Sol–gel transition study and pyrolysis of alumina-based gels prepared from alumatrane precursor

Abstract

Abstract Alumina gels were prepared by the sol–gel method using alumatrane or tris(alumatranyloxy-i-propyl)amine as precursor synthesised directly from the reaction of inexpensive and readily available compounds, aluminium hydroxide and triisopropanolamine (TIS), via the one step process. Sol–gel process parameters, such as gel time, were correlated to variables of the initial stage of the process, such as pH, temperature of hydrolysis and hydrolysis ratio. The sol–gel transition of alcoholic alumatrane solutions was monitored by multiple waveform rheological measurements. The gel time could be determined from the evolution of the storage (G′) and loss (G″) moduli versus time at different frequencies using the Winter Chambon criterion (convergence of the loss tangents at the gel point). Increasing pH values, hydrolysis ratio and/or temperature accelerated the kinetics of hydrolysis–condensation reactions and thus reduced the gel time. The apparent activation energy of the cross-linking leading to the gelation calculated from the gel times at various temperatures was found to be approximately 139 kJ mol−1 and independent of hydrolysis ratio. Alumina materials prepared from the heat treatment of obtained gel at 500 °C were analysed using X-ray diffraction and the BET method.