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JAESHI CHOI AXD %‘ALTER J.
MOORE
Vol. 66
mental data. In a review by Everett and Young,16 involving holes of fractional size, as presented in So was computed from experimental data for a this paper, is a convenient extension of prior theolarge number of different adsorbent-adsorbate r i e ~to~ which . ~ it reduces in the limit r = 1. Subject systems. In almost all cases calculated, So us. 0 to the assumptions inherent in the theoretical curves deviated from the “ideal” curve (eq. 11 development, the theory specifies adsorption isowith r = l),but for 0> 1/2 the experimentalvalues therms and other thermodynamic quantities for fcll above the ideal curve rather than below, as in the adsorbed phase in terms of an additional paFig. 4. This is attributed to two effects. In the rameter r. For reasonable numerical values of the particular cases cited by Everett and Young, the latter, the theory is in better accord with a variety surfaces were energetically heterogeneous, and of experimental data than the earlier formulations multilayer formation set in long before the first for which r = 1. layer was completed. Both of these phenomena To obtain further checks on the theory discussed ~ ~ ~it is highly desirable to have data which are contribute to the above mentioned e f f e ~ t . l ~above The only instanct: that has come to the writers’ taken with the specific objective of testing the attention where the deviation of the experimental results cited here. In particular, the data should from the ideal So us. e curves is as indicated in be amenable to the determination of So. If systemFig. 4 is the work by Hill, Emmett, and Joyner18 atic deviations from the above theory are noted, f_or the adsorption of nitrogen on graphon. The it may be necessary to resort to a more sophistiS, us. 0 ciirve cited in the above reference roughly cated derivation in which the self-contradictory matches the curve in Fig. 4 for which r = 3. assumptions concerning the random distribution Summarizing, it may be said that the theory coupled with a non-zero configurational energy are eliminated. (16) D. H. Everett and D. M. Young, Trans. Faraday Soc., 48, 1164 (1952). Acknowledgment.-The authors are very greatly (17) L. E. Drain and J. A. Morrison, ibid., 48, 316 (1952); 49, 654 indebted to Dr. Walter H. Kleiner for his un(1953). stinting assistance in the preparation of this (18) T. L Hill, P. H. Emmett, and L. G. Joyner, J . Am. Chem. manuscript and for many fruitful discussions. Soc., 73, 5102 (1951).
DIFFUSIOX OF NICKEL I N SINGLE CRYSTALS OF NICKEL OXIDE’ BY JAESHI CHOIAND WALTERJ. MOORE Chemical Laboratory, l n d i a n a University, Bloonaington, Indiana Received January 18, 1988
The diffusion of 63Ni in single crystals of NiO has been measured by a sectioning method. From 1000 to 1470’ for NiO in air, D(Ni) = 1.83 x 10-3 exp( -45.6 kcal,/RT). The D was almost the same in crystals containing 4 X lo-* atom fraction trivalent impurities as in those containing 60 x 10-4 cobalt. A mechanism based on singly ionized cationic vacancies gives a quantitative interpretation of the AH* and AX* for the diffusion.
Previous studies of the diffusion of 83Niin NiO have yielded discordant results. Shim and Moore2 reported D N ~ = 4.4 X e x p ( 4 4 . 2 kcal./RT) ems2set.-?, whereas Lindner and Akerstrom,ausing similar techniques and in some cases crystals from the same boule, found D N ~= 1.72 X exp(-56.0 kcal./RT). We have undertaken the further measurements described in this paper in an effort to resolve this discrepancy. Both earlier studies were made by the method of decline in surface activity. The isotope BaNiis not well suited to this method since it emits a soft (63 kv.) p, and consequently very thin layers of the nickel oxide suffice to absorb most of the radiation. We therefore used in the present measurement of D a different method, which is more suitable for this soft tracer radiation. This is the method of surface activity after ~ectioning.~We also made some special tests of the activation energy of D by the method of Zhoukho~itzky,~ which is indepen(1) Work assisted by the U. S. Atomio Energy Commission, Contract
AT .(11-1)-250. (2) M. T. Shim and W. J. Moore, J . Cham. Phgs., 26, 802 (1957). (3) R. Lindner and A. Akerstrom Dzscussions Faraday SOC.,23, 133
(1957). (4) R. H. Condit and C. E. Birchenall. J . Metals, 8 , 1341 11956). (5) A. A. Zhoukhoyitzky. J . A p p l . Rad. and Isotopes, 6 , 159 (1959).
dent of the value of the absorption coefficient. A further improvement in technique was the annealing of the crystals before the diffusion run. Recent work6 has emphasized the necessity of such preannealing of crystals made by the Verneuil method. All our new results support the lower value of the activation energy. From 1000 to 1400” for monocrystalline NiO in air, D = 1.83 X exp(45.9 i 2.0 kcal./RT). The activation energy by the Russian method was E = 41 kcal. for polycrystalline specimens. Experimental Methods The single crystals of nickel oxide were cut as 4 to 5 mm. squares, 2 to 2.5 mm. thick. Crystals were used from two sources: Tochigi Chemical Industry Company, Osaka, Japan, and General Electric Company, Schenectady, New York. Spectrographic analyses were made of these materials. The Japanese NiO contained 0.6’% cobalt and 0.1% Mg, with traces of other elements. The G.E. crybtals contained less than 10 p.p.m. cobalt.’ Both square faces of a specimen were polished flat on a precision grinder, using silicon carbide paper of grades 1/0 to 4/0. The specimens then were pre-annealed in a stream of dry tank (6) Y. Oishi and W. D. Kingery, J . Chem. Phys., 33, 480 (1960). (7) Analysis %: A1 0.003, Co
