Mercury Intrusion Porosimetry
Mercury intrusion porosimetry (MIP) is a powerful technique utilized for the evaluation of porosity, pore size distribution, and pore volume (among others) to characterize a wide variety of solid and powder materials. The instrument, known as a porosimeter, employs a pressurized chamber to force mercury to intrude into the voids in a porous substrate. As pressure is applied, mercury fills the larger pores first. As pressure increases, the filling proceeds to smaller and smaller pores. Both the inter-particle pores (between the individual particles) and the intra-particle pores (within the particle itself) can be characterized using this technique.
The Washburn Equation relates the applied pressure to pore diameter using physical properties of the non wetting liquid (mercury in this case). The physical properties include the contact angle between the mercury and the material, as well as surface tension. Instruments utilized at PTL allow for pressures ranging from approximately 1 psi up to 60,000 psi which correlates to measurement of pores from about 250 µm to 0.003 µm (3 nm).
The contact angle of the mercury on the material under test is an important consideration for optimal results. The contact angle can either be provided or measured; otherwise default values can be entered during the analysis.
The volume of mercury intruded into the sample is monitored by a capacitance change in a metal clad capillary analytical cell called a penetrometer. The sample is held in a section of the penetrometer cell, which is available in a variety of volumes to accommodate powder or intact solid pieces. Sample size is limited to dimensions of approximately 2.5 cm long by 1.5 cm wide.
Mercury porosimetry is widely used in the catalyst and petrochemical industries for determining the pore size and pore volume of catalyst substrates such as silica and alumina zeolites. In the biomedical field mercury porosimetry has been used to characterize tricalcium phosphate granules or strips used in bone grafts. The pharmaceutical industry has found porosimetry useful in evaluating tablets formed using varied compression forces, for example.
By using mercury porosimetry to evaluate pore size, pore volume, and porosity of substrates, PTL has identified differences between manufacturers, pinpointed problems in processing conditions, and provided routine quality control testing to numerous industries. Please contact us to discuss how PTL can characterize your material using mercury porosimetry testing.