Wet Salt Melts—A Reaction Medium Suitable for the Preparation of Metastable Oxides and Hydroxides?

Abstract

AbstractSalt melts with a water content from 1 to 50 mole percent, representing systems between salt fluxes and hydrothermal solutions, have not been used for preparation purposes yet. We employed such systems with alkali nitrate and chloride as salt components on the preparation of hydrous gallium oxides. In this way besides α‐GaOOH and β‐Ga2O3, the metastable polymorphs α‐Ga2O3 and ε‐Ga2O3 as well as 5Ga2O3 · H2O and furthermore oxides with the β(2B)‐alumina and the spinel structure are formed. Composition and structure of the product phases are mainly ruled by temperature and molar salt/water ratio. With T < 450°C and pH2o < 10 bars the reaction conditions are rather mild compared with those of hydrothermal growth or flux growth, respectively. The mechanism of the hydrous oxide formation and the applicability of the new method to other oxide systems are discussed shortly.