|Publication number||USH717 H|
|Application number||US 07/243,539|
|Publication date||Dec 5, 1989|
|Filing date||Sep 12, 1988|
|Priority date||Sep 12, 1988|
|Publication number||07243539, 243539, US H717 H, US H717H, US-H-H717, USH717 H, USH717H|
|Inventors||William D. Stephens, Larry C. Warren|
|Original Assignee||The United States Of America As Represented By The Secretary Of The Army|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (12), Classifications (11), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalties thereon.
In line with the Army's continuing efforts to minimize hazards associated with propellant formulations used in its missile systems, a replacement propellant formulation has been sought that reduces some of the hazards associated with ammonium perchlorate propellants that use certain modifiers or additives such as 2,2-bis(ethyldicyclopentadienyliron)propane (also known as the trademark material Catocene) to enhance or increase propellant burn rate. Iron-containing compounds are now the current choice as burn rate enhancers for ammonium perchlorate propellants. Of these iron-containing compounds, ferrocene and its derivatives are the most efficient.
Earlier work with propellants containing solid iron compounds gave inconsistent burn rate enhancement because of the difficulty of getting a homogeneous mixture. Thereafter, liquid iron compounds were sought since it was believed that liquids would be better for mixing purposes. This plan of action lead to the development of bis(ethyldicyclopentadienyliron)methane, registered under Trademark Hycat 6D. Hycat 6D migrated readily within the solid propellant producing unsatisfactory propellant properties. Hycat 6D has a total of six alpha hydrogens (hydrogen adjacent to aromatic ring). It is known that hydrogens adjacent to aromatic ring systems are susceptible to oxidation to form acids and/or hydroperoxides. Hydroperoxides are known to be highly unstable compounds.
Since the alpha hydrogens were believed to be the reason for long term oxidation problems, Catocene was developed by coupling two ethylferrocenes with acetone, thus replacing the two bridged hydrogens with two methyl groups. Catocene then became the choice as a burn rate accelerator for ammonium perchlorate-based propellants. By replacing the two bridged hydrogens with methyl groups, long term oxidation and migration problems were reduced. However, accidental ignitions of solid propellants containing Catocene have occurred in both freshly prepared and aged propellants.
Therefore, the current status of Catocene in light of the concern for safety, where accidental ignition has been a problem for both freshly prepared and aged propellants, has motivated the development of a dicyclopentadienyliron compound that performs at the level of Catocene while having improved safety characteristics.
Therefore, an object of this invention is to provide a solid propellant composition which employs a dicyclopentadienyliron compound as a burn rate enhancer while retaining improved safety characteristics for the propellant formulation as compared with Catocene employed in a similar propellant formulation.
The solid propellant formulation of this invention employing 2,2-bis(t-butyldicylopentadienyliron)propane (TBD) as the burn rate enhancer yields higher threshold values for ignition by impact and improved friction and spark testing values to thereby render the solid propellant formulation less hazardous to personnel during handling. TBD solid propellant formulations also give improved results of the desired pressure exponent, potlife, and maximum stress characteristics when compared to similar solid propellant formulation containing Catocene.
The improved solid propellant composition having the properties described above is comprised of TBD as a burn rate enhancer in amounts from about 2 to about 6 weight percent, of about 68 weight percent of ammonium perchlorate of a trimodel blend of 200, 1.7, and 0.7 micron particle size, of aluminum powder of about 18 weight percent of a burner of hydroxyterminated polybutadience of about 9 weight percent, of an isocyanate curing agent as an additive of about 1 weight percent, and solid propellant processing aids in trace amounts.
The solid propellant composition set forth below under Example illustrates the use of TBD as a burning rate enhancer with the formulation ingredients in weight percent.
______________________________________ WEIGHT WEIGHT PERCENTINGREDIENT PERCENT RANGE______________________________________Binder1,4 9.0 9-10TBD2 5.0 2-6Aluminum powder 18.0 18-20Ammonium Perchlorate3 68.0 66-70______________________________________ Notes: 1 Hydroxyterminated Polybutadiene (HTPB) binder system including an isocyanate curative as an additive up to about 1 weight percent. 2 TBD concentration can be varied from 2-6% to give the desired burn rate. 3 The ammonium perchlorate is a trimodal mix of particle sizes 200, 1.7, and 0.7 microns. 4 Other additives, isocyanate curatives and modifiers can be added i small quantities with adjustment of the percent of content of other ingredients as required for desired performance.
This formulation in above Example is mixed, cast, and cured by techniques and methods that are commonly used in the industry and that are known by personnel skilled in the art of propellant formulations.
The use of this solid propellant formulation is applicable to any program where there is a need for high burn rates and improved safety characteristics.
The structural formulae (A and B) of Hycat 6D, and Catocene, respectively, are presented below for comparison with TBD; the structural formula (C) for TBD is also presented below. Hycat 6D was a good burn rate enhancer, but was susceptible to long term oxidation. Hycat 6D also yielded poor results with respect to migration properties. Hycat 6D has a total of six alpha hydrogens (hydrogen adjacent to aromatic ring). It is believed that hydrogens adjacent to aromatic ring systems are suscepticle to oxidation to form acids and/or hydroperoxides. Hydroperoxides are known to be highly unstable compounds.
Catocene was the next compound developed which showed early promise of meeting the burn rate enhancer requirement; however, it too had problems related to stability in spite of replacing two bridged hydrogens with two methyl groups as discussed below.
Since the alpha hydrogens were believed to be the reason for long term oxidation problems, Catocene was developed by coupling two ethyferrocenes with acetone, thus replacing the two bridged hydrogens with two methyl groups. Catocene became a choice as a burn rate accelerator for ammonium perchlorate-based propellants. By replacing the two bridged hydrogens with methyl groups, long term oxidation and migration problems were reduced. However, accidental ignitions of propellants containing Catocene have occurred in both freshly prepared and aged propellants. Hence, the need for TBD was established.
The purpose of the work relating to TBD is to synthesize a compound that has no alpha hydrogens. TBD does not have hydrogens on carbon adjacent to the aromatic ring structure; therefore, long term oxidation and reduced problem of migration are among the benefits derived. TBD was synthesized and a propellant mix was evaluated and compared to a similar mix containing Catocene. ##STR1##
During the development program for TBD in solid propellants, several areas of interest were evaluated to determine the properties of a solid propellant composition containing TBD as compared to one containing Catocene.
The areas of interest evaluated are summarized in Table I. Sensitivity Results; Table II. One-Gallon Mix Data; and Table III. Pint Mix Preliminary Ballistic Data as follows:
TABLE I______________________________________SENSITIVITY RESULTS Cured Sensitivity Impact Spark FrictionMix No. Percent Catalyst (lb-cm) (joules) (lb)______________________________________27 (TBD) 6 78 0.125 6029 (TBD) 5 66 2.25 6030 (TBD) 5 60 1.00 5031 (TBD) 5 72 4.00 9032 (TBD) 0 74 25 9049 (TBD) 6 78 1.00 ND1-gallon (TBD) 5 74 6.25 80Catocene Mix 5 48 1.00 50______________________________________
TABLE II______________________________________ONE-GALLON MIX DATACatalyst (%) TBD 5% Catocene 5%______________________________________EOM Viscosity, KP 3 4Potlife to 40 Kp, Hr 16.4 14NCO/OH 0.89 0.89Maximum Stress, psi 423 251Strain at Max. Stress, 28 35percentTangent Modulus 1893 812Burn Rate @ 1000 psi 3.12 3.19 @ 2000 psi 4.20 4.33Pressure Exponent 0.43 0.46______________________________________
TABLE III______________________________________PINT MIX PRELIMINARY BALLISTIC DATA Burn Rate @ 1000 2000 PressureMix No. % TBD (psi) (psi) Exponent______________________________________27 6 2.95 3.98 0.4429 5 3.22 4.33 0.4330 5 3.20 4.25 0.4231 5 3.20 4.25 0.4232 0 0.46 0.98 0.72 (1.00 @ 2000 psi)49 6 3.50 4.78 0.45______________________________________
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|U.S. Classification||149/19.2, 149/19.9, 149/19.4, 149/113, 149/20|
|International Classification||C06B45/10, C06B23/00|
|Cooperative Classification||C06B23/007, C06B45/10|
|European Classification||C06B45/10, C06B23/00F|
|Oct 2, 1989||AS||Assignment|
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:STEPHENS, WILLIAM D.;WARREN, LARRY C.;REEL/FRAME:005149/0744;SIGNING DATES FROM 19880901 TO 19880906
Owner name: UNITED STATES OF AMERICA, THE, AS REPRESENTED BY T