PRECIPITATION PROCESSES FOR THE SYNTHESIS OF NANOSTRUCTURED POWDERS
Olivia A. Graeve
Assistant Professor
Department of Chemical and Metallurgical Engineering
University of Nevada, Reno
1664 N. Virginia Street – Mail Stop 388, Reno, NV 89557, USA
This seminar will present an overview of leading precipitation processes for the synthesis of
nanostructured ceramic and metallic powders, with special emphasis placed on reverse micelle
synthesis for the preparation of oxides and combustion synthesis for the preparation of borides.
Specific examples will include the preparation of yttria-doped zirconia (Y-ZrO2) and lanthanum
hexaboride (LaB6).
For the case of Y-ZrO2, the thermal stability of the synthesized particles will be described.
Transmission electron microscopy and Williamson-Hall analysis from x-ray diffraction have shown
that the crystallite size ranges from 5-50 nm. A detailed study on the level of agglomeration and
the particle size of the nanopowders will be described and corroborated using dynamic light
scattering. Reaction parameters such as precursor concentration, aging time, and water-tosurfactant ratio were varied to optimize the synthesis process. Some of the powders were
subsequently sintered using spark plasma sintering (SPS). Dense compacts of >98% density
were obtained in 20 minutes.
The feasibility of preparing nanocrystalline LaB6 powders via a controlled combustion synthesis
process will also be presented. These powders are extraordinarily strong electron emitters with
applications in micro- and nano-satellite propulsions systems, where they can serve as
substitutes for chemical propellants, such that the electrons being emitted by the material are the
source of propulsion. The synthesis reaction for the preparation of the powders is described
below.

La NO3

3  6 B a  H2NNH2 C  O



 LaB6  x NO2  y CO2  other gases
During this process, controlled amounts of lanthanum nitrate (oxidizer) and amorphous boron
were reacted with carbohydrazide (fuel) in a muffle furnace at 500°C. Some reactions made use
of water for dissolving the reactants and some did not. As the reactants were heated, the oxidizer
and fuel reacted to form a fine violet powder that contains both nanocrystalline LaB 6 and
unreacted boron. The presence of water during the reaction promoted the formation of some
lanthanum borate, which is undesirable; thus, reactions without the use of water were more
aminable for the formation of the LaB6. After synthesis, the unreacted boron was removed from
the powders using a controlled acid wash. The resulting phase-pure and faceted LaB6 powders
were then characterized using x-ray diffraction for phase purity and crystallite size, scanning
electron microscopy for particle morphology, and dynamic light scattering for particle size
distribution.
A short description of the synthesis of metallic iron and copper nanopowders will also be
presented.