Salts Melting Between 100 and

Attention is here directed at the low-melting ionic salts Table 5.1 shows the available physicochemical data for the inorganic low-melting salts, gleaned from the relevant tables in Chap. 3 with some additions, and Table 5.2 shows them for the quaternary ammonium salts with a few quaternary phosphonium salts thrown in. 

Ammonium salts constitute a special category, because they are rather unstable in the molten state. The following temperatures have been recorded [41] for the melting 

The transport properties of the inorganic low melting salts can be presented in terms of the Arrhenius-type expressions  

Some structural information is obtained from models that relate bulk properties to the structures. An early attempt to apply this approach was that of Lind et al. [35], who dealt with the Walden product of the molar conductivity A and the viscosity // of molten ILiN BF4, -PFg , and -BPh4 (R = C3 to Cg). This product is rather insensitive to the temperature and was applied to the melts at 250 °C. The hard-sphere model predicted the product At] to be proportional to where r is the radius of the cation. However, only for the R = C3 salts with BF4 and PFg were the predicted values commensurate with the experimental ones, for the other salts the prediction overestimated the product. For such melts with small globular ions the structure is determined mainly by the coulomb forces as for high-melting salts, but with alkyl chains longer than propyl (C3) the thermal movements of these chains clog the interstices in the liquid and obstruct the movement of the ions. 

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Tables 11.1.11.2 and 11.3 [52-548] contain, respectively, 78 records for 67 salts melting below 30°C, 600 records of 553 salts melting between 30 and 100°C and data for a further 149 salts melting between 100 and 112°C. Some late additions are included in the Addendum...

A total of 473 discrete cations are collected in Table 11.5. Forty-seven are found in room-temperature ionic liquids, an additional 350 in ionic liquids. A further 76 are found in salts melting between 100 and 110°C. 

Table 5.1 Temperature of melting, Tm/K, the molar heat of melting, An///kJ moL and the molar heat capacity Cp/J K" moL, and the cohesive energy density, ced/MPa, density, p/g cm", isobaric expansivity, ap/K molar volume, V/cm mol", surface tension, (r/mN m , at 1.1 of highly ionic inorganic salts melting between 100 and 250 °C (370-530 K), from tables in Chap. 3 or as annotated...

Table 11.23 contains nearly 200 structurally characterised salts based on the imidazolium cation (with a further 36 that melt between 100 and 110°C). These cover the conplete range of subtypes, including 1 1, 2 1,1 2 (with two imidazolium moieties connected by linking... 

According to A. Potilitzin, the melting point of trihydrated lithium perchlorate is 95° and, between 98° and 100°, the salt loses approximately two-thirds of its combined water and all the water is lost between 130° and 150° the anhydrous salt melts at 236°, and loses no oxygen at 300° this gas is evolved at about 368°, at 380° the speed of decomposition is rapid—lithium chlorate and chloride are first... 

Tables 11.4 and 11.5 list the constituent anions, [A] , and cations, [cat]" (with those presented in italics found only in salts listed in Table 11.3. that is, with melting temperatures between 100 and ca. 110°C). Anions and cations are grouped together in a pragmatic rational manner, classified according to charge and whether they are aromatic, alicyclic or acyclic. Further classification is somewhat arbitrary, but iV-protonated salts are listed first, then salts containing iV-alltyl and iV-bound substituted alkyl groups, ring-functionalised ions, followed by other materials. The anions and cations are numbered for ease of reference. Figure 11.5 displays the basic structures for the most iii5)ortant series of anions and cations. Where necessary, the structures of other ions or salts are included where first mentioned in the text.

In more recent work, a composition which was claimed to be fusible and melt-extrudable was developed in a joint effort of UNIAX Corp., Santa Barbara, CA, USA, and Neste Oy, Porvoo, Finland, given the tradename PANIPOL [278]. In its typical preparation, a sulfonated P(ANi) salt, a plasticizer, and other "optional additives" are fed into a twin-screw extruder with a typical temperature profile along the screw of between 100 and 180 °C and residence time 5 to 10 mins. The resulting conductive strands are cooled, pelletized and packaged. The conductive pellets are then compounded for such end uses as injection molded articles or extruded films and fibers, or any other conductive thermoplastic products. The authors also claimed to have demonstrated conductive thermosets based on solution-processed PANIPOL. 

According to Goekel,22 this reaction takes place in the following manner Dry ammonium nitrate reacts with calcium hydroxide present in the crude calcium cyanamide to give calcium nitrate, water, and ammonia. The ammonia and water do not escape but are absorbed by the calcium nitrate to give a mixture of hydrated and ammonated salt and also by the ammonium nitrate which is ammono-deliquescent (Diver s solution). These substances melt below 100°C. and provide a solvent in which the reaction between calcium cyanamide and ammonium nitrate may take place. 

Ionic liquids (ILs) are basically salts with poorly coordinated ions, resulting in low melting points. Since low is a relative term (NaCl, for example, is an IL between 801 °C and 1465 °C), chemists use it to refer either to salts which melt below 100 °C, or to salts that are liquid at 25 °C. The latter group is known as room-temperature ionic liquids (RTILs). In most RTILs, one of the ions is organic, with a delocalized charge. Note that ILs are not concentrated salt solutions. They are nonmolecular liquids which contain, in theory, no water (in practice, many ILs contain at least traces of water). 

An ionic liquid is a liquid that consists only of ions and has a melting point below 100 °C. The apparently somewhat arbitrary line drawn between molten salts and ionic liquids at a melting temperature of 100 °C is justified by the possibility to replace water and organic solvents in synthetic applications with salts melting below this temperature. 

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