Effect of Aging Duration on Mineral Composition, Microstructure, and Texture in a Malachite based Co precipitate and its Composite (Metallic) Oxidic Derivatives

This study deals with the dependence of mineral, microstructural, and textural properties on the duration of the indispensable yet easily controlled step of aging. For this purpose, a set of Cu/Zn/Al precursors were synthesized using a conventional constant‑pH method. The precipitates were aged for three different durations of zero, two, and four hours. The obtained precipitates, after several washing cycles and overnight drying, were then calcined at ۶۲۳ K. Precursor and calcined samples were studied in terms of elemental composition, mineral composition, microstructure, texture, porosity, and metallic copper surface area. The results suggest that the dependence of precursor surface area on aging is realized by its dependence on phase composition. In the precipitate aged for two hours, the relative dominance of malachite leads to the highest pre‑calcination surface area of ۵۷ m۲/g. The individual thermal behaviors of the precursor phases and their pre‑calcination surface area values seem to conjointly determine the post‑calcination surface area of the samples. Such that a combination of ripened particle structure and susceptibility to calcination induced surface deterioration yields the lowest post‑calcination surface area after aging for four hours. The calcines derived from the unaged and the two‑hour‑aged precursors yield surface area values of approximately ۵۷–۵۸ m۲/g, sensibly higher than that of the four‑hour‑aged sample. The Cu۰ surface area values of the samples depend on aging duration through the effect it imparts on the Cu/Zn‑interdispersion of the precursor malachite phase. The highest Cu/Zn‑interdispersion is achieved in the two‑hour‑aged sample that finally exhibited a maximum Cu۰ surface of ۱۱۲ m۲/gCu.

کلیدواژه ها:

Cu/Zn/Al based Composite ، Aging ، Microstructure ، Co precipitation ، Hydrotalcite Malachite Transformation