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529. Measurement of oxygen adsorption on silicon by ellipsometry
Classified abstracts 529--542 rate data could be correlated by an exponential equation, while the adsorption isotherms, covering the pressure range 0.01-500tz, satisfied the Freundlich equation. The nature of the RuO~ surface toward 02 adsorption has been characterized by an exponential distribution of adsorption equilibrium functions. The isosteric heats of adsorption in the temperature range of 300 to 385 ° were found to decrease linearly with the logarithm of the surface coverage, and a value greater than 120 kca! mole -1 was indicated for the heat effect at zero coverage. Isosteric activation energies of desorption in the same temperature range were also determined, and were observed to decrease linearly with the surface coverage. The activation energy of desorption at zero coverage was found to be 50.1 kcal mole -t. At temperatures below 300 ° both the isosteric heats of adsorption and the activation energies of desorption increased with decreasing temperature. The application of the absolute rate theory to the desorption results showed that the adsorbed species in the temperature range investigated are both mobile and dissociated. (Author) J T Sommerfeld and G Parravano, J Phys Chem, 69, Jan 1965,
102-115. 16 : 19 529. Measurement of oxygen adsorption on silicon by ellipsometry.
(Great Britain) The kinetics of the first monolayer adsorption as well as the characteristics of the subsequent film growth were found to be profoundly affected by the absence or presence of a Bayard-Alpert gauge in the circuit. With the gauge absent, the results were characteristic of a pure molecular oxygen ambient. The presence of the gauge introduced an unidentified contamination causing a large increase in the sticking coefficient. R T Archer and G W Gobeli, JPhys Chem Solids, 26 (2), Feb 1965,
343-351. 16 530. Low temperature desorption spectrometry by means of pressure records. (Germany) The desorption system under examination consisted of a cold trap of special design. Evacuation was carried out with the help of a three-stage oil diffusion pump using silicone DC705 oil as working fluid. The trap was originally cooled with liquid nitrogen and after a certain absorption time (of the order of 30 min), the nitrogen is siphoned off and the trap allowed to warm up to room temperature at a predetermined rate of approx 1.7 °C per min. Pressure measurements taken with a Bayard-Alpert gauge during this period showed a number of distinct peaks corresponding to the desorption of different species. After prolonged evacuation these peaks were reduced to only two with desorption energies of 10.5 and 18 kcal/ mole respectively. After a 14 hour bakeout at 400°C, all the peaks with the exception of the one at 10.5 kcal/mole (water vapour) disappeared. E B Bas, Vakuum-Techn, 14 (3), April 1965, 65-69, (in German). 16 531. Desorption of hydrogen from platinum catalysts. (USA) Y Kubokawa et al, JPhys Chem, 68, May 1964, 1244-1245. 16 532. Oxygen exchange between chemisorbed carbon monoxide on catalytic nickel. (USA) J T Yates, Jr, JPhys Chem, 68, May 1964, 1245-1250. 16 533. Infrared study of adsorption of ammonia on dry y-alumina.
(USA) J B Peri, JPhys Chem, 69, Jan 1965, 231-239. 16 • 52 534. Oxidation of hydrocarbons adsorbed on oxide catalysts induced by cobalt-60 ~,-rays. (USA) H W Kohn, JPhys Chem, 68, Nov 1964, 3129-3136. 16:40 535. Gaseous diffusion. The systems He-Ar, Ar-Xe, and He-Xe.
(USA) A P Malinauskas, J Chem Phys, 42 (1), Jan 1965, 156-159. 16 : 41 536. Thermal desorption of Sr from W. ( U S A ) T E Madey et al, J Chem Phys, 42 (2), Jan 1965, 479-485. 16 : 41 537. Diffusion versus surface limitations in vapour-solvent growth of germanium. (USA) F Jona, J ChemPhys, 42 (3), Feb 1965, 1025-1027.
17. Thermodynamics 17 A new vacuum insulated cryogenic coupling. See abstract number 568. 17 538. The high temperature vaporization properties of boron carbide and the heat of sublimation of boron. (USA) The vaporization behaviour of boron carbide solid solutions is shown to be the preferential loss of gaseous boron regardless of the sample composition. An invariant system consisting of a graphite crucible and a carbon-saturated boron carbide sample was used to measure the vapour pressure oveT the temperature range 21842522°K. The Knudsen technique employing condensation targets was used, and boron was specifically assayed by a coulometric titration of the mannitol complex. The derived third-law heats of sublimation in kcal/mole of boron are AH°0 = 136.8 ~ 0.1 and AH°29s = 138.0 -5= 0.1 for boron carbide and AH°0 = 133.8 :t: 0.7 and AH°298 : 135.0 :t: 0.7 for boron. (Author) H E Robson and P W Gilles, J Phys Chem, 68, May 1964, 983-989. 17 539. The decomposition pressure of boron carbide and the heat of sublimation of boron. (USA) The boron decomposition pressure over boron carbide, B4C, has been measured by the torsion-effusion method in the range 2350 to 2615°K. A small "hole-size effect" indicates a condensation coefficient of roughly 0.07 for B(g) on B4C(s). The heat of dissociation of BaC to B(g) and C(graphite) at 298 °K has been derived as 138.7 ± 1.2 kcal/mole of boron from a third-law analysis of the vaporization data. F r o m this result, the heat of sublimation of boron at 298 °K has been evaluated as 135.7 :t: 1.3 kcal/mole. An approximate value of 171 kcal/mole has been obtained for the heat of formation of BC~(g) at 298°K. (Author) D L Hildenbrand and W F Hall, J Phys Chem, 68, May 1964,
989-993. 17 540. Torsion-effusion technique for studying the kinetics of gasforming reactions. (USA) The torsion-effusion technique has been applied to the study of the kinetics of thermal decomposition. An apparatus which includes a thermocouple as an integral part of the suspension system is described. The decomposition of polytetrafluoroethylene (teflon) was studied and found to obey first-order kinetics with an activation energy of 76.7 ! 7.3 kcal/mole in the temperature range 544 to 590 °. The first-order rate constant, k (see-X), was found to obey the expression log k = 17.27 --16.66 × 103(1/T). The molecular weight of vaporizing species was calculated and found to be 100.0 ~ 6. (Author) C L Rosen and A J Melveger, J Phys Chem, 68, May 1964, 1079-
1084. 17 541. Mass spectrometry-Knudsen cell studies of the vaporization of uranium dicarbide. (USA) The presence of UC2(g) is important in the vaporization of uranium dicarbide. In the presence of excess carbon, the vaporization of uranium dicarbide as UC~(g) can be represented by a heat of vaporization of 185 kcal/mole and an entropy of 38.3 cal/°K mole in the temperature range 2350 to 2700°K. Good thermodynamic agreement between this work and previous studies of vaporization of uranium dicarbide to U(g) ÷ 2C(s) has been obtained. The values obtained in this study are AH -- 127.3 kcal/mole and AS : 18.6 cal/°K mole in the temperature range 2150 to 2700°K. (Author) J H Norman and P Winchell, J Phys Chem, 68, Dec 1964, 3902-
3905. 17:52 542. Texture of gaseous layers condensed on a cold substrate.
(USSR) Experiments were carried out with the isotopes of hydrogen and neon condensing at 10 -7 torr on glass substrates cooled with liquid helium. At substrate temperature of 4.2 °K both neon isotopes have the (111) axis of the cubic lattice perpendicular to the substrate. Protium has the (001) axis perpendicular at 1.8°K and parallel at 4.2°K. In the case of deuterium, the (001) axis remains perpendicular to the substrate over the whole temperature range. The authors suggest that the texture of the deposit depends on the degree of supersaturation in the chamber, i.e. on the difference between the chamber pressure and the equilibrium pressure at the
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102-115. 16 : 19 529. Measurement of oxygen adsorption on silicon by ellipsometry.
(Great Britain) The kinetics of the first monolayer adsorption as well as the characteristics of the subsequent film growth were found to be profoundly affected by the absence or presence of a Bayard-Alpert gauge in the circuit. With the gauge absent, the results were characteristic of a pure molecular oxygen ambient. The presence of the gauge introduced an unidentified contamination causing a large increase in the sticking coefficient. R T Archer and G W Gobeli, JPhys Chem Solids, 26 (2), Feb 1965,
343-351. 16 530. Low temperature desorption spectrometry by means of pressure records. (Germany) The desorption system under examination consisted of a cold trap of special design. Evacuation was carried out with the help of a three-stage oil diffusion pump using silicone DC705 oil as working fluid. The trap was originally cooled with liquid nitrogen and after a certain absorption time (of the order of 30 min), the nitrogen is siphoned off and the trap allowed to warm up to room temperature at a predetermined rate of approx 1.7 °C per min. Pressure measurements taken with a Bayard-Alpert gauge during this period showed a number of distinct peaks corresponding to the desorption of different species. After prolonged evacuation these peaks were reduced to only two with desorption energies of 10.5 and 18 kcal/ mole respectively. After a 14 hour bakeout at 400°C, all the peaks with the exception of the one at 10.5 kcal/mole (water vapour) disappeared. E B Bas, Vakuum-Techn, 14 (3), April 1965, 65-69, (in German). 16 531. Desorption of hydrogen from platinum catalysts. (USA) Y Kubokawa et al, JPhys Chem, 68, May 1964, 1244-1245. 16 532. Oxygen exchange between chemisorbed carbon monoxide on catalytic nickel. (USA) J T Yates, Jr, JPhys Chem, 68, May 1964, 1245-1250. 16 533. Infrared study of adsorption of ammonia on dry y-alumina.
(USA) J B Peri, JPhys Chem, 69, Jan 1965, 231-239. 16 • 52 534. Oxidation of hydrocarbons adsorbed on oxide catalysts induced by cobalt-60 ~,-rays. (USA) H W Kohn, JPhys Chem, 68, Nov 1964, 3129-3136. 16:40 535. Gaseous diffusion. The systems He-Ar, Ar-Xe, and He-Xe.
(USA) A P Malinauskas, J Chem Phys, 42 (1), Jan 1965, 156-159. 16 : 41 536. Thermal desorption of Sr from W. ( U S A ) T E Madey et al, J Chem Phys, 42 (2), Jan 1965, 479-485. 16 : 41 537. Diffusion versus surface limitations in vapour-solvent growth of germanium. (USA) F Jona, J ChemPhys, 42 (3), Feb 1965, 1025-1027.
17. Thermodynamics 17 A new vacuum insulated cryogenic coupling. See abstract number 568. 17 538. The high temperature vaporization properties of boron carbide and the heat of sublimation of boron. (USA) The vaporization behaviour of boron carbide solid solutions is shown to be the preferential loss of gaseous boron regardless of the sample composition. An invariant system consisting of a graphite crucible and a carbon-saturated boron carbide sample was used to measure the vapour pressure oveT the temperature range 21842522°K. The Knudsen technique employing condensation targets was used, and boron was specifically assayed by a coulometric titration of the mannitol complex. The derived third-law heats of sublimation in kcal/mole of boron are AH°0 = 136.8 ~ 0.1 and AH°29s = 138.0 -5= 0.1 for boron carbide and AH°0 = 133.8 :t: 0.7 and AH°298 : 135.0 :t: 0.7 for boron. (Author) H E Robson and P W Gilles, J Phys Chem, 68, May 1964, 983-989. 17 539. The decomposition pressure of boron carbide and the heat of sublimation of boron. (USA) The boron decomposition pressure over boron carbide, B4C, has been measured by the torsion-effusion method in the range 2350 to 2615°K. A small "hole-size effect" indicates a condensation coefficient of roughly 0.07 for B(g) on B4C(s). The heat of dissociation of BaC to B(g) and C(graphite) at 298 °K has been derived as 138.7 ± 1.2 kcal/mole of boron from a third-law analysis of the vaporization data. F r o m this result, the heat of sublimation of boron at 298 °K has been evaluated as 135.7 :t: 1.3 kcal/mole. An approximate value of 171 kcal/mole has been obtained for the heat of formation of BC~(g) at 298°K. (Author) D L Hildenbrand and W F Hall, J Phys Chem, 68, May 1964,
989-993. 17 540. Torsion-effusion technique for studying the kinetics of gasforming reactions. (USA) The torsion-effusion technique has been applied to the study of the kinetics of thermal decomposition. An apparatus which includes a thermocouple as an integral part of the suspension system is described. The decomposition of polytetrafluoroethylene (teflon) was studied and found to obey first-order kinetics with an activation energy of 76.7 ! 7.3 kcal/mole in the temperature range 544 to 590 °. The first-order rate constant, k (see-X), was found to obey the expression log k = 17.27 --16.66 × 103(1/T). The molecular weight of vaporizing species was calculated and found to be 100.0 ~ 6. (Author) C L Rosen and A J Melveger, J Phys Chem, 68, May 1964, 1079-
1084. 17 541. Mass spectrometry-Knudsen cell studies of the vaporization of uranium dicarbide. (USA) The presence of UC2(g) is important in the vaporization of uranium dicarbide. In the presence of excess carbon, the vaporization of uranium dicarbide as UC~(g) can be represented by a heat of vaporization of 185 kcal/mole and an entropy of 38.3 cal/°K mole in the temperature range 2350 to 2700°K. Good thermodynamic agreement between this work and previous studies of vaporization of uranium dicarbide to U(g) ÷ 2C(s) has been obtained. The values obtained in this study are AH -- 127.3 kcal/mole and AS : 18.6 cal/°K mole in the temperature range 2150 to 2700°K. (Author) J H Norman and P Winchell, J Phys Chem, 68, Dec 1964, 3902-
3905. 17:52 542. Texture of gaseous layers condensed on a cold substrate.
(USSR) Experiments were carried out with the isotopes of hydrogen and neon condensing at 10 -7 torr on glass substrates cooled with liquid helium. At substrate temperature of 4.2 °K both neon isotopes have the (111) axis of the cubic lattice perpendicular to the substrate. Protium has the (001) axis perpendicular at 1.8°K and parallel at 4.2°K. In the case of deuterium, the (001) axis remains perpendicular to the substrate over the whole temperature range. The authors suggest that the texture of the deposit depends on the degree of supersaturation in the chamber, i.e. on the difference between the chamber pressure and the equilibrium pressure at the
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