OXIDATION OF COMPOSITE MATERIALS
BASED ON ALUMINUM NITRIDE
A. R. Beketov,
D. A. Beketov,
L. B. Khoroshavin,
and V. V. Chebykin
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 4, pp. 11 – 15, April, 2002.
A method for studying the heat resistance of composite aluminum nitride-based ceramic materials in air at
1073 – 1273 K is developed that allows the change in mass to be measured with an accuracy of
0.15 – 0.17 mg. The interaction between AlN-based composite materials and a phosphate binder (H
studied and compared with hot-pressed specimens. A mechanism for the effect of the binder on the kinetics of
oxidation is proposed. The relatively low activation energies (152 and 205 kJ/mole) suggest that the oxidation
process is mainly determined by the diffusion of aluminum ions through the a-Al
Nonmetallic composite materials based on aluminum
nitride are promising for use as refractories owing to the
unique physicochemical characteristics of aluminum nitride
such as the high decomposition temperature (2673 K) and
corrosion resistance in gas, salt, and fluid-metal media.
Based on the available literature it is difficult to provide a
consistent interpretation of the oxidation of aluminum nitride
materials [1 – 11] because of the difference in test specimens
and experimental methods used. Therefore knowledge of the
mechanism of interaction of aluminum nitride-based com-
posite materials with corrosive gas media has important tech
nological implications. In this work we present results of a
study of the oxidation of hot-pressed aluminum nitride and
composites based on aluminum nitride and a phosphate
binder in air in the temperature range of 1073 – 1273 K.
The composite materials containing a phosphate binder
were prepared by a semidry pressing method using metal
molds. The composition of the composite mixture was
30 – 50 vol.% H
(85%) and 50 – 70 vol.% aluminum
nitride powder prepared by a gas-phase method at the Rare-
Metals Department (Ural State Technical University, Eka
terinburg) . The molding pressure did not exceed
200 MPa. The preforms were dried in air for 3–4hat303K
and then heated to 1073 K under controlled conditions.
Aluminum nitride specimens doped with yttrium oxide
(0.2 wt.%) were prepared by a hot-pressing method on a
computer-controlled UGP-1 automated general-purpose
high-temperature unit .
The test specimens were cylinders 12 mm in diameter
with a length of between 1 and 13 mm, with an apparent sur-
face area of 3–8cm
. The weight of specimens was varied
from 0.5 to 4 g.
The x-ray phase analysis was carried out on a DRON-2
diffractometer; the infrared spectra of specimens (pressed
into KBr pellets) were measured on a UR-20 spectrophoto-
meter. The microstructure of specimens was examined by
Gravimetric studies of the composite materials were car-
ried out in air using a set shown schematically in Fig. 1. The
total time for experimental measurements was about 45 h.
Specimen 5 was suspended in an electrically heated tube-
type furnace 1 using a platinum wire 7. The temperature was
controlled to within ± 2–5K.ASartorius-Research balance
10 (Sartorius) was used for weighing.
The weighing accuracy was 10
g for loads of up to
42 g. The weight readings were processed on a computer 11
and plotted on m versus
coordinates. This made possible a
larger amount of measurements to be performed in the early
stage when the change in mass was, as a rule, rather small.
The total number of observations (experimental points) was
500 to 2000, reaching occasionally 10,000. A Microsoft
Excel environment was employed for processing experimen
tal data. The change in mass was scaled against the unit sur
The error of gravimetric measurements had a systematic
and a random component. The total error of mass measure
ment did not exceed 0.15 – 0.17 mg.
A typical gravimetric curve of oxidation of the composite
material based on aluminum nitride is shown in Fig. 2. The
initial portion of the curve is associated with the removal of
Refractories and Industrial Ceramics Vol. 43, Nos.3–4, 2002
1083-4877/02/0304-0122$27.00 © 2002 Plenum Publishing Corporation
Ural State Technical University (UPI), Ekaterinburg, Russia;
IVTE Research Institute, Ural Branch of the Russian Academy of
Sciences, Ekaterinburg, Russia; Eastern Institute of Refractories
Joint-Stock Co., Ekaterinburg, Russia.