H 2O and HCl adsorption on single crystal α-Al 2O 3(0001) at stratospheric temperatures
The adsorption of H 2O and HCl on single crystal α-Al 2O 3(0001) at stratospheric temperatures was studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. The α-Al 2O 3(0001) surface was used to model stratospheric Al 2O 3 exhaust particles from...
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Published in | Applied surface science Vol. 171; no. 1; pp. 21 - 33 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier B.V
2001
|
Subjects | |
Online Access | Get full text |
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Summary: | The adsorption of H
2O and HCl on single crystal α-Al
2O
3(0001) at stratospheric temperatures was studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. The α-Al
2O
3(0001) surface was used to model stratospheric Al
2O
3 exhaust particles from solid rocket motors. H
2O and HCl coverages may influence heterogeneous chemistry on Al
2O
3 particles at stratospheric temperatures of ∼200–270
K. Compared with earlier measurements at 298–300
K, the saturation coverages of both H
2O and HCl on α-Al
2O
3(0001) were approximately two times higher at 210
K. The saturation coverages of H
2O and HCl at 210
K were
Θ
H
2O
=4.4×10
14
molecules/cm
2 and
Θ
HCl=2.0×10
14
molecules/cm
2. The sticking coefficients for both H
2O and HCl on α-Al
2O
3(0001) at 210
K were also higher than the corresponding sticking coefficients at 298–300
K. The sticking coefficients (S) for both H
2O and HCl at 210
K were ∼0.08 at the lowest coverages. The TPD spectra revealed that H
2O and HCl desorption occurred over a broad range of temperatures. These results indicate that H
2O and HCl adsorb onto a wide distribution of binding sites on the α-Al
2O
3(0001) surface. The LITD and TPD results predict that α-Al
2O
3 rocket exhaust particles will be covered with chemisorbed H
2O and HCl under stratospheric conditions. Additional H
2O and HCl exposure can also replace the adsorbed HCl and H
2O species, respectively, by exchange reactions. |
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ISSN: | 0169-4332 1873-5584 |
DOI: | 10.1016/S0169-4332(00)00536-5 |