Molten Salts and Room-Temperature Ionic Liquids

This gel is then hydrothermally treated to convert it to the oxide. The gel helps to trap the cations and prevent phase separation. 

MOLTEN SALTS AND ROOM-TEMPERATURE IONIC LIQUIDS 

Both reactive and nonreactive molten salts can be used in nontopochemical routes. An example of a nontopochemical route to inorganic materials utilizing reactive molten salts is when a metallic element is reduced in a low-melting alkali metal polychalcogenide (hiQn, where Q = O, S, Se, Te) to form a ternary metal chalcogenide. Potassium bismuth sulfide (KBi3Ss) has been prepared in 

In nonreactive molten salts, on the other hand, flux components are not incorporated into the product phase. Here, the molten salt acts more in the classical sense as a reagent to promote the reaction at a lower temperature than would be required by the ceramic, or direct, route (Section 5.2). This is accomplished by two attributes of molten salts an acid-base equilibrium that enables the general dissolution-recrystallization of metal oxides and a highly electropositive (oxidizing) environment that stabilizes the highest oxidation state of many transition metals (Gopalakrishnan, 1995), which can lead to mixed valency. A plethora of complex transition metal oxides have been synthesized in nonreactive molten alkali metal hydroxides, carbonates, and hypochlorites. Examples of such molten salt routes to mixed transition metal oxides include (Rao and Raveau, 1998)  

We can see from this list that the main advantage of ILs is their ability to serve as an all-in-one solvent-reactant-template system. The function(s) played by 

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MOLTEN SALTS AND ROOM-TEMPERATURE IONIC LIQUIDS 173... 

A.-L. Rollet and C. Bessada, NMR Studies of Molten Salt and Room Temperature Ionic Liquids, in Annual Reports on NMR Spectroscopy, ed. G. A. Webb, Elsevier Ltd., 2013, vol. 78, p. 149. 

Weiss VC (2010) Guggenheim s rule and the enthalpy of vaporizatimi of simple and polar fluids, molten salts, and room temperature ionic liquids. J Phys Chem B 114 9183—9194... 

Solvents may be classified according to their physical and chemical properties at several levels. The most striking differences among Uquids that could be used as solvents are observed between molecular liquids, ionic liquids (molten salts or salt mixtures, room-temperature ionic liquids), and metals. They can be considered as extreme types, and represented as the three vertices of a triangle (Tremillon, 1974) (see Fig. 1.2). Intermediate types or mixtures can then be located along edges or within the triangle. The room-temperature ionic liquids (see later. Section 8.3), which... 

What constitutes an ionic liquid, as distinct from a molten salt It is generally accepted that ionic liquids have relatively low melting points, ideally below ambient temperature [1, 2]. The distinction is arbitrarily based on the salt exhibiting liquidity at or below a given temperature, often conveniently taken to be 100 °C. However, it is clear from observation that the principle distinction between the materials of interest today as ionic liquids (and more as specifically room-temperature ionic liquids) and conventional molten salts is that ionic liquids contain organic cations rather than inorganic ones. This allows a convenient differentiation without concern that some molten salts may have lower melting points than some ionic liquids . 

So far, there have been few published simulation studies of room-temperature ionic liquids, although a number of groups have started programs in this area. Simulations of molecular liquids have been common for thirty years and have proven important in clarifying our understanding of molecular motion, local stmcture and thermodynamics of neat liquids, solutions and more complex systems at the molecular level [1 ]. There have also been many simulations of molten salts with atomic ions [5]. Room-temperature ionic liquids have polyatomic ions and so combine properties of both molecular liquids and simple molten salts. 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

Commonly is used a short term ionic liquid instead of room temperature ionic liquid or room temperature molten salt , which makes no distinction between salts liquid at room temperature and those liquid below 100°C. 

Ionic liquids are also sometimes referred to as molten salts, nonaqueous ionic liquids (NAILs) or room temperature ionic liquids, and all of these names are entirely valid. The term molten salt is now used less frequently, and generally... 

Ionic liquids are, quite simply, liquids that are composed entirely of ions. Thus, molten sodium chloride is an ionic liquid a solution of sodium chloride in water (a molecular solvent) is an ionic solution. The term ionic liquids was selected with care, as it is our belief that the more commonly used phrase molten salts (or simply melts) is referential, and invokes a flawed image of these solvents as being high-temperature, corrosive, viscous media (cf. molten cryolite). The reality is that room-temperature ionic liquids can be liquid at temperatures as low as — 96°C, and are typically colorless, fluid, and easily handled. To use the term molten salts to describe these novel systems is as archaic as describing a car as a horseless carriage. Moreover, in the patent and recent academic literature, ionic... 

The term ionic liquid (IL) refers to a class of liquids that are composed solely of ions. It is a synonym of molten salt. Although molten salt imphcitly means a high-temperature hquid that is prepared by melting a crystalline salt, IL includes a new class of ionic compounds that are liquids at the ambient temperature [1]. Thus, IL in a narrow sense often stands for room-temperature ionic liquid (RIL). In the present chapter, IL is used in a broader sense and, if necessary, RIL is used to clarify that it is liquid at the ambient temperature. The history of ILs has aheady been reviewed [2]. 

In technical processes, several high-temperature molten salts are employed for electrocoating, and the morphology of the deposit is strongly influenced by the composition of the baths. Some attempts have been made to deposit Nb and Ta from ionic liquids [21, 22]. In [21] the authors focused on the electrodeposition of AlNb alloys from room-temperature ionic liquids containing both AICI3 and chlorides of Nb. 

Ionic liquids (either molten salts or room temperature only ionic bonds) and... 

Recently, room-temperature ionic liquids (molten salts) have been extensively studied in order to replace volatile organic solvents by them in electrochemical devices such as batteries. Interest in these materials is stimulated by their properties (e.g., high ionic conductivity, good electrochemical stability, and low volatility). Among these properties, the low volatility is the most critical for ensuring the long-term stability of electrochemical devices. Room-temperature ionic liq-... 

At present, ionic liquids, also known as room-temperature ionic liquids, nonaqueous ionic liquids, molten salts, liquid organic salts, and fused salts, are considered to be the new generation of solvents. In chemical abstracts, they can be found under the headings ionic liquid or liquids ionic. Publications on ionic liquids are increasing in number. 

This principle serves as the basis for a number of models of fused salt systems. Perhaps the best known of these is the Temkin model, which uses the properties of an ordered lattice to predict thermodynamic quantities for the liquid state [79]. However, certain other models that have been less successful in making quantitative predictions for fused salts may be of interest for their conceptual value in understanding room temperature ionic liquids. The interested reader can find a discussion of the early application of these models in a review by Bloom and Bockris [71], though we caution that with the exception of hole theory (discussed in Section II.C) these models are not currently in widespread use. The development of a general theoretical model accurately describing the full range of phenomena associated with molten salts remains a challenge for the field. 

Room-temperature ionic liquids are the promising electrolytes for the electrodeposition of various metals because they have the merits of both organic electrolytes and high-temperature molten salts. Ionic liquids can be used in a wide temperature range, so temperatures can be elevated to accelerate such phenomena as nucleation, surface diffusion and crystallization associated with the electrodeposition of metals. In addition the process can be safely constracted because ionic liquids are neither flammable nor volatile if they are kept below the thermal decomposition temperature of the organic cations. 

Molten salts at room temperature, so-called ionic liquids [1, 2], attracting the attention of many researchers because of their excellent properties, such as high ion content, liquid-state over a wide temperature range, low viscosity, nonvolatility, nonflammability, and high ionic conductivity. The current literature on these unique salts can be divided into two areas of research neoteric solvents as environmentally benign reaction media [3-7], and electrolyte solutions for electrochemical applications, for example, in the lithium-ion battery [8-12], fuel cell [13-15], solar cell [16-18], and capacitor [19-21],... 

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