CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00
EFFECT OF VOID SIZE ON THE DETONATION PRESSURE OF
EMULSION EXPLOSIVES.
Yoshikazu Hirosaki 1, Kenji Murata 1, Yukio Kato 1 and Shigeru Itoh 2
]
NOFCorporation, 61-1 Kitakomatsudani, Taketoyo-cho, Chita-gun, Aichi 470-2398, JAPAN
"Shock Wave and Condensed Matter Research Center, Kumamoto University
2-39-1 Kurokami, Kumamoto 860-8555, JAPAN
Abstract. To study the effect of void size, detonation pressure as well as detonation velocity was
measured using PVDF pressure gauge for the emulsion explosives sensitized with plastic balloons of
five different size ranging from 0.05mm to 2.42mm. The experimental results were compared with the
detonation pressure and velocity calculated using KHT code. The experimental results showed that the
detonation pressure and velocity were strongly affected by void size, and that the fraction of ammonium
nitrate reacted in the reaction zone was strongly dependent on void size.
reported in many investigations [1-4]. In those studies,
glass microballoons of size smaller than 0.15mm were
used as void In this paper, to study the effect of void
size, detonation pressure as well as detonation velocity
was measured using PVDF (polyvinylidenefluoride)
pressure gauge for the emulsion explosives sensitized
with plastic balloons of five different size ranging from
0.05mm to 2.42mm.
INTRODUCTION
Explosives for civil use, such as emulsion explosives,
slurry explosives and ANFO (Ammonium Nitrate-Fuel
Oil), are usually ammonium nitrate (AN)-based. Those
explosives are well known to show non-ideal
detonation behavior clue to its slow reaction rate
compared to high explosives for military use. The
non-ideal detonation wave propagates steadily but its
characteristics are significantly affected by the
conditions such as charge diameter and confinement.
Detonation pressure and detonation velocity are much
lower than those for infinite charge diameter. This
behavior is depending on the long reaction zone length
due to slow reaction rate of AN.
It is well known that detonation behavior can be
widely controlled by the size and quantity of void
contained in the emulsion explosives. The effect of void
size and quantity on the detonation velocity, critical
diameter and sensitivity of emulsion explosives were
EXPERIMENTALS
Samples
The formulation of the emulsion matrix used in this
study is ammonium nitrate /sodium nitrate /water /wax
and emulsifier = 77.66/4.68/11.22/5.40 in weight ratio.
The oxygen balance of the emulsion matrix is
0.4g/100g, and the density of it is 1.39gfan3. A certain
amount of plastic balloons of mono-cell or multi-cell
structure shown in Table 1 were added into the
emulsion matrix to achieve the desired explosive
930
density. Five different sizes of balloons were used. PB-1
is the smallest balloon of mono-cell structure with the
average diameter of 0.05mm, and others are the
balloons of multi-cell structure with average diameter
ranging from 0.47 to 2.42mm.
Microscopic photographs of both structures are
shown in Fig.l as examples. The particle density of
each balloon was determined from the densities of
explosives that contain different amount of balloons.
The size of balloon was optically measured.
Detonation Pressure Measurement
The emulsion explosive loaded into PVC pipe of
51mm in inner diameter, 60mm in outer diameter and
200mm in length was placed on a PMMA block as
shown in Fig.2. A PVDF film of 10 //m in thickness
thickness. The emulsion explosive was initiated with an
electric detonator. Additional 30grams of emulsion
explosive was also used as a booster explosive, if
necessary. The output of the pressure gauge was
recorded with a digital oscilloscope at sampling rate of
five nanoseconds. Calibration of PVDF pressure gauge
was carried out by measuring electric chaige created
under hydraulic pressure and by comparing with the
pressure measured with a manganin pressure gauge that
has preliminary been calibrated. The pressure profile
observed by PVDF pressure gauge is that transmitted
into PMMA plate, which exists among the explosive
and a PVDF gauge.
Detonation velocity was measured with ionization
gaps that were placed at points 130mm and 180mm
TABLE 1. Characteristics of plastic balloons
Average diameter
(mm)
Standard deviation
(mm)
Particle density
(g/cm3)
Structure
Material
PB-1
0.053
0.023
0.027
Multi-cell
Acrylonitiile / vinylidene chloride
PB-2
0.472
0.062
0.051
Multi-cell
Polystyrene
PB-3
0.795
0.129
0.077
Multi-cell
Polystyrene
PEA
1.728
0.273
0.032
Multi-cell
Polystyrene
PB-5
2.420
0.403
0.064
Multi-cell
Polystyrene
FIGURE 1. Microscopic photographs of plastic balloons PB-1 (left) and PB-2 (right)
apart from the upper end of the chaige.
and 5mm squares was sandwiched with polyimide
films together with electrodes made of copper foil. The
PVDF gauge was put onto a PMMA block and then
covered and glued with a PMMA plate of 1mm in
RESULTS AND DISCUSSIONS
Fig. 3 indicates pressure profiles observed for the
931
emulsion explosives of density 1.05g/cm3 sensitized
with balloons of five different size. The pressure rises
up shaiply to reach its peak pressure within about 75
nanoseconds in the explosives sensitized with balloons
smaller than 0.80mm in diameter: PB-1, PB-2 and PB-3.
The pressure rise time of about 75 nanoseconds can be
explained by the detonation front curvature measured
by optical observation [5] and shock transition time in
PVDF film of 10 jum thick. Pressure decrease in the
reaction zone behind leading shock and following
pressure decay in Taylor wave can be observed in the
emulsion explosives sensitized with balloons PB-1 and
PB-2. Whereas the emulsion explosives sensitized with
larger balloons such as PB-4 or PB-5 require longer
time to reach its peak pressure. This is due to the
important irregularity of detonation front of the
emulsion explosives containing laige balloons, which
was measured in optical observation [5]. The peak
pressure is fairly low compared with that for the
emulsion explosives containing smaller balloons.
The pressure observed in this experiment is that
transmitted into PMMA plate of 1mm in thickness.
PMMA was based on the reference [6], and that of the
unreacted emulsion explosive was supposed to be same
as Universal Hugoniot [7],[8] for AN solution.
The reaction zone length estimated from the
measured pressure profile is about 1.5mm for the
emulsion explosives sensitized with void of 0.05mm.
This value agrees well with the reaction zone length
estimated from the diameter effect of detonation
velocity in the same emulsion explosives [4].
The theoretical detonation pressure and velocity were
calculated with a hydro-thermodynamic code KHT in
which the ingredients other than AN were assumed to
be completely reactive. The measured and calculated
detonation pressure as well as detonation velocity were
summarized in Table 2. The fraction of AN reacted in
the reaction zone was evaluated based on the
comparison between the measured and calculated
detonation pressure and velocity. The fraction of AN
reacted in the reaction zone evaluated from pressure
agrees well with that estimated from detonation velocity.
The fraction of AN reacted in the reaction zone is as
high as 0.87 for the emulsion explosives sensitized with
void of 0.05mm. On the other hand, the fraction of AN
reacted is as low as 0.30 for the emulsion explosives
sensitized with void of 2.42mm. This result is due to
small number of void which act as hot spot, and this
leads to longer reaction zone length and poor reactivity
of AN. The poor reactivity of AN in the emulsion
explosives containing large voids is due not only to the
lateral rarefection waves but also to the rareiaction
waves from void itself.
Electric detonator
Emulsion Explosive
confined in PVC pipe
(VP50)
130
PVDF film sensor.
(10 Wm)
PMMA block
to Oscilloscope
CONCLUSIONS
To examine the effects of void size, detonation
pressure and detonation velocity were measured for the
emulsion explosives sensitized with plastic balloons of
five different size ranging from 0.05mm to 2.42mm in
average diameter.
0100
FIGUER 2. Experimental setup for detonation pressure
measurements
The detonation pressure was therefore determined
from the impedance match method. The Hugoniot of
932
TABLE 2. Effect of balloon size on the detonation properties of emulsion explosives.
Balloon diameter d^mm)
Measured detonation velocity (m/s)
Measured detonation pressure P (GPa)
Calculated CJ pressure PCJ(GPa)
Fraction of AN reacted at C-J state estimated from pressure P
0.05
5230
6.4
8.21
0.84
0.47
L 4480
5.1
8.21
0.69
0.80
3510
2.8
8.21
0.42
1.73
3360
2.5
8.21
0.39
2.42
2960
2.1
8.21
0.33
Fraction of AN reacted at C-J state estimated from detonation
velocity
0.87
0.68
0.43
0.39
0.30
When void size was increased, the difference
between the measured and calculated values was
increased both for detonation pressure and velocity. The
fraction of AN reacted in the reaction zone was as high
as 0.87 for the emulsion explosives sensitized with
voids of 0.05mm. On the other hand, the fraction of AN
reacted is as low as 0.30 for the large void of 2.42mm.
hi the case of the emulsion explosives sensitized with
void smaller than 0.47mm, pressure decrease behind
leading shock and following decay in Taylor wave were
observed. Whereas, in the case of the emulsion
explosives sensitized with void larger than 1.73mm,
detonation pressure rise time is larger than 0.5
microsecond due to the important irregularity of
detonation front.
Time (ii s)
FIGUER 3. Pressure-time curves observed with PVDF gauge
for the detonation of emulsion explosives of density 1.05g/cm3
sensitized with various balloon sizes
573-584.
4.
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