Stability Test of Nitroglycerin-Nitrocellulose Smokeless Powder D. R. WIGGAM AND E.
s. GOODYEAR, Hercules Powder Company, Wilmirigton, Del.
I
N A RECEKT article Lenze double-base powders of varying DESCRIPTIONS are ginen of Jive stability and Metz (9)have discussed nitroglycerin content and varitests for double-base powders. Modifications the value of various staous age. were made in the method and apparatus for bility tests used for single-base . In all of these tests there is carrying out the Taliani test, which made the test powders.' A few powders of some v o l a t i l i a a t i o n of nitrosomewhat simpler to operate. widely varying s t a b i li t y were glycerin, as is shown by the dechosen and compared. It could pendence of the results on the SpeciJications are given f o r a division between be concluded from their data that nitroglycerin content of the stable and unstable powders by the surneillance, a good powder and a bad powder powders. Nevertheless, certain B. J . M . tests. If a single test is Taliani, and were distinguishable readily by of the tests afford a useful method run preference is gicen to the Taliani test. almost any of the ordinary tests. for didtinguishing between good However, it is suggested that a surveillance test T h e r e l a t i v e value of various and bad powders with a fair detests has also been very ably gree of reliability. be made on questionable powders. discussed by de Bruin ( 5 ) . Up All the tests were somewhai dependent on the to the present, no single test has DESCRIPTION OF TESTS nitroglycerin content of powders, the Taliani test, been found to be entirely satishoweeer, being least aflected. factory for judging the probable SURVEILLANCE T E sT . T h e life of a Dowder. surveillance test was carried In the'case of double-base powders, the problem is compli- on a t 78" C. Forty-five grams of the powder were weighed cated further by the volatility of nitroglycerin during the test. into a dry flint-glass 8-ounce (0.23-liter) bottle which had If a low temperature is used in order to obviate this difficulty, been carefully cleaned by washing with acetone and ether, the time required for testing the powder is too great to be of followed by long steeping in boiling distilled water. The practical significance. The "trace tests," such as the Abel glass stoppers were ground to fit with emery slime. The ( I ) and Guttmann (8) tests, in which a sensitive paper is used bottles were placed in a deep double-walled oven provided to detect! the first evolution of nitric oxide, are carried out at with a close-fitting lid. Alcohol was used as the heating liquid a fairly low temperature, but are of doubtful value for gelati- and was maintained at the boiling point by means of a steam nized powders. The quantitative determination of the coil in the liquid. A condenser at the top of the jacket preproducts of decomposition at ordinary temperatures, as in vented loss of the alcohol. The samples were examined daily tests proposed by Chiaraviglio and Corbino ( 6 ) and Pollard and were removed when brown fumes were observed above (IO), have the advantage that the powder is tested under the powder. normal temperature conditions, but it cannot be recommended It \vas found advisable t o use a temperature of 78" C . for general use because of the elaborate apparatus required instead of the usual 65" C., in order to obtain dependable reand the high technic necessults. The variation in test sary to obtain accurate rebetween duplicate samples a t sults. 65" C. was so great that a Of the quantitative tests clear differentiation between the methyl violet, surveilsamples was not always poslance, B e r g m a n n - J u n k sible. Further, the time reM a y r h o f e r (4, and Taliani quired to carry on a test a t ( 1 2 ) may be mentioned as be66" C. is too long for a pracing representative of those tical test. most free from objection. No TALIANI TEST.The prospecial technic m u s t be accedure and a p p a r a t u s were quired to carry on the tests, modifications of those proa very desirable characterisposed by Taliani. A doubletic for control purposes. The walled copper bath, provided products of decomposition rewith a double door, was built main in contact with the pow(Figures 1 and 2). A glass der during the course of the window was built into each tests. These tests, together door, and directly in line with with the Abel test a t 82.2" C., these a double glass window have been used in this investiwas built into the back wall gation for examination of the of the bath. This permitted c o n d i t i o n of a number of an unimpaired view of the c a p i l l a r y tubing inside the I In conformity with general terminology in this oouritry, single-base bath. A well, 1.25 inches powders refer to powders in which (3.17 cm.) in diameter and 2 the main constituent is nitrocelluinches (5.08 cm.) deep, was lose Double-base powder8 include welded into the bottom of the those made of nitrocellulose and nitroglycerin as the mair. constituents. bath. Between the outer FIGURE 1. TALIANI TESTBATH I
73
74
ANALYTICAL EDITION
and inner walls of the bath, a mixture of glycerin and water, boiling at 120" * 0.3" C., was used. The sample is placed in a special test tube (Figure 3) to which is attached a U-bend containing Nujol (a high-boiling neutral paraffin oil). The capillary is attached to a pressure cylinder, which is connected through a needle valve t o the service air line. The pressure cylinder is provided with a
FIGURE 2. DIAGRAM OF TALIANI TEST BATH
gage by means of which the pressure in the apparatus is followed. I n the early part of the work the seal between the test tube and the cap was made by a ground-glass joint. This arrangement, used by Taliani, was unsatisfactory because of leaks through the joint. This was obviated by use of a mercury seal inside the tube. When covered by a small amount of Nujol, the mercury remained unattacked during the test. The tube was tied to the cap by tightly drawn wires secured to projections. In the original Taliani capillary, a stopcock was attached to the tube above the cap to carry off moisture and air evolved in the first part of the test. This stopcock was found to be a continuous source of uncertainty during the latter part of the test when the pressure increased to several pounds. The stopcock has been eliminated and any moisture the or air is allowed to escape thro end of the preliminary heating, t ugh and the open end of the capillary. capillary to the point B is exactly 12 cc. As it is difficult to see a mark etched on the capillary a t the point B, horizontal lines are etched on the glass in the door of the bath and in the glass window in the rear wall. By controlling the pressure in the cylinder, the level of Nujol can be brought in line with the two marks. All powders are well dried over calcium chloride and sodium hydroxide before testing. One gram of powder is weighed into the test tube, The tube and capillary, tied together as described above, are introduced into the bath, the outlet of the capillary passing through an opening in the top of the bath, the test tube resting in the well of the bath. The space between the test tube and the well is filled with Nujol to improve heat transfer. After exactly 30 minutes' heating, a few drops of Nujol are introduced into the top of the capillary and the connection made to the pressure cylinder by rubber tubing. Air is turned into the pressure cylinder until the Nujol thread is forced to the point B (Figure 3). The reading of the gage is taken as the zero reading and is subtracted from all succeeding readings. As the,pressure builds up in the powder tube, it is equalized by admitting air to the pressure cylinder. Readings of time and pressure are taken at each 0.5 pound pressure increment. Plots of some representative data are
Vol. 4, No. 1
given in Figure 4. The test is reported as the time required for the pressure to increase 8 pounds above starting pressure. When the test is completed, the pressure is released from the tank through a needle valve and the rubber tubing disconnected. BERGMANN-JUNK-MAYRHOFER TEST. The usual Bergmann-Junk stability tubes as described by Worden (14) are used. Instead of the special bath described by Worden, an A. S. T. M. bath (2) is used. The decomposition tube is immersed in the bath within 2 inches (5.08 em.) of the top. The adsorption cup is surrounded by a shield to avoid undue cooling of the short connection between the cup and the decomposition tube. Eergmann and Junk have recently called attention to this source of error (3). The bath temperature was maintained a t 120" * 0.3" C. by means of a mixture of glycerin and water. Two grams of powder, well dried over concentrated sulfuric acid, are weighed into the decomposition tube. Ten cubic centimeters of 5 per cent potassium iodide solution are placed in the absorption cup, and after lightly greasing the groundglass connection, the cup is attached to the tube. The whole is placed in the test bath, the wells of which contain Nujol. The protecting shield is put in place and the tubes are heated for exactly 6 hours. At the end of the test, the tubes are removed, 10 cc. of distilled water are added, and on cooling the liquid is drawn into the decomposition tube. After 10 to 15 minutes' cooling, a clean rubber stopper is fitted into the top of the absorption cup and the whole shaken vigorously for several minutes. This absorption cup is rinsed with distilled water and the rinsings are added to the liquid in the decom-
"I
I
h 'rr
9
cI
/ + u FIGURE 3. TALIANI TESTTUBE
position tube. The volume is made up to 50 cc., and after vigorous mixing an aliquot of 25 cc. is withdrawn and titrated with 0.01 N sodium thiosulfate. The nitric oxide equivalent to the thiosulfate is calculated and reported as milligrams of nitric oxide per gram of powder for 6 hours' heating. de Bruin (6) points out that in the B. J. M. test there is a possibility of adsorption of iodine by the powder. With
January 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
poorly gelatinized powders this was found to be the case, but with well-gelatinized powders the amount of iodine adsorbed from a solution of concentration equal t o that in a usual test was found to be equivalent to less than 0.1 mg. of nitric oxide per gram of powder. This is within the limit of error of the B. J. M. test and has a negligible effect on the results of the test. The amount of nitroglycerin had no appreciable effect on the adsorption when well-gelatinized powders were used. METHYLVIOLETTESTAT 134.5' * 0.5" C. (15). Two and five-tenths grams of powder are weighed into a test tube 29 em. long and 15 nim. inside diameter with walls 1.5 mm. thick. A test paper prepared as described by Worden (13) is inserted in the tube about 1.5 inches (4.3 em.) above the sample. The tube is placed in the well of an A. S. T. M. bath, there being enough Nujol in the well to fill completely the space between the tube and the well. After 10 minutes the tube is inspected each minute until near the end point, when the tube is inspected at 30-second intervals. The use of Nujol in the wells permits much more frequent inspection of the samples without appreciably affecting the test than when air fills the space between the tube and the well. The time from the insertion of the sample into the bath until the test paper is turned salmon pink throughout is taken as the methyl violet test. POTASSIUM IODIDE AT 82.2' C. This is merely the Abel test (22) carried out a t a higher temperature. The 65" C. test proved unsatisfactory from the standpoint of duplication of results. When the temperature was raised to 82.2' C.better duplication was obtained. DISCUSSION OF RESULTS The data on a series of powders are given in Table I. Saniples 1, 2, 5, and 6, made without stablizer, appear quite unstable by the surveillance, Taliani, and B. J. M. tests. From the methyl violet test they would be considered stable. Samples 2 and 5 appear stable by the potassium iodide test, whereas 1 and 6 seem unstable. Sample 13 was 22 years old when tested and proved unstable by the surveillance, Taliani, and B. J. M. tests, but appeared of satisfactory stability by the methyl violet and potassium iodide tests. Sample 14 was made prior to 1913, and gave a similar result. Samples 17 and 19 would be considered stable by the methyl violet, potassium iodide, and B. J. M. tests, but definitely unstable by the surveillance and Taliani tests. The available diphenylamine determination supports the view that these two powders are TABLE I. YEAR
SAMPLE MAD^ 1 2 3 4 5 6 7 S
a
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 At 78' C.
1929 1929 1929 1929 1929 1929 1926 1926 1926 1926 1929 1929 1908 1 1914 1916 1917 1917 1920 1923 1 1914 1923 1908 1917 1926 1929 1929
75
unstable. I n the case of the methyl violet test, volatilization of nitroglycerin and decomposition of the latter in the vapor state and on the surface of the test paper undoubtedly play a preponderant role. The potassium iodide test, on the other hand, is not affected to the same extent by this particular
Time, Mln.
FIGURE 4. TALIANI TESTCURVES. 1, 2, 13, unstable powders; 4, 8, 18, stable powders variable, but fails to give results in conformity with the known condition of the powder. It will be generally admitted that powders made with stabilizer have a longer life under normal storage conditions than powders made without stabilizer. A test which fails to differentiate clearly between such powders is unsafe to use. For this reason the methyl violet and potassium iodide tests cannot be recommended for use in arriving a t the probable storage life of double-base powders. The relative value of the surveillance, Taliani, and B. J. M. tests can, perhaps, be brought out best by correlation charts of the results of the tests, Figures 5, 6, and 7 . When the results of surveillance and Taliani tests (Figure 5) are plotted, the chart may be divided into four sections, A, B, C, and D. Powders in section C are undoubtedly stable, and those in section A unstable. Any powders represented in sections B or D are of doubtful stability and should be tested frequently. There is a wider spread between the values for stable and unstable powders by the Taliani test than by the surveillance test. This chart serves to establish limits between stable and unstable powders. Any powder giving a surveillance test of 25 days or more may be regarded as stable by this test. A stable powder will give a Taliani test above 150 minutes. It
STABILITY DATA
YEAR P ~ R C ~ N T TESTED NG ~ T A B I L I Z E R SURVEILLANCE^ TALIAXIb % Days Min. 1930 40 0 4-4 60-65 1930 40 0 4-4 104-106 1930 36-39 40 0 . 5 NO. Id 239-228 1930 40 0 . 5 No. 2d 32-34 218-218 1930 40 0 5-5 80-81 1930 40 0 6-9 89-88 1930 40 0.75s 33-39 177-182 1930 40 0.758 34-35 189-192 1930 40 0.75e 32-35 199-194 40 0.75a 1930 43-52 158-159 1930 258-241 0.50s 23-23 40 1930 242-247-240 40 0.50 NO. l d 28-30 1930 40 1 17-17 77-75 1930 40 1 22-22 67-76 0.308 ' 34-36 1930 40 276-291 1930 40 0.306 32-32 234-238 0.50e 20-21 1930 40 76-72 1930 40 0.50e 42-46 275-280 1930 40 67-70 0.470 20-20 1930 40 292-293 0.478 24-30-31 1930 30 1 30-31 98-93 1930 30 0.308 39-41 280-293 1930 30 0.50s 90-103 327-333 30 1 1930 23-23 136-137 1930 20 0.308 109-120 451-450 1930 20 0.758 143-150 207-209 1930 10 0.586 108-132-148 400+ 1930 10 0.586 135-151 400+ b A t 120' C. e At 82.2O C.
B. J. M. Me. NO 10.2 9.5 5.2 5.2 7.6 8.2 4.1 4.8 4.4 4.6
5.9 6.0 8.9 10.5 4.5 5.4 5.0 4.7 5.5 4.4 2.8 3.0 2.5 2.0 1.9 1.6 0.2 0.6
METHYLPOTASSIUM
VIOLET
IODIDE0
Miin. 14 15 16 16 15 15 15 15 13 15
Min.
15
16 21 18 18 18 20
~~
10 30 11 12 22 8 11 14 12 11 45 8 25 20 14 13 30 22 30 23 30 26
18 20 18 27 19 18 29 12 25 30 21 60+ 29 60+ 22 60+ d Centralite.
REIdARKa
Probably made without stabilizer Made before 1913 Available diphenylamine 0 04% Available diphenylamine: 0:25% Available diphenylamine, 0.04% Made before 1913 Probably made without diphenylamine
Diphenylamine.
ANALYTICAL EDITION
76
should be noted that these limits are for 40 per cent nitroglycerin powders. Section A, Figure 5, contains the four powders made without stabilizer, as well as the two oldest powders. Powders 17 and 19 appear unstable. The reason for this is not known, but the results are supported by the low available diphenylamine content of the samples. 50
010
dS
Vol. 4, No. 1
From these comparisons, it is concluded that of the three tests, the B. J. h4. is fairly satisfactory for judging the condition of a powder, but not so useful as the surveillance and Taliani tests, The surveillance test requires 25 days before a decision can be given as t o the stability of a sample, while the Taliani test can be carried out within a few hours. For this reason the Taliani test is to be preferred. The data indicate, however, that the test is somewhat dependent on the nitroglycerin content and increases with a decreasing amount of nitroglycerin in the powder. This is an undesirable feature. As it seems to be less dependent on the nitroglycerin content than the other tests, it is probably as good as can be done a t present. However, since the test is not entirely satisfactory, entire dependence cannot be placed in the result of a single method, and a check should be made as to the stability of the powder by another method. If time is available, the surveillance test is to be preferred, but the B. J. M. test may be used. Some data are given for 30 per cent nitroglycerin powders. It is evident that the specifications for stable powders should be revised from those for the 40 per cent nitroglycerin type.
Taliant T e d
FIGURE 5.
CORRELATION O F SURVEILLANCE AND TALIANI TESTS
Figure 6 gives the correlation between surveillance and B. J. hl. results. The line of division between stable and unstable powders by the B. J. M. test is placed at a value of 6.5 mg. of nitric oxide. The powders without stabilizer, as well as the old powders, appear in the unstable group, while samples 17 and 19 have shifted to the doubtful group. Sample 11also appears in this group. The remainder of the powders are considered stable. It will be noted that the same powders appear in the stable section as were found in the corresponding section of the preceding chart. In Figure 7, the correlation between the B. J. M. and Taliani tests is given. The same grouping of powders is observed in this chart as was noted in Figure 6 with the exception of sample 11, which now appears in the stable group.
I
40
D
Ora=
Ob
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2
FIGURE6.
3
4
5
s ‘ ,
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d3
8
9
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41 I
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90
60
0
Tnliani T e s t
OF B. J. M. FIGURE 7. CORREL~TION
AND
TALIAVI TESTS
The B. J. 31. test does not differentiate the powders so clearly as the Taliani and surveillance tests. There are insufficient data to fix specifications for the 30, 20, and 10 per cent nitroglycerin powders. However, until a long series of tests for each type is run, it is suggested that the same stability limits be adopted for these as is used for the 40 per cent nitroglycerin type. An unstable powder is readily noted, as in the case of sample 24.
B
I
0
_1
0.J.M. Te I t
CORRELATION O F SURVEILLARCE AND
B. J. M. TESTS
A critical comparison of the results of the 13. J. &I. with the surveillance and Taliani shows the former to be more a function of the nitroglycerin content than either of the latter. When diphenylamine was left out of the powder formula the fact is clearly brought out by the B. J. M. test, but not so strikingly as with the surveillance and Taliani tests. The two samples showing a very low available diphenylamine content were definitely unstable by the surveillance and Taliani tests but were satisfactory by the B. J. If.test.
LITERATURE CITED (1) Bbel, Phil. Trans., 156, 269 (1866). (2) Am. SOC. Testing Materials, “Tentative Standards,” p. 275 (1930). (3) Bergmann and Junk, Jahresber. chem. tech. Reichsanntnlt, 8, 28-31 (1929). (4) Bergmann, Junk, and Mayrhofer, Z . ges. Schiess- Sprengstofw., 13,425 (1918). (5) Bruin, de, Communique de la Ste. Anne, “Fabriques Neetlandaise d’Explosifs,” No. 5 (1927). (6) Chiaraviglio and Corbino, Atti accad. Lincei, 24, 5a, 120 (1915). ( i )Goujon, Mem. Artillerie Fmngaise, 8, No. 32, 837-902 (1929). (8) Guttmrtnn, 2. angew. Chem., 10,233, 265 (1897). (9) Lenze and Meta, 2.ges. Schiess- Sprengstoffw., 23,340-3, 381-4, 428-31 (1928). (10) Pollard, Trans. Optical SOC.,26, 63-73 (1924-5). (11) Taliania, Gam. chim. dal., 51, 184-93 (1920). (12) Worden, “Technology of Cellulose Esters,” Vol. I, Pt. 3, p. 2324, Spon, London, 1921. (13) Torden, Ibtd., p. 2346. (14) Worden, Ibid., p 2354. (16) Worden. Ibid., p. 2371. RECEIVED July 29, 1931.
