Hydrothermal method is a non-conventional method to obtain nanocrystalline inorganic materials. Standard hydrothermal experiments are conducted under isothermal and isobar conditions without agitation. The hydrothermal process have several advantages over other growth processes such as use of simple equipment, catalyst-free growth, low cost, large area uniform production, environmental friendliness, less hazardous no need for use of metal catalysts and low reaction temperatures to integrate into the microelectronics and plastic electronics. High pressure hydrothermal synthesis (HPHS) of nanocrystalline materials has to be controlled by both process parameters like temperature, pressure and time, as well as physical and chemical parameters of the material under investigation.
Hydrothermal Solubility of the inorganic materials increases with pressure, so remarkable synthesis results can be obtained under these conditions. In the hydrothermal synthesis, the precursor materials are taken in a container with solid to water proportion is about 1:10. The closed containers are placed into the sealed stainless steel autoclaves (high temperature, high pressure apparatus) and put into the furnace. Applying the desired hydrothermal synthesis temperature, an autogenous pressure is formed. The external pressure is adjusted as soon as the temperature equilibrium is achieved within the autoclave. By the installation of the hydrothermal pressure, the reaction process takes place. We are mainly concerned with the synthesis and characterization of various nanosized materials of ZnO and ZnGa2O4.