US3009796A - Gas-producing compositions of smokeless powder and metal compound inhibitors - Google Patents

Description

3,009,796 GAS-PRODUCING COMPOSITIONS LESS POWDER AND METAL COMPOUND IN- HIBITORS Ralph F. Preckel, Frostburg, Md., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy No Drawing. Filed Mar. 8, 1.951, Ser. No. 214,629 .1 Claim. (Cl. 52-5) The present application is a continuation-in-part of my copending application entitled, Gas-Producing Charge, Serial No. 102,427, filed June 30, 1949, now abandoned, and as'in the case of said previously filed application, the present invention relates to smokeless powders and more particularly to smokeless powders having ballistic characteristics peculiarily desirable for application in jet actuated devices.

'It is well known that there is a definite and direct relationship between the pressure at which a smokeless powder propellant burns and its burning rate. This relationship may be mathematically expressed as r=cp or as log r=n log P+log c, where r is the burning rate, P is the pressure at which the burning rate is measured, and c and n are constants characteristic of a given propellant. Thus, when a plot of log r against log P is made for the conventional propellant, a straight line of slope n is ob tained showing an increase in burning rate for each increase in pressure. Such a relationship is not disadvantageous in the conventional propellant, and in fact is used to advantage in progressive powders where it is highly desirable to generate increased pressures after the projectile or shot charge has begun to move-along the barrel. However, this relationship presents a serious problem in formulation of propellants for jet-actuated devices, since once the desired operating pressure is reach, totally different considerations obtain.

It is highly desirable, once the operating pressure of a 'jet-actuated device is reached, that the pressure generated by the burning propellant be maintained as nearly constant as possible. Accordingly, if this result is to be attained, the slope n of the line representing the pressureburning rate relationshipv of the particular propellant should preferably approach zero in the zone of useful rocket pressure. In the prior art rocket powders, in all of 'which the slope n has a value of 0.7 or over, any fracturing or slivering'of the propellant charge leads to a pressure build-up because of an increase in linear burning rate resulting from the increase in pressure due to the increase in burning surface." The higher then value of the particular powders, the higher will be the pressure rise encountered. Therefore, the results of such a fracturing or slivering vary from a highly undesirable thrust fluctuation, with consequent aberration in ballistics, to actual failure of the jet device if, as with a propellant of high It value, the pressure build-up is excessive. Even unusual roughness of the charge causes serious changes in burning pressure and burning rate in the presently available rocket propellants, with the result that errors of 1% in the nozzle diameter have been found to buildup to an aberration of'- 5 or more in ballistics. Consequently, with the propellant's now available, there is 'very little allowable tolerance in manufacture of charges and nozzles for jet devices. A propellant having a very low n value within therange of useful rocket pressures, however, would allow for considerable tolerances without appreciabledeviation from the specified ballistics, and accordingly any decrease in ;n value would accordingly enhance the value of a particular propellant.

' A second serious problem confronting producers of propellants for jet-actuated devices is the diminution of the temperature coefiicient of equilibrium pressure at the OF SMOKE- 3,009,796 Patented Nov. 21, 1961 desired operating pressure or pressure range. The temperature coefficient of equilibrium pressure is a measure of the pressure variation to be expected from a given propellant on account of temperature variation alone. It is obtained by firing identical samples of propellant under identical conditions except for changes in temperature and pressure. The coeificient may be expressed as perature range ordinarily specified for such devices in field use.

Since existing propellants generally have temperature coeificients of equilibrium pressure of about 0.8% C. or more, service pressure may change by 100% or more in going from the lowest expected temperature (about 55 C.) to the highest expected temperature (about C.). It is therefore highly desirable to lower the temperature coefficient of equilibrium pressure below' that of existing rocket propellants and thereby hold variations in service pressure due to temperature changes to a minimum. If the coefiicient could be lowered from 0.8%/ C. to 0.4%/ C. or less, service pressure variation would be diminished by at least one half, and similarly any lowering of this temperature coefiicient would correspondingly enhance the value of the propellant.

As a result of the advantages set. .forth above fora propellant having a low n value and/or a low temperature coeificient of equilibrium pressure, either or both of these two ballistic characteristics would allow for important economies in the inert weight of jet actuated devices. This is clearly seen if the equation is examined which relates the ratio between the mass of propellant (m) and the mass of the jet device without propellant (M), the gas velocity of the burning propellant (V), and the highest theoretically obtainable velocity of the jet device (V as follows:

V lOgm With propellants now available, the highest ratio of m/M has been about 1, wheremass of propellantand mass of jet device are about equal. If it is possible, by use of a new propellant which does not build up excessive pressures, to decrease M by 10% and increase the amount of propellant to give the same total initial weight, V would be increased by a factor 1.1 gic (1+ or about 1.15. This would beat 15% improvement.

Therefore, an object of the present invention is the production of propellants for jet-actuated devices which are characterized by low burning rate-pressure relationships throughout a wide pressure region within the range of useful rocket pressures.

A further object of this invention is the production of propellants for jet-actuated devices which are characterized by low temperature coefficients of equilibrium pressure, thus minimizing variations in service pressure due to temperature.

The previously mentioned copending application is directed to smokeless powder propellant explosives which haveincorporated therein atleast one material selected from the group consisting of lead and compounds of lead,

and which have heats of explosion of not more than about 900 calories per gram. As there described the addition of these materials to said propellants causes a substantial reduction in the n value and the temperature coefiicient of tion by uniformly incorporating therein minor amountsof niany other metals and compounds of metals, as more specificaly set out hereinbelow, provided these compositions of propellant and modifier have heats of explosion of not more than about 900calories per gram. As pointed out in detail in the earliermentioned applicationwith specific reference to the lead and compounds of lead moditiers, the smokeless powders to which these ballistic'modi- 'fiers are added may be either single or multiple base a powders. If the-smokeless powder to which one or more of the ballistic modifiers is added is a single-base powder, it should preferably comprise fromf85 to 95% nitrocellu- V lose and from to plasticizer. if the propellantused in a multiple-'base-formula, it shouldpreferably comprise from 40 to 85% nitrocellulose, from 10 to of an explosive liquid ester, and from 5 to 30% of a substantially nonvolatile nonexplosive plasticizer. In any formulation, however, his critical that the heat of explosionfof the additive system be not greaterthan about900 calories per gram. -For, as shown in said previous application, Where formulations have heats of explosion in excessof said i amount, the additiveballistic modifiers lose a considerable amount of their effectiveness in. suppressing the n value and the temperature coeificient of equilibrium pressure in 7 cases where the latter suppression is eifected. As further pointed out in said application, the heats of explosion of 'ValiOfiS formulations can be readily calculated byione skilled in the art to determine whether the formulations are isuita-ble for the purposes of the; present invention. Smokeless powder propellants prepared in accordance various operable additives maybe employed without ad- .versely arfectingithe ballistics ofthe gas produci'ng comwhen indicated modifiers-are added thereto 1n amounts stated.

' Modifier Temp; Pressure coef. of 7 Y Heat of Low-- regionoi pressure Ex. Amt, explosion est n lowest 11. in region Typo pereaL/g. p.s.i. of lowest -centn per- 7 centl O;

0.7 0. 0.5 0.3 1,4003;000 0. 2.0 0.2 l,'500'3,300 0. 4.0 0.2 .l,4003,600 0. 1.0 0.3 1, 000-2, 000v 0. 1.0 0.2 1,300-13800 1 0. 1.0 0.3' 2, 000-2, 400, I 0. 1.0. a 0-2 Lane-2,400. j Q7 0.5 0.3 Loco-2,350 q 0. 1.0 0.3- LOGO-2,500 V 0. 2.0 0.2 1,3002,000 .0. 1.0 0.7; l,3002,000 .0.

1 0 695 0 3 1,?500-1'650 0.4 1 0 695 0 3 l,7502,900 0'3 1 0 695 g 0 6 00-2000 1.2 1 0 695 0 5 -1,3002,000 0.7 1 0 695 0 4 LEGO-2,400 0.6; 1 0 695" 04 1,300-2200 0.3 1 0 695 0 4 'l,5002,250- 0.9

(subcarr g V bon'ate).- j 20-. Arr'rgiorphous. 1.0 695 0.4 2500 .4,000 0. 21;; Mo p'wd.. .i. 1.0 695' 0.4 LOGO-2,600 0. 22 U505 (uraib, 1.0 695 0.4; 6201,350 0.

, ium oxide). v 23-; BaCO;4 1.0 695 0.4 1,100'2,000 0. 24 1.0 695 0. 4' 1, 400-1, 900 0. 1.0 695 0.5 1,200%2,700 .0. 1. 0 695 0. 5' l, 100 1, 900 0. 1.0 695 0.5 l,3002,750 0. 1.0 695 0.5 100 500 l. 1.0 -695' 0:6 1,500 2;500 0. l. 0 695 OI 5 1, 2502, 200 0. g r 1.0 :695 0.5 v .',60,0-2',,0oo 0. a 0. 5 700 0. 5 1350 3, 100v 0. 33.. TiOz 1.0 "695' 0. 5' 1,000-4,0 00 l. 34.. Spwd- .1.0 695 0. 5 300- 890 1. 35.- Di utyltin "1.0 680 0.5,- 200- 600 0. r -diacetate./ I i,

positions -of the invention, however, it is preferred to em ploy only s'ufiicient amounts of additives to effect the desired modification in ballistics. In most cases it has been weight of the smokeless powder employed, is ample.

fouricl that 2% of the various additives, based on the Having now generally described the invention, the following table presents a' plurality of examples' of ballistic modifiers which when employed iii-accordance with the present invention provide substantial decreases in the n value of smokeless powder propellant explosives, and, as

e'quilibriuni'.pressure.' This tableindicates the hea t of explosion, lowest 71, pressure region of lowest n,and temperature c'oefiici'ent of pressure in region of lowest n for a standard rocket propellantcomposition having the follow a binitrotoluene will be noted, some instances alsofeffect a substantial reduction in the prop'ellants temperaturecoefiicient of 'From the examples' given in the fore going table, iit

is apparent that although all of the ballistic modifiers there disclosed are operable in lowering -n value, range of variations in'geifectonn value and ontemperaofapartieular modifier employed. These facts; provide for. considerable flexibility in employing the teachings of the present invention, enabling a wide choice of modifiers and amounts thereof based p11 economic considerations as well as theballistics desired for aparticular application I of the invent-ion. By reference to the foregoing table,

one skilled in. the art can readily determine the nature and amount I ofxmodifier appropriate [for accomplishing the desired ballistic modifications Manyexamples of propellant powder formulationsfoundto respondas indicated to additions of .small percentages of said modifiers have been disclosed in my copending lapplication above- I identified, and furthermore, said application 'clearly dis-" closes the general principles and criteriafor: determining whethenornot .a particular propellant powder respond inrthe manner indicatedin the; f regoing description of the present invention. a

r The foregoing -.spec ific examples [of modifiers amounts of modifiers employed, and'theparticula'r propel lantpowder formulation indicated are presented merely by way of example, to clearly indicate the nature and significance of the resent invemim. Msaificatnns'ef these details will be apparent re mor skilled in the v art, and such modifications as are the spirit and scope of the present invention as defined by the appended claim are within the contemplation of the present patent.

What is claimed is: i

The method of diminishing the n value and temperature coeflicient of equilibrium pressure of a double base rocket propellant in a pressure region suitable for operation of a rocket device, said propellant comprising 40 85% nitrocellulose and 10-35% nitroglycerine and having a heat of explosion not to exceed 900 calories per gram, comprising uniformly dispersing throughout said composition a ballistic modifier selected from the group consisting of silver and silver oxide in quantities adequate to obtain the desired reduction in said It value and temperature coeflicient but not to exceed 10% by weight of said propellant, wherein the n value of said propellant is the slope of the plot of the log of the burning rate (r) against the log of the pressure (p) at which the burning 6 rate is measured, and the temperature coefiici'ent is equal to AP/gTAt wherein AP is the diflerence in pressures due to the temperatures change Ar and 17 is the meanof the pressures.

References Cited in the file of this patent UNITED STATES PATENTS 1,336,463 Henning Apr. 13, 1920 1,357,865 Henning Nov. 2, 1920 1,943,421 Burns et a1 Jan. 16, 1934 1,963,116 Burns et a1. June 19, 1934 2,038,700 Woodbridge Apr. 28, 1936 2,131,352 Marsh Sept. 27, 1938 15 2,344,840 Watt et a1. Mar. 21, 1944 FOREIGN PATENTS 621,685 Great Britain Apr. 14, 1949