Micropore Area and Volume by the t-Plot Method

The t-plot allows one to determine the micropore volume and micropore area from a gas sorption isotherm without the need to measure the low pressure micropore-filling portion of the isotherm. The t-method is applied to the range of multi-layer adsorption and can be applied to isotherms from instruments such as the Nova series, Autosorb, and QUADRASORB evo.


A wide variety of industrially important materials, such as zeolite catalysts and carbon blacks, include a substantial quantity of micropores (pores smaller than 2 nm) and larger mesopores (pores 2-50 nm). Micropore size distributions, volume, and area can be directly accessed through measurement of an N2 (77 K) or Ar (87 K) isotherm starting at low relative pressures (P/P0 < 10-5 ). Measurements at these pressures require the use of low pressure transducers and a turbomolecular pump vacuum, which can be costly additions to an instrument. And, while the method developed by deBoer can be applied in instruments that do have a turbomolecular pump and low pressure transducer (such as the Anton Paar Autosorb), its advantage is in the ability to indirectly measure the contributions of micropores to the total pore volume and surface area without the need for a low pressure transducer or turbomolecular pump, (such as on the Nova series instruments).

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