Naslov
Phase development during high-energy ball- milling of zinc oxide and iron - the impact of grain size on the source and the degree of contamination

Autori
Štefanić, Goran ; Krehula, Stjepko ; Štefanić , Ivka

Izvornik
Dalton transactions (1477-9226) 44 (2015), 43; 18870-18881

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Contamination ; Enamels ; Field emission microscopes ; Grain size and shape ; Iron ; Magnetite ; Milling (machining) ; Oxidation ; Scanning electron microscopy ; Stainless steel ; X ray powder diffraction ; Zinc ; Zinc oxide Energy dispersive x-ray spectrometries (EDS) ; Field emission scanning electron microscopy ; High-energy ball milling ; Microstructural changes ; Planetary ball mill ; Spinel type ferrites ; Ssbauer spectroscopies ; UV-Vis diffuse reflectance spectroscopy

Sažetak
High-energy ball-milling of powder mixtures of zincite (ZnO) and iron (α-Fe) at different weight ratios was performed in air using a planetary ball mill with a stainless steel milling assembly. Structural and microstructural changes during the ball-milling (up to 30 h) were monitored using X-ray powder diffraction, field emission scanning electron microscopy (FE-SEM) and UV-Vis diffuse reflectance spectroscopy. The mechanism of iron oxidation was determined from the results of Mössbauer spectroscopy. It was found that an early phase of ball-milling caused the oxidation of iron from Fe0 to Fe2+ followed by the formation of a solid solution structurally similar to wüstite. The wüstite-type phase rapidly disappeared upon prolonged milling, which was accompanied by further oxidation of iron from Fe2+ to Fe3+ and the formation of spinel-type ferrite structurally similar to franklinite (ZnFe2O4) in the products with a high zinc content, or magnetite (Fe3O4) in the products with a high iron content. Further milling or annealing had a low impact on the franklinite-type phase, but caused the transition of the magnetite-type phase to the phase structurally similar to hematite (α- Fe2O3). The results of energy dispersive X-ray spectrometry (EDS) showed a dramatic increase in the degree of contamination with the increase in the proportion of the starting iron (∼9 times higher contamination during the milling of pure iron compared with pure zincite). It was shown that the source of contamination (balls or vial) strongly depends on the type of milled sample. Ball-milling of relatively big and heavy grains (starting iron) caused preferential contamination from the vial whereas ball-milling of smaller and lighter grains (products obtained after prolonged milling) caused preferential contamination from the balls. After prolonged milling the contamination due to wear of the balls was dominant in all the products. An explanation for the observed impact of grain size on the source and the degree of contamination was proposed.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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