Does anyone knows an apropriate etchant for preparing concrete samples for SEM analysis?
Dear William,
What kind of analysis do you want to do by SEM on concrete samples?
Personnaly, for Imaging or EDS chemical analysis on concrete or clinker samples, I work on well-polished sections with carbon coating (20-50 nm). That works very well.
Regards,
Dear Jean,
I would like to have a BSE image with a better contrast. Could you, or anybody, give me some tips to reach this goal?
Dear William,
In concrete, aggregate are usually easily identified without recourse to staining. Some carbonate aggregates do present problems because distinctions between limestones, dolomites and dolomitic limestones (especially if the rock is fine grained). Sulfate minerals are also sometimes difficult to identify. Development of alkali-silica gel is quite difficult to identify but readily absorbs the uranyl ion which give fluorescence in UV light.
As solutions to your problem, I suggest you the following etchants (which I use in optical microscopy):
1. Sulfates: 2:1 mixture of BaCl2:KMnO4 6% solution, wash with water and saturated oxalic acid
2. Carbonates: etch in 15% HCl. You may use alizarin red for ferroan calcite
3. Alkali-silica gel: immersion in 10% uranyl acetate 1.5% acetic acid solution
Regards,
Daniela Nastac
Dear Daniela,
Thank you so much for your kindness. I think your suggestions are very usefull in optic microscopy. I also concluded that a chemical etchant would not improve a chemical etchant would not be usefull in BSE images, possibly because the contrast depends on instrumental parameters. Do you or any one disagree?
Dear William,
I think you are right concerning usefullness of etching in SEM vs. optical microscopy. Under reflected light microscope, I used to observe rather clinker samples (Nital or borax etching). For concrete samples, I use SEM or petrographic microscope (ne need of etching in thin sections).
Your goal in BSE is to better distinguish the different kinds of hydrates? Which magnification level?
Exactly! I would like to better distinguish the different phases in hydrated cement or concrete with a magnification level of 500x to 800x.
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