EP2516355B1 - Fusible/castable explosive composition having low vulnerability - Google Patents

Description

The technical field of the invention is that of fusible / flowable explosive compositions with reduced vulnerability.

The definition of ammunition with reduced vulnerability, often referred to in French by the acronym MURAT (Attenuated Risk Munitions), is today a major concern for developers.

These munitions must have a vulnerability to external aggressions which is strongly attenuated or even nil. Vulnerability tests are defined, for example, by the procedures described in AFNOR NFT 70510 to 70515 or in UN tests 7d) i (bullet impact), 7e) (fire resistance), 7f) (slow heating up). ), 7g), 7h), 7j) and 7k).

This reduced vulnerability is essentially achieved by the use of an explosive composition with reduced vulnerability.

We have already proposed explosive compositions with reduced vulnerability that can be implemented by casting. The patent EP814069 thus describes a number of compositions associating a fuse part and a solid part. The fusible portion essentially comprises a nitrated aromatic such as Trinitrotoluene (TNT) which is associated with a phlegmatizer such as wax.

The solid part generally comprises oxynitrotriazole (ONTA) which is a grain explosive whose vulnerability is reduced. ONTA is more particularly described by the patent EP-210881 .

It is known to associate with ONTA aluminum powder, to increase the blast effect, and also another explosive solid grain to increase the detonation performance of the composition.

It is thus conventional to associate ONTA with Hexogen (RDX) or Octogen (HMX).

However, increasing the mass of hexogen or octogen is at the expense of the insensitivity of the explosive composition that is obtained.

Also known is a reduced sensitivity Hexogen (RDX) which is obtained by a particular crystallization process. This insensitive Hexogene (known commercially under the brand name i-RDX deposited by Eurenco or under the name RS-RDX) is described in particular by US Pat. FR2887544 and FR2917169 .

It is tempting to use such a Hexogen in combination with ONTA to make explosive compositions with reduced sensitivity and in which the proportion of Hexogen and the detonation performance would be increased.

However, such a substitution does not, a priori, bring the expected benefits.

Compositions were thus made in which 40% by weight of Trinitrotoluene and 60% by weight of insensitive Hexogen (supplied by different sources) were combined. The impact pressure values and the number of punched cards were measured (AFNOR standard test NFT 70-502 "Priming the detonation through a barrier").

According to this sensitivity test, the priming is done through screen cards. The number of cards that is given is the minimum number needed to stop priming so as not to initiate an explosive to test. Concretely an insensitive explosive is not initiated through about 140 cards. Classic explosives require more than 200 cards.

These results were then compared with those obtained for a composition combining conventional Hexogen (or non-insensitive RDX) and TNT in the same proportions.

Table 1 below explains the results obtained: <b> Table 1 </ b> Explosive compositions Number of cards Impact pressure (Giga Pascals) TNT 40% / RDX insensitive 60% (supplier A) 234 1.7 TNT 40% / RDX insensitive 60% (supplier B) 234 1.7 TNT 40% / RDX not insensitive 60% 235 1.7

It can thus be seen that the simple substitution of a RDX insensitive to conventional RDX does not modify the sensitivity of a composition combining TNT and RDX.

Indeed, the number of punched cards remains substantially the same. The use of an RDX of insensitive quality therefore does not improve the insensitivity in TNT-based cast casting compositions. These findings were presented at a NIMIC Technical Meeting on Insensitive RDX (presentation " Australian Reduced Sensitivity RDX and its use in polymer Bonded Explosives "made in MEPPEN (Germany) on 17-20 / 11/2003 (BL Hamshere, IJ Locchert, F. Mark - Australian Government, DoD ).

The aim of the invention is to propose a fuse / flowable explosive composition with reduced vulnerability and in which the proportion of Hexogen (RDX) is increased relative to the proportion of oxynitrotriazole (ONTA) (which increases the detonation performances) but without diminishing the insensitivity of the composition thus obtained.

Thus, the subject of the invention is an explosive fuse / castable composition with reduced vulnerability, and comprising, on the one hand, a fusible part formed of at least one fusible explosive, and on the other hand a solid part comprising oxynitrotriazole. (ONTA) and Hexogen (RDX), a composition which is characterized in that the Hexogen is a Hexogen with reduced sensitivity, the granulometry of the insensitive Hexogene being between 315 micrometers and 800 micrometers, while the particle size of ONTA is between 200 micrometers and 400 micrometers, ONTA also has a bulk density greater than or equal to 0.95 g / cm ³ .

According to various embodiments of the invention, the fusible explosive may be chosen from the following compounds: Trinitrotoluene, 2,4,6-Trinitro-N-methyl-Aniline, 2,4,6-Trinitro-3-methylphenol, 3 -Amino-Trinitrotoluene, 2,4,6-Trinitro-Aniline, 1,3,8-TriNitroNaphthalene and its isomeric mixture fusible at 115 ° C, 2,4-dinitroanisole (DNAN).

The fusible portion will advantageously be between 30% and 40% of the total mass of the composition.

• 15% à 35% en masse d'oxynitrotriazole,
• 24% à 50% en masse d'Hexogène insensible et
• 0 à 25% en masse d'aluminium,

les pourcentages en masse étant ici rapportés à la masse totale de la partie solide.The solid part associates:

• 15% to 35% by weight of oxynitrotriazole,
• 24% to 50% by mass of insensitive Hexogene and
• 0 to 25% by weight of aluminum,

the percentages by mass being here referred to the total mass of the solid part.

• 15% à 30% en masse d'oxynitrotriazole,
• 15% à 30% en masse d'Hexogène insensible,
• 0 à 15% en masse d'aluminium,
• 20% à 33% en masse de trinitrotoluène,
• 7% à 10% en masse d'un mélange de cire et d'additifs de coulée, les pourcentages en masse étant ici rapportés à la masse totale de la composition.

More precisely, it will be possible to produce an explosive composition having the following composition:

• 15% to 30% by weight of oxynitrotriazole,
• 15% to 30% by weight of insensitive Hexogen,
• 0 to 15% by weight of aluminum,
• 20% to 33% by weight of trinitrotoluene,
• 7% to 10% by weight of a mixture of wax and casting additives, the percentages by mass being here referred to the total mass of the composition.

• la figure 1 est une photographie de grains d'un ONTA de type 1 (densité apparente supérieure à 0,95 g/cm3), et
• la figure 2 est une photographie de grains d'un ONTA de type 2 (densité apparente inférieure à 0,95 g/cm3).

The invention will be described with reference to the appended figures in which:

• the figure 1 is a grain photograph of ONTA type 1 (bulk density greater than 0.95 g / cm3), and
• the figure 2 is a grain photograph of ONTA type 2 (bulk density less than 0.95 g / cm3).

The work carried out by the inventors led them first of all to choose a particle size of the hexogen with relatively low reduced sensitivity (315 to 800 microns).

However, the various studies carried out on the subject (by the Saint Louis Institute - ISL for example) indicate that the use of small insensitive hexogen granulometries (most often it is the particle size cut 0 to 100 micrometers is recommended) allows to obtain the best results in terms of insensitivity. This recommendation is based on the recognition that small particle sizes for RDX are less sensitive because of the lower number of crystal defects they present.

The inventors have however chosen a larger particle size (thus a priori less suitable) because its association with the 200 to 400 micrometer particle size cut for ONTA leads to a lower porosity for the ONTA / RDX / Aluminum granular mixture and also for the composition. explosive which is then performed after casting TNT.

Table 2 below makes it possible to compare the relative porosities of different combinations of particle sizes: <b> Table 2 </ b> Type of ONTA ONTA granulometry (micrometers) Insensitive RDX granulometry (micrometers) Aluminum particle size (micrometers) Porosity of the granular mixture (%) Type 1 200 to 400 315 to 800 43 9.3 Type 1 200 to 400 75 to 300 43 15.2 Type 1 200 to 400 0 to 200 43 22.9 Type 1 200 to 400 0 to 100 43 34.2 Type 2 200 to 400 315 to 800 43 24.3 Type 2 200 to 400 75 to 300 43 26.8 Type 2 200 to 400 0 to 200 43 30.3 Type 2 200 to 400 0 to 100 43 35.2

For each assay, 48% by weight of ONTA was combined with 22% by weight of aluminum and 30% by mass of insensitive RDX.

Two types of ONTA have been tried which differ in the morphology of their grains. ONTA type 1 is an ONTA with rounded, spheroidal grains with relatively few surface irregularities.

ONTA type 2 is an ONTA whose grains have a more irregular outer shape.

The figure 1 shows a grain photograph of a type 1 ONTA. figure 2 shows a grain photograph of a type 2 ONTA. These photographs were taken under a scanning electron microscope.

In addition to the external appearance of the grains (rounded for type 1 and irregular for type 2), it is easy to distinguish ONTA on the other by the value of their apparent density ρ _b . This density (expressed in grams per cubic centimeter) is calculated by making the ratio of the mass of uncompacted material contained in a given volume (volume which therefore includes the interstitial spaces between the grains).

This apparent density differs from the true density which is that of the material itself and which differs practically not from one type of ONTA to another. The true density of ONTA is of the order of 1.9 g / cm3. The apparent density ρ _b of ONTA Type I tested is greater than 0.95 g / cm 3 (depending on the samples tested, this apparent density was between 0.95 g / cm 3 and 1 g / cm 3).

The apparent density ρ _b of ONTA Type 2 tested is between 0.75 g / cm3 and 0.85 g / cm3.

It is clear that a high bulk density leads to a reduction in the porosity of the powder mixture.

Thus, it can be seen from Table 2 that it is the RDX insensitive combination 315-800 micrometers with ONTA type 1 and with a particle size of 200-400 micrometers which leads to a minimum porosity (approximately 9%) for the granular mixture.

It is also noted in Table 2, and for a given particle size, that the porosity is lower when the chosen ONTA is type 1, ie when it has rounded grains (apparent density of this ONTA included between 0.95 and 1 g / cm3). Any other apparent density value ρ _b of ONTA greater than 1 would reduce the porosity percentage (the theoretical maximum being the real density of 1.9 g / cm 3).

It is this reduction in the porosity of the granular phase which also makes it possible to reduce the porosity of the composition obtained after TNT casting. The decrease in the porosity of the cast composition will reduce its sensitivity to impacts (hot spot stresses during the compression of the intergranular zones).

The inventors have therefore sought to combine particle size fractions of oxynitrotriazole (having the most rounded grains) and insensitive Hexogene which make it possible to reduce this porosity. Cutting optimization granulometry and the choice of a ONTA with high apparent density have resulted in compactness of the optimal granular phase.

The result was a decrease in the sensitivity of the composition while having a higher level of Hexogen. Moreover, the use of an insensitive hexogen relatively large particle size facilitates the implementation (dlemement of the powder easier). The porosity of the mixture of grains will be chosen less than 10% to be guaranteed to obtain a composition porosity of less than 0.5% after casting TNT. Indeed the porosity after casting must be very low to avoid extragranular defects that can generate hot spots that sensitize the composition. Table 3 (next page) summarizes the comparative tests that have been carried out: All the compositions tested combine an overall weight of the ONTA / RDX mixture of 48% and a mass of a TNT / aluminum / casting additive mixture of 52%. The global mass of aluminum is conventionally comprised between 0 and 15% of the total composition, while the additives (phlegmatizer such as wax, combined with an emulsifier and possibly graphite) represent about 7% in mass of the composition produced. An aluminum mass of at least 5% by mass is preferred, which makes it possible to further reduce the porosity with an aluminum having an average particle size of about 43 microns (Table 2). This choice also makes it possible to increase the density of the composition as well as its thermal conductivity, which improves its resistance to slow or rapid heating tests. The compositions therefore differ only in the relative percentages of ONTA (type 1) 200-400 micrometers and insensitive RDX 315-800 micrometers.

The last two rows of the table show the performances of an insensitive composition without RDX and those of a non-insensitive composition combining TNT (50%) and non-insensitive RDX (50%). <b> Table 3 </ b> ∘ Explosive compositions Por o-sity Detonation speed (meters / sec wave) Simulation rapid heating (time before reaction) Simulati on slow heating (time before reaction) TNT + aluminum and additives 52% ONTA 33% / RDX insensitive 15% 0, 3% 7075 89 seconds 51.3 hours TNT + aluminum and additives 52% ONTA 29% / RDX insensitive 19% 0.3% 7090 90.7 seconds 50.8 hours TNT + aluminum and additives 52% ONTA 24% / RDX insensitive 24% 0.4% 7177 89.2 seconds 50.2 hours TNT + aluminum and additives 52% ONTA 21% / RDX insensitive 27% 0.3% 7250 90.5 seconds 51 hours Composition Reference 1 TNT + aluminum and additives 52% ONTA 48% (insensitive composition without RDX) 1.4% 6960 85 seconds 50.4 hours Composition Reference 2 non-insensitive TNT 50% RDX non-insensitive 50% 2% 7640 Unrealized 42 hours

The simulation tests for slow and fast heating are performed in accordance with the corresponding AFNOR standards. The simulations are carried out with the experimental conditions applied during the actual tests (temperature ramps defined in the NFT 70-503 standard and heat flow ramps defined in the NFT 70-513 standard).

It can be seen from Table 3 that the low-porosity compositions obtained (lines 1 to 4) make it possible to obtain the same level of insensitivity that a reference insensitive composition such as the composition Reference 1 (line No. 5 of FIG. table 3). However, they have a detonation level similar to that of an explosive composition that is not insensitive like that Reference 2 given line No. 6 of Table 3.

• 15% à 30% en masse d'oxynitrotriazole,
• 24% à 50% en masse d'Hexogène insensible et
• 0 à 15% en masse d'aluminium.

Explosive compositions are made in which the solid part combines:

• 15% to 30% by weight of oxynitrotriazole,
• 24% to 50% by mass of insensitive Hexogene and
• 0 to 15% by weight of aluminum.

The percentages by mass being related to the total mass of the solid part.

It is of course possible to implement the invention with other types of fusible explosives that trinitrotoluene (TNT).

It will thus be possible to use the nitro aromatics listed in the patent EP814069 2,4,6-Trinitro-N-methylaniline, 2,4,6-trinitro-3-methylphenol, 3-amino-trinitrotoluene, 2,4,6-trinitroaniline, 1,3,8-triNitroNaphthalene and its mixture of fusible isomers at 115 ° C, 2,4-dinitroanisole (DNAN).

All these explosives have a chemical stability similar to that of TNT, which allows to guarantee a behavior to the tests of detonation by influence and impact of projectiles which is close to that of TNT.

It is understood that in the composition according to the invention the fusible portion combines a fuse explosive and a suitable phlegmatizer (such a wax) whose melting temperature will be chosen substantially equal to that of explosive (to plus or minus 2 ° C), the proportion of phlegmatizer should be chosen greater than 3% and preferably of the order of 25% of the mass of the fuse. The mass of phlegmatizer will thus be from 7% to 10% by weight for a fusible portion mass of between 30% and 40% of the total mass of the composition. It is also well known to those skilled in the art that the phlegmatizer is associated with one or more casting additives such as graphite and emulsifier.

By way of example, various compositions (already listed previously in Table 3) have been made and the criterion of sensitivity CS (expressed in kilocalories per square meter) has been calculated.

This sensitivity criterion (CS) has already been described in the patent EP814069 . It is derived from the work done in the chemical industry ( criterion C4 of the Thermodynamic Code CHETAH ASTM chemical Thermodynamic Energy Release Evaluation Program published in November 1974 - Authors: MM Scaton, Freedman and Treweek ). It was evaluated as part of the thesis of Maryse Vaullerin presented at the University of Orleans in 1997: "Study of the vulnerability of molecules and energetic formulations ".

This criterion is based on the calculation of the thermochemical properties of the various constituents of a composition and in particular the enthalpy and the number of gram atoms. It allows to express with a good degree of reliability the potential risk of thermal explosion. The work has shown that for an explosive composition to be considered as not vulnerable to the main tests required by the standards (Afnor NFT 70510 to 70515 or UN tests 7d) i to 7k), the calculated CS should be less than 100. note that when this CS criterion is less than 100 the composition is still not vulnerable. When the CS criterion is greater than 120 the composition is always vulnerable. There is, however, a transition zone when the CS is between 100 and 120, an area in which the compositions can be non-vulnerable, which is verified by the tests. All the compositions proposed in the following examples have a CS less than 120 and they are non-vulnerable.

Example 1 (Table 3 Line No. 4)

• 21% by weight of oxynitrotriazole,
• 27% by mass of insensitive Hexogene,
• 14% by weight of aluminum,
• 31% by weight of trinitrotoluene,
• 7% by weight of a mixture of wax and casting additives.

This composition has a detonation velocity of 7250 m / s and a sensitivity criterion Cs of 115 Kcal ² / mol. Its porosity is 0.3%.

Example 2 (Table 3 line No. 2)

• 29% by weight of oxynitrotriazole,
• 19% by mass of insensitive Hexogene,
• 14% by weight of aluminum,
• 31% by weight of trinitrotoluene,
• 7% by weight of a mixture of wax and casting additives.

This composition has a detonation velocity of 7090 m / s and a sensitivity criterion Cs of 108 Kcal ² / mol. Its porosity is 0.3%.

Example 3 (Table 3 line No. 3)

• 24% by weight of oxynitrotriazole,
• 24% by mass of insensitive Hexogene,
• 14% by weight of aluminum,
• 31% by weight of trinitrotoluene,
• 7% by weight of a mixture of wax and casting additives.

This composition has a detonation velocity of 7177 m / sec and a test sensitivity of Cs ² 112 kcal / mol. Its porosity is 0.4%.

Example 4 (Table 3 line No. 1)

• 33% by weight of oxynitrotriazole,
• 15% by mass of insensitive Hexogene,
• 14% by weight of aluminum,
• 31% by weight of trinitrotoluene,
• 7% by weight of a mixture of wax and casting additives.

This composition has a detonation velocity of 7075 m / s and a sensitivity criterion Cs of 106 Kcal ² / mol. Its porosity is 0.4%.

The explosive composition according to the invention can be used for the loading of all types of projectiles and military heads. This composition can be used to load artillery shells or the bodies of bombs or missiles.

• d'une part la fonte de l'explosif fusible dans lequel on aura incorporé le flegmatisant et les additifs,
• d'autre part le mélange des différents constituants de la partie solide (ONTA, Aluminium, Hexogène insensible).

From the point of view of the manufacturing process of this composition, it will be realized:

• on the one hand, the melting of the fusible explosive in which the phlegmatizer and the additives have been incorporated,
• on the other hand the mixture of the different constituents of the solid part (ONTA, aluminum, insensitive Hexogene).

The solid part will then be incorporated in the fused part by homogenizing the mixture (in a tank equipped with a mixer). The melting and mixing will be carried out under vacuum. Casting in the ammunition body will also be performed under vacuum. A casting equipment that can be used for such a vacuum casting is described by the patent FR2923005 .

Claims (8)

1. An insensitive melt-cast explosive composition incorporating on the one hand a meltable part formed of at least one meltable explosive and, on the other hand, a solid part incorporating oxynitrotriazole (ONTA) and cyclonite (RDX), and optionally aluminium, composition characterised in that the cyclonite is a cyclonite of reduced sensitivity, the particle size of the insensitive cyclonite being of between 315 micrometers and 800 micrometers, whereas the particle size of the ONTA is of between 200 micrometers and 400 micrometers, the ONTA further having an apparent density greater than or equal to 0.95 g/cm³
   and in that the solid part associates:

   - 15% to 25% in mass of oxynitrotriazole,

   - 24% to 50% in mass of insensitive cyclonite and

   - 0 to 25% in mass of aluminium,

   the percentages in mass being relative to the total mass of the solid part.
2. An explosive composition according to Claim 1, wherein the meltable explosive is selected from among the following compounds: Trinitrotoluene, 2,4,6-Trinitro-N-Methyl Aniline, 2, 4, 6-Trinitro-3-methylphenol, 3-Amino-Trinitrotoluene, 2, 4, 6-Trinitro-Aniline, 1, 3, 8-Trinitronaphtalene and its mixture of isomers meltable at 115°C, 2,4-dinitroanisole (DNAN).
3. An explosive composition according to one of Claims 1 or 2, wherein the meltable part constitutes between 30% and 40% of the total mass of the composition.
4. An explosive composition according to Claim 2, wherein it has the following composition:

   - 15% to 30% in mass of oxynitrotriazole,

   - 15% to 30% in mass of insensitive cyclonite,

   - 0 to 15% in mass of aluminium,

   - 20% to 33% in mass of trinitrotoluene,

   - 7% to 10% in mass of a mixture of wax and casting additives, the percentages in mass being relative to the total mass of the composition.
5. An explosive composition according to Claim 4, wherein it has the.following composition:

   - 21% in mass of oxynitrotriazole,

   - 27% in mass of insensitive cyclonite,

   - 14% in mass of aluminium,

   - 31% in mass of trinitrotoluene,

   - 7% in mass of a mixture of was and casting additives.
6. An explosive composition according to Claim 4, wherein it has the following composition:

   - 24% in mass of oxynitrotriazole,

   - 24% in mass of insensitive cyclonite,

   - 14% in mass of aluminium,

   - 31% in mass of trinitrotoluene,

   - 7% in mass of a mixture of was and casting additives.
7. An explosive composition according to Claim 4, wherein it has the following composition:

   - 29% in mass of oxynitrotriazole,

   - 19% in mass of insensitive cyclonite,

   - 14% in mass of aluminium,

   - 31% in mass of trinitrotoluene,

   - 7% in mass of a mixture of was and casting additives.
8. An explosive composition according to Claim 4, wherein it has the following composition:

   - 33% in mass of oxynitrotriazole,

   - 15% in mass of insensitive cyclonite,

   - 14% in mass of aluminium,

   - 31% in mass of trinitrotoluene,

   - 7% in mass of a mixture of was and casting additives.

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