INTRODUCTION

Porosity is a term typically used to indicate the porous nature of solid material and is more precisely defined as the ratio of the volume of accessible pores and voids to the total volume occupied by a given amount of the solid. Closed or inaccessible pores that are isolated from the external surface are excluded from this definition of pore volume. Pores (or voids) may consist of apertures, channels, or cavities within a solid body or spaces between solid particles in a compact or aggregate. Pores exist in a variety of solid materials beyond compacts and aggregates, such as powders and tablets, and their characterization usually involves the determination of the total pore volume or porosity, as well as the pore size distribution. Pores generally are classified by size into the following groups:

• Micropores—less than 2 nm

• Mesopores—2 to 50 nm

• Macropores—greater than 50 nm