Solvothermal Processes: Definition, Key Factors Governing the Involved Chemical Reactions and New Trends

A solvothermal process can be defined as a process in a closed reaction vessel inducing a decomposition or a chemical reaction(s) between precursor(s) in the presence of a solvent at a temperature higher than the boiling temperature of this solvent. The pressure can be autogeneous (in such a case the pressure value depends on the filling of the reaction vessel) or imposed (the pressure value being higher than 1 bar (105 Pa) at the starting point of the experiment through the compression of the reaction medium). Depending on the experimental conditions (pressure and temperature), the solvothermal system can be heterogeneous or homogeneous and in subcritical or supercritical conditions. The word “solvothermal” can be used whatever the chemical composition of the solvent is (aqueous or non-aqueous) [1]. Originally such processes were developed with water, due to its importance on the surface of the earth. For aqueous solutions the word “hydrothermal” is commonly used [2, 3]. Hydrothermal processes were fist developed in geosciences with the synthesis of minerals [4], in materials science with the crystal growth of functional materials [5, 6], and in hydrometallurgy for developing new methods for leaching ores [7]. During the last ten years solvothermal processes have been extensively used in different domains: