Nuclear magnetic resonance cryoporometry

Abstract

Nuclear Magnetic Resonance (NMR) cryoporometry is a technique for non-destructively determining pore size distributions in porous media through the observation of the depressed melting point of a confined liquid. It is suitable for measuring pore diameters in the range 2 nm -1 µm, depending on the absorbate. Whilst NMR cryoporometry is a pertabative measurement, the results are independent of spin interactions at the pore surface and so can offer direct measurements of pore volume as a function of pore diameter. Pore size distributions obtained with NMR cryoporometry have been shown to compare favourably with those from other methods such as gas adsorption, DSC thermoporosimetry, and SANS. The applications of NMR cryoporometry include studies of silica gels, bones, cements, rocks and many other porous materials. It is also possible to adapt the basic experiment to provide structural resolution in spatially dependent pore size distributions, or behavioural information about the confined liquid.

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

“…Its low field limits the field gradient inside heterogeneous samples, in particular in porous media (Guichet et al, 2008, Mitchell et al, 2008, while the short 90° RF pulse width used enables protons of both solid and liquid phases to be excited.…”

“…Short, interesting introductions to NMR and LF-NMR have been presented by Manalo et al (2003), Todoruk (2003) and Mitchell et al (2008). For a given type of sample, relaxation times are a function of the mobility of the protons and therefore enable a quantitative characterization of water, especially between ice and non-freezing water.…”

“…Bertram et al, 2001, Hills, 2006, in the petroleum sector (e.g. Al-Mahrooqi et al, 2006, Guichet et al, 2008, for cryoporometry (Mitchell et al, 2008) or to study the diffusion of water in cement paste (Hansen et al, 2005).…”

High-pressure cryogelation of nanosilica and surface properties of cryosilicas

“…The freezing point depression for water in narrow pores is described by the GibbsThomson relation (assuming a cylindrical pore shape) at radius R [17,[19][20][21][22] given as Eq. (3);…”

“…Freezing of bound water occurs at low temperatures at T < 260 K (Figs. 7a and 8) because of the freezing point depression for liquids confined in pores [16,17,[19][20][21][22]. Since freezing of bound water occurs at T < 260 K, all of this water can be assigned to strongly bound water (SBW).…”