Solids hydrothermal synthesis

Solids - Hydrothermal Synthesis and Strnctnres of One-Dimensional, 2-Dimensional, and 3-Dimensional Phases of the Oxovanadium-Organodiphosphonate System Angew. Chem. Int. Ed. Engl. 1995, 34, 223. 

Melt growth Vapor growth Hydrothermal synthesis Solid-state reactions... 

Low-temperature solid-state synthesis is preferred in most cases, where appropriate, for obvious reasons such as energy and cost economy and process safety or for critical concerns regarding the accessibility of compounds that are stable only at low temperatures or non-equilibrium phases, i.e., compounds thermodynamically unstable with respect to the obtained phase (e.g., a ternary instead of binary phase). The use of low-temperature eutectics as solvents for the reactants, hydrothermal growth... 

Chesnut, D.J., Kusnetzow, A., Birge, R.R. and Zubieta, J. (1999) Solid state coordination chemistry of the copper halide- and pseudo-halide-organoamine system, Cu-X-[(bis-2,3-(2-pyridyl) pyrazine)] (X = C1, Br, CN) Hydrothermal synthesis and structural characterization. Inoig. Chem., 38, 2663—2671. 

The silica forms of MCM-41, MCM-48, KIT-1, HMS, and SBA-1 were prepared by hydrothermal synthesis following the methods reported in the literature [1,2,3,4,7]. The calcined mesoporous materials were slurried in absolute isopropyl alcohol solution containing TIPOT (10wt%) with magnetic stirring at room temperature for 3h. The solid products obtained were then washed with absolute isopropyl alcohol, dried and calcined in air at 823K... 

Qi, Y.-F., Li, Y.-G., Wang, E. et al. (2007) Hydrothermal synthesis and structures of organic-inorganic hybrid solids based on arsenic-vanadate building blocks. Journal of Coordination Chemistry, 60(13), 1403-18. 

Fig. 5.2 An in-house-developed robotic system for hydrothermal synthesis detail of solid dispensing operation.

This reaction requires very high temperature and the conversion that can be achieved is relatively low. The improved solid phase process is hydrothermal synthesis, in which the mixture of Ca3(P04)2 and Ca(OH)2 or CaC03 is calcined under the condition of steam passing through the material bed [215, 222], and the following reactions occur ... 

Sharma, S., A. Ramanan, and M. Jansen. 2004. Hydrothermal synthesis of new organically intercalated layered vanadates. Solid State Ionics. 170 93-98. 

Lee, K., N.H. Leea, S.H. Shin, H.G. Lee and S.J. Kim (2006). Hydrothermal synthesis and photocatalytic characterizations of transition metals doped nano Ti02 sols. Materials Science and Engineering B-Solid State Materials for Advanced Technology, 129(1-3), 109-115. 

As already mentioned, most of the syntheses use hydrothermal synthesis. The reaction takes place in the autoclave, which acts as a black box for the understanding of the mechanism of formation of the solids which are finally isolated. Nothing was known about the interaction between organic and inorganic species. This needed to choose appropriate systems for the study of the pertinent chemical parameters, to carefully characterize the compounds and use in situ measurements to collect informations able to shed some light on the steps of formation of these solids. Such an approach has been initiated only on oxyfluorinated species, and shall be developped in the following. 

As already mentioned at the end of Sec. 7.2, autoclaves in hydrothermal synthesis are black boxes , and all the attempts to explain the formation of the porous solids originated from ex situ experiments. The above hypothesis concerns reactions within the autoclave and requires for its analysis in situ measurements in hydrothermal conditions which were never performed so far. These experiments must give information both on the solution and on the solid. Moreover, in the systems chosen for such studies, the kinetics of formation must be adapted to the possibilities of observation of the chosen technique. Two of them are particularly useful for this purpose in situ diffraction studies using synchrotron radiation (SR) and in situ NMR (liquid and solid state). 

Solid state reactant Thermal decompositions of a solid Oxidation or reduction of a solid Precipitation Solution heating or cooling Evaporative salting-out Chemical reaction with insoluble product Hydrothermal synthesis Forced insolubility Dissolution reprecipitation Evaporative Condensation Gas phase reaction with solid product Thermal decompositions Oxidation or reduction reactions Combination reactions with a solid product Solvent removal Spray drying Freeze drying Spray roasting Sol-gel synthesis Melt solidification... 

Substantial differences between solid-phase reactions and hydrothermal synthesis reactions have been stated in numerous investigations. In solid-phase processes, the sequence of intermediate products formation does not depend on reagents ratio in the initial mixture, and the excess product appears to be a compound with the highest crystallization temperature. On contrary, for the formation of a definite product by hydrothermal synthesis, the initial mixture should contain reagents at an exact stoichiometric ratio [19,20]. In solid-phase reactions, the interaction rate is determined by the rate of diffusion processes, while in hydrothermal processes the determining factor is the rate of dissolution of the initial products in the water. Water simplifies diffusion transport of particles in the system the formation of nuclei and crystal growth occur faster than in solids. 

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