Studies of Hydrolysis and Polycondensation Process of Al(OBus)3 with and without Si(OEt)4 by Mass Spectrometry

The development of multicomponent oxide-based glasses, homogeneous at molecular leve!, is relevant in many technological fields. In particular, in the last decade extensive work has been done on silica-alumina based materials, since this system can be used in many different types of application, such as semiconductors devices, catalysis, fibers, membranes and reinforced phases for high-temperature composites. The sol-gel process is one of the most used system for producing highly pure and homogeneous materials, using low temperature processing. This chemical route to oxide systems is mainly based on hydrolysis and condensation reactions of metal alkoxides. The stucture of the final ge! is strongly affected by the kinetics of hydrolysis and condensation reactions of the starting compounds. It is evident that the understanding on the mechanisms of hydrolysis and condensation reactions of the different metal alkoxides become essential to better contro I the whole yrocess in order to obtain multicomponent materials with enhanced mechanical, optical and thermal properties. Looking at the interesting resu1ts obtained by mass spectrometry on the initial steps of hydrolysis and condensation reactions of silica and titanium alkoxides, a study on AI(OBuS)3 has been performed using mass spectrometry with different ionization techniques, such as electrospray (ESI), matrix-assisted laser desorptionlionization (MALDI) and laser desorptionlionization (LDI). On the contrary of what observed for Si(OEt)4 and Ti(OBu)4, the direct injection in the ESI source of ethanolic or chloroformic solutions of AI(OBuS)3 do not lead to the detection of Al(OEt)3 molecular ion or to ions originating from hydrolisis and condensation reactions. Only adding chelating agents, i.e. acetylacetone, or complexing agents, i.e. EtO-, peaks corresponding to [AI(acac)2)t and [AI(OEt)4r can be detected. The presence of oligomers with 6 metal atoms are only detected by MALDI and lor LDI. These ionization techniques have been further used for analysing mixed solutions of AI(OBuS)3 and Si(OEt)4 in order to put in evidence the presence of oligomeric species.