http://www.kent.ac.uk

Functional Materials Group
Lab-Tools.com

nano-metrology.co.uk

Nano- to Micro-Scale Volumetric Metrology

Dr. J.B.W. Webber.



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Nano-scale to micro-scale volumetric metrology :

Lab-Tools performs contract analyses of Pore Size Distributions and Pore Volume using NMR Cryoporometry.

The main technique we have developed for nano-scale metrology uses NMR Cryoporometry, based on physical thermodynamics (Gibbs equations), and employs Gas Adsorption and neutron scattering for primary calibration.

Free pore size distributions
on your initial samples.

We will make free measurements on two of your samples, so you can verify the technique at no cost to yourself.

Contact : Dr. Beau Webber .

Nano-scale to micro-scale metrology :

The basic techniques that use these changes in the thermodynamic properties in nano-structured systems are : Of these techniques, NMR Cryoporometry is now often our preferred technique, although the others may provide invaluable comparative information. We have used NMR Cryoporometry in a number of academic research projects and industrial contracts, to measure pore volumes and pore size distributions in materials such as porous carbons, fired and un-fired clays, marine sediments, oil-bearing rocks, meteorite fragments ....

NMR Cryoporometry :

Porous mateials studied:
Sol-gel & CPG silicas
MCM templated silicas
SBA templated silicas
Activated carbons
Zeolites
Cement & Concrete
Fired & unfired clays
Marine Sediments
Chalks, Shales
Sandstones
Oil-bearing rocks
Meteorites
Wood
Paper
Rubbers
Emulsions & Paint
Artificial skin
Bone
Melanised fungal cells

NMR Cryoporometry (NMRC) is a novel pore size distribution measurement technique that we have developed at the University of Kent and at Lab-Tools Ltd. It makes use of the fact that small crystals of a liquid in the pores melt at a lower temperature than the bulk liquid.
This is the Gibbs-Thomson effect : The melting point depression is inversely proportional to the pore size.

A liquid is imbibed into the porous sample, the sample cooled until all the liquid is frozen, and then warmed slowly while measuring the quantity of the liquid that has melted. This data is converted to a pore-size distribution.
(Negligible sample degradation due to the freezing process has as yet been observed, with excellent measurement repeatability.)
More detailed information about NMR Cryoporometry is available by following the link below to our NMR Cryoporometry pages. We have jointly, with Cambridge University, written a Review of NMR Cryoporometry, now published in Physics Reports :
Nuclear Magnetic Resonance Cryoporometry
J. Mitchell, J. Beau W. Webber and J.H. Strange. Physics Reports, 461, 1-36, 2008. doi:10.1016/j.physrep.2008.02.001 .

cryoporometry.com
Further information on Cryoporometry including equations.

Normalised pore size distributions for selected porous silicas, by NMR Cryoporometry. The intrinsic resolution of the technique is better than the red curve, for SBA-15, which is fully resolved.
Figure 1: Normalised pore size distributions for selected porous silicas, as measured by NMR Cryoporometry. The intrinsic resolution of the technique is better than the red curve, for SBA-15, which is fully resolved.

Lab-Tools performs contract analyses of Pore Size Distributions using NMR Cryoporometry :

Lab-Tools has successfully measured pore sizes in a wide range of porous materials, including oil and/or water wet materials. NMR Cryoporometry is one of the few techniques that can be applied to materials that can not be dried out without losing their structure. The technique is non-destructive, and can be used to follow evolution of pore structure for evolving systems.

The Lab-Tools pore-size distribution measurement range extends from about 1nm to over 2m. NMR Cryoporometry measures both the total pore volume and the pore volume distribution as a function of pore diameter.
We frequently find that NMR Cryoporometry (NMRC) may be preferable to more established methods such as BET gas adsorption or DSC thermal porisimetry, and can now also provide information on both pore diameter and pore throat size, unlike Hg Intrusion, which just measures the pore throat.

NMR Cryoporometry measurement costs are very competitive. Cost per sample depends on the pore-size range to be covered, and precision needed, but goes down markedly for multiple-sample batches. Two free pore size distribution measurements are normally available for you to evaluate the technique for your own samples.

Please contact Dr. Beau Webber to discuss pore size measurements on your samples.

Maximum sample size needed : enough sample to fill a tube 4mm dia. x 12mm : usually 30mg to 300mg, depending on density.

NMR Cryoporometry : Measuring Pore Size Distributions - PDF A5 Flier

NMR-C Pore Size Distributions for porous carbonate and sandstone rocks.

Figure 2: NMR Cryoporometric Pore Size Distributions
for porous carbonate and sandstone rocks.
NMR-CIntegral Distributions for porous carbonate and sandstone rocks.

Figure 3: NMR Cryoporometric Integral (cumulative) Pore Size Distributions
for porous carbonate and sandstone rocks.

Note: the divergence in the carbonate data at low pore diameter corresponds to less than a 1μl.g-1 base-line error, as can be seen on the pore integral graph.


X-ray and neutron scattering based metrology calibration program :

With all these thermodynamic techniques, however there is increasingly a supposition that as atomic dimensions are approached, the calibration from the thermodynamics may change.

Thus we have mounted a separate metrology program using neutron and X-ray scattering. These have the advantage that they are inverse techniques, by which is meant that the smaller the structure being observed, the larger is the scattering angle.

Further, there is no existing reason to suppose that these scattering techniques are length-scale dependent. i.e. if one has a good calibration at one length-scale, it should also be good at all other length-scales.

To transform a measured scattering to a metric of the structures in the sample, we create extended models of pore systems, and calculate the scattering using numerical integration. These show very good agreement with measured scattering, figure 4.

Our existing measurements using sol-gel silicas have shown that while the thermodynamic techniques are in close agreement with the scattering measurements for dimensions above 10nm, below this dimension there appears to be an increasing divergence between the scales of the thermodynamic and scattering metrologies.

Dr. Beau Webber has been awarded measurement time at the Institute Laue Langevin (ILL), on the D4 and D22 instruments, and this has enabled him to develop and verify his models.

The equations describing these models have recently been published in Physics Reports :
Nano-metrology of porous structures - I. Using neutron scattering to access pore lattice, diameter and wall parameters, by comparison with direct calculation of scattering from models of extended arrays of regular or randomised pores. J.Beau W. Webber. Physics Reports, 526, 4, 227-248, 2013. DOI: 10.1016/j.physrep.2013.01.002

Dr. Beau Webber was recently awarded further measurement time (as first user) on the excellent new wide-scattering range ISIS Target Station 2 instrument NIMROD, and 17 porous samples were measured on this most successful run, with very pleasing preliminary results. Simulation models are being run to match the results, and the models, results and conclusions will be presented in a paper.

Fully density corrected radial distribution function measured for 7 sol-gel silicas, compared with that calculated for extended arrays of pores with Gaussian variance.
Figure 4: Fully density corrected radial distribution function measured for 7 sol-gel silicas (red lines), compared with that calculated for extended arrays of pores with Gaussian variance (green dots).
Porous-Media.com
Porous Media pages

Characterisation Capabilities

Lab-Tools are based at the Canterbury Enterprise Hub at the University of Kent, U.K. The analytic and research labs have recently moved to new purpose designed premises outside Canterbury, near Ramsgate. One of our main strengths is the range of characterisation techniques we can offer using Nuclear Magnetic Resonance, to study liquids, solids and structured matter.

Users of these services

We have made physical analysis measurements for a number of international companies, including BP, Shell, Unilever, Coates Lorilleux, Lafarge Braas, LCT in New Zealand, IFP in Paris and Schlumberger in the USA. Universities that we have worked with include Kent, Heriot-Watt, Leeds, Leicester, Imperial College, Lancaster, Nottingham Trent, Rice and Texas in the USA, plus a number in Europe.

Publications

Some of our publications in the field of porous-media, nano-scale to micro-scale structured matter, and confined liquids :
For more information : E-mail me : J.B.W.Webber@kent.ac.uk, see : my publications , go to my research home page. Also, see my Thesis.

Content, design & creation Dr. Beau Webber 2005.
2005_03_20 ... 2011-02-19