We have developed a novel method of determining median pore size and pore size distributions of porous materials, both on bulk samples and as a function of spatial position inside a sample with structured porosity.
NMR cryoporometry is based on the technique of freezing a liquid in the pores and measuring the melting temperature by Nuclear Magnetic Resonance. Since the melting point is depressed for crystals of small size, the melting point depression gives a measurement of pore size.
The method is non-destructive, and is suitable for pore diameters in the range of a few nanometers to around 1m.
Commercially important porous materials that we have recently studied include the porous glasses, the alumina and alumino silicates such as clays and zeolites, activated and other porous carbons, cement, and water and oil bearing shales, sandstones and limestones.
NMR cryoporometry is often the method of choice and is always valuable to complement existing porous measurment techniques such as gas adsorption and mercury porosimetry. It shows good linear agreement with gas adsorption measurements in porous silica glasses. One major advantage of NMR cryoporometry over other techniques is in its ability to perform non-destructive spatial imaging.