I have performed TGA of a metal oxide and have found that it is almost constant up to 750 °C i.e there is no weight loss. Therefore, on what parameter or basis its thermal stability can be explained?
Hi Suvankar Deka
Generally the metal oxides are thermodynamically stable. The packing also give them stability and to check the thermal stability TGA is a good tool. TGA will also help you to detect the different mass loss at different temp. What kind of synthesis process you are using in the most important. If you are using solution-combustion method then you will get a black/brown mass (to be calcined to get final product and the calcination temp. idea could be gathered from the TGA profile of the black/brown mass, at what temp. the profile become parallel) where you get some water loss, various gases loss and after a temp. the TGA profile will be parallel to the Temp. axis. and if you are running the TGA of a calcined or metal-oxide directly it will show no water loss or any kind of loss profile if the material is not capable to adsorb water or any atmospheric gases (if exposed).
Regards
Dear all, it is related to the repartion of valences. Please check the following document, and go first to the second point in the conclusion part. My Regards
https://link.springer.com/article/10.1007/BF00775631
Hi ;
It is important to say that the covalent character increases from alkaline earth oxides to noble metal oxides. In general, the stabilities of the ionic oxides of the same column decrease with the increase of the size of the cation, thus going down in the classification. For oxides with little or no ionic activity, the evolution of stability is much more random. We can simply say that the elements possessing OA d of energy close to the OA of valence will have more stable oxides.
Finally, all the oxides of high oxidation degree, which practically all have a covalent structure, are more and more stable as one goes down a column. This is simply due to the increase in the ionic character of the bond.
With my best regards
Dear Suvankar Deka thank you for asking this interesting technical question. I fully agree with Arnab Mukherjee in that most metal oxides are just thermodynamically stable compounds. However, there are large differences in decomposition / melting points. For example, mercury oxide (HgO) decomposes around 500 °C into the elements. This process yould be observed in the TGA. On the other hand, titanium dioxide has a high melting point of 1,843 °C. The melting point of Al2O3 is even higher at 2,072 °C because is has a very high lattice energy (cf. https://en.wikipedia.org/wiki/Lattice_energy)
The decomposition / melting points of common metal oxides are all known and listed in tables. Thus you will not get much new information from a TGA of a metal oxide, unless it is a new compound.
Good luck with your work!
Dear all, usually a good approach via Ellingham diagram is followed to understand the order of stability of compounds including metal oxide. So simple search leads to how the diagram is constructed and used. My Regards
Dear Suvankar Deka,
The high thermal stability of metal oxide compounds could be explained based on the main two parameters, which are the non-hydrate crystal network structure and ionic bonds.
Best regards.
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