Porosimetry Porosimetry   is   the   analysis   of   materials   in   order   to   understand   and   determine   their   porous   characteristics.   Porosimetry   can   provide   numerical values   of   pore   volume,   pore   size   and   pore   area,   together   with   additional   information   such   as   surface   area,   bulk   density   and   volume   porosity.   It   is also possible to determine pore size, pore area and pore volume distributions, often through graphical plots. Pore   sizes   are   usually   divided   into   three   ranges,   micro-pores   (<2   nm),   meso-pores   (2   –   50   nm)   and   macro-pores   (>50   nm)   –   these   sizes   are   the diameter of a cylindric al pore or the width of a slit shaped pore according to IUPAC definitions.

There   is   no   single   technique   that   can   be   used   to   determine   porous   characteristics   throughout   the   three   size   ranges.   Therefore,   it   is   usually necessary   to   select   the   most   appropriate   technique   for   a   given   sample   or   use   a   combination   of   techniques.   At   MCA   Services   we   have   decades   of experience in this an d are always happy to provide our thoughts on the selection of analysis techniques.

Meso-pores and macro-pores. Mercury Porosimetry for the pore size range 3nm to ~ 650 µm Mercury   porosimetry   is   used   for   the   characterisation   of   pores   from   3   nm   (0.003   µm)   up   to   approximately   650   µm   (0.65   mm),   although   the   upper limit does depend on the physical nature of the sample being analysed. The following information can be obtained:       • Pore Volume (numerical value and distribution) • Pore Area (numerical value and distribution) • Pore size (numerical value and distribution) • Bulk (Envelope) Density • Skeletal Density • Volume Porosity • Permeability • Tortuosity Meso-pore and small macro-pore. Gas Adsorption for the pores size range 2nm to ~ 300 nm Gas   adsorption,   usually   using   nitrogen   at   77K,   is   used   for   the   characterisation   of   pores   from   3   nm   up   to   approximately   300   nm,   although   the upper   limit   does   depend   on   the   gas   adsorption   characteristics   of   the   sample   being   analysed   and   may   be   higher   or   lower   than   this.   The   following information can be obtained:   • Pore Volume (numerical value and distribution) • Pore Area (numerical value and distribution) • Pore Size (numerical value and distribution) • Indication of pore geometry from desorption analysis • BET Surface Area • Statistical estimate of micro-pore volume • Choice of adsorptive       Micro-pores. Micro-pore Gas Adsorption for pores < 2nm Micro-pores   are   characterised   via   gas   adsorption   using   dedicated   instrumentation   with   uprated   vacuum   and   pressure   measurement   systems. Nitrogen   adsorption   can   be   used   to   characterise   pores   >   0.5   nm   whilst   for   pores   <   0.5   nm   careful   selection   of   the   adsorptive   must   be   made,   for example CO2 or Ar (at 77K or 87K). The following information can be obtained:   • Pore Volume (numerical value and distribution) • Pore Area (numerical value and distribution) • Pore Size (numerical value and distribution) • Choice of adsorptive (N2, Ar, CO2, H2, O2 etc) • Micro-, meso- and small macro-pore characterisation in a single analysis • Extension of N2 data through combination with CO2 data More   information      can   be   found   on   our   specific   Analytical   Options   pages   and   at   MCA   we   are   happy   to   discuss   particular   requirements   and sample types to determine the most appropriate analytical technique or combination of techniques.