SYNTHESIS OF A DOUBLE ALKOXIDE PRECURSOR TO SPINEL (MGAL2O4) DIRECTLYFROM AL(OH)(3), MGO, AND TRIETHANOLAMINE AND ITS PYROLYTIC TRANSFORMATION TO SPINEL

Reaction of AI(OH)(3) and MgO or Mg(OH)(2) with triethanolamine [TEA, N(CH2CH2OH)(3)] in ethylene glycol (EG) provides, in one step, access to a polymer-like precursor to spinel. On the basis of high-resolution mass spectroscopy, chemical analysis and Al-27 solution NMR, the prec ursor appears to be a trimetallic double alkoxide consisting of two fo ur-coordinate TEAA1 (alumatrane) moieties linked via a bridging TEA gr oup that enfolds the Mg cation. The Al-27 NMR shows only tetracoordina te Al centers (64.8 ppm). The same compound can be prepared stepwise b y reaction of tetrameric alumatrane, (TEAAl)(4), with Mg and TEA. Prod uct evolution upon pyrolysis was followed as a function of temperature using TGA, DTA, XRD, and diffuse reflectance infrared spectroscopy (D RIFTS). Pyrolysis at 700 degrees C for 2 h in air appears to produce a gamma-Al2O3-MgAl2O4 solid solution and a small amount(<5 wt %, by TGA ) of X-ray amorphous MgCO3. Transformation of the solid solution to pu re spinel is a function of pyrolysis temperature and time, with only s pinel evident in the XRD data, after pyrolysis at 1200 degrees C for 2 h. BET analysis of the pyrolysis products gave surface areas as cente red around 10 and 60 Angstrom, accounting for the majority of the surf ace area. The powder morphology was briefly examined using SEM.