Experimental and monte Carlo simulation: The role of urea in mullite synthesis

Abstract

Mullite was synthesized by a sol-gel process employing aqueous solution of silicic acid, aluminum nitrate and urea in high concentration (9 mol/l). t-Mullite crystallizes at temperatures around 1050°C, the fraction of the spinel phase formed was small and the apparent activation energy obtained by fitting the XRD results with the JMAK model was (770±4) kJ mol-1. Monte Carlo simulations were performed to investigate the site-site correlation function for ion (I)-urea (Ou) and ion (I)-water (Ow) interactions, g(rlOu) and g(rlOw,), respectively. The integration of these two correlation functions indicated the presence of four water and two urea molecules in the first Al3+ coordination shell. The 27Al nuclear magnetic resonance (NMR) results also indicate the presence of species like [Al(H2O)4(urea)2]3+. © 2001 Elsevier Science Ltd. All rights reserved.

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