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104. Physical techniques in the study of silver catalysts for ethylene oxidation.
Abstracts 102--108
281
Vacuum Applications 30.
Evaporation and Sputtering 30 : 52
102. Diffusion of Silver in Silver Sulfide. United States. Diffusion of radioactive A g - l l 0 in silver sulfide was measured in polycrystalline specimens. Disk shaped specimens were cut from a rod of vacuum melted and annealed silver sulfide. In the first experiments the radioactive tracer, Ag-110, was evaporated on to the disks from a tantalum ribbon in vaeuo. In later experiments, the tracer was applied by treating the disk with active silver nitrate solution. The coated specimen was placed between two sheets of platinum foil in a vessel evacuated to less than 10 -~ Torr, filled with helium, and then raised quickly to the desired temperature in a bath of Wood's metal. B.B.D. R. L. Allen and W. J. Moore, J. Phys. Chem., 63, 223 226, Feb. 1959. 30 : 52
103. Heterogeneous Reaction Studies by Infrared Absorption. United States. An experimental apparatus and procedure were developed for obtaining the infrared spectra of substances which are adsorbed on the surface of freshly evaporated metal surfaces. In addition, this equipment may be used either to observe changes in the reflectivity of the metal surfaces or to observe changes in gaseous components while a reaction is taking place. The basis of the equipment is the use of a multiple reflection cell whose front surfaced mirrors are covered by freshly evaporated catalyst metal. When ethylene is added in excess to new rhodium mirrors, it is adsorbed with dissociation to produce ethane and an adsorbed substance. Evidence was obtained which indicates this substance is composed of paired carbon atoms which probably are present on the catalyst surface. This adsorbed substance may be hydrogenated to ethane at room temperature and at hydrogen pressures of less than 1 mm. No direct evidence was found for hydrogen-carbon bonds in the adsorbed molecules. The ethylene adsorption is accompanied by a small decrease in film reflecting power while the hydrogenation step is accompanied by a similar increase in reflectivity. When the CO pressure over new rhodium mirrors is 1 ram, an infrared absorption band at 4.854/z is observed. A band of increased reflectivity is also observed at 4.785t~. U p o n evacuation, the absorption band shifts to 4.914tz, whereas the band of increased reflectivity remains unchanged. When CO is added to new nickel mirrors, a large infrared absorption band is observed at 4.859t~, corresponding to gaseous nickel carbonyl. However, no other nickel carbonyl bands are observed. The 4.859tz band disappears upon evacuation. These results show that the CO is more strongly adsorbed on the rhodium catalyst than on the nickel catalyst. The positions of the infrared absorption bands suggest that the CO is chemisorbed as single linear molecules. When hydrogen is added to new rhodium mirrors, a decrease in film reflecting power occurs. Only a fractional recovery in reflectivity occurs upon evacuation. As many as 23 absorption bands are observed which may be attributed to hydrogen on the rhodium surface. (Author) Harold L. Pickering and Hartley C. Eckstrom, J. Phys. Chem., 63, 51~517, April 1959. 30 : 52
104. Physical Techniques in the Study of Silver Catalysts for Ethylene Oxidation, United States. To investigate whether different crystal planes of silver give different results in the catalytic oxidation o f ethylene to ethylene oxide with air, several types of evaporated silver film were used. By evaporating in vacuo or in 1 mm of nitrogen or hydrogen, films containing crystals randomly oriented or with the 110 plane parallel to the glass support were
obtained. Both types were about equally active and selective. Most significantly, it was found that use of an oriented film for ethylene oxidation at 250-280 ° caused recrystallization to randomly oriented material in 2-4 hr. Thus, unusual crystal faces would not be expected to persist in use. Disorientation did not occur when similar films were heated in air at 250 °. Detection of volatile impurities in silver catalysts were done by heating to near-fusion temperature in a small chamber connected to the inlet reservoir of a mass spectrometer. Appreciable amounts of carbon, oxygen, hydrogen and sulfur compounds were shown to be present in silver made by reduction of the oxide or by chemical deposition from solution. Fractional monolayers could be detected on catalysts with surface areas of 0.2 m~/g. Another measurement of possible utility was that of surface potential relative to a gold electrode in air. Values for powdered silver catalysts held in a flat tray ranged from --500 to ÷ 5 0 0 m y and were reproducible to about 10mv. Chemisorption of phosphorus, sulfur or chlorine compounds made the values more negative. (Author) J. N. Wilson, H. H. Voge, D. P. Stevenson, A. E. Smith and L. T. Atkins, J. Phys. Chem., 63, 463 468, April 1959. 30 : 34
105. Temperature Stabilization of Highly Reflecting Spherical Satellites. G. Hass, L. F. Drummeter, Jr., M. Schach, J. Opt. Soc..4mer., 49, 918-924, Sept. 1959. 30 : 52
106. Calculation of the Performance of a High-Vacuum Thermionic Energy Converter. The performance of a high-vacuum thermionic energy converter has been evaluated from Langmuir's 1923 paper on the thermionic diode. The results are presented in the form of a generalized set of curves which show output voltage as a function of current drawn from the device. These general curves have then been applied to a few specific cases to determine what cathode-anode spacings, and cathode and anode properties will be required to produce a practical energy converter. H. F. Webster, J. Appl. Phys., 30, 488-493, April 1959. 30 : 52
107. Selective Delineation of Screw Dislocations by Cathodic Sputtering. A method of revealing screw component dislocations involving low-energy cathodic sputtering with argon ions is presented. It is observed that hillocks having the shape of truncated cones with a spiral pattern on their tops form at the sites of intersection of screw dislocations with the surface. The hillocks probably form by mobile surface atoms attaching themselves to the step provided at the intersection of a screw dislocation with the surface. It is shown that the density of screw dislocations on a given plane depends on the orientation of the plane with respect to the crystal growth axis. B. B. Meckel and R. A. Swalin~ J. Appl. Phys., 30, 89-94, Jan. 1959. 30
108. Improvements in or relating to the Deposition of Metals and the like Substances on Webs by Evaporation in v a c u o . West Germany. This invention relates to the deposition of metals and other materials on for example webs of synthetic materials by evaporation in vacuo. The patent describes how the fibrous surface of the web material may be sealed by impregnation with a resin, for example an iso-cyanate modified polyester resin. Brit. Pat., 800,093, 20 Aug. 1958.
281
Vacuum Applications 30.
Evaporation and Sputtering 30 : 52
102. Diffusion of Silver in Silver Sulfide. United States. Diffusion of radioactive A g - l l 0 in silver sulfide was measured in polycrystalline specimens. Disk shaped specimens were cut from a rod of vacuum melted and annealed silver sulfide. In the first experiments the radioactive tracer, Ag-110, was evaporated on to the disks from a tantalum ribbon in vaeuo. In later experiments, the tracer was applied by treating the disk with active silver nitrate solution. The coated specimen was placed between two sheets of platinum foil in a vessel evacuated to less than 10 -~ Torr, filled with helium, and then raised quickly to the desired temperature in a bath of Wood's metal. B.B.D. R. L. Allen and W. J. Moore, J. Phys. Chem., 63, 223 226, Feb. 1959. 30 : 52
103. Heterogeneous Reaction Studies by Infrared Absorption. United States. An experimental apparatus and procedure were developed for obtaining the infrared spectra of substances which are adsorbed on the surface of freshly evaporated metal surfaces. In addition, this equipment may be used either to observe changes in the reflectivity of the metal surfaces or to observe changes in gaseous components while a reaction is taking place. The basis of the equipment is the use of a multiple reflection cell whose front surfaced mirrors are covered by freshly evaporated catalyst metal. When ethylene is added in excess to new rhodium mirrors, it is adsorbed with dissociation to produce ethane and an adsorbed substance. Evidence was obtained which indicates this substance is composed of paired carbon atoms which probably are present on the catalyst surface. This adsorbed substance may be hydrogenated to ethane at room temperature and at hydrogen pressures of less than 1 mm. No direct evidence was found for hydrogen-carbon bonds in the adsorbed molecules. The ethylene adsorption is accompanied by a small decrease in film reflecting power while the hydrogenation step is accompanied by a similar increase in reflectivity. When the CO pressure over new rhodium mirrors is 1 ram, an infrared absorption band at 4.854/z is observed. A band of increased reflectivity is also observed at 4.785t~. U p o n evacuation, the absorption band shifts to 4.914tz, whereas the band of increased reflectivity remains unchanged. When CO is added to new nickel mirrors, a large infrared absorption band is observed at 4.859t~, corresponding to gaseous nickel carbonyl. However, no other nickel carbonyl bands are observed. The 4.859tz band disappears upon evacuation. These results show that the CO is more strongly adsorbed on the rhodium catalyst than on the nickel catalyst. The positions of the infrared absorption bands suggest that the CO is chemisorbed as single linear molecules. When hydrogen is added to new rhodium mirrors, a decrease in film reflecting power occurs. Only a fractional recovery in reflectivity occurs upon evacuation. As many as 23 absorption bands are observed which may be attributed to hydrogen on the rhodium surface. (Author) Harold L. Pickering and Hartley C. Eckstrom, J. Phys. Chem., 63, 51~517, April 1959. 30 : 52
104. Physical Techniques in the Study of Silver Catalysts for Ethylene Oxidation, United States. To investigate whether different crystal planes of silver give different results in the catalytic oxidation o f ethylene to ethylene oxide with air, several types of evaporated silver film were used. By evaporating in vacuo or in 1 mm of nitrogen or hydrogen, films containing crystals randomly oriented or with the 110 plane parallel to the glass support were
obtained. Both types were about equally active and selective. Most significantly, it was found that use of an oriented film for ethylene oxidation at 250-280 ° caused recrystallization to randomly oriented material in 2-4 hr. Thus, unusual crystal faces would not be expected to persist in use. Disorientation did not occur when similar films were heated in air at 250 °. Detection of volatile impurities in silver catalysts were done by heating to near-fusion temperature in a small chamber connected to the inlet reservoir of a mass spectrometer. Appreciable amounts of carbon, oxygen, hydrogen and sulfur compounds were shown to be present in silver made by reduction of the oxide or by chemical deposition from solution. Fractional monolayers could be detected on catalysts with surface areas of 0.2 m~/g. Another measurement of possible utility was that of surface potential relative to a gold electrode in air. Values for powdered silver catalysts held in a flat tray ranged from --500 to ÷ 5 0 0 m y and were reproducible to about 10mv. Chemisorption of phosphorus, sulfur or chlorine compounds made the values more negative. (Author) J. N. Wilson, H. H. Voge, D. P. Stevenson, A. E. Smith and L. T. Atkins, J. Phys. Chem., 63, 463 468, April 1959. 30 : 34
105. Temperature Stabilization of Highly Reflecting Spherical Satellites. G. Hass, L. F. Drummeter, Jr., M. Schach, J. Opt. Soc..4mer., 49, 918-924, Sept. 1959. 30 : 52
106. Calculation of the Performance of a High-Vacuum Thermionic Energy Converter. The performance of a high-vacuum thermionic energy converter has been evaluated from Langmuir's 1923 paper on the thermionic diode. The results are presented in the form of a generalized set of curves which show output voltage as a function of current drawn from the device. These general curves have then been applied to a few specific cases to determine what cathode-anode spacings, and cathode and anode properties will be required to produce a practical energy converter. H. F. Webster, J. Appl. Phys., 30, 488-493, April 1959. 30 : 52
107. Selective Delineation of Screw Dislocations by Cathodic Sputtering. A method of revealing screw component dislocations involving low-energy cathodic sputtering with argon ions is presented. It is observed that hillocks having the shape of truncated cones with a spiral pattern on their tops form at the sites of intersection of screw dislocations with the surface. The hillocks probably form by mobile surface atoms attaching themselves to the step provided at the intersection of a screw dislocation with the surface. It is shown that the density of screw dislocations on a given plane depends on the orientation of the plane with respect to the crystal growth axis. B. B. Meckel and R. A. Swalin~ J. Appl. Phys., 30, 89-94, Jan. 1959. 30
108. Improvements in or relating to the Deposition of Metals and the like Substances on Webs by Evaporation in v a c u o . West Germany. This invention relates to the deposition of metals and other materials on for example webs of synthetic materials by evaporation in vacuo. The patent describes how the fibrous surface of the web material may be sealed by impregnation with a resin, for example an iso-cyanate modified polyester resin. Brit. Pat., 800,093, 20 Aug. 1958.