Gas-generating composition, its use in a gas generator and use of a basic mixed-metal nitrate

Abstract

A gas-generating composition for a safety device in a vehicle contains an oxidant comprising a basic mixed-metal nitrate, the basic mixed-metal nitrate being based on a basic metal nitrate in which the metal of the basic metal nitrate is replaced to some extent by at least one other element. The invention further relates to the use of such a gas-generating composition and of such a basic mixed-metal nitrate.

Description

[0001] The invention relates to a gas-generating composition, in particular for a safety device in a vehicle, the use of such a gas-generating composition in a gas generator and the use of a basic mixed metal nitrate.

[0002] In addition to the fuels they contain, gas-generating compositions generally require additional oxidizing agents in order to achieve a balanced oxygen balance.

[0003] Common oxidizing agents are, in particular, basic metal nitrates, as described, for example, in Aguirre et al.: "Simple Route for the Synthesis of Copper Hydroxy Salts" (J. Braz. Chem. Soc., Vol. 22(3), 2011, pp. 546 - 551).

[0004] WO 2004 / 067477 A2 discloses a gas-generating composition comprising an oxidizer component and a fuel, wherein the fuel contains a transition metal complex of ethylenediamine-5,5'-bitetrazole. The oxidizer component may comprise at least one basic metal nitrate, for example, a basic metal nitrate selected from the group consisting of basic copper nitrate, basic zinc nitrate, and combinations thereof.

[0005] WO 2012 / 153974 A2 describes gas-generating compositions comprising 35 to 55 weight percent basic copper nitrate as the main oxidant, 30 to 50 weight percent guanidine nitrate as the main fuel, 2 to 15 weight percent of a combustion-rate-enhancing fuel with a nitrogen content of 60 weight percent or more, and 0.5 to 5 weight percent of a mixed catalyst. Furthermore, up to 20 weight percent of an auxiliary oxidant may be added, which is selected in particular from the group consisting of ammonium nitrate, potassium nitrate, and sodium nitrate.

[0006] A balanced oxygen balance is important, for example, for the use of gas bag modules in the interior of a vehicle. In this case, increased requirements apply to the propellant gas produced, as this can, for example, enter the interior and thus reach the vehicle's occupants via outlet openings in the gas bag. However, the limit values ​​for gas components such as CO, NH3, and NOx required by the automotive manufacturers' specifications can only be achieved with fuel mixtures with a substantially balanced oxygen balance.

[0007] Additional requirements for gas-generating compositions may include the coordination of ballistic behavior, for example, the setting of a combustion temperature, a combustion rate and / or slag formation during the decomposition of the gas-generating composition.

[0008] The object of the invention is to provide a gas-generating composition which enables control of the combustion properties and is suitable for use in safety devices.

[0009] The object is achieved according to the invention by a gas-generating composition for a safety device, in particular in a vehicle, with an oxidizing agent comprising a basic mixed metal nitrate, wherein the basic mixed metal nitrate is based on a basic metal nitrate in which the metal of the basic metal nitrate is partially replaced by at least one further element.

[0010] In other words, the invention not only uses a macroscopic mixture of various basic metal nitrates, but also a mixed metal nitrate with a mixture of a structure-determining first metal and at least one further metal and / or semimetal that partially replaces the first metal at the molecular level in the crystal structure. Thus, in addition to the oxidizing agents available in the prior art, the invention provides a further possibility for adapting the combustion behavior for an intended application of the gas-generating composition.

[0011] Basic mixed metal nitrates in the sense of the invention are in particular compounds which are represented by the following general formula (I): (A 1-x B x )(NO 3 ) y · n (A 1-XBX )(OH) z (I)

[0012] In formula (I) indicates: A is the structure-forming first metal, B is the at least one further element, x is the proportion of the at least one further element per formula unit, y is the number of nitrate ions per formula unit, z is the number of hydroxide ions per formula unit, and n is the ratio between nitrate ions and hydroxide ions per formula unit.

[0013] The value of x in formula (I) is in particular in the range 0.1 ≤ x ≤ 0.95, preferably in the range 0.4 ≤ x ≤ 0.8.

[0014] Typical values ​​for n, y and z are in the range from 1 to 4, in particular from 1 to 3, where n, y and z can be chosen independently of each other within the respective range.

[0015] The compounds given in formula (I) can also exist as hydrates.

[0016] In particular, the decomposition of basic mixed metal nitrates can produce at least ternary mixed oxides. Such mixed oxides generally exhibit higher melting or sublimation temperatures than binary metal oxides containing a single metal or elemental metals. Thus, at temperatures encountered during the decomposition of the gas-generating composition, the at least ternary mixed oxides exist as solids that can be more easily filtered from the propellant gas than gases or liquids. In other words, the use of basic mixed metal nitrate improves slag formation during the conversion of the gas-generating composition.

[0017] Cost savings can also be achieved if at least one additional element is cheaper than the metal of the basic metal nitrate on which the basic mixed metal nitrate is based.

[0018] Basic metal nitrates in the sense of the invention are compounds which are represented by the general formula (II) given below, whereby some compounds may also contain hydrates: M(NO 3 ) y · n M(OH) z or M x' (NO 3 ) y' (OH) z' (II) in which: M is a metal, x' is the number of metal atoms per formula unit, y and y' are each the number of nitrate ions per formula unit, z' is the number of hydroxide ions per formula unit and n is the ratio between nitrate ions and hydroxide ions per formula unit.

[0019] Typical values ​​for n, x', y, y', z and z' are in the range from 1 to 4, in particular from 1 to 3, where n, x', y, y', z and z' can be chosen independently of each other within the respective range.

[0020] Examples of the compounds of general formula (II) include those containing copper, cobalt, zinc, manganese, iron, molybdenum, bismuth or cerium as metal M, such as basic copper nitrate (Cu 2 (OH) 2 NO 3 and Cu 3 (NO 3 )(OH) 5 · 2 H 2 O), basic cobalt nitrate (Co 2 (NO 3 )(OH) 3 ), basic zinc nitrate (Zn 2 (NO 3 )(OH) 3 ), basic manganese nitrate (Mn(NO 3 )(OH) 2 ), basic iron nitrate (Fe 4 (NO 3 )(OH) 11 · 2 H 2 O), basic molybdenum nitrate, basic bismuth nitrate [Bi(NO 3 )(OH) 2 ] and basic cerium nitrate [Ce(NO 3 ) 3 (OH) 3H 2 O].

[0021] The basic metal nitrate that determines the structure of the basic mixed metal nitrate is, in particular, a basic transition metal nitrate. The basic metal nitrate is preferably basic copper nitrate.

[0022] Basic copper nitrate is also known as "bCN" (abbreviated for "basic copper nitrate") and can be described by the molecular formula Cu 2 (OH) 2 NO 3 . Basic copper nitrate has been tested for use in gas-generating compositions for safety devices and is available worldwide. Thus, known formulations comprising basic copper nitrate can be easily adapted by at least partially replacing the basic copper nitrate with the basic mixed metal nitrate according to the invention.

[0023] The at least one further element can be selected from the group consisting of alkaline earth metals, transition metals, aluminum, and boron. In any case, the at least one further element is different from the metal of the basic metal nitrate.

[0024] Preferably, the at least one further element is zinc.

[0025] The use of a zinc-containing basic mixed metal nitrate makes it possible to suppress a light phenomenon that occurs during the conversion of the gas-generating composition, also known as "flaming." When zinc is used as an additional element in the basic mixed metal nitrate, zinc oxide is formed during the decomposition of the gas-generating composition. This zinc oxide is at least partially doped with the metal(s) of the basic mixed metal nitrate. Zinc oxide is a semiconductor with a band gap that allows the absorption of ultraviolet and visible light. By doping with additional elements or metals, the size of the band gap can be reduced, shifting the emission that occurs after absorption into the infrared light range.This is especially true for the high temperatures encountered during the decomposition of the gas-generating composition, which can also lead to a narrowing of the band gap, which is further amplified by additional doping. By shifting the light emission into the infrared range, a reduction in the light emission visible to humans can be achieved during the decomposition of the gas-generating composition. Activation of the safety device is therefore perceived less negatively by the user or vehicle occupant.

[0026] The basic mixed metal nitrate is particularly preferably a basic copper-zinc nitrate based on basic copper nitrate and is also referred to below by the abbreviation "bCZN".

[0027] In particular, the basic copper-zinc nitrate is hydrate-free.

[0028] The combustion of basic copper-zinc nitrate produces copper-zinc mixed oxides whose melting or sublimation temperature is higher than that of elemental copper, resulting in improved slag formation. In addition, the previously described effect of at least partial suppression of light emission in the visible range can be achieved when using basic copper-zinc nitrate.

[0029] At the same time, the basic copper-zinc nitrate in the gas-generating composition preferably behaves similarly to basic copper nitrate, so that the selected zinc content in the basic copper-zinc nitrate merely tailors the combustion behavior of the gas-generating composition but does not fundamentally change it. Thus, no complex reformulations of existing compositions based on basic copper nitrate are necessary.

[0030] Optionally, a portion of the copper in the basic copper-zinc nitrate can be replaced by at least one other element.

[0031] In the basic mixed metal nitrate, in particular 10 mol percent or more of the metal in the basic metal nitrate is replaced by the at least one further element, preferably 40 mol percent or more.

[0032] Furthermore, in the basic mixed metal nitrate, 95 mol percent or less of the metal in the basic metal nitrate may be replaced by the at least one further element, preferably 80 mol percent or less.

[0033] The mole percent data refers in particular to the molar amount of metal in the crystal structure of the basic metal nitrate. Preferably, the crystal structure of the basic mixed metal nitrate corresponds to the crystal structure of the basic metal nitrate. In other words, only insignificant distortions in the crystal structure occur compared to the basic metal nitrate. This increases the likelihood that the basic mixed metal nitrate can be used in known formulations for gas-generating compositions without the need for further formulation adjustments.

[0034] The at least one further element can be arranged stochastically or periodically distributed in the basic mixed metal nitrate. In other words, a random distribution of the at least one further element can be provided in the basic mixed metal nitrate on the theoretical lattice sites of the metal in the basic metal nitrate. Alternatively, domains can be formed in the crystal structure of the basic mixed metal nitrate in which the at least one further element is arranged. By selecting the respective distribution of the at least one further element in the crystal structure, the combustion behavior of the basic mixed metal nitrate can be further tailored.

[0035] The basic mixed metal nitrate can be obtained by precipitating one or more basic nitrate solutions of the individual elements, in particular different metal nitrate solutions. For this purpose, production processes can be used that are analogous to those shown in DE 102 96 592 B4 for the synthesis of basic metal nitrates. The inventors have found that the stoichiometry and crystal structure of the precipitated basic mixed metal nitrate are influenced both thermodynamically and kinetically. Thus, the resulting basic mixed metal nitrate can be adjusted via the temperature, pH, the concentrations of the nitrate solutions used and their ratios to one another, as well as the mixing rate of the nitrate solutions. In particular, the molar fraction of at least one additional element can be precisely adjusted in this way.

[0036] The gas-generating composition can contain any fuel known in the art and suitable for safety devices. For example, the fuel can be selected from the group consisting of boron, aluminum, silicon, magnesium, iron, titanium, tungsten, copper, carbon, zirconium, alloys of the aforementioned elements, nitrotriazolone, nitrocellulose, guanidinium compounds, especially guanidinium nitrate, nitroguanidine and double salts of these compounds, tetrazoles, aminotetrazoles, dinitramides, and / or combinations of the aforementioned fuels.

[0037] The fuel is present in the gas-generating composition in a proportion of 5 to 95 percent by weight, preferably in a proportion of 10 to 90 percent by weight or 20 to 80 percent by weight, particularly preferably in a proportion of 35 to 65 percent by weight.

[0038] In addition to the basic mixed metal nitrate, the gas-generating composition may comprise at least one further oxidizing agent selected from the group consisting of nitrates, oxides and / or mixed oxides of alkali metals, alkaline earth metals, and transition metals, transition metal nitrate hydroxides, chlorates, perchlorates, ammonium nitrate, sulfates, phosphates, oxalates, dinitramides, peroxides, water, oxygen, and / or combinations thereof. In principle, all allotropes and all isotropes of the corresponding compounds are also included.

[0039] The gas-generating composition preferably contains 10 to 60 wt.% of the basic mixed metal nitrate and optionally the at least one further oxidizing agent.

[0040] The proportion of basic mixed metal nitrate and optionally of at least one further oxidizing agent in the gas-generating composition is selected in particular so that a balanced oxygen balance is achieved.

[0041] The gas-generating composition may additionally comprise 5% or less by weight of a processing aid, in particular 1 to 5% by weight, based on the total weight of the gas-generating composition. Examples of processing aids include pressing aids, flow aids, and / or lubricants, which, in the specified amount, do not significantly affect the burning rate of the composition. Examples of suitable processing aids include polyethylene glycol, cellulose, methylcellulose, graphite, wax, metal soaps, for example calcium stearate, magnesium stearate, zinc stearate, and / or aluminum stearate, boron nitride, talc, bentonite, silica, and molybdenum sulfide, as well as mixtures thereof.

[0042] In addition, the gas-generating composition according to the invention may contain conventional combustion moderators and / or coolants, for example, 10 wt.% or less, in particular up to 6 wt.% or 0.1 to 6 wt.%, based on the total weight of the gas-generating composition. These additives stabilize the combustion and keep the combustion temperature low. At the same time, the slagging of the combustion residues is improved, thereby preventing the residues from becoming dusty.

[0043] Examples of suitable combustion moderators and / or coolants are B 2 O 3 , Al 2 O 3 , MgO, TiO 2 , SiO 2 , Mg(OH) 2 , basic magnesium carbonate, CaCO 3 and mixtures thereof.

[0044] Furthermore, the gas-generating composition may additionally comprise 5 wt.% or less of another additive, in particular 0.1 to 5 wt.%, based on the total weight of the gas-generating composition. The other additives serve, in particular, to improve the ignitability and mechanical properties of the gas-generating composition.

[0045] The combustion temperature of the gas-generating composition is preferably in a range of 1700 K to 2300 K.

[0046] The object of the invention is further achieved by the use of a gas-generating composition of the type described above in a safety device, in particular for a vehicle.

[0047] Furthermore, the object of the invention is achieved by the use of a basic mixed metal nitrate of the type described above as an oxidizing agent in a gas-generating composition, in particular in a gas-generating composition for safety devices.

[0048] The safety device is arranged, for example, in a vehicle or a vest or protector of a user.

[0049] Further advantages and properties emerge from the following description and the exemplary embodiments listed therein.

[0050] Exemplary gas generating compositions are given in Table 1. Table 1: Gas generating compositions according to the invention. component Material % by weight fuel GuNi 45 to 55 Oxidizing agent bCZN 43 to 53 Processing aids Metal stearates 0 to 3 coolant Al 2 O 3 0 to 3 Burn-off moderator TiO2 0 to 3 The abbreviations used in Table 1 mean: GuNi = guanidinium nitrate bCZN = basic copper-zinc nitrate (basic mixed metal nitrate)

[0051] A mixture of calcium stearate, magnesium stearate and zinc stearate is used as metal stearates.

[0052] The ballistic behavior was determined using a series of tests with three compositions, as shown in Table 2.

[0053] For this purpose, the gas-generating compositions were pressed into cylindrical tablets with a diameter of 4 mm and a thickness of 1.3 mm. The oxidizing agent used had a grain size d 50 of 6 µm. The zinc content of the bCZN used was 22%.

[0054] Subsequently, 10 g of the tablets were weighed into a standard steel combustion chamber with a volume of 100 cm3, ignited using an igniter in the standard combustion chamber, and the pressure profile inside the standard combustion chamber was monitored to determine the burning rate of each tablet. The ballistic test was carried out at a pressure of 10 MPa and 20 MPa, respectively. Each test was carried out in duplicate, and the resulting burning rates were arithmetically averaged. It was found that the burning rates measured with the compositions according to the invention for tablets of the size used and with the oxidizer of the grain size used were within a range suitable for gas-generating compositions for use in safety devices. Table 2: Composition for ballistic tests. Example bCZN (oxidizing agent) GuNi (fuel) Additive 1 45.9 wt% 51.24 wt% 2.86 wt.% 2 48.5% by weight 48.64 wt% 2.86 wt% 3 47.41 wt% 49.73 wt% 2.86 wt.% Table 3: Results of the ballistic tests of the examples from Table 2. Example Burning rate at 10 MPa [mm / s] Burning rate at 20 MPa [mm / s] 1 15,2 19,2 2 15,2 19,4 3 14,8 18,8

[0055] If in Example 1 the bCZN is completely replaced by bCN with a grain size d 50 of 1 µm, burning rates of 17.6 mm / s at 10 MPa and 22.2 mm / s at 20 MPa are obtained.

[0056] If in Example 1 the bCZN is completely replaced by bCN coated with one percent glycerol with a grain size d 50 of 1 µm, burning rates of 19.5 mm / s at 10 MPa and 24.3 mm / s at 20 MPa are obtained.

Claims

1. A gas generating composition for a safety device, specifically in a vehicle, with an oxidant comprising a basic mixed metal nitrate, wherein the basic mixed metal nitrate is based on a basic metal nitrate in which the metal of the basic metal nitrate is partly replaced with at least one further element.

2. The gas generating composition according to claim 1, characterized in that the basic metal nitrate is a basic transition metal nitrate, preferably basic copper nitrate.

3. The gas generating composition according to claim 1 or 2, characterized in that the at least one further element is selected from the group consisting of alkaline earth metals, transition metals, aluminum and boron.

4. The gas generating composition according to any one of the preceding claims, characterized in that the at least one further element comprises or is zinc.

5. The gas generating composition according to any one of the preceding claims, characterized in that, in the basic mixed metal nitrate, 10 mole percent or more of the metal in the basic metal nitrate are replaced with the at least one further element, preferably 40 mole percent or more.

6. The gas generating composition according to any one of the preceding claims, characterized in that, in the basic mixed metal nitrate, 95 mole percent or less of the metal in the basic metal nitrate are replaced with the at least one further element, preferably 80 mole percent or less.

7. The gas generating composition according to any one of the preceding claims, characterized in that a crystal structure of the basic mixed metal nitrate corresponds to a crystal structure of the basic metal nitrate.

8. The gas generating composition according to any one of the preceding claims, characterized in that the at least one further element is arranged to be distributed stochastically or periodically in the basic mixed metal nitrate.

9. A use of a gas generating composition according to any one of the claims 1 to 8 in a gas generator of a safety device for a vehicle.

10. A use of a basic mixed metal nitrate as oxidant in a gas generating composition, specifically a gas generating composition for safety devices, wherein the basic mixed metal nitrate is based on a basic metal nitrate in which the metal of the basic metal nitrate is partly replaced with at least one further element.