crystalline size is smaller than grain or particle size. inside a grain or particle we have many crystals of identical orientation. in case of crystalline size we were able specify a boundary (ie) grain boundary. but in case of grain or particle size where is the boundary? up to where the measurement will be?
I have recently joined this forum and found your post. I hope you must have found a satisfactory answer to your question. However, I would add something further on this subject. The term crystallite have been usually used by physicists and chemists, while grain size is mostly used by metallurgists. To understand the the difference in terminology, you have to look at the hierarchy of micro-structure in the materials. Crystallites are the "coherently diffracting domains" of crystals and grains may contain several of these domains. For example, a single crystal can be termed as a single crystallite. Now if you deform this single crystal, several sub-grains having different orientation are formed. Now each and every subgrain will be considered a crystallite. On the severe plastic deformations, more and more finer subgrains will be formed, and each subgrain will be a crystallite. The same thing happens when you mechanically mill a powder or carry out severe plastic deformation of a metallic specimen. Now, if a grain is a coherently diffracting domain, it can be termed as crystallite. On the other hand, if a grain contains several subgrains, then each subgrain is a crystallite. To understand the effect of hierarchy of microstructure on the results obtained by various characterization methods, XRD, TEM, AFM; you can go through our recent publication in Journal of materials science:
S.K. Vajpai, R.K. Dube and M. Sharma; Studies on the mechanism of the structural evolution in Cu-Al-Ni elemental powder mixture during high energy ball milling; J. Materials Science, Vol. 44, 2009, pp. 4334-4341.
It was very informative about mechanical alloying from your paper. I have a doubt that, from XRD the size which we determine is average crystallite size or average grain size?. Can you please explain me about "coherently diffracting domains" ?
Also how is it different from crystallite size?
Thanks & regards,
Dear surendra....what we measure from XRD is the average crystallite size and not the grain size ...of course when I say grain size..it means i am talking about the conventional notion of grains..separated by high angle grain boundaries. ..as far as your second question is concerned...I mentioned in my last post that coherently diffracting domains are called crystallites...e.g. a single crystal is a crystallite... ..Hopefully..it answers your question..
can you tell me how can I measure the particle size of powder sample...If I have a SEM image of the powder from that what I will measure??is that particle size or grain size??? plz help me
Particle size of the powder can be measured by SEM, but it is very loclized. So you cant conclude onky from SEM. It is better to do laser particle analyser. this gives you the particle size distribution. however the size you get from SEM is particle size.
And Particle size and grain size are not same. one particle can have several grains. unless you produce a particle which is single crystal.