I've polished my pellet using diamond paste after using SiC paper of grit size 2000. But I haven't obtained optical image with clear grain boundaries. What should I do after polishing to get a more clear and well established grain boundaries?
it depends on the exact ceramics being viewed but certainly in a surface that has mixed chemical composition between grains and bonding phases, HF etching preferentially dissolves some components, usually in the bonding phase, making the grain edges clear.
I agree with Dr. Trevor Wilson, but I want to add that surface should be polished with minimal possible roughness (almost like a mirror)
I agree with Dr. Trevor Wilson, HF is a good method to expose the ceramic grains. The % and timing of the etching process depend on the ceramic type. You should start in a moderate % and time and gradually increase till you have good images of the grains.
1, Finer polishing: It's possible that the diamond paste and SiC paper with a grit size of 2000 were not fine enough to fully remove surface imperfections and scratches. Consider using a finer polishing compound, such as diamond paste with a smaller particle size or colloidal silica, to further polish the surface. Gradually reduce the abrasive size to achieve a smoother and more polished surface.
2. Etching: Chemical etching can selectively remove material from the surface of the pellet, highlighting the grain boundaries and making them more visible. The choice of etchant depends on the material you are working with. Research suitable etchants for your specific material and follow the recommended etching procedure to reveal the grain boundaries. Etching time and temperature may need to be optimized to obtain the desired results.
3. Electropolishing: Electropolishing is an electrochemical process that can improve surface finish and reveal grain boundaries. It involves immersing the sample in an electrolyte solution and applying a controlled electrical current. This process can effectively remove surface irregularities and enhance the visibility of grain boundaries. However, electropolishing requires specialized equipment and expertise, so it may not be feasible for everyone.
4. Contrast enhancement techniques: Various staining or contrast enhancement techniques can be employed to improve the visibility of grain boundaries in optical images. For example, you can use specific dyes or chemical solutions that selectively react with grain boundaries or different grain orientations. This can help differentiate the grains and make the boundaries more apparent.
Preparing polished ceramic pellets for optical microscopy with clear grain boundaries often involves more than just a physical polishing process. Here are some steps you can consider:
Remember that the specifics of this process can depend on the ceramic material you are working with. Always follow safety guidelines when handling polishing equipment and chemical etchants. If the grain boundaries are still not clearly visible, you might need to adjust your etching process or consider using advanced imaging techniques like Scanning Electron Microscopy (SEM).
I would start with 50% of HE for 10min. and gradually add time if needed and if needed go up with the concentration. Please handle safely.
Soon after polishing your ceramics surface finely, clean them thoroughly in ultrasonic bath, and then re-anneal your ceramics close to your sintering temperature, and then look at them using SEM. Of course you need a thin gold coating in case they are insulating ceramics.
If I want to get an SEM image to study the grain size of my sample. Can I avoid thermal etching and polishing? I want to coat my sample after sintering with gold on both sides and then test it!!
The best method is to etch the sample!
If your sample has a good enough surface finish you can try using an aggressive ultrasonic cleaning that may clean better to expose the grain size.
The surface looks good, I am thinking to coat it with gold on one side for better image resolution
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