Synthesis and Dimension Control of Ultrafine γ-Aluminum Oxide by
Detonation
R. Y. Li1, X. J. Li, H. H. Yan, X. H. Xie, Y. D. Qu, Z. R. Yang
State Key Lab of Structural Analysis for Industrial Equipment, Dept. of Engineering Mechanics,
Dalian University of Technology Dalian, 116025
Abstract
Ultrafine spherical γ-Aluminum Oxide was successfully obtained by detonation of the mixed explosive made by
aluminum nitrate and cyclotrimethylenetrinitramine (RDX). In order to research the relation between dimension of
ultrafine γ-Aluminum Oxide and explosion velocity of mixed explosive, the four mixed explosives with different
explosion velocities were made. They were detonated in a container in turn, and then the four γ-Aluminum Oxide
powders were prepared by their detonations. They were studied systematically by X-ray diffraction. According to
XRD data, the average granule dimensions of four ultrafine γ-aluminum oxides were worked out by Scherrer
formula. Comparing the average granule dimensions with explosion velocities of four mixed explosives indicated
the average granule dimension was thinner when explosion velocity was higher. The relation between them was
linear inverse ratio approximately.
1. Introduction
At present, there are so many methods reported to synthesize ultrafine aluminum oxide [1~11], the usual
employed methods are mechanical comminution, high-energy ball milling [5], chemical precipitation [6,7],
pyrogenation [8,9] and sol-gel technology [10,11] etc. Each method has its characteristics. We have successfully
prepared ultrafine γ-aluminum oxide which granule dimension varied from 15nm to 20nm by detonation of binary
mixed explosive. Up to now, there have been not other persons who prepared ultrafine aluminum oxide by
detonation at home. Some articles have only been published about nano-diamond by detonation [12~18]. The
person A. A. Bukaemskii1 [19~21] has used detonation to synthesize ultrafine aluminum oxide abroad. The theory
is in an oxygen-containing medium the aluminum powders were heated and drove by explosive, and then the hot
and high-speed aluminum granule reacted with outer oxygen to obtain the ultrafine aluminum oxide. But ours is
aluminum nitrate rapidly decomposed to large numbers of free atoms because of the high temperature
(2000~3000K) and high pressure (20~30Gpa) produced by explosive, then the free aluminum atoms and oxygen
atoms combined to ultrafine aluminum oxide. The method has some excellencies, such as simple technology
process, low-cost equipment, fast synthesis and amplificatory yield. In addition, it has the characteristics of vapor
phase composition, to synthesize high dispersing and high-purity ultrafine aluminum oxide has technique
1
Corresponding author. Tel. :+86-0411-84833303, E-mail address: [email protected] (R. Y. Li)
advantage. So the method has definite value of research. At present researchers can not control the dimension of
nano-material very well during its preparation. So we have done some research about controlling nano-dimension.
In the experiment, we successfully changed the dimension distribution of ultrafine aluminum oxide synthesized by
detonation of the binary mixed explosives through changing the velocity of explosion. And we found an organic
relation between dimension of nano-granule and velocity of explosion. Sequentially in definite range, we can
control the dimension of nano-material initiatively. In the experiment we changed the velocity of explosion by
altering the quality of RDX among the binary mixed explosive.
2. Experiment
The primary materials of four binary mixed explosives are aluminum nitrate powder and RDX powder. In the
experiment, aluminum nitrate and RDX are necessary experiment materials because the ultrafine aluminum oxide
is from heat decomposition of the aluminum nitrate, and RDX named as sensitizer is the condition of heat
decomposition as well as. The velocity of explosion is different when the mass of RDX is different in the binary
mixed explosive. To achieve different explosive with different velocity of explosion, four binary compositions
containing aluminum nitrate and RDX (800g and 200g, 700g and 300g, 600g and 400g, 500g and 500g) were
chosen. According to the design of experiment we weighed up the quantitative aluminum nitrate and RDX to blend
them uniformly, and then put them into a hard-plastic column with a diameter of 65 mm (Fig.1) to form the
columned explosive.
Fig.1. Schematic diagram of columned explosive
The four columned explosives were sequentially put into the explosion vessel with a diameter of 3000 mm (Fig.2)
to be detonated by primers and a little plastic-type explosive (detonated powder). After every explosion, the
white-gray powder was collected through the exhaust hole by the tailor-made equipment of collection.The
apparatus (BC-3) was employed to measure the actual velocities of explosion of four binary mixed explosives. The
synthesized products were characterized by X-ray diffraction (XRD) at a scanning rate of 4°/m (Cu-Kα,
λ=0.15406nm). The morphology and particle size of ultrafine aluminum oxide were determined using a
transmission electron microscope at an accelerating voltage of 100kV.
Fig.2. Schematic diagram of explosion vessel
3. Results and Discussion
Fig.3. Typical photographs of ultrafine aluminum oxides obtained by four binary mixtures: 500g and 500g (a); 600g
and 400g (b); 700g and 300g (c); 800g and 200g (d) in turn.
Fig.3 shows the transmission electron microscope photos of ultrafine aluminum oxides obtained by four binary
binary mixed explosives. From photos we can see that the granules of ultrafine aluminum oxide are spherical and
homogeneous, the dimensions of granules approximately varied from 15nm to 20nm.
Fig.4. X-ray diffraction patterns of aluminum oxides obtained by four binary mixtures: 500g and 500g (a); 600g and
400g (b); 700g and 300g (c); 800g and 200g (d) in turn.
Fig.4 shows the X-ray diffraction patterns of ultrafine aluminum oxide obtained by four binary binary mixed
explosives. From patterns we can see that the shapes of four diffraction curves are same. For each diffraction
curve, the three main peaks at 66.87°, 45.847°and 37.63° corresponding to the three distances of crystal faces
(440), (400) and (311) are 1.39Å, 1.981Å and 2.38Å, and other two little peaks at 39.45° and 60.87° which
corresponding to the two distances of crystal faces are 2.28Å and 1.52Å. According to ASTM catalog data, the
bove data completely accord with the standard data of γ-aluminum oxide. So we can conclude that the four groups
of white-gray powder are all γ-aluminum oxide powder. In addition, the average granule dimension (D) of ultrafine
aluminum oxide by detonation of every binary mixed explosive can be calculated out by Scherrer formula. The
formula is following:
D=kλ/Bcosθ
(1)
where k is a constant taken as 0.89, λ is the wavelength of Cu target taken as 0.154nm, 2θ is the scattering angle,
B is the angular half-width of the peak . According to all the diffraction data, we calculated out the average granule
dimensions of ultrafine aluminum oxide obtained by the four binary mixed explosives detonation by the formula (1).
We can also measure out the actual velocities of explosion (V) of four binary mixed explosives by BC-3 apparatus.
The calculated D and the measured V are shown in Tab.1.
Tab.1 Values of D and V
Binary compositions
D/nm
V/(m⋅s-1)
500g and 500g
15.43
5263
600g and 400g
17.11
4624
700g and 300g
19.61
3846
800g and 200g
22.96
2888
In Tab.1, we can see that the average granule dimension is more and more large from the top down, but the
velocity of explosion turn more and more small. The relation between them is inverse ratio. To show the relation
more distinctly we drew the following fig.5.
Fig.5. Relation curve of nano-dimension and velocity of explosion
Fig.5 indicates that when the velocity of explosion of binary mixed explosive is higher the average granule
dimension of ultrafine aluminum oxide obtained by it is more small, the particle of ultrafine aluminum oxide is
thinner i.e.. The relation is linear inverse ratio approximately. So based on the curve we can easily change the
velocity of explosion to control the dimension of nano-granule initiatively in a definite range.
4. Conclusions
Four binary mixed explosives with different velocities of explosion are made by aluminum nitrate and RDX at
different mass ratios. Ultrafine γ-aluminum oxide is synthesized by detonation of each binary mixed explosive. The
granules of ultrafine γ-aluminum oxide are spherical, the dimensions of granules approximately vary from 15nm to
20nm and the granules are homogeneous. The relation between the velocity of explosion of binary mixed explosive
and granule dimension of ultrafine aluminum oxide is linear inverse ratio approximately. When the velocity of
explosion of binary mixed explosive is higher the granule of ultrafine aluminum oxide by detonation is smaller.
Acknowledgements
The project is partially supported by the National Nature Science Foundation and the Natural Science
Foundation of Liaoning Province under contract No. 10572034 and No. 20042161.
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