Dear Paul,
thank you for starting this valuable thread.
Just my comments to what was already said.
We also face this issue in our lab quite often. The principal problem is the open interconnected porosity typical for many TS coatings.
My additional hints would be:
- first of all, use highly penetrating low viscosity resin. You may need to sacrify speed of the curing process and hardness of the epoxy.
- clean and dry your samples thoroughly before embedding. In the voids, you may have leftovers of cutting liquid which often contains lots of "bad stuff". I would recommend rinsing in acetone or isopropanol and drying of sample for couple of minutes under hot air.
- from the photo you seem to have a serious problem with resin adhesion to the sample. You should use resin with minimal/zero shrinkage, especially if you have a smooth coating surface. BTW, I have seen samples where wrongly chosen epoxy delaminated the whole coating (even after several weeks! - bad for samples archivation) although the coating was otherwise OK.
- in our lab, we use EPOFIX resin from Struers combined with vacuum embedding with satisfactory results.
- minimize polishing times to suppress polishing fluid/lubricant penetration. Also, do not leave samples on the polishing cloths longer than necessary.
- you may try playing with lubricant if applicable as some are "more messy", especially if you see that the "sweat" is "oily".
- I also use the trick with immersion of samples in ethanol or isopropanol.
- I sometimes put the "polished but still sweating" sample in vacuum, so that the "sweat" is driven out (actually, like in SEM), and then use ethanol immersion/cleaning. I had samples where it needed to be repeated, but in the end, result was OK.
- you may also use my favourite TS metallography trick. After the final polishing step, rinse your sample under running water, then put a small drop of dish detergent on the polished surface (we use JAR, which also smells nice :) and rub the it with clean latex glove under running water. This is especially useful for getting rid of OP-S residues and removing stains, but may also help in your case.
- PS: Be very careful with ultrasound, especially with ceramic samples. If you really need to use it, I would recommend to use low intensity of sonication if your ultrasound bath allows it to be set.
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Radek Musalek
Institute of Plasma Physics CAS, Prague, Czechia
Prague
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Original Message:
Sent: 08-25-2022 05:27
From: Paul JUnge
Subject: Liquid leakage from pores during SEM examination
Dear Thermal Spray Community,
currently I`m facing a problem regarding the optical characterization of Al2O3 coatings. During SEM analysis, a liquid is visible on the specimen surface. It comes out of the pores. Probably the liquid is pulled out of the pores by the vacuum in the SEM. I have already tried to fix the problem by placing the samples in the vacuum oven at 80°C for 3 hours. With no success.
The sample was only in contact with ethanol and a water-based suspension while grinding and polishing the sample.
Has anyone had a similar problem in the past and was able to find a solution to it?
Thank you in advance!
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Paul Junge
Research Assistant
Department Coating Technology
Institute for Machine Tools and Factory Management IWF
Berlin University of Technology
✉ Email: paul.junge@tu-berlin.de
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