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Typical hysteresis of adsorption-desorption cycle
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Langmuir isotherm :
influence of the coefficient ‘b’
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Variations on Langmuir and Henry
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Variations of Langmuir and Henry
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Théorie de Brunauer Emmett et Teller (BET)
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Hypothèses
–Starting from the second layer E1»EL energy of molecules in liquid state
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Basic hypothesis of the BET theory
E1 = Energy of adsorption for the first layer
El = Energy of liquid state
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Basic hypothesis of the BET theory
surface so covered with 0 adsorbed layers
… s1 … 1
… … …
… si … i
Accessible surface A = so + s1 + … + si + …
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Derivation of the BET formula
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Derivation of the BET formula
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Derivation of the BET formula
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Theory of Brunauer Emmett and Teller (BET)
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Equations
– N= number of layers
x = p/p0 = relative equilibrium
pressure
––if N ® ¥
–Transformed equation BET
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Influence of number of layers N on the shape of isotherms of adsorption (BET)
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Influence of the constant ‘C’ on the shape of isotherms of adsorption (BET)
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Application for calculation of the adsorption surface
example : alumin NPL / N2 / 77 K
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Verifications of BET results
example : alumin NPL / N2 / 77 K
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Approach thermodynamic – energie of adsorption
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Example:
mesoporous system: MCM-41 et 77K
CO & CH4
Typical for heterogeneous surface
Dadsh (»2 kJ.mol-1) during the capillary condensation
Kr
Dadsh (»5 kJ.mol-1) during the capillary condensationÜ solidification ?
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Milestone properties
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Milestone properties
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Milestone properties
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Nitrogen / black of de carbon (Carbopack)
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Adsorption on precipitated silica
Isotherms : N2 & Ar à 77K
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The conditions of the sample preparation are very important!!!!
…