WO2019162575A1

WO2019162575A1 - Oxidizer agent for a composition generating gas in a protection device of a vehicle, composition for generating gas, and a gas generator for a protection device of a vehicle

Info

Publication number: WO2019162575A1
Application number: PCT/FI2019/050146
Authority: WO
Inventors: Mauno HARJU
Original assignee: Jyväskylän Ammattikorkeakoulu Oy
Priority date: 2018-02-22
Filing date: 2019-02-22
Publication date: 2019-08-29

Abstract

The invention relates to an oxidizer agent for a composition generating gas in a protection device of a vehicle, which as oxidizer agent includes ammonium nitrate, which said oxidizer agent is in a fine-grained form. The ammonium nitrate as the said oxidizer agent is without additives to stabilize the am- monium nitrate against decay caused by temperature changes in the gas-generating composition. In addition, the detonation properties of the ammonium nitrate, as the said fine-grained oxidizer agent, are arranged to remain mainly unchanged in the thermal cycling of the ammonium nitrate. In addition, the in- vention also relates to a composition for generating gas and a gas generator for a vehicle's protection device.

Description

OXIDIZER AGENT FOR A COMPOSITION GENERATING GAS IN A PROTEC TION DEVICE OF A VEHICLE, COMPOSITION FOR GENERATING GAS, AND A GAS GENERATOR FOR A PROTECTION DEVICE OF A VEHICLE

The invention relates to an oxidizer agent for a composition generating gas in a protection device of a vehicle, which oxi dizer agent includes ammonium nitrate, which as said oxidizer agent is in a fine-grained form. In addition, the invention also relates to a composition for generating gas, a gas gener ator for a protection device of a vehicle, and the use of an oxidizer agent and a composition.

In protection devices used in the automotive industry, prob lems have arisen with the ammonium-nitrate-based explosive in airbags exploding more violently than intended. In connection with this, about twenty people have been killed and more than one hundred injured. In accidents, many airbags have released more strongly than intended. The metal parts of the device have then fragmented and flown towards the driver or passen gers. As a result, car manufacturers have already recalled more than 100 million vehicles for repair and the trend is that the number of recalls is still growing. This may be in dustry's largest and most complicated problem relating to the health of consumers.

The cause of the aforementioned problem appears to be the de cay of the ammonium-nitrate used in inflators of the filling system of vehicle airbags, as a result of repeated temperature variations. As a result of the decay, the particle size, po rosity, and specific surface-area of the ammonium nitrate in crease. The phenomenon causes an increase in the detonation velocity, i.e. the explosive force, of the ammonium-nitrate- based explosive. During heating and cooling, ammonium nitrate undergoes several phase transitions. In these, its crystalline structure and volume change. Figure 1 shows a classical graph of the changes in volume (density) caused by the phase transi tions of ammonium nitrate, as a function of temperature. In phase transitions, ammonium nitrate can decay as its physical form breaks down. In the most common inflators, ammonium- nitrate-based explosives are granulated, for example, in a tablet or disc shape.

In the United States, for example, the internal temperature of cars can easily be in the range of 0 - +80 °C. At these tem peratures, ammonium nitrate goes through transitions between phases IV, III, and II. Each transition breaks the structure of ammonium-nitrate tablets.

In industry, the usual approach has been to try to stabilize ammonium nitrate so that the aforementioned transitions do not take place. One can then generally refer to phase stabilized ammonium nitrate (PSAN) . It is characterized in having various additives used to make it such that it is not subject to the aforementioned phase transitions in some desired temperature range. One example of such an additive is potassium nitrate. Ammonium nitrate and potassium nitrate are then used as a dou ble salt. In it the ammonium, potassium, and nitrate ions al ternate in the same crystal lattice. US patent application publication US 2014/0150935 A1 can be given as an example of a publication teaching the prior art relating precisely to PSAN.

Problems with potassium nitrate, however, include the small stabilization effect achieved with it and, additionally, par ticle formation in an explosion. More generally, significant amounts of additives must be used, while nevertheless not achieving a sufficient stability in ammonium nitrate against the decaying effect caused by temperature change. Some addi tives are also toxic and difficult to recycle and, in addi tion, are also expensive. Several reasons support the use of ammonium nitrate, for exam ple, in automobile airbags and safety devices. Ammonium ni trate would be, for example, in terms of the environment easi er and safer to recycle than many other solutions. In addi tion, ammonium nitrate' s most important advantage over alter native explosive components using in airbags, such as, for ex ample, sodium azide, is its low price, easy availability, and small health detriments (for example, non-carcinogenicity and atoxicity) if the substance possibly comes in contact with the human body. The aforementioned problems relating to decay have, however, made ammonium nitrate difficult and expensive to use, precisely on account of these additives and poor sta bilization achieved with them.

The present invention is intended to create an oxidizer agent for a composition generating gas particularly in a protection device of a vehicle, which is stable in its properties, so that its detonation properties do not change as a result of thermal cycles. In addition, the invention also relates to a composition for generating gas, and a gas generator for a pro tection device of a vehicle. The characteristic features of the oxidizer agent according to the invention are stated in Claim 1, of the composition in Claim 7, and of the gas genera tor in Claim 14.

The fine-grained ammonium nitrate belonging to the oxidizer agent is as oxidizer agent without additives for stabilizing the ammonium nitrate against decay caused by temperature changes in a gas generating composition. In addition, the det onation properties of ammonium nitrate are arranged to be pre served mainly unchanged in thermal cycling of ammonium nitrate and thus also of the composition containing it. Corresponding ly, also the fine-grained ammonium nitrate belonging to the composition, in which it is arranged to act as an oxidizer agent, has no additives to stabilize the ammonium nitrate in the gas-generating composition against the decay, caused by temperature changes, of the ammonium nitrate and thus also of the composition containing it. In addition, the detonation properties of the ammonium nitrate and the composition con taining it are arranged to be preserved mainly unchanged in the thermal cycling of the ammonium nitrate and thus also of the composition containing it. The decay is less of the ammo nium nitrate formed using the selected processing as a fine grained, for instance powder-form, substance, in other words non-granular ammonium nitrate, and the composition including it. Thus its particle size and/or specific surface area no longer changes when encountering temperature variations. The properties of the ammonium nitrate are then better preserved.

By means of the oxidizer agent according to the invention, an oxidizer agent more stabilized against the decay caused by temperature changes and a composition containing it are creat ed. Thus, also a better stabilized and predictable reaction is achieved, such as, for example, an explosion or gas produc tion. In other words, the ammonium nitrate used as the oxidiz er agent and the composition containing it are stable, in that their detonation properties do not change as a result of ther mal cycles in applications of ammonium nitrate. The ammonium nitrate used as the oxidizer agent is a fine-grained sub stance, i.e. is non-granular. Thus it can be said to be, for example, a powder-like or powdery substance. Its particle size does not essentially diminish (or enlarge) and its specific surface area does not increase as a result of thermal cycles as a result of diminishing. As a result of this, its detona tion velocity remain mainly unchanged, irrespective of what kind of temperature variations it experiences as the oxidizer agent in the composition. Owing to the invention, the ammonium nitrate material withstands thermal cycles as the oxidizer agent without decaying or crumbling, and its particle size and/or specific surface area does not essentially change as the oxidizer agent in thermal cycles. The aforementioned prop erties relate equally also to compositions, in which ammonium nitrate is a part.

The particle size of the ammonium nitrate used as an oxidizer agent can be, for example, 0.5 - 1000 pm. Being made in the selected manner into a very fine-particle substance, it no longer decays into even smaller particles as a result of tem perature variations. It then reacts, such as, for example ex plodes or generates gas, with the same force, irrespective of, for example, experienced variations in temperature in the storage of the oxidizer agent or the composition containing it and/or in the application device.

By means of the ammonium-nitrate-based oxidizer agent accord^¬ ing to the invention, the same kind of relatively low combus tion velocities and a less aggressive nature, required in pro tection devices are achieved, as also take place, for example, when using phase-stabilized ammonium nitrate (BSAN) according to the prior art.

The ammonium nitrate, more generally the oxidizer agent, ac cording to the invention, as also the composition containing it, has a homogenous non-granular composition and a low mois ture absorption. Its combustion gases are not toxic. It or its combustion products are also not detrimental to the environ ment over their entire life cycle. In addition, the energy consumption relating to it is low over its entire life cycle. Owing to the invention, the amount of oxidizer agent using in protection devices is small, and its price is low. Using the oxidizer agent according to the invention, it is also possible to meet one of the most important properties demanded for ex plosives for the gas generators of protection devices, which is that it produces as few as possible, or preferably no solid combustion products. Thus owing to the invention there are fewer requirements relating to the filtering of combustion products. This simplifies the technical implementation of gas generators and protection devices. Filters are always problem atic due, for example, to the danger of blockage in them.

According to one embodiment, the non-decay of ammonium nitrate can be achieved using at least one of the following pro cessing: thermal cycling, pulverization, recrystallization, vapour crystallization, and/or spraying. For example, by ther mally cycling solid ammonium nitrate in the temperature range -30 C - +100 °C, the particle size of the ammonium nitrate can be regulated and a small-crystal and porous material can be manufactured, by which a high detonation velocity and physical permanence can be achieved.

Owing to the invention, ammonium nitrate always behaves in ex ploding or generating a gas in the same predictable manner, irrespective of what kind of changes in temperature it has ex perienced earlier in the operating location. Less of it than in the prior art can then be dispensed in the product. The am monium nitrate used as the oxidizer agent is not, according to the prior art, compressed or more generally granulated, in stead it is used as an oxidizer agent in a fine-grained form and thus, for example, in a non-granular form in connection with the composition, or, for example, depending on the other components of the composition, for example, in a paste form. More generally, reference can be made to a homogenous bulk substance or mixture. Other additional advantages achieved by the invention are stated in the description portion and the characteristic features in the accompanying Claims.

The invention, which is not restricted to the embodiments pre sented in the following, is described in greater detail with reference to the accompanying figures, in which Figure 1 shows a classical graph of the change in the volume caused by the phase transitions of ammonium nitrate, as a function of tempera ture and

Figure 2 shows an example of an application of a sys tem, in which ammonium nitrate according to the invention can be utilized as an oxidizer agent .

Ammonium nitrate (NH₄NO₃) belongs to the oxidizer agent for a gas-producing composition in a protection device of a vehicle, and even more particularly in its gas generator. As an oxidiz er agent, ammonium nitrate is in a fine-grained form, such as, for example, in a powder form. In addition, the ammonium ni trate is used as an oxidizer agent without additives to stabi lize the ammonium nitrate in a gas-producing composition against the decay caused by changes in temperature. Decay ap pears especially in ammonium nitrate and thus also in a compo sition in which it is used and of which it is a part.

In pilot-stage tests, the applicant has observed that ammonium nitrate can be used with better physical structural integrity and thus also detonation properties when stabilized and thus mainly unchanged as an oxidizer agent, for example, in a gas- producing composition, if the ammonium nitrate is processed in a selected manner into fine-grained, for example, powder-like form. This improves the structural permanence of ammonium ni trate in a use application despite temperature changes possi bly appearing in it. In a powder-like form ammonium nitrate is a fine-grained substance, i.e. it is non-granular . Then it, or a composition comprising it is not specially pressed into pel lets, granules, grains, or tablets, formed of prills or formed into some other corresponding unit structure, of which there would be in the composition several decay-sensitive structural units. Generally, instead of fine-grained ammonium nitrate reference can be made to non-granular ammonium nitrate or a composition comprising it, in which the material is not in an industrial manner intentionally brought to a desired particle size or unit in a solid form, formed of several solids parti cles. For example, as pellets, prills, tablets, grains, or corresponding structural units, the ammonium nitrate's parti cle size, specific surface area, and thus also the ammonium nitrate's reaction properties can change unpredictably, for example, as a result of temperature variations experienced by the composition. Thus the ammonium nitrate according to the invention can be referred to not only as a fine substance but also as loose substance, i.e. more generally as a bulk-like substance or a non-granulated substance. Correspondingly, the composition, in which the ammonium nitrate is a part, can also be referred to in this way.

According to one embodiment, the particle size of ammonium ni trate as a fine-grained oxidizer agent is 0.5 - 1000 pm. More particularly, the particle size can be, for example, on aver age 1 - 500 pm, 1 - 300 pm, 1 - 200 pm, 1 - 100 pm, or 1 - 50 pm. Here the particle size refers to, for example, the small est dimension of the particle. For example, in the case of an elongated crystal, the particle size can regarded as the diam eter of the crystal, which is smaller than its length. The particle size can be determined, for example, by sieving or using a particle-size analyser. Materials, which have differ ent particle sizes can also be compared with the aid of their density by measuring the mass of samples relative to their volume, which is compressed at a low constant pressure.

As the particle size diminishes, the material's specific sur face area increases, as a result of which the velocity of the explosion also increases. If the particle size is sufficiently small, it has been observed that a material is obtained, the explosive force of which temperature variations no longer af- feet. Owing to the invention, the amount of ammonium nitrate to be used can be reduced. The same explosive force is achieved with a smaller mass, so that the explosive force in creased in relation to the explosive mass. The amount of gas formed relative to the mass of the explosive remains, however, the same.

The fine-grained ammonium nitrate, preferably with the afore mentioned particle size, acts in temperature-change situations corresponding to real operating conditions more stably than, for example, an ammonium-nitrate oxidizer agent manufactured using existing methods and is thus also safe, for example, when applied in vehicle airbags. Owing to the invention, ammo nium nitrate is particularly more stable against decay, i.e. its physical structure is more permanent, even though it meets temperature changes, for example, in an operating application. Ammonium nitrate can still, however, experience the phase changes specific to it in temperature variations, but its structure does not, however, owing to the invention essential ly change and the aforementioned properties, i.e. non-decay and the retention of detonation properties are achieved. In pilot-stage tests it has also been observed that the density of ammonium nitrate according to the invention as an oxidizer agent can be less than the density of known ammonium nitrate, for which the values known from the literature are in the range 1.327 - 1.71 g/cm³. On the basis of an observation in the applicant's pilot-stage tests, the volume of the uncom pressed ammonium nitrate according to the invention in an ex plosion pipe was estimated to be about 2.5-times greater than prior-art grades, i.e. the density would then be correspond ingly smaller.

The stabilization of ammonium nitrate against disintegration is achieved by processing the ammonium nitrate in such a way that, as processed the ammonium nitrate is, as an oxidizer agent mainly pure ammonium nitrate, in such way that it is without additives to stabilize the ammonium nitrate against decay in the gas-generating composition. In other words, the ammonium nitrate is then in that sense a pure substance that its lattice structure contains no other ions than ammonium and nitrate-ions. I.e., in its lattice structure there are no oth er additives arranged specifically to stabilize the ammonium nitrate against decay.

Ammonium nitrate intended to be manufactured as the oxidizer agent of a gas-generating composition can be made, for exam ple, using some technique known as such from the prior art. Ammonium nitrate is water-soluble, thus avoiding the use of difficult solvents in the ammonium-nitrate production process. In order to bring better resistance to decay, a small particle size, and through that also a suitable specific surface-area to ammonium nitrate, without additives, the ammonium nitrate can be processed or made by one or more processing methods. According to one embodiment, ammonium nitrate that is essen tially non-decaying, with a suitable particle size and specif ic surface area, without additives to stabilize the ammonium nitrate in a gas-generating composition against decay of the ammonium nitrate caused by temperature changes can be obtained using one or more of the following processing: ammonium- nitrate thermal cycling, ammonium-nitrate grinding, ammonium- nitrate spraying, re-crystallization, and/or vapour crystalli zation. Besides ammonium nitrate, these processes can be equally used, in suitably parts, with the composition, in which ammonium nitrate is a part. An embodiment relating to processing of the composition itself will be described slight ly later in the description.

In the manufacturing stage, the thermal cycling of the ammoni um nitrate can be implemented, for example by first heating the ammonium nitrate in a set manner and then cooling it in a set manner. Heating and also cooling can take place in steps. The steps can be formed, for example, on the basis of the am monium nitrate's phase transitions. Heating and cooling can be performed, for example, in the temperature range -30 - +107 °C, i.e. in the range of ammonium nitrate's phases V - II. Ac cording to one embodiment, the heating and cooling temperature range is divided into parts and the substance is held in heat^¬ ing or cooling at these temperatures for a set time, before changing the temperature to the next step. Thermal cycling continues backwards and forwards for the necessary number of cycles. The number is ascertained on the basis of tests.

Particularly the thermal cycling of ammonium nitrate can be sought to take place through phase III, i.e. through the tem perature range +32 - +84°C. Thermal cycling taking place through phase III has the advantage that the ammonium nitrate is then more thoroughly treated. The treatment then breaks am monium nitrate's crystalline structures, promoting the achievement of a suitable particle size and thus a suitable specific surface-area.

When a sufficient number of back-and-forwards thermal treat ment cycles have been performed, the ammonium nitrate is brought to a more stable form against disintegration. After this, the ammonium nitrate's detonation properties do not es sentially change, even though it undergoes new temperature changes, such as may take place in protection devices in vehi^¬ cles over a wide temperature range, instead it is, for exam ple, sufficiently stabilized in detonation properties and its behaviour is predictable.

The grinding of ammonium nitrate can be implemented, for exam ple, by sufficiently grinding ammonium nitrate, for example, into mm-size-class granules. Using this method grinding is continued until the desired particle size is achieved. For this, samples of the material being grounded are taken and on their basis a rule is formed of a suitable grinding time and manner. After grinding, the ground ammonium nitrate is sieved.

The spraying of ammonium nitrate can be implemented, for exam ple, by spraying a hot and strong solution of ammonium nitrate in water, which when it cools forms small crystals in the spraying. A second way is to spray a melt of ammonium nitrate. A third way is vapour crystallization. In it, ammonia vapour is led with nitric-acid vapour to the same space, when ammoni um nitrate crystallizes. Here the ammonium nitrate is thus made only in connection with the processing.

Ammonium nitrate's particle size can also be influenced in different ways by re-crystallization. The adjustable parame ters are then, for example, the strength of the solution, the temperatures in the different stages of re-crystallization, the speed of cooling of the solution, and/or the use of fil tering .

Ammonium nitrate according to invention that is better stabi lized against decay without additives also has the character istic that its physical properties, such as, for example, par ticle size and/or specific surface-area, is as an oxidizer agent, arranged to remain mainly unchanged in the thermal cy cling of the ammonium nitrate, for example, in the temperature range -40 °C - +107 °C. In addition, its detonation properties are arranged, as an oxidizer agent, to remain mainly unchanged in the thermal cycling of the ammonium nitrate. The ammonium nitrate also has characteristic that its physical structure does not essentially disintegrate, i.e. it remains thermally stable in thermal treatment, which occurs at about 107 °C and the duration of which is about 400 hours. In addition to the oxidizer agent, the invention also relates to a composition for generating a gas, particularly for the gas generator of a protection device in a vehicle. The compo sition includes a combustible agent and an oxidizer agent, which include ammonium nitrate. At least some of the oxidizer agent or all of the oxidizer agent is an oxidizer agent ac cording to the invention, i.e. ammonium nitrate, which is as oxidizer agent in a fine-grained form, i.e. non-granular and in addition without additives to stabilize the ammonium ni trate against decay the ammonium nitrate and thus also of the composition caused by temperature changes in the gas generating composition. In addition, the detonation properties of the ammonium nitrate and thus also of the composition con taining it are arranged to remain mainly unchanged in thermal cycling of the composition containing ammonium nitrate.

The combustible agent can include, for example, carbon, such as, for example, active carbon. The combustible agent can also include one or more organic compounds, such as, for example, hydrocarbons. The one or more organic compounds belonging to the combustible agent does not essentially dissolve ammonium nitrate. Owing to the insolubility of ammonium nitrate in the combustible agent, the porosity of the ammonium nitrate and thus also its specific surface-area remain mainly unchanged in the composition. One example of a hydrocarbon is fuel oil. The ammonium nitrate can then be part of a paste-like substance, which it forms together with the combustible agent, but never theless in such a way that here too its physical structure does not change as a result of temperature changes. Even in the case of a paste-like substance, the composition is homoge nous, i.e. a mixture of even composition. In addition, also in a paste-like substance the ammonium nitrate can still be said to be in a fine-grained form, i.e. as part of the homogenous paste . In addition to the oxidizer agent and the combustible agent, the composition can also include additives that influence the speed of the combustion event. The oxidizer agent can include in addition to ammonium nitrate one or more oxidizer agents. They are, however, characterized by not forming mixed crystals with ammonium nitrate and/or solid solutions in another form in such a way that the typical physical form of the ammonium nitrate changes. The composition is a multi-component mixture of several substances. The composition is packed in such a way that at no stage in its life cycle does its moisture content change .

In explosions, ammonium nitrate produces nitrogen, oxygen, and water (2 NH4NO3 2 N₂ + O2 + 4 H₂0) . In explosives it also re acts with carbon and thus also produces carbon dioxide. The explosion end products are all clean and safe gases. When us ing ammonium nitrate all the oxygen needed is obtained from the ammonium nitrate by using it in the correct stoichiometric ratio in the final explosive mixture. This also avoids the formation of a solid matter created by a non-combustible sub stance and thus the need to filter them, while noxious gases are not formed, but nevertheless a sufficient amount of gas is produced to fill the protective device at a high speed. Physi cally stable ammonium nitrate also facilitates selection of the ratio of the substance in the composition, which reduces the possibility of toxic gases arising, like carbon monoxide and nitrogen nitrates.

The explosives can be either single-component or multi- component. The combustion of multi-component blended gas generating compositions, in which the ammonium nitrate accord ing to the invention can be used as an oxidizing agent, can be better controlled, so that the combustion gases can be safe and the arising of particles can be prevented, and by choosing the materials correctly, metallic vapours will not arise. How- ever, their problem has been structural strength, in which the explosive tablets decay, for example, due to temperature vari ations. By using more stabilized ammonium nitrate against the decay, i.e. physical change caused by temperature variations gas-generating and explosive mixtures can be made, which bet ter resist decay when experiencing temperature variations. Am monium nitrate being a fine-grained powder, or similar loose substance without additives to stabilize the ammonium nitrate in a gas-generating composition against the decay of the ammo nium nitrate, the compositions, in which it exists as an oxi dizer agent, are not tablets or similar other granular struc ture-unit forms liable to decay, which are, for example, formed specifically by mechanical processing from an original ly fine-grained substance, or, for example, from a paste.

Compositions comprising ammonium nitrate ignite easily and without delay, and in addition they have a controlled combus tion speed at the pressure prevailing in the explosion event, not do they contain dangerous easily exploding components. Ex plosives containing ammonium nitrate are not toxic nor do they produce toxic decay products, if the other components of the explosive are chosen correctly. Decay does not appear with products according to the invention or at least it is less, because their particle size cannot be reduced so much that it would have the effect of increasing the detonation velocity. The particle size of the explosive or its components affects the detonation velocity in that with smaller particles the detonation velocity is greater. A material's particle size and its specific surface-area are typically related to each other.

Yet another object of the invention is a gas-generator or gas generating system for a protection device of a vehicle, such as, for example, a car, and a vehicle's safety system, in which a gas-generating composition according to the invention is used. In gas-generators and similar systems a composition according to the invention is used to produce gas. More par ticularly, in a gas-generator, and even more particularly in its explosive charge forming a gas, a composition is used to produce the gas, which includes an oxidizer agent according to the invention, i.e. ammonium nitrate, which is fine-grained in the composition and without additives to stabilize the ammoni um nitrate against the decay of the ammonium nitrate caused by temperature changes in the gas-generating composition. Carbon or an organic substance or both are used as fuel in the gas- generator .

The invention also relates to a process for processing ammoni um nitrate into an oxidizer agent for a gas-generating compo sition, particularly for the gas-generator of a vehicle's pro tection device. In the process, ammonium nitrate is processed using one or more methods to stabilize the ammonium nitrate without additives against decay caused by temperature changes when using it as an oxidizer agent in a gas-generating compo sition in a gas generator. In addition, in the process the am monium nitrate is made into a fine-grained, i.e. a non- granular substance, for example, in a powder form for use as an oxidizer agent in the gas-generating composition of a gas generator. Owing to the process, the invention also relates to an oxidizer agent for a gas-generating composition of a gas generator of a vehicle's protection device and/or a gas gener ator, which is obtainable using the process according to the invention .

Above, ammonium nitrate was mixed with other substance belong ing to the composition into a ready processed non-decaying form according to the invention, with unchanging detonation properties. According to yet another embodiment, also the grinding of the explosive composition containing ammonium ni trate, or even more generally its processing using, for exam ple, one or more of the aforementioned methods, is one way to manufacture a composition according to the invention for the inflators of protection devices. Here too, as a result of the grinding or similar processing of the composition, its explo sive velocity no longer, at least essentially changes as a re sult of the thermal cycles experienced by the composition. More particularly, the specific surface-area of the ground ex plosive composition does not essentially increase as a result of the decay of the explosive, because this does not happen, for example, due to the grinding. In other words, in the case of a composition formed of such a fine-grained substance, each individual particle can be said to form itself an explosive, containing ammonium nitrate as an oxidizing agent and a com bustible substance.

Yet another object of the invention is a process for pro cessing a gas-generating composition for the gas-generator of a vehicle's protection device, which composition includes am monium nitrate as an oxidizing agent in a fine-grained form. In the process, the composition comprising ammonium nitrate is processed using one or more methods to stabilize the composi tion and more particularly the ammonium nitrate in the compo sition without additives against decay in the composition caused by temperature changes. As a result of the processing, the detonation properties of the ammonium nitrate as an oxi dizer agent remain mainly unchanged in the thermal cycling of the composition. The processing can be, for example, grinding of the composition. As a result of processing, a composition for the gas generator of a protection device of a vehicle is obtained .

The composition to be processed can include, as a fuel, for example, tetrazols. The amount ratios of the composition are defined in such a way that the oxygen released by ammonium ni trate and other oxygen-containing compounds suffices just to oxidize all combustibles, i.e. generally carbon, hydrogen, and nitrogen. In addition to solids, there can also be liquids in the composition, which are absorbed in the solids. The grind ing of the composition then takes place after absorption of the liquid substances. The composition is processed, for exam ple, by mechanical treatment to form it into a fine-grained form before use. The processing can be, for example, grinding or pulverization of the composition. As a result, the composi^¬ tion is a ground or pulverized form in the use application.

Yet other object of the invention are also the use of the oxi dizer agent according to the invention in the gas-generating composition of the gas generator of a protection device of a vehicle and/or in a gas generator and also the use of the com position in the gas generator of a protection device of a ve hicle.

Figure 2 shows one example of an inflator or gas-generating system 10, which belongs to the structural totality of an air bag system 200. The airbag system 200 includes at least one airbag 202 and an inflator 10, containing a gas-generating composition according to the invention, connected to the air bag 202 in such a way that it has a fluid connection to the inside of the airbag. The airbag system 200 can also include (or be connected to) a collision detector 210. The collision detector 210 includes a known collision-sensor algorithm, which controls the operation of the airbag system 200, for ex ample activating the inflator 10 in a collision.

The airbag system 200 can also be a broader and more compre hensive vehicle-passenger restraint system 180, which includes additional elements, such as a safety-belt assembly 150. Fig^¬ ure 2 shows a schematic diagram of an example of an embodiment of a restraint system. The safety-belt assembly 150 includes safety-belt casing 152 and a safety belt 100 extending from the casing 152. The airbag's retraction mechanism 154 (for ex- ample, a spring-loaded mechanism) can be connected to the safety belt's end part. In addition, the safety belt's pre tensioner 156, comprising a gas-generating / self-igniting composition, can be connected to the belt's pre-tensioner mechanism 154, to operate the pre-tensioner mechanism in a collision .

The safety-belt assembly 150 can also include (or be connected to) a collision sensor 158 (for example, an inertia sensor or acceleration sensor) including a known collision-sensor algo rithm, which controls the operation of the safety-belt pre^¬ tensioner 156, for example, the operation of a pyrotechnic detonator arranged in the pre-tensioner . The vehicle's protec tion device can equally well be the vehicle's driver's or pas senger's protection device, such as, for example, an airbag, a side-collision airbag, or an airbag arranged to deploy outside the car, for a pedestrian or similar.

It is typical of a vehicle's protection device, and thus also of the composition arranged for it, that they can wait in the use application for years for an event (accident) to trigger their activation. Thus the composition can be said to be as if "stored" for years in the protection device. Compared to the short-term storage time of typically a few months of, for ex ample, explosives, the compositions arranged in protection de vices are subject to several temperature changes that they ex perience in their life cycle of years, and which can be great (-35 °C - +80 °C) . The variation operating conditions caused by life-cycle demands measured in years makes great demands on their properties, for example, in terms of retaining opera tional stability and structural integrity.

Then another object of the invention is also a vehicle's pro tection device, which includes a gas generator. The gas gener ator is according to what is stated above. Owing to the inven- tion, the protection device can be implemented without a fil ter for filtering the gases produced by the gas generator. The operating temperature of the protection device is in the range -35 °C - +80 °C . The life-cycle demand of the protection device is several years.

In addition to airbag inflators, ammonium nitrate charges ac cording to the invention can be used in all devices filled us ing a gas, for example, in vehicles' safety-belt pre tensioners and safety curtains. In addition to airbags, safety curtains, and the pre-tensioners of safety-belt devices, the invention can also be utilized in other applications requiring rapid gas generation and/or filling with gas, which require very economical solutions, which have, compared to other solu tions, a small environmental impact and small health impacts during the device's manufacturing process and the rest of its life cycle.

Owing to the oxidizer agent according to the invention and the composition containing it, the explosive produces a great amount of combustion gases relative to the explosive's weight. The inflators can then be made lighter. The combustion temper ature also remains sufficiently low, which improves passenger safety .

The invention's main application is objects that are protec tion devices and which contain pyrotechnical substances and which are used to improve safety, such as, for example, per sonal safety in vehicles, vessels, or aircraft. Examples in clude airbag gas generators, airbag modules, safety-belt pre tensioners and possibly also pyromechanical devices. Pyrome- chanical devices can be assembled from components that are in tended to, for example, keep separate, lock, or prevent move ment. Typically these are electrically triggered safety devic es and pyrotechnical safety devices, which are installed in vehicles, carriages, vessels, or aircraft or which are in ready-to-install parts, such as, for example, steering col umns, door upholstery, and seats. It should be understood that the above description and the re lated figures are intended only to illustrate the present in vention. The invention is thus not restricted only to the em bodiments described above or defined in the Claims, many dif ferent variations and adaptations of the invention, which are possible within the scope of the inventive idea defined in the accompanying Claims, will be obvious to one skilled in the art .

Claims

1. An oxidizer agent for a composition generating gas in a protection device of a vehicle, which oxidizer agent includes ammonium nitrate, which as said oxidizer agent is in a fine grained form, characterized in that

- the ammonium nitrate as the said oxidizer agent is without additives to stabilize the ammonium nitrate against decay caused by temperature changes in the gas-generating composition,

- detonation properties of the ammonium nitrate, as the said fine-grained oxidizer agent, are arranged to remain mainly unchanged in the thermal cycling of the ammonium nitrate.

2. The oxidizer agent according to Claim 1, characterized in that a particle size of the ammonium nitrate as the oxidizer agent is 0.5 - 1000 pm.

3. The oxidizer agent according to Claim 1 or 2, characterized in that the said ammonium nitrate without additives to stabi lize the ammonium nitrate against decay caused by temperature changes in the gas-generating composition is created by using one or more of the following processing: thermal cycling, grinding, spraying, recrystallization and/or vapour crystalli zation .

4. The oxidizer agent according to Claim 3, characterized in that in thermal cycling the ammonium nitrate is thermally cy cled through phase III.

5. The oxidizer agent according to any of Claims 1 - 4, char acterized in that the particle size and/or specific surface area of the ammonium nitrate as the said oxidizer agent is ar- ranged to remain mainly unchanged in the thermal cycling of the ammonium nitrate.

6. The oxidizer agent according to any of Claims 1 - 5, char acterized in that the physical structure of the ammonium ni trate is essentially such that it does not decay in thermal processing, which takes place at about 107 °C and the duration of which is about 400 hours.

7. A composition for generating a gas for a protection device of a vehicle, which includes a combustible agent and an oxi dizer agent, which includes ammonium nitrate, characterized in that at least part of the oxidizer agent, or all of the oxi dizer agent is an oxidizer agent according to any of Claims 1 - 6.

8. The composition according to Claim 7, characterized in that the combustible agent includes carbon.

9. The composition according to Claim 7 or 8, characterized in that the combustible agent includes one or more organic com pounds that do not essentially dissolve ammonium nitrate.

10. The composition according to any of Claims 7 - 9, charac terized in that the oxidizer agent includes, in addition to ammonium nitrate, one or more oxidizer agents that do not form mixed crystals with ammonium nitrate and/or solid solutions in other forms.

11. The composition according to any of Claims 7 - 10, charac terized in that the composition is a homogenous mixture of the substances belonging to it.

12. The composition according to any of Claims 7 - 11, charac terized in that the composition is in a non-granular form in its application.

13. The composition according to any of Claims 7 - 12, charac terized in that the composition is in a fine-grained form or a paste-like form in its application.

14. A gas generator for a protection device of a vehicle, in which a composition defined in Claims 7 - 13 is used to gener ate gas, or a composition for generating a gas is used, which includes an oxidizer agent defined in Claims 1 - 6.

15. A vehicle's protection device, which includes a gas gener ator, characterized in that the gas generator is according to Claim 14.

16. The protection device according to Claim 15, characterized in that the protection device is implemented without a filter for filtering the gases produced by the gas generator.

17. The protection device according to Claim 15 or 16, charac terized in that

- the operating temperature of the protection device is in the range -35 °C - +80 °C,

- the life-cycle demand of the protection device is several years .

18. A process for processing ammonium nitrate into an oxidizer agent for a gas producing composition for a gas generator of a vehicle's protection device, in which the ammonium nitrate is brought to a fine-grained form for use as an oxidizer agent in the gas producing composition of a gas generator, character ized in that the ammonium nitrate is processed using one or more methods to stabilize the ammonium nitrate without addi- tives against the decay caused by temperature changes when it is used as an oxidizer agent in a gas producing composition in a gas generator, as a result of which processing, the detona tion properties of the ammonium nitrate as the said fine grained oxidizer agent remain mainly unchanged in the thermal cycling of the ammonium nitrate.

19. An oxidizer agent for the gas producing composition of the gas generator of a vehicle's protection device and/or for a gas generator, which is obtainable using a process according to Claim 18.

20. A process for processing a gas-generating composition for the gas generator of a vehicle's protection device, which com position includes as an oxidizer agent ammonium nitrate in a fine-grained form, characterized in that the composition com prising the said ammonium nitrate is processed using one or more methods to stabilize the composition and particularly the said ammonium nitrate in it, without additives, against decay caused by temperature changes in the said composition, as a result of which processing the detonation properties of the ammonium nitrate as the oxidizer agent remain mainly unchanged in thermal cycling of the composition.

21. The process according to Claim 20, characterized in that the processing is grinding of the composition.

22. A composition for the gas generator of a vehicle's protec tion device, which is obtainable using a process according to Claim 20 or 21.

23. Use of an oxidizer agent according to any of Claims 1 - 6 in a gas-generating composition of a gas generator of a vehi cle's protection device and/or in a gas generator.

24. Use of a composition according to any of Claims 7 - 13 in the gas generator of a vehicle's protection device.