A rapid method to obtain nanometric particles of rhabdophane LaPO 4· nH 2O by mechanical milling

Abstract

Rhabdophane-type LaPO 4· nH 2O nanoparticles have been obtained by milling a mixture of La(NO 3) 3·6H 2O and Na 2HPO 4 for only 3 h in a planetary ball mill using a moderate rotating disc speed (350 rpm). As-prepared powders consist basically of needle-like shaped nanometric particles with a high specific surface area (76 m 2/g) and a water content of n ≈ 0.8. According to XRD and infrared spectroscopy, firing this powder sample at temperatures of up to 500 °C produces rhabdophane-type LaPO 4 with different water contents with phase transition to monoclinic monazite taking place between 500 and 600 °C. Samples fired above 600 °C show XRD patterns containing, exclusively, the characteristic reflections of monazite-type LaPO 4 although the IR spectra show the presence of the vibration bands characteristic of the P 2O 7 4− and PO 3 groups. However, at 900 °C the bands corresponding to those groups are very weak. Linear shrinkage curves show the powders reaching full densification at temperatures of ∼1250 °C.