Hydrothermal reactions

For emerald, a hydrothermal reaction arrangement is used, analogous to that of Figure 4. Here the mineralizer is strongly acid, containing 8A[ NH Cl [12125-02-9] and HCl [7647-01-1] to give pH between 0.2 and 4.5. 

Vanadium borophosphates 107-109 that contain cluster anions with different ring sizes can be synthesized by hydrothermal reactions of vanadium(III) oxide, boric acid and an appropriate phosphate salt [145,146]. The ring size of the cluster anion with the composition [(VO)2BP20iol 4-6 is determined by the size of the cation that is, however, included only in the interior of the cages with n = 5 and 6 (Fig. 28). 

The solvothermal reaction between metal halides and polysulfide anions is also a useful method for the synthesis of metal-polysulfide clusters. Hydrothermal reaction of K2PtCl4 with K2S4 (5 eq) at 130 °C in a sealed tube... 

The presence of zinc with bidentate nitrogen donor ligands in the formation of novel composite materials by hydrothermal reactions has been studied. A zinc-containing one-dimensional material, [Zn(phenanthroline)Mo04] was isolated from molybdate, and from vanadium oxide in the presence of zinc 2,2 -bipyridine [Zn(2,2,-bipyridine)2V40i2] was obtained.212,213... 

The alternation of temperature in a hydrothermal reaction was demonstrated to be crucial in changing the crystal phases or morphologies of nanomaterials. In the case of K2Cr207, when the reaction temperature was increased to 180 °C, K-OMS-2 microspheres consisting of nanoneedles were synthesized in contrast to the nanoduster arrays composed of tetragonal prism nanorods synthesized at 120 °C (Figure 8.1a-c). In the case of Na2Cr207, when the reaction temperature was 100 °C, Na-OMS-2 phase was formed. However, when the reaction temperature was... 

Amino acids Spark Discharge Yields in pM Hydrothermal Reactions Yields in pM... 

Fujii and coworkers reported the synthesis and detailed structural analyses of alkylammonium/magnesium phyllosilicate hybrids [88], which were prepared by hydrothermal reaction from a mixture ofoctadecyldimethyl(3-trimethoxysilylpropyl)-ammonium chloride, silica sol, and magnesium hydroxide Mg(OH)2. The structure of the hybrid compound was studied by XRD, TEM, electron diffraction, high-resolution solid-state NMR, TG-DTA/MS, and elemental analysis. The resulting analytical information confirmed the unit structure, which consists of a 2 1... 

Subsurface reactions. The geochemical modifications of groundwater, particularly ion filtration and hydrothermal reactions, must not be of the type which would fractionate the isotopes being studied. 

Fortunately, if enough samples are available from a given aquifer, the variations of 2H and 180 can be compared with Craig s empirical relationship, which for normal surface waters is 62H = 8 6180 + 10°/oo. Large departures from Craig s correlation line could indicate the effects of evapotranspiration or of hydrothermal reactions. 

We assume that the 180/160 ratio of the (water+rock) system is preserved through the hydrothermal reaction (closed system)... 

In the laboratory experiments of Seyfried et al. (1998), naturally altered sea floor basalt (5 Li = +7.4) was reacted with Li-free alkali-chloride aqueous fluid at 350°C for 890 hours (initial fluid/solid mass ratio 2). Samples of the fluid were taken throughout the experiment, and showed initial rapid influx of isotopically heavy-enriched Li released by early-dissolving alteration minerals. However, with progressive reaction, isotopic composition of the fluid decreased and Li concentration reaehed apparent steady state. Although an equilibrium model applies best to the synthetic results, Rayleigh distillation was considered most likely to apply in hydrothermal reactions occurring in nature. 

The resulting CO2 gas is returned to the atmosphere by two means (1) volcanic emissions associated with eruptions near subduction zones, i.e., back-arc volcanoes or (2) diffusion through the sediments of the continental rise into the ocean, followed by gas exchange across the air-sea interfece. The combined production of CO2 from these two settings is thought to exceed that from the high-temperature hydrothermal reaction zones. 

Jander, W., and J. Wurhrer (1938). Hydrothermal reactions (I) Formation of magnesium hydrosilicates. Zeit. Anorg u allgem Chemie 235 273-294. Jefferson, D. A., L. G. Hallinson, J. L. Hutchison, and J. M. Thomas (1976). Structural irregularities in nephrite jade an electron microscope study. Mater. Res. Bull. 11 1557-1562. 

Metal phosphates can be prepared by wet and dry methods. The homogeneous precipitation in aqueous systems is often employed to obtain uniformly sized and well-crystallized particles. The solid reactions can be used for preparation of some metal phosphates however, the particles with controlled morphology are difficult to synthesize. Moreover, the solid reaction consumes more energy than the reaction in aqueous system, except the hydrothermal reaction at elevated temperature. Recently the preparation from aqueous solution at low temperature received attention in view of saving energy and as an application for a wide variety of substances. Therefore the preparation of metal phosphate particles by the precipitation method is described next. Although phosphates include ortho-, pyro-, and polyphosphates, only orthophosphates are dealt with here. 

Highly crystallized CaHAP particles are synthesized by hydrothermal reactions at 300-700°C under 8.6-200 MPa for several days (1,9). The CaHAP particles produced are stoichiometric single crystals and rod- or needlelike particles elongated along the c axis. The reaction systems are CaHAP-H20, Ca2P207-Ca0-H20, Ca(N-0,)-NaOH KH2PO4-H20, HjPC -CafNO - O, etc. Hydrothermal treatment is frequently used for crystallization of low crystalline CaHAP particles and for... 

The hydrothermal method has been employed in recent years to synthesize a variety of solids that include aluminium phosphates (ALPOs) and other microporous transition-metal phosphates and transition-metal polychalcogenides (Davis Lobo, 1992 Haushalter Mundi, 1992 Liao Kanatzidis, 1990, 1992). Unlike zeolites, synthesis of ALPOs requires acidic or mildly basic conditions and no alkali metal cations. A typical synthetic mixture for making ALPO consists of alumina, H3PO4, water and an organic material such as a quaternary ammonium salt or an amine. The hydrothermal reaction occurs around 373-573 K. The use of fluoride ions, instead of hydroxide ions as mineralizer, allows synthesis of novel microporous materials under acidic conditions (Estermann et al, 1991 Ferey et ai, 1994). 

Somiya (ed.) (1989) Hydrothermal Reactions for Materials Science and Engineering, Elsevier Applied Science, London. 

The preparation of cetineite phases is based on a hydrothermal reaction of elementary Sb, Se or S, H2O and NaOH or KOH. In the case of (Na Se) and (K Se) the presence of CH3NH2 or CH3(CH2)2CH(CH3)NH2 as a template is needed, but in both cases the template is not incorporated into the structure, which is proven by elementary analysis. 

New cetineite phases with variable K/Na ratio are synthesized by hydrothermal reaction of elementary Sb and S in an aqueous mixture of NaOH and KOH following the same experimental route. Orange-red single crystals with a maximum length of 1.2 mm and a hexagonal cross section of 9-10 2 mm2 are obtained. The K/Na ratio is determined from single crystals via EDX (Zeiss DSM 950/Tracor Voyager II). 

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