No, it does not have linear relationships with sintering time.

Dear Op Thakur thank you very much for your reply, it is known that with sintering time increases the grain size also increases,I too don't know for sure but i have read it in many literature s.I would like to know if there are any cases the grain size reduces as we increase the sintering time.

As,far,as I know it increases with incressing T and holding time in sintered ceramic powders. But if liquids form at interfaces they may interact with grains and as a result new liquid phases may developp at the expense of grains. Nevertheless it never happened to me as you do not want normally liquid phases to develop.

Sintering temperature has higer effect than time on grain grwoth. , special it will be effective in liquis phase sintering. There are doping materials that eliminate grain growth that will help you to eliminate grain groth in long sintering time

Correct. I agtee.

Dear Karthik.....What system are you dealing with? Consider formation of liquid phase sintering if the system is vulnerable to. Micro structural analysis and chemistry would show if there is any evidence of liquid phase formation, which is probably at the grain boundaries. You may also try thermal analysis to show any phase transformation during sintering. Also, you may have grain refinement elements that act as grain nucleation sites.

Dear karthik,

What material you are preparing. May I know the preparation method. So many parameters affect the grain size and other spectroscopic and physical properties of the material.

Dear Sir Venkata Ramana Mudinepalli

I am preparing BaTiO3 based ceramics via solid state reaction method.

I encountered decrease in grain size after certain sitering time @ 1200 C.Wlhat could be the reason behind it sir, could you help me with this?

With Regards

karthik

What is the starting and end product grain size after sintering. How much time are you sintering?

Could you please let me know the particle size of calcined powder before making pellet for sintering? Could you please let me know the density of sintered pellet when you sintered at 1200.C. I think this temperature is at lower side for BaTiO3 sintering. When you put little drop of water on to it , should not get absorbed very quickly.

You mean first you cold pressed the powder and then sintered it at 1200 C?

Are you comparing the size of powder and ceramic or the ceramics sintered at different temperatures?

Sintering phenomenon is consisted of initial diffusion regarding the powder particles and second part the grain growth. Recrystalisation process is often omitted. It is representing process similar to crystallization, namely, consisted of nucleation and grain growth. The new grains are formed, after the critical diameter and stability of nucleus is reached, what than leads to transition from nucleus to stabile embryo. This happens during the maximal rate of sintering. Growth of the new grains from the embryo is fast and happens on the expense of the deformed powder particles residuals. It is leading afterwards, finally, to a process of the new grains impingement. It is often quoted as a densification an grain growth, and then finely it subsequently leads to a grain growth. So grain growth represents grain boundary movement and is observable as a grains enlargement. It can be stopped intentionally by pinning grain boundary movement - on closed porosity, or at formed piles of dislocations, or on dopant that are positioned inside the grain boundary, (complexion), or with the two step sintering schedule. Also, besides the diffusion, enlargement of the grains can be guided by the Ostwald ripening. i.e. incorporation of the smaller grains by bigger one. Dimensionally, besides specimens microstructure observation, grain growth process is represented by the tail of the sintering curve (represented as the specimens dimensional changes in time during temperature schedule) approaching slowly, asymptotically, in time, the final dimensions of the sintered specimen. Mostly it is happening during isothermal period of holding at the constant temperature.

Now, the grains can diminish in the special conditions, when sintering of the powders with nano particles dimensions is performed, where high sintering rates are achievable. Or when the sintering is performed with different stress inducements evoking different strain responding mechanisms. Mechanisms are - super plasticity, forming of the new grain boundaries inside the existing grains, as well as grain rotations. Also, grains can diminish if there is a reaction during sintering, or a phase transition. But besides all, generally, observing one specimen, grain growth process can be regarded as irreversible. Once formed grains are stabile and they can not diminish by dissolving in a grain boundary.

In your system 1200oC is temperature relatively low for sintering of BaTiO3 and formed grains are small. They are formed since nucleation happened on the numerous defects simultaneously. Look at the reference attached. At the 1380oC the BaTiO3 diffusion enhances and grains are bigger (but the high precautions should be implied since it diffusionaly interchange with alumina substrate and unfortunately for the equipment made of this material, it fuses). But the grain structure is obviously achieving larger grains structure. Holding isothermally does lead to a grain growth, but I agree that temperature must be higher. Also if you have doped the BaTiO3, what is interesting for thermal sintering phenomenon, you should micorstructuraly follow the segregation of the dopant during isothermal holding, what can lead to a smaller grain size comparing relatively (different specimens).