Dear Zhe Zhao!

Thank you for your elucidation. May I ask you some more questions? If I have a porous ceramic sample (relative density is around 50%), which method (BET or Mercury porosimetry) is better for porosity measurement? In the case of dense ceramic, what is your recommendation to measure the porosity?

Best regards

Dear Son Nguyen,

Because the mercury porosimetry technique considers the diameter of small holes to the ink-bottle pore, the obtained pore size distribution should not precisely represent the real pore size of porous material. Then, it is recommended to check the pore size by Scanning Eletronic Microscopy (SEM). Hope this helps your work.

Dear Son Nguyen,

From my personnal experience on numerous soil materials with very different porosities in term of "prore size" and proportion of the material (see my papers available on researchgate), I used both porosimetry techniques (combining Hg-porosimetry and isotherms desorption curves) and scanning electron microscopy techniques (mostly backsactered electron scanning images, BESI). It is indeed often necessary to have direct information on the pore size and morphology in scanning electron microscopy and information on the size of the pores (neck) to which these pores are accessible. Today, many reserachers are also using X-ray microtomography to get 3D information on the pore network geometry.

Regards

Ary

Thank you very much Salvini and Bruand, I will check the pore size with SEM.

To Salvini: I hope you still remember me, we talked at MS&T13 in Montreal, last month :)

To Brauand: I tried to analyse my sample with 3D X-ray CT before, but because of the limited resolution of the device, I couldn't observe the pore smaller than 1um. In this case, would you have some advices for me?

Best regards

The best resolution available on X-ray synchrotron microtomography would be around 0.25 µm. You may ask more information to Olivier Rozenbaum who is familiar with this type of technique. He is on ResarchGate.

Best regards

Ary

In the case of dense ceramics, I would use neither BET nor Hg porosimetry, as connectivity is required for both. Now, in a dense ceramic, closed porosity is highly probable, therefore both methods are useless. If not already known from the composition (e.g. silica, alumina, etc.) I would measure the true density by helium pycnometry after a thorough grinding of the material. Then, I would compare with the bulk density, i.e. the apparent density of your ceramic, measured on a big sample. The difference is due to the porosity. Because the characteristic pore size of your ceramic, is low, pore size and distribution can be obtained from SAXS. But you need a specialist to analyse the corresponding spectra.

Alain

Thank you very much for your answers!

Mercury porosimetry measures a pore diameter of 3 nm to 14 µm, nitrogen adsorption (BET) has a much lower range of 0.3 to 300 nm. This rather useful thesis highlights differences in more detail: http://ethesis.helsinki.fi/julkaisut/mat/farma/vk/westermarck/useofmer.pdf

Thank you very much D

All of those are quite useful comments.

I would add that a 50% dense sample(as mentioned in one of your later comments) will definitely have a connected pore-network and as such you could use either one of those techniques. I also assume that you don't work with truly nano sized powders and as such the pore size may be rather large for nitrogen adsorption. Based on that assumption, I would recommend using mercury porosimetry.

Depending on the instrument  you will be able to measure pore sizes between 0.3 mm and 3 nm. You will also get density information and can compare that value with the helium density data.

Does anyone have any suggestion on analyzing samples with  "big" pores like 70 micron or more along with some small ones like 10/20 micron? Thanks in advance 

Mercury porosimetry would be my preferred technique. It will measure pores smaller than 300 micrometer. However, the pores have to be connected to the outside (network)

Alternatively one could prepare cross sections of the sample and use microscopy to view the pores.

Thank you very much for these useful comments. I found this question very interesting as i am studying green ceramics. 

What about Helium porosimetry? As far, people only recommend intrusion method. What is the drawback of using helium porosimetry?

To Bo Jiang: You probably mean "helium pycnometry", not porosimetry. The technique will give you the skeletal density of your material, ds, provided that the porosity is open . Knowing the bulk density of the porous solid, db, you'll have a direct access to the overall porosity = 1 - db/ds. This is a very important information indeed, but you'll never hace access to the pore size distribution by this way. Therefore, for me, it is not porosimetry but only pycnometry.

Alain