In this work, the critical diameter for detonation was measured for Nitromethane (NM) sensitized with two different amines: Diethylenetriamine (DETA) and Triethylamine (TEA). The critical diameter in glass and polyvinylchloride tubes is found to decrease rapidly as the amount of sensitizer is increased, then increase past a critical amount of sensitizer. Thus the critical diameter reaches a minimum at a critical concentration of sensitizer. It was also found that the critical diameter is lower with DETA than with TEA

Choong, K. H.

Jiang, J.

Lee, J. H. S.

Lee, J. J.

English

J. J. Lee

Crossref

CP505, Shock Compression of Condensed Matter - 1999 edited by M. D. Furnish, L. C. Chhabildas, and R. S. Hixson 0 2000 American Institute of Physics l-56396-923-8/00/$17.00 EFFECT OF DIETHYLENETRIAMINE AND TRIETHYLAMINE SENSITIZATION ON THE CRITICAL DIAMETER OF NITROMETHANE’ J.J. Lee*, J. Jiang?, K.H. Choong’, J.H.S. Lee’ *Graduate Aeronautics Laboratory, California Institute of Technology, Pasadena, CA 9112.5, USA ‘Dept. of Mechanical Engineering, McGill University, Montr&al, Que’bec, Canada, H3A 2K6 In this work, the critical diameter for detonation was measured for Nitromethane (NM) sensitized with two different amines: Diethylenetriamine (DETA) and Triethylamine (TEA). The critical diameter in glass and polyvinylchloride tubes is found to decrease rapidly as the amount of sensitizer is increased, then increase past a critical amount of sensitizer. Thus the critical diameter reaches a minimum at a critical concentration of sensitizer. It was also found that the critical diameter is lower with DETA than with TEA. INTRODUCTION Previous studies have shown that small concentrations of certain substances can strongly increase the explosive sensitivity nitromethane (NM). Amines are found to be the most effective chemical sensitizing agent for NM with ethylenediamine and diethylenetriamine (DETA) producing the largest increase in the card gap value (1). Triethylamine (TEA) is favored in certain low- temperature applications on account of it’s freezing point of -115°C. Although the card gap method has been used to compare various sensitizers, the critical diameter is a more fundamental dynamic parameter for detonation since it is directly related to the chemical length scale of the detonation wave (2). In gaseous detonations, the critical diameter is directly proportional to the cell size parameter. The cell size has been used to formulate many semi-empirical correlations such as the critical energy for direct initiation, the critical tube diameter for detonation propagation in various tubes and channels, and the critical conditions for propagation in porous media (3) . The effect of DETA on the critical diameter of NM has been reported by Engelke (4), who performed measurements with up to 2.5% DETA by mass in NM. Engelke observed a reduction in the critical diameter of over 50% in the range of DETA concentrations used. In this work, the critical diameter measurements in NM are extended for DETA concentrations up to 20% by mass. The critical diameter of NM sensitized with up to 15% TEA by mass is also measured. EXPERIMENTAL DETAILS The critical diameter was measured in tubes of glass or polyvinylchloride (TygonTM). Tubes of different diameter with a length of 15Omm were attached at one end to a 3cc plastic syringe with a length of 70mm and a diameter of 8mrn, as shown in 797 797Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jspdetonator liquid explosive FIGURE 1. Apparatus used for critical diameter measurements of liquid explosives. Fig. 1. The liquid explosive in the syringe-tube assembly is initiated by an electric blasting cap inserted into the syringe end. A steel or aluminium witness plate placed against the tube was used to determine whether the detonation had propagated the full length of the tube or not. NM with different concentrations of sensitizer was tested in tubes of different diameter in order to determine the critical diameter. In certain cases, the critical diameter was measured by using a fixed tube diameter and varying the sensitizer concentration until super-critical and sub-critical concentrations were found. This latter procedure was chosen when high accuracy was desired within a certain range of sensitizer concentrations where tubes were not available in fine enough increments of diameter. The witness plate method provided a clear indication of the distance of propagation of the detonation along the tube, and non-ambiguously showed whether the tube diameter was above or below the critical value. Since the tube length was over 20 times the diameter, there was sufficient distance for the detonation to reach a steady state. Velocity measurements performed in a previous work (6) showed that it was uniform along the tube for super-critical diameters, hence confirming the stability of the wave. 0.001 0.01 0.1 1 10 100 %DETA (by mass) FIGURE 2. Critical diameter on NM sensitized with DETA in glass and TygonTM tubes. Error bars are not shown when they are smaller than the data point symbol. RESULTS AND DISCUSSION The critical diameter for NM was found to decrease sharply with only a small concentration of DETA added. At a concentration of 0.5% DETA, the critical diameter in glass tubes decreased 0.3mm from its value of 16.2rnm for pure NM (4), as seen in Fig. 2. The present results extrapolate well to Engelke’s results with DETA concentrations less than 0.053%. This strong reduction of the critical diameter is an indication of a decreased reaction zone length in the detonation front, or equivalently, an increase in the reaction rate. This can occur when the amine chemically weakens certain bonds in the NM molecule, effectively reducing the activation energy 0 . Independent observations of another rate- dependent parameter, the time-to-detonation in a shocked explosive, also support a strong increase in the reaction rate of NM with the addition of minute amounts of DETA (5). Hence the addition of DETA effectively controls the characteristic chemical time scale of the detonation front. Also apparent from the results (Fig. 2) is that the critical ‘diameter of liquid explosive confined in TygonTM is higher than with glass. This can also be seen in the critical diameter results for NM sensitized with TEA (Fig. 3). This can be explained by the stronger confinement of glass on the explosive due to its higher shock impedance. The 798 798Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jspeffect of confinement on the detonation properties has been recently discussed in Brouillette et al. (6). 14 I '11""~ I I1 ,T Glass 12 - -B- TygonTM 0 I- ’ ’ “““’ ’ ’ “““’ ’ ’ “““I 0.1 1 10 100 % TEA (by mass) FIGURE 3. The critical diameter of NM sensitized with TEA in glass and TygonTM tubes. One of the main features of the critical diameter dependence on the concentration of sensitizer is a minimum critical diameter which occurs at a critical sensitizer concentration. As the concentration of sensitizer increases past the critical value, the critical diameter begins to increase sharply. This phenomenon is once again present with both DETA and TEA mixtures (Figs. 2 and 3). The minimum diameter occurs in DETA-sensitized mixtures at around 15% for Tygon tubes. Although the minimum was not reached for glass tubes (Fig. 2), it would likely occur at the same DETA concentration as for Tygon tubes (O/,1 5) since the sensitizer concentration at the minimum does not seem to be influenced by the confinement (Fig. 3). For TEA mixtures, the minimum diameter occurs around 5%. A possible explanation for the minimum in the critical diameter curve may be deduced from the dilution effect of the sensitizer. As the concentration of sensitizer increases, the energy released in the detonation wave decreases as does the temperature in the wave. This effectively reduces the reaction rate and increases the critical diameter. At small sensitizer concentrations, the critical diameter decreases due to a reduction in the activation energy, however at larger concentrations, the dilution effect takes over and increases the critical diameter. I I I IllIll I I "111'~ -B- DETA .I 1 10 % Sensitizer (by mass) 100 FIGURE 4. The critical diameter of NM sensitized with DETA and TEA in TygonTM tubes. This is further supported by comparing the sensitizing effect of both amines. As seen in Fig. 4, the critical diameter of NM is smaller for DETA sensitization than with TEA. Hence DETA is a more effective sensitizer. Furthermore, the critical diameter minimum for DETA mixtures is shifted towards higher concentrations as compared to TEA mixtures. Since the sensitizing effect is stronger with DETA, a larger decrease in temperature is necessary to counteract the effect of sensitization. Consequently, the minimum occurs at a higher concentration where the dilution effect is stronger. CONCLUSION The addition of DETA and TEA to NM has been found to strongly reduce the critical diameter of the liquid explosive, with DETA producing a stronger reduction. At higher concentrations of the sensitizer, the critical diameter increases sharply, producing a minimum in the critical diameter dependence on sensitizer concentration. This minimum results from a competition between the sensitizing effect and the dilution effect of the sensitizers. 799 799Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jspREFERENCES 1. Murray, S.B., Briosi, G.K., Pinto M.E., Anderson C.J., DRES Suffield Report No. 601, (1994). 2. Lee, J.H.S, “Dynamic parameters of gaseous detonation”, Ann. Rev. Fluid Mech. 16: 31 l-336 (1984). 3. Makris, A., “The propagation of gaseous detonation in porous media”, Ph.D. Thesis, McGill University, Canada, (1993). 4. Engelke, R., “Effect of a chemical inhomogeneity on steady-state detonation velocity”, whys. Fluids 23(5):875- 880 (1980). 5. Walker, F.E., “Initiation and detonation studies in sensitized nitromethane”, Actn Astronnuticn 6: 807-8 13 (1979). 6. Brouillette, M., Dionne, J.-P., Radulescu, M., Jiang, J., Lee, J.J., Lee J.H.S., “Detonation properties in confined liquid explosives “, Proceedings of the 2Ist Iizt ‘1 Symp. on Shock Wmes (on CD), Ed. A.F.P. Howing, ISBN 0-909683- 16-6, Paper 3400, (1997). 7. Engelke, R., Earl, W.L., McMichael Rohling, C., “Microscopic evidence that the nitromethane aci ion is a rate controlling species in the detonation of liquid nitromethane”, J. Chem. Phys.84( 1): 142-146 (1986). 800 800Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp

Effect of Diethylenetriamine and Triethylamine sensitization on the critical diameter of Nitromethane

CP505, Shock Compression of Condensed Matter - 1999 
edited by M. D. Furnish, L. C. Chhabildas, and R. S. Hixson 
0 2000 American Institute of Physics l-56396-923-8/00/$17.00 
EFFECT OF DIETHYLENETRIAMINE AND TRIETHYLAMINE 
SENSITIZATION ON THE CRITICAL DIAMETER OF 
NITROMETHANE’ 
J.J. Lee*, J. Jiang?, K.H. Choong’, J.H.S. Lee’ 
*Graduate Aeronautics Laboratory, California Institute of Technology, Pasadena, CA 9112.5, USA 
‘Dept. of Mechanical Engineering, McGill University, Montr&al, Que’bec, Canada, H3A 2K6 
In this work, the critical diameter for detonation was measured for Nitromethane (NM) sensitized 
with two different amines: Diethylenetriamine (DETA) and Triethylamine (TEA). The critical 
diameter in glass and polyvinylchloride tubes is found to decrease rapidly as the amount of 
sensitizer is increased, then increase past a critical amount of sensitizer. Thus the critical diameter 
reaches a minimum at a critical concentration of sensitizer. It was also found that the critical 
diameter is lower with DETA than with TEA. 
INTRODUCTION 
Previous studies have shown that small 
concentrations of certain substances can strongly 
increase the explosive sensitivity nitromethane 
(NM). Amines are found to be the most effective 
chemical sensitizing agent for NM with 
ethylenediamine and diethylenetriamine (DETA) 
producing the largest increase in the card gap value 
(1). Triethylamine (TEA) is favored in certain low- 
temperature applications on account of it’s freezing 
point of -115°C. 
Although the card gap method has been used to 
compare various sensitizers, the critical diameter is a 
more fundamental dynamic parameter for detonation 
since it is directly related to the chemical length 
scale of the detonation wave (2). In gaseous 
detonations, the critical diameter is directly 
proportional to the cell size parameter. The cell size 
has been used to formulate many semi-empirical 
correlations such as the critical energy for direct 
initiation, the critical tube diameter for detonation 
propagation in various tubes and channels, and the 
critical conditions for propagation in porous media 
(3) . 
The effect of DETA on the critical diameter of 
NM has been reported by Engelke (4), who 
performed measurements with up to 2.5% DETA by 
mass in NM. Engelke observed a reduction in the 
critical diameter of over 50% in the range of DETA 
concentrations used. In this work, the critical 
diameter measurements in NM are extended for 
DETA concentrations up to 20% by mass. The 
critical diameter of NM sensitized with up to 15% 
TEA by mass is also measured. 
EXPERIMENTAL DETAILS 
The critical diameter was measured in tubes of 
glass or polyvinylchloride (TygonTM). Tubes of 
different diameter with a length of 15Omm were 
attached at one end to a 3cc plastic syringe with a 
length of 70mm and a diameter of 8mrn, as shown in 
797 
797
Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp
detonator 
liquid 
explosive 
FIGURE 1. Apparatus used for critical diameter measurements 
of liquid explosives. 
Fig. 1. The liquid explosive in the syringe-tube 
assembly is initiated by an electric blasting cap 
inserted into the syringe end. A steel or aluminium 
witness plate placed against the tube was used to 
determine whether the detonation had propagated 
the full length of the tube or not. 
NM with different concentrations of sensitizer 
was tested in tubes of different diameter in order to 
determine the critical diameter. In certain cases, the 
critical diameter was measured by using a fixed tube 
diameter and varying the sensitizer concentration 
until super-critical and sub-critical concentrations 
were found. This latter procedure was chosen when 
high accuracy was desired within a certain range of 
sensitizer concentrations where tubes were not 
available in fine enough increments of diameter. 
The witness plate method provided a clear 
indication of the distance of propagation of the 
detonation along the tube, and non-ambiguously 
showed whether the tube diameter was above or 
below the critical value. Since the tube length was 
over 20 times the diameter, there was sufficient 
distance for the detonation to reach a steady state. 
Velocity measurements performed in a previous 
work (6) showed that it was uniform along the tube 
for super-critical diameters, hence confirming the 
stability of the wave. 
0.001 0.01 0.1 1 10 100 
%DETA (by mass) 
FIGURE 2. Critical diameter on NM sensitized with DETA in 
glass and TygonTM tubes. Error bars are not shown when they are 
smaller than the data point symbol. 
RESULTS AND DISCUSSION 
The critical diameter for NM was found to 
decrease sharply with only a small concentration of 
DETA added. At a concentration of 0.5% DETA, 
the critical diameter in glass tubes decreased 0.3mm 
from its value of 16.2rnm for pure NM (4), as seen 
in Fig. 2. The present results extrapolate well to 
Engelke’s results with DETA concentrations less 
than 0.053%. 
This strong reduction of the critical diameter is 
an indication of a decreased reaction zone length in 
the detonation front, or equivalently, an increase in 
the reaction rate. This can occur when the amine 
chemically weakens certain bonds in the NM 
molecule, effectively reducing the activation energy 
0 . Independent observations of another rate- 
dependent parameter, the time-to-detonation in a 
shocked explosive, also support a strong increase in 
the reaction rate of NM with the addition of minute 
amounts of DETA (5). Hence the addition of DETA 
effectively controls the characteristic chemical time 
scale of the detonation front. 
Also apparent from the results (Fig. 2) is that 
the critical ‘diameter of liquid explosive confined in 
TygonTM is higher than with glass. This can also be 
seen in the critical diameter results for NM 
sensitized with TEA (Fig. 3). This can be explained 
by the stronger confinement of glass on the 
explosive due to its higher shock impedance. The 
798 
798
Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp
effect of confinement on the detonation properties 
has been recently discussed in Brouillette et al. (6). 
14 I '11""~ I I1 
,T Glass 
12 - -B- TygonTM 
0 I- ’ ’ “““’ ’ ’ “““’ ’ ’ “““I 
0.1 1 10 100 
% TEA (by mass) 
FIGURE 3. The critical diameter of NM sensitized with TEA in 
glass and TygonTM tubes. 
One of the main features of the critical diameter 
dependence on the concentration of sensitizer is a 
minimum critical diameter which occurs at a critical 
sensitizer concentration. As the concentration of 
sensitizer increases past the critical value, the critical 
diameter begins to increase sharply. This 
phenomenon is once again present with both DETA 
and TEA mixtures (Figs. 2 and 3). The minimum 
diameter occurs in DETA-sensitized mixtures at 
around 15% for Tygon tubes. Although the 
minimum was not reached for glass tubes (Fig. 2), it 
would likely occur at the same DETA concentration 
as for Tygon tubes (O/,1 5) since the sensitizer 
concentration at the minimum does not seem to be 
influenced by the confinement (Fig. 3). For TEA 
mixtures, the minimum diameter occurs around 5%. 
A possible explanation for the minimum in the 
critical diameter curve may be deduced from the 
dilution effect of the sensitizer. As the 
concentration of sensitizer increases, the energy 
released in the detonation wave decreases as does 
the temperature in the wave. This effectively 
reduces the reaction rate and increases the critical 
diameter. At small sensitizer concentrations, the 
critical diameter decreases due to a reduction in the 
activation energy, however at larger concentrations, 
the dilution effect takes over and increases the 
critical diameter. 
I I I IllIll I I "111'~ 
-B- DETA 
.I 1 10 
% Sensitizer (by mass) 
100 
FIGURE 4. The critical diameter of NM sensitized with DETA 
and TEA in TygonTM tubes. 
This is further supported by comparing the 
sensitizing effect of both amines. As seen in Fig. 4, 
the critical diameter of NM is smaller for DETA 
sensitization than with TEA. Hence DETA is a 
more effective sensitizer. Furthermore, the critical 
diameter minimum for DETA mixtures is shifted 
towards higher concentrations as compared to TEA 
mixtures. Since the sensitizing effect is stronger 
with DETA, a larger decrease in temperature is 
necessary to counteract the effect of sensitization. 
Consequently, the minimum occurs at a higher 
concentration where the dilution effect is stronger. 
CONCLUSION 
The addition of DETA and TEA to NM has 
been found to strongly reduce the critical diameter 
of the liquid explosive, with DETA producing a 
stronger reduction. At higher concentrations of the 
sensitizer, the critical diameter increases sharply, 
producing a minimum in the critical diameter 
dependence on sensitizer concentration. This 
minimum results from a competition between the 
sensitizing effect and the dilution effect of the 
sensitizers. 
799 
799
Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp
REFERENCES 
1. Murray, S.B., Briosi, G.K., Pinto M.E., Anderson C.J., 
DRES Suffield Report No. 601, (1994). 
2. Lee, J.H.S, “Dynamic parameters of gaseous detonation”, 
Ann. Rev. Fluid Mech. 16: 31 l-336 (1984). 
3. Makris, A., “The propagation of gaseous detonation in 
porous media”, Ph.D. Thesis, McGill University, Canada, 
(1993). 
4. Engelke, R., “Effect of a chemical inhomogeneity on 
steady-state detonation velocity”, whys. Fluids 23(5):875- 
880 (1980). 
5. Walker, F.E., “Initiation and detonation studies in 
sensitized nitromethane”, Actn Astronnuticn 6: 807-8 13 
(1979). 
6. Brouillette, M., Dionne, J.-P., Radulescu, M., Jiang, J., 
Lee, J.J., Lee J.H.S., “Detonation properties in confined 
liquid explosives “, Proceedings of the 2Ist Iizt ‘1 Symp. on 
Shock Wmes (on CD), Ed. A.F.P. Howing, ISBN 0-909683- 
16-6, Paper 3400, (1997). 
7. Engelke, R., Earl, W.L., McMichael Rohling, C., 
“Microscopic evidence that the nitromethane aci ion is a 
rate controlling species in the detonation of liquid 
nitromethane”, J. Chem. Phys.84( 1): 142-146 (1986). 
800 
800
Downloaded 02 Oct 2007 to 131.215.225.176. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp


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Effect of Diethylenetriamine and Triethylamine sensitization on the critical diameter of Nitromethane

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