Hydrothermal recrystallization

Chai B.H.T. (1974) Mass transfer of calcite during hydrothermal recrystallization. In Geochemical Transport and Kinetics, Vol. 634 (ed. A.W. Hofmann, B.J. Giletti, H.S. Yoder, and R.A. Yund), pp. 205-218. Garnegie Institution of Washington Publ. 

Baker P.A., Kastner M., Byerlee J.D. and Lockner D.A. (1980) Pressure solution and hydrothermal recrystallization of carbonate sediments-an experimental study. Mar. Geol. 38, 185-203. 

Zhang and co-workers reported partial conversion of a mesoporous starting material (SBA-15) into a mesoporous aluminosilicate with zeolitic characteristics in a so-called vapour phase transport method.[82] In this process, Al is firstly introduced onto the mesoporous surface, followed by a filling of the mesopores with a carbonaceous species, and finally a partial recrystallization of aluminosilicate in the vapour of the SDA is conducted. The advantage of this method, compared with the hydrothermal recrystallization method of Kloetstra et al., lies in the fact that the mesopore structure collapses to a lesser extent as the crystallization is limited to the surface of the mesoporous precursor. 

Hydrothermal recrystallization is not conhned to quartz. Some II-VI compounds, such as ZnSe, ZnTe, CdSe, and CdTe, have also been recrystallized into large single crystals using the technique (Kolb, 1968), as well as aluminum orthophosphate, AIPO4 (Kolb, 1980). The technique can also be used preparatively as in the case of potassium titanyl phosphate (Laudise et ah, 1986) ... 

Chai BHT (1975) The kinetics and mass transfer of calcite during hydrothermal recrystallization process. 

Davey et al. found that Form I crystals of terephthalic acid could be obtained by crystallization only in the presence of/ -toluic acid [54]. Form II, the more stable polymorph at ambient temperatures, was recovered from a hydrothermal recrystallization experiment. 

Preparation of the composite materials with the FAU and BEA nanodomains has been reported previously [3,4]. The procedure was based on the impregnation of the parent materials with concentrated template solutions and subsequent recrystallization in the hydrothermal conditions. Amorphous aluminosilicates of chemical composition 13%Al20387%Si02 (13A187Si) and 6%Al20394%Si02 (6A194Si) were used as the parent materials for the FAU and BEA composites, respectively. 

Silicate minerals that usually occur as spherulitic aggregates of fibers have formed as a result of the alteration of the many minerals subsumed within the category of biopyriboles. Alteration of the micas under hydrothermal conditions produces compositional variants on recrystallization such as hydrous muscovite. Some of these samples have been labeled asbestiform, probably because they are found in veins that criss-cross rock masses. Fibrous micaceous minerals also occur as discrete disseminated particles, although few detailed analyses of crystallites from the disperse occurrences have been made. Fibrous mica found in veins usually grades (composition-ally) into members of the serpentine mineral group, the clays or the chlorites. 

Rocks that contain talc, or the chemically and structurally similar minerals mentioned previously, are usually the result of alteration and recrystallization of rock formations that contained magnesian silicate minerals. Steati-zation or serpentinization are the terms given the processes that create layered (sheet) silicates from chain or other tetrahedral arrangements adopted by silicate minerals (see Fig. 2.1). The recrystallization process is expedited by temperature and pressure, and especially through the action of hydrothermal solutions. 

Conditions which promote multi-domainic goethites are high ionic strength (either [KOH] or salt) and also low synthesis temperature (<40°C). In alkaline solutions, multi-domainic character decreases and domain width increases as Al substitution increases to Al/(Fe-i-Al) of 0.15, whereas at Al/( Al-nFe) >0.15 single domain crystals result (Schulze Schwertmaim, 1984 Mann et al., 1985). Multidomainic goethites can recrystallize to single domain crystals as a result of hydrothermal treatment at 125-180 °C (Fig. 4.9) (Schwertmann et al., 1985). 

Why must recrystallization of quartz for use in the electronics industry be carried out hydrothermally ... 

A solvothermal process is one in which a material is either recrystallized or chemically synthesized from solution in a sealed container above ambient temperature and pressure. The recrystallization process was discussed in Section 1.5.1. In the present chapter we consider synthesis. The first solvothermal syntheses were carried out by Robert Wilhelm Bunsen (1811-1899) in 1839 at the University of Marburg. Bunsen grew barium carbonate and strontium carbonate at temperatures above 200°C and pressures above 100 bar (Laudise, 1987). In 1845, C. E. Shafhautl observed tiny quartz crystals upon transformation of freshly precipitated silicic acid in a Papin s digester or pressure cooker (Rabenau, 1985). Often, the name solvothermal is replaced with a term to more closely refer to the solvent used. For example, solvothermal becomes hydrothermal if an aqueous solution is used as the solvent, or ammothermal if ammonia is used. In extreme cases, solvothermal synthesis takes place at or over the supercritical point of the solvent. But in most cases, the pressures and temperatures are in the subcritical realm, where the physical properties of the solvent (e.g., density, viscosity, dielectric constant) can be controlled as a function of temperature and pressure. By far, most syntheses have taken place in the subcritical realm of water. Therefore, we focus our discussion of the materials synthesis on the hydrothermal process. 

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