EP2231317A2

EP2231317A2 - Desensitisation by coating crystals of explosive energy substances, coated crystals of such substances, and energy materials

Info

Publication number: EP2231317A2
Application number: EP08865625A
Authority: EP
Inventors: Christine Marraud; Samuel Marre; François CANSELL; Cyril Aymonier
Original assignee: SNPE Materiaux Energetiques SA
Current assignee: Eurenco SA; Safran Ceramics SA
Priority date: 2007-12-19
Filing date: 2008-12-18
Publication date: 2010-09-29
Also published as: WO2009081048A3; RU2010128085A; FR2925488A1; IL206041A0; WO2009081048A2; RU2484887C2; JP2011506262A; FR2925488B1; US20100307648A1; KR20100106493A

Abstract

The invention relates to a desensitisation method that involves coating crystals of an explosive energy substance, wherein said method comprises depositing, in a fluid and not in normal temperature and pressure conditions, preferably in supercritical conditions, a metal and/or polymer film, advantageously a metal film or a polymer film at the surface of said crystals, wherein the metal(s) and/or polymer(s) used have been previously dissolved in a solvent. The invention also relates to coated crystals of an explosive energy substance that can be obtained by said method, and to energy materials containing said coated crystals and/or crystals desensitised by said method.

Description

Desensitization by coating crystals of explosive energy substances; crystals of such coated substances; energetic materials.

The subject of the present invention is: a process for desensitising by coating crystals with an explosive energy substance,

crystals of a coated explosive energy substance, i.e., such desensitized crystals by coating; as well as

the energetic materials containing said coated crystals and / or desensitized crystals by said process.

The present invention more specifically relates to the coating of crystals of explosive energy materials by an inorganic layer

(Metallic) and / or organic (polymer) in order to make said crystals less sensitive to shocks, friction and / or static electricity and to reduce their detonation deflagration transition threshold.

The field of application of the invention covers all that of energetic materials, in particular for defense, space and automobile safety.

• The discovery of ever more powerful energy molecules is a priority for companies working in the field of energy materials. However, the increase in the energy potential of these new molecules, which are in crystalline form, is often accompanied by an increased sensitivity to shocks, friction and / or static electricity as well as a probability of transition from explosion to increased detonation.

In order to desensitize these crystals and facilitate their implementation under satisfactory safety conditions, a known technique is to modify by coating the surface of said crystals for:

+ dissipate heat (and thus slow down the rate of combustion), + absorb energy from inter-crystal shocks and avoid friction

(deformable layer), and

+ promote the flow of electrical charges and thus reduce the sensitivity of the product to static electricity.

The coating material is generally a polymer which can be either inert (US 4,043,850, DE 37 11 995) pyrotechnically or energetically (WO 2000/73245, GB 2 374 867). There are cases where the coating material consists of a polymeric binder charged with a metal in powder form, said metal being used with reference to electrostatic charges (EP 1,500,639).

The coating methods according to US 4,043,850, DE 37 11 995, WO 2000/73245, GB 2 374 867 and EP 1 500 639 are carried out wet. The same is true of the process described in the Journal of Polymer Materials, 21 (2004), 377-382, for the coating of CL-20. The technical problem of removing traces of solvent is then inevitably arisen. Moreover, during the implementation of all these coating processes, the quality of the coating (thickness, continuity of the film, morphology, etc.) can not be satisfactorily controlled.

In general, the prior art does not propose a solution for controlling the deposition of a small predetermined amount of coating material on an explosive crystalline substance. However, the control of the quality and thickness of the coating layer is essential to optimize the compromise between the level of desensitization and the energy of the coated explosive substance. The skilled person is therefore always looking for a method to control at least the amount of coating, so as to obtain a continuous layer as thin as possible. The goal is indeed not to relativize the amount of active product at the expense of a material (coating) less or not energetically active. The method must of course also meet, on the one hand, the handling criteria of explosive materials (that is to say, can be implemented at temperatures low enough not to change the structure of the molecules or crystals) and environmental criteria for the use of volatile solvents (for example, VOC emission).

• At the same time, methods have been developed for the coating of nano- or micron-sized particles for electronic, medical, pharmaceutical or cosmetic applications. The method of depositing thin layers of organic or inorganic materials in supercritical fluid on organic or inorganic particles is thus commonly used in these fields. This method presents the advantage of being operated at low temperature, operating under high pressure, thus allowing its application to organic compounds at low decomposition temperature.

The method of coating with a thin metallic layer of supercritical fluid consists in depositing a thin nanostructured metal layer (ranging from the organization of nanoparticles to the homogeneous nanostructured film) on organic or inorganic compounds. This deposit is made by dissolving a metal precursor in a solvent; said precursor, decomposed, causes precipitation of the metal on the compound to be coated. The method is described in application WO 2000/59622. The reference "Design at the nanometer scale of multifunctional mater / a / s using supercritical fluid chemical deposition, Samuel Marre et al, Nanotechnology Volume 17, Number 18, September 28, 2006, PP 4594-4599" describes the implementation of this method. for the deposition of a copper film (consisting of copper nanoparticles) on submicron silica beads. The process is carried out at temperatures of 100 ^° C. to 150 ^° C. for pressures of 24 MPa. It consists:

contacting, in a fluid containing one or more solvents, the particles to be coated and at least one metal precursor of the coating material; said particles being kept in dispersion in the fluid subjected to supercritical and slightly subcritical temperature and pressure conditions;

causing, within the fluid, the transformation of the precursor of the coating material so that said material is deposited on the particles; then

- To put the fluid under temperature and pressure conditions such that said fluid is in the gaseous state to remove the solvent (s).

The method of coating with a continuous thin layer of polymer in a supercritical medium is also well known, particularly in the pharmaceutical and cosmetic fields. The deposit is made by dissolving the coating agent in a solvent and then by precipitation of said coating agent on the compound to be coated by an anti-solvent effect. By this approach, it is possible to control very finely the deposited layer. WO 2004/91571 discloses a method for depositing a polymer coating on particles using a fluid supercritical, for example supercritical carbon dioxide, as antisolvent which is added a polymer solution and an organic solvent in which the particles are dispersed. The deposition is obtained when the supercritical fluid and the suspended particles are combined to cause the precipitation of the polymer on the particles to be coated.

For the coating of particles, energetic or not, with a polymer, processes in which said polymer intervenes dissolved in a supercritical fluid have also been described, in particular in WO 99/19085, in the review Ind. Eng. Chem. Res., Vol. 44, No. 17, 2005, p. 6523-6533, in DE 197 11 393 and in EP 0 706 821. The implementation of said methods is limited by the generally low solubility of polymers in supercritical fluids. Thus, it is difficult, if not impossible, during the implementation of said methods, to control the quality and thickness of the coating generated.

In such a context, it is the merit of the inventors to have selected a coating technique under pressure and temperature, to have transposed to the field of explosive energy molecules, to have shown that said technique was suitable for generating deposits layers of metal and polymer layers on the surface of the crystals of such molecules, to have shown that said technique could be implemented to generate such deposits, thin, continuous, uniform, over the entire surface of said crystals, so that said crystals are desensitized without their energy performance being significantly altered.

According to its first object, the present invention therefore relates to a desensitization process by coating crystals with an explosive energy substance. Typically, said coating process comprises: - the preparation of a solution, containing, dissolved:

at least one precursor of a coating material, said coating material being chosen from metals and their mixtures, and / or

+ a coating material selected from polymers and mixtures thereof;

suspending the crystals in said solution; the deposition, implemented in a fluid, outside the normal conditions of temperature and pressure, preferably under supercritical conditions, of a metallic and / or polymeric film, advantageously of a metallic film or of a polymeric film on the surface of said crystals (the film in question is generally a metal film or a polymer film but a mixed film (metal + polymer) is not excluded (see below)).

Under such conditions - outside the normal conditions of temperature and pressure, advantageously outside said normal conditions, in the liquid domain of the fluid in question, very advantageously (= preferably) under supercritical conditions - it is possible to obtain the expected result, without having to reach high temperatures that the explosive energy substance in question, sensitive to temperature, could not withstand.

Under such conditions - outside normal temperature and pressure conditions, advantageously outside said normal conditions, in the liquid domain of the fluid in question, very advantageously (= preferably) under supercritical conditions - it has proved possible to generating on the surface of the crystals a metallic coating and / or (generally or) polymer. It has, moreover, proved possible to generate such a coating, thin, continuous, uniform, over the entire surface of the crystals.

Characteristically, in the context of the implementation of the method of the invention:

the coating material or its precursor is previously dissolved in a solvent: this leaves the possibility of optimizing the choice of the couple: coating material or its precursor / solvent, of adjusting the concentrations of said material or precursor in said solvent ... and thus makes it possible to control subsequently the deposition of the coating material; said coating material is deposited at a temperature greater than ambient temperature (greater than 25 ^° C., generally greater than 30 ^° C.) and at a pressure greater than atmospheric pressure. Advantageously, it is implemented in the liquid field of the fluid in question (above the liquid / gas curve) outside said normal temperature and pressure conditions. Preferably, it is implemented under supercritical conditions. The process in question, implemented (for the deposition of the coating material) typically under pressure and temperature, is of the type described for application in other fields (see above); process based on the reduction of a metal precursor in a medium under pressure and temperature, preferably supercritical, for the deposition of a metal film; so-called anti-solvent process for the deposition of a polymer film. These two variants of implementation are specified hereinafter.

The fluid that operates under pressure and temperature during the implementation of the process of the invention is advantageously carbon dioxide (CO ₂ ). In general, it is the fluid most used when one aims to work in supercritical conditions. Indeed, it has critical coordinates easily attainable (T _c = 31 ° C and

P _c = 7.38 MPa). Moreover, it is cheap, nontoxic and chemically stable. However, it is not possible to exclude from the scope of the invention the implementation of the process with the intervention of a fluid, other than CO ₂ , under supercritical conditions.

It has been indicated above that the process of the invention makes it possible to obtain thin, continuous, uniform layers over the entire surface of the crystals. It is particularly suitable for depositing:

a mass of metal film and / or (advantageously or) polymer, on each coated crystal, which represents from 0.3 to 6% of the total mass of said coated crystal; to advantageously deposit: a mass of metal film and / or (advantageously or) polymer, on each coated crystal, which represents 2 to 4% of the total mass of said coated crystal.

Thus, the process of the invention is particularly suitable for depositing a layer of metal particles (Cu) with a thickness of the order of 50 nm, which corresponds to a measured mass ratio of 2.6%.

The metal layer in question is a blanket (continuous layer) made of nanoparticles.

Incidentally, it is noted here that the process of the invention is not limited to obtaining such thin coating layers, but the fact that it makes it possible to obtain such thin, but also continuous, uniform layers is particularly advantageous. interesting. It is now proposed to specify a variant of the method of the invention implemented for the deposition of a metal film. Incidentally, the deposition of such a film on the surface of crystals of explosive energy substances is totally novel. The process of the invention is advantageously used for the deposition of a metal film of at least one metal chosen from nickel, copper, aluminum, titanium, zirconium and / or at least one oxide of such a metal. The metal film in question contains the metal (the metals), the corresponding oxide (s)) or a mixture thereof.

The composition of the coating film is controlled by controlling the parameters of the process and more particularly the pressure and the temperature of implementation of said process as well as the composition of the reaction medium. The method of the invention, implemented for the deposition of a metal film, is advantageously of the type described in WO 2000/59622. It is based on the reduction of a metal precursor. He understands :

- the preparation of a solution containing at least one metal precursor of at least one metal (coating);

suspending the crystals in said solution;

- bringing into contact with the suspension obtained with a solvent fluid of said solution, outside the normal conditions of temperature and pressure; the reduction, within said fluid, outside the normal temperature and pressure conditions, of said at least one precursor so that said at least one metal is deposited on the surface of said crystals.

It therefore comprises contacting, under temperature and pressure, the crystals with a medium containing the dissolved precursor. The heating of the medium causes the precursor to decompose on the surface of the crystals, resulting in the formation of a (metallic) film.

Under the conditions indicated, outside the normal conditions of temperature and pressure (advantageously under such conditions, in the liquid domain of the fluid in question, very advantageously, under supercritical conditions), the fluid used is therefore the solvent of the solution containing said at least one precursor. Said at least one precursor is advantageously chosen from metal acetates and acetylacetonates, advantageously from metal hexafluoroacetylacetonates. Such acetylacetonates have a high solubility in supercritical CO ₂ . Said at least one precursor is very advantageously copper hexafluoroacetylacetonate.

The reduction of the precursor is advantageously carried out in the presence of hydrogen (reducing agent). A catalyst (such as Pd) can also advantageously be involved. As a purely illustrative example, a mode of implementation of this variant of the method of the invention is explained below:

1. A known amount of precursor (Cu [hfac] 2) is solubilized in a cosolvent (alcohol). The charges (crystals) of CL20 are added and then dispersed by stirring. The co-solvent improves the solubility of the precursor (Cu complex) in the supercritical CO ₂ (see below) and assists in the reduction reaction.

2. The mixture is placed in a pressurized reactor with CO ₂ and H ₂ .

3. The reactor (of constant volume) is heated to supercritical conditions. Once the required pressure and temperature levels have been reached, it is stabilized for a definite time to allow the decomposition of the precursor.

4. Cu nanoparticles are deposited on the surface of the crystals. The thickness of the deposited layer is obviously a function, for defined conditions, of time and temperature. It also depends on the initial concentration of precursor.

5. The coated crystals are then recovered either in dispersion in the co-solvent (after decompression and removal of CO ₂ + H ₂ ), or in dry form (after entrainment of the cosolvent by the gases). In general, it can be specified that the thickness of the deposited metal film is controlled, inter alia, by the temperature, the contact time and the concentration. The temperatures for carrying out the reduction vary according to the exact nature of the precursors involved. They generally vary between 70 ^° C. and 270 ^° C., which makes it possible to be below the decomposition temperatures of explosive energetic substances. It is now proposed to specify a variant of the process of the invention implemented for the deposition of a polymer film. Incidentally recall here that the deposition of such a film had been obtained, according to the prior art, wet. The films obtained by the method of the invention are of better quality than those obtained according to the prior art (they are deposited, over the entire surface of the crystals, in a continuous and uniform manner, advantageously in a very small thickness).

The process of the invention is advantageously used for the deposition of a polybutadiene polymer film, in particular a hydroxytelechelic polybutadiene (PBHT), polyurethane (PU), in particular a diethylene glycol polyadipate (PADEG), a polyoxyethylene / polyoxypropylene copolymer (POE / POP), glycidyl polyazide (PAG) or a mixture of such polymers.

The method of the invention, implemented for the deposition of a polymer film, is advantageously of the type described in WO 2004/91571. It is as indicated above an antisolvent process. He understands ;

the preparation of a solution of at least one polymer in a solvent; suspending the crystals in said solution;

- The bringing into contact with the suspension obtained with an anti-solvent fluid, outside the normal conditions of temperature and pressure, to induce (cause) the precipitation of said at least one polymer on the surface of said crystals. The crystals are dispersed in a solution of at least one polymer. This solution is placed in a reactor which is then pressurized with an anti-solvent (miscible with the first solvent), which causes the precipitation of the at least one polymer on the surface of the crystals. For illustrative purposes only, a mode of implementation of this variant of the method of the invention is specified below.

1. PBHT is dissolved in a solvent (dichloromethane, for example). The fillers (crystals of CL20 for example) are added and the mixture is stirred mechanically. 2. This solution is placed in a reactor. 3. CO ₂ (anti-solvent and solvent of the first solvent) is injected under the required conditions. The reactor is then filled with supercritical solvent, resulting in the precipitation of PBHT on the surface of the crystals. 4. The purge valves are then ajar. Traces of solvent (dichloromethane) are entrained, for example by sending a flow of CO ₂ .

This variant of the process of the invention, implemented under supercritical conditions (preferred embodiment), can be described as SAS ("Supercritical Anti-Solvent").

The characterization techniques made it possible to observe the uniformity of the layer (context of CL20 coated with PBHT or PAG). To quantify the deposited layer, it is expressed in mass percentages, perfectly measurable, which speak to those skilled in the art (see above). Layers of PBHT deposited on silica beads according to the process of the invention have thicknesses of 7 ± 2 nm, for a mass ratio of 3% (the density of the silica is obviously not that of CL20). .

The methods of the invention, as specified above, are advantageously implemented:

with a metal precursor: however, it is in no way excluded that at least two such precursors intervene for the deposition of the same metal or for the joint deposition of at least two metals; or

with a polymer: it is however not excluded that at least two such polymers intervene for the joint deposition of said at least two polymers.

Joint deposition of at least one metal and at least one polymer is not totally excluded from the scope of the invention. The control of such a deposit, mixed, is obviously more delicate. It is necessary to involve upstream at least one metal precursor and at least one polymer in solution and determine the conditions of temperature and pressure, in particular, where the at least two reactions provided (reduction of said at least one precursor to at least one metal and precipitation of said at least one polymer) take place. Finally, referring to the process of the invention, it is advantageously used for coating, under pressure and he

temperature, an explosive energy substance of the organic secondary explosive type, in particular selected from: roctahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX or octogen), hexahydro ~ 1, 3 , 5-trinitro-1,3,5-triazine (RDX, hexogen or cyclonite), 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL20 or HNIW), and 4,10-dinitro-2, 4,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX). By implementing the method of the invention, perfectly controllable and reproducible, the coating of explosive substances may have unequaled uniformity and thinness characteristics. The sensitivity of the coated explosive substances can thus be reduced while maintaining energy levels close to those of the uncoated substance.

According to its second object, the present invention relates to coated crystals of an explosive energy substance, obtainable by the method described above: coating process with a metal film and / or (advantageously or) polymer, put typically, outside normal temperature and pressure conditions. Said coated crystals are novel by the nature of the film in question and / or by the characteristics thereof (quality (uniform and continuous character, on any surface of the crystals) and / or deposited quantity). The crystals coated with a metallic film are new per se.

The crystals coated with a polymer film (or even a mixed film: polymer + metal) are new because of the characteristics of the coating. Said characteristics - original and particularly interesting - result from the original implementation of the coating, under pressure and temperature with a suspension, containing in solution the coating material or at least one precursor thereof (said material or said at least one precursor thereof having been dissolved upstream in a solvent (the nature of said solvent and the concentration of said material or said at least one precursor within said solvent having been optimized) (see above). The coated crystals of the invention advantageously have:

a mass of the metal film and / or (advantageously or) polymer which represents, for each coated crystal, from 0.3 to 6% of its total mass; present very advantageously:

a mass of the metal film and / or (advantageously or) polymer which represents, for each coated crystal, from 2 to 4% of its total mass.

In view of the above description of the coating process, it is understood that: the coated crystals of the invention are advantageously coated with a metal film of at least one metal chosen from nickel, copper, aluminum, titanium, zirconium and / or at least one oxide of such a metal; or coated with a polybutadiene polymer film, in particular a hydroxytelechelic polybutadiene (PHBT), polyurethane (PU), in particular a polyadipate diethylene glycol (PADEG), a polyoxyethylene / polyoxypropylene (POE / POP) copolymer, polyazide glycidile

(PAG) or a mixture of these polymers; that said crystals are advantageously crystals of an organic secondary explosive chosen especially from those identified upstream in the present text.

According to its third object, the present invention finally relates to energetic materials incorporating in their composition the crystals of the invention, coated crystals per se and / or desensitized crystals obtained by the process of the invention. The energetic materials contain an effective amount of said coated or desensitized crystals. In fact, generally, they consist of said crystals or contain, in an effective amount, in a binder.

It is now proposed to illustrate the invention, in no way limiting, by the accompanying figures and examples below. - Figures 1-1 to 1-6 show Microscope analysis

Scanning Electronics (SEM) of an initial ε-CL20 crystal (Figure 1-1), a such a copper-coated CL20 crystal (FIG. 1-2) according to the method of the invention of example 1.5 and then elementary maps EDX (X-ray analysis technique associated with SEM analysis) of the surface of such a crystal of CL20 coated according to the invention with copper: image of the crystal coated with Cu by SEM (FIG. 1-3), EDX mapping on this coated crystal making it possible to identify the nitrogen (FIG. 1-4), the carbon (Figure 1-5) and copper (Figure 1-6).

FIG. 2 shows an X-ray photoelectron spectroscopy spectrum (XPS) of a copper coated CL20 crystal according to the method of the invention of example 1.5 (the intensity is plotted on the ordinate in an arbitrary unit (ua); )) - The enlargement of the copper peak allows us to see the proportions of copper metal (right peak) and copper in oxidized form (precursor, copper oxide - left peak) deposited on the surface of the crystal of CL20. Metallic copper is predominantly present on the surface of CL20.

FIG. 3 shows a high resolution scanning electron microscopy image made on Cu coated CL20 crystals according to the method of Example 1.4.

FIGS. 4-1 to 4-3 show scanning electron micrographs taken on CL20 crystals without coating

(Figure 4-1) then on such crystals of CL20 coated with PBHT (Figure 4-2) (Figure 4-3) according to the method of the invention of Example 3. The presence of PBHT is clearly visible at places indicated by the arrows. In the context of the examples, the reaction is carried out, in closed mode (batch), in a high-pressure high temperature reactor of 255 cm ³ of internal volume.

EXAMPLE 1 Coating of CL20 Crystals with a Copper Film

Example 1 relates to the application of the method of the invention to the coating with a copper film of the explosive substance 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW or CL20). Supercritical deposition condition of Example 1.5 of Table 1

The test was carried out by preparing a solution comprising

15 ml of isopropanol + 1.2 g of Cu (hfac) ₂ .H ₂ θ + 60 mg of Pd (hfac) ₂ · H ₂ O.

3.5 g of CL 2 O are added thereto, and the suspension obtained is then placed in the bottom of the reactor. 2.5 MPa of H _{2 are} injected into said reactor, and the pressurization with CO _{2 is completed} up to 9 MPa. The chamber is then brought to the desired conditions (100 ^° C., 22 MPa) for a relatively short exposure time (45 minutes). Then, the reactor is cooled, then depressurized. The powder corresponding to the copper-coated CL20 is recovered at the bottom of the reactor in isopropanol.

Characterization of the products obtained from Example 1.5 of Table 1

Copper-coated CL20 has a gray / black color

(copper red under optical microscope), while the CL20 before coating is white.

The copper deposition on the CL20 crystals was characterized by

5 techniques:

• scanning electron microscopy (SEM),

• analysis of X-ray dispersed energy (EDX), • X-ray photoelectron spectroscopy (XPS),

• Atomic absorption.

The morphology of copper-coated CL20 crystals was characterized by scanning electron microscopy (SEM). In addition, the use of EDX (MEB-associated X-ray analysis technique) allowed surface elemental analysis to determine the elements present (Fig. 1).

It can be seen in the image obtained by SEM that the surface of the CL20 crystals is covered by nanoparticles with a size of between 50 and 300 nm (FIG. 1-2). EDX analyzes allowed surface mapping of the sample by element (Figures 1-4,1-5,1-6). The mappings of certain elements constituting the CL20 (N, C) make it possible to recover the shape of the crystal of the initial image (FIG. 1-3), while FIG. 1-6 corresponds to the detection of copper. We can notice that this one is present on all the surface of the crystal. In order to determine the degree of oxidation of copper on the surface of the CL20 crystals, XPS characterizations (FIG. 2) were carried out.

Peaks corresponding to the binding energies of the carbon, oxygen, nitrogen, copper and palladium atoms can be clearly distinguished. The (low) presence of palladium comes from the precursor of palladium (Pd (hfac) ₂ ) catalyst of the reduction of the copper precursor. The enlargement of the copper peak makes it possible to see the proportions of metallic copper (right peak) and copper in oxidized form (precursor, copper oxide - left peak). Metallic copper is predominantly present on the surface of CL20.

The copper present on the surface was determined by atomic absorption. To do this, the samples were washed twice with isopropanol and then filtered in order to remove unencumbered copper particles on the surface of CL20. A gray / black powder is recovered which is dispersed in a nitric acid solution (30% v / v). The CL20 is not modified during this manipulation, while the copper is dissolved to form a measurable Cu ²⁺ solution. The copper (II) solution can then be determined. The mass percentage of copper present on the surface is 2.76% under the conditions of Example 1.5. However, this value can be varied by varying the parameters of the reaction (initial precursor concentration, catalyst concentration, injection sequences in the precursor and catalyst reactor, reaction time) between 0.3 and 30%. as shown in Table 1. Those skilled in the art will be able to adjust these parameters according to their needs.

Table 1: Percentage of Cu deposited on the CL20 crystals as a function of the reaction parameters.

When the deposited copper content is low, SEM images show non-contiguous nanometric copper particles deposited on the surface of the crystal. This is the case for the deposit presented in FIG. 3 obtained according to the reaction parameters of example 1.4.

Property of the material obtained according to Example 1.5 Sensitivity

The sensitivity of the copper-coated CL20 crystals of Example 1.5 was evaluated by following standardized ISI * impact sensitivity, ISF ** friction, ES *** electrical ignition, and critical height tests. without TDD confinement ****. Table 2 below presents the results obtained by comparison with the initial ε-CL20.

Table 2: Comparison of sensitivity tests for the reference ε-CL20 crystals and the product obtained in Example 1.5.

* ISI: The test carried out corresponds to that described in standard NFT 70-500, itself similar to UN test 3a) ii) resulting from the "Recommendations on the Transport of Dangerous Goods - Manual of Tests and Criteria , Fourth revised edition, ST / SG / AC.10 / ll / Rev.4, ISBN 92-1-239083-8ISSN 1014-7179 ". By a minimum series of 30 tests, the energy resulting in 50% (method of treatment of Bruceton results) of positive results of an explosive substance subjected to shocks of a sheep is determined. The material to be tested is confined in a steel device consisting of two rollers and a guide ring. By modifying the mass and the drop height of the sheep, the energy can be varied from 1 to 50 J. ** ISF: The test performed corresponds to that described in standard NF T 70-503, itself similar to UN test 3b) ii). By a minimum series of 30 tests, the force resulting in 50% positive results of an explosive substance subjected to friction is determined using the Bruceton method. The material to be tested is placed on a porcelain wafer of defined roughness, moved in a single back and forth motion, of 10 mm amplitude at a speed of 7 cm / s when empty, compared to a pencil. porcelain resting on the material. The force applied to the porcelain pencil which is pressed on the material may vary from 7.8 to 353 N.

*** ES: The test performed is a test developed by the Applicant with no equivalent NF or UN. The material to be tested, placed in a cup of diameter 10 mm and height 1.5 mm, is placed between two electrodes and is subjected to an electric spark of variable energy from 5 to 726 ml. pyrotechnic or not and we determine the threshold of energy no longer ensuring the initiation of the material. This value is confirmed by 20 successive tests.

**** Ypp. The test consists of measuring the ability of a mass of divided material (grain bed) to pass from combustion to detonation following ignition, performed on the surface of the bed, specifically for CL20, otherwise at the base of the powder bed. The N ° 55 SNPE test consists of filling a 40 mm diameter metal tube of variable height. The tube is open at one end. The critical height leading to a violent reaction is determined from the effects noted on the tube.

The presence of copper on the surface desensitizes the material, since there is a clear decrease in sensitivity to impact, friction and a quasi insensitivity to static electricity. On the other hand, regarding the results of TDD, the critical height is increased by a factor greater than 2. Energy power

Table 3 below compares the values of density p, pulse Is and pulse volume Isxp calculated for three types of propellants comprising in their composition either ε-CL20 or copper-coated CL20 according to Example 1.5.

Table 3: Comparison of the p, Is and Isxp values obtained by calculation with two different Azalanes® compositions (Al: 18% w / w, ammonium perchlorate: 12% w / w + binder + explosive substance).

The density of the coated substance increases slightly with respect to the initial substance due to the presence of (approximately) 3% copper. The specific impulse of the copper-coated CL20 according to Example 1.5 is, on the other hand, reduced. However, the value of the Isxp, which takes into account the specific pulse and the density of the product is almost equal to that of a composition using ε-CL20.

EXAMPLE 2: Coating TEX crystals with a copper film

Example 2 relates to the application of the process to the coating with a copper film of the explosive substance 4,10-dinitro-2,4,6,8,12-tetraoxa-4,10-diazaisowurtzitane so-called TEX. Table 4 below gives the two reaction parameters and

The amount of copper deposited, assayed according to the method described in Example 1.

Table 4: Percentage of Cu deposited on the TEX crystals as a function of the reaction parameters.

O

EXAMPLE 3 Coating of CL20 Crystals with a PBHT Film (PBHT = Hydroxytelechelic Polybutadiene)

Example 3 relates to the application of the method to the coating with a PBHT polymer film of the explosive substance 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW or CL20).

Operating mode

The principle of polymer deposition on the surface of CL20 crystals is based on an antisolvent process under supercritical conditions. The polymer is dissolved in a dichloromethane solution

(DCM) to which are added the explosive substance crystals, insoluble in DCM. The charged solution is placed in the reactor which is then pressurized with a supercritical antisolvent (ScCO ₂ , miscible with DCM), which causes the precipitation of PBHT on the surface of the crystals of the explosive substance. The removal of the DCM is done by slow depressurization and sweeping of an antisolvent flow for a determined duration (drying time). The crystals coated with the polymer are recovered in the bottom of the reactor in the form of a dry powder. The polymer deposition on the CL20 crystals was characterized by SEM and UV-Visible spectroscopy.

UV-Visible spectroscopy makes it possible to determine the amount of polymer deposited on the surface of the crystals. The principle of the assay is to redissolve the deposited polymer by placing a certain amount of crystals embedded in DCM. The solution is then filtered and the polymer collected is assayed.

The reaction conditions of Example 3 and the percentage of PBHT are given in Table 5 below.

Table 5: Percentage of PBHT deposited on CL20 crystals as a function of reaction parameters.

Characterization of the product

The PBHT coated CL20 crystals are white in color and have an expanded texture compared to the initial powder (Figure 4).

The sensitivity of the PBHT-coated CL20 crystals of Example 3 was evaluated by following the standardized tests described in Example 1. Table 6 below shows the results obtained by comparison with the initial ε-CL20.

Table 6: Comparison of sensitivity tests for the initial substance ε-CL20 and the coated product of Example 3.1.

The PBHT coating reduces sensitivity to ISF friction and static electricity, and to a lesser extent to ISI impact. It significantly decreases the sensitivity to the TDD test.

Claims

1. Process for the desensitization by coating crystals of an explosive energy substance, characterized in that it comprises: - the preparation of a solution, containing, dissolved:

+ a coating material selected from polymers and mixtures thereof;

suspending the crystals in said solution;

the deposition, implemented in a fluid, outside the normal conditions of temperature and pressure, preferably under supercritical conditions, of a metallic and / or polymeric film, advantageously of a metallic film or of a polymeric film on the surface of said crystals.

2. Method according to claim 1, characterized in that said fluid is CO ₂ .

3. Method according to claim 1 or 2, characterized in that the mass of said deposited metal film or polymer represents, for each coated crystal, from 0.3 to 6% of its total mass; in that advantageously, the mass of said deposited metal or polymer film represents, for each coated crystal, from 2 to 4% by weight of its total mass.

4. Method according to any one of claims 1 to 3, characterized in that it comprises the deposition of a metal film of at least one metal selected from nickel, copper, aluminum, titanium, nickel, zirconium and / or at least one oxide of such a metal.

5. Method according to any one of claims 1 to 4, characterized in that it comprises: - the preparation of a solution containing at least one metal precursor of at least one metal;

suspending the crystals in said solution;

- bringing into contact with the suspension obtained with a solvent fluid of said solution, outside the normal conditions of temperature and pressure; the reduction within said fluid, outside normal temperature and pressure conditions, of at least one precursor so that said at least one metal is deposited on the surface of said crystals.

6. Process according to claim 5, characterized in that said at least one precursor is chosen from metal acetates, acetylacetonates of metals, advantageously from metal hexafluoroacetylacetonates; in that said at least one precursor very advantageously consists of copper hexafluoroacetylacetonate.

7. Process according to claim 5 or 6, characterized in that said reduction is carried out in the presence of hydrogen.

8. Process according to any one of Claims 1 to 3, characterized in that it comprises the deposition of a polybutadiene polymer film, in particular of a hydroxytelechelic polybutadiene, of polyurethane, in particular of a diethylene glycol polyadipate, of a polyoxyethylene / polyoxypropylene copolymer, glycidyl polyazide or a mixture of such polymers.

9. Method according to any one of claims 1 to 3 and 8, characterized in that it comprises: - the preparation of a solution of at least one polymer in a solvent;

suspending the crystals in said solution;

- The bringing into contact with the suspension obtained with an anti-solvent fluid, outside the normal conditions of temperature and pressure, to induce the precipitation of said at least one polymer on the surface of said crystals.

10. Method according to any one of claims 1 to 9, characterized in that the explosive energy substance is an organic secondary explosive, especially selected from octahydro-1,3,5,7-tetranitro-l, 3,5 , 7-Tetrazocine, hexahydro-1,3,5-trinitro-1,3,5-triazine, 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane and 4,10-dinitro-2,4,6 , 8,12-tetraoxa-4,10-diazaisowurtzitane.

11. Crystals of a coated explosive energy substance obtainable by the process according to any of claims 1 to 10.

12. Crystals according to claim 11, coated with a metal film.

13. Crystals according to claim 11, coated with a polymer film.

14. Crystals according to any one of claims 11 to 13, characterized in that the mass of said metal film or polymer represents, for each coated crystal, from 0.3 to 6% of its total mass; in that advantageously, the mass of said metal or polymer film represents, for each coated crystal, from 2 to 4% of its total mass.

15. Crystals according to any one of claims 11 to 14, characterized in that they are coated with a metal film of at least one metal selected from nickel, copper, aluminum, titanium, zirconium and or at least one oxide of such a metal.

16. Crystals according to any one of claims 11 to 14, characterized in that they are coated with a polybutadiene polymer film, in particular a hydroxytelechelic polybutadiene, polyurethane, especially a polyadipate diethylene glycol, a copolymer polyoxyethylene / polyoxypropylene, glycidyl polyazide or a mixture of these polymers.

17. Crystals according to any one of claims 11 to 16, characterized in that the explosive energy substance is an organic secondary explosive, especially selected from octahydro-1,3,5,7-tetranitro-l, 3,5 , 7-Tetrazocine, hexahydro-1,3,5-trinitro-1,3,5-triazine, 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane and 4,10-dinitro-2,4 , 6,8,12-tetraoxa-4,10-diazaisowurtzitane.

18. Energy materials, characterized in that they contain an effective amount of coated crystals according to any one of claims 11 to 17 and / or desensitized crystals obtained by the method according to any one of claims 1 to 10.