Both higher temperature and longer duration of annealing can lead to further growth of crystallites which ultimately causes enlargement of particles. Therefore, in order to obtain a finer size distribution, it is more recommended to anneal at the lowest possible temperature for the shortest possible time length.

The above statement is not true when you have several phase transformation in annealing, in that case, it is more complicated to analyze.

Hi,

nano particles formed by nucleation and growth mechanism. You can change the molar ratio of the reactant in such a way that nucleation is more pronounced than growth.  

Dear Krish Na

Hello

With lower temprature in the nanoparticles synthesis you can achived this pourpos.

Dear Dr. Na:

As a whole, in the chemical synthesis process directed to synthesis of sub-micrometric and nanometric particles, in which pirolysis and exothermics events are present, the optmization of the fraction of compounds that provide any kind of further supporting to the previous mentioned phenomena (pyrolysis and/or exothermic phenomenon)  is necessary.

Kind regards

Marcos Nobre

Yes, anneling temperature will be change the size of nanoparticles. The rate of changing will be depend from temperature. Mainly in result of coalessence particle size will be increased. But on Spesial situation size of particle may be decreased. This depended from nature of materials....

Dear Dr. Na:

In a broad sense, post-synthesis thermal-treatment of nanoparticles gives some kind of deleterious effect in the nanopowder morphology. In this sense, annealing process with or without selection and control of atmosphere. Despite, as mentioned in previous answer great part or almost problems of nanopowder are ascribed to synthesis step. This occurs as a function of nanoparticle nature in which nanoparticle surface have a high chemical potential, with high reactivity, In fact, the surface nature provides further condictions to the mass rearrangment and its transport. Please, consider the possibility of read the paper in attach. In this paper it is possible identify effects stemming several temperatures selected under nano/sub-micrometric particles. With relation to mechanisms of nanoparticle growth, also is possible find further information in another paper authored by me:

Particle Growth during Calcination of Polycation Oxides Synthesized by the Polymeric Precursors Method. Journal of the American Ceramic Society, v. 80, n.10, p. 2649-2657, 1997.

Kind regards

You can try milling the nanoparticles to reduce the size. Or else you can choose an entirely different chemical route leading to smaller nanoparticle.

There is no way to reduce the particle size by annealing the particles.

I recommend a recently published related review article shown below for your reference.

Synthesis and stabilization of metal nanocatalysts for reduction reactions–a review. J. Mater. Chem. A, 2015,3, 11157-11182

DOI: 10.1039/C5TA00753D

How can I de/agglomerate the nanoparticles?. Available from: https://www.researchgate.net/post/How_can_I_de_agglomerate_the_nanoparticles [accessed Jun 10, 2015].

I have little experience about high temperature and long duration, as 1000 Celsius degree and longer than 24 hours. But, if your precursors for annealling can be made into small size, the products after annealling tend to be in small size.

Hi,

You not try to prepare nano particles by using microwave irradiation technique. This method produce uniform size particles also it is possible to reduce particle size when the samples irradiated by microwave for longer time 

microwave heating can reduce the size of particle

Particle size will reduce under ultrasonication (Probe). Soft agglomerate must be the product in solid state, so that further dispersion is facilitated.