Zinc aluminate is structurally spinel type material resembling zinc ferrite structure but entirely nonmagnetic. Although these materials are important by its catalytic effect, we have intention only to study the structural change and conduction mechanism in these materials with milling to initiate a debate on conduction mechanism on similar kind of fine particle systems. Reports of possibility of achieving cation redistribution easily in these materials encouraged this work.
X-ray diffraction and EDX studies on dry milled zinc aluminates
XRD patttern indicates highly monophasic phase even after hours of milling. This is entirely different from the zinc ferrite results, where zinc ferrite gets decomposed with milling. This confirms the reports of stability of zinc aluminate against decomposition to the component oxides.
The broad shape of the diffraction peaks replicates the formation of fine particle structure with small crystallite size distribution by the effect of high energy ball milling. Average size of the particle, which is calculated by Debye Scherer formula, were in the nanometer range (4-7nm) and found to be decreasing with milling time. Thus the high energy ball milling reduces the particle size in the initial stage of milling. This reduction in particle size as the milling time increases may be due to the fact that the kinetic energy generated by the series of collisions among balls is transferred to the system but there is no sudden decrease as in the case
of particles prepared by the solid-state reaction method. This is because the starting powder (coprecipitated) itself is of nanometer sized. Also there are reports that within 24 minutes of milling, size reduction may attain its maximum. The reason for not obtaining a great reduction in size with prolonged milling is due to the high local temperature and pressure generated during the combustion as a result of the high energy ball milling. Also the difficulty in maintaining the very high stress during milling slows down reduction of grain size.
Lattice parameter found to be increasing marginally with milling. An attempt to calculate the strain developed in the lattice was made but found to be difficult to extract any value from the plots. This peculiar behaviour could be due to the highly ultrafine nature of the material.
The broad shape of the diffraction peaks replicates the formation of fine particle structure with small crystallite size distribution by the effect of high energy ball milling. Average size of the particle, which is calculated by Debye Scherer formula, were in the nanometer range (4-7nm) and found to be decreasing with milling time. Thus the high energy ball milling reduces the particle size in the initial stage of milling. This reduction in particle size as the milling time increases may be due to the fact that the kinetic energy generated by the series of collisions among balls is transferred to the system but there is no sudden decrease as in the case
of particles prepared by the solid-state reaction method. This is because the starting powder (coprecipitated) itself is of nanometer sized. Also there are reports that within 24 minutes of milling, size reduction may attain its maximum. The reason for not obtaining a great reduction in size with prolonged milling is due to the high local temperature and pressure generated during the combustion as a result of the high energy ball milling. Also the difficulty in maintaining the very high stress during milling slows down reduction of grain size.
Lattice parameter found to be increasing marginally with milling. An attempt to calculate the strain developed in the lattice was made but found to be difficult to extract any value from the plots. This peculiar behaviour could be due to the highly ultrafine nature of the material.
Energy dispersion X-ray intensities were converted to the relative concentrations and tabulated in table. The experiment is carried out over different areas and almost the same composition matching with the theoretical values is observed for dry milled and unmilled zinc aluminates suggesting a high quality chemical homogeneity in these samples.
1 comment:
do you know of a place that i can purchase zinc aluminate spinel powder?
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