Formation and structure of aluminium alkyl phosphates

Abstract

Aluminium alkyl phosphates (AlAPs) synthesized by the reaction of Al(NO₃)₃·9H₂O with monohexyl, monooctyl or monodecyl phosphates in aqueous media have been characterized by various means. The XRD patterns of the AlAPs showed one strong and two weak diffraction peaks at 2θ < 15°. The plate-like AlAP particles prepared using octyl phosphate gave rise to lattice patterns having uniform alternating spacings of ca. 1.1 and 1.5 nm. When treated at 1000 °C, AlAP samples were converted into tridymite AlPO₄. The Al/P molar ratios of AlAP samples approximated to unity and their chemical formula can be written as (ROPO₃)Al(OH)·1.2H₂O. These facts suggest that the AlAPs are composed of alternating bimolecular layers of alkyl phosphates and a hydrated aluminium phosphate phase.