EP1976811A1

EP1976811A1 - Gas-generating pyrotechnical compositions, comprising stabilized ammonium nitrate; corresponding pyrotechnical compounds

Info

Publication number: EP1976811A1
Application number: EP07731511A
Authority: EP
Inventors: Hélène BLANCHARD; Hugues Rocton
Original assignee: SNPE Materiaux Energetiques SA
Current assignee: Safran Ceramics SA
Priority date: 2006-01-25
Filing date: 2007-01-24
Publication date: 2008-10-08
Also published as: FR2896497A1; FR2896497B1; WO2007085761A1

Abstract

The invention concerns gas-generating pyrotechnical compositions designed for civilian uses as well as the corresponding pyrotechnical compounds. Said compositions contain essentially stabilized ammonium nitrate as oxidant filler and a reducing filler which comprises: a first reducing element selected among guanidine nitrate, guanyl urea dinitramide and mixtures thereof; and a second reducing element selected among tetrazole, tetrazole derivatives and salts thereof, bitetrazole salts and derivatives thereof, 5,5'-azobitetrazole salts and mixtures thereof. Said pyrotechnical compositions are particularly efficient in terms of gas yield and combustion speeds. Said speeds have an advantageous plateau starting at 22 MPa.

Description

Pyrotechnic gas generating compositions comprising stabilized ammonium nitrate: corresponding pyrotechnic compounds.

The present invention relates to gas-generating pyrotechnic compositions comprising stabilized ammonium nitrate and the corresponding pyrotechnic compounds.

Powerful pyrotechnic gas generating compositions are sought for many civil applications, such as automobile safety (context of conductive airbags and curtain airbags) and fire fighting (context of pyrotechnic extinguishers). These pyrotechnic compositions, for civil applications, are advantageously optimized in terms of:

- amount of gas generated; the aim is an optimum gas yield;

temperature of said generated gases; we aim for the generation of "cold" gases, Le. gas produced at a temperature of less than about 2,200 K;

pressure of said generated gases: "low" pressures are aimed at. pressures lower than 30 MPa) not involving heavy adaptations of the generators, enclosing said compositions;

- Speed of said gases: it is intended to obtain fast speeds, of the order of 10 to 40 milliseconds, with, optionally, optimization of speed profiles and possibility of adjustment of said speeds;

- Cleanliness of said gases: it is intended to generate gases free of solid particles (which may constitute hot spots that can damage the air-bag wall type air bag conductor) and non-toxic, Le. low in carbon monoxide, oxides of nitrogen and chlorinated products. It is understood that this parameter "cleanliness of said gases" is more or less critical depending on the exact context of use of the pyrotechnic compositions.

Various types of pyrotechnic compositions for civil applications have been proposed to date; in particular compositions containing stabilized ammonium nitrate as oxidizing filler.

The particularity of this oxidant is to burn at a pressure greater than 30 MPa with a suitable pressure exponent n, of the order of 0.3. Below 30 MPa, it burns with a much higher exponent (n close to 1). With reference to this technical problem, it is necessary to provide, for the use of this oxidizer in pyrotechnic generators, devices such as stepped nozzles, pressure regulators, catalysts ... This obviously increases the cost of the generators and / or their operation. The intervention of this oxidant in pyrotechnic compositions has in particular been described in US Patent 5,747,730 and US 2004/0016480. The pyrotechnic compositions of the prior art described in these documents are not as efficient as the compositions of the invention described below, more particularly as regards the rate of combustion, for those described in US Pat. No. 5,747,730 and US Pat. possibility of adjusting said speed, for those described in application US 2004/0016480.

According to its first object, the present invention therefore relates to gas generating pyrotechnic compositions which comprise stabilized ammonium nitrate (PSAN), as an oxidizing charge.

Said compositions also comprise a reducing filler and, typically, said reducing filler is bicomponent. Typically, said reducing charge comprises: a first reducing element chosen from guanidine nitrate, guanyl urea dinitramide and mixtures thereof; and a second reducing element chosen from: + tetrazole,

+ the derivatives of tetrazole and their salts, + the salts of biterazole and its derivatives,

+ the salts of 5,5'-azobiterazole, and + their mixtures.

It is generally referred to a main reducing charge (selected from guanidine nitrate, guanyl urea dinitramide and mixtures thereof); and an additional reducing charge

(selected from tetrazole, tetrazole derivatives and their salts, salts of biterazole and its derivatives, 5,5'-azobiterazole salts and mixtures thereof); in view of the respective advantageous amounts of intervention of said first and second reducing elements (see below).

As regards the second reducing element, the derivatives of the compounds in question are principally those compounds which are substituted, in particular with an amino group; and the salts in question are mainly the alkaline (preferably sodium, potassium,), alkaline earth (calcium, advantageously) salts and the ammonium salts.

Those skilled in the art know per se the first and second reducing elements of the pyrotechnic compositions of the invention. It is the merit of the inventors to have highlighted the value of their joint intervention in combination with ammonium nitrate, as an oxidizing element.

The stabilized ammonium nitrate, which acts as an oxidizing filler in the compositions of the invention, is advantageously ammonium nitrate stabilized at least in part by potassium nitrate.

The skilled person knows this type of oxidizing charge.

It is generally ammonium nitrate containing from 10 to 20% (typically 15%) by weight of potassium nitrate. It may also be ammonium nitrate containing from 1 to 7% by weight of potassium nitrate and from 0.1% to 1% by weight of an organic compound comprising at least one arylsufonate group chosen from the group consisting of by the benzenesulfonate groups and the naphthalenesulphonate groups; said organic compound being advantageously selected from the group consisting of acid magenta and amaranth. This second type of stabilized ammonium nitrate has been described in patent application EP-A-0 786 434.

The first reducing element of the reducing charge of the pyrotechnic compositions of the invention advantageously consists of a mixture of guanidine nitrate and guanyl urea dinitramide.

The second reducing element is advantageously chosen from: tetrazole, 5-aminotetrazole, 5-guanylaminotetrazole,

the potassium salt of 5-aminotetrazole,

the sodium salt of 5-aminotetrazole,

- the calcium salt of 5-aminotetrazole, - the ammonium salt of biterazole,

sodium salt of biterazole,

the ammonium salt of the biterazolamine,

the sodium salt of 5,5'-azobiterazole,

the calcium salt of 5,5'-azobiterazole and their mixtures.

The oxidizing and reducing charges (above) of the compositions of the invention represent at least 95% by weight of said compositions. Advantageously, said fillers represent at least 98% by weight of said compositions. Generally, they represent at least 97% by weight of said compositions.

Said compositions are thus essentially constituted of stabilized ammonium nitrate and the two-component reducing filler, as defined above. The ternary compositions of the invention are thus essentially (at least 95% by weight) constituted by stabilized ammonium nitrate and the two reducing elements. The ternary compositions of the invention may thus consist of 100% by weight of said stabilized ammonium nitrate and said two reducing elements or contain low-content additives (<5% by weight, advantageously <2% by weight, generally < 3%), especially auxiliary manufacturing type (such as silica and / or alumina and / or mica and / or magnesium stearate ...).

The pyrotechnic compositions of the invention generally contain:

from 45 to 80% by weight of oxidizing charge, from 10 to 50% by weight of the first reducing element, and

from 3 to 30% by weight of the second reducing element; advantageously contain:

from 59 to 75% by weight of the oxidizing charge, from 10 to 15% by weight of the first reducing element, and from 13 to 25% by weight of the second reducing element.

The pyrotechnic compositions of the invention therefore generally contain;

from 45 to 80%, advantageously from 59 to 75%, by weight of stabilized ammonium nitrate,

from 10 to 50%, advantageously from 10 to 15%, by weight of the first reducing element, and

from 3 to 30%, advantageously from 13 to 25%, by weight of the second reducing element (tetrazole type). The compositions of the invention are effective. They are high-yield gas (40 mol / kg), with combustion temperatures around 2,200 K. The pressures generated are less than 30 MPa, which is particularly interesting, with reference to equipment (construction of generators ). The burning speeds are fast, with a plateau effect and a possibility of adjustment. Said speeds can be of the order of 25 mm / s to 20 MPa with a plateau effect from 22 MPa. This plateau effect is also particularly interesting. It is furthermore easily understood that, by virtue of the nature and / or the content of the second reducing element, it is possible to control said plateau effect, the rate of combustion can be regulated. In this, the compositions of the invention are particularly interesting.

Said plateau effect is clearly demonstrated in the appended FIG. 1, to be considered with the results of the ballistics given below. The compositions of the invention generate gases that are free of solid particles and are, moreover, capable, according to advantageous variants, of exhibiting an oxygen balance value: OB (OB = oxygen surplus with respect to the quantity of said oxygen required for burn the whole product by transforming C into CO ₂ , I ¹ H into H ₂ O ...) between -2% and + 2%, Le. to generate non-toxic gases and therefore quite suitable for an application in the field of air-bags. The compositions of the invention having such balance oxygen values are particularly preferred.

According to its second subject, the present invention relates to pyrotechnic compounds that can be obtained from pyrotechnic compositions described above (pyrotechnic compositions which they constitute the first object of said invention). Said compounds therefore contain the stabilized ammonium nitrate and the two-component reducing filler, as described above, advantageously in the proportions indicated above.

Such compounds can be obtained in a conventional manner, in particular by granulation and pelleting or by granulation and compression.

Those skilled in the art do not ignore the interest in granulating the compositions of the invention, pulverulent. The powders are granulated to ensure the flow and homogeneity of the composition without obviously affecting the compressibility.

Two conventional granulation modes can be implemented: wet granulation or dry granulation. Whatever the mode chosen, the pulverulent raw materials (essentially said stabilized ammonium nitrate and said first and second reducing elements, or even exclusively said stabilized ammonium nitrate and said first and second reducing elements) are mixed, generally by means of a powder mixer, a kneader or a spray tower.

The wet granulation then involves an organic solvent (for example ethanol) or an aqueous solvent. Such a solvent generally occurs up to 5% by weight. The solvent used is then evaporated. Granules of various grain sizes are recovered in which the constituent ingredients are intimately mixed.

The dry granulometry is done directly from the mixture of powders, in a granulator. In the same way, granules of various grain sizes are recovered in which the constituent ingredients are intimately mixed. The granules obtained are then molded by pelletizing or compression, depending on the desired size of the compounds.

To obtain pellets, of dimensions adapted to the needs of a ballistic point of view (whether in terms of size or volume), pellets are introduced into the hopper of a pelletizer ... In principle, to obtain compounds of larger size (0 = 50 mm, e = 50 mm, for example), which require higher pressurization times than those used with pelletizers, granules are introduced into a geometry mold. fixed, adequate and compressed in said mold.

It is thus possible to obtain pyrotechnic compounds of the monolithic type, mono- or multi-perforated. Such compounds are an integral part of the second object of the present invention.

In the same way, granules, obtainable from the compositions of the invention (or above), are an integral part of said second object.

It is now proposed to illustrate, in a non-limiting manner, the presently claimed invention.

A. Thermodynamic calculations

Pyrotechnic compositions have been evaluated. The compositions of Examples A to C below are presented by way of comparison. The compositions of Examples 1 to 7 below are compositions of the invention.

The mass compositions of said compositions are given in the first part of Table 1 below. Results of thermodynamic calculations are given in the second part of said Table 1. It has more precisely been calculated:

the oxygen balance of the composition (OB),

- the combustion temperature of the latter,

- the gas yield,

- the particle rate. Table 1

OO

PSAN; ammonium nitrate stabilized at 15% by weight of potassium nitrate

NG: guanidine nitrate

DABTZ: diamonium biterazole

HOBT: 1-H benzotriazoie

GUDN: guanyl urea dinitramide.

The results of Table 1 above show the interest of the compositions of the invention. Particular emphasis is placed on the interesting gas yields associated with low oxygen balance and combustion temperature values. It is also noted that the level of DABTZ in the compositions of the invention has little effect on the combustion temperature.

The preferred variant of the invention is the composition of Example 6.

B. Ballistics results

The results indicated below were obtained with pellets (0 ≈ 8 mm, h ≈ 3 mm). Said pellets were prepared from the pyrotechnic compositions of the above examples by wet granulation and then pelletizing.

a) Ballistic characteristics of the compositions at + 20 ^° C.

. Table 2 below gives the results of tank firing 10 liters with GEXT generator with valve. These generator tests show that the compositions of the invention have combustion rates of the order of 20 mm / sec at 20 MPa, associated with a low pressure exponent n (see Table 3 below). The compositions of the prior art, containing ammonium nitrate, have combustion rates of the order of 10 to 11 mm / s at 20 MPa, associated with a high pressure exponent n ≈ 0.9-1. A high pressure exponent implies an adaptation of the mechanical strength of the generators in question (by adding a regulator, for example, to modulate the pressure), which entails an additional cost of the system. The Ptx, expressed in MPa, corresponds to a measured tank pressure, comparable to a useful pressure in an air bag. The higher it is, the better the inflation of the bag in air bag configuration.

The Ttx, expressed in ms, corresponds to the time necessary to reach said Ptx. The toxicity values (CO and NO _x , expressed in ppm) show that, depending on the amount of biterazole salt used, it is possible to reach lower toxicity levels and thus be consistent with an air bag application. .

Table 2 also states in its last columns:

the maximum temperature (Tmax, expressed in ⁰ C) of the released gases,

the average pressure (Pmoy, expressed in MPa) of the said released gases,

- The combustion rate (V (Pmoy), expressed in mm / s) of said released gases, at this average pressure.

Table 2

* presence of unburnt

. Manometric bomb tests show a plateau effect from 20 MPa up to 70 MPa (see Table 3 and Rg. 1)

The composition of Example 1 has a density of 135 kg / m ³ ; that of Example 2 a density of 132 kg / m ³ .

Table 3

b) Ballistic characteristics of the compositions in temperature

. Table 4 below gives the results of 10-liter tank shots at different temperatures. The combustion rates are of the same order of magnitude, regardless of the temperature.

Table 4

. To evaluate the effect of the operating temperature on the ballistic performances, a coefficient ITp has been calculated which can be defined as the variation of the operating time as a function of the temperature, with constant tightening. The higher this coefficient, the more important the action of the temperature on the operation.

The compositions of Examples 1, 2 and 4 were evaluated.

That of Example 2 is the least sensitive to thermal action (see Table 5 below).

Table 5

C. Aging resistance

Aging resistance tests were carried out with samples having the composition of Example 6.

The results of said tests are shown in Table 6 below.

Table 6

The loss of mass after 400 h at 107 ^° C. is low, of the order of 0.3%. Despite the presence of ammonium nitrate within it, the pyrotechnic composition of the invention has good temperature stability.

It has also been verified that the rate of combustion is hardly affected by aging.

Claims

claims

A pyrotechnic composition, a gas generator, comprising stabilized ammonium nitrate as an oxidizing charge and a reducing charge, characterized in that said reducing charge comprises:

a first reducing element chosen from guanidine nitrate, guanyl urea dinitramide and their mixtures; and

a second reducing element chosen from tetrazole, the tetrazole derivatives and their salts, the salts of biterazole and its derivatives, the salts of

5,5'-azobiterazole and mixtures thereof; and in that said oxidizing and reducing charges represent at least 95% by weight of said composition.

2. Pyrotechnic composition according to claim 1, characterized in that said oxidizing charge is constituted by ammonium nitrate stabilized at least in part by potassium nitrate.

Pyrotechnic composition according to claim 2, characterized in that said ammonium nitrate contains from 10 to 20% by weight of potassium nitrate or in that said ammonium nitrate contains from 1 to 7% by weight of nitrate of potassium and 0.1% to 1% by weight of an organic compound having at least one arylsufonate group selected from the group consisting of benzenesulfonate groups and naphthalenesulphonate groups, advantageously chosen from the group consisting of acid magenta and amaranth.

4. Pyrotechnic composition according to any one of claims 1 to 3, characterized in that said first reducing element consists of a mixture of guanidine nitrate and guanyl urea dinitramide.

Pyrotechnic composition according to any one of claims 1 to 4, characterized in that said second reducing element is chosen from:

tetrazole, 5-aminotetrazole,

5-guanylaminotetrazole,

the potassium salt of 5-aminotetrazole,

the sodium salt of 5-aminotetrazole,

- the calcium salt of 5-aminotetrazole, - the ammonium salt of biterazole,

sodium salt of biterazole,

the ammonium salt of the biterazolamine,

the sodium salt of 5,5'-azobiterazole,

the calcium salt of 5,5'-azobiterazole and their mixtures.

6. pyrotechnic composition according to any one of claims 1 to 5, characterized in that said oxidizing and reducing charges represent at least 97% by weight of said composition.

Pyrotechnic composition according to any one of claims 1 to 6, characterized in that it contains:

from 45 to 80%, advantageously from 59 to 75%, by weight of stabilized ammonium nitrate, from 10 to 50%, advantageously from 10 to 15%, by weight, of the first reducing element,

from 3 to 30%, advantageously from 13 to 25%, by weight of the second reducing element.

Pyrotechnic compounds obtainable from a composition according to any one of claims 1 to 7.

9. Pyrotechnic compounds according to claim 8, obtained by granulation and pelleting or by granulation and compression.

10. pyrotechnic compounds according to claim 8 or 9, of the monolithic type, mono- or multi-perforated.