EP3160922A1

EP3160922A1 - Gas-generating pyrotechnical monolithic blocks

Info

Publication number: EP3160922A1
Application number: EP15736572.7A
Authority: EP
Inventors: Stéphane BESOMBES; Frédéric MARLIN
Original assignee: Herakles SA
Current assignee: ArianeGroup SAS
Priority date: 2014-06-30
Filing date: 2015-06-29
Publication date: 2017-05-03
Anticipated expiration: 2035-06-29
Also published as: JP2017530920A; US20170158576A1; FR3022906B1; EP3160922B1; WO2016001549A1; FR3022906A1; US9868678B2; CN107074673A; JP6657128B2; CN107074673B

Abstract

The present invention relates mainly to substantially cylindrical gas-generating pyrotechnical monolithic blocks, characterised by having: a thickness no lower than 10 mm, an equivalent diameter no lower than 10 mm, and a porosity lower than 5%; and a composition, given as weight percentages, which contains, for at least 94% of the weight thereof: + 77.5% to 92.5% of guanidine nitrate, + 5% to 10% of basic copper nitrate, and + 2.5% to 12.5% of at least one inorganic titanate with a melting temperature higher than 2100 K. Said blocks are particularly efficient, in particular as regards their combustion temperature and speed (low), the ease with which they can be obtained, and their gas yield.

Description

Monolithic Pyrotechnic Gas Generator Blocks

The present invention relates to pyrotechnic monolithic blocks ("large" pyrotechnic objects) gas generators; said blocks being adapted to be integrated within devices dedicated to the pressurization of volume structures to a greater or lesser extent, depending on the intended application. Said blocks are more particularly adapted to be integrated within devices requiring for their operation that pressurization is provided over a relatively long period, very significantly greater than the time required for the operation of gas generators for airbags (durations of up to milliseconds) and even gas generators for lift cylinders (durations of about 100 milliseconds).

The pyrotechnic monolithic blocks of the invention, by their intrinsic characteristics of size, porosity and composition, are particularly effective (with reference to specifications with many stringent stipulations). They are particularly efficient, especially with regard to their speed and temperature of combustion (low), their ease of obtaining and their gas yield (see below).

The devices in question are, for example, extinguishers (the gases useful for their operation are used as a propellant, used to expel a quenching liquid through a nozzle), actuators of cylinders for opening doors in emergency situation (the gases useful for their operation are used to mechanically actuate a jack), devices for inflating flexible structures (gases that are useful for their operation ensure the deployment and pressurization of a flexible and watertight envelope ). Inflation of such flexible structures can meet different needs: need obstruction of a pipeline (for example, for anti-effusion systems, aimed at limiting the risk of pollution in the event of an industrial accident), need for the generation of buoyancy cushions (for example for emergency ditching, including a helicopter), need to deploy a flexible slide (eg for the emergency evacuation of passengers from an aircraft), for example.

To date, the operation of such devices, generally emergency or emergency devices, is most often provided by the use of a neutral gas (nitrogen, helium, etc.), stored at high pressure (200 at 400 bar) in a tank. This technology has advantages, as, therefore, the use of a neutral gas (inert), intrinsically non-toxic and moreover cold. In return, to the extent that it uses a pre-compressed gas at high pressure, it has significant disadvantages:

a) the sizing of the gas storage tanks remains important (although the gas is strongly compressed);

b) the presence of gas stored at high pressure in a tank (bottle, etc.) imposes, for obvious safety reasons, that said tank is dimensioned in accordance with the rules of the art and the envelope directives pressurized to withstand the high internal pressure for long periods; which leads to structures either of high thickness (and therefore of significant weight), or using lightweight materials (composites) but high manufacturing cost; finally,

c) Periodic maintenance operations are necessary to ensure optimal and secure operation throughout the operational lifetime of the device. These operations obviously impact operating costs. The disadvantages a and b above are particularly critical for embedded devices (particularly in the field of aeronautics, given the constraints that are imposed in terms of weight and / or dimensioning). The elimination of recurring maintenance operations (disadvantage c above) would of course allow for a significant reduction in operating costs.

The use of solid pyrotechnic objects for the operation of devices of the above type has also been described.

The operating specifications of such devices require that a volume of gas, of a moderate temperature, be generated, from the pyrotechnic objects in question, in a relatively slow and constant manner, over a relatively long specified time, to thereby pressurize a volume structure more or less consistent (we can indicate, in no way limiting, volumes of about 1 L (cylinders for opening doors, for example), about 3000 L (helicopter flotation tanks, for example), or even about 20,000 L (escape slide, for example)).

The patent application WO 2007/113299 thus describes pyrotechnic objects intended for gas generation over a relatively long period (durations of 50 ms to 1 min are indicated), the composition of which, free of binder, contains nitrate of guanidine (NG: as reducing charge) and basic copper nitrate (BCN: as oxidizing charge), in a proportion NG / BCN close to stoichiometric equilibrium. Said composition therefore has a near equilibrium oxygen balance (close to zero). This confers on said pyrotechnic objects too high temperature and burn rate with reference to the specifications currently in question (see below).

The objects described in said application WO 2007/113299, advantageously obtained via a dry process compaction process, are of substantially cylindrical shape and have a thickness greater than 5 mm, a diameter greater than or equal to 10 mm (generally a thickness and / or a diameter between 10 and 60 mm) and a porosity of between 1 and 8%. In fact, low porosities (<5%, and more preferably <3%) can be easily obtained with the described compositions (and their densification characteristic) only for objects of limited size. However, the skilled person does not ignore the criticality of this parameter porosity. A "high" porosity value (in this case greater than 4 - 5%) is, in general, such as to increase the ballistic dispersion of the pyrotechnic object, to confer on the pyrotechnic object insufficient resistance to severe vibratory environments over extended periods of time and, for this family of pyrotechnic compounds (N. based on a mixture NG + BCN), to increase the value of the combustion rate.

In consideration of their particularly advantageous properties in a context of gas generation over time, the pyrotechnic monolithic blocks of the invention (described hereinafter) are analyzed as improvements to pyrotechnic objects according to the teaching of the WO application. 2007/113299.

The inventors propose pyrotechnic monolithic gas generators whose combustion gases replace the pressurized gases of the prior art, to ensure the operation of emergency or emergency devices (for, more generally, to ensure the pressurization of structures) . This substitution, advantageous per se (see above the disadvantages of the use of pressurized gas), is all the more so that said blocks of the invention are particularly effective, with reference to a severe specification. In any case, they are more efficient than the objects described in the application WO 2007/113299. The following are the main stipulations of the said specifications.

To deliver, in a particularly advantageous manner, a flow rate (flow rate = combustion rate x combustion surface) of adapted combustion gas for a relatively long duration (generally at least 500 ms and up to 2 min), the inventors have research :

large blocks (typically of thickness> 10 mm and equivalent diameter> 10 mm), so that their combustion surface is reduced (so that they have a high burn thickness); said densifiable (shaped) shaped blocks (i.e. having a low porosity: <5%, advantageously ≤ 3%, very advantageously ≤ 2%), with a limited compressive force, which is a real advantage. Such blocks make it possible to obtain charges having a density (the density of a charge corresponding to the mass of pyrotechnic product reduced to the occupied loading volume) that is as high as possible (this in order to allow a reduction in the size of the generator of gas, which is particularly interesting in embedded systems, particularly to the aeronautical field.Typically this stipulation de facto prohibits the use of loading in the form of lozenges, such as those conventionally used in gas generators for airbags ). Inhibition (for example, by removal of a thermosetting varnish) of the lateral surface of the blocks may also be provided to increase the burning time of the blocks, in contexts where a very long pressurization time is required;

blocks having a low combustion temperature: less than or equal to 1415 K. Such a low combustion temperature limits the unavoidable loss of pressure due to the cooling of the gases generated. This low combustion temperature is also particularly interesting with reference to the thermal constraints imposed on the gas generator and the structure to be pressurized;

blocks having a low rate of combustion. It is more specifically required 1) a moderate combustion rate at low pressure (the combustion must be done at low pressure (this is particularly interesting with reference to the pressure resistance constraints of the gas generator (and therefore with reference to the weight of the and the structure to be pressurized) and its velocity is typically less than 6 mm / s between 1 and 10 MPa (it is understood that the high-pressure combustion rate (20 MPa) is potentially greater than 6 mm / s but this high-pressure combustion rate is currently irrelevant, given the desired applications (pressurization, over a long time, of large volume structures), and 2) a non-zero speed at atmospheric pressure (it is appropriate that the blocks burn completely);

blocks having good ignitability and ignition efficiency characteristics;

blocks generating combustion residues in agglomerated form (residues thus easily filterable, which advantageously makes it possible to reduce the size of the gas filtration systems to be incorporated in the device);

blocks which also have advantageous gas yields (generally greater than 38 mol / kg, in a preferred variant greater than 42 mol / kg), which makes it possible to limit the mass of pyrotechnic charge to be integrated and therefore the weight of the system (this is particularly favorable for devices destined for the aeronautical market).

With reference to such a specification, the inventors propose pyrotechnic monolithic blocks generating original gases, particularly powerful, which are characterized by their size, their porosity and their composition.

Said pyrotechnic monolithic generators of gas of the invention, of substantially cylindrical shape (it is generally, but not exclusively, cylinders of revolution or quasi cylinders of revolution), combine characteristics

a) in size: a thickness greater than or equal to 10 mm and an equivalent diameter greater than or equal to 10 mm,

b) porosity: a porosity of less than 5% (this parameter, expressed in percentage, corresponds to the ratio of the difference between the theoretical density and the real density on the theoretical density), and,

(c) composition: their composition, expressed as mass percentages, contains, for at least 94% of their mass:

+ 77.5 to 92.5% of guanidine nitrate (NG),

+ 5 to 10% basic copper nitrate (NCB), and

+ 2.5 to 12.5% of at least one inorganic titanate having a melting point greater than 2100 K.

With reference to the size characteristics indicated above, it is understood that the blocks in question consist of large objects. In no way limiting, we can indicate here that they generally have a thickness between 10 and 100 mm (10 mm <e ≤ 100 mm) and / or, very generally and, an equivalent diameter between 10 and 100 mm (10 mm < φ <100 mm). According to an advantageous variant, they have a thickness between 20 and 80 mm (20 mm ≤ e ≤ 80 mm) and / or, preferably, and an equivalent diameter between 20 and 80 mm (20 mm φ 80 80 mm).

With reference to the porosity characteristic indicated above, it is understood that the blocks in question are dense blocks. According to one advantageous variant, the porosity of said blocks is less than or equal to 3%. According to one very advantageous variant, the porosity of said blocks is less than or equal to 2%, even less than or equal to 1% (a low (<2%) or even very low (<1%) porosity value is obtained (with the compositions of the blocks of the invention) via the application of a nominally high compressive force and a lower but already low porosity value (> 2% and <5%) is obtained via the application of an effort reduced compression compared to that required to obtain an equivalent porosity with the compositions according to the teaching of WO 2007/113299 (see the attached figure).

Those skilled in the art have already understood the great interest of the blocks of the invention which combine large size and low porosity. The specific composition of the blocks makes this combination possible and is particularly advantageous with reference to the combustion parameters of said blocks (see the combustion temperature (≤ 1415 K) and the combustion rates (<6 mm / s between 1 and 10 MPa and not zero at atmospheric pressure) indicated in the specifications above).

The composition of the blocks of the invention is a composition which contains, for at least 94% of its mass:

- the three ingredients identified above: guanidine nitrate

(NG), as oxidizing filler, basic copper nitrate (BCN), as reducing filler and inorganic titanate (s), as refractory filler (the melting temperature of this filler (> 2100 K) remains above the temperature of the base NG + BCN in which it is present (such a base, unbalanced (see below), has a combustion temperature always lower than about 1500 K)) ensuring a dual function of agglomeration agent solid residues of combustion and combustion modifier (which allows to achieve, unexpectedly, the severe combustion properties (temperature and burning rates) sought);

in the proportions indicated: in a base NG + BCN strongly imbalanced in oxygen balance (in view of its mass ratio NG / BCN> 7.75, advantageously> 8.5), this imbalance being timely with reference to the desired combustion properties the at least one titanate is present in a significant amount (> 2.5% by weight, ≥ 5% by mass, alternatively, so that the technical effect of optimization on the combustion properties that it develops ( unexpectedly) is significant) but not excessive (≤12.5% by weight, with particular reference to gas efficiency and ignitability.

With reference to the composition of the blocks of the invention, more particularly to the base NG + BCN of said composition, the following can be added.

1) The high guanidine nitrate content of the compositions of the blocks of the invention (from 77.5 to 92.5% by weight) is particularly advantageous, with reference to the density (at the low porosity) of said blocks, due to the fact that the rheoplastic behavior of said guanidine nitrate. It is particularly advantageous for the implementation of compaction step (s) or (and) compression during the preparation of said blocks, in particular by the dry route (see below).

(2) Guanidine nitrate and basic copper nitrate are therefore present in a weight ratio R = NG / NCB (unbalanced) of between 7.75 and 18.5 (see the mass ratios given for NG and BCN). Said mass ratio is advantageously between 8.5 and 15, very advantageously between 8.5 and 12, and particularly preferably between 8.5 and 10. These advantageous, very advantageous and particularly preferred variants are referred to to the combustion properties sought but also in reference to the ignitability and gas performance of the blocks in question.

With reference to the at least one inorganic titanate present in the composition of the blocks of the invention, the following can be added.

Said at least one inorganic titanate is advantageously selected from metal titanates and alkaline earth titanates (= metal titanates, alkaline earth titanates and mixtures thereof). The composition of the blocks of the invention thus very advantageously contains a metal titanate or an alkaline earth titanate. Preferably, the composition of the blocks of the invention contains strontium titanate (SrTiO ₃ , whose melting point is 2353 K) and / or calcium titanate (CaTiO ₃ , whose melting point is 2248 ° C.). K) and / or aluminum titanate (AI ₂ TiO ₅ , whose melting temperature is 2133 K). More preferably, it contains strontium titanate (SrTi0 _3), calcium titanate (CaTi0 ₃₎ or aluminum titanate (Al ₂ Ti0 _5).

The dual function of said titanates is emphasized in the composition of the blocks of the invention. Said titanates act as agglomerating agent for the combustion residues (because of their refractory nature (melting temperature> 2100 K), they retain their physical state of solid powder (they obviously intervene in this form) at the temperature of combustion of the block, from which the agglomeration of the copper residues (residues in liquid form (in whole or in part at the combustion temperature of the composition) generated during the combustion of the NCB) and present within the a NG + BCN base strongly unbalanced in oxygen balance, they make it possible to obtain, surprisingly, the specific combustion properties sought (a combustion temperature less than or equal to 1415 K, a moderate combustion rate, less than or equal to 6 mm / s, low pressure (between 1 and 10 MPa) and a non-zero combustion rate at atmospheric pressure), combustion properties necessary for the intended functional need for pressurization, over a long time (it has been indicated above times of 500 ms to 2 min. ), more or less consistent volumes (mentioned above volumes of 1 L to 20 000 L). Their intervention seems particularly timely with reference to the non-zero combustion rate at atmospheric pressure.

The three essential constitutive ingredients of the blocks of the invention identified above - NG + BCN + at least one inorganic titanate whose melting temperature is greater than 2100 K - therefore represent at least 94% by mass of the total mass of said blocks. . They are quite likely to represent at least 97% of it, at least 99% of it, or even 100% of it.

In addition to said three essential constituent ingredients of the blocks of the invention, the composition of said blocks may contain other ingredients. It is understood that said other ingredients are likely to be present at most at the rate of 6% by weight and, of course, only insofar as their presence does not significantly affect the properties. particularly of combustion, required. Said other ingredients are, not exclusively, but generally, selected from processing additives (processing aids), binders and fluxing agents (see below).

According to a first variant, the composition of the blocks of the invention contains, in addition to said three essential constitutive ingredients, at least one processing additive (manufacturing aid, consisting for example of calcium stearate or graphite). Such an additive for use is generally present in a content not exceeding 1% by weight. It is conventionally present in a content not exceeding 0.5% by weight. Its presence is particularly suitable for obtaining the blocks of the invention by the dry route (see below).

In the context of this first variant, the composition of the blocks of the invention is advantageously composed of 100% by weight of said guanidine nitrate, basic copper nitrate, at least one inorganic titanate and at least one processing additive. The blocks of the invention, having this advantageous composition, are generally obtained by the dry route. However, they can also be obtained by wet process, particularly by a wet process comprising an atomization step (see below).

According to a second variant, the composition of the blocks of the invention contains, in addition to said three essential constitutive ingredients (and, optionally, in addition, said at least one processing additive), at least one binder (for example of the cellulosic type). or acrylic) or at least one fluxing agent (for example of the alkaline chloride salt type, such as NaCl or KCl). The presence of at least one such binder may be particularly suitable for obtaining blocks of the invention by extrusion, possibly wet (the binder then contributing to the formation of a gel in contact with the solvent used (the water being the preferred "solvent" (see below)); the presence of at least one such melting agent may be particularly suitable for obtaining blocks of the invention by the dry route (see below), particularly for obtaining blocks formulated from compositions characterized by a very low combustion temperature. Said at least one such binder or at least one such melting agent is generally present in a content not exceeding 5% by weight, very generally present in a content not exceeding 3% by weight.

In the context of this second variant (and also that of the first variant above), the composition of the blocks of the invention advantageously consists of 100% by weight of said guanidine nitrate, basic copper nitrate, at least one inorganic titanate, at least one processing additive and at least one binder or at least one fluxing agent. It is very advantageously composed of 100% by weight of said guanidine nitrate, basic copper nitrate, at least one inorganic titanate, at least one processing additive and at least one fluxing agent. The blocks of the invention, having this very advantageous composition, are generally obtained by the dry route.

Whatever their exact characteristics - thickness and diameter greater than 10 mm, porosity less than 5% and composition consisting of at least 94% by mass of guanidine nitrate, basic nitrate of copper and at least one inorganic titanate (refractory), present in the proportions indicated - the blocks of the invention can be, on at least part of their surface, inhibited in combustion (covered with a layer of suitable material (combustion inhibitor material), generally in the form of a varnish (non-combustible)). Such an inhibition is a conventional means (in particular described in the patent application FR 2,275,425 and US Pat. No. 5,682,013) which makes it possible to slow down their combustion (already "intrinsically" slow) and thus to obtain very long durations of combustion (see the 2 min above).

On reading the foregoing, those skilled in the art have grasped the interest of the blocks of the invention, whose characteristics of size, porosity and composition, allow them to meet the stringent stipulations of the specification set forth above. . In support of this statement, the results given in the examples below can be considered.

Blocks of the invention can be obtained by conventional, wet or dry methods. It is understood that the original composition of said blocks is at the source of their properties advantageous, and also allows them to be obtained under advantageous conditions.

The blocks of the invention are advantageously obtained by a dry process. The high guanidine nitrate content of their composition has previously been emphasized.

Such a dry process can almost be reduced to a compression of the pulverulent mixture obtained by mixing the constituent ingredients of the blocks (three essential constitutive ingredients and optionally, in addition, at least one other ingredient, advantageously, three essential constitutive ingredients + at least one processing additive and optionally at least one fluxing agent), said ingredients being used, in a conventional manner, in the pulverulent state. The pressure applied to the powder mixture placed in a suitable mold is generally between 10 ⁸ and 6.5 × 10 ⁸ Pa.

Such a dry process may comprise several steps, which have been described in particular in the patent application WO 2006/134311. The first step is a step of compaction (dry) of a mixture of (the) ingredients constituting powdered blocks (all the constituent ingredients (advantageously, the three essential constitutive ingredients + at least one additive for use and optionally at least one fluxing agent) may be mixed or all but the at least one titanate (advantageously, NG + BCN + at least one processing additive and optionally at least one fluxing agent) (see below)). Dry compaction is generally carried out, in a manner known per se, in a roller compactor, at a compaction pressure of between 10 ⁸ and 6 × 10 ⁸ Pa. At the end of said compacting step, the result is generally obtained a flat plate (when two planar surface cylinders are used) or a plate with reliefs (when one of said cylinders used has a surface with cells). The second step is a granulation step of the compacted material obtained (usually a flat plate or a plate with cells). The granules obtained generally have a particle size (a median diameter) of between 200 and 1000 μιτι (and an apparent density of between 0.7 and 1.2 g / cm ³ ). The third step is a compression step (dry) (= shaping step) of the granules obtained. The pressure applied is generally between 10 ⁸ Pa and 6,5.10 ⁸ The at least one titanate interact with the other constituent ingredients of the blocks of the invention. - NG + BCN mainly, if not exclusively - ie at the beginning of the manufacturing process blocks of the invention or is added, further downstream in the manufacturing process, granules, before the implementation of the compression. It can not be totally ruled out that it should be added several times at the beginning (to the powder mixture) and further downstream (to the granules).

The dry process methods (conventional) specified above, are, in the context of the present invention, implemented to obtain blocks that have the characteristics of composition, size and porosity explained above (ie in particular a thickness to burn greater than or equal to 10 mm, generally between 10 and 100 mm, advantageously between 20 and 80 mm).

In such a context of obtaining blocks of the invention by a dry process, the guanidine nitrate (NG) and the basic copper nitrate (BCN) used (in the form of powder) advantageously have a particle size (value the median diameter) fine, less than or equal to 20 μιτι. Said particle size is generally between 1 and 20 pm. It is actually conventional particle size.

The blocks of the invention can also be obtained by a wet process. According to one variant, such a wet process comprises the extrusion of a paste containing all the constituent ingredients of the block (advantageously, guanidine nitrate, basic nitrate of copper, the at least one titanate, at least one additive containing at least one binder) and a solvent (water being the preferred "solvent").

According to another variant, such a wet process method comprises: a) a step of placing in aqueous solution at least one of the essential constituent ingredients (generally at least the reducing charge: NG) and optionally suspending the suspension; at least one of said essential, non-soluble ingredients (generally at least the oxidizing charge: BCN), in said solution, and then

b) obtaining a powder from said solution or suspension by spray drying,

optionally c) the addition to said powder of the constituent ingredient (s) which has not been previously dissolved or suspended (assuming that all the ingredients have not been not been) finally

d) the shaping of the pulverulent mixture thus obtained (= powder obtained after drying by atomization or powder obtained at the end of the spray drying with the addition of the said constituent ingredient (s) complementary) = powder containing all the constituent ingredients of the desired block) for the generation of a block;

said at least one inorganic titanate being added to the solution or suspension to be atomized and / or to the atomized powder (before being shaped).

The shaping of the powder mixture is generally a conventional compression (by a known method of dry compression). As indicated above, in no way limiting, compression pressures of 10 ⁸ to 6.5.10 ⁸ Pa. The wet process methods (conventional) specified above, are, in the context of the present invention, implemented to obtain blocks which have the characteristics of composition, size and porosity explained above (ie in particular a thickness to burn greater than or equal to 10 mm, generally between 10 and 100 mm, advantageously between 20 and 80 mm).

According to another of its objects, the present invention relates to gas generators containing a pyrotechnic solid charge gas generator. Typically, the gas generators of the invention contain a charge which contains at least one block (pyrotechnic monolithic gas generator, of substantially cylindrical shape) of the invention and / or as obtained by the methods mentioned below. above. Such generators, incorporating a pyrotechnic charge containing several blocks of the invention, in an ordered configuration (for example in the form of a stack of several blocks), as opposed to a bulk load, said (stacks of) blocks being able to Moreover, being inhibited on their lateral surface, they are particularly suitable for the pressurization of structures over long periods, or even very long (remember the 500 ms to 2 min indicated above).

It is now proposed to illustrate, in a non-limiting way, the invention.

I. Table 1 below gives 8 examples (Ex.l to Ex.8) of block composition of the present invention as well as the characteristics of said compositions evaluated by means of calculations, in particular thermodynamic calculations.

These compositions and their characteristics are compared with those of Examples A, B and C, given for comparison: the composition of Example A is a composition according to the teaching of WO 2007/113299. It contains 52.44% by weight of NG and 44.87% by mass of NCB (the ratio R = NG / NCB (= 1.2) is close to stoichiometric equilibrium). It also closes 2.69% by weight of alumina ("slaggant" agent (according to WO 2007/113299));

the composition of Example B is a composition "according to the teaching of WO 2007/113299" (see its contents of NG and BCN, close to stoichiometric equilibrium (R = 1.2)) which also contains 4% bulk of strontium titanate;

the composition of Example C is a composition based on

NG + NCB unbalanced (R = NG / BCN = 8.7). In addition to NG and BCN, said composition contains alumina ("slagging agent") at a level identical to that of the composition of Example A.

The compositions of said Examples A, B and C have combustion temperatures above 1415 K.

It is noted that the presence of strontium titanate in a composition having a near equilibrium oxygen balance (close to zero) has little impact on the combustion temperature (see the values of the said combustion temperature for compositions of Examples A (1905 K) and B (1889 K)).

The combustion temperature of the composition of Example C (1438 K) remains greater than 1415 K.

The compositions of Examples 1 to 8 of the invention typically contain guanidine nitrate (NG) and basic copper nitrate (NCB) in an unbalanced mass ratio (greater than or equal to 8.5) and an inorganic titanate at a mass ratio greater than or equal to 3% and less than or equal to 12.5%.

The characteristics of the compositions of Examples 1 to 8 of Table 1 show that the addition of strontium titanate (SrTiOs) or Calcium titanate (CaTiOs), in a composition based on NG + BCN strongly unbalanced oxygen balance (of the type of Example C), provides a low combustion temperature value (below the threshold of 1415 K fixed in the specifications (see above)) while maintaining a high gas yield (greater than or equal to 39.5 mol / kg).

With regard to the rates of combustion, reference is made to paragraph II below.

Table 1

II. The block combustion rates of the invention have been compared with those of blocks according to the teaching of WO 2007/113299.

In fact :

the combustion rates measured at 2 MPa and at 0.1 MPa were measured on blocks (diameter: 24.6 mm and thickness: 10 mm) presenting, respectively, the composition of Example 8 according to the invention and the composition of Example A (according to WO 2007/113299) of Table 1 above, and

the combustion speeds at 20 MPa (high pressure) were applied to pellets (diameter: 6.35 mm and thickness: 2 mm) presenting, respectively, the composition of Example 8 according to the invention and the composition of Example A (according to WO 2007/113299) of Table 1 above. This is only a circumstance geometry suitable for measuring the rate of combustion at high pressure.

The blocks and pellets were obtained by the same dry process (compaction + granulation + compression), implemented under the same conditions (same compaction and compression pressure, in particular), so that the measured combustion rates are comparable. .

Said combustion rates measured are reported in Table 2 below.

The porosities of said blocks and pellets obtained in the same conditions are specified below:

Pastille block

Ex. At 4.5% 4.0%

(porosities greater than 3%)

Ex. 8 1.5% 0.5%

(porosity less than 3%). Table 2

The results above show that the pyrotechnic block according to the invention has combustion speeds (at 2 MPa and at 0.1 MPa) very significantly lower than those of the block of the prior art. It is the same with the burning rate, at 10 MPa, measured on the pellets.

In addition, it has been found that the block according to the invention, despite the significant imbalance of the NG / NCB ratio of its composition, advantageously has a self-sustaining combustion up to the desired minimum value ie up to atmospheric pressure. ).

III. The densification characteristics of the compositions of the blocks of the invention, densification characteristics, which are significantly improved compared with those of the compositions according to the teaching of WO 2007/113299, which make it possible in particular to obtain blocks, are of interest hereinafter. very low porosity (<5%, advantageously ≤ 3%, very advantageously ≤ 2%, even ≤ 1%).

The appended FIG. 1 shows the densification curves (ie the evolution of the porosity value as a function of the pressure applied to the material during a compression step), measured compared with the composition of Example 1 (Ex. 1) according to the invention and with the composition of Comparative Example A (Ex. A) (according to the teaching of WO 2007/113299). These densification curves were established in a pellet manufacturing context (dry process: compaction + granulation + compression), with different values of compressive stress. The compression force value applied is then translated into an equivalent material pressure value according to the following equation: Material pressure (in bar, abscissa) = applied compression force (in N) divided by the area of the punch footprint compression ratio (in m ² ) divided by 10 ⁵ . The porosity value (ordinate) is calculated from the measurement of the dimensions (thickness, diameter) and mass of the tablet (compressed) obtained (it is expressed as a percentage and corresponds to the difference between the mass value theoretical volume and the measured density value, reduced to the theoretical density value (see above)).

For pressure values above 3000 bar, the composition according to Example 1 of the invention makes it possible to obtain pellets characterized by a porosity value of less than or equal to 1%, ie very close to densification. Max. For the same applied pressure value (3000 bars), the measured porosity value for pellets according to the prior art is significantly higher (of the order of 5%).

The person skilled in the art knows that it is advantageous to be able to limit the compression force because this contributes favorably to reducing the mechanical stresses (fatigue, wear) applied to the tooling. This compressive force is all the more important as the dimensions of the object to be compressed are high. In the context of the present invention, the manufacture of monolithic blocks of high diameter (for example of 38 mm) and thickness of 20 mm (as required for certain applications referred)) therefore requires to apply a high compression force to ensure that a densification value is obtained as close as possible to the maximum value of theoretical density.

According to the curves of FIG. 1, obtaining a porosity value of less than or equal to 4% for the composition according to comparative example A requires a high material pressure value, of the order of 4000 bar, ie equivalent compression effort of the order of 45 tons. In comparison, obtaining a porosity value less than or equal to 4% (or preferably less than or equal to 3%) for the composition according to the invention (Example 1) is obtained for a significantly lower material pressure value, of the order of 1000 bar (1500 bar), an equivalent compressive force of the order of 11 tons (17 tons). Thus, the composition according to Example 1 of the present invention advantageously allows either to significantly reduce the compression force (for the same level of targeted porosity), or to obtain a lower porosity value (for the same level compressive force applied).

These advantageous characteristics of densification shown on pellets are obviously transferable to blocks (of the invention).

Claims

1. Pyrotechnic monolithic gas generator block, of substantially cylindrical shape, characterized in that:

- it has a thickness greater than or equal to 10 mm,

an equivalent diameter greater than or equal to 10 mm, and a porosity of less than 5%; and

in that

- its composition, expressed in mass percentages, contains, for at least 94% of its mass:

+ 77.5 to 92.5% of guanidine nitrate,

+ 5 to 10% of basic copper nitrate, and

2. Block according to claim 1, whose thickness is between 10 and 100 mm and / or whose equivalent diameter is between 10 and 100 mm.

3. Block according to claim 1 or 2, whose porosity is less than or equal to 2%.

4. Block according to any one of claims 1 to 3, characterized in that its composition contains said guanidine nitrate and said basic copper nitrate in a ratio, R, of between 8.5 and 15 (8.5 <R <15), advantageously between 8.5 and 12 (8.5 <R <12).

5. Block according to any one of claims 1 to 4, characterized in that said at least one inorganic titanate consists of at least one inorganic titanate selected from metal titanates and alkaline earth titanates.

Block according to any one of Claims 1 to 5, characterized in that the said at least one inorganic titanate consists of strontium titanate (SrTiO ₃ ) and / or calcium titanate (CaTiO ₃ ) and / or titanate. of aluminum (Al ₂ Ti0 ₅ ).

7. Block according to any one of claims 1 to 6, characterized in that said guanidine nitrate, basic copper nitrate and at least one inorganic titanate represent at least 97% by weight, preferably at least 99% by weight, of its mass.

8. Block according to any one of claims 1 to 7, characterized in that its composition closes, in addition to said guanidine nitrate, basic copper nitrate and at least one inorganic titanate, at least one additive implementation, to a mass ratio not exceeding 1%.

9. Block according to any one of claims 1 to 8, characterized in that its composition contains, in addition to said guanidine nitrate, basic copper nitrate and at least one inorganic titanate, at least one binder or at least one fluxing agent. , at a mass ratio not exceeding 5%.

10. Block according to any one of claims 1 to 8, characterized in that its composition contains, for 100% of its mass:

said guanidine nitrate, said basic nitrate of copper,

said at least one inorganic titanate, and

at least one additive used.

11. Block according to any one of claims 1 to 9, characterized in that its composition contains, for 100% of its mass:

said guanidine nitrate,

said basic nitrate of copper,

said at least one inorganic titanate,

at least one processing additive, and

at least one binder or at least one fluxing agent.

12. Process for obtaining a substantially gas-cylindrical pyrotechnic monolithic gas generator block according to any one of Claims 1 to 11, characterized in that it consists of a dry process method or a wet process method. advantageously in a dry process.

13. The method of claim 12, characterized in that it consists of a dry process method, which advantageously comprises:

compressing a powder mixture containing said guanidine nitrate, said basic copper nitrate, said at least one inorganic titanate, at least one processing additive and optionally at least one fluxing agent; or

compacting a powder mixture containing said guanidine nitrate, said basic copper nitrate, at least one processing additive and optionally at least one melting agent to obtain a compacted material, followed by the granulation of said material compacted to obtain granules, itself followed by compression of said granules; said at least one inorganic titanate being added to the powdery mixture to be compacted and / or to the granules to be compressed.

14. Process according to claim 12, characterized in that it consists of a wet process, which advantageously comprises:

extruding a paste containing said guanidine nitrate, said basic copper nitrate, said at least one inorganic titanate, at least one processing additive, at least one binder and a solvent; or

preparing an aqueous solution containing at least said guanidine nitrate, optionally suspending, in said aqueous solution, at least basic copper nitrate, obtaining a powder by spray drying said solution or suspension, if necessary, the addition, to said powder, ingredient (s) constitutive (s) complementary (s) said block and the shaping of the powder, optionally added said (said) ingredient (s) components), containing all the constituent ingredients of said block; said at least one inorganic titanate being added to the solution or suspension to be atomized and / or to the atomized powder.

15. A gas generator, containing a solid pyrotechnic charge gas generator, characterized in that said charge contains at least one block according to any one of claims 1 to 11 and / or obtained according to the method of any one of the claims. 12 to 14.