ULTRAFINE OXIDE POWDERS PRODUCED BY RAPID THERMAL DECOMPOSITION OF PRECURSORS IN SOLUTION

ABSTRACT

The Rapid Thermal Decomposition of precursors in Solution (RTDS) process is described as an approach to nanoscale particle production. The RTDS method involves a brief (< 2 sec) exposure of an aqueous solution containing dissolved metal oxide precursors to hydrothermal conditions amenable to particle nucleation and growth. Particle growth is terminated by passing the solution through a pressure restrictor and into a cooled collection region. Initial RTDS results involving the production of iron, titanium, and zirconium oxide powders from aqueous solutions are described. Powders generated were characterized using transmission electron microscopy, powder X-ray diffraction, BET surface area analysis, and Mossbauer spectroscopy. Iron oxide (hematite phase) having crystallite sizes ranging from a few nanometers to tens-of-nanometers was produced (rom 0.1 M Fe(NO₃) ₃ and Fe(NH₄)(SO₄) ₂ solutions. Crystallite size in the hematite powders was found to be dependent on the temperature to which the solutions were exposed during RTOS processing. Anatase phase TiO₂ powders having crystallite sizes of 3 to 5 ran were generated from K₂TiO(C₂O₄) ₂solutions, and cubic phase ZrO₂ powders with 3.5 nm crystallites were produced using a solution containing a zirconium (IV) citrate ammonium complex.