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SHOZO KISHIMOTO
is equal to that of the specimen completely annealed, it is concluded that dislocations are generated during electrolysis only when D K is larger than 0.1 amp./cm.Z and that the density of the dislocations, hence the degree of distortion in the metal, increases remarkably with DE. It often was observed8 that in electrodeposited metals such as Cu and Ni inclusion of oxide, hydroxide, and other impurities and hardness of metals increase considerably with DK. All of these facts can be attributed to the generation of dislocations which is caused by the lattice distortion due to the inclusion of impurities. (D) Chemically Deposited Copper.-Cu powder usually used for Gatterniann's synthesis is prepared by adding Zn dust in CuS04 solution. The catalytic activity of a 0.1-g. sample at 2.5' was (iii) 42.2 aiid (iv) 12.8 cc. in 20 min., the contribution of dislocations beincz 23%. Dislocations probably may be generated in an analogous manner as electrolysis under high current density. (E) Copper Reduced from Oxide Layer.Pieces of the same dimension as in II(A) were annealed, oxidized, and reduced a t 300". The (8) hl. Rchlotter. Dzscusszons Faradnv Soc., 31, 1177 (1935); W. Blum and C. Kasper, zbzd., 31, 1203 (1935).
Val. 66
induced catalytic activity (iv) a t 27' was 0.9 and 0.5 cc. for specimens the oxide layer of which before reduction was 560 k. thick and far thinner, respectively. This indicates the possibility of generating dislocations in a very thin layer on metals during a chemical change such as reduction. (F) Irradiation with Neutrons.-Well annealed pieces were irradiated with neutrons and the resulting catalytic activity was investigated after the disappearance of the induced radioactivity. Thermal neutrons/cm.2 1-2 X 10'6 1.5 X Induced activity, (iv), cc. 0 0.3 a t 25", 0.7 at 30" (iii) = 1.6-1.0
i.e., dislocations are generated although the efficiency is not high. of Co60 (G) Irradiation with y-Rays.?-Rays amounting to 3.7 X lo* r. were irradiated on a well annealed specimen, resulting in no generation of catalytic activity and dislocations. Acknowledgment.-We wish to thank Dr. H. Wakeshima, Dr. H. Takegoshi, Dr. A. Saika, and Mr. S. Taniguchi for their kind advice and assistance. Our thanks also are due to the Ministry of Education in aid of this research.
STUDIES OK THERMOELECTRIC FORCE AND LATTICE DEFECTS AS ,lCTIVE CENTERS I N METALLIC CATALYSTS' BY SHOZO KISHIJIOTO Chemical Dcparlixcnt, Sczencc Faculty, Kobe I'navcrsify, Hzgashinnda-ku, Kol c, Jnpnii IIpcezied June 1 9 , 1962
Changes in thermoelectric force ( S )by annealing werc measured for copper and nickel cold-worked a t room temperature. I n the case of copper (90 ,- 15% compression), the changes in the region from 120 to 400" are attributed to the disappearance of dislocations ( 2 ' ~ ) . The changes for nickel (80% compression) occurred in two stages, one between 200 and 300" and the other above 400". These are attributed to the disappearance of point defects (vacancies) ( T y ) and dislocations ( TD),respectively. T Dwas considerably shifted to lower temperatures, with increase in the degree of compression. The complete parallelism between changes in S and decreases in the catalytic activities of cold-worked copper and nickel during annealing waa found. Consequently, it is concluded that the lattice defects a t the surface play the part of active centers for various reactions and that the measurement of S is a convenient and effective means of identifying lattice defects with active centers.
Introduction It was assumed by Taylor2 that catalytic reactions take place a t active sites only. There is much evidence that indicates the existence of active sites on the surface of catalyst, but few attempts have been made experimentally to determine their structure. In the last decade, the behaviors of lattice defects in cold-worked, quenched, and irradiated metals have been studied by measuring the release of stored energy, changes in density, extra-resistivity, and hardness during annealing. Consequently, the structure and properties of defects have been el~cidated.~-O (1) Read a t the Annual Meeting of the Chemical Society of JarJan held on April 5 , 1962. (2) H. S. Taylor, Proc. Roy. Soc. (London), AlO8, 10; (1925). (3) L. M. Clarebrough, M. E. Hargreaves, and G . W. West, ibid., AL839, 262 (1955). (4) (a) L. M. Clarebrough, M. E. Hargreaves. and G. W. West, -4cla Metal.. 6, 738 (1957); (b) Phil. Mag., 1, 528 (1956).
It was proposed recently by Uhara and co-workers that lattice defects (point defects and dislocations) a t the surface of metallic catalysts play the part of active centers for various reactions in the case of copper' and nicke1,s in view of the fact that the disappearance temperature of vacancies (T,) or dislocations ( T D )agrees with decreasing temperature of catalytic activities of cold-worked metals during annealing. Since T D is markedly influenced by the impurities as well as by the degree and method of cold-working, it is desirable to make these comparisons with the same specimens. It was found by Tammanng in 1933 that the ( 5 ) L. M. Clarebrough, M. E. Hargreaves, and G. W. West, Acta Metal., 8 , 797 (1960). (6) T. Broom and R. K. Ham, "Vacancies and other point defects in metal and alloys" (Inst. of Metals Monograph 23). (7) I. Uhara, S. Yanagimoto, K. Tani, and G. Adachi, Nature, 192, 867 (1961). ( 8 ) I. Uhara, Y. Numata, H. Hamada, and Y. Kageyama, J . Phys. Chem., 66, 1374 (1962). (9) G. Tammann and G. Bndel, Ann. Physik., 16, 120 (1933).
LATTICEDEFECTS AS ACTIVECETU'TERS I N
Dec., 1962
0.15
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kfETALLIC CATtlLYSTS
I
100 200 300 400 500 Annealing temp. ("C.).
I
I
I
Fig. 3.-Changes in thermoelectric force and catalytic activities of cold-worked copper: (A) thermoelectric force (15% compression); (B) dehydrogenation of ethyl alcohol (Uhara and Teratani); (C) decomposition of diazonium salt (Uhara, Yanagimoto, Tani, and Adachi).
I
I
100 200 300 400 Annealing temp. ("C.).
500
Fig. 1.-Changes in thermoelectric force ( S )of cold-worked copper and their first difference by successive annealing 30 min. a t each temperature: (A) 90% compression; (B) 57% compression; (C) 15% compression.
I 2.2
I
I
I
2.3
I 2.4
I
2.5
1 / T X 103.
Fig. 2.-Determination of activation energy for the disappearance of lattice defects in cold-worked copper (90% compression).
thermoelectric force (S) of cold-worked metals is affected by annealing. Since then, however, little effort has been made to extend his work either theoretically or experimentally.lOsll We have found the complete parallelism between changes in S and decreases in the catalytic activity of coldworked metals on annealing. It is suggested that the measurement of S is a more convenient and effective means for the purpose of identifying lattice defects with active centers than the measurement of the other physical properties mentioned above. I. Thermoelectric Force (S) of Cold-Worked Metals (1) E erimenta1.-Wires well annealed in the atmosor HZat 600 or 900' were compressed at room phere of temperature and S of cold-worked wire was measured against an annealedwire to 10-8volt aa a function of the temperature of the hot junction, the cold junction always being kept a t room temperature in a thermostat. A linear relationship waa found between S and the temperature difference at the junctions below 50". I n order to obtain the disappearance (IO) C. A. Domenicali and F. A. Otter, Phys. Rea.. 95, 1134 (1954). (11) T. L. L. Richards, 9. F. Pugh, and H. J. Stokee, Acta Metal., 4, 75 (1956).
100
200
300 400 500 600 Annealing temp. ("C.).
700
Fig. 4.-Changes in thermoelectric force and catalytic activities of cold-worked nickel: (A) thermoelectric force (80% compression); (B) hydrogenation of ethylene (Eckell); (C) p-o HZconversion (Uhara and Numata); (D) dehydrogenation of ethyl alcohol (Uhara and Numata); (E) hydrogenation of cinnamic acid (Uhara and Hamada); (F) p-0 H Zconversion (Cremer and Kerber). range of defects, the cold-worked wire was annealed in Ns or H? at various temperatures for a definite time (30 min.), and the changes in S were memured.
(2) Results. The changes in S of cold-worked copper (15,57, and 90% compression) by annealing are shown in Fig. 1. As the degree of compression increases, the recovery temperatures of X ( T D )is shifted to lower temperatures. The peaks of A S / A T curves were found at 300, 200, and 150°, respectively. I n comparison with Clarebrough and his co-workers' results3.*(measurements on stored energy, etc.), these phenomena are attributed t o the disappearance of dislocations in cold-worked copper, because point defects disappear by annealing below room temperature. On the assumption
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H. B. HETZER,R. A. ROBISSOS,. ~ N DROGERG. BATES
that S of cold-worked metals is proportional to the concentration of defects, the activation energy for the motion of dislocations (E,) could be determined for a specimen of 90% compression. From the curve shown in Fig. 2, Emis estimated to be 1.4 e.v. in the region between 140 and 200°, which agrees with the values obtained by Phillips'z (1 2 e.v. a t 200"). The recovery curve for cold-worked nickel (80% compression) has two stages, one between 200 and 300" and the other above 400" as shown in Fig. 4A. According to Clarebrough and his co-w0rkers,~-5 these are attributed to the disappearance of vacancies ( Tv) and dislocations (TD), respectively. Tammann reports that the changes in S occur only in the region from 150 to 350". 11. Lattice Defects as Active Centers in Heterogeneous Catalysts Uhara and his co-worker~~.'~ found that the activities of twisted copper for the decomposition of diazonium salt and dehydrogenation of ethyl alcohol considerably decrease by annealing at about 350°, as shown in Fig. 3 . This temperature range coincides with the recovery temperature of S (Fig. 1) for a slightly cold-worked specimen (the compression is usually more severe working than twisting as shown by the comparison of induced catalytic activity). I n 1933, it was found by Eckell14that the catalytic activity of nickel for the hydrogenation of ethylene was enhanced by a factor of 600 to 1000 after rolling. Since the activity is eliminated by annealing in the region from 200 to 300°, as shown in Fig. 4B, we may conclude that the active center
-
(12) V . A. Phillips, J . Inst. Metals, 81, 185 (1952). (13) I. Uhara, S. Yanagirnoto, K. Tani, G. Adachi, and S.Teratani, J . Phys Chem, 66, 2691 (1962). (14) J. Eckell, 2. Eiektroeheni., 39, 433 (1933).
Vol. 66
is some kind of point defect a t the surface, contrary to Cratty and Granato's postulate15 ascribing the activity to dislocations. Uhara, et. aL,8 found that the catalytic activities of cold-worked nickel for para-ortho (p-0) Hz conversion, dehydrogenation of ethyl alcohol, and hydrogenation of cinnamic acid decrease suddenly in the two temperature ranges Tv and T D , perfectly in parallel with the change in S as shown in Fig. 4 C 4 E , when the measurements were carried out with the same cold-worked specimens. Consequently, active centers in these catalysts may be both point defects and the termination of dislocations a t the surface. iiccording to Cremer and Kerber,16 the activity of nickel foil for p-o Ht conversion was decreased by raising the temperature of annealing as shown in Fig. 4F. Since the foil was prepared by severe deformation, it is felt that T Dwas shifted to lower temperatures, eventually overlapping Tv. Similarly, it is almost impossible to find the distinction between TV and T D for active centers in ordinary catalysts, which are prepared by chemical procedures and contain a large number of defects, as shown by X-ray studies. The measurement of S of cold-worked metals can be carried out readily by a simple technique with a small quantity of the sample, and hence it offers a very convenient method for identifying lattice defects with active centers in metallic catalysts. Studies on platinum catalysts will be reported in forthcoming papers. Acknowledgment.-The author wishes to express sincere thanks to professor Uhara for his kind guidance and to Dr. Saika for his advice. (15) L. E. Crattyand A. V. Granato, J. Chem. Phys., 26,96 (1957). (16) E. Cremer and R. Kerber, Advan. Catalysis,7 , 82 (1955).
DISSOCIATION CONSTANT OF t-BUTYLAJIMONIUM ION AND RELATED THERMODYNAMIC QUAXTITIES FROM 5 TO 35' BY HANNAH B. HETZER,R. A. ROBINSON, .4ND ROGER G. BATES Solution Chemistry Section, National Bureau of Standards, Washington 26, D. C. Received June 26, 1963
The acidic dissociation constant of t-butylammonium ion has been determined from 5 to 35" by e.m.f. measurements of hydrogen-silver bromide cells without liquid junction. At 25", -log Kt,h = 10.685, and the temperature coefficient of the dissociation constant gives the values AH0 = 60,070 j. mole-' and ASo = -3.1 j. mole-' deg.-'. These thermodynamic constants are compared with the corresponding values for the acidic dissociation of the protonated forms of the aminoalcohols related structurally to t-butylamine.
Introduction The relationship between basic strength and molecular structure has long been of interest.' Recent studies of the basic dissociation of the aminoalcohols have shed further light on the influence of structural factors in this class of com-
pounds. To this end, the dissociation constants for the three ethanol-ammonium ions were deterIn addition, the three structurally related substituted ammonium ions, namely, 2ammonium- 2 - (hydroxymethyl) - 1,3- pr~panediol,~ 2-ammonium-2-methyl-1,3-propanediol,6~7 and 2-
(2) Monoethanolamrnonium: R. G. Bates and G. D. Pinching, (1) See, for example, D. H. Everett and W. F. K. Wynne-Jones, J. Res. Natl. Bur. Std., 46, 349 (1951). Proc. Roy. Soe. (London), A177, 499 (1941); A. G. Evans and S. D. (3) Diethanolammonium: V. E. Bower, R. 9.Robinson, and R. G. Hamann, Trans. Faraday Soc., 47, 34 (1951); D. H. Everett and B. R. Bates, ibid., 66A, 71 (1962). W . Pinsent, Proc. Roy. SOC.(London), U 1 6 , 416 (1952); R. P. Bell, (4) Triethanolarnrnonium: R,G. Bates and G. F. Allen, ibid., M A , "The Proton i n Chemistry," CornelJ University Press, Ithaea, N. Y., 343 (1960). 4959 chapter 5.
