Investigations of a Sodium-Polyacrylate-Containing System Yielding Nanosized Boehmite Particles

The formation of nanosized boehmite particles under hydrothermal conditions from a sodium polyacrylate (NaPa) containing system was studied. Precursor mixtures prior to hydrothermal treatment were in particular investigated by DLS and multinuclear (Al-27 and Na-23) liquid and solid state NMR spectroscopy to get a better understanding of the formation of boehmite particles and the role of the NaPa polymer. The final product was also studied by solid state NMR. Experimental data showed that amorphous particles were first formed for a pH ranging from 9.5 to 10.2 via polycondensation reactions between octahedral species followed by a crystallization step leading to the formation of boehmite particles (pH >= 10.5). It was found that the agglomeration state of the boehmite primary particles formed before hydrothermal treatment is strongly dependent to the pH. After the hydrothermal treatment, the agglomeration state of boehmite particles was limited due to the formation of a complex between the boehmite surface and carboxylate groups of sodium polyacrylate thus preventing particles from coalescence with each other.