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Russ. Chem. Bull., Int. Ed., Vol. 66, No. 6, June, 2017
Mikhailov et al.
Guanidinium nitrate, anthracene, and hydroquinone (pure
dynamic type (Germany) at 300 0.1 K using a CCS-850 helium
cryostat (Janis) with a 332 temperature controller (Lake Shore
Cryotronics). The source of Mössbauer radiation was 57Co(Rh)
with an activity of 1.1 GBq. Mössbauer spectra were processed
using the standard least-squares programs (LOREN developed
at the Institute of Chemical Physics of the Russian Academy of
Sciences and NORMOS purchased from Germany) assuming
the Lorentzian line shape. Isomer shifts were counted from
the center of the magnetic hyperfine structure (HFS) of metal-
lic iron.
grade), 5-aminotetrazole (Aldrich) with a content of the major
substance of 99.5% and a particle size of 5—10 m, and aluminum
hydride with a particle size of 10—20 m (pure grade) were used
as additives affecting the composition of the conversion products
in the studied system.
Samples for experimental studies were prepared according to
the following general procedure. The starting components includ-
ing hexogen, iron formate, and an organic binder, as well as
special additives if necessary taken in required ratios were mixed
in a Teflon mortar for 10 min at ~20 °C. Then cylindrical samples
with a height of ~20 mm and a diameter of 15 mm were formed
from the obtained mixture by the dead pressing method under
a pressure of 30—60 MPa. The formed samples were solidified
for 2 h at 350 K. As a result, oligoisocyanurate converts to poly-
isocyanurate (PIC).
To organize flameless combustion, the prepared sample was
placed in a cylindrical 310-mL quartz reactor and purged with
nitrogen. The process of wave conversion in a sample of filled
hexogen was initiated by a nichrome electrical coil with a tem-
perature of ~750 K. Then the conversion wave propagated along
the sample in the flameless autowave regime due to the heat
released upon the decomposition of the energetic component.
The course of the process can be monitored by the propagation
of an increasing black-colored zone of the reaction products. The
evolved vapor—gas reaction products were filtered through the
formed porous mixture of solid conversion products, entered
the reaction, leaved the sample, and were removed with a nitro-
gen flow.
The temperature in the reaction zone was measured by
chromel —alumel thermocouples (type K) with a diameter of
~180 m pressed in the sample. After digitization on an ATsP
L-780 analog-to-digital converter (ZAO “L-Card”), the signal
from the thermocouples was detected and processed on a com-
puter using a PowerGraph 3.3.5 program oscillograph (OOO
"DISoft"). The accuracy of temperature measurement was 5 K,
and that of time measurement was 0.1 s. The rate of process
propagation was determined by signals of two thermocouples
remote from each other at a distance of 10 mm.
The compounds in the composition of the obtained solid
products were identified by X-ray phase analysis on an ADP-2-01
diffractometer (Сu-К radiation, Ni filter) as a suspension in
Nujol.
Results and Discussion
The flameless combustion of the initial mixtures con-
taining hexogen, iron formate, and polyisourethane affords
a partially carbonized highly porous polymer matrix filled
with nanosized particles of iron compounds. It was estab-
lished using an electron microscope that the synthesized
material was a highly porous sponge (Fig. 1). Its specific
surface reaches 80 m2 g–1
.
If the composition of the initial mixture is that the
temperature in the wave propagating along the sample is
lower than 600 K, only iron(III) oxide is formed. At
higher temperatures nanosized particles of FeO, Fe3O4,
Fe2O3, and Fe3N or their mixtures are formed in the reac-
tion zone of flameless combustion. It depends on the ratio
of the inorganic precursor and energetic component, the
nature of introduced additives, and the temperature de-
veloped in the combustion zone what precisely iron com-
pounds are formed. Mixtures of the listed iron compounds
with the predomination of one of the components are
formed most frequently, which is confirmed by the results
of X-ray phase analysis and Mössbauer spectroscopy.
A microheterogeneous mixture of products containing
about 52% nitride and 48% oxide components is formed
by the combustion of a mixture of hexogen, iron formate,
and PIC at ~650 K (Fig. 2, Table 1). Iron nitride presum-
ably has the formula Fe2.66N and corresponds to the
hexagonal -phase. Nonstoichiometric magnetite Fe3O4+δ
The content of iron in the samples was determined by
atomic absorption spectrophotometry from the resonance line
at 248.3 nm in an acetylene—air flame using a deuterium cor-
rector on an AAS-3 spectrophotometer (Carl Ceiss).
The internal structure and morphology of the samples were
studied using scanning electron microscopy (SEM) on a Zeiss
LEO SUPRA 25 microscope. The specific surface of the obtained
materials was determined by the Brunauer—Emmett—Teller
(BET) method from low-temperature nitrogen sorption on
a QUADRA-SORB SI analyzer (Quantachrome Instruments
Corp.).
The sizes of the formed particles of iron and its derivatives
were estimated by the data of transmission electron microcopy
(TEM) on an ЕМ-304 microscope (Philips). The data obtained
on the particle sizes were monitored by the broadening of the
corresponding reflections on X-ray diffractograms using the
Debye—Scherer method.6 The both estimation methods gave
close values for the same sample.
30 m
The Mössbauer spectra of solid products of flameless com-
bustion were recorded on a Wissel spectrometer of the electro-
Fig. 1. SEM image of the products of the flameless combustion
of a mixture of hexogen, iron formate, and HDI.
Mikhailov, Yu. M.
