EP1500639A2 - Pyrotechnic material and method for manufacturing - Google Patents

Abstract

Powder comprising cores of a first material coated with a binder layer containing nanoparticles of a second material is new. An independent claim is also included for producing a powder as above by preparing a solution of the binder in a first solvent (S1), preparing a bath of carrier liquid immiscible with S1, dispersing particles of the first material in the bath, adding nanoparticles of the second material while stirring the bath, adding the binder solution, adding a surfactant, stirring, removing S1 by washing with a second solvent, and filtering and/or drying the resulting powder.

Description

The technical field of the invention is that of pulverulent substances and more particularly pyrotechnic substances incorporating a primary explosive.

Such pyrotechnic substances are commonly used for the manufacture of primers or detonators.

They most often include a primary explosive associated with a binder and one or more additives.

Patent FR2599361 thus describes a priming substance combining 40 to 70% by mass of lead trinitroresorcinate and 60 to 30% aluminum with less than 1% of a binder formed by gum arabic.

Aluminum is used in this component of allow the evacuation of the calories generated by heating of the primer filament under the effect of electromagnetic fields. This avoids a warm-up inopportune that may lead to the initiation of the composition and thus increases the security of the component.

The explosive and aluminum powders are associated under the form of a homogeneous mixture maintained by a binder. The granulometry of the primary explosive and powder are of the same order of magnitude and less than 40 micrometers.

This pyrotechnic substance has the drawback to require a significant amount of aluminum for reduce the susceptibility of the component to radiation electromagnetic.

The relative percentage of primary explosive is correlatively reduced and the detonation efficiency of the component is therefore also reduced, except to increase the mass of primary explosive so the volume of the component.

Moreover, the homogeneity of the explosive / aluminum mixture is difficult to ensure in a reproducible way. It results from variable performance from one batch to another of the point of view of sensitivity to electrostatic discharge or friction.

The object of the invention is to propose a substance pulverulent material having processing properties (especially improved flowability).

The object of the invention is more particularly to propose a pyrotechnic substance that retains its effectiveness while having reduced sensitivity, particularly to electric shocks and friction.

Thus, the subject of the invention is a powdery substance and in particular a pyrotechnic substance which is characterized in that it comprises at least a first material formed of grains coated with a binder layer incorporating granules of a second nanoscale material.

The second material may be made of aluminum or silicon.

Nanometric materials and in particular aluminum are known. It has already been proposed to implement them in the pyrotechnic components. The US5717159 patent thus proposes a primer comprising 45% by weight of nanometric aluminum and 55% by weight of nanometric molybdenum trioxide.

However in such a component all the materials put into are nanometric and form a homogeneous mixture.

The invention proposes instead to associate a material, in particular a pyrotechnic material, with granulometric classical micrometer (of the order of 100 micrometers) with a material with nanometric granulometry (from 0.05 to 0.1 microns).

In order to ensure an intimate and homogeneous mixture of these materials, nanoscale material granules surround the grains of the micrometric material. A binder ensures the binding of granules and grains.

So every grain of micrometric material has its surface externally practically covered (more than 90%) by nanoscale granules. There is no more segregation of materials despite their very different grain sizes and the micrometric material is protected.

More particularly, the coating of a material pyrotechnics by a nanometric metal, in particular by aluminum, makes the whole pyrotechnic substance conducted, both heat and electricity, which makes it easier to evacuate calories and therefore increases the resistance of the substance pyrotechnic to self ignition.

This pyrotechnic substance also sees its sensitivity to electrostatic discharge and friction diminished, which makes the industrial implementation of the safer pyrotechnic substance.

In the case of a coating of a micrometric material by nanometric silicon, the coating also facilitates industrial implementation of the substance by reducing including sensitivity to friction and facilitating flowability.

As a binder we can choose from the materials nitrocellulose, polyvinylidene fluoride (PVDF), vinyl chloroacetate (CVA) copolymer, copolymer of chlorofluoroethylene, polytetrafluoroethylene, polyvinyl alcohol (better known under the trademark "Rhodoviol"). The nitrocellulose has the advantage of being an active binder which participate in the pyrotechnic reaction by bringing Energy. The other binders mentioned are inert binders.

The proportion chosen for the binder will preferably be less than 3% of the total mass (that of the coated material plus that of the nanoscale material).

This will advantageously produce a substance pyrotechnic powder comprising from 95% to 60% by weight a first pyrotechnic material, 5 to 40% by weight of nanoscale aluminum and a binder in a proportion of 0.5% to 3% of the overall mass of the material mixture pyrotechnics / nanoscale aluminum.

The first pyrotechnic material may be an oxidant (such as copper oxide CuO, potassium nitrate or potassium perchlorate) or a secondary explosive (such as Octogen, or Hexogen). A secondary explosive is a explosive that requires significant activation energy to detonate (energy brought for example by an explosive primary).

The first pyrotechnic material can also be a detonating or explosive primary explosive. An explosive says primary is an explosive material that is characterized by a great sensitivity under at least one of the solicitations following: shock, friction, flame, electric spark.

The primary explosive detonators have a decomposition that goes very quickly to the same detonation without confinement. Explosive primary explosives have a decomposition regime that only detonates in certain conditions of confinement or initiation.

We will thus be able to choose the first pyrotechnic material primary explosive from the following materials: dinitrobenzofuroxane, lead azide, silver azide, diazodinitrophenol (DDNP), lead styphnate.

As dinitrobenzofuroxane salts it will be possible to potassium salt (KDNBF) or the salts of Rubidium (RbDNBF), Sodium (NaDNBF), Cesium (CsDNBF) or of Barium (BaDNBF).

• 60 à 95 % en masse de dinitrobenzofuroxane de potassium (KDNBF),
• 5 à 40% d'aluminium nanométrique,
• un liant dans une proportion de 0,5 à 3% de la masse globale du mélange matériau pyrotechnique/aluminium nanométrique de la composition.

The powdery substance according to the invention may thus comprise:

• 60 to 95% by weight of potassium dinitrobenzofuroxane (KDNBF),
• 5 to 40% of nanometric aluminum,
• a binder in a proportion of 0.5 to 3% of the overall mass of the pyrotechnic material / nanometric aluminum mixture of the composition.

More particularly, a substance can be made combining: 79% by weight of dinitrobenzofuroxane potassium (KDNBF), 18% of nanometric aluminum, and 3% mass of nitrocellulose.

The subject of the invention is also a method of preparation of a powdery substance, in particular a pyrotechnic substance, comprising at least a first material formed of grains coated with a layer of binder incorporating granules of a second material of nanometric particle size. The process according to the invention making it easy and safe to prepare such substance.

• on prépare une solution du liant dans un premier solvant de ce dernier,
• on prépare par ailleurs un bain de liquide support non miscible avec le premier solvant,
• on introduit dans le bain un premier matériau à enrober tout en agitant pour assurer une répartition homogène des grains de ce matériau dans le bain,
• on introduit un second matériau de granulométrie nanométrique dans le bain tout en maintenant l'agitation,
• on introduit la solution de liant dans le bain,
• on introduit un tensioactif dans le bain,
• après agitation on lave au moins une fois avec un deuxième solvant approprié permettant d'éliminer le premier solvant du liant,
• on essore et/ou sèche la substance pulvérulente obtenue.

Thus, the method according to the invention is characterized by the following succession of steps:

• a solution of the binder is prepared in a first solvent of the latter,
• a bath of immiscible support liquid is also prepared with the first solvent,
• a first material to be coated is introduced into the bath while stirring to ensure a homogeneous distribution of the grains of this material in the bath,
• a second material of nanometric granulometry is introduced into the bath while maintaining agitation,
• the binder solution is introduced into the bath,
• a surfactant is introduced into the bath,
• after stirring, washing is carried out at least once with a second appropriate solvent for removing the first solvent from the binder,
• the pulverulent substance obtained is filtered off and / or dried.

The carrier liquid may be silicone oil, binding being nitrocellulose and the first solvent being the methyl ethyl ketone.

The surfactant may be a sugar ester.

The first micrometric material can then be a detonating or explosive primary explosive and the second nanometric material be made of aluminum.

The invention will be better understood on reading the following description of different embodiments, description made with reference to the accompanying drawing which represents schematically, in section and greatly enlarged, a particle of the powdery substance according to the invention.

This particle 1 is formed by a grain 2 of a first material which is coated with a binder layer 3 incorporating granules 4 of a second granulometry material nanometric (for example nanometric aluminum).

Nanoscale materials (and in particular aluminum) are easy to obtain commercially. These materials can be obtained for example from the company Technanogy (2146 Michelson Drive Irvine California USA).

We will choose a nanometric material having a particle size between 50 and 100 nanometers (or between 0.05 micrometers and 0.1 micrometers).

The granules 4 thus surround virtually the entire external surface of the grains 2 of the first material. The different particles 1 thus constituted and which form the powdery substance are therefore always in contact mutually with each other through the intermediary of granules 4.

When the granules are formed of a metal, and especially aluminum, the contact between the granules makes the conductive pyrotechnic substance.

The first material coated with aluminum may be a pyrotechnic material such as a primary explosive. In that case the starting pyrotechnic powdery substance obtained will have improved behavior. She will be more resistant to electrostatic discharge, friction and heating.

The first pyrotechnic material may be an explosive secondary such as hexogen or octogen. In that case the coating of the grains of explosives may, in addition to conductivity of the composition, give a breath effect complementary to the explosive charge that will be made with such a substance.

The first pyrotechnic material may be an oxidant (such as copper oxide, potassium nitrate or potassium perchlorate). In this case the coating of the grains oxidant with a suitable nanoscale reducer (such as aluminum for copper oxide, boron for nitrate of potassium or Zirconium for perchlorate potassium), will ensure a more intimate contact between oxidizing and reducing agent.

In general, a coating of a material micrometric with nanometric silica will allow improve the flowability of the powdery substance.

It will also be possible to improve the implementation of a pyrotechnic redox composition to coat a reducer with nanometric silica and mix this reducer coated with an oxidant also coated with silica.

The coating of grains with a granulometry material micrometric with nanoscale granules is a operation a priori delicate.

The very fine granules disperse in suspension in air during a dry implementation. They can also be charge in static electricity and stick to the tools of loading.

In addition, nanometric aluminum powder reacts strongly in the presence of moisture and is therefore dangerous To manipulate.

The invention also aims to propose a method to ensure in a safe and reproducible way that coating.

The material according to the invention is thus produced by a coating process in emulsion.

According to this process, the first material is suspended micrometric and the second nano material within a liquid carrier.

Then, we add in this liquid a binder, itself dissolved in a first solvent. This results in an emulsion of binder / solvent droplets in the carrier liquid.

By agitation of the emulsion, it is trapped within each drop of binder / solvent of the grains of the mixture suspension (first micrometric material and granules nanometer).

An adjustment of the temperature of the liquid support will allow to control the size of the droplets of the emulsion. More the temperature will be high plus the droplets will be fines.

The first solvent is then extracted by adding to the emulsion a second solvent. The latter is chosen from so that the first solvent has a higher affinity great with him than he has for the binding material.

This operation has the effect of removing the solvent from the binding, so harden the one that traps the granules nanoscale around the grains of the first material micrometer.

Then just filter and dry the substance powder obtained.

If the first material is a pyrotechnic material, the substance obtained will be implemented in a conventional manner in a pyrotechnic component, for example a component to hot wire, exploded wire or percussion wire ...

If the first pyrotechnic material is an explosive secondary school, it will be implemented later conventional loading techniques (casting, compression, polymerization).

According to an essential characteristic of the invention adds to the solvent / binder emulsion in the carrier liquid a surfactant for stabilizing it.

Conventionally, surfactant molecules reduce surface tension between two liquids.

In the process according to the invention, the surfactant for role of creating binder bubbles / volume solvent equivalent.

Indeed, when the agitation of an emulsion is stopped, every element of it has a strong tendency to recover his equilibrium state. After a while there is a separation of the two liquid phases. It is therefore not possible in this case to precisely control the size of the grains made.

The surfactant makes it possible to stabilize this step before hardening of the grains by the addition of the second solvent.

These binder / solvent bubbles are thus stabilized, the flocculation phenomenon will be diminished by the forces of repulsion between the drops of binder / solvent. The Stabilization of the size of the bubbles makes it possible to control and to homogenize the final size of the grains of the substance powder.

This control also makes it possible to control the quantity of granules of nanoscale material present in each bubble of binder / solvent, so also to control the coating of the grains of the first material with the material nanoscale.

The choice of surfactant will depend on the nature of the solvents as well as that of the carrier liquid.

We will choose a surfactant comprising a polar head soluble in the first solvent and a fatty carbon chain soluble in the carrier liquid.

The advantage of the process according to the invention is that it avoids dry mixing of the powders. This increases the security implementation. If the first material is an explosive primary, it is phlegmatized by the liquid support. By besides the nano aluminum which is highly reactive to the open air (because of the humidity of the air) is mixed safely in the carrier liquid (for example silicone oil).

We will choose the binder according to the nature of the material to coat and so that it is not miscible in the liquid carrier.

We will then choose the first solvent based of the nature of the chosen binder and finally the second solvent in depending on the nature of the first solvent.

As an example for a binder such as nitrocellulose methyl ethyl ketone will be used as the first solvent and will adopt Heptane as the second solvent harden the grains. The carrier liquid chosen is the oil of silicone and the appropriate surfactant is a sugar ester.

Avec R1 : chaíne alcane C_nH_2n+1 avec n = 4 à 12.

Avec R2 : glucose (C₆H₁₂O₆) ou saccharose (C₁₂H₂₂O₁₁) ou fructose (C₆H₁₂O₆) ou tout autre sucre possédant des groupements OH.

This surfactant will have a general formula: R ₁ - COO - R ₂

With R1: alkane chain C _n H _{2n + 1} with n = 4 to 12.

With R2: glucose (C ₆ H ₁₂ O ₆ ) or sucrose (C ₁₂ H ₂₂ O ₁₁ ) or fructose (C ₆ H ₁₂ O ₆ ) or any other sugar having OH groups.

Such an ester has a long carbon chain which has more affinity with silicone oil than with the methyl ethyl ketone. It has a polar head formed by many OH groups that form hydrogen bonds with the C-Os of methyl ethyl ketone. The sugar ester is so has the interphase between the first solvent and silicone oil, ensuring the stabilization of droplets.

For a binder such as formamide polyvinyl (PVDF) or polyvinyl alcohol we can choose as the first solvent acetone.

The method according to the invention can also be used to coat a non-pyrotechnic material with granules nanoscale. The skilled person will easily choose the different solvents depending on the materials used.

Example 1

By way of example, a substance has been produced powdery pyrotechnics associating 78% of potassium dinitrobenzofuroxane (KDNBF) (granulometry) average 85 micrometers), 19% of nanometric aluminum (particle size between 50 nanometers and 100 nanometers) and 3% nitrocellulose.

To achieve the desired coating and for 10 grams of prepared pyrotechnic substance next :

A solution of the binder is first prepared in a first solvent. For this purpose, between 0.1 g and 0.25 g is mixed of nitrocellulose in 40 to 60 ml of methyl ethyl ketone.

It is also introduced in a thermostatic beaker between 150 and 300 ml of silicone oil.

The temperature of the silicone oil bath is maintained between 18 ° C and 30 ° C. An agitator is present in the beaker.

Between 6 and 8 g of KDNBF are introduced and the powder is left behind. of pyrotechnic material to be distributed in the Becher, then introduced between 2 and 4 g of nanometric aluminum.

The mixture is stirred for 5 minutes.

The binder solution is then introduced into the beaker. previously prepared, then 1 to 5 ml of a surfactant solution (sugar ester).

Stirred for 5 minutes.

Finally, 10 to 60 ml of the second solvent are added (heptane), shake and then remove the mother liquors.

Heptane rinsing can be repeated once or twice time then we recover the composition on a buchner. We squeeze a few minutes then we recover the composition coated which can be stored.

Tests have been conducted to compare the pyrotechnic substance thus obtained with the KDNBF alone, and with a coated composition associating the KDNBF with micrometric aluminum (particle size between 40 microns and 80 microns).

This last composition was prepared by putting into the same process as that described above.

It was first checked that the coated KDNBF of nanoscale aluminum was conducting while the KDNBF associated with micrometric aluminum was insulating (just like the KDNBF alone).

This is because the KDNBF can not be coated with micrometric aluminum. The composition obtained is rather close to a dry mix of both products in which there are no conductive paths through aluminum particles.

Behavioral tests were also conducted pyrotechnic substances to electric shocks.

This has been achieved by capacitive discharges using an assembly associating a capacity and a resistance.

This classic test is conducted according to the procedure following: a quantity of pyrotechnic substance of approximately 15 mm3 is disposed in a conductive cup. A needle is placed above the substance (without contact). We applied between the bucket containing the pyrotechnic substance and the needle discharging a capacitor with a capacitance 1000 pF charged at 25 kV with a resistance of 10 kilo Ohms serial.

The voltage at which different samples of the pyrotechnic substance were initiated was measured. The table below summarizes the test results: Substance tested Voltage of the average initiation threshold (kilo volts) KDNBF only powdery 2.88 kV KDNBF (79%) nanometric aluminum (18%) binder (3%) 3.41 kV KDNBF (79%) micrometric aluminum (18%) binder (3%) The lots are not homogeneous
Variable value of 2.88 kV at non-initiation (we only have aluminum)

It can be seen that the pyrotechnic substance the invention has a higher initiation threshold. His sensitivity to electric shocks is therefore less.

The pyrotechnic substance implementing micrometric aluminum is not homogeneous from one batch to the other. The results are not reproducible for a such substance. The threshold varies from 2.88 kV (KDNBF only) to non-initiationn (aluminum only).

Behavioral tests were also conducted pyrotechnic substances to friction.

This has been achieved by friction tests with the device Julius Peters (this test is described in the GEMO FA-500-A-1).

In a conventional manner, a sample of the order of 10 mg of the pyrotechnic substance to be tested is deposited in the form a small pile in the middle of a ceramic plate rough. This plate is then fixed on the carriage mobile device that can print a movement linear reproducible speed and amplitude.

On the wafer just rub a cylindrical punch to curved end (made in the same ceramic as the wafer). This punch receives via a plague of balance a known vertical force that can take a number of values. This is the expression of strength applied which causes a certain reaction of the sample which will characterize the sensitivity of the substance to linear friction. This determined the minimum effort leading to the failure of ten samples.

The table below summarizes the test results: Substance tested Sensitivity to friction KDNBF only powdery 10 non-functioning for a 600 g effort KDNBF (79%) nanometric aluminum (18%) binder (3%) 10 non-functioning for an effort of 1.2 kg KDNBF (79%) micrometric aluminum (18%) binder (9%) The lots are not homogeneous
Results not exploitable. From operation to 600 g at non-operation (only aluminum

It can be seen that the pyrotechnic substance the invention is much more resistant to friction than the KDNBF alone. Indeed it takes a force greater than 1.2 kg for get initiation. Such behavior is due to a improvement of the external surface of the grain (assured smoothing by the nanometric material).

The pyrotechnic substance implementing micrometric aluminum is not homogeneous from one batch to the other, the results of the friction tests are very variables. Such a composition is not reproducible.

In addition, it was possible to verify that the characteristics detonations of the pyrotechnic substance according to the invention are not degraded by the coating with aluminum nanoscale.

Compositions can be made with the same process teaming up :

Example 2

• 80% by weight of silver azide,
• 20% of nanometric aluminum,
• nitrocellulose in a proportion of 3% of the overall mass of the pyrotechnic material / aluminum mixture nanoscale.

Example 3

• 70% by weight of lead styphnate,
• 30% of nanometric aluminum,
• nitrocellulose in a proportion of 3% of the overall mass of the pyrotechnic material / aluminum mixture nanoscale.

Claims (21)

Powdered substance, and in particular pyrotechnic substance, characterized in that it comprises at least a first material formed of grains (2) coated with a layer of binder (3) incorporating granules (4) of a second material of nanometric particle size. Powdery substance according to Claim 1, characterized in that the particle size of the nanometric material is between 50 and 100 nanometers. Powdery substance according to one of claims 1 or 2, characterized in that the second material is aluminum. Powdery substance according to one of claims 1 or 2, characterized in that the second material consists of silicon. Powdery substance according to one of claims 1 to 4, characterized in that the binder is selected from the following materials: nitrocellulose, polyvinylidene fluoride (PVDF), polyvinyl alcohol, chlorofluoroethylene copolymer, polytetrafluoroethylene, vinyl chloroacetate copolymer (CVA). Powdery substance according to one of claims 1 to 5, characterized in that it comprises from 95% to 60% by weight of a first pyrotechnic material, from 5 to 40% by weight of nanometric aluminum and a binder in a proportion of 0.5% to 3% of the overall mass of the pyrotechnic material / nanometric aluminum mixture. Powdery substance according to one of claims 1 to 6, characterized in that the first pyrotechnic material is an oxidant. Powdered substance according to one of claims 1 to 6, characterized in that the first pyrotechnic material is a secondary explosive. Powdered substance according to one of Claims 1 to 6, characterized in that the first pyrotechnic material is a primary explosive. A pulverulent substance according to claim 9, characterized in that the first pyrotechnic material is selected from the following materials: dinitrobenzofuroxane salts (sodium, potassium, cesium, barium or rubidium salts), lead azide, silver azide , diazodinitrophenol, lead styphnate. Powdery substance according to claim 10, characterized in that it comprises: 60 to 95% by weight of potassium dinitrobenzofuroxane (KDNBF), 5 to 40% by weight of nanometric aluminum, a binder in a proportion of 0.5 to 3% of the overall mass of the pyrotechnic material / nanometric aluminum mixture. Powdery substance according to claim 11, characterized in that it comprises: 79% by weight of potassium dinitrobenzofuroxane (KDNBF), 18% by weight of nanometric aluminum, 3% by weight of nitrocellulose. Powdery substance according to claim 10, characterized in that it comprises: 60 to 95% by weight of silver azide, 5 to 40% of nanometric aluminum, a binder in a proportion of 0.5 to 3% of the overall mass of the pyrotechnic material / nanometric aluminum mixture. Powdery substance according to claim 13, characterized in that it comprises: 80% by weight of silver azide, 20% of nanometric aluminum, nitrocellulose in a proportion of 3% of the overall mass of the pyrotechnic material / nanometric aluminum mixture. Powdery substance according to claim 10, characterized in that it comprises: 60 to 95% by weight of lead styphnate, 5 to 40% of nanometric aluminum, a binder in a proportion of 0.5 to 3% of the overall mass of the pyrotechnic material / nanometric aluminum mixture. Powdery substance according to claim 15, characterized in that it comprises: 70% by weight of lead styphnate, 30% of nanometric aluminum, nitrocellulose in a proportion of 3% of the overall mass of the pyrotechnic material / nanometric aluminum mixture. Process for preparing a powdery substance, in particular a pyrotechnic substance, comprising at least a first material formed of grains coated with a layer of binder incorporating granules of a second nanometric particle size material, characterized in the following steps: a solution of the binder is prepared in a first solvent of the latter, a bath of immiscible support liquid is also prepared with the first solvent, a first material to be coated is introduced into the bath while stirring to ensure a homogeneous distribution of the grains of this material in the bath, a second material of nanometric granulometry is introduced into the bath while maintaining agitation, the binder solution is introduced into the bath, a surfactant is introduced into the bath, after stirring, washing is carried out at least once with a second appropriate solvent for removing the first solvent from the binder, the pulverulent substance obtained is filtered off and / or dried. Preparation process according to Claim 17, characterized in that the carrier liquid is silicone oil, the binder is nitrocellulose and the first solvent is methyl ethyl ketone. Preparation process according to Claim 18, characterized in that the surfactant is a sugar ester. Preparation process according to one of Claims 17 to 19, characterized in that the first material is a detonating or explosive primary explosive. Preparation process according to one of Claims 17 to 20, characterized in that the second nanometric material consists of aluminum.

Images