Surface Area Determination
•White Paper: Surface Area Determination
Introduction
The surface of a material is the dividing line between a solid and its surroundings, liquid, gas or another solid. We can anticipate therefore, that the amount of surface, or surface area, is an important factor in the behavior of a solid. Surface area affects, for example, dissolution rates of pharmaceuticals, the activity of an industrial catalyst, how fast cement hydrates, adsorption capacity of air and water purifiers, and the processing of most powders and porous materials. Whenever solid matter is divided into smaller particles new surfaces are created thereby increasing the surface area. Similarly, when pores are created within the particle interior (by dissolution, decomposition or some other physical or chemical means) the surface area is also increased.
Gas Sorption
The true surface area, including surface irregularities and pore interiors, cannot be calculated
from particle size information, but is rather determined at the atomic level by the adsorption of an
unreactive, or inert gas. The amount adsorbed, let's call it X, is a function not only of the total
amount of exposed surface, but also (i) temperature, (ii) gas pressure and (iii) the strength of
interaction between gas and solid. Because most gases and solids interact weakly, the surface
must be cooled substantially in order to cause measurable amounts of adsorption – enough to
cover the entire surface. As the gas pressure is increased, more is adsorbed on the surface (in a
non-linear way). But, adsorption of a cold gas does not stop when it has covered the surface in a
complete layer one molecule thick (let's call the theoretical monolayer amount of gas Xm)! As the
relative pressure is increased, excess gas is adsorbed to form "multilayers".
Click Here To Download:
•White Paper: Surface Area Determination