Morphological control of vertically self-aligned nanosheets formed on magnesium alloy by surfactant-free hydrothermal synthesis

Crystalline nanosheets were successfully formed on magnesium alloy AZ31 by a facile surfactant-free hydrothermal treatment using aqueous solution. The crystal structures and shapes of the nanosheets changed with the treatment temperature. On treatment at 120 °C, rosette-like structures made from curved nanosheets of crystalline Mg_1−xAl_x(OH)₂(NO₃)_x·nH₂O were formed. At 150 °C, plate-like nanosheets of crystalline Mg_1−xAl_x(OH)₂(NO₃)_x·nH₂O and Mg(OH)₂ were formed. Further increase in the treatment temperature to 180 °C yielded larger crystals with sharp edges. The crystallites were crystalline Mg(OH)₂ with a distinct plate-like shape with the edges preferentially directed out of the magnesium alloy. The formation mechanism of this morphology is also discussed.