My query is, from XRD we get crystallite size in the order of nanometer as I have synthesized my Hydroxy-apatite from co-precipitation route from the Scherrer's formula. I did SEM analysis of a pellet, which was sintered at 1100 degrees for 24 hours, although poor quality coated with carbon, but tend to find individual particle size using ImageJ software, there i find the size to be of the range of micrometer order(roughly about 0.76 micrometer). The thing is as it is a pellet, according to the image (which I have attached) I did not see any grain boundary regions rather than individual particles which are visible. Thus the large size is because of the pellet made and SEM of powder is not done or something else? So what should one do in this case. Also in many papers, people do SEM of powder sample and they report it as grain size rather than particle size. So what information do one get, the grain size or the particle size from it.
Chaitanya Kumar
Thank you for you valuable response. The difference you said between the two which arouse me a question. But the issue is if you see the image I attached, do you see any grain boundary, as I see individual particles as a result, so what are those are they grain or particles as I have an image at low magnification and I don't see any grain boundaries which I have attached now. that is why I am confused, what I am visualizing.
Dear Anshul Sharma ,
you are right; you see an agglomeration of particles; but your image (196_170.tif) is too blurred be able to see any grain boundaries at the particle surfaces...
The magnification of the other images is too poor to see grain boundaries.
With respect to the relation of crystallite, grain and particle please search for that at e.g. Google, on Researchgate here and on Youtube.
But, I think, you know the differences...
See for example:
https://www.youtube.com/watch?v=hjUp2pkONRM
https://www.researchgate.net/post/is_there_a_difference_between_crystallite_size_and_particle_size
https://www.researchgate.net/post/What_is_the_difference_between_crystallite_size_grain_size_and_particle_size
Best regards
G.M.
Thank you so much Gerhard Martens for your valuable response. Dear sir, What should I conclude at last then? Because I am unclear of what to conclude, whether they are grains or particle. Due to image being blurred out due to carbon coating and less magnification, we do not see grain boundaries or they are particle itself. As the pellet for sintered at 1100 degree for 12 hours, and I pretty much expected to see proper grains boundaries and grain regions but according to this results I am pretty much confused sir?
Dear Anshul Sharma ,
from that data we cannot conclude whether the structures in your SEM image are a) particles containing one grain or b) are particles containing more than one grain...
Is there anyone or any circumstance which forces you to make such a conclusion/decision?
Melting point of hydroxyapatite is around 1100C; so the particle's smooth surfaces may arise from your sinter process.
You may mill your sample (or part of it) and damage your particles in order to break their the smooth surfaces and perform SEM again...
Anshul Sharma,
Particles and grains are often misinterpreted in papers, but the difference is not so small. As I understand, here you have powders synthesized by coprecipitation which are pressed in pellet and watched under SEM. There were no any processes needed for the formation of grains. During precipitation you obtained nuclei which grew into crystallites and particles. Those particles are usually composed of several crystallites - primary particles, and more primary paricles are often agglomerated into larger particles.
To obtain grains, you need to conduct thermal treatment after pressing the particles. Solid-state reaction occurs, paricles in contact interact, grow or dissapear and the grains and grain boundaries are formed. This is the process of sintering, during which the powder consisted of particles is becoming ceramics consisted of grains.
Images confirm these are separate particles, joined together only by pressure and not intimately.
You could try TEM plus find a suitable solution to disperse your sample to overcome the agglomeration of your particles.
Nikola Ilić , Thanks sir for your valuable response. I forgot to mentioned and thus have edited my question again. The pellet I made was sintered for 24 hours at 1100 degree from the calcined powder. Can you sir share your thoughts and comment now sir? Do we should not see grains and grain boundaries.
You bring up an important point regarding the characterization of particles. Bulk particle observations often reveal agglomerated structures rather than the true particle size. This can lead to inaccuracies in understanding the particle size distribution and surface area.
X-ray Diffraction (XRD)peak-based calculations provide a more accurate determination of particle size. By analyzing the broadening of diffraction peaks, one can use the Scherrer equation to estimate the crystallite size. This method is particularly useful for nanomaterials, where the particle size significantly impacts their properties and applications.
This equation allows us to obtain a more accurate measure of the particle size by considering the intrinsic broadening of the diffraction peaks due to the finite size of the crystallites.
Dear Anshul Sharma, that is different, but images still show the sintering wasn't conduct well. To confirm if anything happened, it would be useful to measure the density of pellet before and after sintering. And compare it to theoretical density of hydroxyapatite. It is fine that pressed pellet is around 40-70 % dense, but for good sintering it is needed that the density is at least 90 % and, preferrably, more than 95 %. I looked briefly through literature, and it seems that at least 1200 °C is needed for good syntering of hydroxyapatite. Even you used really long time, it probably wasn't enough. I suggest that you measure the densities and also try to sinter at higher temperatures if you want to obtain clearly formed grains.
In your current case, sample was sintered but, in my oppinion, microstructure still couldn't be interpreted by grains since the reaction in solid state didn't go to the end.
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