Dear Dr. Lakshaman Kumar ,

you can try to use the two-step sintering (TSS).

TSS is one of the simple and cost‐effective methods to obtain near‐theoretical density materials with controlled grain growth without adding any dopants. Many recent works have reported the use of TSS as a processing method to fabricate nanoceramics for various applications.

For more details, please see the source:

-Two-Step Sintering of Ceramics

Ubenthiran Sutharsini, Murugathas Thanihaichelvan and Ramesh Singh

Intechopen Books - Sintering of Functional Materials (2018)

Available at: https://www.intechopen.com/books/sintering-of-functional-materials/two-step-sintering-of-ceramics

An on RG at: https://www.researchgate.net/publication/322998997_Two-Step_Sintering_of_Ceramics

About your specific material, you can have a look at the following papers:

-Sintering of Titania Nanoceramics: Densification and Grain Growth

M. Mazaheri, Z. Razavi Hesabi, A. M. Zahedi, S. K. Sadrnezhaad

Proceedings of the 2ndConference on Nanostructures (NS2008) March 11-14, 2008, Kish University, Kish Island, I.R. Iran

Available at: https://wiki.epfl.ch/mazaheri/documents/Publication/Conference/19.pdf

and a more complex method to produce TiO2 bulk ceramics with nano-sized grain were fabricated successfully by combination of spark plasma sintering (SPS) with the two step sintering method (TSS):

-Two-step sintering assisted consolidation of bulk titania nano-ceramics by spark plasma sintering

Bao-rang Li, Dong-yu Liu, Jing-jing Liu, Zhi-wei Yang

Ceramics International 38(5):3693-3699 (2012)

Available on RG at: https://www.researchgate.net/publication/271559921_Two-step_sintering_assisted_consolidation_of_bulk_titania_nano-ceramics_by_spark_plasma_sintering

Best regards, Pierluigi Traverso

Lakshaman Kumar,

To get enough strength (dense ceramics) by conventional pelletization followed by heating you need to consider a) the initial particle size of the powder, b) the sintering temperature, c) additive (either sintering aid or green binder) and d) pelletization technique.

If you have a larger particle size (in a few micron-scale, e.g., 50 microns), then your sintering temperature would be much higher. So, a) you need to grind the powder into finer (high specific surface area) to allow the diffusion process easier, b) you can increase the sintering temperature, c) I presume that you need a pure TiO2 without any secondary phases, so in that case, you can use a green organic binder (e.g., PVA solution) which eventually evaporate at mentioned temperature before helping in the densification process, and d) probably you did a cold uniaxial pressing, so you could further do a cold isostatic pressing for better green particle packing.

Now, these are mostly applicable to the conventional process which you choose. There are several other methods available in the literature as a few of them are mentioned by Pierluigi Traverso.

Best regards

MN

Pressure alone will not help you applied something like 5000 bar, 1000 bar (~1t/10mm diameter) should be enough. Too high pressure will lead to delamination. If it still does not work try to find a finer powder in the 500 nm range or mill your powder down to that size, then it should be no problem.

Dear Pierluigi Traverso Sir,

I thank you very much for your mail. I read these articles and your suggestions, hope it will be a great help.

Best regards

Lakshaman

Dear Mithun Nath Sir,

Thank you very much for your details Suggestions. By keeping these points in mind, I will design further experiments.

Best regards

Lakshaman

Dear Frank Kern Sir,

Thank you very much for your Suggestions. The size of this powder is less than 500nm even it showed the mentioned problem.

Best regards

Lakshaman

Dear Lakhasaman,

can you give some more details on the powders you used ?

If your powder is below 500 nm, is it a hard agglomerated nanopowder like P25 ?

Then the approach is completely different...

With the spark plasma sintering

I would recommend using a nanopowder. Make sure you sieve the powder!

Then use 150-200 MPa. Kindly play in this step before going to sintering: check the strength of the green pellet/cracking at the side. If you use the binder, then mix the binder and then sieve again!

I am pretty sure you will get a dense pellet.

Dear Lakshaman Kumar, Obtaining a strong monolithic block of TiO2 from particulate matter is a challenge. As is known from powder metallurgy, in order to achieve a high compaction density, a large force (pressure) and most often hydraulic presses are required. Another approach is to use dynamic pressing (percussion) from knee machines. However, small nano cavities always remain. For better bonding after pressing, powder ceramic firing is applied. This leads to an increase in the bond between the hotel molecules and an increase in strength. Baking temperatures depend on the type of powder pressed. This formation of TiO2 firing can be found in the scientific literature.

Interested to know for what application you are looking at using this?

Lakshaman

500nm TiO2 powder is fine. Mix the powder with 1.00% stearate acid powder and ball mill the mixture for 30 minutes. Press them at 50 to 70 Mpa and sinter them at 1400 C in argon or helium for 50 to 60 minutes and you would have dense compact with 90 to 93% density.

Read one of my paper " Sintering of Al203, published in 1964 in J of Nuclear Materials. Good luck.

Dr. K

Thanks Dr K, much appreciated.

Shahed

Dear Lakshaman Kumar ,

The easiest way to sinter high quality ceramics without external pressue, like in hot pressing, hot isostatic pressing, spark plasma etc. is to pressureless sinter nanoparticles which are trated carefully to avoid agglomeration. Sintering pressure is proportional to the reciprocal of grain/particle diameter. Hence the smaller the dimension the higher is the sintering pressure. 10 nm is hard to get but easy to sinter, see recent paper of Yavo et al. on sintering of various cerium oxide compounds, https://doi.org/10.1111/jace.15743.

Good luck, Ori

You may try to use this as a lower sintering temperature

Article Lowering the Sintering Temperature of Solid Oxide Fuel Cell ...