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y-Irradiation Effects on the Thermal Stability and Decomposition of Ammonium Perchlorate
tures the induction period was not completely eliminated even with very long irradiation times.
I. Experimental Apparatus and Procedure by Scott Fogler Division of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48104
and David Lawson Jet Propulsion Laboratories, California Institute of Technology, Pasadena, California 91105 (Received March 26, 1969)
Studies were conducted on the decomposition of y-irradiated and unirradiated ammonium perchlorate a t temperatures around 135", whereas most similar investigations have been undertaken at substantially higher temperatures. One technique of observing the decomposition of ammonium perchlorate (AP) is to measure its weight loss as a function of time. Large variations in the amount of weight losses have been observed between different lots of ammonium perchlorate.' Some lots of ammonium perchlorate lost no weight after being stored at 135" for 600 hr, while other lots lost a very large percentage of their initial weight. The lot used in this study (lot 253 manufactured by the American Potash and Chemical Co.) was typical of those lots which lost substantial amounts of weight. The decomposition of ammonium perchlorate can be considered to take place in three periods: the induction period, the acceleration period, and the decay period. The induction period is that time during which the ammonium perchlorate has decomposed a negligible amount so as to be almost undetectable in terms of per cent weight loss ( i e . , approximately 0.5% weight loss). Bircumshaw and Sewman studied the decomposition of ammonium perchlorate in the temperature range of 200-300" and found the induction period to be of the order of 10-40 mim2 However, in the studies reported in the present work at 135", the induction period is the order of 300-400 hr. The effects of y irradiation on the decomposition process were studied in experiments by Herley and Levy3 and Freeman and A n d e r s ~ n . ~However, .~ these irradiation decomposition studies were undertaken at high temperatures in which there was essentially very little or no induction period. In Herley's study, it was found that at high temperatures, induction period was totally eliminated with y radiation. However, in the study reported here it was found that a t lower tempera-
The experiments conducted in this study were divided into three segments: a qualitative analysis of the product gases given off by the ammonium perchlorate (AP) at various times during the decomposition, the effect of y irradiation on the decomposition of unground AP at low temperatures, and the effect of y radiation on ground AP a t low temperatures. I n the first phase of this study, a mass spectrometer was used in the qualitative analysis of the gaseous decomposition products. In these tests approximately 2.0 g of AP were placed in a 0.75-in. test tube which had two stopcock outlets at the top of the tube. The tube containing the AP was immersed in a Haillikaner Instrument Thermotrol silicone oil constant-temperature bath which maintained the temperature of the AP sample at 135 i 0.01". The AP sample tube was removed from the bath at approximately 24-hr intervals, and the gas above the AP was analyzed in a mass spectrometer. In the second segment of this study a sample of the AP was irradiated with y rays for different lengths of time. The 6oCo source emitted approximately 1.1 R h d s of y rays into H20/hr. After irradiation the AP samples were weighed and then placed in a constanttemperature air oven maintained at 135 1". Control samples which had not been irradiated were also placed in the constant-temperature bath. The samples were removed a t various times and weighed. The weight loss of the samples a t various times was obtained and recorded as per cent weight loss. In the third series of experiments samples of lot 253 were ground up with an L S P Micropulverizer. The average particle size was determined by utilizing stainless steel ASTM sieves. The ground AP particle size was about 15 p, while the unground AP had an average particle size of about 200 p ,
*
11. Discussion and Results In the first series of experiments it was observed that (1) D. Udlock, Jet Propulsion Laboratory, private communication, 1968. (2) L. L. Bircumshaw and B. H. Newman, Proc. R o y . SOC.A227, 115 (1954). (3) P. J . Herley and P . W, Levy, Nature, 221, 128 (1966). (4) E. S. Freeman and D. A. Anderson, J . P h y s . Chem., 65, 1662 (1961). (5) E. 9. Freeman and D. A. Anderson, ASTM Special Publication, No. 359, 1963, p 58.
Volume 74, Number 7 April 8 , 1970
1638
Figure 1. Decomposition curves for unground ammonium perchlorate maintained at 135'.
essentially no gaseous products could be detected in the sample tubes during the first 280 hr they were in the 135" temperature bath. At the end of 280 hr, however, a small peak on the mass spectrometer output was observed, corresponding to a trace of NO. This was the only gas that appeared above the sample in addition to air, which had appeared in the previous analyses. For the sample which was not exposed to y radiation, it is observed from Figure 1 that at the end of 280 hr the first measurable weight loss was observed. By the time the sample had been in the 135" bath for 360 hr the NO peak had become significant, and a trace amount of HC1 could be observed from the analysis. After being immersed in the bath 400 hr, very large peaks ( L e . , m/e) of HzO, Nz, NO, 0 2 , HC1, and C1 appeared in the analysis of the gas phase above the ammonium perchlorate sample. At the end of 500 hr, the following additional m/e peaks were observed on the output from the mass spectrometer: 97, 81, 60, 55, 45, 41, and 38. It is plausible that these mle ratios could represent combinations of N, 0, and C1 (e.g., NC102, nitryl chloride). Residual peaks above the background of nearly all other mass to charge ratios of 25 to 95 were also observed in the 500-hr gas analysis. The nitric oxide and hydrochloric acid were also the first and second detectable compounds to be observed in the decomposition of the samples exposed to y irradiation. Since it was observed that the first gas to be liberated was nitric oxide and since some of the products are thought to be nitrosyl chlorides, it was believed that possibly nitric oxide was one of the gases which was autocatalytically attacking the solid phase. To determine if AP would react with nitric oxide, it was placed in a sample tube which was first flushed with helium, after which nitric oxide was passed through the system replacing the helium and the tube was closed. At the end of 3 hr the contents in the gas phase above the AP were analyzed in a mass spectrometer. Various products were given off , which included water, CIOZ, The Journal of Physical Chemistry
KOTES
with several other compounds being present in small amounts. These results indicate that X O did indeed react with AP and €hat once NO is liberated, it could autocatalytically attack the remaining AP. In Figure 1 the per cent weight loss is plotted as a function of time (in hours) for unground AP samples undergoing 1000,300, 60, and 30 sec of y irradiation and a sample undergoing no irradiation. Samples were also irradiated for 1500 and 2000 sec, and the weight loss curves for these tests were found to coincide with the weight loss curve for the 1000-sec irradiation. In other words, irradiating a sample for more than 1000 sec did not appear to produce any further changes in decomposition rate or induction time. The rates of decomposition given in Table I are expressed in terms of per cent weight loss per hour.
Table I : Acceleratory Period Decomposition Rates of Ammonium Perchlorate Type AP
7-Irradiation time, sec
Unground Unground Unground Unground Unground Ground Ground Ground
Xone 30 GO 300 1000 None 60 300
Rate, 70/111
0.0275 0.0650 0.0680 0,0930 0.0950 0.0013 0.0023 0,0024
By observing the decomposition rate below a weight loss of 1%, it appears that the transition time in going from induction to the acceleratory period increases with decreasing irradiation time. This transition period can particularly be seen in the case of the sample that was not irradiated, as it required approximately 150 hr between the time at which the induction period ends and the time at which the acceleratory period is reached. After irradiating the sample with y radiation, one observes that the rates during the acceleratory period only differ by approximately 50%. Consequently, the main difference in exposure times to y radiation is manifested in the length of time of the induction period. As previously mentioned, one could take the induction time as that time required to reach 0.5% weight loss or 0.5% decomposition. An alternate way of expressing the induction time would be to extrapolate the acceleratory rate period down to 0% weight loss and then take this intercept as being the induction time. Utilizing this latter method, a plot of log of the irradiation time vs. induction period is shown in Figure 2. The third phase of this study is concerned with the decomposition of ground AP. The per cent weight loss-time curves with and without y radiation for
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NOTES
variety of tests conducted at the Jet Propulsion Laboratory. The induction time of ground AP was roughly 600 hr longer than that of unground AP. The decomposition rate during the acceleratory period of ground AP (Table I) is approximately l / the ~ rate of unground AP during this same period.
50
\! I
40
30
20
IO
i
0,
I
-1
1
111. Summary In this study, one of the first gases detected in the decomposition of ammonium perchlorate at 135" was nitric oxide. It was also found that nitric oxide reacted rapidly with ammonium perchlorate when it was injected in a test tube above the ammonium perchlorate. Some of the gases detected in the long-term decomposition, other than nitric oxide, were HC1, water, and certain nitrosyl chlorides. When samples of ammonium perchlorate were exposed to y radiation, it was found that the induction time decreased with increasing irradiation time up to an irradiation time of 1000 sec. The induction time was found to be directly proportional to the log of the irradiation time for samples which were irradiated less than 1000 sec. When the ammonium perchlorate was ground, it took a substantially longer time to decompose than the unground ammonium perchlorate. Acknowledgments. This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS 7-100, sponsored by the National Aeronautics and Space Administration.
A Note on Optimum Parameters for the Generalized Lennard-Jones Intermolecular Potential
by Robert C. Ahlert, Gabriel Biguria, and John W. Gaston, Jr. Rutgers, The State University, New Brunswick, New Jersey 08906
TIME, hrs
Figure 3. Decomposition curves for ground ammonium perchlorate maintained at 135'.
ground AP are shown in Figure 3. A comparison of Figures 1 and 3 reveals that the ground ammonium perchlorate takes a substantially longer time to decompose. Although the mechanism which produces these differences in stability is unknown a t this time, these results were consistent and quite reproducible in a
(Received Awil 28, 1969)
In ref 1, the use of equilibrium and nonequilibrium data in the development of optimum potential function parameters was discussed. Emphasis wm placed on use of data in the range of temperatures below Te-12* = 2, as recommended by Klein and H a n l e ~ . ~An ,~ objective function defined on low-pressure transport properties yielded numerous local minimum points for both argon and methane. An objective function based (1) W. F. Vogl and R. C. Ahlert, J. Phw. Chem., 73, 2304 (1969). (2) M.Klein, J. Res. Nut. Bur. Stand., 70A, 259 (1966). (3) H. J. M. Hanley and M. Klein, National Bureau of Standards Technical Note 360,U. 8.Government Printing Office, Washington, D. C., 1967.
Volume 74, Number 7 April 2, 2.970
