the limit of the microprobe sensitivity