NEW HYDROTALCITE-LIKE COMPOUNDS CONTAINING YTTRIUM

Layered double hydroxides (LDHs) containing Mg2+, Al3+, and Y3+ in the brucite-like layers and with carbonate as counteranion have been prep ared following the coprecipitation method at constant pH. The Al/Y rat io depends on the concentrations in the starting solutions. The crysta llinity of the layered materials decreases as the Al/Y ratio increases , probably due to the distortions introduced by the large difference i n the ionic radii of the cations. On calcination at 750 degrees C MgO (probably containing Al3+ cations) and Y2O3 are formed from the sample richest in Y, while the other samples lead to formation of MgO and pr esumably Al2Y4O9. At 1000 degrees C, MgO, MgAl2O4, and Al2Y4O9 are for med in all cases. Exposure of samples calcined at 750 degrees C in air at room temperature leads to reconstruction of a Mg,Al hydrotalcite a nd segregation of Y-containing phases.