Solubility peritectic temperature

Phase diagrams are the roadmaps from which the number of phases, their compositions, and their fractions can determined as a function of temperature. In general, binary-phase diagrams can be characterized as exhibiting complete or partial solid solubility between the end members. In case of the latter, they will contain one or both of the following reactions depending on the species present. The first is the eutectic reaction is which a liquid becomes saturated with respect to the end members such that at the eutectic temperature two solids precipitate out of the liquid simultaneously. The second reaction is known as the peritectic reaction in which a solid dissociates into a liquid and a second solid of a different composition at the peritectic temperature. The eutectic and peritectic transformations also have their solid state analogues, which are called eutectoid and peritectoid reactions, respectively. 

If an unsaturated solution of composition g is heated, anhydrous salt will crystallize at/ if it is cooled, the decahydrate will crystallize at h. It is possible to supercool the solution to a temperature below /i then the heptahydrate will crystallize at i Fig. 15-15(b). The curve e b is the solubility curve for the heptahydrate, Na2S04 7H20. The peritectic temperature for anhydrous salt-heptahydrate-saturated solution is at 24.2 °C. In Fig. 15.15(b), the dashed lines are the curves for the decahydrate. The solubility curve for the heptahydrate lies for the most part in the region of stability of solid decahydrate-saturated solution. Therefore the equilibrium between solid heptahydrate and its saturated solution is a metastable one the system in such a state can precipitate the less soluble decahydrate spontaneously. 

A zone comprising (a-Pb + liquid) phases with maximum solubility of 0.1 wt% Ca in Pb is formed in the system at the peritectic temperature of 328 °C. At room temperature, the solubility of Ca is 0.01 wt%. This 10-fold difference in Ca content is a result of a solid-phase recrystallization process, which changes the microstructure of the alloys and hence its mechanical properties. 

Pure hydrates are crystalline ice-like solids usually prepared from water or ice and an appropriate guest species. Hydrates of water-soluble guests have well-defined phase diagrams characteristic of two-phase systems with compound formation."." If the hydrate melts congruently, it is simply a matter of freezing a solution of the correct composition to obtain the hydrate. For systems that melt incongruently, the aqueous solution must be quenched below the peritectic temperature and conditioned so that the crystalline hydrate can form on... 

The peritectic temperature Tp is established by bends in the slope of the solubility curve since an equilibrium solid phase and its dissolution enthalpy are different below and above Tp. 

Real crystals are often not in the equilibrium state in aqueous surfactant mixtures. Sometimes, this is true simply because the equilibrium crystal is disordered. In other cases, a nonequilibrium situation exists because the crystal present is not the equilibrium coexisting phase [48]. If a crystal that is not the equilibrium phase is mixed with water, the solubility initially observed will typically be higher than the equilibrium solubility. An excellent illustration of this behavior is found in the sodium sulfate—water diagram (Fig. 5), where the equilibrium coexisting crystal below 32.4°C is the decahydrate (X Wio). A metastable heptahydrate crystal (X W,) also exists in this system, which can be seen from the diagram to be significantly more soluble and have a lower peritectic temperature (23.7 C) than the equilibrium decahydrate. 

Figure 2.10. Examples of binary systems characterized by complete mutual solubility in the liquid state and, depending on temperature and/or composition, partial solubility in the solid state and presenting (in certain composition ranges) an invariant (three-phase) reaction (eutectic in the Cu-Ag, peritectic in the Ru-Ni and Re-Co and eutectoidal in Ti-W (one) and in Th-Zr (two)).

Pb, where retrograde solubility for the solid in equilibrium with the liquid can also occur. As a critical value of n " is approached the liquid forms its own miscibility gap and the diagram then exhibits two forms of liquid invariant reaction, the lower temperature reaction being either eutectic or peritectic, while the higher temperature reaction becomes monotectic. Examples of such systems are Cu-Pb and Cu-Tl. When n becomes even larger, the top of the liquid miscibility gap rises above scale of the graph and there is little solubility of either element in the liquid. Such a diagram is typical of Mg systems such as Mg-Fe or Mg-Mn. 

Fig. 6.3 Schematic phase diagram for lamellar PS-PB diblocks in PS homopolymer (volume fraction 0h). where the homopolymer Mv is comparable to that of the PS block (Jeon and Roe 1994). L is a lamellar phase, I, and I2 are disordered phases, M may correspond to microphase-separated copolymer micelles in a homopolymer matrix. Point A is the order-disorder transition.The horizontal lines BCD and EFG are lines where three phases coexist at a fixed temperature and are lines of peritectic points. The lines BE and EH denote the limit of solubility of the PS in the copolymer as a function of temperature.

The plutonium-uranium ratio in liquid solution was not consistent with that added. There seems little doubt that this discrepancy resulted from the precipitation of two different compounds as the alloy cooled from higher temperatures. Pu2Zn17 decomposes peritectically at 1083° K. to form PuZn8 and liquid (3). Presumably the PuZn8-based three-component form dissolves and reprecipitates on the U2Zn17 matrix near this temperature, as the temperature is lowered. The selected data of P/540 (5) show slightly different slopes for the plots of log solubility vs. reciprocal temperature for Pu-Zn and U-Zn. This variance probably reflects difference in technique by the two groups of experimenters, since it does not show in parallel Pu-Zn and U-Zn experiments by Elliott and coworkers on which that part of P/540 was based. 

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