Freezing eutectic

Conditions on primeval Earth which led to eutectic freezing, and thus to concentration of the HCN solutions... 

Nitroglycerine percentage in eutectic Freezing temperature of eutectic °C Nitroglycerine percentage in eutectic Freezing temperature of eutectic °C... 

Microscopic investigation of the solid formed when a eutectic freezes indicates that it is a mixture of very fine particles of pure A and pure B, rather than a solid solution of A and B. If a solution that has the eutectic composition is cooled, freezing occurs at a single concentration, just like a pure component. A eutectic can be distinguished from a pure component either by microscopic inspection of the solid or by adding one of the pure components. In the eutectic case, the freezing point of the solution will be increased by this addition, rather than decreased as occurs for a pure substance. 

Other mixtures do not freeze at a definite temperature as the molten alloy cools, the constituent which is in excess begins to separate at a definite temperature the temperature continues to fall because the composition of the liquid changes as the result of the separation of the pure metal. When the composition of the liquid becomes that of the eutectic the temperature at which freezing takes place becomes constant, namely, that at which the eutectic freezes. 

This paper reports cryoscopic measurements for NiS04 aqueous solutions in saturated potassium perchlorate solutions (eutectic freezing point 272.99 K, freezing point depressions, AT, are between 0.0673 K and 0.181 K). Thus, the measurements were done with less variation of ionic strength than for measurements done in water. The results of this study are assessed in our discussion of a later paper [58KEN] by the same author. 

This paper reports cryoscopic measurements for NiS04 aqueous solutions in saturated potassium chlorate solution (freezing point 272.55 K) and saturated potassium nitrate solution (freezing point 270.32 K). The eutectic freezing point depressions, AT, are between 0.0296 K and 0.178 K. Thus, together with the measurements reported in [56KEN], the variation in the complexation constant, K, with ionic strength was examined. 

If the melt has eutectic composition from the start (in our example, Xb = 0.6), it will continuously cool imtil it reaches the eutectic freezing temperature. When the mixture s temperature falls below this temperature, a simultaneous precipitation of A and B takes place imtil the entire sample has solidified. Correspondingly, the temperature remains crmstant over a Irmger period of time compared to other mixtures. A micrograph shows a heterogeneous mixture of A and B microcrystals of approximately the same size. 

Another liquid eutectic (freezing point of white phosphorus... 

Arslan Ahmad (removal of arsenic, chromium, fluoride, iron, manganese, pharmaceutical residues, emerging compounds from drinking water, and industrial water treatment for recovery of salts through eutectic freeze crystallization process), KWR Watercycle Research... 

When freshly exposed to air, thallium exhibits a metallic luster, but soon develops a bluish-gray tinge, resembling lead in appearance. A heavy oxide builds up on thallium if left in air, and in the presence of water the hydride is formed. The metal is very soft and malleable. It can be cut with a knife. Twenty five isotopic forms of thallium, with atomic masses ranging from 184 to 210 are recognized. Natural thallium is a mixture of two isotopes. A mercury-thallium alloy, which forms a eutectic at 8.5% thallium, is reported to freeze at -60C, some 20 degrees below the freezing point of mercury. 

Ciyst lliz tion. Low temperature fractional crystallization was the first and for many years the only commercial technique for separating PX from mixed xylenes. As shown in Table 2, PX has a much higher freezing point than the other xylene isomers. Thus, upon cooling, a pure soHd phase of PX crystallizes first. Eventually, upon further cooling, a temperature is reached where soHd crystals of another isomer also form. This is called the eutectic point. PX crystals usually form at about —4° C and the PX-MX eutectic is reached at about —68° C. In commercial practice, PX crystallization is carried out at a temperature just above the eutectic point. At all temperatures above the eutectic point, PX is stiU soluble in the remaining Cg aromatics Hquid solution,... 

The freezing point diagram for the hydrazine—water system (Eig. 1) shows two low melting eutectics and a compound at 64 wt % hydrazine having a melting point of —51.6°C. The latter corresponds to hydrazine hydrate [7803-57-8] which has a 1 1 molar ratio of hydrazine to water. The anomalous behavior of certain physical properties such as viscosity and density at the hydrate composition indicates that the hydrate exists both in the Hquid as well as in the soHd phase. In the vapor phase, hydrazine hydrate partially dissociates. 

Commercial appHcations of calcium chloride and its hydrates exploit one or more of its properties with regard to aqueous solubiUty, hygroscopic nature, the heat gained or lost when one hydrated phase changes to another, and the depressed freezing point of the eutectic solution at a composition of about 30% by weight calcium chloride. 

Na2Cr2 07-2H2 0, which is close to the eutectic composition freezing at —48.2°C. 

Salt Brines The typical curve of freezing point is shown in Fig. II-IIO. Brine of concentration x (water concentration is I-x) will not solidify at 0°C (freezing temperature for water, point A). When the temperature drops to B, the first ciystal of ice is formed. As the temperature decreases to C, ice ciystals continue to form and their mixture with the brine solution forms the slush. At the point C there will be part ice in the mixture /(/i+L), and liquid (brine) /i/(/i-t-L). At point D there is mixture of mi parts eutectic brine solution Di [concentration mi/(mi-t-mg)], and mo parts of ice [concentration mol m -t- mo)]. Coohng the mixture below D solidifies the entire solution at the eutectic temperature. Eutectic temperature is the lowest temperature that can be reached with no solidification. 

Pure ethylene glycol freezes at —I2,7°C, Exact composition and temperature for eutectic point are unknown, since solutions in this region turn to viscous, glassy mass that makes it difficult to determine the true freezing point. For the concentrations lower than eutectic, ice forms on freezing, while on the concentrated, solid glycol separates from the solution. 

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