Molten hydrated salts

Another method for the estimation of the intrinsic volumes of electrolytes, independent of values of the ionic radii, was proposed by Pedersen et al. [53], who employed the molar volume of the molten alkali metal halides, extrapolated to ambient temperatures, as a measure of their intrinsic volumes in aqueous solutions, but the extrapolation is quite long. A variant of this idea is to use the molar volumes of molten hydrated salts, proposed by Marcus [54], where the temperature extrapolation to 25°C is much shorter. It is then necessary to subtract the volume of the water of hydration, which is n times the molar volume of electrostricted water, 15.2 cm mok at 25°C [55], from the extrapolated molar volume of the undercooled molten hydrated salt containing n water molecules per formula unit of the salt. A cogent method, applicable to highly soluble salts, was proposed by Marcus [56]. The volumes considered, applied to aqueous solutions, are intrinsic, so they should be independent of the concentration c and to a certain extent also of the temperature T. The partial molar volume of an electrolyte, V c, T), describes the volume that it actually occupies in the solution and does not include the volume of the water. Therefore, a fairly short extrapolation of the hnear 25°C) from c = 3M to such high concentrations at which all of the solvent is as closely packed as possible (completely electrostricted) is equivalent to considering the electrolyte as an undercooled molten hydrated salt... 

The volumetric properties density, p, isobaric expansibility, p, and molar volume, V, of molten hydrated salts at the corresponding temperature T = TlTm, taken from [60], are shown in Table 5.5. 

Jain SK (1978) Density, viscosity, and surface tension of some single molten hydrated salts. J Chem Eng Data 23 170-173... 

Ramana KV, Sharma RC, Gaur HC (1986) Volumetric properties of molten hydrated salts. 7. Mixtures of ferric nitrate nonahydrate with hydrates of calcium, cadmium, zinc, and magnesium nitrates. J Chem Eng Data 31 288-291... 

Bhatia K, Sharma RC, Gaur HC (1978) Conductivity of molten hydrated salts manganese nitrate hexahydrate -1- ammonium nitrate system. Electrochim Acta 23 1367-1369... 

For this preparation, it is particularly necessary that the sodium acetate should be free from traces of water. The anhydrous material can be prepared by gently heating the hydrated salt (CHsCOONa,3HjO) in an esaporating-basin over a small Bunsen flame. The salt dissolves in its water of ciystallisation and resolidifies as this water is driven off further heating then causes the anhydrous material to melt. Stir the molten anhydrous material to avoid charring, and then allow it to cool in a desiccator. Powder the cold material rapidly in a mortar, and bottle without delay. 

In organic solvents Many of the free acids and a few of the salts are very soluble in organic solvents, especially if the latter contain oxygen. Ethers, alcohols, and ketones (in that order) are generally the best solvents. The dehydrated salts sometimes dissolve readily in organic solvents the hydrated salts are insoluble. Both 12-molybdophosphoric acid and its cobalt salt can be dissolved and recovered intact from molten benzoic acid solutions5. ... 

S. Fischer, H. Leipner, E. Brendler, W. Voigt, and K. Fiseher, Molten inorganie salt hydrates as eellulose solvents, in M. A. El-Nokaly and H. A. Soini (Eds.), Polysaccharide Applications, Cosmetics and Pharmaceuticals, Ameriean Chemical Society, Washington DC, 1999, pp. 143-150. 

Cobalt ion, Co(H20)6 , in solution and in hydrated salts is red or pink in color. Cobalt chloride, CoCb-bHaO, forms red crystals, which when dehydrated change into a deep blue powder. Writing made with a dilute solution of cobalt chloride is almost invisible, but becomes blue when the paper is warmed, dehydrating the salt. Cobalt oxide, CoO, is a black substance which dissolves in molten glass to give it a blue color cobalt glass). 

Jain SK, Prashar S, Jain SK (1999) Physical properties of some molten hydrated calcium salts. Indian J Chem 38A 778-782... 

Sharma SK, Jotshi CK, Singh A (1984) Viscosity of molten sodium salt hydrates. J Chem Eng Data 29 245-246... 

If the metallisable dye is insoluble in water, a miscible solvent such as ethanol or ethylene glycol may be added. Polar solvents such as formamide or molten urea have sometimes been preferred. It is likely that such solvents will preferentially displace water molecules and coordinate with the chromium (III) ion as the first step in the reaction. If colourless organic chelates of chromium, such as those derived from oxalic or tartaric acid, are used instead of or in addition to hydrated chromium (III) salts, the difficulty of replacing the strongly coordinated water molecules in the first stage of the reaction is eliminated. In this way the initial reaction can be carried out at high pH without contamination by the precipitation of chromium hydroxide. Use of the complex ammonium chromisalicylate (5.12) in this connection should also be noted (section 5.4-1). 

This model may possibly be adapted to metal-water thermal explosions if one assumes that there are reactions between the molten metal and water (and substrate) that form a soluble salt bridge across the interface between the two liquids. This salt solution would then be the material which could superheat and, when finally nucleated, would initiate the thermal explosion. As noted, the model rests on the premise that there are chemical reactions which occur very quickly between metal and water to form soluble products. There is experimental evidence of some reactions taking place, but the exact nature of these is not known. Perhaps, in the case of aluminum, the hydroxide or hydrated oxides form. With substrates covered by rust or an inorganic salt [e.g., Ca(OH)2], these too could play an important role in forming a salt solution. 

The electrolyte concentration is very important when it comes to discussing mechanisms of ion transport. Molar conductivity-concentration data show conductivity behaviour characteristic of ion association, even at very low salt concentrations (0.01 mol dm ). Vibrational spectra show that by increasing the salt concentration, there is a change in the environment of the ions due to coulomb interactions. In fact, many polymer electrolyte systems are studied at concentrations greatly in excess of 1.0 mol dm (corresponding to ether oxygen to cation ratios of less than 20 1) and charge transport in such systems may have more in common with that of molten salt hydrates or coulomb fluids. However, it is unlikely that any of the models discussed here will offer a unique description of ion transport in a dynamic polymer electrolyte host. Models which have been used or developed to describe ion transport in polymer electrolytes are outlined below. 

Prospects for TR Electrolyte SBs. In view of the harmful effects often cited in the literature of even small traces of water on the operation of non-aqueous batteries with alkali metal anodes, it might be supposed that electrolytes of the TR composition cannot be applied in such batteries. This same idea may dominate when molten salt SBs are considered. Such a general conclusion cannot be justified. A dilute solution of water in a salt has the structure either of this salt proper or its adjacent hydrate, and the energy, properties and reactions of this water are quite different from those of pure water or of dilute solutions of various compounds in it. On the other hand, a small amount of water in the electrolyte system will decrease its melting point and increase its conductivity. Mixtures of water with such liquids as some alcohols or dioxane and other aprotic and even proton-forming substances, may open new prospects for... 

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