Dear Experts,
I have tried to sinter Ni-GDC (Metallic Ni mixed with Gadolinium-Doped Ceria in different wt %) at 1300°C for 6 hrs. The volume of the sintered pellets were increased drastically (about 2 cm) with poor density. Can anyone explain about the sintering (thermal expansion) behavior of Ni-GDC?
Thanks for your answer Sir.
I have sintered under room atmosphere only. No external gas has been used. So as you said there can be possibility of oxidation (NiO formation). But this volume expansion has not been observed for Ni-YSZ composite under ideal conditions.
I am sure your Ni oxidized to NiO, that is evidenced also by the color of your sample (NiO is green in color). In order for Ni to remain metallic, you should use a protective (reducing) atmosphere, but for ceria based materials it might be problematic due to their reduction. Typically sintering these cermets is performed on mixed oxides (NiO+CGO) and then reduction at lower temperature (~working temperature). This is a somewhat standard operation procedure. Good luck and best regards!
Thanks Molin,
I do agree, but as you suggested when we do sintering the composite under reducing atmosphere, can CGO (ceramic component) also be reduced right. How the reduction would selectively take place on metallic part (NiO to Ni).
You cannot selectively reduce NiO. CGO will also get reduced, but not to pure metal at normal conditions, it will just loose some oxgen and become highly defected. Sintering of CGO in reducing atmospheres enhances sintering, however further reoxidation will lead to chemical stresses etc. As I have mentioned, I would suggest mixing of NiO+CGO, sintering and further reducing it. You can also of course oxidize Ni first and then mix it. Best regards!
Hi Ajith,
Have you try use argon or nitrogen as a shielding atmosphere when you sinter the sample
Hi Ng Kei Hoa,
I havent used any such gases. Sintered at ambient conditions.
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