Eutectic mixtures, definition

As an example, liquefied mixtures are easily formed by using some amino acids protected with acetyl, Boc-, Fmoc- and Z-groups. Some authors have called the resulting systems eutectic mixtures , but this term should be reserved for the textbook definition as the composition of minimum melting point that freezes isothermally at the eutectic temperature. Hence we refer to them as eutectic melts . 

The terminal numbers with potassium, rubidium, and csesium nitrates represent the b.p. of sat. soln. at nearly normal press. for sodium nitrate the corresponding value is 67 6 (119°). Determinations of the solubility of sodium nitrate have been made by G. J. Mulder, Earl of Berkeley, A. Ditte, L. Maumene, A. fitard, etc.30 The solubility curve of sodium nitrate has been carried upwards 781 (180°), 83 5 (220°), 915 (225°), and 100 (313°), the last-named temp, represents the m.p. of the salt. According to L. C. de Coppet, the eutectic or cryohydric temp, of sodium nitrate is —18"5°, and the eutectic mixture is not a definite hydrate, NaN03.7H20, as A. Ditte once supposed. A. fitard represents the solubility S... 

These ai gumente have led Guthrie to renounce the hypothesis of definite cryohydrates and to propose, to denote these substances, the name of eutectic mixtures, which is generally employed to-day. 

As soon as we decrease below 6 the temperature of the system whose mean composition is S, this system must form a heterogeneous mixture consisting of the mixed crystals of composition fi, and of the mixed aj crystals of composition fj, therefore, if we continue to cool our liquid, it will entirely freeze furnishing such a solid mixture this mixture is produced in the same way as the eidectic mixtures studied in Art. 207 like them, it has a definite mean composition like them, it is a heterogeneous mixture of two kinds of crystals only these cr3rstals, instead of being of definite chemical kinds, are mixed crystals each of the two kinds of mixed crystals enclosed in the eutectic mixture has, furthermore, a fixed composition. 

Pure substances and eutectic mixtures solidify and melt at definite temperatures dE, which differ from substance to substance and are barely dependent on the pressure. The best known example of this is water which at atmospheric pressure, freezes at E = 0 °C. This releases the fusion enthalpy of hE = 333kJ/kg. When a solid body melts the enthalpy of fusion must be supplied to the solid as heat. 

There can be a possibility that the substance is a eutectic mixture of two or more compounds. A eutectic mixture has a definite composition and melts sharply , that is, at a constant temperature, just as a pure compound does. The chance of a given mixture containing two or more compounds in just the proportion to give a sharp melting eutectic mixture is remote. All the same, to remove any doubt in this regard, mixed melting points should be determined for mixtures of more than one composition. 

Now what happens if a melt with a eutectic composition of x is cooled A Uquid with this composition will solidify as a whole at a single definite temperature (like a pure substance). This means that none of the components have separated out before. A heterogeneous mixture has been formed of simultaneously precipitated a and p mixed crystals that also exhibits a total composition of Jt (for simplicity, the lever rule is not drawn here). In contrast to all the others, the eutectic mixture does not need to be cooled slowly in order to have conditions for equilibrium and one obtains a uniform and very fine-grained structure (microcrystals). 

Just taking a quick look at the different chapters, one can realize which areas of each field are mature and which can evolve immediately. Although it is very difficult to venture a general trend for the whole area, we could emphasize that there is not a tmly enantioselective version for the mono-activated hydrogen autotransfer reaction. The use of first-row transition metals is almost an unexplored Blue Ocean , in all aspects. Furthermore, the possible impact of green neoteric solvents, including deep eutectic mixtures, supercritical fluids, and bio-based solvents, on the hydrogen transfer process is definitely unknown. 

Silver Arsenides.—A study of the system Ag-As gives no evidence of the existence of any definite compound of the two elements.10 When the mixtures were heated in sealed tubes it was observed that the addition of silver lowered the melting point of arsenic to a eutectic point... 

By a similar usage in petrology, a euleeltc is a discrete mixture of two or more minerals, in definite proportions, which have simultaneously crystallized front the mutual solution of their constituents The eutectic point is the lowest temperature at any given pressure at which the above physical-chemical process may lake pluce, The eutectic ratio is the ratio hy weight of two minerals dial originate bv the above process. 

According to R. Boulouch, the f.p. curve of varying proportions of phosphorus and sulphur associated by fusion at temp, below 100° consists of two lines, Fig. 51, which cut sharply at the eutectic temp., 9-8° and 22-8 per cent, of sulphur. Hence, there is no evidence of the formation of a definite compound of the two elements below 100°. Mixed crystals, or solid soln., rich in sulphur are formed, and these are isomorphous with octohedral sulphur similarly, mixed crystals, or solid soln., rich in phosphorus, are isomorphous with phosphorus. F. Isambert found that when a mixture of phosphorus, even with a large excess of sulphur, is distilled at 100° in vacuo, all the phosphorus distils over, and a residue of sulphur remains. H. Giran heated mixtures of the two elements in sealed tubes at about 200°, and... 

Fig. 1.13. Temperature as a function of the concentration of water-glycerine mixture at which phase transformations occur (Figure 14 from [1.10]) Definitions by Luyet AE, formation of small crystals or mo lecular groups E, eutectic point EB, formation of clusters R, eruptive recrystallization G, glass transition...

Recent high-temperature DTA experiments yielded the expected region of two liquids in the metal-rich portion above 1950 °C28),but neither the exact composition of the monotectic (liquid 1) nor that of the coexisting liquid 2 is known. The DTA results of a successful experiment with a mixture of Mo and M02.06S3, of 18 at.% S composition, definitely showed the eutectic temperature to be 1620 °C, the monotectic temperature to be 1950 °C, and a third effect at 2050 °C, which may indicate a homogeneous liquid above that temperature. 

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