Nitrogen gas generator

Abstract

The present invention is directed to a nitrogen gas generator comprising a housing having two ends, an ignition means at one end of the housing and a gas outlet opening at the other end of the housing, a volume of a filter at the outlet opening and a volume of a solid propellant comprising sodium azide, a binder, a coolant and between 1 and 10% by weight of iron (III) oxide. Between the ignition means and the volume of solid propellant there is an active layer. The active layer comprises between 60 and 90% by weight of sodium azide, between 1 and 15% by weight of a binder, between 0.1 and 10% by weight of a coolant and between 5 and 30% by weight of iron (III) oxide. The content of iron (III) oxide in the active layer is higher than the content of iron (III) oxide in the solid propellant.

Description

Technical Field

[0001] The present invention includes a housing having two ends, ignition means at one end of the housing, a gas outflow opening at the other end of the housing, a certain volume of filter at the outflow opening, and a certain volume of solid propellant containing sodium azide, a binder, a coolant, and iron(III) oxide, which is present between the ignition means and the certain volume of filter, and targets a nitrogen gas generator. Nitrogen gas is generated when the solid propellant burns.

Background Art

[0002] Such a gas generator is known from the applicants' WO2014 / 073970. This publication describes a nitrogen gas generator present in a tubular housing. At one end, there is ignition means which can be a conventional gunpowder igniter. Between these ignition means and a filter which may be a sand filter, a composition consisting of sodium azide, potassium silicate, iron(III) oxide, and lithium fluoride exists as a solid propellant or nitrogen generation composition. When ignited at one end of the nitrogen generation composition, nitrogen gas is formed, which flows through the still unburned nitrogen generation composition and the sand filter to the outflow opening. Through the outflow opening, relatively cold nitrogen gas is released into the environment. Such a nitrogen gas generator is advantageously used to protect electrical devices such as computer servers from fire. This is because relatively cold nitrogen gas does not damage electrical components such as other equipment or servers near the fire.

[0003] US4203787 describes a solid propellant, also called a nitrogen gas generation composition, based on sodium azide. According to this publication, to successfully initiate the combustion of a sodium azide composition, a sufficient amount of initiator is required to ensure that the sufficiently high-temperature combustion products of the initiator come into sufficient contact with the exposed sodium azide composition to sweep the self-sustaining flame front. A potassium borate nitrate-lead azide initiator is described in this publication.

[0004] US4817828 describes a nitrogen gas generator consisting of 61-68 wt% sodium azide, 0-5 wt% sodium nitrate, 0-5 wt% bentonite, 23-28 wt% iron oxide, 2-6 wt% graphite fibers, and 1-2 wt% fumed silicon dioxide particles. The described igniter is made of potassium boronitrate, which is preferable because it can minimize peak pressure and thus avoid particle damage.

[0005] EP0619284 describes a nitrogen gas generator. Its solid propellant consists of iron gamma oxide and sodium azide in approximately stoichiometric ratios to each other. More preferably, the composition contains iron gamma oxide in an amount between about 29–40% by weight and sodium azide in an amount between about 71–60% by weight. A preferred igniter may be a conventional igniter described in US4902036. This igniter includes a squib, such as one present to ignite an enhancer packet containing potassium boronitrate present in a sealed space. A conductor transmits current to the squib, thereby igniting the squib and also igniting the enhancer packet. Ignition of the rapidly combustible material provides the threshold energy required to ignite the nitrogen gas generating composition. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2014 / 073970 [Patent Document 2] U.S. Patent No. 4203787 [Patent Document 3] U.S. Patent No. 4817828 [Patent Document 4] European Patent Application Publication No. 0619284 [Patent Document 5] U.S. Patent No. 4902036 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The problem with prior art nitrogen gas generators is the reliability of their performance. Nitrogen gas generators, especially those installed to extinguish fires, should ideally not malfunction during ignition. However, in practice, a small percentage of installed nitrogen generators may fail to produce the optimal amount of nitrogen gas. This invention relates to a nitrogen gas generator that does not malfunction during ignition, or at least consistently produces a minimum amount of nitrogen gas. [Means for solving the problem]

[0008] This is achieved by the following nitrogen gas generator. A housing having two ends, an ignition means at one end of the housing, and a gas outlet opening at the other end of the housing, A filter of a certain volume at the outlet opening, Between the ignition means and a filter of a certain volume, Sodium azide in an amount of 70-90% by weight, a binder in an amount of 1-15% by weight, a coolant in an amount of 0.1-20% by weight, and bi1 A certain volume of solid propellant containing iron(III) oxide between ~10% by weight, A nitrogen gas generator comprising an ignition means and an active layer between it and a certain volume of solid propellant, wherein the active layer comprises 60-90% by weight of sodium azide, 1-15% by weight of a binder, 0.1-10% by weight of a coolant, and 5-30% by weight of iron(III) oxide, and the iron(III) oxide content in the active layer is higher than the iron(III) oxide content in the solid propellant. [Modes for carrying out the invention]

[0009] The applicants have found that a more reliable nitrogen gas generator can be obtained when an activated layer containing a relatively high iron oxide content is used. Furthermore, nitrogen gas is generated more rapidly. Another advantage is that the sodium azide-containing activated layer also generates nitrogen gas, thus increasing the volume of nitrogen gas that can be produced by a single nitrogen gas generator according to the present invention.

[0010] The present invention is particularly suitable for gas generators having an ignition means including a squib and an enhancer packet. Preferably, the enhancer packet contains potassium boronitrate, i.e., KBNO3. It has been found that when an active layer is present according to the present invention, propagation after initiation is enhanced. This enhancement has been demonstrated to improve reliability with the same amount of BKNO3 and even allow for a reduction in the amount of BKNO3. Nitrogen gas generators according to the present invention can release nitrogen more rapidly than nitrogen generators without an active layer and with a high potassium boronitrate content. This feature is relevant to applications requiring a rapid response to threats. Reducing the amount of potassium boronitrate used is advantageous because it improves safety during manufacturing and improves product safety. A further advantage is that a lower amount of potassium boronitrate used results in a higher purity of released nitrogen gas.

[0011] A problem with the above system, which includes squibs and enhancer packets, is that special safety measures must be taken when assembling the nitrogen gas generator due to their explosive properties. A further disadvantage is that a special compartment must exist within the nitrogen gas generator for the squibs and enhancer packets. For this reason, it may be preferable that the ignition means include an electric initiator, such as a glow plug. Electric initiators are advantageous because they do not require squibs when combined with potassium boronitrate enhancer packets. Thus, the nitrogen gas generator can be assembled much more simply and safely. Furthermore, a special compartment for the enhancer packets containing potassium boronitrate is not required, resulting in a simpler design. A further advantage of not needing to use potassium boronitrate is that when the nitrogen gas generator is in use, nitric oxide is not formed, or only significantly less. A further advantage is that electric initiators do not cause gas surges or shock waves within the nitrogen gas generator that could damage the gas generator. Such gas surges or shock waves can occur when squibs and enhancer packets are used as ignition means. The next advantage is that the combination of an electrothermal initiator and an active layer provides a more reliable nitrogen gas generator for operation at lower ambient temperatures, such as minus 25°C.

[0012] The electro-initiator may be a glow plug, for example, used in self-ignition engines such as diesel engines. In many applications, one glow plug will suffice. In high-reliability applications such as aerospace applications, it may be beneficial to have two glow plugs to achieve a dual, or redundant, system. Glow plugs are typically designed to be temporarily energized to a pre-selected temperature in the range of 200 to 1200°C in a short period of time, preferably by electro-resistive heating. A glow plug preferably comprises a heating element assembly including a sheath having relatively thin, generally annular walls defining a blind bore, advantageously a monolithic sheath, and a heating element positioned within the blind bore and adapted to dissipate heat, and preferably a heat transfer device adapted to transfer heat from the heating element to the sheath.

[0013] The glow plug may preferably have a conventional heating element at or near its tip, which includes a metal coil or metal filament enclosed in a heat-resistant metal or ceramic sheath.

[0014] The heating element preferably includes at least one metal filament or metal coil having high electrical resistance, so that at least one of the metal filaments or metal coils is rapidly heated when current passes through the heating element, thereby rapidly heating the sheath surrounding the heating element. The heating element may preferably further include an insulator to protect the heating element from direct contact with the sheath. This insulator can be formed from any suitable material, preferably a ceramic material.

[0015] One or more heating filaments or coils may preferably be protected from direct contact with the sheath by being enclosed in an insulator, thereby enclosing the heating assembly, which includes both the heating filaments or coils and the insulator, within the sheath.

[0016] The sheath can be formed from a pre-selected material, chosen and configured to minimize failure of the heating element assembly caused by thermal stress, oxidation, and / or corrosion, and to avoid any stability or performance issues due to proximity to the solid propellant. The sheath must not contain heavy metals such as copper, lead, iron, nickel, silver, and mercury, which may evaporate or otherwise migrate, thus forming explosive and / or toxic heavy metal azides or other undesirable compounds within the gas generator. This has the advantage that conventional metal coils or filaments containing heavy metal alloys may be employed, otherwise they would be unsuitable due to the risks involved in direct contact with the propellant load.

[0017] The metal coil or filament of the glow plug's heating element is connected to a power source. A preferred power source can supply the glow plug with volts between 10 and 30 and amperes between 5 and 20 for at least 5 to 20 seconds, thereby rapidly heating the glow plug sheath to a steady-state operating temperature of at least 200°C, more preferably at least 250°C, more preferably at least 500°C, even more preferably at least 750°C, preferably between 900 and 1200°C, and even more preferably between 900 and 1000°C. A particularly preferred power source is a battery that can supply at least 12 volts and at least 10 amperes to the glow plug for at least 10 seconds and can be attached to a gas generator. The actual temperature to be achieved is preferably above the autodecomposition temperature of the active layer. This temperature should be sufficient to ignite the active layer.

[0018] When an electric current is passed through the metal coil of the heating element of the glow plug, the coil heats up due to its electrical resistance and heats until its sheath glows. By applying only partial power to the glow plug, the sheath of the glow plug is heated to a temperature significantly lower than its operating temperature, and in this state, it can be used to warm the solid propellant around the generator, and as a result, the propellant can be started immediately. When full power is supplied to the coil of the heating element of the glow plug, its sheath begins to glow and heats the solid propellant around the generator very significantly. When the part of the active layer surrounding the glowing sheath of the glow plug reaches the decomposition temperature, such part of the active layer begins to activate and burns other parts of the active layer farther from the glow plug sheath.

[0019] Preferably, the part of the active layer, particularly the sodium azide propellant of the layer, can start to activate within 10 seconds, more preferably within 5 seconds, after full power is supplied to the coil of the heating element of the glow plug. The solid propellant layer itself can activate within 20 - 90 seconds, more preferably within 30 - 60 seconds, after full power is supplied to the coil of the heating element of the glow plug.

[0020] Preferably, once activated, the glow plug reaches the desired temperature in less than 5 seconds, more preferably in less than 3 seconds, even more preferably in less than 2 seconds. The amount of power that must be supplied to the glow plug according to the present invention to initiate the decomposition of the active layer depends on the composition and physical appearance of the layer. Appropriately, at least 30 watts, preferably about 50 - 100 watts of electricity must usually be sufficient to initiate the controlled self-sustaining decomposition of the active layer.

[0021] The heating element of the glow plug is preferably arranged in the center within the housing of the gas generator. The heating element of the glow plug is preferably enclosed by the active layer. More specifically, the sheath surrounding one or more metal filaments or metal coils having a high electrical resistance is at least partially enclosed by the active layer. This allows for the easy use of commercially available glow plugs.

[0022] The solid propellant and active layer may include a binder and a coolant, as is known in the prior art and as described in the applicant's WO2014 / 073970, which was referenced earlier.

[0023] The solid propellant and the binder contained in the active layer may be the same or different, preferably the same. The binder can be polytetrazole, preferably an alkaline non-organic binder material, more preferably an alkali metal silicate such as potassium silicate (K2SiO3). Preferably, the binder is potassium silicate (K2SiO3) for the solid propellant and the active layer.

[0024] The solid propellant and the coolant contained in the active layer may be the same or different. A preferred coolant is an inorganic salt having a heat capacity of at least 1400 J / K / kg, measured at 600 K, to provide sufficient cooling. The coolant also has an important function as a slag modifier, which helps to keep the slag in place after the gas generator is functionalized. The heat capacity of the coolant is preferably at least 1900 J / K / kg. The coolant should be inert so as not to decompose or react with other components in the generator at the reaction temperature of gas generation. Preferred coolants are LiF, Li3N3, Li2SO4, Li2SiO3, or one or more compounds selected from NaCl, NaF, KF, CaF2, Li2B2O4, and Li2B4O7. From the viewpoint of excellent combination properties as a slag modifier, lithium compounds are more preferred, and LiF is most preferred.

[0025] The solid propellant contains between 1 and 10% by weight of iron(III) oxide, preferably between 1 and 5% by weight of iron(III) oxide, and more preferably between 1 and 4% by weight of iron(III) oxide.

[0026] The solid propellant is appropriately present as an extruder, or more preferably as a tablet. The extruder or tablet is preferably of uniform size and shape. This ensures that a uniform filler with clearly defined voids is present within these extruders or pellets. The presence of voids is preferable because it provides a channel for nitrogen gas, which is initially generated by the ignited active layer and subsequently by the solid propellant, and a channel through which the nitrogen gas flows toward the outflow opening at the other end of the housing, through these voids, which are present between the unreacted extruder or solid propellant tablets. Preferably, the solid propellant extruder or tablet is 25-1000 mm 3 Between 50 and 500 mm is preferable. 3 It is present in a certain volume of solid propellant having a volume between [a certain value]. The voids between extruded or tablet particles in the volume of solid propellant are preferably between 20 and 75% (volume / volume), more preferably between 40 and 60% (volume / volume), of the total volume taken up by the solid propellant in the housing.

[0027] Preferably, the tablets are bonded together. This can be achieved by adding an interparticle binder, which is preferably an aqueous solution of K2SiO3 having a K2SiO3 content between 10 and 30% by weight relative to the solid propellant tablets when the tablets are placed in the housing of the nitrogen gas generator. Bonding the tablets together is advantageous because it allows them to maintain their structure over time, i.e., maintain the relevant voids, resulting in improved packing that avoids the formation of packing defects such as short breaks and dead zones.

[0028] The active layer may exist as a homogeneous powder layer or as laminated particles such as an extruded product or a tablet. For example, the active layer may be a cylindrical tablet having a diameter that just allows for placement within a tubular housing.

[0029] Preferably, the active layer exists as a layer of homogeneous powder. More preferably, such an active layer of homogeneous powder is combined with a certain volume of solid propellant, preferably in the form of a tablet. A very preferred embodiment is when such an active layer of homogeneous powder is combined with a certain volume of solid propellant, preferably in the form of a tablet, and the ignition means includes a glow plug. Even more preferably, a channel exists through the active layer that fluidly connects the volume of solid propellant and the side of the active layer, where the ignition means also exists. Such a channel may preferably have a maximum cross-sectional dimension between 5 and 20 mm, for example, a diameter.

[0030] The active layer contains 60-90% by weight of sodium azide, 1-15% by weight of a binder, 0.1-10% by weight of a coolant, and 5-30% by weight of iron(III) oxide.

[0031] The volume ratio of the active layer to the solid propellant is between 5:95 and 30:70 (volume / volume). The volume refers to the total volume of space within the housing occupied by the active layer and all solid propellant, including any voids, not the space occupied by individual tablets.

[0032] The filter can be any intermediate material that allows nitrogen gas to pass through and has the heat capacity to lower the temperature of the nitrogen gas. Suitable filters are described in WO2014 / 073970 cited above and may be activated carbon, sand, zeolite, or metal. The volume ratio of the filter volume to the volume of the solid propellant is between 20:80 and 60:40 (volume / volume), more preferably between 30:70 and 60:40 (volume / volume).

[0033] The housing can have any shape. Preferably, the housing is elongated so as to allow a combustion front of the solid propellant moving from one end to the end containing the outlet opening. Its cross-section can have any shape. A preferred shape is tubular in order to provide optimal strength per unit mass of the housing. [Examples]

[0034] The present invention is illustrated by the following non-limiting embodiments.

[0035] [Example 1] A tube having a housing with two ends, an ignition means at one end of the housing, and a gas outlet opening at the other end of the housing is filled with a layer of solid propellant LE tablets having the composition described in Table 1. The volume of the solid propellant LE tablets is 117 mm³. 3 It was a tablet. The void space in this layer was approximately 49% (volume / volume). The length of the layer was 168 mm.

[0036] A 90 mm layer of sand was present between the solid propellant layer and the gas outlet opening. On the opposite side was a 12 mm active layer of TL powder having the composition shown in Table 1. This layer contained small axial channels with a diameter of approximately 12 mm, connecting the igniter to the solid propellant LE tablet layer. In the active layer, an enhancer packet containing squib and KBNO3 particles was present as the igniter.

[0037] [Table 1]

[0038] After holding the above-mentioned tube at ambient temperature for several hours, the activated layer was ignited, and the pressure, temperature, and time at which nitrogen was released from the gas generator were measured. The time at which the highest pressure was reached at the gas outlet opening was measured. The time at which 75% by weight (T75) and 95% by weight (T95) of the theoretically possible amount of nitrogen gas was released was measured. The results are shown in Table 2.

[0039] [Example 2] Example 1 was repeated, except that HE tablets were used instead of LE tablets. The results are shown in Table 2.

[0040] [Example 3] Example 2 was repeated, except that the axial channels were not present in the TL powder layer. The results are shown in Table 2.

[0041] [Comparative Experiment A] Example 2 was repeated, except that the active layer of TL powder was absent. An enhancer packet containing squib and KBNO3 particles was present as an igniter in direct contact with the solid propellant HE tablet. The results are shown in Table 2.

[0042] [Table 2]

[0043] The results in Table 2 show that when an active layer is present, more nitrogen gas is generated and released in a shorter time compared to when such an active layer is absent.

[0044] [Example 4] Example 2 was repeated three times under ambient conditions, and the results are shown in Table 3 (Examples 4a, 4b, 4c). In this table, the conversion rate is also shown as weight %. The conversion rate is the percentage of nitrogen produced compared to the theoretically maximum possible nitrogen that can be produced based on the available NaN3 in the HE tablets and TL powder.

[0045] [Comparative Experiment B] Comparative experiment A was repeated three times. In all experiments, propagation failed, resulting in a very low conversion rate. The results are shown in Table 3 as B1, B2, B3, and B4.

[0046] [Table 3]

[0047] The results in Table 3 show that the reproducibility and reliability of nitrogen gas generators equipped with an active layer are better than those obtained with nitrogen gas generators that do not have such an active layer.

[0048] [Example 5] Example 1 was repeated, except that the tube was kept at -25°C (-25°C) for several hours before igniting the active layer. The results are shown in Table 4.

[0049] [Comparative Experiment C] Comparative experiment A was repeated, except that the tube was kept at -25°C (-25°C) for several hours before ignition. The results are shown in Table 4.

[0050] [Example 6] Example 1 was repeated, except that the tube was maintained at 65°C (+65°C) for several hours before igniting the active layer. The results are shown in Table 4.

[0051] [Comparative Experiment D] Comparative experiment A was repeated, except that the tube was maintained at 65°C (+65°C) for several hours before ignition. The results are shown in Table 4.

[0052] [Table 4]

[0053] Comparing the results of Example 5 and Experiment C with those of Example 6 and Experiment D, it is shown that at cryogenic and high temperatures, the presence of the active layer results in much faster nitrogen gas generation, as indicated by the shorter T75 and T95 times.

[0054] All generators in Examples 4-6 and Experiments B-D were allowed to cool and opened under controlled conditions. Gas generators with an active layer were observed to exhibit better radial conversion, which is thought to contribute to the desired and more reliable propagation in the axial direction.

[0055] [Comparative Experiment E] A small cooling gas generator consisting of 58 grams of HE tablets (Table 1), with a N2 generating capacity and porosity similar to that of previous examples, was started using a standard glow plug. The decomposition reaction began 20 seconds after glow plug activation and reached complete decomposition 10 seconds after startup (or 30 seconds after glow plug activation).

[0056] [Comparative Experiment F] A second small-scale cooling gas generator, similar to the apparatus used in Experiment E, was started using a high-speed, high-T glow plug. The decomposition reaction began 7 seconds after the glow plug was activated and reached complete decomposition again 10 seconds after activation (or 17 seconds after the glow plug was activated).

[0057] [Example 7] In a small-scale generator similar to the apparatus used in Experiment F, 10 wt% HE tablet particles were replaced with a high-energy top layer consisting of TL powder (Table 1). Here, the decomposition reaction began 3 seconds after glow plug activation and reached complete decomposition 4 seconds after startup (or 7 seconds after glow plug activation). Example 7 demonstrates that the presence of an active layer, initiated by a glow plug, results in more than twice the startup and complete decomposition compared to a gas generator without such an active layer.

Claims

1. A nitrogen gas generator, A housing having two ends, an ignition means at one end of the housing, and a gas outlet opening at the other end of the housing, A filter of a certain volume at the outlet opening, A certain volume of solid propellant comprising 70 to 90% by weight of sodium azide, 1 to 15% by weight of a binder, 0.1 to 20% by weight of a coolant, and 1 to 10% by weight of iron(III) oxide, is present between the ignition means and a certain volume of filter. A nitrogen gas generator comprising an ignition means and an active layer between it and a certain volume of solid propellant, wherein the active layer comprises 60 to 90% by weight of sodium azide, 1 to 15% by weight of a binder, 0.1 to 10% by weight of a coolant, and 5 to 30% by weight of iron(III) oxide, and the content of iron(III) oxide in the active layer is at least twice the content of iron(III) oxide in the solid propellant.

2. The gas generator according to claim 1, wherein the solid propellant contains iron(III) oxide in an amount between 1 and 4% by weight.

3. The gas generator according to claim 1, wherein the content of iron(III) oxide in the active layer is at least three times the content of iron(III) oxide in the solid propellant.

4. The gas generator according to any one of claims 1 to 3, wherein the ignition means includes a squib and an enhancer packet.

5. The enhancer packet is KBNO ３ The gas generator according to claim 4, including the gas generator described in claim 4.

6. The gas generator according to any one of claims 1 to 3, wherein the ignition means includes a glow plug.

7. The gas generator according to claim 6, wherein the glow plug has a heating element sealed by an active layer.

8. The gas generator according to any one of claims 1 to 7, wherein the solid propellant and / or the binder in the active layer is made of a non-organic binder material.

9. The gas generator according to claim 8, wherein the solid propellant and / or the binder in the active layer is composed of an alkaline non-organic binder material.

10. The aforementioned binder is potassium silicate (K ２ SiO ３ The gas generator according to claim 9, which is the gas generator described in claim 9.

11. The gas generator according to any one of claims 1 to 10, wherein the coolant is LiF.

12. The solid propellant is 50 to 500 mm ３ A gas generator according to any one of claims 1 to 11, which exists as a tablet having a volume between [a certain value].

13. The gas generator according to claim 12, wherein the tablets are bound together with each other.

14. The gas generator according to any one of claims 12 to 13, wherein the voids between the tablets in the volume of the solid propellant are between 40 and 60% (volume / volume) of the total volume occupied by the solid propellant in the housing.

15. The gas generator according to any one of claims 12 to 14, wherein the active layer is a homogeneous powder layer and the ignition means includes a glow plug.

16. The gas generator according to any one of claims 1 to 15, wherein the volume ratio of the volume of the active layer to the volume of the solid propellant is between 5:95 and 30:70 (volume / volume).

17. The gas generator according to any one of claims 1 to 16, wherein the volume ratio of a certain volume of the filter to the volume of the solid propellant is between 30:70 and 60:40 (volume / volume).

18. The gas generator according to any one of claims 1 to 17, wherein the housing is a tubular housing.

19. The gas generator according to any one of claims 1 to 18, wherein a channel exists through the active layer that fluidly connects the volume of the solid propellant to the side surface of the active layer where the ignition means is located.

20. The gas generator according to claim 19, wherein the channel has a maximum cross-sectional dimension between 5 and 20 mm.

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