The Combustion Method for the preparation of the Hexa-ferrite

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 The Combustion Method


Why do we select the combustion method for the preparation of Hexa-ferrite?

              The advantage of the combustion method for the preparation of the hexaferrite is that we get the precursor material in a quick and easy manner, without any special setup or complicated chemical reaction, in contrast with some of the other methods used for the preparation of hexaferrite.  


Combustion Method:-


The mixture containing the solution of salts, ammonia, and citric acid at pH 7 was evaporated to dryness on a hot plate, at which point a self-propagating decomposition occurred. A violent exothermic reaction ignited and a foamy mass swelled up that propagated through the entire sample within a few seconds after which CO2 evolved and citric acid got polymerized and the cations got converted completely to alpha-Fe2O3 and BaCO3. The violent exothermic reaction that occurred first is the combustion of the NH4NO3 formed in the neutralization of the solution, and it produced a reaction temperature of 227*C. The maintenance of the homogeneity of the gas was ensured by the speed of the reaction and the evolution of gas produced a very porous foam structure that yielded a loose agglomeration (a mass or collection of things) when powdered. After heating the sample at 700*C the sample was mostly BaM with some a-Fe2O3 present in it, and it had formed pure BaM at 1000 C, but the problem is that the sample preparation has poor magnetic properties may be because of the small grain size resulting in poor magnetic ordering. The process of citrate-combustion can proceed either via direct combustion of an aqueous gel containing sufficient levels of oxidizer (Aqueous Combustion Synthesis, ACS) or the ignition of a dried citrate gel powder (Low-temperature Combustion Synthesis, LCS). Citrate: metal ions ratio was required to be around 0.68 to enable the wet gel to ignite at 200*C for the Aqueous Combustion Synthesis method, the gel ratio 1:1 required to dried for 18 hours at 120*C for the combustion to occur in the Low-temperature Combustion Synthesis method. The reason behind it is that because higher levels of citric acid absorbed more water via hydrogen bonding, inhibiting the reaction. Tetraformaltrisazine (TFTA, C4H12N6) and Oxalic acid dihydrate (ODH, C2H6N4O2) are other reducing agents that have also been used, which spontaneously ignite on dehydration and produce higher temperatures over 300*C, to yield BaM with a grain size of 0.2 lm and good magnetic properties at 850*C. To induce combustion, microwave heating can be used as well, heat is generated by the interaction of the microwaves with the material usually at 2.45 GHz, the frequency at which domestic microwave ovens operate. BaM nanopowders of single-phase were obtained by stirring a stoichiometric mixture of nitrates with citric acid in ethylenediaminetetraacetic acid and ethylene glycol, it was adjusted to pH 6.5 with ammonia solution and to oxidize all the chelating hydrocarbons it was required excess amount of ammonium nitrate also adjust with it. Now the mixture was freeze-dried and in a microwave oven, the mixture was auto combusted in a specially designed quartz vessel and sintered ferrite support to maximize the heating conditions. Single-phase BaM nanopowder is easily formed without any complication with the help of the auto combustion process.

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