ABSTRACT
Water is an inevitable component of hydrothermal systems and both temperature and pressure have a great inuence on the resulting properties of water. When water attains supercritical state, its surface tension approaches nearly zero. At this point, the distinction between gas and liquid phase breaks down and water effectively occupies the pores of the material and facilitates the hydrothermal process [1]. Hydrothermal processing can be dened as “any homogeneous (nanoparticles) or heterogeneous (bulk materials) reaction in the presence of aqueous solvents or mineralizers under high pressure (above 1 atmospheric) and temperature (above a room temperature) conditions to dissolve and recrystallize (recover) materials that are relatively insoluble under ordinary conditions” [1, p.1]. Hydrothermal synthesis of materials indeed has a longstanding history. Schafthaul was the rst person who used hydrothermal treatment to prepare ne particles of quartz in a Papin’s digester during 1845 [2]. In the early 1900s, more than 150 mineral species, including diamond, were synthesized by hydrothermal methods [3]. Since 1940s, the early stage of hydrothermal research was conducted by several groups in the United States, Europe, and Japan. They mostly focused on crystal growth of articial Zeolite and Quartz as indicated in a review by Somiya [4]. During the years between 1950s and 1970s, hydrothermal processes
14.1 Introduction .......................................................................................................................... 395 14.2 Different Forms of Carbons .................................................................................................. 396
14.2.1 Carbons from Carbides ............................................................................................. 396 14.2.2 Formation of Amorphous Carbon from Carbides .................................................... 398 14.2.3 Formation of Diamond by Hydrothermal Process ................................................... 399
14.2.3.1 Identication Diamond from Carbides ......................................................400 14.2.3.2 Formation of Disordered Carbon by Hydrothermal Treatment ................. 401
14.2.4 Hydrothermal Synthesis of Filamentous Carbons .................................................... 401 14.2.5 Hydrothermal Synthesis of Graphitic Carbons ........................................................403 14.2.6 Carbon Nanotube ......................................................................................................405
