Palladium Foil Research Articles

Oxidation of CO on a Pd surface: application of IR-RAS to the study of the steady state surface reaction

The catalytic oxidation of CO and O 2 to form CO 2 has been studied on a polycrystalline palladium foil in a pressure range from 10 -4 to 1 Pa. The concentrations of both reactants and products were analyzed by a quadrupole mass spectrometer, while the coverage and binding states of the adsorbed species were determined by infrared reflection-absorption spectroscopy (IR-RAS), using an FT-IR spectrometer. This reaction was found to proceed via the Langmuir- Hinshelwood mechanism on the basis of the finding that the rate of steady state reaction of CO 2 formation was associated not with the gaseous pressures, but with the amounts of adsorbates. A reaction intermediate, adsorbed CO, was bridge-bonded on the Pd surface. It was also shown that the density of adsorbed CO depended only on the ratio of the gaseous pressure of CO to O 2 and not on the partial pressure of CO.

UV-photoelectron spectroscopy from xenon adsorbed on heterogeneous metal surfaces

UV-photoelectron spectra of xenon adsorbed on a series of homogeneous transition metal surfaces demonstrate a strict correlation between the Xe 5p 3 2 , 1/2 electron binding energies (referred to the substrate Fermi level) and the work function of the substrate. The same concept holds for xenon adsorption on heterogeneous surfaces. The effect is interpreted in terms of a pure dipole shift of the Xe 5p 3 2 , 1/2 states and has been utilized to titrate the relative abundance of different crystallographic facets on a polycrystalline palladium foil.

水素透過減少法に関する実験 Ｉ 液体金属介在法

A multi-purpose high-temperature gas-cooled reactor, excluding a power generation, is being designed to be operated as a heat source of the reducing gas which is applied to a direct steel-making process.The protection of hydrogen permeation through the heat exchanger tubes of the high-temperature gas-cooled reactor into a primary coolant is one of the most severe problems. Also in a thermonuclear fusion reactor the protection of tritium diffusion is considered to be essential from the standpoint of environmental contamination, because tritium has radioactivity.In the 1st report, a “liquid-metal-inbetween” method-hydrogen permeation is reduced by degassing through a palladium foil which is installed in a liquid metal region inbetween two metallic walls -is proposed, and the experiment verified the possibility of this idea. Moreover, it is shown that the reducing rate of hydrogen permeation can be lowered to any amount, if the area of palladium foil is large enough.In addition, the necessary development or technological problems when applied to an actual heat exchanger are also described.

The application of SIMS to the study of CO adsorption on polycrystalline metal surfaces

Secondary ion mass spectroscopy (SIMS) was used to study the adsorption of carbon monoxide on polycrystalline nickel, copper, iron, palladium and tungsten foils. The results demonstrate the ability of SIMS to distinguish, qualitatively, between molecular and dissociative adsorption. A correlation between SIMS results and those obtained by infra-red spectroscopy for molecular adsorption is also suggested.

α-鉄の表面自己拡散係数におよぼす酸素ポデンシャルの影響

The surface self-diffusivity of α-Fe was measured by the grain boundary grooving method in hydrogen atomospheres with dew points of −60 and +13°C. The groove width measurement was made through all runs with the same region of grain boundary of a coarse-grained specimen. The diffusion anneal was carried out at 800, 850 and 890°C.In dry hydrogen (dew point −60°C) purified through a palladium foil, the surface self-diffusivity of α-Fe can be expressed by the following equation:(This article is not displayable. Please see full text pdf.) The value of activation energy agrees well with that obtained by Blakely et al.In moist hydrogen (d.p.+13°C), however, the rate of groove development was varied, depending on whether or not the specimen had been equilibrated with the atmosphere. When the specimen, which had been in equilibrium with dry hydrogen, was annealed in moist hydrogen, the development rate of groove was larger than that in dry hydrogen in the early stage, but it decreased with annealing time. On the other hand, if the specimen had been equilibrated with the same atmosphere, the grooving rate was smaller than that in dry hydrogen. In the former case, surface roughening would occur more than in thermal equilibrium owing to the adsorption and solution reactions of oxygen at the surface, which would lead to an enhancement of surface diffusivity. On the contrary, on the surface of the specimen, which is equilibrated with moist hydrogen, the blocking of kink and adatom would occur by adsorption of oxygen, which would lower the surface diffusivity.A marked decrease in surface diffusivity in hydrogen with a dew point of +13°C was observed at 800°C with the specimen equilibrated with the same atmosphere, which could be attributed to an incidental adsorption of impurities during the sample preparation.

On the mechanism and kinetics of the CO-oxidation reaction on polycrystalline palladium: I. The reaction paths

Transient phenomena, which occur in the oxidation reaction of carbon monoxide catalyzed by palladium, have been characterized. The substrate, a polycrystalline palladium foil initially exposed to relatively large amounts of oxygen at high temperatures, was dosed alternately with oxygen and carbon monoxide and transient carbon dioxide production was monitored mass spectrometrically. Two different reaction paths were found to prevail. When oxygen is preadsorbed, exposure to carbon monoxide leads to carbon dioxide through CO(g) + O(a) → CO 2(g), an Eley-Rideal path. When the dosing sequence is reversed, a Langmuir-Hinshelwood reaction occurs, CO(a) + O(a) → CO 2(g). The former reaction can be used to quantitatively titrate surface oxygen and two methods of analysis can be used to determine the amount of adsorbed oxygen under working conditions. One method is useful when the working pressure of CO is low while the other is useful when it is high.

On the mechanism and kinetics of the CO-oxidation reaction on polycrystalline palladium: II. The kinetics

The kinetics of the oxidation of carbon monoxide have been studied extensively over polycrystalline palladium foils which were prepared by exposure to relatively large amounts of oxygen at high temperatures. Reaction orders with respect to CO 2, CO and O 2 were determined over various intervals of partial pressure, total pressure and temperature; 0.1 ⩽ P CO p O2 ⩽ 20, 10 −7 < p < 10 −3 Pa, and 450 < T < 873 K . The order with respect to CO 2 was zero under all the conditions tested. The orders with respect to O 2 and CO depended on the partial pressure ratio and showed very little dependence on total pressure. For p O2 < p CO the rate was first order in oxygen and negative 0.5 to 0.8 order in CO below 473 K. When p O 2 > p CO in this temperature range, the orders with respect to oxygen and carbon monoxide were zero and unity respectively. The inhibitory effect of CO vanished at T = 573 K. In this case the orders were the same as above except when p O 2 < p CO the order with respect to CO was zero. The amount of adsorbed oxygen was measured under working conditions at 473 K using a CO-titration method. For p O 2 >] p CO the amount of adsorbed oxygen is almost independent of p O 2 . The amount decreases sharply around P O 2 = P CO and is very small for p O 2 < p CO. The kinetic behaviour can be explained in terms of a change in the rate determining step, depending on the amount of adsorbed oxygen.

ChemInform Abstract: SURFACE AREA EFFECTS ON THE SORPTION OF HYDROGEN BY PALLADIUM

AbstractDie Isothermen Druck gegen Zusammensetzung für verdünnte Lösungen von Wasserstoff in Pd werden zwischen 100 und 240°C bei Drücken bis zu 1000 Torr mittels einer konventionellen volumetrischen Methode gemessen.

Surface Area Effects on the Sorption of Hydrogen by Palladium

Pressure–composition isotherms for dilute solutions of hydrogen in palladium have been measured at temperatures between 100 and 240 °C at pressures of up to 1000 Torr using a conventional volumetric technique. For palladium foil the isotherms are consistent with data over lower temperature ranges and with existing theoretical isotherms. With samples having appreciable surface area, however, a higher sorptive capacity is found which, it is suggested, is due to the formation of a layer of adsorbed hydrogen on the metal surface. It is demonstrated that correction can be made for this effect, to some extent, giving better agreement between the experimental data and the theoretical isotherm.The variation of partial molar enthalpy of absorbed hydrogen with hydrogen content is also affected by this surface phenomenon, although the data available at present are not sufficiently accurate for a detailed discussion.

Electrochemical methods for diffusion measurements

AbstractThe hydrogen pressure at the surface of a metal sheet, e.g. a palladium foil immersed in an electrolyte, can be measured by means of the electrochemical potential. With proper activation of the metal surface the partition equilibrium between hydrogen dissolved in the metal and in the electrolyte prevails at all times. This yields the relationship between the atomic ratio H/Me within the metal and the electrochemical potential.On this basis various techniques have been developed for the measurement of diffusion coefficients of hydrogen in Pd. ‐ These methods are described in a short review.The great advantage of electrochemical methods compared to other techniques will become clear by a more detailed description of two electrochemical time‐lag methods, the step and the pulse technique, which have been used to investigate the diffusion of hydrogen and deuterium in Pd and Pd/Ag alloys up to 60 percent silver content and more recently in Ta.With simple equipment the dependence of the diffusion coefficient on hydrogen concentration from extremely low pressures up to one atmosphere could be measured very precisely. The values obtained with these convenient methods range from 10−6 cm2 s−1 in pure Pd to 10−10 cm2 s−1 in Pd/Ag 40/60. Furthermore the methods are sensitive enough to yield the differences in diffusion coefficients of H and D in these alloys. The isotope effect will not be discussed here. A more detailed interpretation is given in following papers.

High Yield, Long-Lived Tritium Targets

In order to extend the lifetime of conventional nonrotating tritium targets (say, TiT2), a new design concept for neutron generator targets has been tested successfully. It consists of a device which allows the target area to be replenished during operation. It has been used to produce neutrons [T(d,n)4He reaction] for about ten hours at a sustained 4? yield of 2-4 × 1010 n/mA-s. Tritium diffuses through a palladium foil into the target area when the foil is heated by a deuteron beam. Control of the flow of tritium is accomplished by regulating gas pressure in the reservoir and water flow in the cooling system.

Chemisorption of xenon and fluorine on nickel and palladium

A radiotracer technique was used to study the adsorption of xenon in the presence of fluorine on nickel and palladium foils. Isotherms measured at temperatures of 243–373 °K showed that xenon was adsorbed. Examination of the surfaces by electron microscopy showed that the presence of xenon markedly influences the attack of fluorine on the metal. It is suggested that xenon is chemically bound to fluorine in the absorbed state, and that this constitutes the intermediate in the catalyic formation of xenon difluoride.

The preparation of palladium foil objective aperture diaphragms with increased contamination resistance

A new type of foil objective aperture diaphragm for the electron microscope is described. The aperture which is a double layer of palladium and gold, has successfully been made with a total thickness down to approx. 0.4μm of which the gold layer, which is required for extra strength during stripping, only represented a thickness of approx. 0.1μm. The total life span of this palladium aperture was 7–800 hours of beam current irradiation before any axial astigmatism was observed, and approximately twice the life span of gold foil apertures. The optimum conditions for preparing the vacuum evaporated foil apertures are described. In order to increase the reproducibility of foil thicknesses, both for identical and different aperture materials, an evaporation nomogram has been made.

The Surface Area of the Annealed Palladium Foil Catalyst as Determined by a Novel Method of Measuring a Small Surface Area

Abstract In order to measure the small surface area of metal foils down to a few ten square centimeters by making use of gas adsorption, an apparatus was developed, which made it possible to estimate the amount of adsorbed xenon at 77.5°K from the desorption of the gas on the surface by moving the foil from the adsorbing bulb into the hot furnace; the change in the surface area of palladium foil catalysts which had been annealed at various temperatures was followed by the use of this method. The roughness factor, the ratio of the real surface area to the geometrical one, of the palladium foil decreased from 1.7 to 1.1 with the progress of annealing at 150–300°C, but it increased to 1.9 after heating at 400°C and then decreased again under treatment at high temperatures to 1.0 for 800°C. The chemisorption of carbon monoxide on the same foil catalyst, which is often used for the surface-area determination, was also studied, and the difference between the adsorbed states of the respective molecule on the palladium surface was briefly discussed in order to compare these methods.

Decay ofAg103

Natural palladium foil was irradiated with 18-MeV protons to produce 1.1-h ${\mathrm{Ag}}^{103}$ by ($p,xn$) reactions. The target foil was placed directly into the ion source of the Princeton isotope separator, and the silver isotopes were volatilized, dispersed, and collected. Spectroscopic data were obtained using Ge(Li) gamma-ray detectors, an orange-type electron spectrometer, and permanent magnet spectrographs. Transitions were observed at 118.66, 148.26, 244.5, 266.9, 532.2, (555.9), 578.8, 741.9, 940.6, 1007.1, 1030.3, 1155.8, 1183.6, and 1274.6 keV. (Energies of doubtful transitions are mentioned in parentheses.) Gamma-ray spectra in coincidence with several conversion-electron lines, taken with a NaI(Tl) detector in conjunction with the orange spectrometer, gave evidence for levels in ${\mathrm{Pd}}^{103}$ at 0, 118.7, 244.5, 266.9, (532), (823), (1184), and 1274.4 keV.

Attempts to Confirm the Existence of the 10-Minute Isotope of 102

In many score of experiments conducted in various ways over a period of many months they find that they are unable to confirm the element 102 discovery work of Fields et al. reported in 1957. These experimenters ascribed to an isotope of element 102 an alpha particle activity having an energy of 8.5 {+-} 0.1 Mev and a half-life of approximately 10 minutes. It was reported to be produced by bombardments of a 1 mg/cm{sup 2} curium target with 0.03-0.10 mter-microamperes of C{sup 13} ions of about 90 Mev energy in the internal beam of the Nobel Institute 225 cm cyclotron. Our attempts to reproduce this activity were made with the monoenergetic ion beam available from the Berkeley heavy ion linear accelerator (HILAC). Curium with a similar isotopic composition was used, except that instead of one target they used six separate electroplated targets, four with 0.4 mg/cm{sup 2} curium and two with 0.1 mg/cm{sup 2} curium. These were mounted in vacuum so that the heavy ion beam could pass through and knock the transmutation recoils into 0.9 mg/cm{sup 2} palladium foils. After a suitable bombardment the six catcher foils were dissolved in a few drops of concentrated aqua regia and an actinide element fraction quickly separated from palladium by elution with 2M HCl from a column packed with Dowex-1 anion exchange resin. It was possible to examine a trans-plutonium fraction within 8 minutes from the end of bombardment. A wide range of energies (60-100 Mev) of both C{sup 12} and C{sup 13} projectiles and (+6) ion currents up to 0.2 microamperes were used. In order to compare these bombardments with those which were reported to have produced the 8.5 Mev alpha activity one can compare the amounts of the other alpha particle activities that are produced in such bombardments. The nuclides Fm{sup 250}, Cf{sup 245}, Cr{sup 244}, and Cf{sup 246} were found in far greater amount in the experiments than in the aforementioned cyclotron runs. In the case of Cf{sup 246}, for example, which is produced with a relatively flat excitation function they found in a typical experiment about 40 alpha counts per minute. This should be compared with 0.1 alpha counts per minute of Cf{sup 246} found in the cyclotron experiment which was reported to have yielded four 8.5 Mev events.

Deuteron Bombardment of Silver

THROUGH the kindness of Messrs. Krishnan and Gant, I have been able to examine the radiations from a silver foil of 20 mgm./cm.2 bombarded with 9 Mv. deuterons, using the method of critical absorption previously adopted in the case of the fission products of uranium1. For the quantum radiations from the 6·8-hour body, a palladium foil of 24 mgm./cm.2 was considerably more transparent than a foil of molybdenum of only 14 mgm./cm.2. This is in agreement with the findings reported above, although it does not allow a decision to be made as to whether the K-radiations of silver or cadmium are involved (it is hoped, later, to use an absorber containing ruthenium in order to examine this point more closely).

On a new kind of glow from palladium in vacuum tubes

The phenomenon described in this paper was first noticed when making some preliminary experiments in an investigation suggested by Prof. Sir J. J. Thomson. The effect of the gases contained in metals on the nature of the discharge obtained when these metals are employed as electrodes in vacuum tubes has long been a question of interest. It was suggested that by employing palladium one might hope to obtain interesting results, owing to the property possessed by this metal of absorbing large quantities of hydrogen. The result of these preliminary experiments has already been briefly stated, but as the effect seems to be a new one, it seemed of sufficient interest to call for a fuller investigation. Apparatus .—A tube was fitted up containing an ebonite plug through which two stout brass leads were passed. To the extremities of the leads was attached, by means of screws, a piece of palladium foil about an inch in length and a tenth of an inch wide. The leads and plugs were fixed in position by sealing-wax. The tube was sealed by the blow-pipe to a mercury pump and was in connection with a pressure gauge, drying-bulb, etc. The tube could be isolated from the rest of the apparatus by means of a barometric mercury seal. By passing an electric current through the palladium, it could be heated to any required temperature.

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