Eutectic INDEX

Law D, Wang W, Schmitt EA, Long MA. 2002. Prediction of poly(ethylene) glycol-drug eutectic compositions using an index based on the van t Hoff equation. Pharm. Res. 19(3) 315-321. 

Orthophosphorio Acid —Preparation—Physical Properties of Solid Hydrates of P2Os—Solubilities, Melting-points and Eutectics of the System HjP04-Ha0—Densities of Aqueous Solutions—Vapour Pressures—Conductivities of Concentrated and Dilute Solutions—Viscosities—Refractive Index—Basicity and Neutralisation of the Phosphoric Acids—Constitution... 

Molecular Weight Boiling Point Melting Point Freeze Point (eutectic) Specific Heat Refractive Index Flash Point Fire Point Autoignition Point... 

Despite the above observation, we discovered only a slight gradation in composition from top to bottom in the sample via refractive index studies. The eutectic microstructures we present below are observed throughout their respective specimens with only minor variations in scale and primary-phase abundance. 

All known investigations of the relative acidic properties of ionic melts are based just on the determination of the equilibrium constants of reaction (1.3.6) in these media. Since the applicability of these data for estimating the equilibrium parameters and conditions was not checked experimentally, there was no reason to doubt the correctness of the use of equilibrium (1.3.6) as an indicator one for f estimations. Indeed, we shall now consider the data presented in Ref. [169], where the acidic properties of the KCl-LiCl eutectic at 600 °C were investigated using equilibrium (1.3.6). The shift of the oxoacidity scale as compared with the KCl-NaCl equimolar mixture was found to be close to 8. Such a considerable difference in acidities for KCl-NaCl and KCl-LiCl melts is unexpected, since the index of the Li20 dissociation constant (pK) ... 

High-temperature ionic solvents are known to contain relatively high total concentrations of cations (e.g. in the KCl-LiCl eutectic, the concentration of Li+ is approximately equal to 8.5 mol kg-1 of the melt). Usually, cation-anion complexes in molten salts are characterized by co-ordination numbers of the order of 4-6. This means that the maximal consumption of acidic cations does not exceed 0.4-0.6 mol kg-1 in diluted solutions with concentrations close to 0.1 mol kg-1. This estimate is considerably lesser than the initial concentration of acidic cations in the pure melt. In the case of the KCl-LiCl eutectic melt, this consumption is only of the order of 5-7%, and the value of NMe+ in equation (1.3.16) may be assumed to be constant. Therefore, for each ionic solvent of the second kind (kind II) the denominator in equation (1.3.16) is a constant which characterizes its acidic properties. We shall define p/L = -log /L to be the relative measure of acidic properties of a solvent and call it the oxobasicity index of ionic melt [37, 162, 181]. Since the direct determination of the absolute concentration of free oxide ions in molten salts is practically impossible, the reference melt should be chosen— for this melt, /L is assumed to be 1 and p/L = 0. The equimolar KCl-NaCl... 

As follows from Part 1, the ionic melts based on molten alkali metal halides are referred to the solvents of the Second Kind (Kind II), and, therefore, the acid-base ranges for these media are half-open (see Fig. 1.1.1, scheme N3). Therefore, to form an idea of the relative oxoacidic properties of the studied chloride melts it is enough to know their oxobasicity indices. The necessary experimental parameters obtained at 600 °C are presented in Table 1.3.1. The data in this Table show that the KCl-LiCl eutectic melt possesses appreciable acidic properties, the corresponding oxobasicity index being equal to 3.2. 

Investigations of oxide solubilities in the molten KCl-LiCl eutectic at 700 °C have been reported in Refs. [162, 189, 190]. Oxide solubilities in this melt were found to be considerably larger than those in the equimolar KCl-NaCl mixture at the same temperature (see p. 296). The value of the p/VMeO shift as compared with the KCl-NaCl was calculated to be close to 3.4 logarithmic units, this value being the oxobasicity index, p/Kci-ucts = 3.4. It is remarkable that the shifts are so close to each other, which demonstrates the applicability of the parameter introduced for the melt acidity estimations—at least, for calculations of the solubility parameters. Aside from the solubility investigations, the equilibrium constant of the addition of O2- to dichromate ion, Cr202- in the KCl-LiCl eutectic at 700 °C was performed in Ref. [163]. The shift of pK value in this melt as compared with the KCl-NaCl equimolar... 

According to Fig. 1.3.4, in order to determine the oxobasicity index of NaBr with respect to the CsCl-KCl-NaCl eutectic it is necessary to know, at least, two experimental magnitudes. The first set is the oxobasicity index of NaCl, and the difference of pK of CO dissociation in molten NaBr and NaCl. The second set is the difference of pKof CO > dissociation in molten CsBr-KBr-NaBr and CsCl-KCl-NaCl and the difference of pPMeo in molten CsBr-KBr-NaBr and NaBr. The former case is obviously more convenient since the investigation of the oxide solubility products in molten bromides and iodides is more complicated than the determination of the pK of CO in the said melts. 

Now let us to estimate the equilibrium molarity of the constituent acidic cations in the melt, e.g., the eutectic KCl-LiCl melt (0.4 0.6) contains 8.5 mole of Lfr per 1 kg. Usually the ionic complexes in melts are characterized by the coordination number 4-6. For the solution of O of the 0.1 mole/kg concentration, the maximum possible quantity of fixed LU concentration may be estimated as 0.4-0.6 mole/kg, i.e., efficiently lower than 8.5. In this case the change of actual LF concentration is approximately equal to 5-7% and m,.[5+ in this case may be suggested as constant. Therefore, for each melt the sum in the denominator of [10.4.12] is the constant reflecting its acidic properties. So, pli= -loglj is a measure of melt acidities and may be denoted as the oxobasicity index of the melt. Since the determination of the absolute concentration of free O is practically impossible one should choose the standard melt , for which Ij is conditionally equal to 1 and pl =0. It is reasonable to choose the equimolar mixture KCl-NaCl as the standard melt , since this melt is most frequently investigated. Further, one should choose standard equilibria and formulate the non-ther-modynamic assumptions which usually postulate that the constant of the standard equilibrium calculated using absolute oxide ion eoncentrations remains flie same for all other melts. 

Vieillard P (1987) A new set of values for Pauling s ionic radii. Acta Cryst B43 513-517 Iwadate Y, Fukushima K (1995) Electronic polarizability of a fluoride ion estimated by refractive indexes and molar volumes of molten eutectic LiF-NaF-KF. 1 Chem Phys 103 6300-6302... 

The structure of crazes in bulk specimens was studied by Kambour [15], who used the critical angle for total reflection at the craze/polymer interface to determine the reliactive index of the craze, and showed that the craze was roughly 50 per cent polymer and 50 per cent void. Another investigation involved transmission electron microscopy of polystyrene crazes impregnated with an iodine-sulphur eutectic to maintain the craze in its extended state [33, 34]. The structure of the craze was clearly revealed as fibrils separated by the voids that are responsible for the overall low density. 

Although this index has been developed to describe drug-PEG eutectic systems, it is expected to apply with reasonable accuracy in a variety of similar drug-semicrystalline polymer systems. 

Figures 5a and 5b show the growth of benzil LlkT = 6). Figure 5a shows pure benzil and Fig. 5b shows the benzil-azobenzene eutectic. Both phases are present in Fig. 5b and both are bounded by low index faces, despite the diffusion processes involved. The growth here is quite anisotropic.

Literature data, A chosen derivative can be considered as advantageous if the literature pves a maximum number of identification constants for a maximum number of substances of the considered type of compound. We should not forget that the final stage of identification is the interpretation of the data obtained. Such determined values as melting point, eutectic temperature, and refractive index of the melt are compared with the values given in the literature, and a substance is sought the constants of which correspond to known data. In case we are unable to find the values for the substance under consideration in the literature, it is necessary to prepare a derivative of an authentic substance and to compare its properties with those of the analyzed substance. 

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