STUDY OF SODIUM POLYALUMINATE REACTION MECHANISMS
WITH AN AIR ATMOSPHERE
G. B. Tel’nova,
L. I. Shvorneva,
and S. V. Kutsev
Translated from Novye Ogneupory, No. 5, pp. 31 – 41, May, 2012.
Original article submitted December 16, 2011.
X-ray-phase and thermal analysis methods, and also IR-spectrometry are used to study reaction mechanisms
for sodium polyaluminate (SPA) nanopowder and high-temperature ceramic based on sodium b²-alumina
with water vapor and air carbon dioxide. It is shown that with exposure of SPA in a moist air atmosphere as a
result of forming the hydroxonium form of b²alumina (H
O-b²-alumina) and hydroxyl OH
groups, there is
breakdown of the sodium-beta-alumina structure. Features of SPA phase transformations with prolonged stor
age in air at room temperature and heating products of decomposition up to 1200°C are studied. Processes of
beta-alumina structure breakdown are reversible in nature, but in ceramic lead to irreversible changes of sur
face layer composition.
Keywords: ceramic based on sodium beta-alumina (Na-b-alumina), sodium polyaluminate (SPA), plasma-
chemical synthesis, IR-spectra, diffraction patterns.
Ceramics based structurally similar versions of sodium
beta-alumina of hexagonal (b-Al
) and rhombohedral
) symmetry with formulas close to b-NaAl
are used as solid electrolyte with conductiv
ity by sodium ions in batteries and thermo-electrochemical
generators with a sodium anode. In air sodium beta-alumina
reacts with water vapor and carbon dioxide gas with forma
tion at a material surface of sodium carbonate compounds,
which leads to an increase in its resistance.
A study of the stability of sodium polyaluminates (SPA)
in an air atmosphere has been the subject of a number of
works [1 – 6]. With exposure of thin powder particles of
beta-alumina in an atmosphere of moist air or carbon dioxide
gas at the surface of particles there is development of a layer
of sodium carbonate. Its formation is connected with occur
rence at the surface of particles of a volumetric reaction with
participation of a gas phase, within whose process Na
beta-alumina crystal conductivity layers are replaced by
hydroxonium ions H
. According to another opinion
 the substitution reaction for Na
occurs with for
mation of sodium hydroxide by a scheme Na
+ NaOH. Some authors  point to formation of a
layer of hydrocarbonate Na
O. at a ceramic sur
face of sodium b²-alumina (Na-b²-alumina) after exposure
in moist carbon dioxide gas atmosphere. Published sources
point to the chemical nature of breakdown of sodium beta-
alumina and its reaction with water vapor and carbon dioxide
gas from air.
During storage of ceramic solid electrolytes in the open
air only a thin surface layer of ceramic is hydrated, which
leads to an increase in specific resistance in a direction per
pendicular to the material surface. In this case resistance may
be restored to the original value with heating of beta-alumina
in dry air at 600°C . However, the possibility of restoring
material electrophysical properties is determined by the
structural condition of conductivity planes within beta-alu
mina crystals and depends on the degree of breakdown under
the action of water.
The aim of this work is to study mechanisms of SPA re
action with an air atmosphere.
The objects for study were SPA nanopowders prepared
by plasma-chemical synthesis, before and after heat treat
ment in an air atmosphere in the range 1200 – 1300°C, and
also ceramic specimens based on sodium beta-alumina
freshly prepared and after prolonged storage in an air atmo
sphere (in sealed polyethylene packages or in a dessicator).
The procedure for preparing SPA nanopowders in binary
Refractories and Industrial Ceramics Vol. 53, No. 3, September, 2012
1083-4877/12/05303-0162 © 2012 Springer Science+Business Media New York