ENGELHARD INDUSTRIES, Inc. TECHNICAL BULLETIN Volume vII Numbers 1/2 JUNE/SEPTEMBER 1966 () HI/I{ N.( - 21(vZ!A?; ~r .jk. ~yo:zjA~ .w/orTjo/t le!.. riL()"'-'"'t k (j . Z/ (e ~te ~u-i~ e.JffJ#~ Z Z - 2 T A'rf - Q».-)( ENGELHARD INDUSTRIES, Inc. TECHNICAL BULLETIN Volume VII Numbers 1/2 JUNE/SEPTEMBER 1966 THOMAS GRAHAM COMMEMORATIVE ISSUE Ted B. Flanagan, Guest Editor Engelhard Industries Technical Bulletin CONTENTS VOL. VII, NOS. 1/2 JUNE/SEPTEMBER, 1966 FOREWORD E. F. Rosenblatt .............................................................................................................. . 7 INTRODUCTION TO THE COMMEMORATION OF THE CENTENNIAL OF THOMAS GRAHAM'S DISCOVERY OF THE ABSORPTION OF HYDROGEN BY PALLADIUM Ted B. Flanagan (University of Vermont) .................................................................... 9 THERMODYNAMIC STUDIES ON THE HYDROGEN-PALLADIUM SYSTEM John G. Aston (Pennsylvania State University) ............................................................ 14 LOW TEMPERATURE ELECTRONIC EFFECTS AND NEUTRON DIFFRACTION STUDIES OF PALLADIUM CONTAINING ABSORBED HYDROGEN A. 1. Schindler (U.S. Naval Research Laboratory) ...................................................... 21 LATTICE-DISTENSION AND THE MAGNETIC SUSCEPTIBILITY OF PALLADIUM HYDRIDE Thomas R. P. Gibb, Jr. (Tufts University) ................................................................ 28 USE OF CHANGES OF THE ELECTRICAL RESISTANCE OF PALLADIUM AS A GUIDE TO CHANGES OF HYDROGEN CONTENT R. Burch and F. A. Lewis (Queen's University) ........................................................ 36 SOLUBILITY AND DIFFUSION OF HYDROGEN AND DEUTERIUM IN PALLADIUM AND PALLADIUM ALLOYS H. Brodowsky and E. Wicke (Universit~it Munster) .................... ............................... 41 DIFFUSION OF HYDROGEN THROUGH PALLADIUM A. C. Makrides and D. N. Jewett (Tyco Laboratories, Inc.) ...................................... 51 PERMEATION OF DEUTERIUM AND HYDROGEN THROUGH PALLADIUM AND 75 PALLADIUM-25 SILVER AT ELEVATED TEMPERATURES AND PRESSURES Leonard R. Rubin............. ............................................................ .................................. 55 ABSTRACTS OF SELECTED U.S. PATENTS JANUARY 1966 - JUNE 1966 1. Patents Assigned to Engelhard Industries, Inc. ......................... ........... ............... 63 n. Othcr Patents on Applications of Platinum Metals and Gold ...... ... .................. 65 Physical Applications .................................................................... ......... ............ 65 Electrochemistry and Surface Coating ...................................... ........................ 69 Catalytic Hydrogenation ...................................................................................... 73 Catalytic Petroleum Processing .......................................................................... 75 Other Catalytic Processing .................................................................................. 81 Refining, Analysis and Miscellancous ......................................... ...... ................. 86 INDICES TO VOLUMES I-VI ............................................................................................. 89 Please address all correspondence to Laura A. Magistrate, Editor Enge1hard Industries, Inc. Research and Development Division 497 De1ancy Street Newark, N. J. 07105 COPYRIGHT 1966, ENGELHARD INDUSTRIES, INC. PRINTED IN THE UNITED STATES OF AMERICA ------------------- FOREWORD T HE present issue of Engelhard Industries Technical Bulletin has been devoted to commemorate the centennial of Graham's discovery of the unique proper ties of the palladium-hydrogen system, notably the high solubility of hydrogen in palladium and its mobility in and through palladium. Since that time extensive research has been and continues to be carried out in this field. However, only during the past ten years has the status of the palladium-hydrogen system changed from one of academic interest to only one of considerable technical significance for either the extraction of hydrogen from various gas streams or for the production of ultra-pure hydrogen on an industrial scale. The preparation of a commemorative Graham issue was suggested by Professor Ted B. Flanagan of the University of Vermont. Professor Flanagan was also kind enough to serve as editor for the present issue. He has enlisted outstanding experts in the field who have contributed comprehensive surveys as well as critical discussions on the palladium-hydrogen and palladium-deuterium systems or on the corresponding systems with palladium alloys. Areas discussed include the thermodynamics, physical properties such as electrical resistivity, magnetic sus ceptibility, thermal electromotive force, etc., the structure and the nature of the bond in palladium-hydrogen or palladium-deuterium alloys, as well as the kinetics and the models of diffusion and permeation through palladium or palladium alloys. We gratefully acknowledge the efforts of Professor Flanagan and of the contributors which have made this issue possible. Newark, New Jersey E. F. Rosenblatt July 29, 1966 President 7 Introduction to the Commemoration of the Centennial of Thomas Graham's Discovery of the Absorption of Hydrogen by Palladium TED B. FLANAGAN T HIS year, 1966, marks the centennial of istry; for example, in 1833 he discovered the the discovery by Thomas Graham of the three different forms of phosphoric acid.2 phenomenon of the absorption of hydrogen by Graham did pioneering research with colloids palladium. This collection of papers by well and, in fact, invented the word colloid.3 The known workers in the field was assembled to terms sol and gel were also coined by Graham. commemorate the centennial of his discovery. In keeping with his century he was keenly in The contributions in this Bulletin attest to the terested in problems of technology; one exam continued fascmation of this system. It should ple of this interest was his invention of a be added that these papers appear at a useful life saving jacket. time because the hydrogen-palladium system Graham published his observations of the has not been reviewed for many years and much phenomenon of hydrogen absorption by palla important work has appeared recently. dium when he was sixty-onc years old-ex actly one hundred years ago.4 In the same year he investigated the absorption of hydrogen by Thomas Graham a silver-palladium aIloy.4 It is of interest that Thomas Graham (1805-1869) was a key fig Graham happened to choose the palladium al ure in the development of modern chemistry loy system of perhaps the greatest current in in the British Isles. A student at the Univer terest in connection with hydrogen absorption sity of Glasgow, he obtained his M.A. there in both from the theoretical and the technological 1826. His scientific studies were continued at point of view. Also in 1866 Graham made the Edinburgh. In 1828 he was admitted to the observation that a palladium membrane could Royal Society and two years later was ap be employed to purify hydrogen. Two years pointed Professor of Chemistry at the Univer later he found that palladium could be charged sity of Glasgow. In 1841 Graham joined with electrolytically with hydrogen.5 Further re some friends to form the Chemical Society of searches on this system were published by London; he was elected its first president. Graham in 1869 (the year of his death); in Graham was appointed Master of the Mint in these publications he described measurements 1855 where, in addition to his other duties, he of the electrical resistivity and magnetic prop continued his chemical investigations. As erties of hydrogen-containing palladium and Master of the Mint he contributed significantly coined the word "hydrogenium."6 In this year to problems of coinage and the first bronze coin he also measured diffusion rates of hydrogen age in the British Isles was introduced under his in palladium. supervision. Graham did not believe that a definite stoi His publications span a large part of the nine chiometric compound was formed between hy teenth century (1826 to 1869) and include sev drogen and palladium; he believed rather that eral influential textbooks, e.g., "Elements of a homogeneous alloy resulted in which the ab Chemistry" (1833). Primarily his interests cen sorbed gas acts like a quasi-metal ("hydrogen tered on diffusion phenomena in gases and ium"). Although the nature of the bonding of liquids. From expcriments on the diffusion the hydrogen atoms to the palladium lattice re rates of gases1 Graham concluded that the rates mains controversial, it is fair to say that the of diffusion were inversely proportional to the most widely accepted model is not too far from square root of their densities; this is, of course, Graham's "hydrogenium." now known as Graham's law of diffusion. He With regard to Graham's work on this sys contributed significantly to other areas of chem- tem two facts stand out in the reviewer's mind: the advanced age at which Graham did his pioneering experiments and his choice of key From the Chemistry Department. University of Ver experiments. mont, Burlington, Vermont. 9 Thus Graham set the stage for the multitude ceptibility change with hydrogen content above of investigations of the system which followed the critical temperature. An additional effect in the next one hundred years. Physical chem ought to be considered, as Gibb points out, ists, physicists and metallurgists have all con namely that the expansion of the lattice itself tributed to the present understanding of the in the transition from pure palladium to the system but it must be emphasized that despite hydride phases would be expected to decrease the efforts of the last one hundred years many the susceptibility. problems remain to be solved. Although it had been postulated earlier that The many facets of the hydrogen-palladium the hydrogen atoms which enter the palladium system will be illustrated Ly the following brief lattice ionize into protons and electrons, Mott historical survey which emphasizes the role that and Jo nes16 specified that the electrons enter the system has played in the application of the partially empty d-band of palladium. This theories and experimental techniques which appears to have been the first application of have been developed since 1866. the band theory of metals to a process of chem ical interest. Mott's suggestion was undoubtedly Review of the a forerunner of the more recent applications of Hydrogen-Palladium System electronic band theory to the two-dimensional problem of chemisorption and catalysis on In 1887 Roozeboom pointed out the utility transition metals. It can be forcefully argued of the phase rule which until then had been that this is yet the best extant example of the obscured in the abstract work of Gibbs. Not role of the electronic band structure of metals long after (1895) Roozeboom and Hoitsema7 on a process of chemical interest. Although the applied the phase rule to the hydrogen-palla value of 0.6 holes in the d-band of palladium dium system and concluded that two solid is supported by a series of diverse experiments, phases were formed, although the isotherms this value nonetheless depends on one of the were not perfectly horizontal and the issue re following assumptions: the validity of the rigid mained somewhat in doubt. band model; analogies with the behavior of The great interest in nonstoichiometric com nickel; or approximate theories of paramagnet pounds is fairly recent despite the fact that an ism. It appears to the author and to others extreme example of such a system, i.e., one ex (see Gibb's article in this volume) that the hibiting large deviations from stoichiometry, magnetic behavior of the hydrogen-palladium hydrogen-palladium, dates back one hundred system in terms of holes in the d-band has, since years. Anderson8 recently pointed out that this 1936,16 subtly and unjustifiably changed from was probably the first nonstoichiometric system a reasonable explanation of a phenomenon to for which equilibrium measurements were avail strong evidence in favor of 0.6 holes. Recent able.7.9-10 Early attempts to force onto the evidence, in fact, suggests that there may only ~-phase the stoichiometry of Pd2H were, of be 0.36 holes in the d_band17-18 (see also course, doomed to failure. Schindler's article in this volume). The model As early as 1877 R. Blondlotll made the ob of electron donation is not invalidated by this servation that the paramagnetism of palladium recent finding, only the rigid-band approxima decreased as hydrogen was absorbed. More tion. Schindler and co-workers have recently quantitative investigations followed.12-15 It is obtained direct evidence in favor of the elec generally accepted that at room temperature tron donation model by utilizing low tempera the magnetic susceptibility falls to a diamag ture electronic heat capacity measurements on netic value at HjPd;:::0.6. Many investigators the hydrogen-palladium system. This signifi have also observed that the addition of noble cant research is discussed in this volume. metals to palladium leads to a similar decrease Ten years after von Laue's discovery that in the susceptibility.16 The apparent continu x-rays are diffracted by crystalline substances, ous decrease in susceptibility when hydrogen is McKeehan19 used x-ray diffraction to confirm added to palladium has been frequently misin the existence of two phases in the hydrogen terpreted (as has been pointed out in this vol palladium system. This was the start of many ume by both Schindler and Gibb) because the x-ray investigations of the system which, while two-phase nature of the system is ignored. In useful, did not resolve the crucial question of fact, the often-obtained magnetic data imply the location of the hydrogen atoms. Neutron merely that the ~-phase has approximately zero diffraction subsequently was employed to locate paramagnetism. In this connection it would be the positions of the hydrogen atoms (see of interest to examine the paramagnetic sus- page 11). 10 In 1937 J. R. Lacher20 applied statistical co-workers.40 Aston and co-workers have ex mechanics to the hydrogen-palladium equili tended their calorimetric studies of this system brium isothermal data obtained by Gillespie to below 1 ° K;38 in this vicinity they have noted and co-workers.10 This was a step of consider an activated process. This represents the lowest able importance for two reasons: it constituted temperature at which a chemical process has an important example of a genuine three been observed in the solid state. dimensional lattice gas to which statistical me The extreme usefulness of new physical tools chanics could be successfully employed, and it in the elucidation of a system can be well illus was the first statistical mechanical treatment of trated by neutron scattering experiments on nonstoichiometry. At the least Lacher's original hydrogen-palladium. The ~-phase was found treatment can be said to have been semi to consist of randomly arranged hydrogen quantitatively very successful. More recent atoms occupying octahedral positions about the treatments have included specifically the change palladium atoms.4!.42 The positions of the hy in the approximate density of states relation drogen atoms have not been located in the ship in the d-band with added hydrogen2!.22 a-phase but Maeland43 has found that the octa thereby explaining the decline in the heat of hedral positions are occupied in the a-phase of absorption at high hydrogen contents.23-25 25% gold-palladium (weight percent gold) Lacher did not specify the nature of the hydro alloy. Neutron scattering experiments, in addi gen-hydrogen attractive interaction which must tion, have yielded mean vibrational amplitudes be included in the model to explain the forma of both hydrogen and palladium and the fre tion of the ~-phase. Recently Makrides,26 quency spectrum of the hydrogen.42 Schindler Stackelberg,27 Brodowsky and co-workers22,28 describes in this Bulletin some exceedingly im and Aston29 have discussed possible origins of portant results from recent experiments using this interaction. neutron diffraction at low temperatures where Diffusion of hydrogen in palladium was in evidence is found for an octahedral tetrahedral vestigated first by Graham himself. Interest in transition near 45 OK. This ties in beautifully this diffusion problem has continued because of with Aston's calorimetric data. its technological interest and because of its The electrical resistivity of the hydrogen fundamental importance as the most well palladium system is very useful as a convenient defined example of interstitial diffusion within tool for the determination of the specimen's a transition metal. hydrogen content, and in addition has some Many papers have been published on the dif inherent interest. The former aspect of the re fusion of hydrogen in pure a-phase, ~-phase sistivity is discussed in this volume in detail by and the mixed phase region. One example Burch and Lewis. A recent interesting applica which stands out is the elegant work of Jost and tion of resistivity for the determination of hy Widmann.3o They employed spheres of palla drogen content was utilized by Burke, Kemball dium with activated surfaces under conditions and Lewis44,45 in following catalytic processes where the complete diffusion equation could be at palladium electrodes. Because of the near solved. Their value for the activation energy, impossibility of making quantitative calcula 5,740 cal./mole H, in the a-phase compares tions on transition metals, resistivity is usually favorably with recent determinations in the not one of the more useful solid state properties a-phase.S!. 32 This low value is noteworthy from the fundamental point of view; however, because it possibly represents the smallest ob in certain cases useful quantitative results have served activation energy for interstitial diffu been obtained. For example, Coles and Tay- sion in a metal. Recent research in this field 10r46 have quantitatively accounted for the has extended the diffusion studies to palladium electrical conductivity of a series of silver rich alloys. Contributions in this area have been palladium alloys. Since relative resistivity in made by Makrides and co-workers33 and Wicke the hydrogen-palladium system, i.e., the ratio and his co-workers34.35 and are discussed in of the resistivity at any hydrogen content to the this Bulletin. hydrogen-free resistivity, may be determined as Low-temperature heat capacity determina a function of hydrogen content, quantitative tions on the hydrogen-palladium system were a priori calculations of the resistivity are not not done until the work of Aston and his co required - only the effects of the added hydro workers.36-39 They observed a heat capacity gen. Simons and Flanagan47 have examined peak in the vicinity of 55°K, the detailed ex recently the relative resistivity changes of pal planation of which followed later from the ladium in the a-phase (0° to 90°C) (see also neutron diffraction studies of Schindler and his Ref. 48); some limited progress was made in 11 the interpretation of the data in terms of Mott's dium-rich alloys is to determine whether the theory of the resistance of transition metals. model of electron donation to the empty metal The hydrogen-palladium system holds a bands is capable of explaining the absorption unique position in the investigation of the elec behavior of palladium alloys. Although reliable trochemical mechanisms of hydrogen reactions. data are just now being obtained, the interpre Hydrogen atoms can be deposited electrochem tation of the results in terms of the model ap ically at the surface of palladium and instead pears very encouraging (see Brodowsky and of recombining on the surface to yield gaseous Wicke in this volume). The author would like hydrogen, as is the case of platinum, gold, etc., to point out that these results and their inter the hydrogen atoms enter the metal. At equili pretation should be of great interest to workers brium with respect to the surrounding hydrogen in the field of heterogeneous catalysis and pressure, the hydrogen-palladium electrode chemisorption. If this model is capable of ex functions as a reversible hydrogen electrode. plaining the behavior of absorption by palla Frumkin has recently reviewed this area of dium and its alloys, then the more difficult research.49 two-dimensional problem of catalysis and chemisorption may be understandable in terms Absorption isotherms of palladium and its of the electronic structure of the metals when alloys have been obtained electrochemically. the nature of surface states is understood more One technique is to charge or discharge the fully. specimen and to record electrode potentials at various hydrogen contents. The Russian work Acknowledgments ers have used this technique extensively with electrolytically co-deposited palladium-rich al The author's research in this area is spon loy samples. 50 An alternate procedure is to sored by the V.S. Atomic Energy Commission bubble hydrogen gas through an acidic solution for which he is most grateful. Drs. Arnulf containing the sample and to record the spon Maeland and John Simons are thanked for taneous resistivity and electrode potential many stimulating discussions. Thanks are also changes as the specimen absorbs hydrogen from extended to Engelhard Industries, Inc., for pub solution (e.g., see Refs. 51-54). A somewhat lishing this special edition of Engelhard Indus modified version of the latter technique has tries Technical Bulletin and to the authors of been utilized to obtain equilibrium isothermal the articles for their cooperation and valuable data. The slow step in the absorption process contributions. is diffusion of dissolved hydrogen up to the References surface. In order to attain equilibrium within the specimen, the over-all rate of absorption is 1. Graham, T. Phil. Trans. Roy. Soc. (London) 136,349,573 (1846). reduced by decreasing the partial pressure of 2. Graham, T. Phil. Trans. Roy. Soc. (London) hydrogen gas in hydrogen-helium streams so 123,253 (1833). that time is allowed for internal equilibration 3. Graham, T. Phil. Trans. Roy. Soc. (London) to occur. This technique has been successfully 151, 183 (1851). applied to obtain data in the a-phase of pure 4. Graham, T. Phil. Trans. Roy. Soc. (London) palladium;55 arguments based on diffusion 156,415 (1866). 5. Graham, T. Proc. Roy. Soc. (London) 16, measurements support the equilibrium nature 422 (1868); Phil. Mag. 36, 63 (1868). of the data obtained. Equilibrium data below 6. Graham, T. Proc. Roy. Soc. (London) 17, 120°C have been difficult to obtain in the past 212, 500 (1869); Comptes rend. 68, 101, on either palladium or palladium-rich alloys 1511 (1869); Ann. Chem. Phys. (Paris) 16, using conventional gas phase techniques. The 188 (1869); Ann. Chem. 152, 168 (1869). 7. Hoitsema, C. and H. W. B. Roozeboom. technique described above has proved success Z. physik. Chem. 17, 1 (1895). ful in obtaining such data because special pro 8. Anderson, J. S. "Current Problems in Non cedures to insure surface activity can be carried stoichiometry," in Nonstoichiometric Com out in solution. pounds, Advances in Chemistry Series No. 39, Am. Ch em. Soc., Washington (D.C.), An alternate procedure has been recently 1963, p. 1. developed by Wicke, Brodowsky and their col 9. Sieverts, A. Z. physik. Chem. 88, 451 leagues for the obtaining of equilibrium iso (1914). thermal data below 120°C. Their important 10. Gillespie, L. J. and F. P. Hall.]. Am. Ch em. hydrogen transfer-catalyst technique is de Soc. 48,1207 (1926). 11. Blondlot, R. Compt. rend. 85,68 (1877). scribed in detail by these authors in this volume 12. Biggs, H. F. Phil. Mag. 32,131 (1916). where pertinent references are given. 13. Oxley, A. E. Prac. Ray. Soc. (London) The main purpose of the research with palla- AlOl, 264 (1922). 12