V O L U M E 2 7 , N O . 6, J U N E 1955
957
lysine and the very poor recovery of thiamine under all conditions examined, it may be concluded that other factors influence the completeness of elution of some compounds.
(6) Grant, E. W., and Hilty,
(7)
(8)
(9)
ACKNOWLEDGMENT
The author thanks Clara E. McGrew for technical assistance and Bettye L. Wilson for spectrophotometric assays.
(1954).
B.,and
(11) (12) (13)
(14)
LITERATURE CITED
(1) .ichor, L.
(10)
Geiling. E. 11. K., ANIL. CHEM.,26, 1061
( 2 ) Adamson, D . C. AI., and Handisyde, F. P., Andust, 70, 305
(1945).
(3) Baggesgaard. 11. H.. Fuchs. D., and Lundberg, L., J . Pharnz. Pharmacol., 4, 566 (1952). (4) Davies, C . W., and Thomas. G. G., J . C'henz. SOC., 1951, 2624. ( 5 ) Denel, H.. Solnis. J . . and Anyas-Weiss, L., Hell'. Chim. Acta, 33,
2171 (1950).
(15)
(16)
W.W., J . A m . Pharm. Assoc., 42, 150 (1953). Gregor, H. P., Gutoff, F., and Bregman, J. I., J . Colloid Sei., 6 , 245 (1951). Herr, D. S . , I n d . Eng. CRen?., 37, 631 (1945). .Jindra, A., J. Pharm. Phar?nacoZ., 1, 87 (1949). Jindra, A , , and Pohorsky, J.,I h i d . , 2,361 (1950). Kolthoff, J. hl., Biochcm. Z., 162, 338 (1925). Kressman, T. R. E., J . Phys. Cliem., 56, 118 (1952). Kunin, It., and Myers, R. J., DZ:scussio?~sFaraday SOC., 7, 114 (1949). Levi, L., and Farmilo, C. G., Can. J . Chem., 30, 793 (1952). Aloore, S.. and Stein, W. H., J . Riol. Chem., 192, 663 (1951). VanEtten, C. H., and Wiele, 11. B., ANAL.CHEM.,25, 1109 (1953).
RECEIVEDf o r review November 86, l Y X . Accepted February 26, 195.5. Presented a t the 16th Midwest Regional Meeting of the AIIERICANCHEMICIL SOCIETY, Omaha, Xeb., November 4 and .5, 1954. Mention of firm names or commercial products under a proprietary name or names of their manufacturer does not constitute a n endorsement of siich firins or products by the U. S. Department of Agriculture.
Test for Establishing Residual Safe Life of Stabilized Solid Propellants CARL BOYARS and W. G. GOUGH Research and Development Department,
U. S.
Naval Powder Factory, Indian Head,
Accelerated decomposition of propellants subsequent to depletion of stabilizer results i n extensive deterioration and possible spontaneous ignition. Chemical analysis is n o t a practical method of measuring t h e loss in stabilizing power because of t h e stepwise formation during storage of niany nitrated stabilizer derivatives. .i test has been deiisetl which does measure t h e stabilizer loss i n terms of t h e proportion of original safe life remaining. I t has been evaluated with propellants subjected to varying amounts of high-temperature storage. This stability test involves heating t h e volatile-free propellant a t constant temperature i n a constantvolume system containing an oxygen atmosphere. The time required to reach a predetermined positit e pressure correlates well with residual safe life as measured by t h e length of preliminary storage of the propellant a t high temperature. Data are presented comparing the variation of pressure with time i n tests carried o u t under atmospheres of nitrogen, air, and oxygen. IIypotheses about the niechanism of degradation of propellants, based on this work, are offered.
N
Md.
complicated by the separations :inti interpretations required. A good stability test which gives a precise measure of degree of deterioration is desirahle, and this requirement, together with the need for more inforniation about the phenomena of degradation of propellants, inspired this investigation. The stability test devised by Taliani (6) and modified by Kiggam and .Goodyear ( 8 ) differentiates bet\\-ecn ,stable and unstable propellants by observing the increase of pressure \\-ith time in a constanttemperature, constant-volume system containing 'the propellant and air. However, this test provides no means of differentiating h e t w e n the various degrees of residual stability.
MANOMETER
VACUUM PUMP AND NITROGEN SUPPLY
II F
II E
HELIX
F E
EARLY all solid propellants based on nitrate esters contain a uniformly distributed stabilizer. The function of the
stabilizer is the removal of nitrogen dioxide, which is formed as a primary decomposition product during storage of thc, propellant ( 2 ) and which would othern-ise autocatalytically accelerate the decomposition. Accelerated decomposition subsequent to depletion of the stabilizer results in spontaneous ignition if heat is generated by the exot,hermic reaction more rapidly than it can be dissipated. Even where ignition does not occur, extensive deterioration of the propellant follow stabilizer depletion. I t is important for an organization that uses formulations containing nitrate esters and stabilizer to know how much of the stabilizing power incorporated in manufacture remains after storage for any length of time. The problem is complicated by the fact that the common stabilizers, which are secondary aromatic amines or urea derivatives containing AV-aromaticlinkages, go stepwise to their higher nitrated forms, each of the less completely substituted nitro compounds retaining some stabilizing power (1, 4, 5'). An analytical technique would thewfort. he
H E A T I N G BLOCK
BALL JOINT
1
k
MERCURY RESERVOIR
MERCURY LEYELING DEVICE
Figure 1. Diagram of Taliani test equipment
A N A L Y T I C A L CHEMISTRY
958 APPARATUS
I n the work described in this paper, a highly modified Taliani apparatus was used, similar to that shown in a Bureau of Ordnance publication ( 7 ) . Figure I is reproduced from t h a t source. The only important differences in apparatus design between the original apparatus ( 7 ) and the present work were an improved mercury-leveling device, a closed system of 7.35 =k 0.05-cc. volume rather than 6.00 cc., and mercury capillary-type thermo-
I
37
d 3
I
regulators (Princo Magna-set or Mumberg Magnet-o-set), which allow more precise temperature control. EXPERIMENTAL PROCEDURE
Propellant samples with a nitrocellulose-nitroglycerin base and containing either 1% sym-diethyldiphenylurea or 2% 2nitrodiphenylamine as a stabilizer were stored a t 65.5" or a t 80' C. for different lengths of time to provide samples of varying residual safe life. After storage the samples were ground in a Wiley cutting mill. Portions which passed a U. S. 18 and were retained on a U. S. 50 sieve were selected. Ground 1-gram samples were weighed into Taliani test tubes. The experiments were
/
t
37 d
I
I
I
I
I
I
I
4
'HOURS
0
20-
I
~-
IO-
Figure 2. 110' C. test under nitrogen on 1% symdiethyldiphenylurea-stabilized propellant stored at
80" C.
7 I
Time to fumes, 51 days
,
1
I
HOURS3
4
Figure 4. 110' C. test under nitrogen on 2% 2nitrodiphenylaminestabilized propellant stored a t 65.5'' C. I
2
I
3
HOURS
I 4
I
5
Figure 3. 110" C. test under nitrogen on 2% %-Nitrodiphenylamine-stabilized propellant stored at 80" C. Time to fumes, 93 days
-4
0
I
I
2
4HOURS
1
'
8
Figure 5. 110' C. test under air on 1% sym-diethyldiphenylurea-stabilized propellant stored at 80" C. Time t o fumes, 51 days
V O L U M E 2 7 , N O . 6, J U N E 1 9 5 5
959
m4
w
a c
I
Figure 6. 110' C. test under air o n 2% 2-nitrodiphenylamine-stabilized propellant stored at 80" C. Time to fumes. 93 days
t
- 4d0
,
I
2
I
I
4
HOGURS
,
I 8
I
IO
!
Figure 8. 110" C. test under oxygen on 1% syni-diethyldiphenylurea-stabilized propellant stored at 80" C. Time to fumes, 51 da)s
10-
-
tion in slope or time to reach any arbitrary positive pressure that correlates n ith length of previous high-temperature storage. Figures 5 , 6, and 7 indicate that constant-volume tests under air reveal deterioration only during the latter stages of a propellant's safe life. Figures 8, 9, and 10 show that the tests a t 110" C. under oxygen correlate well nith residual safe life if the time to reach a pressure of 100 mm. of mercury is measured. Figures 11 and 12 illustrate how the oxygen test is speeded up Tvhen performed a t 120" C. nithout an\- sacrifice in correlation.
E 80E .
-
23 4. v)
u40E
-
l l 201-
0MECHANISM OF PROPELLANT DEGRADATIO\ 4UD STABILITY TEST
-24
Figure 7. 110" C. test under air on 2970 2-nitrodiyhenj-laniinestabilized propellant stored at 65.5" C.
conducted under air, ozygcii, arid nitrogcii. For the test conducted uiider air, the saniplw were preheated in the bath for 30 minutes a t atmospheric pressure, after which the stopcock \vas turned to close the system and the initial reading was taken. For the tests under oxygen and nitrogen, t,he samples were preheated under air in the same manner, but after the preheating period the system was evacuated and flushed four times with the test gas. -4final addition of gas brought the internal pressure above the external pressurr. The pressure of the system was then reduced to that of the atmosphere by rapidly opening and closing the st,opcock. Pressure measurements were made every half hour (every 15 minutes when the evolution rate increased markedlv) immediately after adjusting the mercury level to the fidurjal h a r k (Figure 1). The test n-as discontinued bcfore a po~itivepressure of 200 mm. of mercury \vas reached.
Some reasonable interpretations of these results in terms of the natuie of the decomposition and stabilization procese can be made. The initial decomposition product, nitrogen dioxide, is usually rapidly reduced to nitric oxide (3). Because only 1 or 2% of stabilizer is incorporated in the common nitroglycerinnitrocellulose formulations, statistical probability favors the reaction of nitrogen dioxide with the nonstabilizing components rather than n i t h the stabilizer, unless the reaction with the stabiluei is much more rapid. This series of reactions can be represented as follom: Initial decomposition
Subsequent degradation
T h r data obtained are surnmaiiaed in Figures 2 through 12, M herein pressuie differences from the prevailing atmospheric pressure are plotted. Storage time, in days, prior to testing is indicated for each sample. The "time to fumes" shonn is the length of storage sufficient to produce nitrogen dioxide fumes a t the indicated storage temperature. The appearance of visible nitrogen dioxide fumes marks the end of the propellant's safe life. Figures 2, 3, and 4 show that there is no correlation betueeri re~idualsafe life and the rate of pressure evolution in constant-volume tests under nitrogen; there is no consistent varia-
I
+ KO2
(1)
+
CHO. YO? + S O , N 2 0 , CO, COS, HzO, and various solid and liquid products
Stabilization EXPERI\IENTAL RESULTS
I I I
CHON02 + AHO.
+
oxidized
organic
(2)
2C6H03x02 + 2OzSC8HdH20
+
+X0
(3).
If the relative reaction rates are such that the stabilizernitrogen dioxide reactions compete strongly with the other nitrogen dioxide reactions, then the slopes of the pressure-time plots of the constant-volume tests under nitrogen should be progressively greater for samples hose stabilizer content is decreased by high-temperature storage prior to testing. Figures 2, 3, and 4 indicate that this increase in slope is not found. The data obtained lend support to the following hypotheses. Under nitrogen the nitric oxide does not contribute further t o
ANALYTICAL CHEMISTRY
960
Figure 9.
110" C. test under oxygen on 27c 2-nitrodiphenylaniinestabilized propellant stored at 80" C. Time tn fumes, 93 days
ventional Taliani test, carried out under air, on a powder of reasonably good stability measures only the point of disappearance of oxygen from the system. Although the preceding discussion resorts to oversimplification by ignoring the effect on stability of deterioration in components other than the stabilizer, abundant evidence has been presented here to show the usefulness of the constant-volume test under oxygen in estimating the degree of deterioration of propellants. The test also has the advantage of providing a more objective measurement than that given by the color change in an indicator paper. It should perhaps be emphasized that the test obviously cannot be applied to propellants containing appreciable quantities of volatile constituents unless they are firit removed. By a suitable adjustment of the size of the sample or of the gas-evolution system, the test should be applicable to any other stabilized propellant formulation containing nitrate esters. The problem of stability is a complex one and this paper treats only one of its facets, presenting a test i ~ h o s eresults correlate well n-ith the pre-
W 54oc
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I-
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-8
-
-12d
0
,
2
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4
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1
12
14
HOURS
16
,
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20
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22
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I
Figure 10. 110" C. test under oxygen on 2% 2-nitrodiphenylaminestabilized propellant stored a t 65.5" C.
2
Figure 11. 120" C. test under oxygen on 1YOsym-diethyldiphenylureastabilized propellant stored at 80" C. Time to fumes, 51 days
the decomposition process during the test period. Under air or oxygen, nitric oxide reacts to form nitrogen dioxide 2N0 0 2 --* 2N01 (4)
+
and the reduction-oxidation sequence continues until the chain is broken by the reaction of the stabilizer with nitrogen dioxide. Thus the immediate net result is a decrease in the amount of gas present in the system so long as effective quantities of stabilizer are present to pick up nitrogen dioxide. If gas evolution due to reaction 2 exceeds gas removed by Reactions 4 and 3, then the system shows an increase in pressure. When the stabilizer becomes depleted, the nitrogen dioxide attacks the nitrate esters primarily and increases the decomposition rate of the propellant. If the test is carried out under oxygen, sufficient nitrogen dioxide can be formed to completely use up the stabilizer in 1 gram of a propellant initially containing 1 or 2% of sym-diethyldiphenylurea or 2-nitrodiphenylamine. Under air, depletion of the stabilizer with an apparatus and sample of the size specified would be possible only if the propellant has already been aged substantially. Consequently the con-
3 E
HOURS Figure 12. 120" C. test under oxygen on 25%~ 2-nitrodiphenylamine-stabilized propellant stored a t 80" C. Time to fumes, 105 days
V O L U M E 27, N O . 6, J U N E 1 9 5 5 vious storage history of the propellant. Those unfamiliar with considerations of propellant stability should be cautioned that autoignition is a function of many factors, including composition, temperature, pressure, size, and others. Even a fresh, stable propellant may be ignited, indeed this is a requirement for its use. ACKNOWLEDGMENT
Unpublished data by H . 11. Spurlin and .4. G. Sandhoff of the Hercules Powder Co. lvere responsible for the interest of the senior author in constant-volume tests. The encouragement of F. C. Thames during the course of these investigations is much appreciated. 11. E. Baicar, C. I-.Jamen, and Celia J. Wright assisted in carrying out the tPst9. LITERATU-RE CITED
(1) Davis. T. L., "Chemistry of Powder and Explosives," pp. 30713, Wiley, Sew York, 1913.
961 Phillips, L., Nature, 160, 753 (1947). Robertson, R., and Napper, S. S., J . Chem. SOC.,91, 764 (1907). Schroeder, W-.A . , hlalmberg, E. W., Fong, L. L., Trueblood, K. X . , Landerl, J. D., and Hoerger, Earl, Ind. Eng. Chem., 41, 2818 (1949).
Schroeder, W.A., Wilson, 11.K., Green, C., Wilcox, P. E., Mills, R. S.,and Trueblood, K. K.,Ihid., 42, 539 (1950). Taliani, AI., Garz. chim.ital., 51(1), 184 (1921). U. S. Navy, Bureau of Ordnance, "Taliani Test for Determination of Stability of Solid Propellants," NavOrd OS 7904 (-4pril 5, 1951). Wiggam, D. R., and Goodyear, E. ED.,4, 73 (1932).
S.,IND.EXG.CHEM.,ANAL.
R E C E I V Efor D review November 2 , 1954. Accepted January 27, 1955. Published with perniission of the Bureau of Ordnance, Kavy Department. The opinions and conclusions are those of the authors. Presented before the Propellant Power Symposium, Ameriran Institute of Cheniical Engineers, Louisville, Ky., M a r r h 23, 1'355.
Fluorimetric Determinations of Aluminum and Gallium in Mixtures of Their Oxinates JUSTIN W. COLLAT'
and
L. B. ROGERS
Department o f Chemistry and Laboratory o f Nuclear Science, Massachusetts lnstitute o f Technology, Cambridge 39, Mass,
This study was designed to test the feasibilitj of determining tw-o substances in a mixture, when each has nearlj the same fluorescence spectrum, by taking advantage of the difference in their sensitivities to different wave lengths of exciting radiation. A Beclcnian DU spectrophotometer was modified to enable one to determine the fluorescence spectra of the individual components, while another was employed to provide monochromatic exciting radiation. Aluminum and gallium oxinates, which have nearl!, the same fluorescence spectra in chloroform, hate been analjzed with moderate success bj this technique. Determination of mixtures of substances having different fluorescence spectra can probablj be facilitated bj taking advantage of this additional variable.
A
Y.1LYTICAL use of fluorescence has been based almost entirely on the measurement of fluorescent light emitted from a sample under excitation by one or more mercury lines selected bv means of a glass filter. The 3650 A. emission line has been used most frequent11 because it can pass through g1a.F optics, whereas shorter wave lengths require fused silica or quartz. Furthermore, fluorescence hay heen limited to the estimation of a single constituent in a medium which does not contain any other interfering fluorescent compounds. Little effort has been directed tonard the determination of mixtures of fluorescent materials by taking advantage either of differences in their fluorescent spectra or in the differing intensities of fluorescence produced by different exciting wave lengths. The anal! tical possibilities of fluorescence spectra were realized by Huke, Heidel, and Fassel ( 4 ) , who modified a Beckman Model DE spectrophotometer to obtain fluorescence gpectra for the study of rare-earth solutions; by Peattie ( 6 ) , mho determined samarium and europium in ignited calcium sulfate; and by Aitken and Preedy ( I ) , who studied the fluorescence spectra cf estrone, estradiol l i p , and estriol compounds. The present study was designed to explore further the feasibility of fluorescence analysis for the determination of more than one 1 Present address, Department of Chemistry, Ohio State Unix eraity, Columbus 10, Ohio
compound in a mixture, using differences in the responses of the compounds t o different exciting wave lengths. The system chosen for study was a mixture of aluminum and gallium oxinates (salts of 8-quinolinol), both of which are easily extracted from water into chloroform, in which solvent they have essentially identical fluorescence spectra. The fact that one can determine these two compounds in this unfavorable case indicates t h a t t h e determination of two constituents which possess different fluorescence spectra should be even more readily attacked in this way. The determination of gallium by the fluorescence of its oxinate in chloroform and conditions for extracting the oxinate into chloroform have been described by Sandell ( 7 ) . The oxinate of aluminum has been applied most recently in fluorimetric analysis by Goon and coworkers ( 3 ) . Both oxinates emit a strong yellow-green fluorescence in chloroform solution \Then irradiated with the 3650-A. incrcnrj. line. EXPERIMENTAL DETAILS
Reagents and Solutions. +4Lciwivux STOCK SOLUTION. Aluminum chloride hexahydrate was used to prepare a stock solution of aluminum containing about 1.00 mg. of metal per ml. Solutions containing 100, 10, 1.0, 2.5, 0.28 y of aluminum per ml. were prepared as needed by dilution of the stock solution with 0.05M hydrochloric acid. GALLIUMSTOCKSOLUTIOS. A sample of gallium oxide which was shown spectroscopically to contain less than 100 p.p.m. of aluminum was used t o prepare a stock solution by dissolving it in hydrochloric acid. The final gallium concentration was 100 y per ml. ; the final hydrochloric acid concentration was O.05M. This solut'ion was diluted with 0.05Jf hydrochloric acid to prepare a solution with 10 y of gallium per ml. as required. OXINE SOLUTION.A 0.1% solution of oxine was prepared according to directions given by Sandell ( 7 ) . XMUOSI~M ACETATE. A 1M solution was added to the acidic solutions of gallium and aluminum to provide buffering action. Ten milligrams of quinine QUINISE SULFATESTANDARDS. sulfate U.S.P. was dissolved in 1 liter of 0.1M sulfuric acid to S. Pharmacopoeia prepare the stock solution described in the I?. (8). A portion of this was diluted with 0.1M sulfuric acid daily to obtain solutions containing 3.0 and 0.3 p.p.m. of quinine for comparison with the oxinate extracts. CHLOROFORM. Reagent grade chloroform was used for all extractions. METAL OXINATES. Solid aluminum and zinc oxinates were prepared by the method of Rolthoff and Sandell ( 5 ) . These were
