Effect of Urea on Synthesis of Ceramics Materials by the Modified Combustion Method

The proportion of urea in the modified combustion method to prepare lithium metasilicate (Li₂SiO₃) powders was investigated. Reactions were performed using LiOH:H₂SiO₃:CH₄N₂O in molar ratios of 1:1:1, 1:1:2, 1:1:3, 1:1:4 and 1:1:5 which were heated at 450°C during 5 min. It was found, by X-ray diffraction, that LiOH:H₂SiO₃:CH₄N₂O in the ratio of 1:1:3 was the more adequate molar ratio to produce mainly Li₂SiO₃. It was observed that excess of urea produced mainly silicium dioxide (SiO₂) in coesite phase instead Li₂SiO₃. Thermogravimetric analyses showed that decomposition products of urea, such as biuret, cyanic acid and cyanuric acid, were found in samples prepared with high proportions of urea (1:1:4 and 1:1:5). Carbonates identified by IR spectroscopy were found in samples prepared with LiOH:H₂SiO₃:CH₄N₂O in 1:1:1, 1:1:2, 1:1:3, 1:1:14 and 1:1:5 molar ratios.