Molten flux methods

This method emplosrs a molten flux which dissolves the material and re-deposits it upon a seleeted substrate. That is, the molten flux acts as a transport medium. The temperature of the flux can be varied to suit the material and to promote high solubility of the solute material in the molten solvent. One example is YIG", yttrium iron garnet, i.e.- Y3FesOi2 -This material is used in the Electronics Industry as single crystals for microwave generating devices. It can be grown via the molten flux method. 

The synthetic concepts by which these compounds are synthesized are as nvunerous as the different materials themselves. They range from classical hydrothermal reactions, via molten flux methods to pure precipitation reactions. As diverse as the conditions employed to synthesize such compoimds are... 

The preparation of some polychalcogenide solids can be achieved at 200-450 °C by molten salt (flux) methods. The reaction of tin with alkali metal sulfides in the presence of Ss at 200-450 °C gives a variety of alkali metal tin sulfides depending on the ratio of the starting materials, the reaction temperature, and the alkah metals (Scheme 30) [90]. These alkali metal tin sul-... 

Rb4Ge2Seg containing two MSe4 tetrahedra Hnked through Se-Se bonds (Fig. 14.11), were found to be isostructural to Gs4Ge2Seg, although this latter phase was prepared by a solvatothermal method versus our molten flux process [98]. 

The use of strong alkaline media, either in the form of solid fluxes or molten (or aqueous) solutions, has enabled the synthesis of novel oxides. The alkali flux method stabilizes higher oxidation states of the metal by providing an oxidizing atmosphere. Alkali car-... 

The flux method is a well-known method used for single crystal growth. It has not been applied to the synthesis of fine powders because usually high temperature heating is necessary to obtain molten salts. However, the modified flux method has been reported for the preparation of fine panicles of Ce,. Pr Oj solid solutions.In the preparation of the powders by the flux method, molten salts of alkali metal hydroxides, nitrates, and chlorides are used as solvents. The use of molten salts. 

In the sodium carbonate sodium dioxide flux method a possible side reaction has to be taken into account. Molten sodium hydroxide, which may form from... 

The apparatus is simple and consists of a furnace whose temperature can be accurately controlled, a crucible to hold the molten flux, and a method of rotating the crucible to stir the flux containing the dissolved material. Single crystals can be induced to grow along the sides of the crucible by controlling the temperature and supercooling of the molten flux. 

In the fusion methods, cesium iodide is often added to the fusion mixture as a nonwetting agent to prevent the molten flux from adhering to the walls of the vessel, as well as to prevent incomplete transfer of the bead to the acid solution. In wet digestion of coal and fly ash using the Parr bomb, boric acid is added after digestion and the sample is heated for a further time on a water bath allowing the removal of unburned carbon. 

Pure perovskite phase Bao.7Sro.3Ti03 nanoparticles were synthesized by the molten-salt method in NQ-KCl flux at a low temperature of 850°C. The molten salts accelerated the formation of the Bao.ySrojTiOs, and the calcination temperature played an important role in the development of BST particle morphology [79]. 

Molten salt synthesis based on the use of salts with low melting point has been reported to be one of the simplest techniques for preparing ceramic materials [57]. Well-faced LNM crystals were synthesized by molten salt technology using stoichiometric amount of LiOH, Ni(OH)2, and y-MnOOH (2 1 3) calcined at 700-1000 °C [57]. Micro-sized LNM crystals in plate and octahedral shapes were synthesized by molten-salt method in LiCl and LiCl-KCl fluxes the main surface facets on the plates were determined to be (112) crystal planes [58]. Recenfly, microscale LNM was synthesized using nanothom stmctured MnOa mixed with Li and Ni precursors [59]. 

Compared to the MW-assisted method [11], Bi-YIG nanopartides were successfully synthesized by the molten salt method in NaCl-KCl flux at 650 °C. XRD, SEM, dynamic light scattering, VSM, and Faraday rotation meter were used to characterize the phase, morphology, size distribution, magnetic properties, and Faraday rotation... 

Since the use of reactive molten or fluxes of the type A2Q/Q (A = alkali metal, Q = S or Se) were described in the synthesis of ternary polychalcogeni-des, there have been a number of sulfldes and selenides reported that employ this synthetic technique. The compounds typically exhibit low dimensionality, novel structure types, and interesting chalcogen-chalcogen bonding modes. Unlike the sulfldes and selenides, no tellurides had been synthesized with this molten-salt method. The formation of intercalation compounds of the type (M = group IV, V, or VI Q = S, Se, or... 

In the parallel-plate method, the heat flux downward is measured hy a fluxmeter under which the thermal bond material and the molten salt of interest are located. Because the thermal transfer is only conductive if the thermal contacts are perfect, the balance of heat flow through the... 

This means that addition of elemental E to alkali metal polychalcogenide fluxes (200-600°C) will promote the formation of longer chains as potential ligands, when such molten salts are employed as reaction media for the preparation of polychalcogenide complexes. Speciation analysis for polychalcogenides in solution has been performed by a variety of physical methods including UV/vis absorption spectroscopy, Raman spectroscopy, Se, Te and Te NMR, electron spin resonance and electrospray mass spectrometry. 

The synthesis of chalcogenides such as those of the rare earth elements has traditionally been performed through the reaction of rare earth metals or oxides with a molten or vaporous chalcogen source in a high-temperature environment. Soft synthetic methods utilizing lower temperature conditions, such as hydrothermal or flux syntheses, can allow access also to thermodynamically metastable phases. Flux syntheses of R chalcogenides via an alkali poly-chalcogenide flux have been shown to be extremely versatile for the preparation of many new structures, some of which cannot be obtained by direct synthesis from the elements. 

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