Spinel Formation from Magnesium Aluminium Double Alkoxides

Abstract

Double alkoxides of the general formula Mg[Al(OR) 42 where R is iso-Pr or sec-Bu were prepared by reacting aluminium and magnesium metals together with the alcohol ROH and purifie5 7 by vacuum distillation.They were characterised by IR, proton and Al NMR spectroscopy and MW determination. A magnesium aluminium double alkoxide was also prepared by treating the commercially available aluminium alkoxide 'Aliso B' [a mixed aluminium (iso-propoxide)(sec-butoxide)] with magnesium and iso-propanol. Treatment of magnesium aluminium double alkoxides with water and an alkanolamine (preferably triet~qnolamine) gives a rigid coherent gel. Viscosity measurements andAl NMR spectroscopy suggest that the double alkoxide does not break down to its constituents during hydrolysis.The air-dried gel was shown by 'XRD to convert quantitatively to spinel on firing to 1500 0 C. The resistance of the double alkoxide moiety to hydrolysis explains the ease of conversion to spinel on firing.The gel has been used to bind alumina and magnesia grain.Gels suitable for binding refractory grain were obtained only when the alkanolamine content corresponded to one alkanolamine group per metal atom. Electron micrographic and XRD studies showed that in fired refractory pieces, the bonding phase was spinel.

Thin Film Deposition By Sol-Gel and CVD Processing of Metal-Organic Precursors

“…However, the extension of this molecular strategy to multicomponent oxides is limited to a few systems (e.g., MgAI 2 0 4 [27], BaTi0 3 [28], LiNb0 3 [29]), mainly due to the (mis)belief that the heterometal molecule would break-down into the homometal constituents during the hydrolysis. The application of molecular routes to multi-metallic ceramics demands well-characterised precursors with metal ratios compatible to the targeted material because the higher level of homogeneity promised by the chemical methods is generally not achievable from a heterogeneous 'precursor cocktail'.…”

“…Stoichiometric MgAIz04 films have been successfully prepared from magnesiumaluminium iso-propoxide containing the appropriate Mg:AI ratio (1 :2) [27]. However, the preparation of transition metal-aluminium, -gallium or -iron spinels is limited to the fusion of the two component oxides [62,63] at high temperatures (1000-1600 0c) or by co-precipitation reactions [64,65], in solution.…”

Studies on the hydrolysis of {Cu[Al(OPr )4]2}, a single source precursor for CuAl2O4 spinel

“…Technologically important multimetallic oxides were synthesized from single source precursors in which the control of stoichiometry and high homogeneity of the final products could easily be achieved [4,5]. The very first use of bimetallic alkoxide, magnesium bis-tetra-alkoxy aluminate, Mg[Al(OR) 4 ] 2 to fabricate the spinel MgAl 2 O 4 was described by Jones et al [6] in 1986. Although double alkoxides of bivalent transition metals with Al (III) represented by the general formula M[Al(OR) 4 ] 2 where (M = Fe, Co, Ni and Cu and R = Me, Et, Pr and Bu) were synthesized by Mehrotra and Singh [7] in 1979, its single crystal X-ray diffraction structure, thermal stability have been reported only very recently by Veith et al [8].…”

Mesoporous spinel MgAl2O4 prepared by in situ modification of boehmite sol particle surface: I Synthesis and characterization of the unsupported membranes

“…In their work Mg(Al(OR) 4 ) 2 is used as the precursor to prepare sol. The synthesis process of the double metal alkoxides is somewhat dangerous because HgCl 2 is used as the catalyst to facilitate the dissolution of aluminum and magnesium metals [4][5][6] and mercury dissolves out after the reaction [7]. As an irresistible trend to develop environment friendly processes in the chemical industry, any contaminative chemicals like mercury should be avoided.…”

“…In addition, the conventional sol-gel process requires a strict stoichiometry between magnesium and aluminum. Sometimes 'modifier', such as triethanolamine is necessary in the hydrolysis and gellation [4].…”