Does Archemedes's method give accurate results? Can you suggest any other method?
It can be precise if you precise equipments and avoid errors: use the most precise scale and avoid gas buble trapping for apparent porosity, eg by addind the solid in an certain amount of liquid and stirr/agitate the suspension before to complete the volume. Bulk density can be performed in several ways: adding carefully the particles in an flask or after tapping to increase the mass by compaction.
Dear Awani,
Mercury Intrusion Porosimetry (MIP) is a widely used technique for mesuring the porosity, total pore volume, total pore surface area, pore size distribution etc. covering a wide range of materials including catalysts, resrvoir rocks, ceramics, graphites and many other porous materials.
If you wanna get bulk density---the Archemedes's method is reliable, it would be needed to obtain true density by employing He-pycnometer. You can then get all bulk density, true density, opened porosity and closed porosity.
If you have a sample with a very uneaven shape, better using powder pycnometry, see :
http://www.micromeritics.com/pressroom/press-release-list/geopyc-1360-press-release.aspx
Then, through helium pycnometry, we will get the skeletal density, see :
http://www.micromeritics.com/product-showcase/accupyc-ii-1340.aspx
Finally, the porosity is 1 - bulk density/skeletal density.
I have both devices, and it works quite well.
Alain
I did the experiment Using Archemedes' method but the soaked weight and dry weight difference is about .017 gram for 6 gm cuboidal specimen. and porsity measurement is about 0.1% for graphite material. So i think there is a problem in socking of specimen. So plz suggest me to how to soaked the specimen properly?
Dear Awani, there is a measurement equipment called densitec by Exelia, Switzerland. This method allows the bulk density measurement of soaking samples properly. We have very positive experiences.
by flotation in a mixture of bad solvents. Porosity can be determined by BET.
As has been mentioned by prof. Mesa, I also think the BET method can be used to measure the por size (average), pore volumen and % porosity of graphite through their N2 adsorption-desorption curves.
Mercury Intrusion Porosimetry (MIP) will be a possible technique to characterise porosity, pore size distribution, pore surface area, total pore surface areas the porosity. Hope this will help.
Alternatively you may look into helium pycnometry. For a sample of given outer geometry (e.g. cylinder with precisely measured diameter and height) you can measure the apparent density (weight/volume) and the density of the solid forming the porous sample. One minus the ratio of the two gives you the pore volume fraction. The advantage of this method is that it is not limitted by capilary forces. Problems of adsorption/film condensation in very fine pores are minimalized by using He gas.
On the downside, you will not get pore size distribution. Hope that helps.
Mercury porosimetry is a best to measure the apparent porosity.
Use glass and balance to measure the bulk density.
Porosity can also be measured with micro-CT. However, this is no cheap method of measurement.
You may also try image analysis. For this you need to impregnate your sample with (metallography) resin and polish it. using image analysis method, you can obtain the apparent volume of your sample (including the pores) and subsequently the apparent density. The difference between the apparent density and real density is the apparent porosity in the sample (porosity=1-AD/RD).
Maybe try sedimentation. You should create the gradient of density, put it to the centrifuge and see, where your graphite stops.
1. determine the true density of your sample by helium pycnometry;
2. paint the graphite sample with a varnish of known density (in order to avoid that water enters into the structure) and determine the bulk density of your samples using the Archimedes's method;
3. determine the total porosity according to the equation: P = 1- bulk density/true density
Regards,
Fernando Costa Oliveira
A think that the notion of "apparent porosity" does not exist. while, "closed porosity" and "total porosity" or "open porosity" is used instead.
if you talk about the open or accessible porosity , you can determine it using the vacuum saturation method.
For the bulk density determination, the method proposed by our collegue Fernando Oliveira is the most common used method " paint the graphite sample with a varnish of known density (in order to avoid that water enters into the structure) and determine the bulk density of your samples using the Archimedes's method"
The Archimedes' method is the most practical method when an irregular shape, porous body is in concern. Try and contact a ferrites manufacturer if there is one reachable around, as they use mercury for this measurement, and they may come cheapest of all... Image analysis is also a solution if the distribution of the pores is uniform, and a random cut through the body of the sample can be taken as representative.
For answers to another graphite density related question posed at this forum ─ «How do we find the bulk density and particle density of exfoliated graphite flaks in Lab?», see: https://www.researchgate.net/post/How_do_we_find_the_bulk_density_and_particle_density_of_exfoliated_graphite_flaks_in_Lab
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