US 3259531 A
Description (OCR text may contain errors)
United States Patent 3,259,531 PROPELLANT WITH AMMONIUM PERCHLORATE- PERMANGANATE LATTICE OXIDIZER Robert T. Lofberg, Kensington, Md.,'assiguor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware N0 Drawing. Filed Apr. 30, 1963, Ser. No. 277,036
5 Claims. (Cl. 1492) This invention relates to a unique, activated oxidizer for use in solid propellant formulations and to the method for preparing said oxidizer.
An oxidizer ingredient often used in the formulation of solid propellants is ammonium perchlorate to which various catalysts or burning rate accelerators, such as potassium permanganate, are added in order to increase the grain burning rate. In the past, it has been the practice to incorporate the finely divided accelerators or catalysts in the binder phase of the propellant grain. A homogeneous distribution has been difficult to achieve in the binder. Moreover, the catalytic additive often adversely affect the curing characteristics of the binder.
In accordance with the present invention, an ammonium perchlorate oxidizer is provided wherein its rate of combustion is substantially increased by means of an accelerator or catalyst which is an integral part of the crystalline structure of the oxidizer.
It is, therefore, an object of the present invention to provide an oxidizer for solid propellant formulations having greater uniformity in burning rate than has heretofore been possible.
Another object of this invention is to provide an activated oxidizer for a solid propellant wherein the oxidizer incorporates a burning rate accelerator as an integral part of the crystalline structure of the oxidizer.
Other objects and features of the invention will be apparent from the balance of the specification.
To produce the activated oxidizer of the present invention, ammonium perchlorate and a small quantity of sodium permanganate are dissolved in heated water; the resulting solution is then chilled to effect precipitation of a unique crystalline material believed to he, basically, ammonium perchlorate containing a small quantity of per manganate anion in the crystal lattice in lieu of the perchlorate anion whereupon the permanganate ion acts as a burning rate accelerator. The resulting ammonium perchlorate-permanganate compound can be represented as follows:
( 4( 4)1 4) wherein y amount of perchlorate is replaced by permanganate in the crystalline make-up of the compound.
If the rhombohedral crystal lattice of ammonium perchlorate is considered as being comprised of ions of NH,+ and C105, the crystalline structure of the unique ammonium perchlorate-permanganate of Formula 1 can be viewed as being comprised of a quantity of positive ions of NH, and an equal quantity of negative ions comprised of C; and MnO With the catalytic permanganate as an integral part of the crystalline structure of the oxidizer, it is significantly more effective than when the permanganate, in the form of potassium permanganate, for example, is mixed in with the binder having only incidental contact with the ammonium perchlorate. Moreover, it has been found that the permanganate in this form does not adversely affect the curing process of the binder.
The amount of sodium permanganate required to place a given percent by weight of permanganate anions in the ammonium perchlorate crystal lattice is calculated by the following equation:
3,250,531 Patented July 5, 1966 The sodium ions in the solution formed by dissolving sodium permanganate and ammonium perchlorate are not compatible to the rhombohedral structure of ammonium perchlorate and appear to be retained in solution without entrainment to any substantial degree within the crystalline material. After separation, the crystalline ammonium perchlorate-permanganate is dried, ground, and used to prepare a solid propellant grain in the conventional manner.
By heating the thus prepared ammonium perchloratepermanganate to a temperature a few degrees below the decomposition point, the purple coloration disappears and a highly activated brown form of the compound is produced. This change probably introduces extreme strain into the lattice, particularly in the transformation between orthorhombic and cubic structures.
In order that one skilled in the art may practice the present invention, the following example sets forth in detail the method for preparation of a typical preferred formulation. The ingredients which are necessary to formulate a solid propellant grain are as follows:
In order to prepare the ammonium perchlorate-permanganate 50 grams of substantially pure sodium permaganate trihydrate is dissolved in three liters of water and heated to C. for several hours and filtered. A quantity of 1,125 grams of ammonium perchlorate is then added to the hot solution and stirred vigorously until the ammonium perchlorate is completely dissolved. The solution is then chilled in an ice-salt bath and the crystalline precipitate is then removed by filtration. This crystalline material, which is the activated oxidizer of the present invention as set forth in the Formula 1, is then dried at C. and ground in a micropulverizer to form a finely divided powder.
Methyl nadic anhydride, copper chromite, triethyleneglycol dinitrate, and polybutadiene acrylic acid are placed in a single blade mixer maintained at 60 C. and mixed until substantially homogeneous. Aluminum powder is then added as the fuel constituent and permitted to mix until uniformly dispersed. The mixer is then stopped and the activated oxidizer of ammonium perchlorate-permanganate as prepared above is added, as well as the conventional ammonium perchlorate. After mixing for an additional three minutes, vacuum is applied for 15 minutes. The diopoxide is added and the mixing is continued under vacuum for an additional 15 minutes. The solid mix is then cast by pouring into molds and vibrating to remove entrapped air bubbles. The propellant is cured by maintaining at 60 C. for 48 hours.
Upon ignition of the above propellant, a regression rate of approximately 0.67 inch per second resulted at a combustion pressure of 1000 pounds per square inch. In a propellant prepared in identically the same manner but substituting ordinary ammonium perchlorate for the ammonium perchlorate-permanganate, a regression rate of 0.61 inch per second at 1000 pounds per square inch resulted, a regression rate over 9 percent less.
To achieve varying degrees of activity in the oxidizer, the quantity of sodium permanganate used or the temperature of the water meployed may be adjusted accordingly.
It is obvious that the activated oxidizer of the present invention, comprised of a compound of ammonium perchlorate-permanganate can be used in conjunction with a large variety of binders and fuels to produce a solid propellant grain. Consequently, various modifications are contemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention as hereinafter described by the appended claims as only a preferred embodiment of the present invention has been disclosed.
Having thus described the invention, what is claimed is:
1. An oxidizer for use in a solid propellant grain comprised of ammonium perchlorate and ionic permanganate substituted for a predetermined quantity of the perchlorate in the ammonium perchlorate crystal lattice.
2. A new composition of matter comprised of ammonium perchlorate and ionic permanganate forming a coherent crystal lattice.
3. A method for producing highly activated propellant oxidizer having a distinctive crystalline structure comprised of dissolving said oxidizer in a compatible solvent, dissolving in said solvent a second crystalline material having an ion which is catalytic to said oxidizer and cooling the water solution to precipitate crystals of said oxidizer having coherently interspersed therein ions of the catalytic material whereby a highly activated oxidizer results thereby.
4. A method for producing highly activated ammonium perchlorate comprising dissolving a predetermined quantity of ammonium perchlorate in water, dissolving a predetermined quantity of sodium permanganate in said water, and cooling said water solution to precipitate crystals of ammonium perchlorate having catalytic ions of permanganate integral with the crystal lattice of said ammonium perchlorate.
5. A solid propellant formulation comprised of an oxidizer phase consisting of ammonium perchlorate and ionic permanganate substituted for a predetermined quantity of the perchlorate in the ammonium perchlorate crystal lattice in combination with conventional solid propellant constituents.
References fitted by the Examiner UNITED STATES PATENTS 792,511 6/1905 Frank l4976X LEON D. ROSDOL, Primary Examiner.
CARL D. QUARFORTH, BENJAMIN R. PADGETT,