Explosion-Time Test of Double-Base Powders D. R.WIGGAM AND E. S. GOODYEAR, Hercules Powder Co., Wilmington, Del. F THE s p e c i f i c a t i o n s sample to explode. If explosion BY CAREFUL control of the method of placed on smokeless has not occurred a t the end of heating it is possible to obtain fairly accurate powder there are none 5 hours, the tube is removed check results in the explosion-time test. more stringent and important and the test reported as 300f The absence of stabilizer from a powder forthan those covering the chemical minutes. mula is not detected by the explosion-time test, stability. Uany of the stability Data obtained on a series of tests are based on measurement samples are given in Table I, and this is not a function of the amount of of traces of acidic products of deand, for comparative purposes, nitroglycerin in the powder. M u n y salts lower composition. These p r o d u c t s data are given on surveillance the lest markedly without lowering the storage life. may react as a sensitive suband methyl v i o l e t tests. By Other salts have no effect. The eflect seems to be stance impregnated in an absorbthese two tests all of the powders limited to salts of the uni-univalent type, such as ent paper, as in the case of the would be considered satisfacAbel test, the methyl violet test, tory, yet a number of t h e m potassium nitrate. Metallic oxides increase 2he exploded in less than 5 hours. and the litmus test. If the test explosion test without improving the storage When only one test is given in is carried on at t e m p e r a t u r e s stability of the powders. Powders which were the last column of the tables, above 100" C. the sample is rendered unstable by long heating in a closed the value is the average of two commonly allowed to remain in container gave satisfactory explosion tests. closely a g r e e i n g r e s u l t s . It the test bath until brown fumes will be shown in a subsequent of nitrogen t e t r o x i d e develop. A s the explosion test does not measure the true The time for this result to be atpaper that the surveillance test stability of double-base powders, it is of no value tained is noted, or the products is of much g r e a t e r value for in deciding their chemical condition. m a y be a b s o r b e d in various judging the stability of doubleliquids and determined subsebase powders than the methyl quently by suitable means. The test may be carried out in a violet test, which detects only seriously decomposed powders. closed container at an elevated temperature and the time It will be noted that in some cases there is an utter lack of determined for visible fumes to develop above the powder agreement in the explosion time. This is due chiefly to differsample (surveillance test). Other methods based on the ences in heat conductivity from the powder to the bath liquid. rate of pressure development in a closed system have been In one case the heat of decomposition is dissipated to the bath proposed. Finally, a test in general use in this country more quickly than in the other. The poor heat conductivity depends on the determination of the time for a powder sample allows the sample to heat to its ignition temperature more to explode when heated at 134.5' C. It is probable that no rapidly. When a neutral paraffin-base oil was used in the single test is entirely satisfactory for judging the condition of a wells surrounding the tubes (Bath A, Table 111), better agreegiven powder for chemical stability. The comparative value ment in the results was obtained.2 A special oil bath was of the various tests for double-base powders1will be considered built, heated by an immersed resistance coil and controlled in another place; it is the purpose of this paper to point out by a thermostat to *0.05" C. This closely controlled bath the entire inadequacy of the explosion-time test for judging (Bath B, Table 111) gave no more concordant results than the chemical stability of nitroglycerin powders. the A. S. T. M. bath when oil was used in the wells of the From a study of methods of measuring stability of smokeless latter. powder, principally with those of the single-base type, Sy TABLE I. COMPARATIVE STABILITY DATA 2),gavethe following limits for the explosion time at 135" C.:
0
Uncolloided nitrocellulose, no explosion in 5 hours Nitrocellulose powders, no explosion in 5 hours Nitroglycerin powders, no explosion in 5 hours In the case of uncolloided nitrocellulose and nitrocellulose powders, these limits should be met, as it is well known that insufficiently stabilized nitrocellulose-i, e., nitrocellulose retaining traces of combined sulfuric acid-is very sensitive to heating a t this temperature. Powders made from such nitrocellulose will, of course, be unstable. However, i t will be shown thstt double-base powders made from well-stabilized nitrocellulose may give explosions in considerably less time than 5 hours and still be perfectly stable, in the usual sense, when certain chemically inert substances are added to the powder formula. It is unfortunate that tests based on the work of Sy are still used in this country for double-base powders. In conducting the test, 2.5 grams of powder are weighed into a glass test tube 15 mm. inside diameter and 29 cm. long, with tube walls 1.5 mm. thick. The tube is placed in an A. S. T. M. (1) heat-test bath and the time noted for the 1 Double-base powders refer to those containing nitrocellulose and nitroglyoerin as the chief ingredients.
NO.
2 4 6 20 lo 32 40 50 78 79 80 81
NITROGLYCERIN
KNOi
Ba(NOs)t . ,
%
%
%
25 25 25 25 25 35 30 30 30 30 30 30
0.81 0.38 0.45 0.57 0.59 0.50 0.50 0.40 0.50 0.60 0.50 0.50
1.01 0.88 1.06 1.31 1.16 1.50 1.50 0.97 1.50 1.50 1.50 1.50
SURVEIL-METHYL VIOLET
EXPLOSION
LANCIAT
AT
53 91 55 71 52 44
17 17 14 13 14 14
TIMUAT 134.5' C. Min. 170 300+ 160; 300+ 300 f 300+ 300+ 162; 300f 300 150 163; 300f 150 150
78' C. 134.5' C. Days Min. 52 17 82 17 17 68 58 17 60 17 56 16
+
A study of the effect of varying powder composition is given in Table 11. I n this case paraffin oil was used in the wells. When even small amounts of potassium nitrate are added to the formula, the explosion time is decreased markedly, although the methyl violet and surveillance tests indicate satisfactory stability. When diphenylamine was omitted from the formula, the surveillance test dropped to a low value, 2 The oil uaed inside the wells should not be oonfused with the heating mixture of xylol and toluene used in the body of the bath. The latter is kept at its boiling point in order to maintain the bath a t constant temperature. The paraffin oil merely replaoes the air between the outside of the glass test tubes and the inside of the brass wells.
ANALYTICAL EDITION
78
Vol. 4, No. 1
exists between potassium and barium nitrates. The chlorides give sensitive powders in the case of sodium and potassium, but not in the case of strontium. Sulfates have a smaller effect than either the nitrates or chlorides. The oxides lead TABLE11. EFFECTOF VARYINGPOWDER COMPOSITION METHYL EXPLO-SURYBIL- to powders which are quite insensitive, probably because of DIVIOLET SION LANCE absorption of the acid products of decomposition. The inNITROPHENYLAT TIMEAT AT clusion of such large amounts of basic oxides is not to be No. GLYCERIN KNOBBa(N0a)z AMINE 134.5' C. 134.5' C. 78' C. Days Min. Min. % % % % recommended, as powders so produced usually prove unstable 0 0.1 16 300+ 34 952.1 40 0 by the surveillance test. 0 0.5 15 140 23 1060.1 40 2
yet in the absence of potassium nitrate the powder would be considered stable by the explosion-time test.
.
673.3 673.7 673.10 679.17 951.1 953.1
40 40 40 40 40 40
0.5 0.5 0.5 0.5
1.8 1.5 1.5 1.5 0 0
0
4
0.75 0.75 0.75 0.75 0 0
15 15 13 15 15 15
36 34 33 47 5 7
150 146 157 119 300+ 150
TABLE111. EFFECT OF TYPEOF BATH ON 40 PERCENT NITROGLYCERIN POWDERS (Explosion test) BATEA
LOT No. 146 165 166 167 168 170
Min.
BATHB Min.
347+ 267 276,258 347% 322 347 355% 317, 3454-
385 268, 247, 289 380, 385+ 313 285 362' 347, 378 291: 298
+
TABLEIV. EFFECTOF VARIOUSADDITIONAGENTSON EXPLOSION TEST (40% nitroglycerin powders; N. C. = 59.25% (Nz = 13.08); diphenylamine = 0.75%)
No. D-32 D-40 D-42 D-43 D-44 D-48 1137 1138 1117 D-53 1116 D-59 D-57 1113 El-55 - . D-58 D-49 D-36 1136 D-50 D-51 D-52
ADDEDSUBSTANCE % KClOa KClOs KClOs KClOs
.
KMnO4
KMnOd Ba Mn04)n Ba!NOs)i
KNOa
NaNOs KC1 NaCL SrCln
KzSOi
MgSO4 KnCRnO7 MnOz
SnOz Fez03
1 2 3 4 4 2 2 2 4 2 4 4 2 4 4 4 4 2 4 4 4
METHYL EXPLOSION TIME VIOLET AT 134.5' C. Min. M i n. 19.5 22 20 21.5 21.5 9.5 9 12 17 20.5 17 14 20.5 14 22 13 20.5 18 18.5 16.5 19.5 22.5
247; 265 191 125 124 123 29 184; 192 300 300 80: 85 190: 212 135. 134 97: '94 300 174; 177 260; 245 250 300 300 296 300+ 300
++
OF TABLE v. EFFECTOF VARYINQ PROPORTIONS POTASSIUM NITRATEAND FERRIC OXIDE
(40% nitroglycerin powder)
No.
KNOB
%
%
915.1 916.1 959 960 965 966 967 920.1 918 817 919.1
4 2 0.5 0.25 0.10 0 0 3.5 3.0 2.0 1.0
0 2 3.5 3.75 3.90 4.0 0 0.50 1.0 2.0 3.0
TABLEVI. EFFECTOF HOTSTORAGE (78' C.) EXPLOSION TIMEAT 134.5' C. BEFORE HEATING NITROQLYC-
NO.
1
From the preceding it is evident that the amount of nitroglycerin contained in the powder is not the controlling factor in this test. A number of salts and oxides were incorporated in a series of 40 per cent nitroglycerin powders. The data on these powders are given in Table IV. It is well known that traces of acid will cause failure of the powder in any of the stability tests. It was first thought that minute traces of decomposition products of 'the salts were responsible for the low explosion tests obtained. However, this view is untenable when it is recalled that many of the compounds were salts of strong acids and strong bases. Such compounds are extremely stable to hydrolysis and so would not develop either acid or base on heating to 135" C. The action of each salt on the test seems to be specific. The explosion test of D-32, made without added substance, is the result to which the other tests are referred. Potassium chlorate has a marked effect in lowering the test, and in amounts greater than 2 per cent the effect is not additive. If the effect of this compound were due to acidic decomposition, one would expect the test to fall off markedly with increase in amount. Two, three, and four per cent did not produce this result. When potassium permanganate is added, a powder of very low explosion test results. On the other hand, barium permanganate seems to be without effect. A similar relation
METHYL EXPLOSION DIPHINYL-VIOLET AT TIMEAT AMINE 134.5O C. 134.5' c. % Min. Min. 0 15.5 150 157 0 15.5 151.155 0 15.5 2021 230 0 15.5 235. 240 0 14.5 2941315 0 14.5 410: 420+ 0 14.5 318;333 0.50 16.5 130; 133 0.50 16.5 150; 160 0.50 17 157; 165 0.50 16.5 163; 165
As potassium nitrate is a common oxidizing agent added to smokeless powders and, as it has a very definite effect in lowering the explosion test, it was of interest to determine the effect of relatively small amounts of this ingredient (Table V). The total added substance amounted to 4 per cent, being made up of a mixture of potassium nitrate and iron oxide. Potassium nitrate in an amount as small as 0.10 per cent has a distinct effect. The addition of diphenylamine as stabilizer does not give a powder of longer explosion test, although it improves the surveillance test several hundred per cent. Potassium nitrate has been added to powders for many years, and records of this laboratory do not show a single case of such powders failing because of lack of stability.
+
++ +
FenOa
2 4 5
Q
E1RIN
%
30 30 40
30 Brown
Me yl viott at Explo134.5' c. 81011
ON
AFTER HEATINGO
TIMH~Methyl
Violet HEAT- at SALT ING 134.5' c. Min. Min. Days Min. % 0.5 KNOa 14 130 93 1.5 Ba(N03)z 14 130 94 5 15 300$ 89 6 20 300f 92 5.5 fumes showed above powders in test bottles. OF
Explo81011
Min. 73 101 300+ 300+
Some powders which had been stored a t 78" C. until brown fumes were noted in the bottles above the powders were tested by the methyl violet and explosion tests (Table VI). Even after this severe treatment the explosion test did not distinguish between good and bad powders. Powders which were obviously unstable gave satisfactory explosion tests. Such a test is unsafe to use.
LITERATURE CITED (1) Am. SOC.Testing Materials,, "Tentative Standards," p. 1075 (1930). (2) Sy, J . Am. Chem. Boc., 25, 550 (1903). RECBIVED July 29, 1931.
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