EP1553070A2 - Explosive composition, process for its preparation and use of the explosive composition - Google Patents

Abstract

An explosive composition comprises a fuel made from a micro- or nano-structured porous solid and an oxidant made from sulfur, selenium, tellurium, bromine, iodine, phosphorus and/or arsenic and/or their oxygen-free compounds. The oxidant is liquid or solid at room temperature. An independent claim is also included for the production of the explosive composition.

Description

The invention relates to an explosive composition for use in a safety device for vehicles, with a fuel off a micro- or nanostructured porous solid and one at room temperature solid or liquid oxidizing agent.

DE 102 04 834 A1 describes a generic explosive Composition wherein the room temperature solid or liquid oxidant is introduced into the pores of the porous fuel and at least 50% by weight from the group of the organic nitro compounds or nitrates, Alkali metal or alkaline earth metal nitrates, metal nitrites, metal chlorates, metal perchlorates, Metal bromates, metal iodates, metal oxides, metal peroxides, ammonium perchlorate, Ammonium nitrate, hydrogen peroxide, hydroxylammonium nitrate is selected. The known composition is particularly suitable for Use as ignition.

Furthermore, DE 102 04 895 describes a nanostructured, porous Reactive material consisting of reactive bodies whose cavities are in one Size range from 1 to 1000 nm and are provided with oxidizing agent, wherein the reactive substance consists of mutually independent, protective layer-coated, consists of reactive particles. The reactive bodies can be made of silicon, Boron, aluminum, titanium or zirconium exist. In particular, oxidizing agents are used Alkali metal nitrates and alkaline earth metal nitrates and other oxygenated Oxidizing agent proposed.

From DE 101 62 413 A1 finally an integrated blasting element or Ignition element is known, which has a base body made of silicon and a having associated reaction region, wherein the reaction region is porous Silicon and an oxidizing agent for silicon. As a reagent inorganic or organic compounds are proposed which are included in Heating Oxygen, fluorine, chlorine or other oxidizing substances release. Examples are in particular inorganic nitrates and inorganic Called peroxides and other oxygenated salts. The chemical reaction between the oxidizing agent and the porous silicon is by heating triggered by current-carrying conductor tracks. The integrated blasting or Ignition element is intended for use in a microreactor, a micro-booster for course correction of satellites, as ignition element in a gas generator for a belt tensioner or an airbag, or as an initial ignition element for ignition be suitable for explosive charges.

Many of those proposed in the prior art for use with porous silicon However, oxidizers are hygroscopic and / or form hydrated waters Modifications. As a result, however, the storage stability of the compositions be adversely affected. Also, these oxidizers show only one low solubility in organic solvents or have a high Melting point on. The filling of the porous fuel must therefore in several Steps or under increased safety precautions. Because of the high Viscosity of molten salts is the filling of the pores with oxidizing agent also in this case often incomplete. But this results in difficulties in the exact setting of the ratio between porous fuel and Oxidants. The explosive properties of the compositions thus obtained can therefore vary over a wide range and are therefore only difficult to standardize. A number of the oxidizing agents mentioned in the prior art can not be displayed purely. The in this oxidizing agent Contaminants also affect the explosion behavior the compositions prepared therewith.

The invention is based on the object, the above To avoid disadvantages and a cost-effectively manufacturable and in particular for civil applications stable explosive composition provide.

According to the invention, this is an explosive composition for Use in a safety device for vehicles, with a fuel from a micro- or nanostructured porous solid and a at Room temperature solid or liquid oxidizing agent proposed characterized in that the oxidizing agent is selected from sulfur, selenium, Tellurium, bromine, iodine, phosphorus and arsenic and mixtures thereof and oxygen-free compounds existing group is selected. Preferably the composition according to the invention consists of the fuel and the Oxidant.

The oxidizing agents to be used according to the invention show a high level of Bonding energy to silicon and thereby also a sufficiently high heat of explosion. They are also easily evaporable or sublimable and can be therefore good in chemical or physical deposition processes use the gas phase (CVD or PVD method). A number of the invention oxidant to be used is also good in non-polar, volatile organic solvents soluble. These oxidants, like For example, sulfur and iodine dissolve beyond that as well nonpolar solvent carbon dioxide much better than the polar oxygen salts. Therefore, the oxidizing agents to be used in the present invention very easy using supercritical carbon dioxide in the pores of the micro- or nanostructured fuel are introduced. After this Evaporation of the solvent remains residue-free, only the oxidizing agent in the porous structure of the fuel.

When using sulfur as the oxidant is due to the low Melting point of 113 ° C also the direct introduction of the molten Oxidant in the pores of the micro- or nanostructured fuel possible without impurities.

The said oxidizing agents can thus be much easier in stoichiometric Quantities are introduced into the nanostructured fuel. she thus simultaneously provide a high heat of explosion and a good Handling in the filling of the pores of the nanostructured fuel.

Common oxygen-containing and salt-like oxidants are also distinguished by more or less pronounced hygroscopicity. These substances thus require a high procedural effort, since the present must be excluded safely from water or humidity. About that In addition, the compositions made with these materials must be hermetic be closed to the functionality over the entire life structure of up to 15 years. By use the oxidizing agent according to the invention, in particular of the non-hygroscopic Sulfur, these disadvantages are also safely eliminated.

The invention further provides a process for the preparation of the explosive composition according to the invention, which is characterized in that the oxidizing agent 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 the equally non-polar oxidants according to the present invention. Furthermore, the solvent should be able to evaporate without residue from the porous fuel structure. Thus, the adjustment of stoichiometric compositions of fuel and oxidant is much easier. Particularly suitable solvents are supercritical carbon dioxide, carbon disulfide, carbon tetrachloride and aromatic and saturated aliphatic hydrocarbons. Generally, it can be considered that solvents having a Reichardt polarity of E _T (30) / kcal / mol ≥ 50 can be used.

The micro- or nanostructured fuel is preferably a solid having a sponge-like framework of amorphous, semi-crystalline or crystalline particles having a feature size of between about 2 nm and 1000 nm, and has a porosity (V _pores / V _sample ) of between 10% and 98 %, preferably between 40 and 80%. The fuel may have a specific surface area of up to 1000 m ² / cm ³ , preferably between 200 and 1000 m ² / cm ³ .

The structure size or the size and shape of the pores, can thereby vary within a wide range. The structure size gives the average Size of the particles from which the fuel is constructed, and is preferred in a range of 2 to 50 nm, more preferably between 2 nm and 10 nm. The pore size is preferably in a range of between 2 nm and 1000 nm.

The porous fuel is preferably a semiconductor material, and more particularly preferably from the group consisting of Si, Ge, SiGe, SiC, InP and GaAs selected. The production of micro- or nanostructured porous materials from these substances is described in the scientific literature. When Manufacturing processes are particularly suitable chemical or physical Deposition methods, such as electrochemical deposition, CVD, PVD or Sputtering or pressing of nanofine particles. In the case of silicon are these nanofine particles are obtained by slow burning of silane.

Particularly preferably, the fuel is so-called "porous silicon", which is particularly easy by electrochemical etching of silicon in fluoride-containing solutions can be prepared. The use of porous Semiconductor materials, e.g. Silicon, allows easy integration into known semiconductor devices using conventional semiconductor process techniques.

Advantageously, the porous fuel is at least partially passivated, that is, the inner surface of the fuel is at least partially with Oxygen saturated or otherwise altered so that one to the reaction is increased with the oxidizer to be overcome activation energy. The passivation For example, by heating the fuel in an oxygen-containing Atmosphere or air done. Passivation becomes another Adjustability of the pyrotechnic properties of the invention Composition, such as their ignitability by electrical Discharge or exposure to UV light, possible.

Because the chemical reaction of the porous fuel from the surface can be done by means of a less reactive protective layer on the surface of Nanoparticles the activation energy to overcome for the ignition of the fuel increase. This passivation layer can be retrofitted to the porous fuel applied and made of an inert material (e.g., Teflon) consist. The passivation layer can also be obtained by means of thermal, chemical, built physical or electrochemical treatment of the fuel become.

A stable passivation layer may e.g. by annealing the porous silicon in air, preferably following the electrochemical etching and before filling the pores with the oxidizer. If the annealing in the Range of between 150 ° C and 300 ° C, preferably at about 200 ° C, is formed after up to about 1600 minutes an oxygen submonolayer of silicon-oxygen bonds (Si-O), which has a higher binding energy than the silicon-hydrogen bonds exhibit. The surface of the silicon nanocrystals consists here after annealing from H-Si-O complexes, since at about 200 ° C of the Hydrogen is retained on the surface of the nanoparticles and oxygen bonded to silicon under the first monolayer. Will the annealing at Temperatures above about 300 ° C are performed (e.g., 700 ° C, 30 seconds) Hydrogen is driven off the surface of the nanoparticles and it forms Layers of "pure" Si-O bonds. So tempered and with oxidizing agent filled samples are extremely stable and handling safe, but can nevertheless be exploded by means of a sudden warming.

The passivation of the surface of the porous fuel also increases the Long-term stability of the explosive composition, as a temporal Change in the surface properties of the fuel under the influence of Oxidizing agent can no longer occur.

The oxidizing agent is preferably wholly or partially of iodine, sulfur or oxygen-free sulfur compounds. These oxidants are in nonpolar organic solvents easily soluble and can be left without residue into the porous fuel structure. They are also opposite non-passivated porous silicon storage stable. For these oxidants Thus, depending on the existing requirements on the production of the above be omitted described passivation layer.

The oxidizer and the fuel may be approximately in a stoichiometric Ratio present. Depending on the application, the oxidizer in proportion to the fuel but also over-balanced or under-balanced.

The composition of the invention also has a high structural strength because the fuel is present as a solid, forming matrix. The Composition can thus be used as a supporting component in pyrotechnic articles, z. As lighters are used. In addition, the from the Semiconductor technology and micromechanics known manufacturing method applicable. This provides the opportunity for cost-effective production using of standard components. In particular, the full integration of inventive composition in semiconductor circuits allows.

The invention thus also relates to the use of the invention Composition as part of a lighter. This lighter may be advantageously integrated in a semiconductor circuit. Especially the lighter may be part of a safety system in vehicles, such as a gas generator for a belt tensioner or a gas bag module be.

Further features and advantages of the invention will become apparent from the following Description of a preferred embodiment.

For the preparation of the explosive composition according to the invention, initially porous, nanostructured silicon was obtained by electrochemical etching according to the method described in Materials Science and Engineering B 69-70 (2000) 11-22 or Phys. Rev. Lett. (2001), 87, 68 301 et seq. For this purpose, a silicon substrate was connected as an anode in an etching cell and treated in a hydrogen fluoride-containing electrolyte, for example a mixture of equal volume proportions of ethanol and concentrated hydrofluoric acid (50% strength) at an anodization current of between 20 and 70 mA / cm ² . The porosity of the silicon thus obtained ranged between 40% and 80%. The structure size varied between 2 and 10 nm.

The thus-obtained porous silicon was annealed at 200 ° C for 26 hours in air, then impregnated with a saturated solution of sulfur in carbon disulfide and then dried in air. With the help of an electric spark could a strong explosion will be triggered. The composition showed in one Storage test at 104 ° C for 400 hours no significant increase in weight.

In further experiments, tempered and untempered samples of the porous silicon filled with sulfur from the melt. The sulfur was in solid state applied to the sample of porous silicon and the sample was heated to about 125 ± 5 ° C with a hot plate warmed up with molten sulfur. The molten sulfur became about Leave on the sample for 30 seconds, leaving the sulfur in the pores of the porous Silicon penetrated. Thereafter, the excess sulfur from the specimen away. In this way could be determined by gravimetric measurements Filling levels of over 90% can be achieved.

For lowering the melting point and / or the viscosity of Sulfur melt can sulfur further additives, such as ethylene glycol or sugar, to be mixed. The filling of the samples with sulfur from the Melting can be done in air or in a vacuum. Furthermore, it is possible the filling of the samples of tempered or untempered porous silicon with sulfur by sublimation in a vacuum chamber or through physical separation of sulfur from the gas phase.

All sulfur-filled samples of porous silicon thus prepared could by rapid heating on a hot plate or by means of a electrically heated ignition bridge to be exploded.

The samples filled with molten sulfur from the annealed porous silicon showed an initialization temperature in the range between 239 and 267 ° C. The comparison values determined by DSC measurements of samples of annealed porous silicon, filled with Calcium perchlorate or sodium perchlorate ranged between 185 up to 210 ° C or 208 to 237 ° C.

The results show that the system is porous silicon / sulfur Use as explosive material. About the porosity of the porous Silicon, the strength of the explosion can be controlled because the pore volume the amount of oxidant introduced and thus the stoichiometry of the Determines reactants. The oxidation is not spontaneous, but lets For example, trigger targeted by a current pulse. Furthermore are the samples of sulfur-filled porous silicon mechanically and chemically extremely stable and therefore very safe to handle. They let themselves for example, in the wafer process while maintaining full functionality with part of a standard water-cooled wafer saw.

The composition according to the invention can be used in particular in a lighter of safety equipment for vehicles, for example Gas bag modules or Gurtstraffem be used. Such lighters can be advantageous with known methods of semiconductor or Siliziumprozesstechnik getting produced. In particular, a simple and inexpensive Production with high precision already in the batch process on wafer level possible.

Claims (11)

An explosive composition for use in a vehicle safety device comprising a fuel of a microporous or nanostructured porous solid and an oxidant solid or liquid at room temperature, characterized in that the oxidizing agent is selected from sulfur, selenium, tellurium, bromine, iodine, phosphorus and arsenic and mixtures thereof and oxygen-free compounds. Explosive composition according to claim 1, characterized in that the oxidizing agent is iodine, sulfur or an oxygen-free sulfur compound. Explosive composition according to claim 1 or 2, characterized in that the fuel is porous silicon. Process for preparing the explosive composition according to one of Claims 1 to 3, characterized in that the oxidizing agent is dissolved in a solvent and introduced into the pores of the nanostructured fuel. Process according to claim 4, characterized in that supercritical carbon dioxide is used as solvent. Process according to Claim 4, characterized in that carbon disulfide is used as the solvent. Process for the preparation of an explosive composition with a fuel of a microstructured or nanoporous solid and sulfur as oxidizing agent, comprising the following steps: Providing the porous fuel; and Introducing the sulfur into the pores of the porous fuel from the melt. Process according to claim 7, characterized in that the sulfur is heated to 125 ± 5 ° C to form the melt. Method according to one of claims 4 to 8, characterized in that the fuel is obtained by anodic etching of silicon in fluoride-containing solution to form porous silicon. Method according to one of claims 4 to 9, characterized in that the porous fuel is passivated before introducing the oxidizer into the pores. Use of the explosive composition according to any one of Claims 1 to 3 in a lighter for activating a safety device in vehicles.