GAS GENERATING COMPOSITION, USE THEREOF IN A GAS GENERATOR AND USE OF A BASIC MIXED METAL NITRATE
A gas generating composition for a safety device in a vehicle comprises an oxidant which comprises 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. The disclosure further states the use of such gas generating composition and of such basic mixed metal nitrate.
This application is a national stage of International Application No. PCT/EP2021/062940, filed May 17, 2021, the disclosure of which is incorporated herein by reference in its entirety, and which claimed priority to German Patent Application No. 102020113381.2, filed May 18, 2020, the disclosure of which is incorporated herein by reference in its entirety.
TECHNICAL FIELDThe disclosure relates to a gas generating composition, specifically for a safety device in a vehicle, to the use of such gas generating composition in a gas generator as well as the use of a basic mixed metal nitrate.
BACKGROUNDGas generating compositions usually require, apart from the fuels contained, additional oxidants to show an equilibrated oxygen balance.
Common oxidants are specifically 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).
An equilibrated oxygen balance is important, for example, to the use of airbag modules in the interior of a vehicle. In this case, increased requirements apply to the propellant gas generated, as said propellant gas may arrive at the interior and thus at occupants of the vehicle via discharge openings in the airbag, for example. The thresholds of gas components such as CO, NH3 and NOx required in the specifications of the car manufacturers can only be achieved by propellant mixtures having a substantially equilibrated oxygen balance, however.
Additional requirements to gas generating compositions may be the adjustment of the ballistic behavior, such as the setting of a burning temperature, a burning rate and/or a slag formation while the gas generating composition is decomposing.
SUMMARYThe disclosure describes a gas generating composition that allows the burning properties to be controlled and is suitable for use in safety devices.
According to the disclosure a gas generating composition is described 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.
DETAILED DESCRIPTIONIn other words, in accordance with the disclosure, not only a macroscopic mixture of different basic metal nitrates is used, but a mixed metal nitrate with a mixture of a first metal defining the structure and at least one further metal and/or partial metal which partly replaces the first metal on a molecular basis in the crystal structure. Thus, according to the disclosure, another option is provided, apart from the oxidants present in the state of the art, to adapt the burning behavior to an intended application of the gas generating composition.
Basic mixed metal nitrates in accordance with the disclosure are specifically compounds which are represented by the following general formula (I):
(A1-xBx)(NO3)y.n(A1-xBx)(OH)z (I)
In formula (I):
A s 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.
The value of x in formula (I) is specifically in the range of 0.1≤x≤0.95, or in the range of 0.4≤x≤0.8.
Typical values for n, y and z are in the range from 1 to 4, in particular from 1 to 3, wherein n, y and z can be selected independently of each other in the respective range.
The compounds stated in formula (I) may also be provided as hydrates.
In particular, when the basic mixed metal nitrates decompose, at least ternary mixed oxides can form. Such mixed oxides generally have higher melting temperatures or sublimation temperatures than binary metal oxides having one single metal, or than elementary metals, respectively. Thus, at temperatures occurring when the gas generating composition decomposes, the at least ternary mixed oxides are provided as solids which can be filtered out of the propellant gas more easily than gases or liquids. In other words, the use of the basic mixed metal nitrate improves slag formation when the gas generating composition is converted.
Also, cost savings can be achieved when the at least one further element is cheaper than the metal of the basic metal nitrate on which the basic mixed metal nitrate is based.
Basic metal nitrates in accordance with the disclosure are compounds which are represented by the following general formula (II), wherein some compounds may also contain hydrates:
M(NO3)y.nM(OH)z oder Mx′(NO3)y′(OH)z′ (II)
wherein:
M is a metal,
X is the number of metal atoms per formula unit,
y and y′ each are the number of nitrate ions per formula unit,
z′ is the number of the hydroxide ions per formula unit, and
n is the ratio between nitrate ions and hydroxide ions per formula unit.
Typical values for n, x′, y, y′, z and z′ are in the range from 1 to 4, specifically from 1 to 3, wherein n, x′, y, y′, z and z′ can be selected independently of each other in the respective range.
Examples of the compounds of the general formula (II) include those containing as metal M copper, cobalt, zinc, manganese, iron, molybdenum, bismuth or cerium, such as basic copper nitrate (Cu2(OH)2NO3 and Cu3(NO3)(OH)5.2H2O), basic cobalt nitrate (CO2(NO3)(OH)3), basic zinc nitrate (Zn2(NO3)(OH)3), basic manganese nitrate (Mn(NO3)(OH)2), basic iron nitrate (Fe4(NO3)(OH)11.2H2O), basic molybdenum nitrate, basic bismuth nitrate ([Bi(NO3)(OH)2] and basic cerium nitrate [Ce(NO3)3(OH).3H2O].
The basic metal nitrate defining the structure of the basic mixed metal nitrate specifically is a basic transition metal nitrate. The basic metal nitrate can be basic copper nitrate.
Basic copper nitrate is also known as “bCN” (abbreviated for “basic copper nitrate”) and can be described by the sum formula Cu2(OH)2NO3. Basic copper nitrate is tested for use in gas generating compositions for safety devices and is available all over the world. As a result, known formulations comprising basic copper nitrate can be easily adjusted by the at least partial replacement of the basic copper nitrate with the basic mixed metal nitrate according to the disclosure.
The at least one further element can be selected from the group consisting of alkaline earth metals, transition metals, aluminum and boron. In each case, the at least one further element is different from the metal of the basic metal nitrate.
The at least one further element can be zinc.
The use of a zinc-containing basic mixed metal nitrate allows to suppress a light phenomenon occurring when the gas generating composition is converted, which is also referred to as “flaming”. When zinc is used as further element in the basic mixed metal nitrate, zinc oxide which is doped, at least partially, with the metal and the further elements of the basic mixed metal nitrate, respectively, is formed during the decomposition of the gas generating composition. Zinc oxide is a semiconductor having a band gap that enables ultraviolet and visible light to be absorbed. The doping with further elements and metals, respectively, allows to reduce the size of the band gap, resulting in the emission occurring after absorption to be shifted to the infrared light range. This applies in particular to the case of the high temperatures occurring during decomposition of the gas generating composition by which also a reduction of the band gap may occur which is even intensified by the further doping. Thus, by shifting the light emission to the range of the infrared light, a reduction of the light emission visible to humans during decomposition of the gas generating composition can be achieved. Therefore, a user or vehicle occupant will perceive the activation of the safety device as being less negative.
The basic mixed metal nitrate can be a basic copper zinc nitrate, which is based on basic copper nitrate and hereinafter shall be designated with the abbreviation “bCZN”.
The basic copper zinc nitrate is specifically free of hydrate.
During combustion of basic copper zinc nitrate, copper zinc mixed oxides are formed the melting temperature or sublimation temperature of which is higher than that of elementary copper so that improved slag formation occurs. In addition, the afore-described effect of the at least partial suppression of a light emission in the visible range can be achieved when basic copper zinc nitrate is used.
At the same time, the basic copper zinc nitrate in the gas generating composition still can behave similarly to basic copper nitrate so that the burning behavior of the gas generating composition is merely tailored but not basically changed via the selected proportion of zinc in the basic copper zinc nitrate. Thus, no expensive new formulations of known compositions based on basic copper nitrate are required.
Optionally, in the basic copper zinc nitrate a proportion of the copper can be replaced with at least one further element.
In the basic mixed metal nitrate, specifically 10 mole percent or more of the metal in the basic metal nitrate are replaced with the at least one further element, or 40 mole percent or more.
Furthermore, in the basic mixed metal nitrate, 95 mole percent or less of the metal can be replaced in the basic metal nitrate with the at least one further element, or 80 mole percent or less.
The mole percent indications refer particularly to the molar amount of the metal in the crystal structure of the basic metal nitrate. A crystal structure of the basic mixed metal nitrate can correspond to the crystal structure of the basic metal nitrate. In other words, only insignificant distortions should occur in the crystal structure as compared to the basic metal nitrate. In this way, the probability increases that the basic mixed metal nitrate can be used in known formulations for gas generating composition without the formulations having to be further adapted.
The at least one further element can be arranged to be stochastically or periodically distributed in the basic mixed metal nitrate. In other words, in the basic mixed metal nitrate, an arbitrary distribution of the at least one further element can be provided on the theoretical lattice sites of the metal in the basic metal nitrate. As an alternative, domains can be formed in the crystal structure of the basic mixed metal nitrate, in which the at least one further element is arranged. The burning behavior of the basic mixed metal nitrate can be further tailored by appropriately selecting the distribution of the at least one further element in the crystal structure.
The basic mixed metal nitrate can be obtained by precipitation of one or more basic nitrate solutions of the individual elements, specifically of different metal nitrate solutions. For this purpose, production methods can be used which are analogous to the methods illustrated in DE 102 96 592 B4 for the synthesis of basic metal nitrates. The inventors found the stoichiometry and the crystal structure of the precipitating basic mixed metal nitrate is influenced both thermodynamically and kinetically. Thus, adaptation of the basic mixed metal nitrate obtained can be influenced via the temperature, the pH value, the concentrations of the nitrate solutions used and their mutual ratio as well as the mixing rate of the nitrate solutions. In particular, the molar proportion of the at least one further element can be precisely adjusted in this way.
The gas generating composition may include, as a fuel, all fuels known in the state of the art and suited for safety devices. For example, the fuel may be selected from the group consisting of boron, aluminum, silicon, magnesium, iron, titanium, tungsten, copper, carbon, zirconium, alloys of the afore-mentioned elements, nitrotriazolone, nitrocellulose, guanidinium compounds, specifically guanidinium nitrate, nitroguanidine and double salts of said compounds, tetrazoles, aminotetrazoles, dinitramides and/or combinations of the above-mentioned fuels.
The fuel is provided in the gas generating composition in a proportion from 5 to 95 percent by weight, or in a proportion from 10 to 90 percent by weight or from 20 to 80 percent by weight, or in a proportion from 35 to 65 percent by weight.
The gas generating composition may comprise, apart from the basic mixed metal nitrate, at least one further oxidant selected from the group consisting of nitrates, oxides and/or mixed oxides of the alkaline 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. Basically, all allotropes and all isotropic materials of the corresponding compounds are also included.
The gas generating composition can contain 10 to 60 weight-% of the basic mixed metal nitrate and, optionally, of the at least one further oxidant.
The proportion of basic mixed metal nitrate and, optionally, of the at least one further oxidant in the gas generating composition is specifically selected so that an equilibrated oxygen balance is obtained.
The gas generating composition may additionally comprise 5 weight-% or less of a processing aid, specifically 1 to 5 weight-%, based on the total weight of the gas generating composition. Processing aids are, e.g., pressing aids, anti-caking aids and/or sliding aids which in the given amount have no substantial effect on the burning rate of the composition.
Examples of suitable processing aids are polyethylene glycol, cellulose, methyl cellulose, graphite, wax, metal soaps, such as calcium stearate, magnesium stearate, zinc stearate and/or aluminum stearate, boron nitride, talcum, bentonite, silica and molybdenum sulfide as well as the mixtures thereof.
In addition, the gas generating composition according to the disclosure may contain common burning moderators and/or coolants, for example 10 weight-% or less, specifically up to 6 weight-% or 0.1 to 6 weight-%, based on the total weight of the gas generating composition. The above-mentioned additives have a stabilizing effect on burning and keep the combustion temperature low. At the same time, slagging of the combustion residues is improved, which prevents the residues from being dusted.
Examples of suitable burning moderators and/or coolants are B2O3, Al2O3, MgO, TiO2, SiO2, Mg(OH)2, basic magnesium carbonate, CaCO3 and mixtures thereof.
Further, the gas generating composition may additionally comprise 5 weight-% or less of a further additive, specifically 0.1 to 5 weight-%, based on the total weight of the gas generating composition. The further additives serve specifically for improving the ignitability and the mechanical properties of the gas generating composition.
The burning temperature of the gas generating composition can range from 1700 K to 2300 K.
The disclosure further describes the use of a gas generating composition of the above-described type in a safety device, specifically for a vehicle.
Moreover, the disclosure describes the use of a basic mixed metal nitrate of the above-described type as oxidant in a gas generating composition, specifically in a gas generating composition for safety devices.
The safety device is arranged, for example, in a vehicle or in a vest or, resp., a protector of a user.
Further advantages and characteristics will result from the following description and the examples in the description.
Exemplary gas generating compositions are listed in Table 1.
The abbreviations used in Table 1 have the following meaning:
GuNi=guanidinium nitrate
bCZN=basic copper-zinc-nitrate (basic mixed metal nitrate)
As metal stearates, a mixture of calcium stearate, magnesium stearate, zinc stearate is used.
The ballistic behavior was carried out based on a test series with three compositions as stated in Table 2.
To this end, the gas generating compositions were compressed into cylindrical tablets having a diameter of 4 mm and a thickness of 1.3 mm. The oxidant used had a grain size d50 of 6 μm. The zinc content in the bCZN used was 22%.
Subsequently, 10 g of the tablets were weighed in a standard combustion chamber made of steel having a volume of 100 cm3, were ignited via an igniter of the standard combustion chamber, and the pressure curve inside the standard combustion chamber was observed to determine the combustion rate of the respective tablet. The ballistic test was carried out at a pressure of 10 MPa or 20 MPa, respectively. Each test was carried out twice and the combustion rates obtained were averaged arithmetically. It turned out that combustion rates measured with the compositions according to the disclosure for tablets of the size used and with oxidant of the grain size used are in a range which is suitable for gas generating compositions for use in safety devices.
When, in Example 1, bCZN is completely replaced with bCN having a grain size d50 of 1 μm, combustion rates of 17.6 mm/s at 10 MPa and of 22.2 mm/s at 20 MPa are resulting.
When, in Example 1, bCZN is completely replaced with bCN, which was coated with one percent of glycerin, having a grain size d50 of 1 μm, combustion rates of 19.5 mm/s at 10 MPa and 24.3 mm/s at 20 MPa are resulting.
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, wherein the basic metal nitrate is a basic transition metal nitrate, preferably basic copper nitrate.
3. The gas generating composition according to claim 1, wherein the at least one further element is selected from a group consisting of alkaline earth metals, transition metals, aluminum and boron.
4. The gas generating composition according to claim 1, characterized in that wherein the at least one further element comprises or is zinc.
5. The gas generating composition according to claim 1, wherein, 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.
6. The gas generating composition according to claim 1, wherein, 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.
7. The gas generating composition according to claim 1, wherein 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 claim 1, wherein the at least one further element is arranged to be distributed stochastically or periodically in the basic mixed metal nitrate.
9. (canceled)
10. (canceled)
11. The gas generating composition according to claim 1, wherein, in the basic mixed metal nitrate, 40 mole percent or more of the metal in the basic metal nitrate are replaced with the at least one further element.
12. The gas generating composition according to claim 1, wherein, in the basic mixed metal nitrate, 80 mole percent or less of the metal in the basic metal nitrate are replaced with the at least one further element.
Type: Application
Filed: May 17, 2021
Publication Date: Jun 8, 2023
Inventor: Michael KÖNIG (Waldkraiburg)
Application Number: 17/926,193
