Dear David

I suggest that you break your sample into smaller pieces or slice them if it is possible. You won't be able to see the distribution or structure of a heterogeneous sample if you pulverize it. 

The decision mostly depends of the nature of your materials, but I don't see how pulverizing it will be advantageous. 

Dear Fernando,

  Thank you very much!

Regards

Dear David, samples can be used as films (slices) or powder in SEM, all depends on the nature of your samples. You also need to make sure that samples sometimes needed to be coated by carbon or gold to obtain good SEM images.

Thank you Dr Amer!

Since the intent is to study the products of cement hydration, what you need for the SEM is a polished thin section. The slices should serve the purpose. 8 mm thickness however seems too much. I suggest you make the slices smaller for it to fit well in the SEM machine. Pulverising the sample will obviate the structure of the hydrated mortar. The coating is to be carbon or gold depending on what is available in your Lab. You however need to pay attention to the process of polishing your specimen. It has to be a flat and well polished sample with constituents well exposed for x-ray to pick.

Dear David,

based on my research generally I recommend as little interference in the sample as possible - even its drying can significantly affect on its microstructure, particularly in the early stages of hydration. If you examine the sample in the early stage of hydration also remember to stop the reaction. For example, by immersing the samples in acetone.

The SEM image quality also depends on the microscope mode / operating parameters in which they work. It happened to me testing non-coated samples in the ESEM microscope (Environmental SEM) and obtain good images of hydration products. The reduction of sample volume also makes its easier analysis in the SEM, however you don't need its pulverized

What samples you testing, cement paste or mortar prisms?. In the cement pastes easier is observed mcrostructer/phase changes occurring during hydration. The introduction of aggregates has a significant impact on the microstructure - appears the transition zone between cement paste and aggregate; nucleation of hydration products on the aggregate.

Dear Przemysław,

  Thank you so much!. It is cement paste actually I am testing. I will like you to elaborate on the following

"even its drying can significantly affect on its microstructure": are you saying the sample  shouldn't be dried? because I thought a temperature between 60-65 degrees is fine after immersion in acetone

"The reduction of sample volume also makes its easier analysis in the SEM" would you please elaborate on this point"sample volume"

Regards

Dr Olawuyi,

  Thank you very much sir.  You mentioned polishing sir. Please would you elaborate on this sir

"even its drying can significantly affect on its microstructure"

When I conducted a testing various cemenet pastes, I observed in the some samples (during the first 4 hours of hydration ) greater microstructure changes - formation C-S-H phase and ettryngitu (relative to the sample dried at 60 ° C) - when I analyzes the samples dried up to 10 min in the standard state - 20 ° C(after mixing with acetone). Small amount the cement paste sticked to the carbon tape, and after drying blew out its excess.

During drying, the water phase C-S-H can also be removed, and thus can change the microstructure. If I remember correctly, in this articles you can read something about basic of this phenomenon::

-          Feldman R. F., 5th ICCC Tokyo, t. II, s. 58, Tokyo 1968.

-          Seligmann P., Greening N.R., “Phase Equilibria of cement-water”, 5th ICCC Tokyo, t. II, s. 179, Tokyo 1968.

-          http://www.sciencedirect.com/science/article/pii/000888468490084X

"The reduction of sample volume also makes its easier analysis in the SEM" would you please elaborate on this point"sample volume"

This is related to the microscope specification. By testing a larger sample is harder to get proper vacuum (For example due to the water contained in the sample - ESEM), so optimal conditions to conduct this analysis.

In response to your question on Polishing, my answer and explanation is as follows:

The polishing process as you requested requires making the surface smooth just as they do in Terrazzo flooring. However in this case you will use polishing papers otherwise referred to as "sand paper" on construction sites in Nigeria. You will require them of various level of roughness/fineness. The flat surface will be made to run on the polishing papers until the constituents of the mortar/concrete are well exposed. The final stage of polishing is then to put in little polishing fluid and make it run through the polishing paper placed on a polishing machine till it gives a shinning surface. The finished polished surface is expected to look similar to a polished Terrazzo floor. If you however have an Environmental SEM machine, polishing might not be required.

I do hope my response is very useful. I also sent you a personal message on this too.

On the drying question, a temperature of 40 - 45 oC  for 1 hr. should okay for drying to avert influence of the drying on material structure.

Dear Przemysław,

  Thank you so much for the insight. It is much appreciated

Dr Olawuyi,

  Thank you so much sir.I really appreciate. I got the personal message as well.

Use the ASTM standard for sample preparation for concrete.

solvent exchange method  for the hydration stoppage (use solvent - isopropanol )

  ASTM C1723 − 10 Standard Guide for Examination of Hardened Concrete Using Scanning Electron Microscopy

Dear Karnal,

  Thank you for your answer.It is indeed helpful

Regards,

David