Gas-generating pyrotechnic monolithic blocks

Abstract

A substantially cylindrical gas-generating pyrotechnical monolithic block has 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.

Claims

1. A gas-generating pyrotechnic monolithic block, of substantially cylindrical shape, wherein: the gas-generating pyrotechnic monolithic block has a thickness greater than or equal to 10 mm, an equivalent diameter greater than or equal to 10 mm, and a porosity below 5%; and wherein a composition of the gas-generating pyrotechnic monolithic block, expressed in percentage by weight, contains, for at least 94% of its weight: +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 whose melting point is above 2100 K.

2. The block as claimed in claim 1, whose thickness is between 10 and 100 mm and/or whose equivalent diameter is between 10 and 100 mm.

3. The block as claimed in claim 1, whose porosity is less than or equal to 2%.

4. The block as claimed in claim 1, wherein the composition of the gas-generating pyrotechnic monolithic block contains said guanidine nitrate and said basic copper nitrate in a ratio, R, between 8.5 and 15 (8.5R15).

5. The block as claimed in claim 1, wherein said at least one inorganic titanate consists of at least one inorganic titanate selected from the group consisting of metal titanates and alkaline-earth titanates.

6. The block as claimed in claim 1, wherein said at least one inorganic titanate consists of strontium titanate (SrTiO.sub.3) and/or calcium titanate (CaTiO.sub.3) and/or aluminum titanate (Al.sub.2TiO.sub.5).

7. The block as claimed in claim 1, wherein said guanidine nitrate, basic copper nitrate and at least one inorganic titanate represent at least 97 wt % of its weight.

8. The block as claimed in claim 1, wherein the composition of the gas-generating pyrotechnic monolithic block contains, in addition to said guanidine nitrate, basic copper nitrate and at least one inorganic titanate, at least one processing additive, in a proportion by weight not exceeding 1%.

9. The block as claimed in claim 1, wherein the composition of the gas-generating pyrotechnic monolithic block contains, in addition to said guanidine nitrate, basic copper nitrate and at least one inorganic titanate, at least one binder or at least one flux, in a proportion by weight not exceeding 5%.

10. The block as claimed in claim 1, wherein the composition of the gas-generating pyrotechnic monolithic block contains, for 100% of its weight: said guanidine nitrate, said basic copper nitrate, said at least one inorganic titanate, and at least one processing additive.

11. The block as claimed in claim 1, wherein the composition of the gas-generating pyrotechnic monolithic block contains, for 100% of its weight: said guanidine nitrate, said basic copper nitrate, said at least one inorganic titanate, at least one processing additive, and at least one binder or at least one flux.

12. A method for obtaining a gas-generating pyrotechnic monolithic block, of substantially cylindrical shape, as claimed in claim 1, wherein the method consists of a dry process or a wet process.

13. The method as claimed in claim 12, wherein the method consists of a dry process, which comprises: compressing a pulverulent 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 flux; or compacting a pulverulent mixture containing said guanidine nitrate, said basic copper nitrate, at least one processing additive and optionally at least one melting agent for obtaining a compacted material, followed by granulating said compacted material to obtain granules, followed by compressing said granules; said at least one inorganic titanate being added to the pulverulent mixture to be compacted and/or to the granules to be compressed.

14. The method as claimed in claim 12, wherein the method consists of a wet process, which 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 at least basic copper nitrate in said aqueous solution, obtaining a powder by spray-drying said solution or suspension, if necessary adding complementary constituent(s) of said block to said powder and shaping the powder, optionally added with said complementary constituent(s), containing all the constituents of said block; said at least one inorganic titanate being added to the solution or suspension to be spray-dried and/or to the spray-dried powder.

15. A gas generator, containing a gas-generating solid pyrotechnic charge, wherein said charge contains at least one block as claimed in claim 1.

16. The block as claimed in claim 1, wherein the composition of the gas-generating pyrotechnic monolithic block contains said guanidine nitrate and said basic copper nitrate in a ratio, R, between 8.5 and 12 (8.5R12).

17. The block as claimed in claim 1, wherein said guanidine nitrate, basic copper nitrate and at least one inorganic titanate represent at least 99 wt. % of its weight.

18. A method as claimed in claim 12, wherein said method consists of a dry process.

19. A gas generator, containing a gas-generating solid pyrotechnic charge, wherein said charge contains at least one block obtained according to the method of claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows the variation of the porosity value as a function of the pressure applied on the material during a compression step, measured in comparison with the composition in example 1 (Ex. 1) according to an embodiment of the invention and with the composition of comparative example A (Ex. A) (according to the teaching of WO 2007/113299).

(2) It is now proposed to illustrate the invention, not in any way limiting.

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

(4) These compositions and their characteristics are to be compared with those of examples A, B and C, given for comparison: the composition in example A is a composition according to the teaching of WO 2007/113299. It contains 52.44 wt. % of GN and 44.87 wt. % of BCN (ratio R=GN/BCN (=1.2) is close to the stoichiometric equilibrium). It also contains 2.69 wt. % of alumina (slagging agent (according to WO 2007/113299)); the composition in example B is a composition according to the teaching of WO 2007/113299 (see its contents of GN and BCN, close to the stoichiometric equilibrium (R=1.2)) which further contains 4 wt. % of strontium titanate; the composition in example C is an unbalanced GN+BCN base composition (R=GN/BCN=8.7). Besides GN and BCN, said composition contains alumina (slagging agent) at a level identical to that of the composition of example A.

(5) The compositions of said examples A, B and C have combustion temperatures above 1415 K.

(6) It is noted that the presence of strontium titanate in a composition having an almost equilibrated oxygen balance (close to zero) has hardly any effect on the combustion temperature (see the values of said combustion temperature for the compositions in examples A (1905 K) and B (1889 K)).

(7) The combustion temperature of the composition in example C (1438 K) is still above 1415 K.

(8) The compositions in examples 1 to 8 of the invention contain, characteristically, guanidine nitrate (GN) and basic copper nitrate (BCN), in an unbalanced weight ratio (greater than or equal to 8.5), as well as an inorganic titanate at a percentage by weight greater than or equal to 3% and less than or equal to 12.5%.

(9) The characteristics of the compositions of examples 1 to 8 in Table 1 show that adding strontium titanate (SrTiO.sub.3) or calcium titanate (CaTiO.sub.3) to a composition based on GN+BCN that is highly unbalanced in oxygen balance (of the type in example C) makes it possible to obtain a low value of combustion temperature (below the threshold of 1415 K stipulated in the specifications (see above)) while maintaining a high gas yield (greater than or equal to 39.5 mol/kg).

(10) Regarding the rates of combustion, reference may be made to paragraph II below.

(11) TABLE-US-00001 TABLE 1 Examples Ex. A Ex. B Ex. C Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ingredients Guanidine Nitrate (GN) % 52.44 52 87.31 85 82.7 80.3 85 82.7 80.3 78.2 86.9 Basic Copper Nitrate (BCN) % 44.87 44 10 9.8 9.6 9.5 9.8 9.6 9.5 9.1 9.9 Alumina (Al.sub.2O.sub.3) % 2.69 2.69 Ca Stearate % 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Strontium titanate (SrTiO.sub.3) % 4 5 7.5 10 3 Calcium titanate (CaTiO.sub.3) % 5 7.5 10 12.5 Characteristics Weight ratio (R) GN/BCN 1.2 1.2 8.7 8.7 8.6 8.5 8.7 8.6 8.5 8.6 8.8 Oxygen balance % 3.3 3.3 20.5 20.4 19.8 19.1 20.4 19.7 19.0 18.5 20.9 Combustion temperature K 1905 1889 1438 1398 1377 1358 1411 1396 1382 1364 1414 Density g/cm.sup.3 1.99 2.01 1.55 1.58 1.61 1.64 1.58 1.60 1.63 1.66 1.56 Gas yield mol/kg 29.5 29.2 43.7 42.8 41.6 40.5 42.8 41.6 40.5 39.5 43.8 at 1bar - 1000 K

(12) II. The combustion rates of blocks of the invention were compared with those of blocks according to the teaching of WO 2007/113299.

(13) In fact: the combustion rates measured at 2 MPa and at 0.1 MPa were measured on blocks (with a diameter: 24.6 mm and a thickness: 10 mm) having, respectively, the composition of example 8 according to the invention and the composition of example A (according to WO 2007/113299) in Table 1 above, and the combustion rates at 20 MPa (high pressure) were measured on pellets (with a diameter: 6.35 mm and a thickness: 2 mm) having, respectively, the composition of example 8 according to the invention and the composition of example A (according to WO 2007/113299) in Table 1 above. This is purely a suitable geometry for measuring the combustion rate at high pressure.

(14) The blocks and pellets were obtained by the same dry process (compacting+granulation+compression), carried out in the same conditions (notably the same compacting and compression pressure), so that the combustion rates measured are comparable.

(15) These measured combustion rates are presented in Table 2 below.

(16) The porosities of said blocks and pellets obtained in said same conditions are stated below:

(17) TABLE-US-00002 Block Pellet Ex. A 4.5% 4.0% (porosities above 3%) Ex. 8 1.5% 0.5% (porosities below 3%)

(18) TABLE-US-00003 TABLE 2 Examples Characteristics Ex. A Ex. 8 Combustion rate at 10 MPa mm/s 16 5 Combustion rate at 2 MPa mm/s 8 2 Combustion rate at 0.1 MPa mm/s 1 0.4 Agglomerated appearance of the yes yes combustion residues (in the form of a skeleton of the pyrotechnic block)

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

(20) Moreover, it was found that the block according to the invention, despite the considerable imbalance of the GN/BCN ratio in its composition, advantageously displays self-sustaining combustion up to the minimum value desired (i.e. up to atmospheric pressure).

(21) III. In the following, the densification characteristics of the compositions of the blocks of the invention are now considered. These densification characteristics are significantly improved relative to those of the compositions according to the teaching of WO 2007/113299. These densification characteristics notably allow the obtaining of blocks with very low porosity (<5%, advantageously 3%, very advantageously 2%, or even 1%).

(22) The accompanying FIG. 1 shows the densification curves (i.e. the variation of the porosity value as a function of the pressure applied on the material during a compression step), measured in comparison with the composition in 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 context of manufacture of pellets (dry process: compacting+granulation+compression), with different values of the compression force. The value of compression force applied is then translated into an equivalent value of material pressure according to the following equation: Material pressure (in bar; abscissa)=compression force applied (in N) divided by the surface area of the imprint of the compression punch (in m.sup.2) divided by 10.sup.5. The porosity value (ordinate) is calculated from measurement of the dimensions (thickness, diameter) and weight of the pellet (tablet) obtained (it is expressed as a percentage; it corresponds to the difference between the theoretical density value and the measured density value, relative to the theoretical density value (see above)).

(23) For values of pressure above 3000 bar, the composition according to example 1 of the invention allows pellets to be obtained, characterized by a porosity value less than or equal to 1%, i.e. very close to the maximum densification. For one and the same value of pressure applied (3000 bar), the measured porosity value for pellets according to the prior art is significantly higher (of the order of 5%).

(24) A person skilled in the art knows that it is advantageous to be able to limit the compression force, as this contributes favorably to reducing the mechanical stresses (fatigue, wear) applied on the tooling. This compression force is greater for larger dimensions of the object to be compressed. In the context of the present invention, the manufacture of monolithic blocks of large diameter (for example 38 mm) and with thickness of 20 mm (such as is required for certain intended applications) then requires applying a high compression force in order to guarantee the obtaining of a value of densification as close as possible to the maximum theoretical density value.

(25) According to the curves in FIG. 1, the obtaining of a porosity value less than or equal to 4% for the composition according to comparative example A requires a high value of material pressure, of the order of 4000 bar, that is to say an equivalent compression force of the order of 45 tonnes. In comparison, 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 value of material pressure, of the order of 1000 bar (1500 bar), that is to say an equivalent compression force of the order of 11 tonnes (17 tonnes). Thus, the composition according to example 1 of the present invention advantageously makes it possible either to reduce the compression force significantly (for one and the same intended level of porosity), or obtain a lower value of porosity (for one and the same level of compression force applied).

(26) These advantageous characteristics of densification shown on pellets are of course transposable to blocks (of the invention).