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169

A Study of the Solid Reaction between and Ferric Oxide by the Use of Fission Product Rare Gas

Sumio Ichiba

SYNOPSIS

In order to study the solid reaction between zinc oxide and ferric oxide over

a wide temperature range the fission gas emanation method was applied. It

was found that the reaction occurs in two processes, the first which occurs at

temperature below about 900•Ž is due to the structure sensitive properties of

ferric oxide and the second is attributed to the lattice loosening of the zinc

oxide. The reaction process could be investigated more sensitively by the fission

gas emanation method than by the radon emanation method.

(Received July 12, 1962)

I Introduction

In the preceding papers it was reported by the author that the solid reactions of fine

powder, such as change, dehydration, decomposition, oxidation and reduction

reactions can be observed by the heating curves of emanating radioactive xenon which was

previously incorporated into fine powders by fission recoiling. It was further pointed outs'

that the heating curves of fine powders like graphite in which no phase change occurs

may represent the characteristic properties involved in particle size distribution, imperfections,

surface area, pretreatment, etc. The radioactive xenon captured by imperfections of the

crystalline powder will be released successively as the imperfections disppear with rising

temperature. Since the heating curve of emanating xenon represent the characteristic property

of fine powder, the reaction process between solid powders will be observed continuously.

In the present experiment, the process of solid state reaction between zinc oxide and ferric

oxide was studied by the fission gas emanation method. The solid reaction between zinc

oxide and ferric oxide has been studied by many workers". Especially, W. SchrSder" studied

extensively the reaction process by Hahn's emanation method, which uses radon as tracer. By

the author's method in which xenon is used as tracer, the reaction process can be studied

more sensitively, and the relation between the reactivity and the powder property of the re-

actants could be made clear.

II Sample

Zinc carbonate of G. R. grade of Kanto Kagaku K. K. was used in the present work. The

zinc oxide, samples fo Nos. I and 2, was prepared by thermal decomposition of zinc carbonate by heating at 300•Ž and 1000•Ž, respectively, for 30 min. In all cases, zinc carbonate and zinc

oxide powders were ground in a agar mortar and filtered through a 250 mesh sieve. The preparation methods of ferric oxide samples are shown in Table 1. The ferric oxide samples

were also ground in a agar mortar and filtered through a 250 mesh sieve.

* Presented at the Annual Meeting of Japan Society of Powder Metallurgy, Tokyo, May, 1962. ** Chemistry Division, Japan Atomic Energy Resarch Institute.

昭 和37年10月 (7) 170 A Study of the Solid Reaction between Zinc Oxide and Ferric Oxide by the Use of Fission Product Rare Gas

Table 1 The preparation methods of the ferric oxide samples

The sample powder was mixed with formvar films containing dioxide powder

of small size, then irradiated with thermal neutrons of about 5•~10 15 per cm2 in a pneumatic

tube of JRR-1 or JRR-2 and cooled for a day. Ethyl alcohol was added to the irradiated

sample. The sample powder was separated from the films, after irradiation ; the whole

procedure consists of the procedures of passing through a wire gauze, a filtration by filter

paper and subsquent drying. In order to prepare the mixture for the solid reaction, another

nonactive reactant powder was added to the specimen previously incorporated with the fission

product rare gas, which was suspended in the ethyl alcohol. The resultant mixture was

separated by pouring on a wire gauze with hard stirring.

III Apparatus and Measurements

The apparatus used in the experiment was the same as that for the previous experiment.

In order to obtain the heating curves, the sample incorporated with the fission rare gas

was placed in the heating tube surrounded by an electric furnace, then the tube was evacuated

with a vacuum pump. The tube was filled with purified argon and then argon was flowed

at a constant rate of 50ml/min. The temperature of the furnace was raised at a constant rate

of 5•Ž/min. up to 1150•Ž. The radioactivity of the released xenon, which was carried by the

flowing argon, was continuously measured by passing the stream through the counting cell

inserted in a well of Nal scintillation crystal. Thus the heating curve could be obtained by

plotting the released xenon activities against temperatures.

IV Results and Discussion

The heating curves of zinc carbonate and zinc mixture are shown in Fig. 1. The

peak at 235•Ž of curve (a) shows the decomposition of the zinc carbonate. The peaks of curve

(b) represent the peak due to the imperfections in zinc oxide crystalline powder of sample No. 1

but the peaks disappeared in curve (c) of sample No. 2 of zinc oxide because of its high

decomposition temperature of 1000•Ž. The rise of curve (c) in the high temperature range

may be attributed to the lattice loosening which occurs at higher temperature than "Tamman

temperature". The X-ray diffraction diagrams of the zinc oxide samples show that the crystal-

lization was completed in sample No. 2 (Fig. 2).

The heating curves of ferric oxides are shown in Fig. 3. All the ferric oxides were iden-

tified as et-Fe2O3 by X-ray analysis, but their heating curves differ as shown in Fig. 3.

Three peaks appeared in curve (a) of sampe No. 1 ; these may also correspond to the imper-

fections existing in ferric oxide crystalline, as in the case of zinc oxide of sample No. 1. In

curve (b) of sample No. 2, however, those peaks appearing on the lower temperature side

in curve (a) disappeared, and only a single high peak remained. In sample No. 3 (curve (c))

* Japan Resarch Reactor-1, boiler type, operated at 50KW thermal out-put. ** Japan Resarch Reactor-2 , CP-5 type, operated at 3000KW thermal out-put.

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•u•²‘Ì‚¨‚æ‚Ñ•²–––è‹à•v‘æ9Šª‘æ5•† Sumio Ichiba 171

Fig. I Heating curves of zinc carbonate and zinc oxide samples. (a) : ZnCO3, (b):ZnO (No.1), and (c):ZnO (No.2).

Fig. 2 X-ray diffraction diagrams of oxide samples.(a):ZnO sample of No. 1 and (b) : ZnO sample of No, 2.

the same peak shifted to higher temperature, due to the longer duration of heating at the decomposition temperature. Furthermore, in samples Nos. 4 and 5 (curves (d) and (e)), the peak shifted to higher temperatures correspording to the respective decomposition temp- eratures.

昭和37年10月 (9) 172 A Study of the Solid Reaction Between Zinc Oxide and Ferric Oxide by the Use of Fission Product Rare Gas

Fig. 3 Heating curves of xenon release of ferric oxide samples.

The peak height of these curves will vary with thermal neutron dosage ; the numbers of imperfections formed in different samples cannot be compared with one another by the comparison of peak height. In the single curve, however, the relative aboundances of imperfections corresponding to each peak may be estimated from the peak height.

To investigate the solid reaction between ferric oxide and zinc oxide the radioactive xenon must be retained in zinc oxide powder up to high temperatures. Therefore , the zinc oxide of sample No. 2 incorporated with radioactive xenon was used as one reactant and the ferric oxide samples as the other reactants. The heating curves of the several mixtures are shown in Fig. 4. In the mixture with sample No.1 (curve (a)), a peak appeared at 590•Ž .

The X-ray diffraction diagrams (Fig. 5) of the same mixtures which were heated up to 400•K

630•‹and 800•Ž, corresponding to the changing points on the curve (a), showed that the reaction occurred at 400°C and was completed at 800°C. However, in the cases of (b) , (c),

(d) and (e), two peaks appeared in each curve, and it was ascertained by X-ray diffraction that the reaction proceeds through two processes. The X-ray diffraction diagrams of the mixtures of ferric oxide of sample No. 3 and zinc oxide which were heated up to the changing

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Fig. 4 Heating curves of the mixtures of Fe2O3 samples and labelled ZnO of sample No.2. points of curve (c) are shown in Fig. 6. The spinel pattern of zinc ferrite appeared at the the reaction temperature corresponding to the first peak of curve (c) of Fig. 4 ; it does not grow remarkably at the temperature range near to the first peak, but grows rapidly at the temperature of the second peak. The diffraction patterns of the starting materials can still be observed at the ascending part of the peak, and disappear at the temperatures beyond the peak and the spinel formation is completed. The relation between reactivity of ferric oxide and structure sensitivity may be seen in Fig. 3 and 4. That is, the first peak is predominant when ferric oxides were prepared by thermal decomposition at lower temperatures or for shorter heating period; the height decreases, as compared with the second peak, with increasing decomposition temperature and duration, and the situation is reversed in curve (e). The ferric oxide sample of No. 5 incorporated with fission rare gas was used as one reactant and zinc carbonate and zinc oxides samples as the other reactants. In this case, the curves do not differ remarkably from one another, as shown in Fig. 7. From the Figure, it

昭 和37年10月 (11) 174 A Study of the Solid Reaction between Zinc Oxide and Ferric Oxide by the Use of Fission Product Rare Gas

Fig. 5 X-ray diffraction diagrams of the mixtures of ferric oxide of sample No. 1 and zinc oxide of sample No. 2 which were heated to the tempera- tures of the changing points of the heating curve (a) in Fig. 4.

can be said that the reaction between zinc oxide and ferric oxide is not due to the structure sensitive properties of zinc oxide.

The reaction of zinc ferrite formation has been studied by many workers. The reaction rate varies with the method of preparation of ferric oxide. The ferric oxides prepared by thermal decomposition of ferric oxalate, ferric nitrate and ferric hydroxide, etc., have been used as starting material. The ferric oxide prepared from ferric oxalate reacted most rapidly with zinc oxide, the reaction being completed by heating at 800•Žfor 5min . When ferric oxide prepared from ferric nitrate was used as the starting material, the reaction was not completed by ordinary heat treatment. In the case of the ferric oxide from ferric hydroxide, the reaction was nearly completed by heating at 1300•Ž for 30 min. The reaction rate will largely depend on the calcination conditions of ferric oxide. It is known that the lower the temperature of decomposition is, the more rapid the reaction velocity is. These facts are clearly seen in the results of the present work.

The results obtained in this paper cannot be directly compared with those by W. Schroder5' which used radioactive radon as tracer, because of the different starting materials and of the existence of the radon precauser as an impurity. The reaction process between zinc oxide and ferric oxide can be followed more sensitively by this fission gas emanation method than by radon emanation method. Xenon is released only by diffusion, but the radioactive radon is

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Fig. 6 X-ray diffraction diagrams of the mixtures of ferric oxide of sample No. 3 and zinc oxide of sample No. 2, which were heated to the temperatures of the changing points of the heating curve (c) in Fig. 4. released by both diffusion and recoiling which constitutes background activity. The problem of the so-called "deposited background" in the counting chambers' in the case of radon is also eliminated.

V Summary

The process of solid reaction between zinc oxide and ferric oxide was stutied by the fission gas emanation method and the following conclusions were obtained.

1) The solid reaction between zinc oxide and ferric oxide proceeds through two processes; the reaction occurring at temperatures below 900•Žis sensitive to the structure of ferric oxide and the reaction above this temperature is attributed to the lattice loosening of zinc oxide.

2) The solid reaction involving no volatile substances could also be followed by the fission gas emanation method.

3) The fission gas emanation method proposed by present author is more sensitive than the radon emanation method.

昭和37年10月 (13) 176 A Study of the Solid Reaction between Zinc Oxide and Ferric Oxide by the Use of Fission Product Rare Gas

Fig. 7 (a) : Heating curve of the mixture of zinc carbonate and labelled ferric oxide sample of No. 5. (b) and (c) : Heating curves of each mixture of zinc oxide sample of Nos. 1 and 2 and labelled ferric oxide sample No. 5.

Acknowledgment The author is indebted to Prof. S. Kachi for his helpfull suggestions and to Drs. T. Nakai and S. Yajima for their continuing encouragement. The author also is gratefull to Miss S. Nemoto for her technical assistance during experiments.

References

1) S. Ichiba, J. Japan Soc. of Powder Metallurgy, 8 (1961), 137 2) S. Ichiba, J. Atomic Energy Soc. Japan, 3 (1961), 705 3) S. Ichiba, ibid., 3 (1961), 763 4) e. g., Huttig, Handbuch der Katalyse, edited by G. M. Schwab, Vol. VI, Wien, 1943, pp. 318-577, T. Takei, "The Theory and Application of Ferrite", edited by T. Takei, Maruzen, 1960, pp. 80. 5) W. Schroder, Ztschr. Elektrochem. 48 (1942), 241 W. Schroder, ibid., 48 (1942), 301 W. Schroder, ibid., 49 (1943), 6) G. Tammann and A. Sworykin, Z. anorg. allgem. Chem., 176 (1928), 46 7) S. B. Skladzien, "A Study of the Emanation Method for the Determination of the Surface Area of Oxide", ANL-6335 (1961).

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