Showing papers by "Ripudaman Manchanda published in 2008"
TL;DR: In this article, the structure of the dawsonite was reconstructed from thermal decomposition of ammonium carbonate in a parallel-reactor system under mild conditions at pH ∼ 10.
Abstract: The products derived from thermal decomposition of NH4, K, and Na dawsonites have structural memory; that is, the original mineral structure in ammonium form (NH4AlCO3(OH)2) is recovered upon treatment of the oxide in aqueous (NH4)2CO3 solution under mild conditions at pH ∼ 10. The memory effect holds in aluminas doped with transition metals such as chromium or iron. In contrast, treatment of calcined dawsonites in K2CO3 and Na2CO3 solutions leads to bayerite. The mechanism and kinetics of the reconstruction process were investigated by experiments in a parallel-reactor system varying treatment time, temperature, molar (NH4)2CO3/Al2O3 ratio, (NH4)2CO3 concentration, solvent, and dawsonite composition. The samples at different stages of the treatment in ammonium carbonate were characterized by X-ray diffraction, infrared spectroscopy, transmission and scanning electron microscopies, nitrogen adsorption, mercury intrusion porosimetry, and thermogravimetry. The reconstruction of the dawsonite structure from ...
27 citations