Production of Fe and Cu nanocrystalline particles by thermal decomposition of ferro- and copper-cyanides

Nanocrystalline Fe and Cu particles have been produced at 653 K in an open vertical tube (filled with pure argon) by thermal decomposition of ferrocyanide and copper-ferrocyanide, produced from the precipitates of the solution K4Fe(CN)(6)+(NH4)(2)Fe(SO4)(2) as well as K4Fe(CN)(6)+CuSO4, respectively. Depending on the time of the thermal processing (between 0 and 96 hours) small metallic particles (d congruent to 2-100 nm d is the diameter) were observed by TEM. X-ray diffraction patterns also showed that in the case of copper-ferrocyanide the initial grain size was about 20-25 nm and after the heat treatment this decomposed to a mixture of microcrystalline Cu2Fe(CN)(6), K2CuFe(CN)(6), (CN), as well as pure copper (up to about d=100 nm) and iron (with d<20 nm) particles. In the case of the pure ferrocyanide the X-ray diffraction indicated a probable mixture of Fe-4(Fe(CN)(6))(3) and K4Fe(CN)(6) in the initial state with grain size of about 16 nm and 40 nm, respectively (the expected main product in the precipitate, Fe2Fe(CN)(6), is amorphous and can not be identified by X-ray diffraction). After the heat treatments there is still a mixture of the above two cyanides (with a slightly larger grain sizes and with a relatively less amount of Fe-4(Fe(CN)(6))(3)) and there are also small iron and ironoxide particles (d<50 nm) present (the main matrix after the decomposition is the polycyan, (CN)(n), but there are no X-ray data published for it). The above conclusions were also confirmed by energy dispersive analysis of X-rays in TEM and by magnetic hysteresis behaviour. It was shown that the initial normal paramagnetic behaviour changed to be a mixture of superparamagnetic (due to the small magnetic particles) and normal paramagnetic components (due to the remaining matrix) at room temperature.