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Reaction kinetics of hydrogen atoms with carbon films
130
Classified Abstracts 246--252
in oxygen than the condensed phase. Above 1550°K there are no congruently evaporating compositions. Standard free energies, enthalpies, and entropies of formation for the four major vapor species and for the WlsO49, W30Oss, and WO3.~6 solid phases are given. (U.S.A.) (Author) R. J. Ackermann and E. G. Rauh, J. Phys. Chem., 67, Dec. 1963, 2596-2601.
BN and AIN at 298 °K have been derived from the dissociation pressures as --59.8 ± 0.6 and --76.1 ± 2.1 kcal/mole, respectively. The magnitude of the hole-size dependence indicates that the gross condensation coefficient for BN is < 6 × 10 -3, while that for A1N is < 2 × 10-3. (U.S.A.) (Author)
17:30 246. The reaction between oxygen and evaporated films of sodium.
17 : 30 249. Reaction kinetics of hydrogen atoms with carbon films.
(U.S.A.) The kinetics of the reaction between oxygen and evaporated films of sodium have been studied at 90, 195, and 273°K in the pressure range 10 -3 to 10 -1 mm. Provided an adequate standard of purity was achieved for the reactants and provided the oxygen pressure above the film was sufficiently high, a protective oxide layer was produced and at 90 and 195°K the results obeyed a logarithmic inverse rate law. At 273 °K no single rate law gave a satisfactory fit over the entire uptake range but a cubic rate law was found to hold after an oxide layer of sufficient thickness had been formed. Data, including those from an electron diffraction examination, indicated that under these conditions the oxide layer corresponded to sodium superoxide, NaO~. The surface potential, measured in the initial stages of oxidation by the diode method, was positive. The slow addition of oxygen to the system which maintained an oxygen pressure above the film not greater than about 10 -3 mm resulted in an augmented total oxygen uptake. Impure reactants resulted in extensive and irreproducible oxidation with no protective behavior and the oxide formed corresponded approximately to sodium monoxide, Na20. The mechanism of oxidation is discussed. (U.S.A.) (Author) J. R. Anderson and N. J. Clark, J. Phys. Chem., 67, Oct. 1963, 2135-2141. 17 247. Vaporization properties of iron phosphides. (U.S.A.) The equilibrium dissociation of FeP~, FeP, and Fe2P to phosphorus vapor and the next lower phosphide has been studied by the effusion method using a direct mass loss technique, employing a vitreous silica helix as a microbalance. A " second law " treatment of the dependence of the dissociation pressure upon temperature yielded the following heats of dissociation per mole of P2 v a p o r : FePzAH°~o0o : 70.6 ~ 2 kcal, AS°1000 = 52.9 ~= 1 cal. mole -1 deg -1 ; FePAHO12~0 : 84.8 ~= 2 kcal, ~S°lzs0 = 50.3 ± 1 cal. mole -1 deg -1 ; Fe~P~H°135o : 111.2 ± 2 kcal. Combination of these data with appropriate data from the literature yielded the following heats of formation of the iron phosphides from solid iron and red phosphorus at 900°K : Fe3P, --35.2 kcal (not determined in this w o r k ) ; Fe~P, --35.2 ~= 2 k c a l ; FeP, --28.6 ± 2 k c a l ; and 1/2 FeP~, --21,8 ~ 2 kcal. (U.S.A.) (Author) G. Lewis and C. E. Myers, J. Phys. Chem., 67, June 1963, 1289-1292. 17 248. The vaporization behavior of boron nitride and aluminum nitrite. (U.S.A.) The dissociation pressures of crystalline boron nitride and aluminum nitride have been measured by the torsion-effusion method over the ranges 1850 to 2160°K and 1780 to 1970°K, respectively. Although the measured pressures for both substances showed a strong dependence on effusion orifice area, a simple expression relating equilibrium and observed pressures to effusion cell geometry was found to correlate the data quite satisfactorily. Equilibrium pressures evaluated by extrapolation of observed pressures to zero effective orifice area are in good agreement with dissociation pressures calculated from available thermodynamic data. The heats of formation of crystalline
D. L. Hildenbrand and W. F. Hall, J. Phys. Chem., 67, April 1963, 888-893.
(U.S.A.) The reaction kinetics of hydrogen atoms with evaporated carbon films have been studied in the temperature range from 365 to 500 ° K and at total gas pressures from 0.02 to 0.10 mm. The removal of carbon by chemical reaction, as detected by the variation of film thickness with time, was found to occur at two distinct rates with activation energies of 9.2 and 7.1 kcal/mole. The kinetics appear to be related to the degree of crystallinity of the film. Simple hydrocarbons such as methane and ethane are the principal reaction products. In addition, formation of hydrogen molecules by atom recombination on the carbon film takes place ; this reaction, with an activation energy of 2.3 kcal/mole, predominates over hydrocarbon formation in the temperature range studied. (U.S.A.) (Author) A. B. King and H. Wise, J. Phys. Chem., 67, June, 1963 1163-1170. 17 250. The sublimation pressure of calcium (II) fluoride and the dissociation energy of calcium (I) fluoride. (U.S.A.) A vacuum microbalance and a mass spectrometer have been used to determine sublimation pressures and heats of sublimation for CaF~(s) over the range 1242-1669°K. The data are represented by log Patna : --(95.46 ± 0.49)/45.76 × lO~/Tq- 8.141 ~= 0.006. The errors quoted are standard deviations of the leastsquares fit. The heat of sublimation at 298°K is 103.3 ~ 2.0 kcal/mole. F r o m studies of the reaction of CaF~ with aluminum over the range 1271-1351 °K, D°29s for CaF(g) was determined to be 5.4 ~ 0.2 eV from two independent equilibria. Close agreement with other investigators is found for the sublimation of CaF2(s) but the dissociation energy of CaF(g) is much greater than the previously accepted value, (U.S.A.) (Author) G. D. Blue, J. W. Green, R. G. Bautista, and J. L. Margrave, J. Phys. Chem., 67, April 1963, 877-882. 17 251. Kinetics of the low pressure nitrous oxide decomposition on a platinum filament. (U.S.A.) The decomposition of nitrous oxide on a platinum filament has been investigated over a pressure range of 0.02 to 4.0 m m and a temperature range of 545 to 820 ° . The reaction kinetics have been found to fit the Langmuir-Hinshelwood equation for a unimolecular decomposition with poisoning by atomic oxygen. The apparent activation energy is 32 ± 1 kcal/mole. Added oxygen has the same poisoning effect on the reaction rate as the product oxygen. Nitric oxide is produced in small amounts during the decomposition at the higher pressures, However, neither nitric oxide nor nitrogen has been found to poison the reaction. (U.S.A.) (Author) J. P. Redmond, J. Phys. Chem., 67, April 1963, 788-793. 17 252. The thermodynamic and physical properties of beryllium compounds. (IV) Heat and entropy of sublimation of beryllium chloride. (U.S.A.) The vapor pressure curve of BcCI2(s) has been determined over the temperature range 440-600°K using Knudsen gravimetric and torsion effusion procedures. F r o m analysis of the vapor pressure data, second-law values for the heat and entropy of
Classified Abstracts 246--252
in oxygen than the condensed phase. Above 1550°K there are no congruently evaporating compositions. Standard free energies, enthalpies, and entropies of formation for the four major vapor species and for the WlsO49, W30Oss, and WO3.~6 solid phases are given. (U.S.A.) (Author) R. J. Ackermann and E. G. Rauh, J. Phys. Chem., 67, Dec. 1963, 2596-2601.
BN and AIN at 298 °K have been derived from the dissociation pressures as --59.8 ± 0.6 and --76.1 ± 2.1 kcal/mole, respectively. The magnitude of the hole-size dependence indicates that the gross condensation coefficient for BN is < 6 × 10 -3, while that for A1N is < 2 × 10-3. (U.S.A.) (Author)
17:30 246. The reaction between oxygen and evaporated films of sodium.
17 : 30 249. Reaction kinetics of hydrogen atoms with carbon films.
(U.S.A.) The kinetics of the reaction between oxygen and evaporated films of sodium have been studied at 90, 195, and 273°K in the pressure range 10 -3 to 10 -1 mm. Provided an adequate standard of purity was achieved for the reactants and provided the oxygen pressure above the film was sufficiently high, a protective oxide layer was produced and at 90 and 195°K the results obeyed a logarithmic inverse rate law. At 273 °K no single rate law gave a satisfactory fit over the entire uptake range but a cubic rate law was found to hold after an oxide layer of sufficient thickness had been formed. Data, including those from an electron diffraction examination, indicated that under these conditions the oxide layer corresponded to sodium superoxide, NaO~. The surface potential, measured in the initial stages of oxidation by the diode method, was positive. The slow addition of oxygen to the system which maintained an oxygen pressure above the film not greater than about 10 -3 mm resulted in an augmented total oxygen uptake. Impure reactants resulted in extensive and irreproducible oxidation with no protective behavior and the oxide formed corresponded approximately to sodium monoxide, Na20. The mechanism of oxidation is discussed. (U.S.A.) (Author) J. R. Anderson and N. J. Clark, J. Phys. Chem., 67, Oct. 1963, 2135-2141. 17 247. Vaporization properties of iron phosphides. (U.S.A.) The equilibrium dissociation of FeP~, FeP, and Fe2P to phosphorus vapor and the next lower phosphide has been studied by the effusion method using a direct mass loss technique, employing a vitreous silica helix as a microbalance. A " second law " treatment of the dependence of the dissociation pressure upon temperature yielded the following heats of dissociation per mole of P2 v a p o r : FePzAH°~o0o : 70.6 ~ 2 kcal, AS°1000 = 52.9 ~= 1 cal. mole -1 deg -1 ; FePAHO12~0 : 84.8 ~= 2 kcal, ~S°lzs0 = 50.3 ± 1 cal. mole -1 deg -1 ; Fe~P~H°135o : 111.2 ± 2 kcal. Combination of these data with appropriate data from the literature yielded the following heats of formation of the iron phosphides from solid iron and red phosphorus at 900°K : Fe3P, --35.2 kcal (not determined in this w o r k ) ; Fe~P, --35.2 ~= 2 k c a l ; FeP, --28.6 ± 2 k c a l ; and 1/2 FeP~, --21,8 ~ 2 kcal. (U.S.A.) (Author) G. Lewis and C. E. Myers, J. Phys. Chem., 67, June 1963, 1289-1292. 17 248. The vaporization behavior of boron nitride and aluminum nitrite. (U.S.A.) The dissociation pressures of crystalline boron nitride and aluminum nitride have been measured by the torsion-effusion method over the ranges 1850 to 2160°K and 1780 to 1970°K, respectively. Although the measured pressures for both substances showed a strong dependence on effusion orifice area, a simple expression relating equilibrium and observed pressures to effusion cell geometry was found to correlate the data quite satisfactorily. Equilibrium pressures evaluated by extrapolation of observed pressures to zero effective orifice area are in good agreement with dissociation pressures calculated from available thermodynamic data. The heats of formation of crystalline
D. L. Hildenbrand and W. F. Hall, J. Phys. Chem., 67, April 1963, 888-893.
(U.S.A.) The reaction kinetics of hydrogen atoms with evaporated carbon films have been studied in the temperature range from 365 to 500 ° K and at total gas pressures from 0.02 to 0.10 mm. The removal of carbon by chemical reaction, as detected by the variation of film thickness with time, was found to occur at two distinct rates with activation energies of 9.2 and 7.1 kcal/mole. The kinetics appear to be related to the degree of crystallinity of the film. Simple hydrocarbons such as methane and ethane are the principal reaction products. In addition, formation of hydrogen molecules by atom recombination on the carbon film takes place ; this reaction, with an activation energy of 2.3 kcal/mole, predominates over hydrocarbon formation in the temperature range studied. (U.S.A.) (Author) A. B. King and H. Wise, J. Phys. Chem., 67, June, 1963 1163-1170. 17 250. The sublimation pressure of calcium (II) fluoride and the dissociation energy of calcium (I) fluoride. (U.S.A.) A vacuum microbalance and a mass spectrometer have been used to determine sublimation pressures and heats of sublimation for CaF~(s) over the range 1242-1669°K. The data are represented by log Patna : --(95.46 ± 0.49)/45.76 × lO~/Tq- 8.141 ~= 0.006. The errors quoted are standard deviations of the leastsquares fit. The heat of sublimation at 298°K is 103.3 ~ 2.0 kcal/mole. F r o m studies of the reaction of CaF~ with aluminum over the range 1271-1351 °K, D°29s for CaF(g) was determined to be 5.4 ~ 0.2 eV from two independent equilibria. Close agreement with other investigators is found for the sublimation of CaF2(s) but the dissociation energy of CaF(g) is much greater than the previously accepted value, (U.S.A.) (Author) G. D. Blue, J. W. Green, R. G. Bautista, and J. L. Margrave, J. Phys. Chem., 67, April 1963, 877-882. 17 251. Kinetics of the low pressure nitrous oxide decomposition on a platinum filament. (U.S.A.) The decomposition of nitrous oxide on a platinum filament has been investigated over a pressure range of 0.02 to 4.0 m m and a temperature range of 545 to 820 ° . The reaction kinetics have been found to fit the Langmuir-Hinshelwood equation for a unimolecular decomposition with poisoning by atomic oxygen. The apparent activation energy is 32 ± 1 kcal/mole. Added oxygen has the same poisoning effect on the reaction rate as the product oxygen. Nitric oxide is produced in small amounts during the decomposition at the higher pressures, However, neither nitric oxide nor nitrogen has been found to poison the reaction. (U.S.A.) (Author) J. P. Redmond, J. Phys. Chem., 67, April 1963, 788-793. 17 252. The thermodynamic and physical properties of beryllium compounds. (IV) Heat and entropy of sublimation of beryllium chloride. (U.S.A.) The vapor pressure curve of BcCI2(s) has been determined over the temperature range 440-600°K using Knudsen gravimetric and torsion effusion procedures. F r o m analysis of the vapor pressure data, second-law values for the heat and entropy of