JP2005225750A - Explosive composition and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an explosive composition capable of being used for a safety device for vehicle at an advantageous cost. <P>SOLUTION: The explosive composition contains fuel of a micro-structural or nano-structural porous solid material and an oxidizing agent solid or liquid at an environmental temperature. The oxidizing agent is selected from a group comprising sulfur, selenium, tellurium, bromine, iodine, phosphorus and arsenic, these mixture and their compounds containing no oxygen. The explosive composition is manufactured by dissolving the oxidizing agent in a solvent and introducing into the pores of the fuel. A material particularly preferable as the fuel is porous silicon. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an explosive composition for use in a vehicle safety device, comprising a fuel of a porous solid material having a microstructure or nanostructure, and an oxidant that is solid or liquid at ambient temperature.

  A general explosive composition is known from German Patent Publication DE 102 04 834 A1. In conventional compositions, an oxidizer that is solid or liquid at ambient temperature is introduced into the pores of the porous fuel. At least 50% of the oxidizing agent is organic nitrogen compound or nitrate, alkali metal nitrate or alkaline earth metal nitrate, metal nitrate, metal chlorate, metal perchlorate, metal bromate, metal iodate, metal oxidation Product, metal peroxide, ammonium perchlorate, ammonium nitrate, hydrogen peroxide and hydroxyammonium nitrate. The known compositions are particularly suitable for use as ignition compositions.

  Furthermore, the German patent publication DE 102 04 895 is composed of a reactive body and cavities with dimensions in the range of 1-1000 nm and comprising an oxidant, and are surrounded by a protective film independently of each other. Disclosed is a nanostructured porous reactive material comprised of reactive particles. The reactive body may consist of silicon, boron, aluminum, titanium or zirconium. The oxidants are in particular alkali metal nitrates and alkaline earth metal nitrates, and also oxygen-containing oxidants.

  Finally, German Patent Publication DE 101 62 413 A1 discloses an integral explosive or ignition element having a silicon substrate and associated reaction zone. The reaction zone contains porous silicon and an oxidizing agent for silicon. Inorganic or organic compounds have been proposed as oxidants and release oxygen, fluorine, chlorine or other oxidants when heated. In particular, inorganic nitrates and inorganic peroxides as well as oxygen-containing salts are mentioned as examples. The chemical reaction between the oxidant and the porous silicon is initiated by heating with a conducting wire carrying current. The integral explosive element or ignition element is used in a microreactor, in a satellite orbit correction microbooster, as an ignition element in a belt tensioner or airbag gas generator, or as an initial ignition element for the ignition of an explosive filler. Intended to be used.

  However, some of the oxidants proposed in the prior art for use with porous silicon form a modification that is hydrous and / or contains crystal water. For this reason, the storage stability of the composition may be adversely affected, and furthermore, these oxidants only exhibit low solubility in organic solvents or only have a high melting point. . Therefore, the filling of the porous fuel must be carried out in several steps or with enhanced safety measures. Due to the high viscosity of the salt melt, it is often incomplete in this case to fill the pores with oxidant. Therefore, it is difficult to accurately set the ratio between the porous fuel and the oxidant. Therefore, the explosive properties of the resulting composition can vary over a wide range and are difficult to standardize. In addition, the range of oxidants shown in the prior art cannot simply be obtained. Similarly, impurities contained in these oxidants impair the explosive properties of compositions made with these oxidants.

The object of the present invention is to provide a stable explosive composition which avoids the above-mentioned drawbacks and which can be used at an advantageous cost, in particular for consumer use.
According to the present invention, an explosive composition is provided for use in a vehicle safety device. The composition comprises a microstructured or nanostructured porous solid material and an oxidizing agent that is solid or liquid at ambient temperature. The oxidizing agent is selected from the group consisting of sulfur, selenium, tellurium, bromine, iodine, phosphorus, arsenic and mixtures thereof and these oxygen-free compounds. Preferably, the composition according to the invention consists of a fuel and an oxidant.

  Oxidizing agents that can be used according to the invention exhibit a high binding energy for silicon and therefore also a sufficiently high heat of explosion. In addition, they can be easily vaporized or sublimated and can therefore be easily used for chemical vapor deposition or physical vapor deposition (CVD or PVD). Furthermore, the range of oxidants that can be used according to the present invention is readily soluble in non-polar volatile organic solvents. In addition, these oxidants, such as sulfur and iodine, dissolve substantially better in the same nonpolar solvent carbon dioxide than polar oxygen salts. Thus, the oxidant that can be used according to the present invention can be introduced very simply into the pores of a microstructured or nanostructured fuel using supercritical carbon dioxide. After volatilization of the solvent, only the oxidant free of residues remains in the porous structure of the fuel.

The use of sulfur as the oxidant allows the direct introduction of the oxidant in the molten state into the pores of the microstructured or nanostructured fuel without impurities due to the low melting point of 113 ° C.
Thus, the oxidants described above can be introduced into nanostructured fuels substantially more easily in stoichiometric amounts. They simultaneously provide a high amount of heat for explosion and can be handled well when filling the pores of the nanostructured fuel.

  In addition, conventional oxygen-containing oxidants and salt-like oxidants are distinguished by more or less outstanding hygroscopicity. Thus, these materials require a high degree of effort in processing technology. This is because the presence of moisture in the air, ie humidity, must be reliably removed. Furthermore, compositions made with these materials must be hermetically sealed to ensure that they can function for up to 15 years, the total useful life of the structure. Through the use of the oxidant according to the invention, these disadvantages are easily eliminated, in particular by the use of non-hygroscopic sulfur.

A further subject of the present invention is a process for producing an explosive composition according to the invention. The method is characterized in that the oxidant is dissolved in a solvent and introduced into the pores of the nanostructured fuel. In particular, the use of a nonpolar solvent ensures good solubility of similar nonpolar oxidants according to the invention. In addition, the solvent should be able to evaporate from the porous fuel structure without residue. Thus, adjustment of the stoichiometric composition of fuel and oxidant is substantially facilitated. In particular, supercritical carbon dioxide, carbon disulfide, tetrachloromethane, aromatic hydrocarbons and saturated aliphatic hydrocarbons are also suitable as the solvent. In general, it can be assumed that a solvent having a Reichardt polarity of E _T (30) / kcal / mol ≧ 50 can be used.

The microstructured or nanostructured fuel preferably has a structure size between about 2 nm and 1000 nm and a porosity (V _pores / V _sample ) between 10% and 98%, preferably between 40% and 80%. It is a solid having a sponge-like structure of amorphous, partially crystalline or crystalline particles. Fuel, 1000 m ² / cm ³ have the following specific surface area, preferably at having a specific surface area of 200~1000m ² / cm ^3.

  The structure dimensions as well as the hole dimensions and morphology can vary widely. The structure size indicates the average size of the particles constituting the fuel, and is preferably in the range of about 2 to 50 nm, particularly preferably between about 2 nm and 10 nm. The pore size is preferably in the range between 2 nm and 1000 nm.

  The porous fuel is preferably a semiconductor material, particularly preferably selected from the group consisting of Si, Ge, SiGe, SiC, InP and GaAs. The production of microstructured or nanostructured porous materials from these materials has been described in the scientific literature. Particularly suitable as a production method are electrochemical vapor deposition, chemical vapor deposition such as CVD, PVD or sputtering, or physical vapor deposition, or pressure forming of nano fine particles. In the case of silicon, these nanofine particles can be obtained by gently burning silane.

  Particularly preferably, the fuel is so-called “porous silicon”. Porous silicon can be produced particularly easily by electrochemically etching silicon in a fluoride-containing solution. The use of a porous semiconductor material, such as silicon, allows for easy integration into known semiconductor components using conventional semiconductor processing techniques.

  Advantageously, the porous fuel is at least partially passivated. This means at least partially saturating the internal surface of the fuel with oxygen, or otherwise altering the starting energy to be overcome for reaction with the oxidant. Passivation can be performed, for example, by heating the fuel in an oxygen-containing atmosphere or air. Through passivation, it is possible to further adjust the pyrotechnic properties of the composition according to the invention, such as ignitability by the action of discharge or UV light.

  Since the chemical reaction of the porous fuel occurs from the surface, the activation energy to be overcome for fuel ignition can be increased by a less reactive protective film on the surface of the nanoparticles. The passivating film may be continuously applied to the porous fuel and may be made of an inert substance (for example, Teflon (registered trademark)). The passivation film can also be formed by heat treatment, chemical treatment, physical treatment or electrochemical treatment of fuel.

  A stable passivating film can be formed, for example by tempering porous silicon in air, preferably after the electrochemical etching step and before filling the pores with an oxidant. When tempering is carried out in the range between 150 ° C. and 300 ° C., preferably about 200 ° C., silicon / oxygen bonds (Si—O) oxygen having a higher bond energy than silicon / hydrogen bonds within about 1600 minutes. A submono-layer is formed. Thus, after tempering, the surface of the silicon nanocrystals is composed of H-Si-O complexes. This is because at about 200 ° C., hydrogen is constrained to the surface of the nanoparticles and oxygen binds to silicon under the first monolayer. When tempering at temperatures above about 300 ° C. (eg, at 700 ° C. for 30 seconds), hydrogen is pushed out of the surface of the nanoparticles to form a layer of “pure” Si—O bonds. Samples tempered in this manner and filled with an oxidant are very stable and safe to handle, but may nevertheless lead to an explosion due to sudden heating.

  Passivation of the porous fuel surface also improves the long-term stability of the explosive composition. This is because time-dependent changes to the surface properties of the fuel under the influence of the oxidant no longer occur.

  The oxidizing agent is preferably composed entirely or partly of sulfur compounds that do not contain iodine, sulfur or oxygen. These oxidants are readily soluble in nonpolar organic solvents and can be introduced without residue into the porous fuel structure. In addition, they are storage stable when combined with non-passivated porous silicon. Thus, according to existing requirements, the use of these oxidants can obviate the need to produce the passivation layer described above.

The oxidant and fuel may be present in a stoichiometric ratio, for example. However, depending on the purpose of the application, the oxidant may be in an amount that exceeds or does not exceed the ratio to fuel.
In addition, the composition according to the invention has a high structural strength. This is because the fuel exists as a solid dimensional stability matrix. Therefore, this composition can also be used as, for example, an igniter as a supporting component in a pyrotechnic. In addition, manufacturing processes known from semiconductor technology and micromachines can be used. This has the potential of producing a preferred value using standard ingredients. In particular, it allows complete integration of the composition of the invention in semiconductor circuits.

  Therefore, the use of the composition according to the invention as a component of an igniter is also an object of the invention. This igniter can advantageously be integrated into the semiconductor circuit. In particular, the igniter can be a component of a vehicle safety device, for example a belt tensioner or a gas generator component of a gas bag module.

Preferred embodiment

Further features and advantages of the present invention will become apparent from the following preferred embodiments.
For the production of explosive compositions according to the invention, firstly “Materials Science and Engineering” B 69-70 (2000) 11-22 or “Phys. Rev. Lett.” (2001), 87, 68 301 ff The porous nanostructured silicon is prepared by electrochemical etching according to the method described in. The silicon substrate is connected to the etching cell as an anode, and for example, 20 to 70 mA / cm ^{2 in} an electrolyte containing hydrofluoric acid, which is a mixture of equal proportions of ethanol and concentrated hydrofluoric acid (50%). Treat with anodizing current between. The porosity of the resulting porous silicon was in the range between 40% and 80%. The structure dimensions varied between 2 and 10 nm.

  The porous silicon thus obtained was treated in air at 200 ° C. for 26 hours, then impregnated with a saturated carbon disulfide solution of sulfur and subsequently dried in air. Electric sparks could cause powerful explosions. In a storage test over 400 hours at 104 ° C., the composition did not show any substantial mass gain.

  In further testing, the porous silicon tempered and non-tempered samples described above were filled with molten sulfur. Sulfur was placed in a solid state on a porous silicon sample and the sample was heated on a hot plate to about 125 ± 5 ° C. to form molten sulfur. Molten sulfur was maintained on the sample for 30 seconds to allow molten sulfur to enter the porous silicon pores. Thereafter, excess sulfur was removed from the sample body. In this manner, a degree of filling greater than 90% could be obtained as calculated from the weight measurements.

  Additional additives such as ethylene glycol or sugar may be mixed with the sulfur to reduce the melting point and / or the viscosity of the molten sulfur. Samples can be filled with molten sulfur in air or in vacuum. It is also possible to fill a sample of porous silicon that has been tempered or not tempered with sulfur through sublimation in a vacuum chamber or by physical vapor deposition of sulfur.

All of the porous silicon samples filled with sulfur by the method described above were exploded by rapid heating on a hot plate or by an electrically heated ignition bridge.
By using molten sulfur to fill the tempered porous silicon sample, a sample having an ignition temperature in the range between 239 ° C. and 267 ° C. was obtained. Comparative values for samples of tempered porous silicon filled with calcium perchlorate or sodium perchlorate obtained by digital scanning calorimetry (DSC) range from 185 ° C to 210 ° C and from 208 ° C to 208 ° C, respectively. The range was between 237 ° C.

  The results show that the porous silicon / sulfur system is suitable for use as an explosive material. The intensity of the explosion can be controlled by the porosity of the porous silicon. This is because the pore volume controls the amount of oxidant introduced and thus the stoichiometry of the reaction partner. However, oxidation does not occur spontaneously, but rather can be caused specifically by stimulation of current. In addition, samples composed of porous silicon filled with sulfur have high mechanical and chemical stability and are therefore very safe to handle. For example, the sample will maintain full viability even when split using a conventional water-cooled wafer saw in wafer processing.

  The composition according to the invention can be used in particular in vehicle safety devices such as gas bag modules or belt tensioner igniters. Such an igniter can be advantageously produced by known methods of semiconductor technology or silicon processing technology. In particular, high-precision, simple and advantageous production is already possible with wafer-level batch processes.

Claims (11)

A micro- or nano-structured porous solid material fuel; and
An oxidizing agent that is solid or liquid at an ambient temperature selected from the group consisting of sulfur, selenium, tellurium, bromine, iodine, phosphorus, arsenic and mixtures thereof and these oxygen-free compounds;
An explosive composition for use in a vehicle safety device.   The explosive composition according to claim 1, wherein the oxidizing agent is selected from the group consisting of iodine, sulfur or sulfur compounds not containing oxygen.   The explosive composition according to claim 1 or 2, wherein the fuel is porous silicon. A micro- or nano-structured porous solid material fuel; and
An oxidizing agent that is solid or liquid at an ambient temperature selected from the group consisting of sulfur, selenium, tellurium, bromine, iodine, phosphorus, arsenic and mixtures thereof and these oxygen-free compounds;
A method for producing an explosive composition comprising:
Dissolving the oxidizing agent in a solvent;
Introducing the dissolved oxidant into the pores of the fuel;
Including methods.   The method of claim 4, wherein the solvent is supercritical carbon dioxide.   The method of claim 4, wherein the solvent is carbon disulfide. A method for producing an explosive composition comprising a microstructured or nanostructured porous solid material fuel, and an oxidizing agent that is sulfur,
Providing the porous fuel;
Introducing sulfur in a molten state into the pores of the porous fuel;
Including methods.   The method of claim 7, wherein the sulfur is heated to about 125 ± 5 ° C. to a molten state.   The method according to any one of claims 4 to 8, wherein the step of preparing the porous fuel includes the step of anodic etching silicon in a fluoride-containing solution to form porous silicon.   10. The method according to any one of claims 4 to 9, further comprising passivating the porous fuel prior to introducing the oxidant into the pores.   Use of the explosive composition according to any one of claims 1 to 3 as an igniter for starting a safety device of a vehicle.