A rapid method to obtain nanometric particles of rhabdophane LaPO4·nH2O by mechanical milling

Rhabdophane-type LaPO4·nH2O nanoparticles have been obtained by milling a mixture of La(NO3)3·6H2O and Na2HPO4 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 m2/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 LaPO4 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 LaPO4 although the IR spectra show the presence of the vibration bands characteristic of the P2O74− and PO3 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.