Radiolysis of Ammonium Perchlorate under X-ray Irradiation

V. A. Nevostruev, Yu. A. Zakharov, V. V. Anikeeva

(Presented by the scientific seminar of the Department of Radiation Chemistry, Faculty of Chemical Technology)

In works [1, 2] we studied the radiation-chemical decomposition of ammonium perchlorate under the action of accelerated protons. When the data obtained in these works were compared with data on the γ-radiolysis of \(\mathrm{NH_4ClO_4}\) [3], a conclusion was drawn regarding the influence of LET on the ratio of the yields of the radiolysis products of the \(\mathrm{ClO_4^-}\) ion. It was of interest to verify this conclusion by studying the radiolysis of ammonium perchlorate under the action of radiation with an LET different from that of γ-radiation and protons.

The present work gives the results of a study of the radiolysis products of \(\mathrm{ClO_4^-}\) in \(\mathrm{NH_4ClO_4}\) under the action of X-rays with a maximum energy of \(0.18\) MeV. Irradiation and dosimetry in this case did not differ from those described in [4]; the absorbed-dose rate in ammonium perchlorate was \(9.3 \cdot 10^{15}\) eV/g·sec. The yield of decomposition of \(\mathrm{ClO_4^-}\) was determined as described in [1]. A description of the procedure for determining the individual decomposition products of \(\mathrm{ClO_4^-}\) may be found in [2].

Results and Discussion

Figure 1 shows the accumulation of the radiolysis products of ammonium perchlorate with dose. In the dose range studied, only the decomposition of the \(\mathrm{ClO_4^-}\) ion proved to be linear. The accumulation of products of deep radiolysis (chloride and chlorine) occurs with an increase in the radiation-chemical yield, whereas the concentration of \(\mathrm{ClO_3^-}\) tends toward saturation with increasing dose.

Such a pattern of product accumulation may be expected if one assumes mutual transformation of radiolysis products during irradiation. Since in the radiolysis of metal perchlorates no formation of \(\mathrm{Cl_2}\) was observed, and the main radiolysis product in that case is chlorate [5, 6], it was natural to assume that the products of deep decomposition of \(\mathrm{ClO_4^-}\) in ammonium perchlorate are formed in the course of secondary reactions. If the mechanism of chloride formation through ionization of the cation, proposed for metal perchlorates [5], is adopted, then one should expect that \(G_0(\mathrm{Cl^-})\) in ammonium perchlorate will be equal to zero, since upon ionization of the ammonium ion its decomposition will occur

Fig. 1. Accumulation of radiolysis products of ammonium perchlorate with dose:
1—decomposition of \(\mathrm{ClO_4^-}\), 2—\(\mathrm{ClO_3^-}\), 3—\(\mathrm{Cl^-}\), 4—\(\mathrm{ClO^- + Cl_2}\).

As can be seen from Fig. 1 (curve 3), the initial \(G(\mathrm{Cl^-})\) is indeed close to zero.

All the foregoing allowed us to assume that in ammonium perchlorate, as in metal perchlorates, the primary product of radiolysis of \(\mathrm{ClO_4^-}\) is the ion \(\mathrm{ClO_3^-}\), whose formation may be represented by the following reaction scheme:

\[ \mathrm{Cl_4^{--} \rightsquigarrow \overline{ClO_4},\ 1,\ [ClO_4^-]^*.} \tag{1} \]

After losing excess kinetic energy, the secondary electron may recombine, according to the Samuel–Magee hypothesis [7], with the radical \(\mathrm{ClO_4}\)

\[ \mathrm{ClO_4 + \bar e \to [ClO_4^-]^*} \tag{2} \]

or, having moved a considerable distance away from the parent radical, be captured by some trap. Such traps in the present case may be lattice defects, radiolysis products, or \(\mathrm{ClO_4^-}\) ions. The \(\mathrm{ClO_4}\) radical can apparently decompose spontaneously [5]

\[ \mathrm{ClO_4 \to ClO_2 + O_2.} \tag{3} \]

However, the probability of this reaction is small, since the yield of \(\mathrm{ClO_2}\) in the radiolysis of perchlorates is low. The excited ions \([\mathrm{ClO_4^-}]^*\), formed by reactions (1) and (2), give chlorate

\[ \mathrm{[ClO_4^-]^* \to ClO_3^- + O.} \tag{4} \]

The chlorate formed in this reaction is stable in the case of a metal cation. In the case of ammonium perchlorate, the chlorate ion formed should oxidize the ammonium ion. To confirm this

...the assumption, ammonium perchlorate irradiated with a single dose was analyzed by us after different storage times at room temperature. From the data obtained (Fig. 2) it is seen that the content

Fig. 2. Change in the concentration of radiolysis products in ammonium perchlorate irradiated with a dose of \(6.7 \cdot 10^{19}\) eV/g, as a function of storage time at room temperature. The designations are the same as in Fig. 1.

of chlorate decreases with a parallel increase in the concentration of chloride and chlorine, which is consistent with literature data concerning the instability of ammonium chlorate at room temperature [8]. On the basis of the foregoing, it may be concluded that the products of deep decomposition of the \(\mathrm{ClO_4^-}\) ion in the case of ammonium perchlorate are formed as a result of the nonradiation decomposition of ammonium chlorate.

\[ \mathrm{NH_4ClO_3 \to N_2O,\ H_2O,\ Cl^-,\ Cl_2,\ O_2.} \tag{5} \]

The data presented in Fig. 1 on the accumulation of radiolysis products of \(\mathrm{NH_4ClO_4}\) agree well with the proposed scheme of the elementary stages of radiolysis of ammonium perchlorate. It should be noted that chloride and chlorine may apparently also be formed in part as a result of the decomposition of ammonium chlorite and hypochlorite, which is confirmed by the presence of optical-absorption maxima in irradiated \(\mathrm{NH_4ClO_4}\) single crystals characteristic of \(\mathrm{ClO^-}\) and \(\mathrm{ClO_2^-}\) [9]. Judging from the small yields of the latter in metal perchlorates, it may be assumed that their contribution to the formation of \(\mathrm{Cl^-}\) and \(\mathrm{Cl_2}\) is smaller than by reaction (5).

The values of the radiation-chemical yields calculated from the linear portions of the curves in Fig. 1 are \(2.1 \pm 0.1\), \(0.78 \pm 0.10\), \(1.78 \pm 0.15\), and \(4.36 \pm 0.15\) for \(\mathrm{Cl^-}\), \(\mathrm{ClO^- + Cl_2}\), \(\mathrm{ClO_3^-}\), and for the decomposition of \(\mathrm{ClO_4^-}\), respectively. Comparison of these values with the data of the table given in [2] confirms the hypothesis advanced earlier [2] that the LET value has a substantial effect on the ratio of the yields of radiolysis products. This also agrees with the assumption of the important role of secondary processes in the formation of radiolysis products in ammonium perchlorate.

REFERENCES

1. V. A. Nevostruev, G. N. Bazhenova, Yu. A. Zakharov. In the collection: Chemical Reactions Involving Solids. Tomsk State University Press, Tomsk, 1968, in press.

2. V. A. Nevostruev, L. G. Bugaenko, Yu. A. Zakharov. Khimiya vysokikh energii 1, 406, 1967.

3. G. Odian, T. Acker, Th. Pletzki, J. Phys. Chem. 69, 2477, (1965).

4. V. A. Nevostruev, Yu. A. Zakharov. Kinetics and Catalysis 8, 210, (1967).

5. Van-Ven-Sin, L. G. Bugaenko, V. N. Belevskii. ZhFKh 40, 2766, (1966).

6. A. Prince, E. R. Johnson, J. Phys. Chem. 69, 359, (1965).

7. A. H. Samuel, J. L. Magee, J. Phys. Chem. 21, 1080, (1953).

8. F. Solymosi, T. Bansagi, K. Jaky, Z. Phys. Chem. (BRD), 48, 242, (1966).

9. V. A. Nevostruev, I. F. Kolesnikova, Yu. A. Zakharov. In the collection: Chemical Reactions Involving Solids. Tomsk State University Press, Tomsk, 1968, in press.

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