Studies of porous media by thermally polarized gas NMR: current status (original) (raw)
Related papers
NMR imaging of gas imbibed into porous ceramic
Journal of Magnetic Resonance (1969), 1991
Imaging results are presented for C,F, gas imbibed into a porous ceramic matrix-ceramic fiber composite. The images display delaminations and voids and reveal the layered nature of the material. Thus, NMR of imbibed gas is a potential nondestructive technique for advanced ceramics. The role of the gas molecules is more complicated and more rich than simply providing an NMR signal with long T2. The combination of surface adsorption and the small feature sizes causes order of magnitude changes in the spin density, T, , and the diffusion rate from those of the bulk gas. We suggest that these effects may be used to distinguish features of specified size ranges or, equivalently, specified local surface-tovolume ratios.
Probing Porous Media with Gas Diffusion NMR
Physical Review Letters, 1999
We show that gas diffusion nuclear magnetic resonance (GD-NMR) provides a powerful technique for probing the structure of porous media. In random packs of glass beads, using both laser-polarized and thermally polarized xenon gas, we find that GD-NMR can accurately measure the pore space surfacearea -to -volume ratio, S͞V p , and the tortuosity, a (the latter quantity being directly related to the system's transport properties). We also show that GD-NMR provides a good measure of the tortuosity of sandstone and complex carbonate rocks.
NMR imaging applied to various studies of porous media
Magnetic Resonance Imaging, 1991
We present results of various studies performed in porous media by NMR hnaghtg: discontinuity in the water spatial repartition during drying of a limestone block, drying of cement pastes, progressive melting of a natural clay soil, and quantitative evaluation of dispersion coefficients in glass bead packs. Moreover, the technique has been as well used to obtain the spatial distribution of the relaxation times. The results have been obtained at a magnetic field of 0.1 tesla with samples of approximately 10 cm sire. The 3-D spatial distribution has been obtained with a resolution of the order of 1 mm using the standard method of a spin echo in coincidence with a gradient echo for an echo time of 6 to 20 ms and field gradients of 1 G/cm on a whole body access.
Characterization of porous solids by NMR
Physical Review Letters, 1993
We are using a novel NMR method, that has been developed in our laboratory and employs the depression of the freezing point (AT,) of confined liquid within porous media, to investigate the effect of pre-drying silica with average pore diameter ranging from 60 A to 1000 A. Cyclohexane was the confined liquid. Pre-drying was found to affect only the smallest pores. A study to compare partially filled and over-filled samples showed that the average AT, for partially filled samples is greater than for over-filled. We have also investigated the use of water as the absorbed liquid and compared results with those obtained from cyclobexane studies. Reasonable agreement was found but cvclohexane was more sensitive. The method is fast and is suitable for monitoring pore size distributions in the range of 50-1000 A.
The implementation of an easy-to-apply NMR cryoporometric instrument for porous materials
Magnetic Resonance Imaging, 2023
Time-domain NMR has been extensively utilised to study various characteristics of fluid-saturated porous,materials for instance their mobility, dynamics, stiffness, viscosity and rigidity features, particularly for solid hydrocarbons, rubbers and other polymers. As a unique time-domain technique available for over 30 years, NMR cryoporometry (NMRC) may be used to obtain pore-size distributions of the measured samples. To accurately control the sample temperature, a Peltier thermo-electrically cooled variable temperature probe has been developed and integrated with a highly compact precision NMR time-domain relaxation spectrometer, therefore providing the community with a high-performance instrument for NMR Cryoporometry. To extend the application of aforementioned high-performance NMRC instrument into more senarios, we designed a series of lightweight, compact and integral models with optional NMR frequencies from 12 MHz up to 23 MHz. The measured sample temperature can be precisely controlled from about − 60 ◦C to +80 ◦C, with an excellent temperature resolution of 10 mK or better near the probe liquid bulk melting point. Therefore, it offers a fairly wide NMRC pore-size distribution ranging from about 1 nm to 2 μm by using water as the probe liquid in the pores, signifcantly wider than is possible when applying generic NMR Spectrometers for NMRC. A preliminary example of NMR Cryoporometric measurements on two special cement samples is shown in the paper in which the measured pore scales as well as their repeatability are demonstrated. Furthermore, various nano-materials, such as MOF, zeolite and shale kerogen would be potential materials to study by using these new available NMRC instrument models. We aim to offer this technique as a quantitative and easy-to-apply unitary benck-top tool for an even wider range of porous material.
Spatially resolved pore size distributions by NMR
Measurement Science and …, 1997
We have developed a novel method of determining median pore size and pore size distributions as a function of spatial position inside a porous sample. Pore sizes have been measured with one-, two- and three-dimensional spatial resolutions, using nuclear magnetic resonance (NMR) cryoporometry in conjunction with magnetic resonance imaging techniques. NMR cryoporometry is a method of measuring pore sizes and pore size distributions in the range of less than 40 °A to over 2000 °A pore diameter, by the technique of freezing a liquid in the pores and measuring the melting temperature by NMR. Since the melting point is depressed for crystals of small size, the melting point depression gives a measurement of pore size.
Pore surface exploration by NMR
Magnetic resonance imaging, 2003
A carefully chosen set of experimental techniques applied to porous media characterization provides results that can be much greater than the sum of the individual parts. The inter-relation and complementarity of a number of techniques will be considered. NMR cryoporometry provides a valuable method of pore size measurement. An NMR method that is more widely used to assess pore dimensions relies on relaxation time analysis of a liquid that fills the pores and the enhanced relaxation that occurs in a liquid at the solid/liquid interface. Thermoporometry, a method based on the application of Differential Scanning Calorimetry (DSC), is closely related to cryoporometry, but employs a different set of assumptions to evaluate pore size distributions. Comparison of the results obtained on the same samples using all these methods together with gas adsorption serves to validate the methods and provide significantly more information about surface-fluid interaction and the behavior of nano-scale material within pores than each method employed in isolation. Technique developments will be discussed and applications of these methods to ideal silicas will be used to illustrate their power, particularly in combination. © 2003 Elsevier Science Inc. All rights reserved. Keywords: Porous media; Nuclear magnetic resonance; Cryoporometry; Relaxometry
Ceramic microstructure detected by NMR relaxation and imaging of fluids in the pores
Magnetic Resonance Imaging, 1996
NMR Relaxation and Imaging have been applied to study preparation processes of ceramic porous samples. Relaxation analysis gives a clear characterization of the materials, with high sensitivity. Differences in the method of preparation and steps as low as 25°C in the firing temperatures are well detectable. Furthermore, the images permit distinguishing the diierent samples. The effects of the contrast in relaxation times dominate those due to the different porosities of the samples. Scanning Electron Microscopy confums the interpretation that the changes in relaxation times are due to diierent pore space structures associated with the different firing temperatures. The higher the firing temperature, the larger are the pores and the higher is the amount of compact, sintered matrix, leading to higher relaxation times. Copyright 0 1996 Elsevier Science Inc.
Probing the structure of porous media using NMR spin echoes
Magnetic Resonance Imaging, 1994
gator of the molecules of a fluid diffusing in the pores of a porous medium. For small values of k = 'yg&, where g is the gradient strength, 6 is the duration of the gradient pulse, and y the gyromagnetic ratio, the PFGSE amplitude gives the diffusion coefficient o(t). The exact short-time diffusion coefficient, D(t)/&, = 1 -(4m,S)/ (9& &?) -D&L!V(12 5) + ptS/6Y,, provides an important method for determining the surface to pore-volume ratio S/V,. Here the mean surface curvature H = (l/R1 + l/R&. Combining early II(f) with the magnetization decay one obtains the surface relaxivity p. The long-time effective diffusion constant derived from PFGSE gives information on the tortuosity of the connected space. The diffusion coefficient measured by PFGSE equals that derived from electrical conductivity only when p = 0. Exact solutions with partially absorbing boundary conditions for a periodic structure are used to illustrate the influence of p on the diffusion coefficient. M(k,t) can be well represented by a convolution of the structure factor of the connected pore space with an appropriate Gaussian propagator. This ansatz provides a model-independent way of obtaining the structure factor. Kevwords: Restricted diffusion: Porous medium: NMR surface relaxation; NMR pulsed field gradient; Surfaceto-volume ratio; Formation factor. 12(2):279-284; 1994. Kleinberg, R.L. Pore-size distribution, pore coupling, and transverse relaxation spectra of porous rocks. Magn. Reson. Imaging 12(2):271-274; 1994. Callaghan, P.T.; MacGowan, D.; Packer, K.J.; Zelaya, F.O. Diffraction like effects in NMR diffusion studies of fluids in porous solids. Nature 351:467-468; 1991.
The Journal of Chemical Physics, 2010
Noninvasive characterization of pore size and shape in opaque porous media is a formidable challenge. NMR diffusion-diffraction patterns were found to be exceptionally useful for obtaining such morphological features, but only when pores are monodisperse and coherently placed. When locally anisotropic pores are randomly oriented, conventional diffusion NMR methods fail. Here, we present a simple, direct, and general approach to obtain both compartment size and shape even in such settings and even when pores are characterized by internal field gradients. Using controlled porous media, we show that the bipolar-double-pulsed-field-gradient ͑bp-d-PFG͒ methodology yields diffusion-diffraction patterns from which pore size can be directly obtained. Moreover, we show that pore shape, which cannot be obtained by conventional methods, can be directly inferred from the modulation of the signal in angular bp-d-PFG experiments. This new methodology significantly broadens the types of porous media that can be studied using noninvasive diffusion-diffraction NMR.