Fluorocarbon solid propellant with burning rate modifier

Abstract

Solid fluorocarbon propellant compositions containing burning rate modifi which have high structural integrity and a long storage life under varying environmental conditions.

Description

The invention described herein may be manufactured and used by or for the Government of the U.S.A. for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to improved solid propellants. A specific aspect relates to solid fluorocarbon propellants containing burning rate modifiers.

The fluorocarbon family of polymers has developed as excellent binders for composite solid propellants. Because of their high density, thermal stability, water impermeability, compatibility with a wide range of propellant ingredients, and high heat of reaction with metals, the fluorinated binders possess many desirable properties for propellant compositions. The propellants prepared with these binders have high structural integrity, long storage life, and good physical properties. The present invention provides a composition with increased burning rates, low pressure exponent or low temperature coefficient.

It is therefore an object of the present invention to provide a propellant with an improved burning rate for use in rocket motors and similar vehicles.

Another object is to provide a propellant with exceptionally high structural integrity and a long storage life under varying environmental conditions.

Yet another object is to provide an improved propellant composition which can be produced in large volumes at low cost.

Other objects and many attendant advantages of this invention will be readily appreciated as the same become better understood from the following description:

According to the present invention there is provided a propellant comprising up to 60 percent by weight of an oxidizer from 5 to 65 percent by weight of a binder consisting of a mixture of fluorocarbon polymers; up to 30 percent by weight metal fuel; and from 1 to 3 percent by weight chemical modifiers.

The oxidants which are applicable to the solid propellant of this invention are those oxygen-containing solids which readily give up oxygen and include ammonium, alkali metal and alkaline earth metal salts of nitric, perchloric, and chloric acids, and mixtures thereof. Ammonium perchlorate, potassium perchlorate, ammonium nitrate and hydrazine diperchlorate are preferred oxidizers for this invention.

The fluorocarbon polymers used in the composition consist of polytetrafluoroethylene (hereinafter referred to as Teflon) and a copolymer of vinylidene fluoride and hexafluoropropylene (hereinafter referred to as Viton-A) and mixtures thereof.

The high energy fuels preferred are aluminum, magnesium, zirconium, uranium, thorium, beryllium and mixtures thereof. These metals will usually have a particle size within the ranges of 1 to 100 microns.

The chemical modifiers preferred for the present composition consist of copper, lead, tin, sodium, ammonium and potassium fluoborates; sodium, potassium, lithium, lead, copper, and calcium fluorides; potassium and ammonium dichromate; lead and zinc stearate; cesium carbonate; potassium and ammonium sulfate; copper chromite; oxides of magnesium, copper and manganese; boron; zinc dust; and carbon black.

One convenient method, and the presently preferred method, of preparing this composition comprises, first, dissolving the Viton-A in a solvent selected from a low-boiling ketone; acetone was used. The Teflon and other ingredients (fuel, oxidizer and modifier) were then thoroughly mixed into the Viton-A solution to form a uniform slurry or suspension. The slurry was washed for from 5 to 10 minutes with hexane, the volume of hexane being from 1 to 4 times the volume of slurry. By this step the Viton precipitates onto the other solids in the slurry. After the suspension had settled, the supernatant hexane was decanted and the resulting residue was dried under ambient conditions for from 8 to 24 hours. The slurry may be washed with normal hexane 2 or 3 times, as necessary.

A general formulation for a propellant composition prepared in accordance with the invention is as follows:

Ingredients Percent by weight ______________________________________ Binder 5 to 65 Viton-A 10 to 15 Teflon 5 to 50 Oxidizer up to 65 Metal Fuel up to 35 Chemical modifier 1 to 3 ______________________________________

The following examples will serve to further illustrate the invention.

EXAMPLE I ______________________________________ Ingredients % by weight Function ______________________________________ Teflon 25 Binder Viton-A 15 Binder Aluminum 20 Fuel Potassium perchlorate 35 Oxidizer Sodium fluoride 2.5 Chemical modifier Potassium dichromate 2.5 Chemical modifier ______________________________________

The above ingredients were processed by the shock-gel technique described hereinbefore. The Viton is available in acetone solution for which an assay should be available. The solution should contain a minimum of 8 and a maximum of 22 weight percent Viton. All of the ingredients are added to a slurry pot. A volume of hexane equal to 4 times the volume of the Viton solution is placed in a container. While stirring the slurry, hexane is added slowly and mixing continues for about 15 minutes. The Viton is precipitated or shock-gelled onto the solids in the slurry. The supernatant hexane is siphoned off and an additional volume of fresh hexane, equal to the first volume, is added. Again, the supernatant hexane is siphoned off and the resulting composition is collected in a cloth bag and dried in a drying oven for from 8 to 24 hours at approximately 140.degree. F. Some of the material was extruded into strands for burning tests. This composition showed a burning rate at 1000 psi of 0.298-inch per second and a pressure exponent of 0.61.

EXAMPLE II ______________________________________ Ingredients percent by weight Function ______________________________________ Teflon 15 Binder Viton-A 15 Binder Aluminum 25 Fuel Potassium perchlorate 43 Oxidizer Sodium fluoride 2 Modifier ______________________________________

The Viton-A is dissolved in acetone. To this solution the Teflon, aluminum, potassium perchlorate and sodium fluoride were added and mixed for about 10 minutes forming a slurry. The slurry was washed with hexane (4 volumes of hexane to 1 volume of Viton solution) for 10 minutes. The resulting mixture was let settle and hexane was siphoned off. The residue was washed with an additional volume of hexane for about 5 minutes. The supernatant hexane was again siphoned off, the composition collected in a cloth bag and dried. This material extrudes well. It showed a burning rate at 2000 psia of 0.63 inch per second and a pressure exponent of 0.53.

EXAMPLE III

The following three samples (a, b and c) using 300 grams each of the product prepared in Example II were modified with boron and copper chromite:

(a) Ingredients Weight in grams ______________________________________ Composition of Example II 300 Boron 6 ______________________________________

About 300 grams of the cured composition prepared in Example II were placed in a small sigma-blade mixer. The boron was suspended in about 100 ml of hexane, then poured into the mixer and thoroughly stirred for about 10 minutes. The product was transferred to a stainless steel container and dried overnight. Strands were extruded for burn rate determination.

______________________________________ (b) Ingredients Weight in grams ______________________________________ Composition of Example II 300 Copper chromite 6 ______________________________________

The above ingredients were processed in the same manner as described in (a) above.

______________________________________ (c) Ingredients Weight in grams ______________________________________ Composition of Example II 300 Boron 3 Copper chromite 3 ______________________________________

The boron and copper chromite were stirred into hexane, and the process proceeded as described hereinabove. Burn strands were extruded for burning rate determination.

Burning rate results for these three compositions are as follows:

(a) .98 in/sec; pressure exponent .68 (b) .68 in/sec; pressure exponent .60 (c) .81 in/sec; pressure exponent .62

EXAMPLE IV ______________________________________ Ingredients Percent by weight Function ______________________________________ Teflon 16.3 Binder Viton-A 16.3 Binder Potassium perchlorate 65.2 Oxidizer Sodium fluoride 2.2 Chemical modifier ______________________________________

The Viton was dissolved in acetone and all the ingredients were stirred therein for about 10 minutes forming a slurry or suspension. The suspension was dropped into rapidly agitated hexane and stirred for 10 minutes. (About 4 volumes of hexane to one of Viton solution). After letting the composition settle out, the hexane was siphoned off. The composition was washed again with hexane which was decanted and the material was collected and dried. Some of this composition was extruded for burn rate determination.

EXAMPLE V ______________________________________ Ingredients Percent by weight Function ______________________________________ Viton-A 15 Binder Teflon 15 Binder Potassium perchlorate 49 Oxidizer Aluminum 18 Fuel Zinc(dust) 2 Modifier Sodium fluoride 1 Modifier ______________________________________

These ingredients were processed as those in the previous examples. Burn strands formed from this composition showed a burning rate at 2000 psi of 0.74 inch per second and a pressure exponent of 0.77.

EXAMPLE VI ______________________________________ Ingredients Percent by weight Function ______________________________________ Viton-A 15 Binder Teflon 15 Binder Potassium perchlorate 49 Oxidizer Aluminum 18 Fuel Cupric oxide 2 Modifier Sodium fluoride 1 Modifier ______________________________________

Strands of this composition gave a burning rate at 2000 psi of 0.68 inch per second and a pressure exponent of 0.82.

EXAMPLE VII ______________________________________ Ingredients Percent by weight Function ______________________________________ Viton-A 15 Binder Teflon 15 Binder Ammonium perchlorate 49 Oxidizer Aluminum 18 Fuel Lead 2 Modifier Sodium fluoride 1 Modifier ______________________________________

Strands were extruded of this composition which gave a burning rate at 2000 psi of 0.76 inch per second and a pressure exponent of 0.78.

EXAMPLE VIII ______________________________________ Ingredients Percent by weight Function ______________________________________ Teflon 51 Binder Viton-A 15 Binder Magnesium 31 Fuel Cupric fluoride 3 Modifier ______________________________________

The ingredients were processed in accordance with the prior samples and strands were extruded for burning rate determination.

EXAMPLE IX ______________________________________ Ingredients Percent by weight Function ______________________________________ Viton-A 14.7 Binder Teflon 4.9 Binder Zirconium 36.9 Fuel Ammonium perchlorate 41.5 Oxidizer Magnesium oxide 2.0 Modifier ______________________________________

The same basic ingredients consisting of Viton, Teflon, Zirconium, and ammonium perchlorate used in this sample were modified with 2`% by weight each of the member selected from manganese dioxide, cellulose acetate, dibutyl tin maleate, potassium sulfate, potassium dichromate, lithium fluoride, lead fluoride, and potassium acid tartrate. These modified fluorocarbon compositions were all extruded into strands and the burning rate determination were made.

EXAMPLE X ______________________________________ Ingredients Weight in grams ______________________________________ Composition of Example II 300 Copper fluoroborate 8 ______________________________________

Since the fluoroborate used herein is hygroscopic, it is mixed into the basic formulation immediately prior to extrusion. Strands were extruded and burned with double dipped Viton inhibitor.

The above examples clearly demonstrate the effectiveness of the chemical modifiers on the fluorocarbon propellants which have great potential in the missile field today.

As will be evident to those skilled in the art various other modifications of the invention can be made, or followed, in view of the above disclosure, without departing from the spirit or scope of the invention.

Claims

1. A solid propellant composition consisting essentially of the following:

2. A solid propellant composition consisting essentially of the following:

3. A solid propellant composition consisting essentially of the following:

4. A solid propellant composition consisting essentially of the following:

5. A solid propellant composition consisting essentially of the following:

6. A solid propellant composition consisting essentially of the following: