Growth mechanism of lanthanum phosphate particles by continuous precipitation

Lanthanum phosphate, a matrix material of green phosphor, was synthesized by using a T-shaped mixer-type tubular reactor which enabled continuous precipitation of the particles having a uniform diameter. Effects of precursor concentrations and residence time on the yield, number density, diameter, and aspect ratio of particles were investigated for discussing the particle growth mechanism. Particularly, in order to observe the initial stage of particle growth, the residence time was varied over six orders ranging from 0.4 ms to 120 s by employing tubes of 250μm in inner diameter and a newly developed fast particle sampling device. The lanthanum phosphate yield was proportional to the concentration product of the precursors, lanthanum ion and dihydrogen phosphate ion, at the inlet of the reactor, while the number density of the particles was proportional to the 2.3th power of the precursor concentration product. The particles formation was practically completed within 0.01 s. Then, the particles grew slowly up to a few micrometers in diameter by growth of radiating acicular crystallites.