05 powder charzterization 3

05 powder charzterization 3 - Monolayer Adsorption...

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Monolayer Adsorption (Langmuir-Isotherm) A d sorbed a mount V Relative pressure
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Implications of the specific surface area: uantifying colloidal material in a (complex) Quantifying colloidal material in a (complex) particle system that is not or only poorly accessible y particle size analysis. by pa c e s e a a ys s. Measurement of adsorption capacity of a powder to estimate the influence of a surface modification. The difference in surface area/surface energy from powder to a monolith is the main driving force for t i sintering
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Gas adsorption techniques (e.g. BET) • Nitrogen adsorption at -196 o C olecule can penetrate into all ores: N 2 molecule can penetrate into all pores: meso, macro and micropores urface area accessible to the itrogen • Surface area accessible to the nitrogen molecule is being measured
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N 2 -Adsorption isotherm on kaolinite and calculation using the linear relationship
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as adsorption techniques (e g BET) Gas adsorption techniques (e.g. BET)
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BET-Method Brunauer, Emmett and Teller use isothermal sorption in the relative pressure range 0,05 < p/p 0 < 0,35 So-called BET-equation: ( ) ( ) 0 1 1 p p p p p m C C V V + = V : Adsorbed volume of gas 0 0 0 p p p C : Constant (depending on amount adsorped) p 0 : Equilibrium pressure of the specific gas used V m : Volume of an adsorbed monomolecular layer
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Transforming the equation yields a linear equation 1 1 p C p + = a+ b ( ) 0 0 p C V C V p p V m m y = a + b x with x = p/p 0 . 1 C 1 and sing a and b the monolayer adsorbed volume and constant C C V a m = C V b m = Using a and b the monolayer adsorbed volume and constant C can be calculated.
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Note the digits after the point!
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Specific surface area measurements Sorption methods V N F S m A = F : Area per adsorbed molecule e.g. for N 2 (0.0154 (M/ ρ ) 2/3 nm 2 , 162 0 0
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05 powder charzterization 3 - Monolayer Adsorption...

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