Effect of a static magnetic field on the preparation of MnOOH and Mn3O4 by a hydrothermal process

In this paper, manganese oxides/oxyhydroxides were prepared by a low-temperature hydrothermal process in a static magnetic field. The products were analyzed with XRD, TEM, HRTEM and VSM. Single-crystalline nanowires (20 nm in diameter and 1 mm in length) of MnOOH were obtained under zero magnetic fields. However, some cubic particles of Mn3O4 were formed when a static magnetic field was applied. Furthermore, the quantity of Mn3O4 increased with the increase of the magnetic flux density. Quantitative thermodynamic calculation results showed that the magnetic Gibbs energy would change the direction of the chemical reaction to obtain Mn3O4.