For different samples, i got decrease of particle size with annealing. Can anyone explain me about this?
Hi Fouzia,
What kind of material do you calcine and under what conditions?
Fouzia Khan
More information needed as your description does not hold with Herring's Law:
- Material and annealing conditions
- Measurement techniques and actual results
At the moment you have a story with no plot. When you provide a statement of something that is highly unusual and highly unlikely then much more evidence is required in comparison to the situation where a result is in line with literature and expectation.
Vadim Verlotski . This is cobalt ferrite, since it is magnetic, I have heated it in induction heating at 160 deg C in air for 1 hr at constant temperature.
Alan F Rawle
I calculated size of Cobalt ferrite nano-powder with X-ray diffraction peaks using Scherrer's formula. Inductively heated at 150deg.C for 1hour in air.
At such low temperatures of calcination it is only a question of drying. Indeed, on drying the agglomerated particles may become smaller, because water is removed and the agglomerates partially disintegrate.
Fouzia Khan
XRD/Scherrer doesn't measure particle size - it measures crystallite size. Again more information - what peak(s) are you using to quantify the peak broadening? How are you accounting for instrumental and strain broadening which are other contributors to peak broadening in XRD? How do you know your XRD equipment is correctly aligned? What standard(s) have you ran to confirm instrument performance?
In a powder there cannot be free independent discrete particles < 100 nm in size, so 'nanopowder' is an oxymoron. Do you have SSA results for your preparations? This would be the most important set of experimental results. You still have not provided a single result of the extent of 'decrease in size'. Is this a time or temperature related event? Do you have a plot of 'Parameter X' versus 'Parameter Y' that provides clarity to your comments?
Fouzia Khan
I suspect an artifact. You’ve increased the line broadening by increasing the strain in the system or an instrumental/sample issue (too high sample). This increased broadening is ‘seen’ by Scherrer (incorrectly) as a decrease in size. Use a Williamson-Hall or Rietveld approach and quantify the instrumental broadening by an appropriate standard material e.g. the LaB6 from NIST.
Alan F Rawle
Sir, nowadays XRD instruments have softwares that give crystallite size based on Wiliamson-Hall method. May be the crystallite size she is talking about has been already calculated by the software.
2. Sir, since she has used temperature (150 oC) that is normally used for drying of nanopowders, isn't it possible that she has actually achieved removal of water from the samples resulting in an increase in the size. In short, deagglomeration has occurred at this temperature.
Fouzia Khan
I also observed in particle size during drying at 80 oC.
Article Effect of Thermal Treatment on the Phase Composition and Sur...
Aarif Hussain Shah
I agree with you about Willamson-Hall and modern software. Unfortunately W-H is not mentioned by the poster in any post. She states only the Scherrer equation.
As you know, crystallite size and particle size are not the same. For example:
https://www.researchgate.net/post/What_is_the_difference_between_crystallite_size_grain_size_and_particle_size
Yes, drying the sample could increase the particle size through agglomeration but this is not measured by line broadening (crystallite size) which runs out of steam around 100 nm or so (but can be extended in certain circumstances). Increased (crystallite) size results in reduced line broadening and this is the total opposite of the effect described (reduced size of whatever type).
You need to try and address changes in crystallite size, strain, and instrumental broadening by the temperature elevation. Cold aggregation (not agglomeration) occurs at room temperature for powders where the primary size is starting at < 100 nm. 'Nano powders' is an oxymoron as you'll know from reading many of my posts on this matter - there are no free, independent, discrete particles < 100 nm in a powder. And line broadening will not be seen by the particles in a powder with particle size > 1 micron (crystallite size will be seen if < 100 nm or so).
Again I state, we have not seen a single result of the magnitude of the 'changes' or the prime data in the form of a plot showing the effect.
If the TiO2 NPs are prepared by chemical process (e.g., sol-gel), its quite normal that the size (particle size) decreases with annealing (in air or in inert atmosphere). Higher is the temperature (or annealing time) higher is the change in particle size, but until a limit.
The main reason for size decrease is the particles become more compact (i.e., the porosity of the particles decreases on annealing). I would suggest to have a look here: Article Size-Controlled Synthesis of Spherical TiO2 Nanoparticles: M...
Umapada Pal
I agree with you but please explain how the crystallite size is reduced because this is what the poster is apparently measuring.
If the average grain size (not the particle size) decrease on annealing, the XRD peaks should broaden, which is very much unexpected. While estimating the av. grain size using Scherrar relation, frequently people do not properly subtract the background of the XRD spectra, and hence error in the value of av. grain size is introduced. I would suggest Fouzia to reestimate the Av. grain size of her sample with proper background correction of the XRD spectra and inform how the values she get.
I think annealing/ heat treatment causes to a reduction in the crystallite size.
Sikander Hayat
What evidence do you have for your statement? I’m sure that the poster of this question (and I) would be interested in any references/literature that you can cite.
@fouzia khan Grain size reduction on nanostructured TiO2 thin films due to annealing.
You can refer this article https://pubs.rsc.org/en/content/articlehtml/2017/ra/c7ra00706j
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