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Solution Technique Hydrothermal

Pure finely divided particles of mineral quartz are [Pg.517]

FIGURE 29.11 A silver-lined laboratory hydrothermal autoclave, about 35cm long. It can be much longer. [Pg.518]

FIGURE 29.12 Hydrothermally grown quartz crystal note the colorless seed and the Pt support wire at the top. [Pg.518]

Crystal Solvent Growth zone temperature (°C) Dissolution zone temperature C) Pressure or degree of fill [Pg.518]

SrMo04, BaMo04 5-7wt% NH4CI or 15-20wt% LiCI or 30-40 wt% NaCI 430-485 450-500 65-70% [Pg.518]


Synthetic Insoluble Silicates. Insoluble crystalline siUcates, ie, mineral-type compounds, are synthesized from soluble siUcates by precipitation, gelation, ion exchange, and hydrothermal techniques. Hydrothermal treatment of partially neutralized, high mole ratio (m = 12—50), sodium siUcate solutions yields neutral alkaU polysiUcates that exhibit a layered stmcture and high ion-exchange capacity (135,136). These and other lamellar siUcates can be utilized either alone or modified via pillaring (137) as adsorbents and catalysts. [Pg.13]

The authors report the syntheses of Th2(P04)2HP04-H20 and Th(0H)P04 from aqueous solutions under hydrothermal conditions at temperatures around 150°C. A combination of techniques (SEM, XRD, IR, electron probe microanalyses, DTA and TGA) are used. It is indicated that the dissolution reactions of Tli4(P04)4P207 in water results in the formation of Th2(P04)2HP04-H20. No original thermodynamic data were obtained in this study. [Pg.661]

Precipitation of simple and complex oxide nanoparticles from water solutions under hydrothermal conditions (high-temperature hydrolysis) is well known technique for several decades [69]. In the past 20 years, interest has increased to hydrothermal synthesis due to the extensive miniaturization electronic devices and the increasing demand for nanosize high quality powders. [Pg.306]

In view of the production of alkaline supernatant/waste solution after hydrothermal and fusion methods, a molten salt method has been demonstrated by previous researchers for synthesis of zeolites by employing a dry conversion technique without use of water. In tune with this, mixture of chemicals/salts and fly ash has been reported to yield zeolites by reaction of salts in molten condition for a period up to 3 days. A flow chart of the synthesis process is depicted in Fig. 3.4 [15, 16]. [Pg.46]

Dissolved Minerals. The most significant source of minerals for sustainable recovery may be ocean waters which contain nearly all the known elements in some degree of solution. Production of dissolved minerals from seawater is limited to fresh water, magnesium, magnesium compounds (qv), salt, bromine, and heavy water, ie, deuterium oxide. Considerable development of techniques for recovery of copper, gold, and uranium by solution or bacterial methods has been carried out in several countries for appHcation onshore. These methods are expected to be fully transferable to the marine environment (5). The potential for extraction of dissolved materials from naturally enriched sources, such as hydrothermal vents, may be high. [Pg.288]

A specific feature of reactions occurring in the autoclave is that the least soluble compounds are always precipitated from the homogeneous phase of the reaction. As a result, the equilibrium of the reaction is always shifted to the formation of these very insoluble compounds. Thus, it becomes clear that by varying the composition of the reaction mixture (mainly due to the introduction of new cations and anions) practically all types of the cluster forms being generated in the given system can be obtained in the solution. This is a clear advantage of the hydrothermal technique for cluster synthesis in the autoclave. [Pg.225]

The nonlinear optical oxide crystals recently developed are grown by flux (and hydrothermal solution for KTP) techniques to prevent decomposition (KTP, KTA, LBO) or to obtain a low temperature phase (BBO). The intrinsic nonstoichiometry and the impurity contents of the as-grown crystals is determined by the solutions and temperatures used for growth. The intrinsic defect concentrations in these materials are relatively low, compared to the more traditional nonlinear optical oxides having the... [Pg.393]

The in situ membrane growth technique cannot be applied using the zeolite-based ceramic porous membrane as support, under hydrothermal conditions in a solution containing sodium hydroxide. The high pH conditions will cause membrane amorphization and lead to final dissolution. Therefore, we tried to synthesize an aluminophosphate zeolite such as AlP04-5 [105] over a zeolite porous ceramic membrane. For the synthesis of the AlP04-5-zeolite-based porous membrane composite, the in situ membrane growth technique [7,13,22] was chosen. Then, the support, that is, the zeolite-based porous ceramic membrane, was placed in contact with the synthesis mixture and, subsequently, subjected to a hydrothermal synthesis process [18]. The batch preparation was as follows [106] ... [Pg.482]

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). [Pg.222]

The second in situ technique is NMR. An autoclave fitting with the NMR cavity was designed by Gerardin et al. [59] and allows to follow the evolution of many parameters of the synthesis via the NMR characteristics of the different nuclei versus temperature and reaction time. The first measurement that can be reached now is the absolute value of the pH in hydrothermal conditions and the quantitative evolution of the concentration of protons in the bomb with the parameters of the synthesis [60], They proved that 14N NMR chemical shifts of well chosen amine compounds (imidazole and DABCO which possess complementary pKas) are precise pH indicators in aqueous solutions from room temperature to 475 K. Use of both amines permit to cover a wide range of about 9 pH units, with a precision of 0.1 pH unit. [Pg.223]


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