Combustion, Explosion, and Shock Waves, Vol. 37, No. 4, pp. 490 491, 2001
URGENT COMMUNICATION
Products of Combustion of Aluminum Hydride in Air
A. P. Il in,1 N. V. Bychin,1 and A. A. Gromov1 UDC 541.16:182
Translated from Fizika Goreniya i Vzryva, Vol. 37, No. 4, pp. 139 140, July August, 2001.
Original article submitted April 7, 2000.
The paper reports results of studying the process and products of combustion of
aluminum hydride in air. It is shown that the final combustion products of alu-
minum hydride contain H"50% aluminum nitride (by weight) for large sample weights
of 1000 g. The formation mechanism of the final combustion products of aluminum
hydride is similar to that of ultradisperse aluminum powder.
Il in and Proskurovskaya [1, 2] showed that in the Nichrome wire, probably because of the high thermal
combustion of ultradisperse aluminum powder (UDAP) conductivity of this powder, which is also characteris-
in air, the final products can contain 50% or more (by tic of commercial ASD powders. As hydrogen burned
weight) AlN [1, 2]. After initiation, a mixture of com- up, the flame descended and touched the sample. Af-
mercial aluminum powders (10 100 µm) and ultradis- ter that, aluminum ignited, and low-temperature com-
perse aluminum oxide powder burns in air, like UDAP, bustion was observed, as in the case of the combustion
in two stages with stabilization of oxinitride and alu- of UDAP [1]. After a certain time, which depended on
minum nitride [3]. It is of interest to study the final the sample weight of aluminum hydride, the combustion
combustion products of not only aluminum powders entered the next stage, in which the sample tempera-
but also of aluminum compounds, in particular, alu- ture reached 2000 2400ć%C. After cooling, the solid final
minum hydride. In the slow thermal decomposition of products of combustion were analyzed for the metallic
aluminum hydride in vacuum, the solid final product aluminum content by dissolving them in a 4-normal so-
is elemental aluminum in the form of small particles of lution of hydrochloric acid and measuring the volume
irregular shape [4]. of hydrogen [6]. The content of chemically bound nitro-
In the present work, we used aluminum hydride gen was determined by the Kjeldahl method [7]. The
powder produced by the well-known method [5]. The products were analyzed by x-ray phase analysis using
purity of the synthesized aluminum hydride was 94% a DRON-3 diffractometer. According to x-ray phase
(by weight) according to results of thermal analysis. analysis data, the final products contained the follow-
Samples were placed on ceramic substrates and shaped ing crystal phases: Ä…- and Å‚-Al2O3, AlN, and Al0. The
like a cone. Combustion was initiated by a Nichrome experimental results are given in Table 1.
wire. For all sample weights studied (m = 0.0005 1.00), With increase in the sample weight of aluminum
combustion proceeded in three stages. After initiation, hydride, an increase in the AlN content and a de-
we observed a hydrogen flame, which was separated crease in the content of aluminum oxides (III) were ob-
from the sample with a nonluminous zone. At this served, whereas the metallic aluminum content first in-
stage, the combustion could be interrupted by placing creased and, then, decreased. For large sample weights
a foil between the sample and the flame. The product (m = 1 kg), the AlN content in the combustion prod-
of incomplete combustion is an aluminum powder con- ucts of aluminum hydride reaches H"50%, and the com-
sisting of spherical particles of micron diameter. We bustion products of UDAP can contain more than 50%
were unable to initiate combustion of this powder by a AlN even for sample weights of 2 3 g. We note that
in the combustion of large samples (m > 1 kg) in air,
1
High-Voltage Institute, Tomsk Polytechnic University,
the metallic aluminum content in the final products de-
Tomsk 634050.
490 0010-5082/01/3704-0490 $25.00 © 2001 Plenum Publishing Corporation
Products of Combustion of Aluminum Hydride in Air 491
creases to trace amounts. According to electron mi-
TABLE 1
croscopy data, the combustion products of aluminum
Composition of the Final Combustion Products
hydride (m = 3 g) are weakly aggregated, hollow, cut
of Aluminum Hydride Samples of Different Weights
particles (see Fig. 1a) and anisotropic acicular crystals
Content, % (by weight)
grow from their bulk (see Fig. 1b). The acicular crystals
No.
m, g
are several tens of microns in length and less than 1 µm
AlN Al0 Ä…-Al2O3 + Å‚-Al2O3
in diameter. The final products of aluminum hydride
1 0.5 10.2 6.7 83.1
combustion are similar in morphological properties to
2 1 11.7 7.7 80.6
the final products of combustion of UDAP [3].
Thus, the stabilization of aluminum nitride as an
3 3 19.9 13.7 66.4
independent phase in the final products of combustion is
4 4 24.3 16.7 59.0
observed not only for the aluminum powder but also for
5 5 26.1 16.1 57.8
aluminum hydride. The combustion proceeds in air, and
the content of aluminum nitride in the final products
6 6 27.5 15.4 57.1
can exceed 50%. The combustion of aluminum hydride
7 7 28.7 14.9 56.4
differs from the combustion of UDAP in the presence
8 10 32.5 2.8 54.7
of the additional stage of hydrogen combustion at a rel-
atively low temperature of aluminum hydride, and the
9 1000 50.7 0.5 48.8
aluminum powder formed burns in two stages: a low-
Note. Al0 is unoxidized metallic aluminum.
temperature stage and a high-temperature stage, which
is accompanied by chemical fixation of air nitrogen.
a
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magnifications.