Transcription of Surface Area and Porosity - Iowa State University
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Surface area and PorosityOutline Background Techniques Surface area Total - physical adsorption External Porosity meso micro12 Tuesday, December 4, 12 Length1 mm1 m1 nm1 macromesomicrometalcrystallite10-3m10-4m 10-5m10-6m10-7m10-8m10-9m10-10mhumanhair red bloodcellred antC-CbondCarbonnanotubeTransistorgatece ll membrane1010010100 TechniquesMercury intrusion AdsorptionPhysicalChemicalTemperature Programmed Methods34 Tuesday, December 4, 12 Physical AdsorptionCharacterization via AdsorptionMaterial Characterization Physical properties DifferentiateGas Adsorption Quantity adsorbed on a Surface as a function of pressure, volume, and temperature Modeled properties Surface area Pore structure Non-destructuve56 Tuesday, December 4, 12 Static AdsorptionXXPVGXA dsorptionQuantity adsorbed - always normalized for mass - cm3/g or moles/gRelative pressure - equilibrium pressure divided by saturation pressure - p/po Equilibrium pressure - vapor pressure above the sample - corrected for temperature (thermal transpiration) Saturation pressure - vapor pressure above a liquidSurface energy - solid/fluid interaction, strength, and heterogeneity78 Tuesday, December 4, 12 Sample PreparationClean the Surface Remove volatiles Water CO2 SolventsControlled environment!
Surface Area Surface Area •Area from adsorption •n m - monolayer •N A - Avogadro’s number •Total area - physical adsorption •area of adsorbed molecule - nitrogen or krypton •Active area - chemical adsorption •area of a surface site - metal atom •Stoichiometry 31 32 Tuesday, December 4, 12
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