Global InformationThermoporometry and cryoporometry information
Thermoporometry and cryoporometry are methods for measuring porosity and pore-size distributions. A small region of solid melts at a lower temperature than the bulk solid, as given by the Gibbs–Thomson equation. Thus, if a liquid is imbibed into a porous material, and then frozen, the melting temperature will provide information on the pore-size distribution. The detection of the melting can be done by sensing the transient heat flows during phase transitions using differential scanning calorimetry – DSC thermoporometry,[1] measuring the quantity of mobile liquid using nuclear magnetic resonance – NMR cryoporometry (NMRC)[2][3] or measuring the amplitude of neutron scattering from the imbibed crystalline or liquid phases – ND cryoporometry (NDC).[4]
To make a thermoporometry / cryoporometry measurement, a liquid is imbibed into the porous sample, the sample cooled until all the liquid is frozen, and then warmed until all the liquid is again melted. Measurements are made of the phase changes or of the quantity of the liquid that is crystalline / liquid (depending on the measurement technique used).
The techniques make use of the Gibbs–Thomson effect: small crystals of a liquid in the pores melt at a lower temperature than the bulk liquid : The melting point depression is inversely proportional to the pore size. The technique is closely related to that of use of gas adsorption to measure pore sizes but uses the Gibbs–Thomson equation rather than the Kelvin equation. They are both particular cases of the Gibbs Equations (Josiah Willard Gibbs): the Kelvin equation is the constant temperature case, and the Gibbs–Thomson equation is the constant pressure case.[2]
- ^ Brun, M.; Lallemand, A.; Quinson, J-F.; Eyraud, C. (1977), "A new method for the simultaneous determination of the size and the shape of pores: The Thermoporometry", Thermochimica Acta, 21: 59–88, doi:10.1016/0040-6031(77)85122-8
- ^ a b Mitchell, J.; Webber, J. Beau W.; Strange, J.H. (2008), "Nuclear Magnetic Resonance Cryoporometry" (PDF), Phys. Rep., 461 (1): 1–36, Bibcode:2008PhR...461....1M, doi:10.1016/j.physrep.2008.02.001
- ^ Petrov, Oleg V.; Furo, Istvan (2009), "NMR cryoporometry: Principles applications and potential", Prog. Nucl. Mag. Res. Sp., 54 (2): 97–122, doi:10.1016/j.pnmrs.2008.06.001
- ^ Webber, J. Beau W.; Dore, John C. (2008), "Neutron Diffraction Cryoporometry – a measurement technique for studying mesoporous materials and the phases of contained liquids and their crystalline forms" (PDF), Nucl. Instrum. Methods A, 586 (2): 356–366, Bibcode:2008NIMPA.586..356W, doi:10.1016/j.nima.2007.12.004