We have prepared a BaNd2ZnO5 by combustion synthesis method. After XRD analysis we have found that there is 55% content or phase of BaNd2ZnO5 and 45% content/phase of BaCO3. This means there is mixed phase formation. We are unable to find out the reason for the extra phase i.e. BaCO3. Can any suggest how we can get rid of this extra phase?
Thank you.
Hello Vijay,
this is certainly a very interesting technical question. It is not easy to provide you with a definite answer, because you did not specify the starting materials in your preparation of BaNd2ZnO5 by the combustion synthesis method. The key question here is where the carbon in the BaCO3 by-product comes from. One possibility is that you used a carbon-containing starting material such as a citrate salt of one of the three metals in your system. Quite often, the combustion synthesis method comprises the use of nitrate salts as metal precursors. In that case you don't have any carbon present in the initial reaction mixture. Then one could suspect that the carbon came from CO2 in the air. A third possibility is an impurity in one of the starting materials. For example, BaO can be already contained with BaCO3.
With best wishes, Frank Edelmann
Thank you so much, Prof. Edelmann, for your useful answer. Here, I would like to mention that we have used nitrate salt of all the precursors in a stoichiometric ratio and urea as a fuel. We have used Barium Nitrate Hexahydrate, Neodymium nitrate hexahydrate, and Zinc Nitrate. All the chemicals were purchased from Sigma-Aldrich.
Dear Vijay,
many thanks for your kind response and explanation. Then the possible answer to your question becomes more clear: Urea is the only carbon-containing compound in your reaction system. This makes it the likely cause of the formation of BaCO3 by-product. Unfortunately most (if not all) common fuels for combustion synthesis contain carbon (urea, glycine, hexamethylentetramine etc.). Thus you might want to look for alternatives. One hint can be found in the following article which is freely accessible as public full text on RG:
Fuel effect on solution combustion synthesis of Co(Cr,Al)2O4 pigments
Article Fuel effect on solution combustion synthesis of Co(Cr,Al) 2 ...
In the introduction the authors mention that "hydrazine and its derivatives" can also be used. This led me to the following research article, in which hydrazine is indeed used as non-carbon fuel in combustion synthesis in combination with metal nitrates:
New combustion synthesis technique for the production of (InxGa1−x)2O3 powders: Hydrazine/metal nitrate method
http://maeresearch.ucsd.edu/mckittrick/pubs/2001_JMR_p1059.pdf
(please see attached pdf file)
Please read especially the safety advices given in this paper. Hydrazine is highly toxic, and it can form explosive mixtures with air. Thus working with hydrazine requires particular precautions! Personally I would not want to work with mixtures of metal nitrates and hydrazine...😳
Good luck with your work!
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