Molten salt synthesis

Many techniques have been developed for the synthesis of nanoparticles, such as solid-state reactions [5-14], molten salt synthesis [15-21], hydrothermal methods [22-29], sol-gel processing [30-36], co-precipitation [37-46], thermal evaporation [47-50], plasma methods [51-54], chemical vapor deposition [55-60], pulsed laser deposition [61-66], and magnetron sputtering [67-72], 

The solid-state reaction has the advantages of low cost and simple operability. 

Wu et al. [73] prepared Ba Sri Ti03 (BST) nanoparticles via solid-state techniques by heating stoichiometric amounts of the raw materials BaCOs, SrCOg, and Ti02. The BST ceramics showed good dielectric properties at both low frequencies and microwave frequency (2 GHz). 

Shao et al. [74] prepared BaTiOs ceramic with a high piezoelectric coefficient by solid-state reaction, and found that the ceramic showed good dielectric properties. 

Compared with the traditional sintering method, the molten salt method is one of the simplest methods for controlling the morphology of particles and obtaining highly reactive powders of a single phase at low temperatures in a short soaking time. This is because the molten salt can accelerate the reaction kinetics at this low temperature and facilitate the formation of ceramic particles. 

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One synthesis approach that does not rely on CNT formation from the gas phase is molten salt synthesis. The reactor consists of a vertically oriented quartz tube that contains two graphite electrodes (i.e. anode is also the crucible) and is filled with ionic salts (e.g. LiCl or LiBr). An external furnace keeps the temperature at around 600 °C, which leads to the melting of the salt. Upon applying an electric field the ions penetrate and exfoliate the graphite cathode, producing graphene-type sheets that wrap up into CNTs on the cathode surface. Subsequently, the reactor is allowed to cool down, washed with water, and nanocarbon materials are extracted with toluene [83]. This process typically yields 20-30 % MWCNTs of low purity. 

The need for precise control of properties has resulted in modifications of the mixed oxide technique. These include chemical coprecipitation from various precursors , freeze-drying, and molten salt synthesis. The coprecipitation technique is particularly suited to large scale production. 

The relation between the drying method and the surface area of powders is important. There are many drying methods, such as air, vacuum, and freeze drying. This point is illustrated with the examples of (Bao.2Pbo.8)Ti03. In powder preparation, the surface reactivity, that is, the specific surface area, plays a very important role. Specific surface areas are often determined by the BET (Brunauer, Eminett, and Teller) method. Typical BET plots of the sol-gel, CMO (calcined mixed oxide method), and MSS (molten salt synthesis method) [15] derived powders are shown in Fig. 1. 

There are two other methods for producing ferrite powders that deserve attention molten-salt synthesis and shock-wave loading. In molten-salt synthesis, Fe203 and the corresponding carbonate, oxide, hydroxide or nitrate needed to produce the ferrite phase are dry blended with a mixture of NaCl and KCl. This reaction mixture, in a Pt crucible, is placed in a furnace at 800-1100 °C for lh the chloride solvent is melted and provides an efficient heating medium for the reaction. After cooling, the solvent is separated from the ferrite by dissolution in water. The product can be finally collected by filtration. Ba and Sr hexaferrite powders have been prepared by this method (Arendt, 1973). Submicron, high-quality crystallites with a low ferrous content were obtained. 

Arendt, R. H. (1973). The molten salt synthesis of single domain BaFei20j9 and SrFeijOi, crystals. Journal of Solid State Chemistry, 8, 339-47. 

Arendt, R.H. (1973) The molten salt synthesis of single magnetic domain BaFei20]9 and SrFei20ig crystals./. Solid State Chem., 8 (4), 339-347. 

Duran, C., Messing, G.L., and Trolier-McKinstry, S. (2004) Molten salt synthesis of anisometric particles in the SrO-Nb20s-BaO system. Mater Res. Bull, 39 (11), 1679-1689. 

Many routes for obtaining template particles are known using molten salt synthesis, hydrothermal synthesis, sol—gel processing, as well as hybrid, multistep methods. The TGG method has been widely used for the development and texturing of piezoelectric ceramics [44]. One of the reasons for this widespread use is the cost consideration, since TGG enables the relatively inexpensive fabrication of textured ceramics with single crystal-Uke properties. However, our present discussion pivots around the mechanical properties. 

Afimasiev, P. (2007) Molten salt synthesis of barium molybdate and tungstate microcrystals. Mater. Lett, 61,4622-4626. 

Arney, D., Porter, B., Greve, B., and Maggard, P.A. (2008) New molten-salt synthesis and photocatalytic properties of La2Tl207 particles. /. Photochem. Photobiol. A Chem., 199, 230-235. 

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]. 

Kim JH, Myung ST, Sun YK (2004) Molten salt synthesis of LLNio(5Mni(504 spinel for 5 V class cathode material of Li-ion secondary battery. Electrochim Acta 49 219-227... 

Molten Salt Synthesis of Bisubstituted Yttrium Carnet Nanopartides... 

Besides wet-synthesis methods, another two novel methods have been used to synthesize MA spinel powders. These are mechanochemical alloying and molten salt synthesis (MSS). 

Han CH, Hong YS, Park CM, Kim K (2001) Synthesis and electrochemical properties of lithium cobalt oxides prepared by molten-salt synthesis using the eutectic mixture of LiCl-Li2C03. J Power Some 92 95—101... 

Zhenyao W, Biao L, Jin M, Dingguo X (2014) Molten salt synthesis and high-performance of nanocrystalline Li-rich cathode materials. RSC Adv 4 15825-15829... 

Zhao X, Cui Y, Xiao L, Liang H, Liu H (2011) Molten salt synthesis of Lii+x(Nio.5Mno5)i-x02 as cathode material for Li-ion batteries. Solid State Ionics 192 321-325... 

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