Evaluation of Mechanochemical and Hydrothermal Transformations in a Wet-Milled Alumina by Transmission Electron Microscopy and Thermal Analysis

Abstract

Milling and hydrothermal treatment of alumina powders in aqueous medium can result in surface transformations generating aluminum hydroxides. The aim of this work was to advance the understanding on these transformations. A α-alumina powder was ball milled in water at different pHs for 10 h, and then autoclaved (150 °C, 3 atm, 3 h). The powders were analyzed by transmission electron microscopy, differential scanning calorimetry simultaneously with thermogravimetry, X-ray diffraction, and infrared spectroscopy. It was observed that milling in basic medium caused the formation of doyleite [Al (OH3)] nanoparticles, which were fully converted to boehmite (AlOOH) by hydrothermal treatment. The boehmite fraction determined by thermal analysis was 1.7 wt%. The powder milled in acid medium had no mechanochemical and hydrothermal transformations.

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“…Hydrothermal technique has found its place in many areas of research and has been used in several interdisciplinary fields of science, such as chemistry, physics, biology, metallurgy, and geology (Darr et al, 2017;Zhang Q. et al, 2019;Townley et al, 2019;Sahu et al, 2020). Therefore, there has also been increased interest in combining hydrothermal technology with other processes such as microwaves, ultrasound, mechanochemistry, electrochemistry, and other processes (Meng et al, 2016;Darr et al, 2017;Yoshimura et al, 2017;Long et al, 2020;Svietkina et al, 2020). These combinations offer several advantages for improving the hydrothermal reaction kinetics, reducing the experimental time, and preparing new kind of materials (Meng et al, 2016).…”