Hydrothermal synthesis is a common method for the preparation ofpowder. This method has many advantages: The process is so simple that it reducesthe impurities which come from the outside; it doesn't need a ball mill and hightemperature, so that the reunion doesn't appear in the process; the most crucial is themethod can change the sizes and shapes of the products. However, as the particles arefine and the surface energy between the particles is larger, it is easy to produce thereunion; therefore it needs t...