ABSTRACT
Adsorption has been defined as the phenomenon that concentration of a component in an interfacial layer of vapor-solid, vapor-liquid, liquid-solid, or liquid-liquid becomes higher or lower than that of the bulk phase. The adsorption phenomenon should be distinguished from the absorption, where adsorbate molecules penetrate interior of a solid. Physical adsorption and desorption processes are reversible and a relatively large amount of molecules is adsorbed on a solid surface at temperatures below the boiling point of the adsorptive or under high concentration of adsorptive in solution. The powder particles are usually handled or reserved under the atmosphere. Therefore, water molecules are mainly adsorbed according to its relative vapor pressure surrounding the powder. In order to understand the physical adsorption, the BET equation is most widely used. This equation is derived by expansion of the Langmuir adsorption model to multilayer adsorption under a few assumptions.
