Nano- to Micro-Scale Volumetric Metrology

Dr. J.B.W. Webber.

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Nano-scale to micro-scale volumetric metrology :

The main techniques we are developing for nano-scale metrology uses physical thermodynamics (Gibbs equations), and employs neutron and X-ray scattering for primarily calibration.

Nano-scale to micro-scale metrology :

The basic techniques that use these changes in the thermodynamic properties in nano-structured systems are :

Gas adsorption,
Thermoporosimetry,
NMR Cryoporometry.

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 ....
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 .

Figure 2: 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 measured pore sizes in a wide range of materials, and the technique can be applied to oil and/or water wet materials, and also to materials that can not be dried out without losing their structure.
The Lab-Tools pore-size distribution measurement range extends from about 1nm up to over 2µm. Please contact us to discuss pore size measurements on your samples. Prices are competitive, but depend on the pore-size range to be covered, and precision needed.
We frequently find these techniques may be preferable to more established methods such as BET gas adsorption or DSC thermal porisimetry.

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 2.

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.

Figure 3: 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).

Cryoporometry pages

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 premises just ouside Canterbury, at Hersden. 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 Shell, Unilever, Coates Lorilleux, Lafarge Braas and Schlumberger. Universities that we have worked with include Kent, Heriot-Watt, Leeds, Leicester and Imperial College.

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.