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Surface diffusion of stearic acid on aluminum oxide
Author(s) -
Yang Ralph T.,
Fenn John B.,
Haller Gary L.
Publication year - 1974
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690200415
Subject(s) - stearic acid , monolayer , chemistry , diffusion , adsorption , molecule , analytical chemistry (journal) , activation energy , infrared spectroscopy , oxide , thermodynamics , organic chemistry , biochemistry , physics
By means of infrared internal reflection spectroscopy we measured the time dependence of the surface concentration of stearic acid molecules over a well defined region of the surface. The molecules were diffusing into this region from a source comprising a compressed monolayer or bulk crystalline material outside the field of view. By these measurements in conjunction with solutions to the diffusion equations we determined the diffusion coefficient D s of stearic acid on the (0001) plane of α‐alumina. We also determined the dependence of D s upon the amount of water coadsorbed on the surface. When the surface was free of reversibly adsorbed water, D s had a value of about 2 × 10 −7 cm 2 /s. As the surface coverage of coadsorbed water increased to about a monolayer D s increased to a maximum value of about 4 × 10 −5 cm 2 /s. With further additions of surface water D s then decreased and became less than 10 −8 cm 2 /s at coverages slightly less than about two monolayers. In the region of its maximum value the temperature dependence of D s indicated an activation energy for the diffusion process of about 26 kcal/mole.