DE102007036517A1 - Process for the production of micro and / or nanothermites - Google Patents

Abstract

The invention relates to the field of thermite and in particular relates to a method for producing micro- and / or nanothermites by coating the particles of an oxidizing agent with a reducing agent consisting of a metal or a metal alloy, characterized in that this method comprises the following phase: - A first phase for the preparation of a solution of a precursor of the reducing agent, ie the metal or metal alloy, and micro- and / or nanoparticles of the oxidizing agent; a second phase for evaporation of this solution; a third phase for the thermolysis of the evaporation residues.

Description

The This invention relates to the field of thermites and concerns in particular a process for the production of micro and nanothermites by coating an oxidizing agent with a reducing agent.

The energetic "thermite" mixtures are Materials that are chemically decomposed by suitable ignition can, being a very big one Amount of heat energy is released. In this decomposition process finds a reaction instead, at the oxygen atoms between two solids, one metallic reducing agent that absorbs oxygen, and a metallic oxidant, which gives off oxygen, exchanged become.

The substances produced in this so-called redox process are generally liquids or solids. Especially for this reason, the Thermite are considered not as actual explosives, but as materials with high energy potential. The thermodynamic properties of several hundred binary Thermit blends are from SH Fischer and MC Green in the article "Theoretical energy release of thermite, intermetallics and combustible metals" in the Proceedings of the 24th International Pyrotechnics Seminar, Monterey, California USA 27-31 July, 1998 described.

There the thermal decomposition of these materials by mass transport their rate of burnup is due to size and relative location the particle of each component is limited. The reduction of the size of the oxide and metal particles to achieve nanoscale dimensions leads to an increase responsiveness of these materials and to increase their burning rate.

• – Die physische Durchmischung von nanometrischem Oxidations- und Reduktionsmittelpulver mittels Dispersion unter Ultraschallwirkung in einer Flüssigphase.
• – Die Zerkleinerung von mikrometrischen Mischungen aus Metalloxiden und einem metallischen Reduktionsmittel. Diese beiden Verfahren sind von Natur aus ähnlich. Das zweite Verfahren ist jedoch aufgrund der verursachten mechanischen Belastungen gefährlicher umzusetzen.
• – Die Dispersion von metallischen Nanopartikeln im nanostrukturierten Gitter eines Gels, das aus einem Oxidationsmittel besteht oder ein Oxidationsmittel enthält.

There are currently three methods of producing nanothermites, also called metastable interstitial composites:

• - The physical mixing of nanometric oxidizing and reducing agent powder by means of dispersion under ultrasonic action in a liquid phase.
• - The comminution of micrometric mixtures of metal oxides and a metallic reducing agent. These two methods are inherently similar. However, the second method is more dangerous to implement because of the mechanical stresses caused.
• The dispersion of metallic nanoparticles in the nanostructured lattice of a gel consisting of an oxidizing agent or containing an oxidizing agent.

Of the size Disadvantage of this method is that already existing Metal powder used for it Need to become. These powders can are made in a pure state, but tend to passivation by forming a superficial oxide layer in simple contact with a liquid or gaseous medium with traces of oxygen or moisture. For aluminum, the Passivierungsschicht an even larger relative amount of substance, the smaller the particles are. In the micrometer range is the influence the alumina layer on the particle formation irrelevant. These Alumina layer changes However, the composition of nanoparticles considerably. For this Reason is the production of nanothermites with conventional Method using aluminum particles with a medium Cross-section of less than 30 nm not possible.

by virtue of chemical inertia forms this superficial Oxidschicht also a barrier and thus limits the exchange between reducing and oxidizing agents. To the formation of the superficial Oxide layer counteract, are from the metal powder manufacturers organic polymer films applied to the surface of the metal grains, to minimize the contact between metal and oxygen hold. This is not an ideal solution because the materials with this protective layer are not stable over time are. Furthermore decreases by application of an organic polymer, the degree of purity of the metal.

Using the example of aluminum, the metal commonly used for thermitherposition, the above-mentioned disadvantages become clear. In 1 A commercially available nanometric aluminum powder of the Alex ^® type is commonly used for the formulation of energetic mixtures and characterized by transmission microscopy. The particle center of metallic aluminum (φ ~ 116 nm) is provided with a homogeneous aluminum oxide layer (thickness ~ 5 nm). The mass content of aluminum oxide is about 27%.

In addition, physical mixing and dispersion of metal powder in a gel causes the problem of sample homogeneity due to the size and distribution of the metal particles. This problem was illustrated in the observation of nanothermites under the scanning electron microscope, which were prepared on the one hand by physical mixing in diethyl ether, Alex and nanometric tungsten trioxide (WO ₃ ) and on the other hand by dispersion of Alex in a nano-composite gel of agar and ammonium molybdate. In the first case, the diameter of the WO ₃ nanoparticles is an order of magnitude lower compared to the Alex nanoparticles, the mixture being non-homogeneous since the tungsten trioxide particles aggregate are arranged instead of covering the spherical Alex particles, and exist geometrically only punctiform contacts between the spherical particles.

in the second case, the Alex particles form agglomerates in the gel, instead evenly in the three-dimensional Distribute grid.

moreover is the cost of the metallic nanoparticles very high.

Thus, the nanometric aluminum particles of the type Alex (φ = 50 to 100 nm) are sold by the company Argonide in a price range of 0.37 to 1.50 $ .g ^-1 .

Nanotechnologies' aluminum Al-50-P (φ = 50 nm), which has better technical characteristics than Alex, is available for $ 3.5 to $ 10 .g ^-1 .

The term POWDERMET also discloses a process for encapsulating various particles which serve as a substrate into a metal disclosed by the American patent US 5,876,793 is protected and are applied to the metals in the vapor state to a particle fluidized bed. However, this method is not suitable for nanoparticles because they assemble on the one hand to agglomerates that can not be redissolved, and on the other hand, because they are entrained by a gaseous medium.

• – chemisch gesehen die inerte Aluminiumoxid-Schicht zwischen den Aluminium- und Metalloxid-Partikeln beseitigt werden kann;
• – geometrisch gesehen ein fortlaufender Kontakt zwischen den Oberflächen der reaktiven Materialien hergestellt werden kann, obwohl zwischen den kugeligen Partikeln lediglich punktförmige Kontakte bestehen;
• – hinsichtlich der Reaktionsfähigkeit die Empfindlichkeit der Thermite verringert werden kann, da sich die beschichteten Partikel untereinander wie Metallpartikel verhalten;
• – wirtschaftlich gesehen der Kostenaufwand für Aluminium, das für die Formulierung von Nanothermiten erforderlich ist, erheblich gesenkt werden kann.

The object of the invention is to find a solution to the disadvantages of the processes according to the current state of the art and thus to propose a process for the production of micro- or nanothermites, with which:

• Chemically, the inert aluminum oxide layer between the aluminum and metal oxide particles can be eliminated;
• - Geometrically, continuous contact between the surfaces of the reactive materials can be made, although there are only punctiform contacts between the spherical particles;
• - In terms of reactivity, the sensitivity of the thermite can be reduced because the coated particles behave with each other as metal particles;
• - Economically, the cost of aluminum required for the formulation of nanothermites can be significantly reduced.

• – eine erste Phase zur Herstellung einer Lösung aus einem Precursor des Reduktionsmittels, d.h. des Metalls bzw. der Metalllegierung, und in dieser Lösung dispergierten Mikro- und/oder Nanopartikeln des Oxidationsmittels;
• – eine zweite Phase zur Verdampfung dieser Lösung;
• – eine dritte Phase zur Thermolyse der Verdampfungsrückstände

auf den Partikeln des Oxidationsmittels.This object is achieved by a method for producing micro- and / or nanothermites by coating the particles of an oxidizing agent with a reducing agent consisting of a metal or a metal alloy, characterized in that this method comprises the following phases:

• A first phase for producing a solution of a precursor of the reducing agent, ie the metal or the metal alloy, and micro-particles and / or nanoparticles of the oxidizing agent dispersed in this solution;
• A second phase for evaporation of this solution;
• A third phase for the thermolysis of the evaporation residues

on the particles of the oxidizing agent.

According to one first embodiment for one more homogeneous solution The process also includes a phase for adding additives to the solution for one better dispersion of the precursor.

According to one second embodiment for one more homogeneous solution includes the method as well a phase for mixing the solution, for example by mechanical, magnetic, ultrasonic mixing or a combination these techniques.

According to one particular embodiment, the solution contains a organic solvent, such as e.g. Ether, or an inorganic solvent.

According to a particular embodiment, the particle dimensions are between 0.1 and 10 ⁶ nm, preferably between 1 and 1000 nm.

According to one another embodiment belongs the metallic reducing agent to the groups 1a, 2a, 3b, 4b, Lanthanides and actinides of the Periodic Table or preferably from one of the metals Li, Be, B, Mg, Al, Se, Y, La, Ti, Zr, Hf, Ta, Nd, Th, Zn, Pb and Sn or of an alloy with at least one the mentioned Metals.

According to another embodiment, the oxidizing agent (MO _x ) is a transition metal oxide of groups 6b, 7b, 8, 1b and 2b of the periodic table, the actinides or lanthanides, a vanadium, tin or lead oxide, a non-metal oxide, such as iodine, or a mixed oxide of at least one of said oxides.

According to one another embodiment the particles of the oxidizing agent have any or special geometric shape, for example a flat leaf shape, a compact spherical or cylindrical shape, a hollow tube, nanotube or hollow spherical shape.

According to one another embodiment In the second phase, the temperature of the solution is increased and / or the pressure, the the solution exposed, reduced.

According to a particular embodiment, the metallic reducing agent is aluminum and the oxidizing agent is tungsten trioxide (WO ₃ ) or molybdenum trioxide (MoO ₃ ).

The The invention also relates to a method according to the invention produced nanothermites, characterized in that they have a Decomposition temperature of less than 400 ° C.

Further Advantages and characteristics of the invention will become apparent from the description a particular embodiment the invention and the appended Figures show, wherein:

In 1 a transmission electron micrograph of commercial nanometric aluminum particles of the type Alex is shown.

In 2a and 2 B two scanning electron micrographs of the structure of an untreated n-WO ₃ powder and an aluminized n-WO ₃ powder produced by a method according to the invention are shown, wherein the observations were carried out with the same magnification factor.

In 3a . 3b and 3c three transmission electron micrographs, in connection with the qualitative energy-dispersive elemental analysis, the structure of untreated n-WO ₃ nanoparticles, produced by a process according to the invention aluminized n-WO ₃ nanothermites with Al = 3.6 and prepared by a method according to the invention aluminized n-WO ₃ nanothermites with Al = 1.6.

In 4 presented by means of differential scanning calorimetry (DSC) obtained curves of the decomposition of nanothermites. The first curve (a) shows the thermal behavior of a nanothermite prepared by the conventional method of physical mixing of n-WO ₃ and ^Alex® particles. The curves (b) and (c) each show the thermal behavior of the nanothermites Al = 3.6 and Al = 1.6, which are prepared by aluminizing n-WO ₃ with a method according to the invention.

In 5 Two electron microscope structure photographs are shown. The first scanning electron microscope (SEM) receptacle 5a shows crushed and subsequently sieved MoO ₃ particles (Φ <50 μm). The second transmission electron microscope (TEM) receptacle 5b shows the same particles which are coated with aluminum in a method according to the invention.

At the so-called. EOR method of coating the oxidant with a reducing agent the reducing agent is applied directly to the surface of the oxide particles. To is a precursor of the metallic reducing agent, e.g. a hydride, an alkyl or carbonyl derivative, and generally each Material from which the metal with the oxidation number zero is produced can, for the time being with the help of a solution, containing the precursor, in the oxide, however, not soluble is, on the surface the oxide particles applied. After evaporation of the solvent the precursor is subjected to a thermolysis, so that the metal is generated directly on the oxide particles. With this procedure the contact between oxide and metal is improved, with no Interface operations due to the oxidation on the surface the metallic nanoparticles occur more. The metal becomes homogeneous distributed because the entire surface, the with the solution comes in contact, is covered.

When using, for example, aluminum, the metal can be applied by means of thermolysis of a precursor, such as hydride AlH ₃ . This compound is obtained in an ether solution by a reaction in which a double decomposition takes place: AlCl ₃ + 3LiAlH ₄ → 4AlH ₃ + 3LiCl

In the previous and following description is a molecular, ionic or mixed liquid or liquid mixture as a solvent designated. The chemical composition of the solvent must be the dispersion of the precursor, so that either a true or a colloidal solution arises. The dispersion can be used directly or with the aid of additives for their introduction or triggering, such as. surfactants Substances are made.

For the experimental Implementation of the method, the metal oxide by mechanical, magnetic, Ultrasonic mixing or a combination of these techniques dispersed become. The dispersion can either be in a liquid before adding the Precursor solution or directly in this solution respectively. The solvent can be by evaporation, by sublimation or by a combination these two methods are withdrawn.

The Evaporation and sublimation can be spontaneous or, in particular by adjusting the temperature and pressure conditions are triggered.

MO_x:

Beschichtetes Primäroxid, dessen Reduktion anschließend durch das Metal M' beim Abbrand des Thermits erfolgt.

M':

Metallisches Reduktionsmittel, das als Beschichtung des Primäroxids MO_x dient und dessen Oxidation beim Kontakt mit dem Primäroxid MO_x beim Abbrand erfolgt.

M'O_x:

Sekundäroxid, das durch die Zersetzung des Thermits erzeugt wird.

M:

Metall aus der Reduktion des Primäroxids M'O_x durch das Metall M'.

Regarding the nature of the applied metal le and coated oxide particles, the entire decomposition reaction of a thermite should be considered: MO _x + M '→ M'O _x + M

MO _x :

Coated primary oxide, the reduction of which is then effected by the metal M 'during the combustion of the thermite.

M ':

Metallic reducing agent which serves as a coating of the primary oxide MO _x and whose oxidation takes place on contact with the primary oxide MO _x during combustion.

M'O _x :

Secondary oxide generated by the decomposition of the thermite.

M:

Metal from the reduction of the primary oxide M'O _x by the metal M '.

The metal M 'applied to the particles of the oxidizing agent must be sufficiently reducing to cause the oxygen atoms of the metallic primary oxide MO _x to move. In other words, from a thermodynamic point of view, the secondary oxide M'O _x formed on burning of the thermite must be more stable than the primary oxide MO _x . All oxophilic metals (groups 1a, 2a, 3b, 4b, lanthanides and actinides) and in particular the metals Li, Be, B, Mg, Al, Se, Y, La, Ti, Zr, Hf, Ta, Nd, Th and Zn , Pb and Sn can be used as the reducing agent (M '). The reducing agent may also be an alloy of several metals with at least one of the above-mentioned metals. All transition metal oxides of Groups 6b, 7b, 8, 1b, 2b of the Periodic Table of the Elements, the Actinoiden- and Lanthanoidenoxide and the vanadium, tin, lead and iodine oxides (non-metal) can be used as the oxidizing agent (MO _x ). In the context of the invention, mixed oxides can also be used with at least one of the abovementioned metallic elements. The metallic oxide particles may have any geometric shape. The size of these particles may be between 0.1 and 10 ⁶ nm, but is preferably 1 to 1000 nm.

Regarding The production of metallic oxide particles can be a method according to the invention for metallic Oxide particles independently used by the manufacturing processes used, too Examples of techniques include sol-gel, hydro- or solvothermal synthesis, direct or reverse micellar synthesis, Synthesis by burning, deflagration or detonation, off or co-precipitation, Duplicate method, evaporation, electrolysis.

According to a first embodiment WO ₃ nanoparticles were aluminized by a method according to the invention. Commercially available tungsten trioxide nanoparticles (chemical symbol n-WO ₃ , φ <50 nm) are dispersed under ultrasonic action in an ether solution of aluminum hydride. After evaporation of ether, a one-hour thermolysis of hydride in vacuo at a temperature of 120 ° C.

Structural characterization by scanning electron microscopy shows that the materials produced consist of nanoparticles. Thus, an untreated n-WO ₃ powder ( 2a ) and an aluminized n-WO ₃ powder produced by a process according to the invention ( 2 B ), the observations being made at the same magnification factor. The nanothermite consists of particles of larger dimensions than the underlying tungsten oxide. When observing particular areas, it becomes clear that the n-type WO ₃ particles are covered with aluminum, with the largest particles being nanocomposite materials.

In 3a . 3b and 3c are three transmission electron micrographs, in conjunction with the qualitative energy-dispersive elemental analysis, the structure of untreated n-WO ₃ nanoparticles, produced by a process according to the invention aluminized n-WO ₃ nanothermites with Al = 3.6 and by a method of the invention prepared aluminized n-WO ₃ nanothermites with Al = 1.6. It becomes clear that the WO ₃ nanoparticles ( 3a ) with a partially crystallized nanometric aluminum layer ( 3b . 3c ) are surrounded.

In 4 The DSC (Dynamic Differential Scanning Calorimetry) plots the decomposition of nanothermites. The first curve (a) corresponds to the thermal behavior of a nanothermite prepared by the conventional method of physical mixing of n-WO ₃ and ^Alex® particles. Curves (b) and (c) correspond respectively to the thermal behavior of the nanothermites Al = 3.6 and Al = 1.6, which are prepared by aluminizing n-WO ₃ with a method according to the invention. With regard to the energy released, the materials produced by a method according to the invention have standard characteristics for this type of material.

The required duration for ignition of a compact produced by pressing an EOR thermite of n-WO ₃ (n-WO ₃ : Al = 1.6) by means of a laser beam was examined. At a power density of 80 W.cm ^-2 , the ignition duration is more than 5 seconds, while at a power density of 1270 W.cm ^-2 a duration of only 12 milliseconds is observed. This non-linear behavior proves that the EOR material is a good heat sink and thus has a low sensitivity, but reacts very quickly when a large load occurs.

According to a second embodiment, MoO ₃ microparticles were aluminized by a process according to the invention. In this case, aluminum was applied with the EOR method according to the invention to comminuted and subsequently sieved molybdenum trioxide (φ <50 μm). Molybdenum trioxide consists of particles in the micrometer range as well as particles in the submicron and nanometer range with a strong anisotropy, giving them a needle shape, as in 5a shown, have. These smallest particles were observed under the transmission electron microscope. The MoO ₃ particles are then surrounded with an aluminum layer, wherein the Nanothermite produced in this way 5b are shown.

• – in Zünd- oder Anzündvorrichtungen,
• – als Mittel zum Temperaturanstieg in bestimmten Waffen,
• – für Mikroschweißverbindungen von metallischen Maschinenteilen.

The main planned application of this invention involves the production of pyrotechnic mixtures with high burn-off temperature, high energy density potential and controllable specific properties (ignition duration, burning rate, sensitivity). Subsequently, these mixtures can be used unchanged as follows:

• - in ignition or ignition devices,
• As a means of increasing the temperature in certain weapons,
• - for micro-welding connections of metallic machine parts.

to Increase their energy performance they can in conjunction with actual explosives are used.

With A method according to the invention can be and / or Nanothermite are made, which is an extremely homogeneous Mixture on a nanoscale scale between oxidizing and reducing phases, and may the presence of an oxidation layer on the surface of the metallic nanoparticles are avoided.

• – Die Steigerung der Festigkeit der metastabilen interstitiellen EOR-Verbundwerkstoffe, da sich die Verbundwerkstoffpartikel bei Auftreten einer Belastung untereinander wie einfache Metallpartikel verhalten.
• – Durch den guten mechanischen Zusammenhalt der Werkstoffe, der durch Pressen der metastabilen interstitiellen EOR-Verbundwerkstoffe erzielt wird, wird deren Formgebung und Anwendung erleichtert. Somit können sie unter mechanischen Belastungsbedingungen eingesetzt werden, ohne beliebige Bindemittel beifügen zu müssen.

The other advantages of such a method include:

• - Increasing the strength of the metastable EOR interstitial composites, as the composite particles behave like simple metal particles when loaded with each other.
• - The good mechanical integrity of the materials obtained by pressing the metastable EOR interstitial composites will facilitate their shaping and application. Thus, they can be used under mechanical stress conditions without having to add any binder.

Finally, aluminum used for the production of the metastable intermolecular compounds according to the EOR process has a much lower cost price than the commercial aluminum nanoparticles (0.1 EUR.g ^-1 instead of 0.37 to 10 $ .g ^{- 1} ).

Claims (10)

Method for producing micro- and / or nanothermites by coating the particles of an oxidizing agent with a reducing agent consisting of a metal or a metal alloy, characterized in that this method comprises the following phases: a first phase for producing a solution of a precursor of the reducing agent ie, the metal or metal alloy, and micro- and / or nanoparticles of the oxidizing agent dispersed in this solution; A second phase for evaporation of this solution; - A third phase for thermolysis of the evaporation residues on the particles of the oxidizing agent. Method according to claim 1, characterized in that that this method also a phase for mixing the solution, for example by mechanical, magnetic, ultrasonic mixing or a combination of these techniques. Method according to any one of the preceding claims 1 or 2, characterized in that this method also a Phase for the addition of additives to the solution for a better dispersion of the Precursors, such as e.g. surfactants Fabrics, owns. Method according to any one of the preceding claims 1 to 3, characterized in that the solution is an organic solvent, such as e.g. Ether, or contains an inorganic solvent. Method according to any of the preceding claims 1 to 4, characterized in that the particle dimensions are between 0.1 and 10 ⁶ nm, preferably between 1 and 1000 nm. Method according to any one of the preceding claims 1 to 5, characterized in that the metallic reducing agent to the groups 1a, 2a, 3b, 4b, lanthanides and actinides of the Periodic Table belongs or preferably one of the metals Li, Be, B, Mg, Al, Se, Y, La, Ti, Zr, Hf, Ta, Nd, Th, Zn, Pb and Sn or of an alloy with at least one of the mentioned Metals exists. A method according to claim 6, characterized in that the precursor of the metallic Re is a hydride, an alkyl or carbonyl derivative of the metallic reducing agent. Process according to any one of the preceding claims 1 to 7, characterized in that the oxidizing agent (MO _x ) comprises a transition metal oxide of groups 6b, 7b, 8, 1b and 2b of the periodic table, actinides and lanthanides, a vanadium, tin, Lead oxide or a non-metal oxide, such as iodine, or a mixed oxide of at least one of said oxides is. Method according to any one of the preceding claims 1 to 8, characterized in that in the second phase, the temperature the solution elevated and / or the pressure to which the solution is exposed is reduced. Process according to any one of the preceding claims 1 to 9, characterized in that the metallic reducing agent is aluminum and the oxidising agent is tungsten trioxide (WO ₃ ) or molybdenum trioxide (MoO ₃ ).