INTERACTION BETWEEN ALUMINUM NITRIDE-BASED COMPOSITE
MATERIALS AND A CaCl
– KCl EUTECTIC MOLTEN SALT SOLUTION
L. B. Khoroshavin,
A. R. Beketov,
D. A. Beketov,
Yu. P. Zaikov,
and V. V. Chebykin
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 10, pp. 11 – 17, October, 2002.
The interaction between composite materials based on aluminum nitride and a phosphate binder (PB) and a
– KCl molten salt solution is studied as a function of time (10 – 220 h) by a gravimetric method. The
test specimens studied were sintered (AlN + PB)-based composite, hot-pressed Y
nitride, graphite, and (AlN + PB)-coated graphite. The concentration of aluminum and phosphor in the molten
phase tend to increase with time; presumably, Al and P occur in solution in the form of calcium aluminates,
phosphates, or alumophosphates. Of the two processes — dissolution of the phosphate binder and oxidation of
the aluminum nitride matrix — the former is prevailing.
Composite materials based on aluminum nitride can be a
good choice for large-scale applications as structural materi-
als and protective coatings in various high-temperature elec-
trochemical processes, in particular, in the electrolytic pro-
duction and refining of magnesium, calcium, aluminum, and
other metals. Therefore knowledge of the interaction of these
materials with aggressive media is of significant practical
importance. Our goal in the present work was to study the re-
sistance of a number of aluminum nitride-based composites
exposed to a molted chloride electrolyte in air. The interac-
tion between composite materials and molten salts was stud
ied at 1133 – 1153 K over time intervals of 12 to 220 h.
The electrolyte was an eutectic mixture of 73.5 mol.%
and 26.5 mol.% KCl with a melting point of 913 K.
The salt mixture was prepared using reagents of grade “pure”
) and “chemically pure” (KCl).
Because of the high hygroscopicity of calcium chloride
and its propensity for hydrolysis, the molten mixture con
tained a minor amount (0.5 – 1 mol.%) of dissolved calcium
The following composite materials were studied for in
teraction with the molten salt mixture:
(1) composite material based on aluminum nitride and a
phosphate binder (AlN + PB) sintered at 1273 K, with a po
rosity of 25 – 30%;
(2) hot-pressed (HP) aluminum nitride (porosity 6%)
doped with yttrium oxide (0.2 wt.%);
(3) ÉG-0-grade graphite with a composite coating based
on aluminum nitride and a phosphate binder;
(4) ÉG-0-grade graphite.
Graphite materials with a composite coating based on
aluminum nitride and a phosphate binder were also studied
for resistance, kept half-immersed in molten salt under an at-
mosphere of chlorine.
Compact specimens of AlN + 0.2 wt.% Y
molded by hot pressing on a UGP-1 computer-controlled,
automated general-purpose high-temperature unit . The
molded specimens had a porosity not exceeding 6%, a heat
conductivity of about 60 W/(m × K), and a Mohs-scale hard
ness of about 9. Specimens for testing were cut out of a
hot-pressed preform using a diamond grinding wheel. The
test specimens had the shape of a disk or a sector with an
The composite materials with an inorganic binder were
prepared by finely grinding the precursor components in an
agate mortar. For compact specimens, preforms were pre
pared by a semi-dry pressing method using a metal press
mold. The composite mixture was: 30 – 50 vol.% H
(85%) and 50 – 70 vol.% aluminum nitride. The molding
pressure did not exceed 200 MPa. The preforms were left to
dryinairfor3–4hat303K.After that, the dried preforms
were heated slowly under controlled conditions.
Graphite specimens with a composite coating (aluminum
nitride + phosphate binder) were prepared in the following
manner. Cubes with a side length of 1 cm were cut out of
ÉG-0-grade electrode graphite, and a freshly prepared coat
ing composite was applied layer-by-layer. After each coat
ing, the specimen was allowed to dry in air at 373 – 423 K
for 2 h, and then heated at 1073 K for 30 min under vacuum.
Refractories and Industrial Ceramics Vol. 43, Nos. 9 – 10, 2002
1083-4877/02/0910-0289$27.00 © 2002 Plenum Publishing Corporation
Eastern Institute of Refractories Research and Production Associ
ation Joint-Stock Co., Ekaterinburg, Russia.
Ural State Technical University, Ekaterinburg, Russia.
Institute of High-Temperature Electrochemistry, Ural Branch of
the Russian Academy of Sciences, Ekaterinburg, Russia.