GB2278840A

GB2278840A - Pyrotechnic bodies

Info

Publication number: GB2278840A
Application number: GB9311513A
Authority: GB
Inventors: Sek Kwan Chan
Original assignee: ICI Canada Inc
Current assignee: PPG Architectural Coatings Canada Inc
Priority date: 1992-06-08
Filing date: 1993-06-03
Publication date: 1994-12-14
Also published as: CA2097995A1; JPH06199588A; EP0576161A1; ZA933881B; KR940005523A; GB9311513D0

Abstract

Pyrotechnic bodies comprise a combination of an azide component and an oxidizer component capable of controlled combustion. The average azide particle size is less than 8 microns and the average oxidizer particle size is less than 1 micron. The bodies are useful for vehicle gas bag inflation.

Description

PYROTECHNIC BODIES Background The present invention is directed to the manufacture of pyrotechnic bodies of a particular dimension to provide more efficient combustion.

This art knows about the combinations of certain pyrotechnic materials to provide combustion for a variety of purposes. U.S.

patent 3,931,040 discloses compositions of sodium azides and metal oxides to form a composition found advantageous for combustion purposes. Therein, the invention was directed toward the production of nitrogen for use in lasers. U.S. patent 4,021,275 discloses a similar combination of azide, oxide, and nitrate combinations to produce gas generated for safety air bags. U.S.

patent 4,376,002 discloses a combination of azide, metal oxides, and a residue control agent for the production of nitrogen gas.

A continuing problem in this art is the production of some composition of pyrotechnic wherein the pyrotechnic reaction ingredients advance toward complete combustion. Heretofore, mixing methods have produced bodies with erratic and uncontrolled metal azide/metal oxide surface coverage. The product generally contained disproportionate metal oxide dispersions on the surface of the metal azide. The present discovery advances this art by directing those skilled in this art toward a means of integral juxtaposed reactant placement within a combined body. By appropriate placement of the reactants about a fixed body, the pyrotechnic of the present invention provides a pyrotechnic body of controlled combustion. A pyrotechnic structure comprised of the pyrotechnic bodies may then be combusted by a means known by those skilled in this art with the desired burn rate.

The pyrotechnic of the present invention is found useful in the fast production of gas for use in an air bag safety restraint system in automobiles, trucks, buses, and/or any other vehicles wherein safety air bags may be found useful. Additionally, military uses, such as gas generating systems for ballasts would be a useful application. Any system, such as gases generated for lasers, which would require the quick production of a gas would find the present invention useful.

Brief Description of the Figure The Figure shows a typical scanning electron micrograph of the pyrotechnic body.

Summary of the Invention A pyrotechnic body comprising an azide-oxidizer redox couple components wherein said redox couple produces an exothermic reaction, said azide component comprising average particle sizes of less than about 8 microns in its longest crystal dimension and said oxidizer comprising average particle sizes of less than about 1.0 micron in diameter. The azide component present in the pyrotechnic body comprises 40 to 90 weight percent of the body, preferably 60 to 70 weight percent and most preferably 64 to 66 weight percent.

The average particle size is less than about 8 microns in length in its longest crystal dimension, preferably less than 5 microns, and most preferably less than 3 microns. The azide is usually combined with a metal or salt of a metal. The metal must be an oxidant capable of interacting in a redox couple with an oxidizer.

Preferably the metal is either an alkali metal and/or an alkaline earth metal. In particular the metal azide combination consists essentially of sodium azide, potassium azide, lithium azide, calcium azide and/or barium azide, most preferably sodium azide.

The oxidizer is comprised of an element or elements of the first, second, and/or third transition series elements of the Periodic Chart. The oxidizer may be a single species of the transition series or may be some combination thereof and/or therebetween. Preferably, the oxidizer and/or slagging agent is a metal oxide from the first transition series and/or second transition series such as but not limited to iron, nickel, vanadium, copper, titanium, manganese, zinc, tantalum and/or niobium oxides, and other oxides such as silicon and/or aluminum, most preferably the metal is a species from iron oxides and/or silicon oxides.Metal oxides are the preferred genus of the present invention, it is contemplated, however, that other generic groups are operable herewith such as the carbonates, sulfides, sulfites, oxalates, halides, in particular chloride, and nitrides and are within the scope of the present invention. A limit of the oxidizer component in its application to the azide is its solubility characteristic in an aqueous solution. However, the limit of operability of the oxidizer component in said body combustion performance is the promotion of the reaction of the companion component of the azide as it is coupled to the oxidizer component.Essentially, the scope of the present invention includes any reduction/oxidation interaction otherwise known to those skilled in this art as a redox couple, whereby an exothermic reaction is produced by the azide/oxidizer redox couple and said reaction is sufficient to sustain the combustion of the azide.

The oxidizer component is generally spherical dimensionally, however, spherical geometry is not required. Of the geometries produced as the oxidizer component, on the average the shortest dimension is no greater than 1.0 micron, preferably no greater than 0.5 microns and most preferably no greater than 0.2 microns. The longest dimension of the oxidizer component is not critical to the present invention. Geometries such as platelets, spheres, needles, fibers, and variable geometries may be advantageously combined with the azide component. Spheres are the preferred geometry.

Particle sizes were measured by a Brinkmann 2010 PSA (particle size analyzer) Sybron Corp. Westbury, N.Y.. The average size was a distribution measured from about 0.5 up to about 30 microns with a mean size of less than 8 microns. Normally in the preferred embodiments the azide component averages for the particle size show consistent particle size measurements in the 1 to 3 micron range.

The oxidizer component is integrally juxtaposed and/or in communication with the azide component. The juxtaposition and/or communication may take a variety of forms, including a core/shell form and a continuous and/or a discontinuous layer encapsulating the azide. Preferably, the azide is evenly coated with the oxidizer. The azide is usually the core in any core/shell combination. In such combination the oxidizer and azide comprise the body. The body may take the form of platelets, spheres, needles, fibers, and other geometrical shapes. Once the body is formed a plurality of bodies are combined by a forming means to make a structure. The structure may then be used as a final product.

In its most general form, at least one species of the oxidizer component must be present. This requirement is simply to provide a complete redox couple and to provide a complimentary component to communicate with the azide. Communication means that the two components physically interact in some manner so that when combustion initiates there is a continued reaction between the two components. It has been observed that combinations of metal oxides provide excellent body components for the production of operable and preferred bodies. In particular, combinations of iron oxide and silicon oxide are preferred embodiments for the oxidizer component. However, both the iron oxide and/or the silicon oxide may be used individually in the absence of the other, in a preferred embodiment.The oxidizer component should be present from about 10 to 60 weight percent, preferably 30 to 40 weight percent and most preferably 34 to 36 weight percent. Of the combined iron oxide and silicon oxide components it is preferred that the iron oxide range is O to 60 weight percent, most preferably 20 to 30 weight percent. The silicon oxide is preferred in O to 50 weight percent, most preferably 5 to 15 weight percent.

The present preferred combination is about 65 weight percent sodium azide (NaN3), 25 weight percent iron oxide (Fe2O3),and 10 weight percent silicon dioxide (SiO2).

In its most general form, the method of combining the azide and oxidizer components is by a wet chemistry technique. The wet chemistry is generally known to those skilled in this art as a coprecipitation. The invention hereof, while taking advantage of coprecipitation techniques, actually precipitates a saturated solubilized component with a colloidal suspension and subsequently provides a means for the separate components to combine in a body form. Specifically, the inventive step in the method of producing this invention is the means of providing communication in the pyrotechnic body. This means may be accomplished by chemical precipitation techniques, preferably the dispersion is accomplished by mechanical mixing means to insure dispersion of the colloidal solution and henceforth the thorough mixing of the two component system.Finally, the precipitation is effected by mixing the aqueous solution with an alcohol. Other alcohols that are operable for the purposes of the present invention are ethanol, iso propanol, methanol, n-propyl alcohol. Ketones such as but not limited to acetone are operable as well.

A method of making pyrotechnic bodies comprises the steps of a) combining an azide component in a saturated first solution with a suspension of a single or a plurality of oxidizer components in a vessel by mechanically mixing, b) discharging said first solution as a controlled spray, c) precipitating said combined azide component and oxidizer component with a second solution, d) forming a pyrotechnic body. Any means for controlling a spray may be used in the above method such as a spray nozzle, atomizer, or some pressurized system. It is preferred when controlled mixing that the atomizing means achieves particle sizes from about less than 12 microns to preferably about 7 microns. Particle sizes are measured in diameter. It is preferred that a spray nozzle be used. The second solution in the above method is preferably an alcohol, most preferably isopropyl alcohol.

The above pyrotechnic bodies may be made into structures to make the final manufactured product. Any pressing or forming technique may be used such as a hydraulic press, mechanical press, extrusion techniques or any means of pressing the bodies into a unified structure.

Description of Embodiments The following examples are disclosed to further illustrate the above invention and are not intended to limit the scope thereof.

EXAMPLE 1 In Example 1, 800 grams of analytical grade NaN3 per 2000 grams of distilled water were combined to obtain a saturated solution of NaN3. 134 grams of Fe203(R-1599D grade, 0.2 micron particle size, obtained from Harcros Pigments, Toronto Canada) and 48 grams of Cab-O-Sil fumed silica (0.014 micron particle size, obtained from Cabot, Shakerheights, Ohio) were mixed with the saturated solution and vibrated in an ultrasonic bath to form a dispersed colloidal suspension. The solution is contained and constantly stirred, then pumped under pressure of 20 psi in "Jetmixer" as the mixing process is described in U.S. patent 4,911,770, incorporated herein by reference, through a nozzle (obtained from Spraying Systems Company, Wheaton, Ill) of 1.6 mm diameter at a rate of 0.5 liters per minute into a mixing chamber.

4 liters of isopropyl alcohol was pumped into the mixing chamber at 1 liter per minute to form an aqueous/alcohol mixture. The mixture was passed through a 1 micron fiberglass filter. The filtered cake was dried in a steel jacketed vessel producing the pyrotechnic bodies as a powder. The Figure shows a typical scanning electron micrograph of the pyrotechnic body.

The powder was mixed with 4 weight percent water (in the form of a mixture of Tullanox (obtained from Cabot, Shakerheights, Ohio) and water. The powder was pressed into a mold to form pellets of 6.4 mm by 6.4 mm by 25.4 mm dimension and dried. The pellets had a density of 1.93 grams per cubic centimeter. The pellets were coated on all sides except one with an epoxy thermoset. The pellets were placed in a high pressure vessel and pressurized to an initial pressure of 1000 psi with nitrogen. The pellets were ignited at the uncoated end by a squib and the linear burn rate was measured. The burn rate was measured at 47 mm per second.

EXAMPLE 2 Example 2 was prepared as Example 1, except that the iron oxide was needle shaped synthetic red iron oxide (Grade 403, average particle size 0.4 microns, Harcros Pigment, Toronto, Canada). The burn rate was measured at 43 mm/s.

EXAMPLE 3 The slurry was mixed as in Example 1, except that isopropanol was poured directly into the slurry without any applied pressure.

The filtered cake was treated the same as in Example 1 to give the powdered pyrotechnic body.

The pellet was pressed to a density of 2 g per cc. The linear burn rate was measured at 44 mm/s.

EXAMPLE 4 40 grams of sodium azide, 16.4 grams of iron oxide (R-1599D), and 5.6 grams of silicon oxide (Cab-O-Sil fumed silica) were mechanically combined and ball-milled. The pellet pressed from the ball milled powder had a density of 2.0 g/cc. The resultant linear burn rate was 39 mm/s.

EXAMPLE 5 In Example 5, the same amount of sodium azide, iron oxide, and silicon oxide were mixed as in Example 4 with 110 ml of water. The mixture was then dried in a steam jacketed vessel. The pellet pressed from the dried powder had a density of 1.93 g/cc. The resultant linear burn rate was 29 mm/s.

The linear burn rate indicates the efficiency of the combustion process. The higher the linear burn rate per mm/s, the more efficient the combustion process. It is noted that the invention hereof shows an increase linear burn rate of 62%.

Claims

I CLAIM:

1. A pyrotechnic body comprising azide-oxidizer redox couple components wherein said redox couple produces an exothermic reaction, said azide component comprising average particle sizes of less than about 8 microns in its longest crystal dimension and said metal oxide comprising average particle sizes of less than about 1.0 microns in diameter.

2. The body in claim 1 wherein said azide component is combined with metals and/or the salts thereof selected from the group consisting of an alkali metal, an alkaline earth metal and/or some combination thereof and/or therebetween.

3. The body of claim 2 wherein said metal is sodium.

4. The body of claim 1 wherein said oxidizer component is combined with metals selected from the group consisting of iron, silicon, nickel, vanadium, copper, titanium, manganese, aluminum, zinc, tantalum, niobium, some combination thereof and/or therebetween.

5. The body of claim 1 wherein said oxidizer component consists of iron oxide, silicon oxide, and/or some combination thereof and or therebetween.

6. The body of claim 1 wherein said azide component dimension is less than 5 microns.

7. The body of claim 1 wherein said azide component dimension is less than 3 microns.

8. The body of claim 1 wherein said oxidizer component dimension is less than 0.5 microns.

9. The body of claim 1 wherein said oxidizer component dimension is less than 0.2 microns.

10. The body of claim 1 wherein said azide component comprises 40 to 90 weight percent and said oxidizer component comprises 10 to 60 weight percent.

11. The body of claim 1 wherein said azide component comprises 60 to 70 weight percent and said oxidizer component comprises 30 to 40 weight percent.

12. The body of claim 1 wherein said azide component comprises 64 to 66 weight percent and said oxidizer component comprises 34 to 36 weight percent.

13. The body of claim 1 wherein said oxidizer component is in communication with said azide component.

14. The body of claim 11 wherein said oxidizer component is 0 to 60 weight percent iron oxide or 0 to 50 weight percent silicon dioxide and some combination thereof and/or therebetween.

15 The body of claim 14 wherein said oxidizer component is 20 to 30 weight percent iron oxide and 5 to 15 weight percent silicon dioxide.

16. The body of claim 1 wherein a plurality of said body are combined to form a structure.

17. The structure of claim 16 wherein said structure is combined with an air bag safety restraint system.

18. A method of making pyrotechnic bodies comprising the steps: a) combining an azide component in a saturated first solution with a suspension of a single or a plurality of oxidizer components in a vessel by mechanically mixing, b) discharging said first solution as a controlled spray; c) precipitating said combined azide component and oxidizer component with a second solution, and d) forming a pyrotechnic body.

19. The method of claim 18 wherein said controlled spray is formed by a nozzle.

20. The method of claim 18 wherein said second solution is isopropyl alcohol.

21. The method of claim 18 wherein said controlled spray achieves a particle size of from about 7 to about 12 microns.