The use of solvents and uniaxial pr

The use of solvents and uniaxial pressure to densify inorganic materials was first demonstrated by Della M. Roy et al. in the early 1970’s to fabricate cement pastes with excellent mechanical properties. Heat and pressure were used to control the porosity and accommodate volume changes occurring during the cement hydration [1,2]. Within the same decade, advances in hydrothermal processing were carried out by S.Somiya et al. to densify oxides through a reactive approach from metal powders at temperatures below 1000
C [3,4]. In the 1980’s, N. Yamasaki, K. Yanagisawa et al. developed an apparatus for “hydrothermal hot pressing” combining the two previous approaches, based on the uniaxial pressure of a mixture of powder and an aqueous solutions in a system sealed with PTFE (Teflon™) gaskets [5]. This technique led to the sintering of several oxides through a dissolution-precipitation mechanism,as stated by authors [6–10]. As the technique was limited in terms of relative densities achieved, a high-performance “solvo-/hydrothermal sintering” apparatus was designed by Goglio et al. to reach higher temperatures and pressures without damaging the Teflon™ gaskets while maintaining the hermetic sealing of the system [11,12]. These improvements led to the fabrication of high density SiO2, SiO2-based composites [13–15] and metal composites [16] through mecha nical-chemical effects in synergy with chemical effects [12,13]. Riman et al. developed the " Reactive Hydrothermal Liquid Phase Densification” (rHLPD) for the reactive crystallization and densification of materials [17]. In this process, a porous preform is infiltrated with precursors then exposed to mild isostatic pressures and temperatures to drive hydrothermal reactions between the preform and precursors [18,19].