THERMAL-BEHAVIOR OF HYDROTALCITE-LIKE [MG1-XGAX(OH)(2)](CO3)(X 2)CENTER-DOT-MH(2)O AS A FUNCTION OF GALLIUM CONTENT/

The thermal behavior of a series of Ga-substituted hydrotalcites [Mg1- xGax(OH)(2)] (CO3)(x/2). mH(2)O, where x = 0.072-0.35, was examined by means of thermal gravimetric analysis, (TGA), differential thermal an alysis (DTA) and x-ray diffraction (XRD) measurements. The weight loss patterns of Ga-hydrotalcites depend on the Mg/Ga molar ratios. For ex ample, a high [CO3](2-) density in the interlayer region of Ga-rich sa mples (i.e. Mg/Ga = 1.8) makes them more difficult to dehydrate and sl ower to decompose than Ga-poor samples (i.e. Mg/Ga = 12.9). Removal of interlamellar water molecules in Ga-rich hydrotalcites consumes less energy than that in Ga-poor ones. The decomposition stage, regardless of Mg/Ga ratios, takes place at a constant temperature of approximate to 410 K, but this process requires much less energy in Ga-rich (Mg/Ga = 1.8; 22 J g(-1)) than in Ga-poor samples (Mg/Ga = 12.9; 202 J g(-1) ). XRD analysis indicates that the layered structure is destroyed belo w 573 K, and that between 623 and 973 K, Ga-hydrotalcites convert into MgO-like materials, probably substituted by a(3+). Calcination temper atures above 1073 K yield MgO-MgGa2O4 mixtures. (C) 1997 Elsevier Scie nce Ltd.