scholarly journals The rate of water vapor evaporation from ice substrates in the presence of HCl and HBr: implications for the lifetime of atmospheric ice particles

2003 ◽  
Vol 3 (4) ◽  
pp. 1131-1145 ◽  
Author(s):  
C. Delval ◽  
B. Fluckiger ◽  
M. J. Rossi
Keyword(s):  
Activation Energy ◽  
Water Vapor ◽  
Vapor Pressure ◽  
Absorption Spectra ◽  
Mole Fraction ◽  
Rate Constant ◽  
Enthalpy Of Sublimation ◽  
Experimental Uncertainty ◽  
Ice Particles ◽  
Ftir Absorption Spectra

Abstract. Using a multidiagnostic approach the rate Rev [ molec cm-3 s-1] or flux Jev [ molec cm-2 s-1] of evaporation of H2O and its corresponding rate constant for condensation, kcond [s-1 ], on a 1 µm thick ice film have been studied in the temperature range 190 to 240 K as well as in the presence of small amounts of HCl and HBr that left the vapor pressure of H2O on ice unchanged. The resulting Arrhenius expressions for pure ice are Jev = 1.6 · 10 28 ± 1 · exp  (- 10.3 ± 1.2/ RT)  [ molec cm-2 s-1] , kcond = 1.7 · 10 - 2 ± 1 · exp  (+ 1.6 ± 1.5/ RT ) [s -1], in the presence of a HCl mole fraction in the range 3.2 · 10 - 5 - 6.4 · 10 - 3 : Jev = 6.4 · 10 26 ± 1 · exp  (- 9.7 ± 1.2/ RT)  [ molec cm-2 s-1] , kcond = 2.8 · 10 - 2 ± 1 · exp ( + 1.5 ± 1.6 /RT)  [s -1], and a HBr mole fraction smaller than 6.4 · 10 - 3 : Jev = 7.4 · 10 25 ± 1 · exp ( - 9.1 ± 1.2 /RT)  [ molec cm-2 s-1] , kcond = 7.1 · 10 - 5 ± 1 · exp (+ 2.6 ± 1.5/ RT) [s -1]. The small negative activation energy for H2O condensation on ice points to a precursor mechanism. The corresponding enthalpy of sublimation is DHsubl = Eev - Econd = 11.9 ± 2.7 kcal mol-1 , DHsubl = 11.2 ± 2.8 kcal mol-1, and DHsubl = 11.7 ± 2.8 kcal mol-1 whose values are identical within experimental uncertainty to the accepted literature value of 12.3 kcal mol-1 . Interferometric data at 633 nm and FTIR absorption spectra in transmission support the kinetic results. The data are consistent with a significant lifetime enhancement for HCl- and HBr-contaminated ice particles by a factor of 3–6 and 10–20, respectively, for submonolayer coverages of HX once the fraction of the ice not contaminated by HX has evaporated.

scholarly journals The rate of water vapor evaporation from ice substrates in the presence of HCl and HBr: Implications for the lifetime of atmospheric ice particles

2003 ◽  
Vol 3 (3) ◽  
pp. 2179-2218
Author(s):  
C. Delval ◽  
B. Fluckiger ◽  
M. J. Rossi
Keyword(s):  
Activation Energy ◽  
Water Vapor ◽  
Vapor Pressure ◽  
Absorption Spectra ◽  
Mole Fraction ◽  
Enthalpy Of Sublimation ◽  
Experimental Uncertainty ◽  
Temperature Range ◽  
Ice Particles ◽  
Ftir Absorption Spectra

Abstract. Using a multidiagnostic approach the rate Rev or flux Jevof evaporation of H2O and its condensation, kcond, on a 1mm thick ice film have been studied in the temperature range 190 to 240 K as well as in the presence of small amounts of HCl and HBr that left the vapor pressure of H2O on ice unchanged. The resulting Arrhenius expressions with RT in kcal mol-1 for pure ice are Jev=1.6×1028+/−1·exp({−10.3+\\−1.2}/{RT}) [molec cm−2 s−1], kcond=1.7×10−2+\\-1×exp({+1.6+\\−1.5}/{RT}) [s−1], in the presence of an HCl mole fraction in the range 3.2×10−5-6.4×10−3: Jev=6.4×1026+/−1×exp({−9.7+/−1.2}/{RT}) [molec cm−2 s−1], kcond=2.8×10−2+/-1×exp({+1.5+/−1.6}/{RT}) [s−1], and an HBr mole fraction smaller than 6.4×10−3:Jev=7.4×1025+/−1×exp({−9.1+/−1.2}/{RT}) [molec cm−2 s−1], kcond=7.1×10−5+\\−1×exp({+2.6+/−1.5}/{RT}) [s−1]}. The small negative activation energy for H2O condensation on ice points to a precursor mechanism. The corresponding enthalpy of sublimation is DHsubl=Eev-Econd=11.9+/−2.7 kcal mol−1, DHsubl=11.2+/−2.8 kcal mol−1, and DHsubl=11.7+/−2.8 kcal mol−1 whose values are identical within experimental uncertainty to the accepted literature value of 12.3 kcal mol−1. Interferometric data at 633 nm and FTIR absorption spectra in transmission support the kinetic results. The data are consistent with a significant lifetime enhancement for HCl- and HBr-contaminated ice particles by a factor of 3–6 and 10–20, respectively, for submonolayer coverages of HX.

Oxidation of nanocrystalline Mo–Si–N and nanolayered Mo–Si–N/SiC coatings

1999 ◽  
Vol 14 (9) ◽  
pp. 3552-3558 ◽  
Author(s):  
P. Torri
Keyword(s):  
Activation Energy ◽  
Water Vapor ◽  
Oxidation Resistance ◽  
Rate Constant ◽  
Arrhenius Plot ◽  
Single Layer ◽  
Water Vapor Atmosphere ◽  
Oxidation Properties ◽  
Sputter Deposited ◽  
Sic Coatings

Oxidation of sputter-deposited nanocrystalline Mo–Si–N (MoSi2.2N2.5) coatings in oxygen–water vapor atmosphere has been studied in the temperature range 400–850 °C. In addition, the oxidation properties of nanolayered Mo–Si–N/SiC coatings at 700 °C were studied and compared to those of single-layer coatings of both components. No pest disintegration was observed in Mo–Si–N up to 200 h of oxidation. A preexponential rate constant of (3.7 ± 0.5) × 109 (1015 atoms/cm2)2/h and activation energy 1.03 ± 0.02 eV were determined from an Arrhenius plot for parabolic oxygen buildup on Mo–Si–N. Up to 20% less oxygen was detected in the oxidized nanolayered coatings compared to either of the components as a single layer, indicating an improvement in oxidation resistance.

The thermal decomposition of cyclobutane-1,2-dione

1985 ◽  
Vol 63 (11) ◽  
pp. 2945-2948 ◽  
Author(s):  
J.-R. Cao ◽  
R. A. Back
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Vapor Pressure ◽  
Gas Phase ◽  
Rate Constant ◽  
Surface Reaction ◽  
Order Rate Constant ◽  
Reaction Vessel ◽  
Arrhenius Parameters ◽  
First Order

The thermal decomposition of cyclobutane-1,2-dione has been studied in the gas phase at temperatures from 120 to 250 °C and pressures from 0.2 to 1.5 Torr. Products were C2H4 + 2CO, apparently formed in a simple unimolecular process. The first-order rate constant was strongly pressure dependent, and values of k∞ were obtained by extrapolation of plots of 1/k vs. 1/p to1/p = 0. Experiments in a packed reaction vessel showed that the reaction was enhanced by surface at the lower temperatures. Arrhenius parameters for k∞, corrected for surface reaction, were log A (s−1) = 15.07(±0.3) and E = 39.3(±2) kcal/mol. This activation energy seems too low for a biradical mechanism, and it is suggested that the decomposition is probably a concerted process. The vapor pressure of solid cyclobutane-1,2-dione was measured at temperatures from 22 to 62 °C and a heat of sublimation of 13.1 kcal/mol was estimated.

Hydration Chamber for Jeolco 200 Kv Microscope

1970 ◽  
Vol 28 ◽  
pp. 542-543
Author(s):  
V. R. Matricardi ◽  
G. G. Hausner ◽  
D. F. Parsons
Keyword(s):  
Electron Microscope ◽  
Water Vapor ◽  
Vapor Pressure ◽  
Pressure Gradient ◽  
Room Temperature ◽  
List Type ◽  
Type Number ◽  
Equilibrium Vapor Pressure

In order to observe room temperature hydrated specimens in an electron microscope, the following conditions should be satisfied: The specimen should be surrounded by water vapor as close as possible to the equilibrium vapor pressure corresponding to the temperature of the specimen.The specimen grid should be inserted, focused and photo graphed in the shortest possible time in order to minimize dehydration.The full area of the specimen grid should be visible in order to minimize the number of changes of specimen required.There should be no pressure gradient across the grid so that specimens can be straddled across holes.Leakage of water vapor to the column should be minimized.

THE OXIDATION OF NITRITE AND IODATE IONS BY HYPOCHLORITE IONS

1961 ◽  
Vol 39 (8) ◽  
pp. 1645-1651 ◽  
Author(s):  
M. W. Lister ◽  
P. Rosenblum
Keyword(s):  
Activation Energy ◽  
Aqueous Solution ◽  
Rate Constant ◽  
Hypochlorous Acid ◽  
Slow Stage ◽  
Iodate Ions

The oxidation of nitrite ions and of iodate ions by hypochlorite ions in aqueous solution has been examined. The oxidation of nitrite is really a reaction of hypochlorous acid, with the slow stage HOCl + NO2− + H2O → H3O+ + Cl− + NO3−. The rate constant is given by log k = 7.36−6450/RT (time in minutes, and the activation energy in calories). The oxidation of iodate is chiefly a reaction of hypochlorite ions, probably ClO− + IO3− → Cl− + IO4−, although the rate is somewhat increased by a higher concentration of hydroxide ions. The rate constant is given by log k = 16.15−26,100/RT. These results are compared with other oxidations by hypochlorite ions, to see if any general trends are apparent.

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