Experimental and Monte Carlo simulation: the role of urea in mullite synthesis

Abstract

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(r IOu ) and g(r IOw ,), respectively. The integration of these two correlation functions indicated the presence of four water and two urea molecules in the first Al 3+ coordination shell. The 27 Al nuclear magnetic resonance (NMR) results also indicate the presence of species like [Al(H 2 O) 4 (urea) 2 ] 3+ .