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 the porosity measurement is about 0.1% for graphite material. So I think there is a problem in soaking of specimen. So please suggest how to soak the specimen properly?
Depends on your sample... If bubbles are present after immersion, it may require sonication in order to remove them from the surface. You may also consider changing water to a different liquid if the bubbles cannot be removed.
Do you familiar with the method outlined by ASTM C373 standard?
Basically, a specimen should be boiled in water for 5 hours and only then the suspended in water mass is measured
another point from this standard - at least 50 gr specimens should be used.
I agree with Belenky and De Gaudenzi. A major point is that you obviously took the sample out of the water before weighing it to get such a small difference in weight. In Archimedes' method, the sample is weighed covered by the liquid, as described by Belenky. You cannot use this method since it measures the true volume of your wet material, which you know from your weight and the graphite density.
If you use a low surface tension liquid such as xylene, it can wet and penetrate better than water. If your material is a block rather than a thin slab, you will need to give the liquid time to penetrate and eject the gas. That is why Belenky boiled his samples for hours in water. Another method is to place the sample under the liquid inside a vacuum chamber and pull a vacuum strong enough to make the liquid boil. Repeat this several times with a half hour at atmospheric pressure between repeats. This should replace all the air with liquid. If the block is removed from the liquid, its surface dried and the sample reweighed, you have the weight gain. Reweighing after each vacuum treatment until the weight no longer changes will ensure that all the air has been ejected. Since you know the densities of pure graphite and xylene, the two weights should give you a measure of the porosity. You can also take precautions against liquid evaporation by weighing the sample inside a sealed plastic bag. I gather that this was your intended procedure.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science