Classifications

• • C—CHEMISTRY; METALLURGY
  • C06—EXPLOSIVES; MATCHES
  • C06D—MEANS FOR GENERATING SMOKE OR MIST; GAS-ATTACK COMPOSITIONS; GENERATION OF GAS FOR BLASTING OR PROPULSION (CHEMICAL PART)
  • C06D5/00—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets
  • C06D5/06—Generation of pressure gas, e.g. for blasting cartridges, starting cartridges, rockets by reaction of two or more solids

Definitions

• the present invention relates to the field of pyrotechnic production of gases intended for open systems. More specifically, the invention relates new pyrotechnic compositions generating clean gases, rich in nitrogen but low in content nitrogen oxides and intended to operate fire extinguishers, for inflating structures protective covers or protective cushions for occupants of a motor vehicle.
• compositions based on sodium azide like, for example, those described in the patent US-A-4,929,290.
• the compositions based sodium azide have many disadvantages.
• azide-based compositions are very sensitive to humidity and do not keep well over time.
• sodium azide which can lead to explosives primary, by combination with metals to form for example lead azide, these compositions must be subject to precautions when manufacturing and disposal of waste.
• compositions as a propellant for rocket and missile engines are known and described in numerous patents such as, for example, the US-A-3,725,516 which describes propellants for rocket engines constituted by a fluorinated binder, a salt oxidant such as ammonium nitrate or perchlorate potassium and a metal in powder form.
• propellants are not usable in the applications covered by this invention for at least two reasons.
• compositions based on ammonium nitrate and / or potassium perchlorate in combination with tetrazole derivatives and compounds metallic like boron oxide, vanadium oxide or silicates Such compositions which are, for example, described in US-A-5,035,757 give many non-toxic nitrogen-rich gases but still produce many solid residues which make it necessary to have a important filtration.
• compositions expressly excluding the presence of metallic compounds and comprising essentially an oxygenated thermoplastic binder, a energy plasticizer such as polyazide glycidyl and a compound oxidizing charge for at least 85% of its weight by ammonium nitrate.
• the composition contains at least 8% by weight of binder not to mention the energy plasticizer and the skilled person is, at least for some applications, again faced with the problem of gas toxicity.
• compositions whose oxidizing charge is based on ammonium nitrate and which contain less than 6% by weight of an oxygenated organic binder and between 0.5% and 5% by weight of a light metal chosen from the group consisting of boron and aluminum.
• These compositions which are advantageously put in the form of pellets by compression, have a burning rate satisfactory, they do not produce by combustion of heavy solid residues and the gases generated have a content in extremely low carbon monoxide.
• the gases generated by these compositions have a content of nitrogen oxides still a little too high when they're intended to operate in open systems on outside.
• composition contains as nitrogen compound oxidant of ammonium perchlorate the latter will advantageously combined with sodium nitrate which will function, during combustion, as a sensor chlorine.
• the nitrate weight ratio of sodium / ammonium perchlorate will advantageously close to 0.95.
• compositions according to the invention will contain advantageously cupric oxide CuO, the content of which by weight relative to the total weight of the composition could be up to 10%.
• compositions according to the invention may also advantageously contain up to 5% by weight of lithium carbonate and up to 1% by weight of silica SiO 2 . If one wants compositions having a good combustion rate and producing gases very poor in nitrogen oxides, it will be ensured that these compositions contain cupric oxide as indicated above and that the said nitrogenous compound reagent of either nitroguanidine and / or guanidinium nitrate excluding oxamide.
• Such compositions are very suitable for constituting pyrotechnic charges intended to inflate protective cushions for occupants of a motor vehicle.
• the weight content y of said reactive nitrogen compound will preferably be between 5% and 10% of the total weight of the composition and more preferably close to 6%.
• compositions will be put in the form of tablets or tablet dragees, the oxygenated binder crosslinkable being preferably chosen from polymers or copolymers with epoxy units or units silicone. After tableting the pellets obtained are cooked for a few hours at a similar temperature 100 ° C to cause crosslinking of the binder.
• composition pellets are then intended to constitute bulk loads of pyrotechnic gas generators for systems open to the outside like fire extinguishers pyrotechnics, inflation devices external structures or protective cushions for occupants of a motor vehicle.
• compositions according to the invention are therefore basically composite pyrotechnic compositions based on ammonium nitrate and containing a binder and a light metal of the type described in French patent application 96.08050.
• the binder is a crosslinkable oxygenated binder preferably chosen from binders based on epoxy resin or silicone resin based. Content by weight of the said binder relative to the total weight of the composition will be between 1% and 6%.
• the main oxidant of the compositions according to the invention is ammonium nitrate the content of which by weight relative to the total weight of the composition can be understood according to a first characteristic of the invention between 29% and 93.5%, but will preferably between 60% and 75%.
• the ammonium nitrate will be nitrate of ammonium stabilized, for example with nitrate of potassium and amaranth as described in the application French patent 2,743,797. In this case, we will use advantageously a stabilized mixture containing 96.5% in weight of ammonium nitrate, 3% by weight of nitrate of potassium and 0.5% by weight of amaranth.
• the light metal is chosen exclusively from the boron and aluminum and its weight content compared the total weight of the composition is between 0.5% and 5%.
• the compositions according to the invention may also contain other oxidants. They can thus contain perchlorate of potassium, the weight content of the latter relative the total weight of the composition which may be included between 0% and 30%. This weight content will often between 10% and 20%. They can also contain an oxidizing nitrogen compound selected from the group consisting of ammonium perchlorate, nitrate of triaminoguanidine, hexogen, octogen and hexanitrohexaazaisowurtzitane. Weight content x of this oxidizing nitrogenous compound relative to the total weight of the composition satisfies the relation 0% ⁇ x ⁇ 15%.
• ammonium perchlorate When ammonium perchlorate is used as oxidizing nitrogen compound, it will advantageously be combination with sodium nitrate so that avoid the formation of hydrochloric acid in the gases combustion. In this case the nitrate weight ratio sodium / ammonium perchlorate will advantageously close to 0.95.
• the pyrotechnic compositions imperatively contain a reactive organic nitrogen compound chosen from the group consisting of nitroguanidine, guanidinium nitrate and oxamide.
• a reactive organic nitrogen compound chosen from the group consisting of nitroguanidine, guanidinium nitrate and oxamide.
• compositions according to the invention can also contain various additives such as, for example, cupric oxide CuO, lithium carbonate Li 2 CO 3 or silica SiO 2 .
• additives have various functions, the silica which will generally be used at contents less than or equal to 1% by weight has an anti-caking effect on the ammonium nitrate during formulation and shaping of the composition before crosslinking of the binder.
• the lithium carbonate which will generally be used at contents less than or equal to 5% by weight makes it possible to lower the combustion temperature of the compositions according to the invention while the cupric oxide which will generally be used at lower weight contents or equal to 10%, most often close to 6%, makes it possible to improve the ignition of the compositions according to the invention and to increase their combustion rates.
• Vehicle safety compositions will therefore preferably contain cupric oxide. Gases intended to inflate protective cushions for occupants of a motor vehicle must not only be very poor in nitrogen oxides but must also be very low in monoxide carbon CO. To meet this last requirement we avoid the use of oxamide as a nitrogen component reactive in safety compositions automotive and we will limit our, for these compositions, to the use of nitroguanidine or guanidinium nitrate as reactive nitrogen compound.
• the weight content of reactive nitrogen compound will, for these compositions, between 5% and 10% compared to the total weight of the composition, and more particularly close to 6%.
• compositions according to the invention are used form by tableting after a mixing phase performed in a mixer.
• the oxygenated binder is then added in the state liquid, not completely polymerized.
• a thermosetting binder it will be liquid resin mixed with its hardener.
• the hardener will be advantageously a polyamine which is not very reactive so as to have a "pot life" for the binder of about 24 hours.
• compositions according to the invention being to contain only very little binder compared to usual compositions for propellants or low powders "LOVA" type vulnerability, a difficulty not negligible formulation of compositions according to the invention consists in successfully permeating the whole solid constituents, and in particular nitrate ammonium, with this small amount of liquid binder.
• the liquid binder will advantageously be introduced into the mixer in diluted form in a solvent very volatile and inert towards constituents of the composition.
• a polyepoxy binder advantageously use trichloroethane as a diluent.
• the mixer is then started and left on turn, bowl covered, for about an hour. In these conditions we can permeate all of the solid constituents by the binder and all of the diluent was removed by evaporation during the mixing operation.
• composition which appears at this stage under the appearance of a slightly wet powder is brought to the desired shape by compression. In general it is put in the form of pellets.
• the polymerization of the binder takes place at a temperature close to 100 ° C and after 7 hours, in the case of a polyepoxy binder, the loads pyrotechnics obtained show good performance mechanical allowing their use in a generator gas pyrotechnics.
• compositions according to the invention contain a low level of binder which is not sufficient for fill all the gaps between the nitrate grains ammonium. Therefore putting into the form of pellets by compression leads to objects having a natural porosity corresponding to an increase in the area available for combustion, which is very favorable in terms of the rate of combustion of the composition.
• ammonium nitrate stabilized as described above promotes the conservation over time of the material's properties gas generator.
• Example 1 Example 2
• Example 3 Example 4
• Example 6 epoxy binder 6 6 6 6 6 6 6 6 6 NH 4 NO 3 stabilized 71 62 71 71 62 62 boron 3 1 1 1 1 1 1 KClO 4 20 10 10 - 10 12 NH 4 CLO 4 + NaNO 3 - - - 10 - - CuO - 6 6 6 6 6 6 Nitroguanidine - 15 6 6 - - Oxamide - - - - - 15 13
• Example 1 relates to a composition such that described in French patent application 96.08050 and is given for comparison.
• Tables 1 and 2 shows that all the compositions according to the invention (example 2 to 6) reduce the oxide content of the gases nitrogen compared to the reference (example 1), the most dramatic results being achieved with oxamide (examples 5 and 6). Nevertheless the compositions with oxamide provide gases too rich in carbon monoxide for automotive safety. Those are compositions rich in ammonium nitrate and using nitroguanidine (examples 3 and 4) which provide the most attractive gases for the automotive safety.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Organic Chemistry (AREA)
• Air Bags (AREA)

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• 1997
  • 1997-12-22 FR FR9716216A patent/FR2772750B1/fr not_active Expired - Fee Related
• 1998
  • 1998-12-03 US US09/204,466 patent/US6024811A/en not_active Expired - Lifetime
  • 1998-12-10 DE DE69807177T patent/DE69807177T2/de not_active Expired - Lifetime
  • 1998-12-10 EP EP98403120A patent/EP0924177B1/de not_active Expired - Lifetime

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