Kinetics of growth of submicrometer crystalline lanthanum fluoride particles using the pF-stat method

Abstract

The constant composition method (pF-stat method) was employed to prepare submicrometer-sized (few tens of nanometers to several hundred nanometers), very stable, positively charged LaF₃ particles of narrow size distribution in the acidic region from pH 4 to 4.5. Polarizing microscope pictures (an-isotropic clusters) and dynamic light scattering (DLS) data demonstrate that the submicrometer structure is self-similar and a fractal with the dimension going from D _f = 1.4 to 2.1 (±0.05), i.e. the aggregation process proceeds from diffusion-limited to reaction-limited with increasing supersaturation of the solution. The pF-stat rate in acidic solution obeys first-order kinetics (p = 1.09 ± 0.08). Also the rate of growth from the DLS data, i.e. the slope of the change in the size (normalized median hydrodynamic diameter) with mass increment (which is proportional to time), is about 1; more precisely it increases from 0.85 to 1.05 with increasing supersaturation.