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THE EFFECTS OF REACTOR IRRADIATION UPON THE SUBSEQUENT THERMAL DECOMPOSITION OF LEAD STYPHNATEl BY TEDB. FLANAGAN~ Explosives Research Section, Picatinny Arsenal, Dover, New Jersey, and Brookhaven National Laboratory, Upton, L. I., New York Received August 21, 1861
The kinetics of the thermal decomposition of lead styphnate have been examined after being subjected to a series of irradiations in the Brookhaven National Laboratory graphite reactor. It was observed that the decomposition rate is enhanced and the activation energy for at least part of the decomposition is significantly decreased by nuclear irradiation. It also was found that it did not make any difference in the subsequent thermal decomposition whether the material was irradiated as the anhydride or as the monohydrate. Possible mechanisms for the decomposition of the irradiated salt are discussed.
Introduction The dehydration and decomposition of the primary explosive lead styphnate monohydratea NOz I
in a desiccator prior to the decomposition studies. The samples were evacuated overnight in a hard vacuum prior to the decomposition runs. The decomposition apparatus has been described previously4b and the preparation of the well-aged, small, unground styphnate crystals used for the decomposition studies (1-4 mg.) also has been described before.'&*b A few dehydration runs were performed using c1 quartz helix balance (sensitivity, 1 cm./mg.) purchased from Microchemical Specialties, Berkeley, California.
Results and Discussion General.-Samples of lead styphnate monohyhave been investigated r e ~ e n t l y . ~The detailed drate were subjected to a series of reactor irradiakinetics of the dehydration and decomposition of barium styphnate monohydrate also have been ex- tions in a water-coded hole (30-50") of the Brookamined.6 It was observed by Tompkins and Young6a haven National Laboratory reactor. Evidence is that prior irradiation with ultraviolet light did not presented here which strongly supports the view affect the subsequent thermal decomposition of the that the samples were irradiated as the monobarium salt. With respect to gas evolved during hydrate, i.e., they were not dehydrated during the y-ray irradiation, lead styphnate monohydrate was actual irradiation. Subsequent decomposition found to be the most stable of several explosives in- studies then were performed in the temperature vestigated.6 In addition, it was found that y-ray range 200-225' ; dehydration occurs rapidly a t irradiation (up to 1.8 X lo8 r.) had negligible effect these temperatures, e.g., dehydration is complete upon the subsequent decomp~sition.~~ Thus it for unirradiated samples in 1 min. at 197' and less appeared that lead styphnate was quite stable than this for irradiated samples.4a Hence, it is toward ionizing radiation. It was of interest to believed that during decomposition runs dehydraexamine how radiation from a nuclear reactor tion is complete before significant decomposition would affect the subsequent decomposition. This has occurred. The decomposition of unirradiated lead styphwas of particular interest because lead styphnate exists as a stable monohydrate and could, therefore, nate has been described elsewhere4band a deeombe irradiated either as the monohydrate or as the position curve (pressure us. time) is shown in Fig. 1 in comparison to curves of reactor-irradiated anhydride. samples (222.5', 1 mg.). It can be seen that Experimental only after comparatively large doses of radiation is The specimens were irradiated in a water-cooled "hole" the subsequent decomposition aff e ~ t e d . The ~ de(-30-50") in the Brookhaven National Laboratory re- composition curves shown in Fig. l are quite reactor where the approximate neutron fluxes were: 4.5 X 1012 ncm.-a see.-> (total), 1 x 1012 ncm.-2 sec.-I (fast, > producible for samples which have been taken from 0.6 Mev.), and 2.1 X 10'2 ncm.-2 sec.-l (thermal). The a batch of irradiated material and also are reasonaccompanying y r a y irradiation was approximately 2.7 X ably reproducible with respect to radiation dose, 10ar./hr. Some samples were irradiated a t a higher thermal i.e., a sample irradiated under similar conditions flux (see below). The majority of the samples were irradiated while exposed to the atmosphere. Upon removal and for the same length of time as those shown in of the irradiated samples irom the reactor, they were stored Fig. 1 exhibits a similar decomposition curve. In addition, the irradiated material shows stability (1) This work was performed a t Brookhaven National Laboratory towards aging effects, e.g., a heavily irradiated and was supported jointly by Picatinny Arsenal and the U. S. Atomic sample stored for 3 years a t room temperature exEnergy Commission. hibited virtually the same decomposition curves as (2) Chemistry Department, University of Vermont, Burlington, Vt. a sample investigated several days after .irradia(3) Evidence for an alternative structure is discussed by Zingaro ( J . Am. Cham. Soc., 76, 816 (1954)). tion. (4) (a) T. B. Flanagan. Trans. Faraday Soc., 55, 114 (1959); (b) A sample irradiated in vucuo (1.1 X lo1*ncm.-2, 57, 797 (1961): (0) F. C. Tompkins and D. A. Young, J . Chem. Soc., C) yielded a nearly identical decomposition curve 331 (1956). curve as a sample irradiated in the atmosphere of the ( 5 ) (a) F, C. Tompkins and D. A. Young, Trans. Faraday Soc., 62, 1245 (1956); (b) F. C.Tonipkins and D. A. Young, J . Chem. Soc., reactor (the normal conditions employed). Thus, 4281 (1957). (6) J. V. R. Kaufman, Proc. Roy. SOC.(London), 8346, 219 (1958).
(7) E. G. Prout, Nature, 183, 884 (1959).
March, 1962
KINETICS OF
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it appears that interaction with the atmosphere during irradiation does not influence the subsequent theirmal decomposition. The gas evolved during an average irradiation was negligible, e.g., for sample C less than 0.8% of Pfwas found (Pf = final pressure after complete decomposition). Figure 2 shows the variation of maximum rate of decomposition and the length of the induction periiod (222.5') plotted as a function of total neutron dose. It may be seen that the maximum rate of decom,position has increased by a factor of 3 in passing from an unirradiated sample to sample A (the sample irradiated for a given total neutron dose hereafter will be referred to as labeled by the curves shown in Fig. 1). It is of interest that the maximum rate observed for heavily irradiated samples, e.g., A, under conditions where selfheating apparently is not a factor, is greater than that for rzn uiiirradiated sample in the vicinity of the latter samples' detonation temperature, e.g., a t 225.2'ithemaxirnumrateof Ais 4.5 pmin.-Img.-' whereas a t 227.9' the corresponding rate for an unirradiated sample is 1.3 pmin.-' mg.-l (at 228.7' self-heating is observed and at temperatures >229' detonation Because of the short acceieratory period the value of the maximum rate is not very accurate and, therefore, two other quantities also have been plot,ted (Fig. 3), i.e., the rate of the early linear period4b and the pressure evolved after a given time interval. These quantitiecr show a similar dependence upon dose as does the maximum rate (Fig. 2). The cuirves A through E shown in Fig. 1 refer to samples irradiated with a flux 4.5 X 10l2ncm.-2 sec.-l (total), 1.0 X 10I2 sec.-l (fast, >0.6 MeV.), and 2.1 X 1012 ncm.+ sec.-1 (thermal). The curves F and G refer to samples irradiated with a flux 1.3 X 1013 ncm.V2 set.-' (total) with approximately the same fast neutron flux as the A through €1: series. It may be seen from Fig. 2 and 3 that the data of both irradiations fall on approximately the same curves. Thus it appears that the total neutron dose is the important quantity. Role of the Dehydration Reaction.-Although the samples were irradiated in a water-cooled hole (30--50°), the temperature of the sample may be somewhat, higher than its environment due to radiation heating. However, for the small samples and containers (aluminum foil and thin quartz tubing) employed here, the temperature mould not be expected to rise more than a few degrees above 50'. Evidence now will be presented which supports the conclusion that the samples were not dehydrated during irradiation. Previous studies on the dehydration of lead styphilate have been made in ~ c t c u o . ~It~ was observed here that the dehydration at 120' in the laboratory atmosphere was approximately the rate in vacuo. Assuming the same activation energy applies as in uacuo, dehydration would be complete in approximately 100 and 40 hr. a t 90 and loo", respectively. In support of these values, it was found that insignificant dehydration occurred after 12 hr. a t 87' in an atmosphere of air. Virgin samples exhibit zero order dehydration kinetics with respect to
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Fig. 1.-The effect of reactor irradiation upon the subsequent thermal decomposition of lead styphnate (222.5', 1 mg. PI = 135 fi). A, 2.2 X 1018 ncm.-2; B, 1.6 X 1018 ncm.-2* C, 1.1 X 10'8 ncm.-a; D, 5.3 x 1017 ncm.-2; E, 0.7 k 10'' ncm.-2; F, 7.5 X 1017 ncm.-2; G, 1.8 X 10'6 ncm.-2; and U, an unirradiated sample. The doses are total neutron doses; samples G and F have been irradiated with a different ratio of thermal to fast neutrons than A-E (see text). 1
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Fig. 2.-The effect of reactor irradiation upon the maximuin rate and the induction time of the thermal decomposition of lead styphnate (222.5', 1 mg., Pf= 135 p). The approximate neutron fluxes employed for the runs represented by the circles are: 4.5 x 10l2 ncm.-2 sec.-1 (total), 1 X 1012 ncm.-2 sec.-l (fast), and 2.1 x 1012 ncm.72 sec.-1 (thermal) and for the runs represented by the triangles: 1.3 X 10'3 ncm.-'2 set.-' (total), 1 X 1012 ncm.-2 sec.-l (fast), and 6.5 X 10'2 ncm.-2 sec.-l (thermal).
-10
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Fig. %-The effect of reactor irradiation upon the pressure evolved at the end of an arbitrary time interval (45 min.) and the rate constant of phase ( b ) of the thermal decomposition of lead styphnate (222.5', l mg., Pt = 135 p ) . The symbols have the same meaning as in Fig. 2.
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TEDB. FLANAGAN
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T I M E ( MIN.). Fig. 4.-The thermal decomposition of lead styphnate (222.5'): 0, irradiated as the monohydrate; 0 , dehydrated and rehydrated before irradiation; A, irradiated as the anhydride; (7.5 X 1017 ncm.-2, total); n, unirradiated sample. I
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time whereas rehydrated material shows firstorder kinetic behavior.4a Two samples were irradiated under similar conditions, one of which had been dehydrated and rehydrated prior to irradiation and the other was irradiated as the virgin monohydrate ; the former showed first-order dehydration kinetics and the latter exhibited a linear dehydration rate (enhanced compared to an unirradiated sample). This suggests that the irradiated material was not dehydrated during irradiation. Finally, an X-ray powder pattern of irradiated material more closely resembled virgin rather than dehydrated (or rehydrated) material.
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It might be expected that the gross changes introduced into the salt as a result of dehydration would partially mask any effects upon the subsequent thermal decomposition of irradiated material. Although the details of the pressure-time curves differ somewhat, the effect of irradiation (7.5 X 1017 ncni.12 (total)) upon the decomposition of a sample dehydrated and rehydrated before irradiation closely resembled that of a sample irradiated as the virgin monohydrate (Fig. 4). Shown together with these data in Fig. 4 is a decomposition curve of a sample irradiated in l;acuo as the anhydride; it may be seen that this curve also agrees fairly well
March, 1962
KINETICSOB THE THERMAL DECOMPOSITION OF LEADSTYPHSATE
with the other data. This general behavior was reproduced for samples irradiated for a total neutron dose ad 1.8 X lo1*ncm.-2 (total). It will be recalled from earlier work4&lbthat the decomposition of lead styphnate monohydrate dehydrated in 0.8 mm. of water vapor prior to decomposition differed greatly from the decomposition of material dehydrated in vacuo; the former decomposition rate was linear, after an induction period, to w = 80% whereas the latter showed the behavior illustrated in Fig. 1 (the unirradiated sample). It was of interest to examine the decomposition of an irradiated sample which had been dehydrated in 0.8 mm. of water vapor after irradiation. Figure 5 shows the behavior of an irradiated sample dehydrated in this way as compared to a, sample irradiated for the same period and then dehydrated in vacuo. It may be seen that the irradiated sample, previously dehydrated in 0.8 mm. of water vapor, shows a closely linear decomposition rate only to about 20% decomposition, a t which point an acceleratory period commences. The linear rate is approximately twice that of the unirradiated decomposition; the values of to, the hme intercept, for both unirradiated and irradiated Jamples are comparable. Growth starts from opposite faces in the more perfectly crystallized material resulting from dehydration in 0.8 mm. The absence of an early gas of water evolution E,hows that the decomposition of internal “irradiation nuclei’’ has not contributed to the observed pressure in the early stages of reaction. Uni-directional growth, enhanced by the radiation damage as it is uncovered, is an unstable condition when extensive internal nucleation is present, as shown by the onset of an acceleratory period presumably caused by cracking of the crystal either due t o escape of internal gas or t o extensive internal decoinposition. Nature of the Radiation Damage.-It has been observed previously that aromatic material exhibits greater stability toward nuclear irradiation than does rzliphatic material.* Hence, the relative stability oi? lead styphnate toward irradiation observed hero is not unexpected. y-Ray irradiation of 1.13 x llOs r. was shown t o have an insignificant effect upon the decomposition The y-ray dose accompanying the reactor irradiation slightly exceeded this for sample C and was 1ess.than this for sample D. For the purpose of this discussion, the effect of y-ray irradiation and the resulting ionization will be neglected. Suclear transformations and atomic displacement can result from neutron capture by N14, ie., W4 n --+ C14 p; atomic displacement also can result from fast neutron knock-on collisions. For 1 mg. of lead styphnate monohydrate, an irradiation of 2.2 x 1OI8 ncm.-2 (total), would result in -6 x 1012 transformalions yielding C14 atoms with a recoil energy of 45,000 e.v. and a corresponding number of 0.56 Mev. protons. The recoil of the C14 would, of course, immediately rupture the original C-N bond in the C-KO, linkage and the recoil
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(8) I?. Seitz and J. Koehler, ”Solid State Physics,” Ed. 8‘. Seitz and D. Turnbull, Academic Press, Inc., New York, N. Y., 1956, Vol. 2. p 305.
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carbon subsequently would damage the lattice through elastic collisions after sufficient energy had been lost through inelastic processes. Similarly the ejected protons will produce atomic displacements. Experimentally, transmutation plus resultant processes and fast neutron damage appear to have similar efficiency (Fig. 2 and 3). A very approximate model predicts fast neutron damage to be more effective; the discrepancy probably is due to some chemical damage caused by inelastic processes resulting from the slowing down of the recoil C14 and the ejected proton. I n any case, the damaged regions are believed to be homogeneously distributed throughout the material forming “irradiation nuclei.’’ Apparently dehydration does not remove any of these nuclei. Analysis of the Pressure-Time Relationships.The general time sequence of events during the decomposition of irradiated samples, dehydrated in vacuo, e.g., Fig. 1, appears to be the same as that of unirradiated material, although the relative importance of each phase is altered progressively with increasing level of radiation, and consequently the appearance of the pressure-time curves has been modified. The general sequence of events is: (a) an initial evolution of gas, (b) a linear period of gas evolution, (c) an acceleratory period, and finally, (d) a deceleratory phase which is linear over a significant time interval for samples C and D, but the linearity disappears as the inflection point comes a t greater values of the percentage decomposition. It is of interest t o examine separately the influence of radiation upon each of the phases of the decomposition. I n unirradiated material, phase a was describable by a first-order rate law and was attributed to reaction a t energetically favorable sites. 4b The total gas evolved a t the end of phase a was independent of temperature and depended only upon the mass of sample employed.4b This also was true for sample C, whose decomposition was investigated at a series of temperatures. The pressure developed a t the end of phase a for a 1-mg. sample is shown as a function of radiation dosage in Table I. TABLEI EFFECTOF REACTOR RADIATION O N INITIAL GASEVOLUTIOS AND ISFLECTIOK POINT (1 mg., PfE 135 ,u, 222.5’) Sample
A B C D E U
Pressure b)a t end of phase b
Pressure ( p ) a t inflection point
5-6 2 1.0
23 20 14 14 2.0
74 35 37 33
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32
Pressure (ill at end of phase a
11 9
80
An especially large sample of irradiated material (A) was employed to obtain detailed data for the early region of reaction (phases a and b), this is shown corrected t o 1 mg. (197.0’) in comparison to an unirradiated run (Fig. 6). Because of the shortened induction period and the enhanced rates of phases a and b, it was difficult to obtain a value the pressure a t the end of phase a, and hence of Pf,
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the results are shown in Fig. 7 together with the results for unirradiated material. The activation energies for phase b have decreased with increase of radiation dosage : unirradiated, AE = 41.0 f 0.5 kcal./mole; C, AE = 36.1 f 1.1 kcal./mole; A, AB = 36.2 ==I 0.6 kcal./mole. The rate constants a t 222.5’ are 6.3, 42, and 119 X p min.-’ mg.-l for an unirradiated sample, sample C, and sample A, respectively. In irradiated material it is believed that phase b is no longer confined to the surface of the blocks as in unirradiated material4b; it is suggested that decomposition starts from the “irradiation nuclei” TIME (MINI. (which decomposed during phase a) producing Fig. 6.-Compariscn of the initial stages of decomposition rod-like nuclei which grow internally in one crystalof a heavily irradiated sample, (A), and an unirradiated sample (197.0°, 1 mg.): 0, irradiated sample, 2.2 x 10’8 lographic direction with a diameter equal to that of the original damaged region. Evidence has ncm. -2 (total) and e, unirradiated sample. been presented to indicate the anhydride consists of a t least partially aligned micr~crystallites.~~ The 1,OL , , , , , , q 10.0 porous structure of the anhydride resulting from dehydration in vacuo allows the gaseous products to escape during decomposition. Since decomposi\ tion during the early, linear phase of the irradiated 0.1 . and unirradiated samples takes place in different regions of the crystal (with different interfacial ‘5 areas) discussion of the relative values of & 3. appears unwarranted. ‘X Phase c represents acceleration from the internal 0.01 E rod-shaped decomposition centers formed during phase b. Detailed analysis of the acceleratory period of heavily irradiated material, e.g., samples A, B, and C, is difficult because of the large and uncertain corrections which must be applied to the ob0 001 0 01 194 198 202 206 210 214 2 18 served pressure due to the contributions from the preceding phases of the decomposition. Follow! I T x io3, Fig. 7.-The Arrhenius plot of the rate constant for the ing a technique suggested by Hill and Welsh,g decomposition of phase (b), (1 mg. sample): 0, unirradi- functions of dac/dt were plotted against cy. Howated sample: A, irradiated sample C, 1.1 X 1018 ncm.-2; ever, the straight line relationships expected for and e, irradiated sample A, 2.2 X 10’8 ncm.-2. simple power or exponential rate laws were not to apply a first-order rate law to phase a. Conse- found; (the errors due to assigning values of po quently, the method of initial rates was employed and to are eliminated in using this approach). This to obtain an activation energy of -10 kcal./mole suggests that phase b continues to contribute to for sample A as compared to 31 kcal./mole for un- the pressure during the acceleratory period and as irradiated samples; the latter value also was deter- the fraction of its contribution at various times mined from initial rates and compares favorably during phase c is unknown, it seems pointless to try with the value obtained from first-order rate con- to obtain a fit of the p-t data. In any case, acs t a n t ~ .As ~ ~expected from the magnitude of this celeration starts from a larger number of internal activation energy, gaseous products were evolved sites as the radiation dose increases as evidenced from sample A even a t temperatures as low as 100’ by the location of the inflection point (Table I). ‘4 p in one hour with reference to the scale in Fig. This seems compatible with the interesting result 1). Since phase a was not eliminated by dehydra- that the decomposition rate of heavily irradiated tion, it probably can be attributed to reaction at samples considerably exceeds that of unirradiated active sites formed by irradiation and not to de- samples immediately below the detonation temsorption of trapped gases. These sites are be- perature of the latter. In unirradiated samples, lieved to be the “irradiation nuclei” and are dis- the acceleratory phase must represent decomposition in much more localized regions of the crystal tributed throughout the crystal mass. Following phase a, a period of constant gas evolu- in order for self-heating and detonation to occur. tion occurs (b) ; this has an activation energy of 41 This suggests that the chain branching mechanism kcal./mole for unirradiated material and was as- suggested for the decomposition of lead styphnate must be localized next to cribed to reaction starting from the surface of de- dehydrated in hydrated blocks which comprise the anhydride. the opposite faces from which branching comFigure 3 shows the dependence of the rate constant, menced, or next to internal surfaces formed by cracking due to interfacial strain induced by phase k b , upon the radiation dosage. After a dose of 2.2 X lo1* ncm.-2, the kb for sample A has increased b. 19 (Fig. 3). Activation energies by a factor of (9) R. A. W. Hill and J. N. Welsh, Trans. Faraday Soc., 66, 1050 were determined from kb for samples A and (1960). +.-.-+4-4--4
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THERMAL DECOMPOSITION OF CY-LEAD AZIDE
Mechanism.-The result that dehydration does not remove any of the radiation damage with respect, to the subsequent thermal decomposition is noteworthy. It has been shown that the anhydride and the original monohydrate exhibit different X-ray patterns4&and, therefore, although crystallization occurs following dehydration, it does not remove or significantly alter the regions of radiation damage. This suggests that the significant form of radiation damage is irreversibly altered styphnate units rather than displaced ions and vacancies, e.g., Pb++. This does not seem unreasonable since, in contrast to a metal where the clamage due to displaced atoms and vacancies can anneal readily, an atom displaced from the complex styphnate ion would result in a chemically
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altered species which could decompose further, rearrange, or perhaps even polymerize in the regions of extensive damage. The very low activation energy for the initial gas evolution, 10 kcal./ mole, must represent decomposition of such chemically altered styphnates since it is unlikely that physical changes in the lattice could lower the activation energy to such a small value. The chemically altered styphnates appear to be stabilized in the lattice in some manner because of the stability of the radiation damage and the small quantity of gas evolved during irradiation. Acknowledgments.-The author thanks Drs. G. J. Dienes and J. Jach for valuable discussions. The interest of Drs. J. V. R. Kaufman and P. W. Levy in this work is greatly appreciated.
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THERMAL DECOMPOSITION OF SILVER-COATED a-LEAD AZIDE BY BRUNO REITZNER, J. V. RICHARD KAUFMAN, AND EUGENE F. BARTELL Explosives Research Section, Explosives and Propellants Laboratory, Picatinny Arsenal, Dover, New Jersey Receiaed August $1, 1.961
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The induction times of the thermolysis reaction Pb(N& +. Pb 3Nz can be reduced by coating Pb(N& with metallic silver. This effect is attributed to the catalytic effect of the silver. The induction time of the slow thermolysis in vacuum a t 2401’ is substantially the same with 1.0 and 10.0 atom% Ag. Water incorporated into the lead azide during the coating procedure reverses the effect of the silver causing a poisoning of the autocatalytic reaction. Mass spectrometric analysis shows that the water undergoes a hydrolysis reaction with Pb(N& whereby hydrogen azide is formed. A bridge propagation mechanism is assumed to occur in the later stages of the decomposition in the mass of crystals to explain some anomalies occurring with the silver-coated materials. The sensitization effect of the silver also was found when Pb(Tu’& was ignited in air at high,er temperatures, although the presence of air caused some anomalies.
Introduction The thermal decomposition of a-lead azide is considered to be an autocatalytic process in which the decom.position product-metallic lead-acts as the catalyst.’ I n previous work2 it was shown that the :zutocatalytic reaction was suppressed when the decomposition was carried out in an atmosphere containing water vapor. It was concluded that the water destroyed the lead nuclei which are necessary for the autocatalytic reaction. On this basis it should be possible, therefore, to enhance the autocatalytic reaction by depositing metallic lead on the lead azide surface. This is, however, difficult to achieve. Therefore, the hypothesis was made that the autocatalytic reaction is enhanced1 not only by lead, but also by any other metall. A confirmation of this hypothesis could be found in the work by Hill and W i t t e n b ~ r nwho ,~ decomposed lead azide in the presence of zinc powder. A. sensitization of the lead azide was obtained which was attributed to the catalytic action of the zinc. Since in mechanical mixtures the contact betweon the metal and the lead azide is not very good it was decided to use a more intimate mixture. One way of preparing such a mixture is to precipitate a metal on the lead azide by reducing a solution of a salt of this metal. Silver was con(1) W. E. Garner, “Chemistry of the Solid State,” London, 1955, Ch. 7 and 9. (2) B. Reitzner, J. Phys. Chem., 68, Q48 (1961). (3) 0.H. Hill and A. F. Wittenborn, Appendix A to Final Report DRL-A-125 under Army Contract DA-44-099-ENG-2566, Univ. of Texas, 1957.
sidered favorable in this respect since its salts can be reduced easily. Materials.-The a-lead azide used for this study had an average particle size of about 7 p . The cationic impurities (Na, Cu, Mg, Si, Fe, Ag), as determined by spectral analysis, were less than 0.1%. Silver was deposited on this material according to the following procedure: A suspension of 1.46 g. (0.005 mole) of a-lead azide in 100 cc. of a 9: 1 methanol-water mixture‘ was stirred for 15 min. A measured amount6 of 0.1 N AgNOs solution was added to the suspension. After an additional 10 min. of stirring no silver could be detected in the solution (hydrazine as test reagent). It was assumed that the reaction Pb(N& 2AgN01 2A8Ns 4 Pb(N0t)S had occurred, and that AgNI was deposited on the non-reacted lead azide grains. An excess of hydrazine hydrate (0.3 cc.) then was added to this suspension to reduce the AgNr, and stirring was continued for another 30 min. The samples darkened in color to a degree dependent on the amount of silver deposited. To test whether all of the silver azide was reduced, a small portion of the sample was shaken with ammonia, the solution filtered off, and acidified with “21. The absence of a precipitate indicated complete reduction. As a control for investigating the effect of hydrazine hydrate alone, a duplicate preparation was made omitting the addition of the silver nitrate. The silver-coated batches and the batch trqated with hydrazine hydrate alone were filtered, washed with 100 eo. of 9:l methanol-water mixture, and sucked to dryness. The dry batches were stored in a lightproof desiccator over CaCle The precipitation of silver caused a reduction in the bulk density of the lead azide. The values as determined by suspending weighed portions of the individual batches in
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( 4 ) An aqueous suspenaion of lead azide yielded a product which waa not uniformly coated with silver. ( 5 ) The amount of ailver nitrate solution wan varied depending upon the amount of ailver desired in the final hatch. For instance, 0.5 CC. was used for the batoh containing 1.0 atom% Ag.
