CA2123170A1 - Nitromethane liquid explosive composition - Google Patents

Abstract

According to this invention, there is provided a nitromethane liquid explosive composition having a freezing point of <-40°C which is rendered insensitive to detonation relative to neat nitromethane for the purpose of safe storage, handling, and tranportation to the site where it is to be used, and then resensitized at the time of use by adding 4 to 10 weight % triethylamine based on the total weight of the resensitized mixture. There is also provided a process for preparing said nitromethane liquid explosive composition. The nitromethane liquid explosive composition is rendered insensitive by the addition of nitroethane or 1-nitropropane.
Prefered compositions for the resensitized mixtures include 70 wt% nitromethane and 30 wt% nitroethane with 4 wt%
triethylamine, and 50 wt% nitromethane and 50 wt% 1-nitropropane with 10 wt% triethylamine.

Description

This invention relates to liquid explosive compositions and processes for handling said compositions. More particularly, this invention relates to nitromethane liquid explosive compositions and processes for desensitizing said compositions for safety of storage, handling, and transport and then resensitizing said compositions at the site of use.
Many engineering tasks require the use of high-explosive materials. Liquid explosives (LEX) tend to be more attractive than solid-phase explosives because they can be poured or pumped and they will conform to any container shape.
Liquid explosives may also be gelled or foamed. Anti-tank ditching is a typical military engineering task. Here, a standard mole plough on a bulldozer is used to install an empty plastic pipe 2 meters below ground level. Subsequently, the pipe is filled with LEX and detonated to form a deep V-shaped channel which can impede a battle tank. Liquid explosives can also be pumped into a surface hose and either detonated in a high-order fashion or dispersed into a droplet cloud and detonated as a means of clearing a safe lane through a minefield. Cutting charges consisting of an explosive-filled container fitted with a specially designed V-shaped metallic liner can be used to demolish structures ranging in scale from a simple I-beam to an entire bridge deck. A similar axisymmetric device can be used to create a deep "borehole" in the ground which is later lined, filled with LEX, and detonated. The resulting crater can be used to hide armoured vehicles, disrupt 212~317:0 -supply routes, or impede the progress of enemy forces. The attractiveness of LEX has also been recognized by the mining industry, albeit to a lesser extent.
The list of practical liquid explosives is a short one, and when issues of cost and safety are taken into account, nitromethane (NM) emerges as the most attractive candidate for widespread use. However, even NM has certain disadvantages. It is considerably more sensitive to detonation than the other members of the nitroparaffin family which includes nitroethane (NE), 1-nitropropane (1-NP) and 2-nitropropane (2-NP). A
phenomenon known as adiabatic bubble compression can occur in large volumes of NM under certain dynamic conditions. For example, if an air bubble in liquid NM is compressed suddenly from 1 atm to 23.8 atm, its temperature rises from 20C to 450C. Since this temperature is well above the critical temperature for NM, thermal decomposition of the material surrounding the bubble becomes possible and detonation may ensue if some critical volume criterion is met. This is believed to be a contributing factor in unexplained rail car explosions in the past. For this reason, the transport of neat NM in many countries is only possible in relatively small, thin-walled containers. Bulk road (not rail) transport is also permitted if significant quantities of specific co-solvents are added to the NM.
The sensitivity of NM is of particular concern to the military in view of the real possibility of initiation by projectiles or fragments in a battlefield scenario. Another disadvantage is that NM freezes at -28.5C which is above the lower limit of -40C dictated by Canadian military requirements and can make use of NM problematic in countries with severe climates.
It is well known that nitroparaffins can be sensitized to detonation by the addition of relatively small amounts of various amines. For example, Canadian Patent 490744 of Laurence discloses a mono-nitromethane explosive composition sensitized with from a trace to about 40% by volume of the amines from the group consisting of aniline, diphenylethylene diamine, phenylbetanapthylamine, diethylamine, tetraethylene pentamine, and morpholine. Canadian Patent 1015952 of Runge et al.
discloses an explosive composition sensitized to detonation and having a freezing point below -40F (= -40C) consisting of a mixture of 65-75 wt% nitromethane, 25-35 wt% methylene chloride, and additionally 2-12 wt% of diethylene triamine. As well, U.S. Patent 3309251 of Audreith et al. teaches a liquid organic explosive consisting essentially of mono-nitromethane and from 1 to about 20 % by weight of ethylene diamine. U.S. Patent 4892597 of Sullivan teaches a liquid explosive composition comprising nitromethane, trinitrotoluene, and pyridine. Only one of these compositions, however, is shown to have a freezing point of <-40C, and none of them suggest triethylamine as a possible sensitizing agent.
U.S. Patent 3746588 (Brunetz et al.) discloses a process for desensitizing a nitroparaffin liquid explosive composition containing an amine sensitizer in a manner such that it cannot be resensitized, by adding to the composition a desensitizing agent.
An object of the invention is to provide a nitromethane liquid explosive composition having a freezing point of <-40C
which can be rendered relatively insensitive to detonation during storage, handling, and transport to the site of use, and then resensitized. Another object of the invention is to provide a process for preparing the above nitromethane liquid explosive composition.
In accordance with one aspect of the present invention there is provided a liquid explosive composition sensitized to detonation and having a freezing point below -40C, consisting of a mixture of nitromethane and a second nitroparaffin selected from the group consisting of nitroethane and l-nitropropane in an amount adequate to depress the freezing point of nitromethane to below -40C and render the mixture insensitive to detonation relative to neat nitromethane, and additionally containing from 4 to 10% by weight of triethylamine based on the total weight of the sensitized composition.
Preferably, the composition comprises about 70 wt%
nitromethane and about 30 wt% nitroethane with about 4 wt%
triethylamine. Another preferred composition comprises about 50 wt% nitromethane and about 50 wt% nitroethane with about 10 wt~ triethylamine. A preferred composition containing l-nitropropane comprises about 50 wt% nitromethane and about 50 wt% l-nitropropane with about 10 wt% triethylamine.

In accordance with another aspect of the present invention there is provided a process for preparing a nitromethane liquid explosive composition comprising:
mixing together nitromethane liquid explosive with an amount of a second nitroparaffin selected from the group consisting of nitroethane and 1-nitropropane sufficient to depress the freezing point of nitromethane to below -40C and render the mixture insensitive to detonation relative to neat nitromethane;
transporting said insensitive mixture to the site where the mixture is to be used; and adding to said insensitive mixture, at the time of use, from 4 to 10 wt% of triethylamine based on the total weight of the mixture, the resulting resensitized liquid explosive composition having a detonation sensitivity and energy very close to that of neat nitromethane.
The advantages of the present invention are that the compositions exist in a liquid state at -40C and they can be stored, handled, and transported safely in bulk quantities in their insensitive form while having a detonation sensitivity close to that for neat nitromethane when resensitized. As well, these compositions are considerably cheaper than neat nitromethane and can be detonated over a large range of temperatures i.e. approximately -40C to 40C with about 1 kg or less of primer.

212~170 -In the drawings which illustrate embodiments of the invention, Figure 1 is a graph depicting freezing point depression data for nitromethane/methyl chloride blends, Figure 2 is a graph depicting freezing point depression data for nitromethane/nitroethane blends, Figure 3 is a graph depicting freezing point depression data for nitromethane/2-nitropropane blends, Figure 4 is a schematic diagram of the apparatus used to perform the experiments, Figure 5 is a graph depicting critical primer mass vs.
temperature for nitromethane/nitroethane blends, Figure 6 is a graph depicting critical diameter vs.
temperature for nitromethane/nitroethane blends, Figure 7 is a graph depicting critical primer mass vs.
temperature for nitromethane/nitroethane blends with 4%
triethylamine, Figure 8 is a graph depicting critical primer mass vs.
temperature for nitromethane/nitroethane blends with 10%
triethylamine, Figure 9 is a graph depicting critical primer mass vs.
temperature for 50/50 nitromethane/nitroethane with various amounts of triethylamine, Figure 10 is a graph depicting critical primer mass vs.
temperature for neat nitroethane with various amounts of triethylamine, Figure 11 is a graph depicting critical primer mass vs.
temperature for 50/50 nitromethane/l-nitropropane with various amounts of triethylamine, Figure 12 is a graph depicting the velocity of detonation and heat of explosion for triethylamine sensitized nitromethane/nitroethane blends, Figure 13 is a graph depicting the velocity of detonation and heat of explosion for triethylamine sensitized 50/50 nitromethane/nitroethane and nitromethane/l-nitropropane blends.
From the list of co-solvents already approved by the United States Department of Transport (DOT) for the bulk transport of nitromethane (NM), compounds can be found which can be blended with NM to both desensitize it and depress its freezing point. These co-solvents, the required degree of dilution under DOT regulations, and the approximate cost are shown in Table 1. As the freezing points of cyclohexanone, 1,4-dioxane, and methyl chloroform are too high for blends with NM to be in liquid phase at -40C, these compounds are not useful in the present invention. As well, 1,2-butylene oxide and methyl chloroform are too costly for use in bulk. The remaining co-solvents, methanol (ME), l-NP and 2-NP have freezing points ranging from -91C to -104C.
Three additional compounds not approved by DOT are also shown in Table 1: acetone (AC), methylene chloride (MC), and nitroethane (NE).

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The compound chosen as a desensitizer for the nitromethane blend of the invention must be capable of depressing the freezing point of the blend to <-40C. When a solution is cooled, solid begins to separate from the liquid when the temperature reaches the freezing point of the solvent.
For solutions which are not too concentrated, and in which the solvent is either water or one of the more common organic solvents, the solid is pure solvent. Only rarely does the solid consist of solution. Depression of the freezing point can be written as follows:
Tf = kfm where m is the total molality of all the solutes in the solution, and kf is the "molal freezing point depression constant." The value of kf depends only on the nature of the solvent, not on the solute. The above formula is applicable to solutions which are fairly dilute, but with increasing concentration of solute there is some deviation from linearity.
This deviation is due to the tendency of the solute to act as the solvent as the solute's concentration is increased.
Freezing point depression data for NM/MC blends are plotted in Figure 1. The data indicate that a blend freezing point of -40C is possible when approximately 30% MC is present in the blend.
Similar data for NM/NE and NM/2-NP blends are shown in Figures 2 and 3. The data show that a freezing point of - 40C
is possible with a NE or 2-NP content of approximately 23-24%.
Freezing point depression data for blends of NM with ME, l-NP

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and AC are not available but similar trends are anticipated in view of these compounds all having very similar freezing points.
A preliminary evaluation of the influence of the remaining desensitizing compounds on the explosive performance of NM can be made by comparing the velocities of detonation (VOD's). Experimentally determined VOD's for various NM/desensitizer blends from R. Egly, "Recent Developments in Nitromethane-Based Liquid Explosives", Proceedings of the Symposium on Military Applications of Commercial Explosives, The Technical Cooperation Program, Defence Research Establishment Valcartier Report M-2241/72 (1972) (marked "a") and Kusakabe et al., Proceedings of the Sixth International Detonation Symposium, NSWC White Oak, Maryland, U.S.A., NSWC MP 86-194, P.133 (1985) (marked "b") are listed in Table 2 along with the theoretical values given by the TIGER code developed by Cowperrwaite et al., "Tiger Computer Program Documentation"
report No. Z106, Stanford Research Institute, Menlo Park, California, U.S.A. (1973) using a modified BKW equation of state. This data confirms that MC gives the largest degradation in explosive performance (i.e. the largest decreases in VOD) for a specified degree of dilution. The reduction in propagation velocity, and hence post-shock temperature, also suggests that NM/MC blends will be very insensitive to detonation. Based on this conclusion, MC would not provide the advantages of the present invention.
The theoretical VOD's for NM/2-NP blends ranging from 80/20 to 50/50 are only slightly below that for neat NM, however, concern that 2-NP may be a carcinogen makes this compound an undesirable choice as safe handling and transport would not likely be possible.
After consideration of the many relevant issues including statutory regulations, cost, toxicity, carcinogenicity, volatility, freezing point, and explosive performance, only ME, AC, l-NP and NE appear to be desirable for use in the desensitization and freezing point depression of NM.

Experimental Procedure:

In order to assess the relative detonability of various blends of NM with ME, AC, l-NP, and NE, testing was done to determine the critical primer mass for direct initiation of detonation as well as the critical diameter for propagation of detonation. These parameters not only quantify the detonation sensitivity of explosive mixtures from a fundamental perspective, but they also are of direct practical importance in meeting certain engineering requirements.
Testing of the blends was conducted using plastic pipes,l, with a cap,2, fitted to one end. Each pipe,l, was placed on the ground,4, in a vertical position with the capped end at the bottom. Nominal pipe diameters of 5, 7.5, 10, 15, and 20 cm were employed at various stages throughout the study.
The pipes,l, were typically 70-75 cm in length. In general, relatively thin-walled polyethylene (PE), polyvinyl chloride (PVC) or acrylonitrile butadiene styrene (ABS) pipe was used.

However, higher degrees of confinement were imposed on the detonating medium in some of the early tests by burying the pipe,l, and/or using pipes,l, of more substantial construction (Schedule 40 steel or Schedule 80 PVC).
The NM/diluent blends,6, were prepared on a mass percent basis. Mass percent was used for ease of mixing and because this is the method used to classify NM/diluent mixtures in accordance with DOT classification DOT-E6484. Cooling of the blends was performed in a metal container submerged in a slurry of methanol and dry ice. As a given mixture was cooled, it was continuously agitated to ensure homogeneity in both composition and temperature. A digital thermometer was used to monitor the temperature. The mixtures were cooled until they were approximately 2C below the desired test temperature in order to allow for warming during liquid transfer to the pipes,l, and the subsequent time required to arm and fire the charge.
Each mixture was initiated from the capped end of the pipe,l, using a primer,8, of the military explosive DM12 or Composition C-4. Initiation of the primer was accomplished by an electric blasting cap (EBC),10. Primers,8, larger than one kilogram were not used because this size of primer,8, was considered to be an upper practical limit from a military user's standpoint.
All tests were of a "Go"-"No Go" nature. The diagnostic method was straight-forward, consisting of a continuous VOD
probe,12, affixed to the exterior wall of the pipe,l, to monitor the movement of the detonation head through mixture. Output from the VOD probe,12, is transmitted to an oscilloscope for analysis. The EBC,10, is initiated by electrical input transmitted from the firing line by way of a transmission line,16. Details of the setup appear in Figure 4.
The critical primer mass depends on the type of explosive used. DM12 consists of 85% pentaerythritol ( PETN) and 15% grease by mass. Using the trinitrotoluene (TNT) equivalency of 1.169 for PETN the TNT equivalency for DM12 will be very close to unity if the grease binder is assumed to be inert. The actual equivalency could be slightly higher if the binder makes a contribution to the energy release. The TNT equivalency for C-4 is 1.129. Therefore, the critical primer mass based on C-4 is expected to be somewhat smaller than that determined using DM12.
Charge geometry and degree of confinement are also important factors in the initiation phenomenon. When the charge dimensions are small in comparison to the pipe diameter, initiation of a hemispherical detonation wave takes place in the mixture,6. In contrast, a planar detonation wave is formed if the same charge is placed in a rigid pipe having a diameter close to the characteristic dimensions of the charge. Because the high rate of radial divergence makes spherical initiation more difficult than planar initiation, the experimentally determined critical primer mass is expected to be higher in the former scenario than the latter. It should also be noted that the effective charge mass in these experiments is approximately twice the actual mass due to the fact that the charge is sitting on a semi-rigid surface (i.e. the ground,4).

Experimental Results:

Prior to evaluating the detonation sensitivity of the blends, a series of tests (Series "A") was carried out to establish a baseline for neat nitromethane. The results in Table 3 show that undiluted NM at both mild temperatures (10C) and at temperatures approaching its freezing point can be initiated by as little as 25 grams of high explosive primer (HE). The data also point to a critical diameter below 5 cm at low temperatures.
Results of the initial experiments with blends of NM
with AC, ME, and NE appear in Table 4. All tests involved thin-walled plastic pipes. The blend temperature was not controlled during these early trials, but ambient temperatures between 10 and 25C did exist in all cases. As noted previously. a diluent content of at least 23-24% by mass is required to depress the blend freezing point to -40C. Consequently, most of the trials focussed on diluent mass fractions between 30 and 50 percent.
Neither a mixture of 80/20 NM/AC nor 70/30 NM/ME could be detonated using a one kilogram charge, even under these relatively favourable temperature conditions. For this reason, acetone and methanol were dropped from the study.

The test results for NM/NE blends indicate that 70/30 and 60/40 NM/NE blends can be detonated with 250 and 1000 gram primers, respectively. Although a 50/50 blend could not be detonated with one kilogram, it is not clear whether the initiation energy or the pipe diameter (or both) was the cause.
Apart from appearing to be a viable desensitizer and freezing point depressant, the use of NE could have other practical advantages. For instance, NM and NE are both nitroparaffins. As such, they are produced by similar methods and are available from the same supplier. NE is also about half the cost of NM.
Next, an assessment of the detonation sensitivity of NM/NE blends over a wider range of temperatures and confinement scenarios was carried out. Bearing in mind that a 1 kg charge was required to initiate a 60/40 NM/NE blend under mild temperature conditions in Trial Series "B," and appreciating that this blend would become even less sensitive with decreasing temperature, it was concluded that a 60/40 mixture would not meet the"maximum one kilogram primer criterion" over the temperature range of interest. At the same time, the freezing point depression curve for NM/NE (Figure 2) points out the need for a NE content of at least 23-24% to ensure a liquid-phase mixture at -40C. Jointly, these constraints led to the decision to focus on 70/30 NM/NE blends in the next trial series.
Table 5 summaries the results of Trial Series "C".
Tests C-l through C-10 confirm that initiation of detonation of .
this blend is possible under different conditions of confinement at mild temperatures, but not at temperatures near -40C.
However, supplementary tests with a lower NE content (C-ll through C-13) indicate that a blend somewhere between 75/25 and 80/20 NM/NE will come very close to satisfying both the freezing point and maximum primer criteria.
In view of these promising results, it was decided to further expand the data base for NM/NE mixtures. Table 6 summarizes the results of numerous trials conducted in mild or warm weather. Data from additional experiments at nominal temperatures of -40C, 0C, and 40C are compiled in Table 7.
All trials involved thin-walled plastic pipes.
Figure 5 shows a plot of the critical primer mass versus temperature for various NM/NE blends. The curves through the data have no mathematical basis. They are the inventors' best estimates of the likely relationships based on rather limited data. Care must be exercised in interpreting the tabulated data because failure of detonation could be the result of either the critical energy or the critical diameter requirement not being met. For example, the data for a 80/20 NM/NE blend in the 0C temperature range (see Table 7) confirm that detonation occurred using a 50 gram primer in a 10 cm pipe, but did not occur when a 100 gram primer was used in a 5 ~m pipe. Clearly, the inability of the 100 gram charge to initiate detonation in the smaller pipe was due to the charge diameter, and not the primer mass, being too small. Therefore, the lowest "GO" points on the graph for a given mixture define the correct relationship between critical primer mass and temperature.
The data in Figure 5 show that a 75/25 NM/NE blend can be initiated by a primer of 1 kg or less down to temperatures approaching the lower operational limit. The estimated critical primer mass of 620 grams at -28.5C compares to a value of about 25 grams for neat NM at the same temperature. Assuming this ratio remains relatively constant over the narrow temperature range of interest here, it can be concluded that the critical initiation energy for 75/25 NM/NE blends is about 25 times higher than that for neat NM.
A plot of critical diameter versus temperature for the various blends is presented in Figure 6. Although the data are fairly sparse, it is nonetheless possible to identify the relative trends. The critical diameters for 80/20, 75/25 and 70/30 NM/NE blends are estimated to be 10, 15, and 18 cm, respectively, at temperatures approaching -40C.
According to the J.H. Lee and H. Matsui in their 1977 article "A Comparison of the Critical Energies for Direct Initiation of Spherical Detonations in Acetylene-Oxygen Mixtures", Combustion and Flame 28 pp. 61-66, a unique relationship exists between the critical diameter dC for transmission from a round pipe to an unconfined volume and the critical energy Ec for direct initiation of spherical detonation.
These authors proposed that a detonation wave emerging from a tube delivers energy to the outside volume via the work done by the interface separating the expanding combustion productsgenerated in the tube and the gas originally in the larger volume. This so-called "work model" concludes that EC = ~P,.,~UC,~ . dc3 24CC_J
where PC-J~ UC_J~ and CC_J are the Chapman-Jouguet (C-J) pressure, flow velocity, and sonic velocity, respectively. Since the C-J
parameters do not vary significantly for these detonable mixtures, it can be concluded that the critical diameter is proportional to the cube root of the critical energy. Using the above-mentioned factor of 25 between critical energies for 75/25 NM/NE and neat NM, one would expect the critical diameters to differ by a factor of 251/3 or 2.9. Figure 6 shows this to be approximately true.
Based on the above experimental results, the recommended blend for Canadian Forces use would be 75/25 NM/NE.
This blend freezes below -40C, it has a critical diameter of 15 cm at that temperature, and it can be initiated over the range of operational temperatures by a primer of about 1 kg mass or less.
The blends identified above are less sensitive to detonation than neat NM. Although this implies enhanced safety, it has been pointed out that such blends are characterized by critical diameters which might make them unacceptable for use in military applications involving small pipes, hoses, or containers. there is also no guarantee that any of these blends will be approved for bulk road transport by the DOT.

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An approach which might address both concerns is to identify the most insensitive nitroparaffin blend that can still be resensitized back to a useful state at the time of use in the field. If this can be done, it might be possible to classify the unsensitized mixture as a simple flammable liquid for the purposes of transportation and storage. It would only become an explosive compound after adding the sensitizer. Ideally, the end product would have a detonation energy and sensitivity not unlike those of neat NM.
In a military context, the sensitizer could simply be added to the mixture just prior to use in areas of low intensity conflict. In situations of higher intensity conflict where the real possibility of exposure to enemy fire exists, the equipment used by the military engineers could be designed to introduce the sensitizer into the blend either as it leaves the storage reservoir, or after it has been pumped into the container (e.g.
hose, pipe, etc.). Several possibilities exist along these lines. in the case of the high-explosive line charge for minefield breaching, it would be a simple matter to inject the sensitizer into the hose at a safe distance from the personnel and equipment. Appropriate sizing of the hose would ensure that a detonation initiated by enemy fire would not propagate back to the pumping apparatus. Another possibility would be to thread a small diameter sensitizer-filled tube through the hose. Mixing of the sensitizer and nitroparaffin blend would be effected by an explosive burster charge inside the tube. Alternately, the tube could be manufactured from a material that dissolves in the presence of the blend. The inside wall of the hose could also be coated with a slowly dissolving solid-phase sensitizer.
Numerous possibilities exist.
It is well known that NM can be sensitized either by mechanical means such microballoons, or by the addition of certain chemical additives, particularly the amines. Table 8 shows the effect on the card-gap value for NM by adding 5% by mass of various sensitizers. The melting points of these sensitizers, along with their approximate costs, are also included in the table.
Several factors have to be considered when selecting a sensitizer for the present purposes. The most effective sensitizers are ethylenediamine, diethylenetriamine, triethylenetetramine, furfurylamine, propylamine, diethylamine and triethylamine. The first three of these compounds have freezing points above -35C. It is highly likely, therefore, that these sensitizers will precipitate out of solution if they are present in blends at the lowest temperatures of interest here. The fourth compound has an acceptable freezing point (-70C), but it is prohibitively expensive. The final three compounds satisfy both temperature and cost constraints.
However, all are quite caustic and toxic. Triethylamine (TEA), being the least volatile of the group (it boils at 89C) appears to be the best compromise between sensitizing ability, freezing point, safety, and cost.
The following discussion describes the outcome of experiments involving TEA-sensitized NM/NE and NM/l-NP blends.

The test setup and procedures were identical to those outlined above with the exception that the required amount of sensitizer had to be added to the nitroparaffins when the mixtures were prepared.
Tables 9 and 10 summarize the test conditions and results for 80/20 and 70/30 NM/NE blends sensitized by the presence of 4 wt% TEA based on the total weight of the sensitized blend. The effects of adding higher amounts of TEA
(up to 10%) to the more highly diluted 50/50, 40/60, and 25/75 NM/NE mixtures are shown in Tables 11, 12, and 13, respectively.
Tables 14 and 15 summarize the experimental findings for sensitized and unsensitized neat NE.
There are several informative ways to express the data graphically. Figure 7 shows the effect of 4 wt% TEA sensitizer on the critical primer mass for various NM/NE blends. Whereas a 1 kg primer was unable to initiate 50/50 NM/NE under mild temperature conditions in the first part of the study, initiation of the same sensitized blend is now possible at the lower temperature extremes using only 200-300 grams of HE.
Another observation of interest is that sensitized 70/30 NM/NE
has about the same detonation sensitivity as neat NM (e.g. both can be initiated by approx. 25 grams of HE at -40C). A final point worth noting is that sensitized NE can easily be detonated at mild temperatures, while unsensitized NE cannot (see Table 15). The critical primer mass is somewhere in the 250-500 gram range at 20C.

The effect of 10% TEA on the critical primer mass for these blends is illustrated at Figure 8. By comparing Figures 7 and 8, it can be seen that the critical initiation energy decreases by a factor of about 2 when the TEA content is increased from 4% to 10% for blends containing relatively low amounts of NE diluent (i.e. <=30%). This factor increases to about 3 for blends with a high proportion of NE, and to a value near 10 for neat NE. The corresponding reductions in critical diameter would be 20%, 30%, and 50%, respectively, according to the work model of Lee and Matsui.
Figure 9 shows the influence of various amounts of TEA
sensitizer on the critical primer mass for a 50/50 blend of NM
and NE. The data indicate that approximately 40 grams of HE are required to initiate this mixture at -40C if it is sensitized by the presence of 10 wt% TEA. Consequently, this explosive composition is just about as sensitive as neat NM.
In view of the sensitizing ability of TEA on NM/NE
blends, it was decided to examine more carefully the effect of adding various amounts of TEA to neat NE. The results, which are plotted in Figure 10, show that NE is detonable over a wide range of temperatures if appropriately sensitized. It would appear that initiation of detonation by a 1 kg primer might be possible at temperatures near -20C if 10% sensitizer is present in the mixture. This would not be acceptable in a country having a severe climate such as Canada, but it might be acceptable to nations having a more temperate climate.

-A final round of trials focussed on the potential of neat or blended 1-NP as an explosive. An attempt was first made to detonate sensitized 1-NP under the most favourable conditions possible. A mixture containing 12.5 wt% TEA was prepared and heated to a temperature of 45C. A 1 kg charge of C-4 failed to initiate detonation of this mixture in a 20 cm diameter pipe.
Subsequently, it was decided to investigate the detonability of sensitized 50/50 NM/1-NP mixtures. A 50/50 blend was chosen because the DOT has already approved bulk road transport of this formulation. The test results are compiled in Table 16 and plotted in Figure 11. They are indeed encouraging.
Detonation of this composition is possible at -40C using a HE
charge of about 400 grams if the TEA content in the resultant mixture is 10%.
An estimate of the critical diameter for propagation at this temperature can be made by assuming that the relationship between EC and dc that exists for unsensitized NM/NE blends also applies to this explosive composition. It is apparent from Figure 5 that the critical primer mass for an unsensitized 80/20 NM/NE blend at -25C is also about 400 grams. In other words, a 80/20 NM/NE blend at -25C has the same detonation sensitivity as a 50/50 NM/1-NP blend with 10% TEA content at -40C. The corresponding critical diameter for the NM/NE blend is about 8 cm based on the results in Figure 6. Thus, 8 cm would be a reasonable estimate of the critical diameter for the sensitized NM/1-NP mixture at -40C. Note that this diameter would be adequate for most military engineering applications.

One concern about these blends from a user standpoint is that any enhancement in safety might be more than offset by a degradation in explosive performance. Figures 12A and 12B show the results of TIGER calculations for various TEA sensitized NM/NE blends. Although the addition of NE to NM does result in booth a reduced velocity of detonation and heat of explosion, it can be seen that part of this deficit is recovered with the addition of TEA sensitizer. A 50/50 NM/NE blend, for example, has a detonation velocity of 5982 m/s. This is 4.9% below that of 6293 m/s for neat NM. However, the addition of 10% TEA
causes the detonation velocity of the mixture to increase to 6083 m/s. In other words, about one third of the deficit is recovered. A similar trend is apparent in Figures 13A and 13B
for TEA sensitized NM/l-NP blends.
Although a preferred embodiment of the present invention has been described and depicted herein, the present invention may be varied within the scope of the following claims without departing from the spirit of the invention.

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Table 1 Candidate Diluents for the Bulk Transport of Nitromethane Required Degree Approximate Freezing Chemical of Dilution Cost Point (mass %) ($ per litre) ( C) 1,2-Butylene Oxide 40 20 -95 Cyclohexanone 25 5 -16 1,4-Dioxane 35 7 12 Methanol 45 2 -94 Methyl Chloroform 50 15 -30 1 -Nitropropane 48 2 -104 2-Nitropropane 47 2 -91 Acetone - 2 -95 Methylene Chloride - 5 -95 Nitroethane - 2 -90 DOT approved diluents Table 2 Detonation Velocities for Mixtures of Nitromethane with Candidate Desensitizer/Freezillg-Poillt Depres.sants Detonation Velocity (m/s) Candidate Blen(l ~ ass %) Calculated Experimental NM (100) 6300 NM/Methanol (80/20) 6288 NM/Methanol (70/30) 6324 NM/Methanol (60/40) 6368 NM/Methanol (50/50) 6461 NM/Acetone (85/15) 5800b NM/Acetone (80/20) 5754 NM/Acetone (70/30) 5570 NM/Acetone (60/40) 5396 NM/Acetone (50/50) 5266 NM/Methylene Chloride (80/20) 5639 NM/Methylene Chloride (70/30) 5292 5300a NM/Mcthylcllc Chlori(lc (G0/40) 49GG
NM/Methylene Cllloride (50/S0) 4655 NM/1-Nitropropane (80/20) G084 NM/1-Nitropropane (70/30) 6000 NM/1-Nitropropane (60/40) 5898 NM/1-Nitropropane (SS/45) NM/1-Nitropropane (S0/S0) 5863 NM/2-Nitropropane (80/20) 6114 NM/2-NitroproE)alle (70/30) G055 NM/2-Nitropropane (60/40) 6004 NM/2-Nitropropane (50/50) 6028 NM/Nitroetllane (80/20) 6198 NM/Nitroethane (70/30) 6130 NM/Nitroethane (60/40) 6063 NM/Nitroethane (50/50) 5999 - 21~317U

Table 3 Detonability of Nitromethane at Various Temperatures and Degrees of Confinement Trial Charge Temper- Primer Detonation NumberDiameter Confinement1 ature Mass Velocity (cm) ( C) (g HE) (m/s) A-l 15.2 Cor PE 10 25 6400 A-2 15.2 Cor PE 10 50 6150 A-3 15.2 Cor I'E 10 100 G150 A-4 14.6 Sch 80 PVC -25 25 6350 A-5 14.6 Sch 80 PVC -25 100 6300 A-6 7.5 PVC or ABS -25 25 No Trace A-7 7.5 PVC or ABS -26 25 6480 A-8 5.0 PVC or ABS -23 25 Failed A-9 5.0 PVC or ABS -27 50 6500 Cor = Corrugated; Sch = Schedule Table 4 Detonability o~ Mixtures of NitromethaIIe with Candidate Diluents at Ambielltl Temperatures l~ial NM Diluent Charge Primer Detonation Number Mixture Content Content Diameter Mass Velocity (mass %) (mass %) (cm) (g HE) (m/s) ~1 NM/AC 80 20 15.2 1000 Failed ~2 NM/AC 70 30 15.2 1000 F~iled ~3 NM/AC 50 50 15.2 1000 Failed ~4 NM/ME 70 30 15.2 1000 Failed ~5 NM/NE 70 30 10.2 500 5400 13 6 NM/NE 70 30 15.2 100 Failed E~7 NM/NE 70 30 15.2 250 5950 ~8 NM/NE 60 40 15.2 500 Failed ~9 NM/NE 60 40 15.2 1000 5800 ~10 NM/NE 50 50 10.2 500 Failed ~11 NM/NE 50 50 15.2 500 Ambiguous ~12 NM/NE 50 50 15.2 500 Failed ~13 NM/NE 50 50 15.2 1000 Failed Mild weather conditions -Table 5 Detonability of Nitromethane/Nitroethane Mixtures at Various Temperatures and Degrees of Confinement l~ial NM NE Charge Temper- Primer Dctonation Number Content ContentDiametcr Confinementature Mass Velocity (mass 5'o) (mass %) (cm) (C) (g HE) (rn/s) C-1 70 30 15.2 Cor PE 15 100 Failcd C-2 70 30 15.2 Cor PE 15 250 Detonated C-3 70 30 14.6 Sch 80 PVC 15 100 Failcd C-4 70 30 14.6 Sch 80 PVC 15 250 G150 C-5 70 30 15.2 Sch 40 Stecl 40 1000 Failed C-6 70 30 14.6 Sch 80 PVC 40 250 Failed C-7 70 30 14.6 Sch 80 PVC 40 500 Failcd C-8 70 30 14.G Scll 80 rvc40 1000 F;-ilc(l C-9 70 30 15.2 Cor PE 40 1000 (1) C-10 70 30 15.2 Cor PE 40 1000 Failed C-11 75 25 14.6 Sch 80 PVC -39 1000 Failed C-12 80 20 15.2 Cor PE 35 1000 (1) C-13 80 20 15.2 Thin PVC -35 1000 6000 (1) C-4 primer ~iled to detonate with EBC at bw kmperature.

Table 6 Detonability o~ Nitromethallc/Nitroethane Mixtures at Ambient l(~lnpcratures ~ial NM NE Cllargcl~mlper- ~rimer Detonation Number Content Content Diameter ature Mass Velocity (mass %) (mass %) (cm) (C) (g ~E) (m/s) -16 73 27 5 16 100 F~iled 14 73 27 10 17 50 Failed 852 70 30 10 24 100 F~iled 8 G3 37 10 15 100 F~iled 11 63 37 15 16 50 F~iled 9 G3 37 15 15 lU0 6075 342 52 48 15 12 500 Failed 3 52 48 20 15 250 F~iled 152 50 50 15 17 500 F~iled 272 50 50 20 13 500 Failed 472 50 50 20 20 1000 Failcd 1 Mild weathcr conditions.
2 Fornlulated firom indi~idual drum~ of NM and NEI. RPm~ining blcnds ~rrmllated from - drums of neat NE and a 92/8 (NM/NE) blend prepared ~y Angus Chemicals.

-- 29 ~

- Table 7 Detonability of Nltromethane/Nitroethane Mixtures at TcIrll)cratllrc E~ctrclllc~

l~ial NM NE Charge Temper- Primer Dctonation Numbcr Contcnt ContclltDialllctcr.3turc M~ss Vclocity (IllaSS %)(InaSS %)(Clll) (C) (g HE) (III/S) EI~C Failcd 0 100 Failed 33 80 20 10 -1 25 Failcd 32 80 20 10 -2 50 ~2(~0 31 80 20 10 -2 100 Dctonatcd 41 80 20 10 -31 500 Failcd 26 77.5 22.5 5 39 25 Failcd 77.5 22.5 5 40 5() 59()0 24 77.5 æ.5 5 38 100 6()25 46 77.5 22.5 10 1 25 Failed 38 77.5 Z.5 10 0 50 6050 37 77.5 æ.5 10 0 100 6250 21 75 25 5 40 100 Failed 83 75 25 5 43 100 Failcd æ 75 25 10 40 100 5925 0 50 Failcd 1() -1 100 Failcd 36 75 25 10 0 25() (;~)75 44 75 25 15 331 500 Failed 73 27 15 371 1000 627~
86 70 30 15 401 1000 Failcd Blend could not be cooled further because NM bega~ to come out of solution.

, Table 8 Ef~ect of A~ itiVCS (5% I)y lll.lSS) 011 C~r(l Gap Valuc for SCIISitiZC(l Nitromethane Compound Mclting PointCost Gap Increase (C) ($/kg) (mm) Nitromethane -29 5 5-10 Diphenylamine 52 25 5 2-Propanethiol -131 30 28 1-Octene -101 30 34 Acetic Acid 16 10 70 Hydrochloric Acid n/a 5 73 Nitrogen Tetroxide -11l 250 75 2-Propyn-l-ol -53 25 84 Aniline -G 35 145 Sulfuric Acid n/a 7 lG5 Butylamine 49 25 250 Dibutylamille -G2 20 250 Pyridine 42 20 283 Triethylamine -1152 30 287 Fhrfurylamine -70 75 290 Triethylenetetramine 12 20 392 Diethylenetriamine -35 15 428 Ethylenediamine 8 10 458 Diethylamine -503 10 Propylamine -834 25 l Boiling Point = 21 C.
2 Boiling Point = 89 C.
3 Boilil~g Point = 55 C.

4 Boilin~ Point = 48 C.

Table g Dcton~l)ility ~ 80/2() Nitrolrl( tllall( /Nitroctllallc Mixtnr(~s Scllsiti~c(l witll ~iCtllyl~ lillc l~ial NM NE Sensi- Cllarge Temller- Prirner Detonatio NumberContentContent tizer Diameter ature Mass Velocity (mass %) (mass %) (mass %) (cm) (C) (g HE) (In/8) C-14 77 19 41 10.2 - 50 6100 77 19 4 2.5 25 EBC 6000 54 77 19 4 2.5 25 12.5 5925 53 77 19 4 5 æ 12.5 5975 49 77 19 4 10 19 EBC Failed 77 19 4 10 20 12.5 5825 72 77 19 4 5 -30 EBC Failed 73 77 19 4 5 -30 12.5 6150 Dietllylenetriamine sensitizer used in this test. Tricthylamine ænsitizer use(l in all other tcsts.

Table 10 Detonability of 70/30 NitromethaIIe/Nitroethane Mixtures Sensitized with Triethylamine Trial NM NE Sensi- Charge Temper- Primer DctonatiorNumberContentContent tizer Diameter ature Mass Velocity (mass Yo?(mass %) (mass 5~) (cm) (C) (g HE) (m/s) 57 G7 29 4 2.5 28 EI~C Failed 56 67 29 4 2.5 28 12.5 5850 52 67 29 4 10 24 12.5 5775 51 ~7 29 4 1(~ 20 25 58(~(~
71 67 29 4 5 -30 EUC Faile(l Table 11 Dctonability of 50/50 Nitrolllcthalle/Nitroctllalle Mixtures Sensitized with ~iethylamine l}ial NM NE Sensi- Charge Temper- Primer Detonation Number Content Content tizer Diameter ature Mass Velocity (mass %) (mass %)(mass %) (cm) (C) (g E~E) (m/s) 0 15 17 500 Failed 27 50 50 0 20 13 500 Failed 47 50 50 0 20 20 1000 F~iled ~15 48 48 41 7.6 - 50 5500 59 48 48 4 2.5 31 12.5 Failed 58 48 48 4 5 30 12.5 5625 104 48 48 4 5 0 EI~C F~iled 76 48 48 4 10 -35 100 Failed 105 47 47 6 10 -38 50 Failed 99 46 46 8 7.5 -38 50 F~iled - 101 45 45 10 7.5 -37 25 Fàiled 100 45 45 10 7.5 -37 50 5940 I)iethylenetriamine ~Pn~iti7~ r used in this tcst. I~iethylamine ænsitizer used in all other tests.

212317~
-T~hlc '1 ~
Detonability of 40/60 Nitromethane/Nitroethane Mixtures Sensitized with Triethylamine l~ial NM NE Sensi- Chargc Temper- I'rirner I)etonAtio Number Content Content tizer Diamctcr ature M~ss Vclocity (rnass %)(mass %)(Illa~ss %) (Clll) (C) (g HE) (Ill/~) 122 38.4 57.6 4 7.5 8 25 5820 121 38.4 57.6 4 7.5 7 50 5835 120 38.4 57.6 4 10 9 50 5715 119 38.4 57.6 4 10 8 100 5750 106 36 54 10 10 -39 100 Failcd 107 36 54 10 10 -39 250 Failed 109 36 54 10 15 -33 50 Failed 108 36 54 10 15 40 100 5g35 Table 13 Detonability of 25/75 Nitromethane/Nitroethane Mixtures Sensitize(l with Trietllylamille l~ial NM NE Sensi- Charge Temper- Primer Detonation Number Content Content tizer Diameter ature Ma~ss Velocity (mass %) (mass %)(ma~ss %) (clrl) (C) (g HE) (m/s) 125 24 72 4 7.5 5 25 Failcd 124 24 72 4 I.5 3 50 540() 116 22.5 G7.5 10 15 -38 100 Failcd 115 22.5 67.5 10 15 -39 250 5330 110 22.5 67.5 10 15 42 500 5735 -Table 14 l}etonability of ~ltroethanl~ Sensitized by Diethylenetriamine or l~iethylami~e l~ial NE SCllSi- Charge Temper- Primer Dctonation Number Content tizer Diameter ature Mass Velocity (mass ~o)(mass ~) (cm) (C) (g HE) (m/s) ~1 96 41 7.6 - EBC Failed ~2 96 41 7.6 - 250 Detonated ~3 96 41 10.2 - 50 5600 ~4 96 41,2 15.2 30 1000 Failed 96 4 5 27 25 F~iled 61 96 4 5 28 50 Failed 62 96 4 10 29 50 Failed 63 96 4 10 30 100 Failed 64 96 4 10 20 250 Failed 96 4 10 19 500 Failcd 93 96 4 15 14 100 Failed 96 94 6 15 14 100 Failed 103 90 10 15 11 50 Failed 114 94 6 10 0 500 Failed 111 90 10 10 -2 100 Failed 112 90 10 10 -7 250 F~iled 67 96 4 15 42 500 Failed 68 96 4 15 42 1000 Failed 92 90 10 15 -38 1000 Failed Diethylenetriamine scnsitizer used in this tcst. I~icthylamille .scnsitizcr uscd in all other tests.
2 Sensitizer came out of solution when coolcd.

-Table .1.5 Detonability of Neat Nitroethanel l~ial Charge Temper- Primer Detonation Number Diameter ConfineIIlentature Mass Velocity (cm) (C) (g HE) (m/s) El 10.2 Thin PVC - 250 Failed E2 10.2 Thin PVC - 500 Failed E3 10.2 Thin PVC - 1000 Failed E4 15.2 Thin PVC - 1000 Failed ~ld weather conditions 212317~

Table 16 Detonability of 50/50 ~1tromethane/1-Nitropropane Mixtures Sensitize(l with l~iethylamine l~ial NM 1-NP Sensi- Charge Temper- Primer Detonation NumberContentContent ti~er ~iameter ature Mass Velocity (ma8s %)(ma8s %) (mass %) (cm) (C) (g E~E) (m/8) 74 48 48 4 5 20 25 Failed 48 48 4 5 20 50 Failed 77 48 48 4 5 19 100 Failed 79 48 48 4 10 18 50 Failed 127 47 47 6 10 3 50 Failed 128 47 47 G 10 2 100 F~iled 129 46 46 8 10 0 100 Failed 130 45 45 10 10 0 50 F~iled 48 48 4 10 -31 250 Failed 81 48 48 4 15 -32 500 F~iled 84 48 48 4 15 -39 1000 Failed 118 45 45 10 15 40 250 F~iled

Claims (18)

1. A liquid explosive composition sensitized to detonation and having a freezing point below -40°C, consisting of a mixture of nitromethane and a second nitroparaffin selected from the group consisting of nitroethane and 1-nitropropane in an amount adequate to depress the freezing point of nitromethane to below -40°C and render the mixture insensitive to detonation relative to neat nitromethane, and additionally containing from 4 to 10 % by weight of triethylamine based on the total weight of the sensitized composition.

2. The composition as claimed in claim 1 wherein the nitromethane/nitroparaffin mixture is comprised of about 25 to 80 wt% nitromethane and about 75 to 20 wt% nitroethane.

3. The composition as claimed in claim 2 wherein the nitromethane/nitroethane mixture is comprised of about 75 wt%
nitromethane and about 25 wt% nitroethane.

4. The composition as claimed in claim 2 wherein the nitromethane/nitroethane mixture is comprised of about 70 wt %
nitromethane and about 30 wt% nitroethane.

5. The composition as claimed in claim 4 containing about 4 wt% of triethylamine, said composition having a detonation sensitivity and energy very close to that of neat nitromethane.

6. The composition as claimed in claim 2 wherein the nitromethane/nitroethane mixture is comprised of about 50 wt%
nitromethane and about 50 wt% nitroethane.

7. The composition as claimed in claim 6 containing about 10 wt% of triethylamine, said composition having a detonation sensitivity and energy very close to that of neat nitromethane.

8. The composition as claimed in claim 1 wherein the nitromethane/nitroparaffin mixture is comprised of about 50 wt% nitromethane and about 50 wt% 1-nitropropane.

9. The composition as claimed in claim 8 containing about 10 wt% of triethylamine.

10. A process for preparing a liquid explosive composition comprising:

mixing together nitromethane liquid explosive with an amount of a second nitroparaffin selected from the group consisting of nitroethane and 1-nitropropane sufficient to depress the freezing point of nitromethane to below -40°C and render the mixture insensitive to detonation relative to neat nitromethane;

transporting said insensitive mixture to the site where the mixture is to be used; and adding to said insensitive mixture, at the time of use, from 4 to 10 wt% of triethylamine based on the total weight of the mixture, the resulting resensitized liquid explosive composition having a detonation sensitivity and energy very close to that of neat nitromethane.

11. The process as claimed in claim 10 which comprises mixing together about 25 to 80 wt% nitromethane and about 75 to 20 wt% nitroethane to form said insensitive mixture.

12. The process as claimed in claim 11 which comprises mixing together about 75 wt% nitromethane and about 25 wt%
nitroethane to form said insensitive mixture.

13. The process as claimed in claim 11 which comprises mixing together about 70 wt% nitromethane and about 30 wt%
nitroethane to form said insensitive mixture.

14. The process as claimed in claim 13 in which about 4 wt% triethylamine is added to the insensitive mixture.

15. The process as claimed in claim 11 which comprises mixing together about 50 wt% nitromethane and about 50 wt%
nitroethane to form said insensitive mixture.

16. The process as claimed in claim 15 in which about 10 wt% triethylamine is added to the insensitive mixture.

17. The process as claimed in claim 11 which comprises mixing together about 50 wt% nitromethane and about 50 wt%
1-nitropropane to form said insensitive mixture.

18. The process as claimed in claim 17 in which about 10 wt% triethylamine is added to the insensitive mixture.