SCIENTIFIC RESEARCH AND DEVELOPMENT
SINTERING OF NANOSTRUCTURED POWDERS
A. V. Galakhov,
L. V. Vinogradov,
B. I. Antipov,
and A. G. Kolmakov
Translated from Novye Ogneupory, No. 5, pp. 16 – 19, May 2011.
Original article submitted January 19, 2011.
Results are provided for a study of the internal structure of submicron spherical particles in ZrO
sol powders synthesized by ultrasonic atomization pyrolysis. It is shown the sintering potential for these pow-
ders is determined mainly by their internal nanostructural parameters, and not the degree of starting powder
fineness. It is detected that the activity of submicron nanostructured powders is commensurate with the activ-
ity of ultrafine powders. In contrast to the latter, these powders consist of individual particles not joined in sta-
ble multiparticle formations, i.e., agglomerates. This simplifies considerably their practical application with-
out loss of quality for the material obtained.
Keywords: nanopowders, spherical particles, agglomerates, coherent scattering range (CSR), particle size
distribution, intergranular boundaries.
Aerosol powders (the term relates to powders prepared
by atomization pyrolysis) in contrast to those synthesized
traditionally by chemical methods, exhibit one essential fea-
ture. This feature involves the fact that they are dense,
unagglomerated particles, as a rule of regular spherical shape
with a specific choice of synthesis parameters, and they are
polycrystalline formations with a grain size of the order of
several nanometers and a developed network of intraparticle
intergranular boundaries . With comparatively low fine-
ness (average particle size 1 – 3 mm) the unique energy satu-
ration of these polycrystalline particles provides high activity
during sintering . The regular shape and absence of ag-
glomerate formations promotes preparation of dense particle
packing in a powder mold, sintering at comparatively low
temperature without unjustified active development of
recrystallization, leading to undesirable grain growth. The
authors of this work studied the nature of the development of
the internal structure of these powders on their production
properties, in particular on sintering capacity of powder com-
pacts made from them.
Formation of the internal structure in aerosol powders
occurs in the hot zone of a reactor and it depends on a num-
ber of factors, in particular the from of compounds used for
preparation of the working solution, its concentration, hot
zone temperature, and dwell time for powder particles within
it (aerosol feeding rate), etc. In order to prepare powder with
a markedly different internal structure the aerosol powders
used were prepared from solutions of two different wa-
ter-soluble zirconium compounds, i.e., chemically pure grade
zirconium chloride hydrate ZrOCl
O, and analytical
grade zirconium nitrate hydrate ZrO(NO
from the difference in the type of compounds, i.e., the zirco-
nium cation source, all of the rest of the synthesis production
parameters were entirely identical. In another case aqueous
solutions of 0.5-molar concentration were used (for the zir-
conium cation), solutions were prepared in water, the fre-
quency of the ultrasonic aerosol generator was 2.6 MHz, the
working zone temperature was 800°C, and the aerosol flow
rate through the hot zone of the reactor was 10 liter/min.
Pictures of powders are shown in Fig. 1. In both case
powders consisted of spherical particles of regular shape.
Powders prepared from the zirconium chloride solution (sub-
sequently ZrCl powder, see Fig. 1a ), were visually coarser
and less agglomerated than powder prepared from the zirco-
nyl nitrate solution (subsequently ZrN powder, see Fig. 1b ).
Particle size distribution was plotted with use of electron mi-
croscope pictures (Fig. 2). The average particle size calcu-
lated from them was D
= 1.08 mm for ZrCl powder. The
ZrN powder had a smaller average particle size
= 0.79 mm), and here it had a narrower particle size dis
tribution. Whereas the standard deviation for ZrCl powder
s = 0.75 mm was 6 – 9% of the average, for ZrN powder
Refractories and Industrial Ceramics Vol. 52, No. 3, September, 2011
1083-4877/11/05203-0178 © 2011 Springer Science+Business Media, Inc.
A. A. Baikov Institute of Metallurgy and Materials Science, Rus
sian Academy of Sciences, Moscow, Russia.