Phase diagram phosphate

Jameson, R. F. Salmon, J. E. (1954). Aluminium phosphates Phase-diagram and ion-exchange studies of the system aluminium oxide-phosphoric oxide-water at 25 °C. Journal of the Chemical Society, 4013-17. 

Diphasic liquid systems used in CCC may have a wide variety of polarities. The most polar systems are the ATPS made by two aqueous-liquid phases, one containing a polymer, for example, polyethylene glycol (PEG), the other one being a salt solution, for example, sodium hydrogen phosphate. The less polar systems do not contain water there can be two-solvent systems, such as heptane/acetonitrile or dimethylsulfoxide/hexane systems or mixtures of three or more solvents. Intermediate polarity systems are countless since any proportion of three or more solvents can be mixed. Ternary phase diagrams are used when three solvents are mixed together. 

The IL is mainly located in the upper phases of the ATPS. The lower phases contain the phosphate salt. Water is partitioning almost evenly between the two-liquid phases. By definition, all initial compositions belonging to the same tie-line split into two liquid phases of identical composition only the volume amounts (and the phase ratios) change. Since the tie-lines are, by chance, almost parallel to the water hypotenuse, the phase diagram clearly shows that the chemical composition of the two liquid phases crucially depends on the water content of the system. 

Silica and aluminum phosphate have much in common. They are isoelec-tronic and isostructural, the phase diagrams being nearly identical even down to the transition temperatures. Therefore, aluminum phosphate can replace silica as a support to form an active polymerization catalyst (79,80). However, their catalytic properties are quite different, because on the surface the two supports exhibit quite different chemistries. Hydroxyl groups on A1P04 are more varied (P—OH and A1—OH) and more acidic, and of course the P=0 species has no equivalent on silica. The presence of this third species seems to reduce the hydroxyl population, as can be seen in Fig. 21, so that Cr/AP04 is somewhat more active than Cr/silica at the low calcining temperatures, and it is considerably more active than Cr/alumina. 

Crytal chemitry. Solid solutions of lead phosphate compounds with structures like that of palmierite ((K,Na)2Pb(S04)2) exhibit transition sequences that are well modeled by Landau-Ginzburg excess free energy expressions. Systems that have been especially heavily studied include Pb3(Pi (As (04)2 (Toledano et al. 1975, Torres 1975, Bismayer and Salje 1981, Bismayer et al. 1982, 1986 Salje and Wruck 1983) and (Pbi jcA c)3(P04)2, where A = Sr or Ba (Bismayer et al. 1994, 1995). The phase diagram for the phosphate-arsenate join is not completely mapped, but Bismayer and collaborators have identified a series of transitions for the P-rich and the As-rich fields. The structure consists of two sheets of isolated (P,As)04-tetrahedra with vertices pointing towards each other and a sheet of Pb atoms in the plane of the apical oxygen atoms. Layers of Pb atoms lie between these tetrahedral sheets (Fig. 18) (Viswanathan and Miehe 1978). 

Three possibilities exist when a salt with a polyphosphate x-ray pattern crystallizes from a melt containing an excess of phosphorus pentoxide. 1. The phosphorus pentoxide is incorporated into the polyphosphate chains converting the chains to crystalline ultraphosphates. 2. The excess phosphorus pentoxide does not enter the polyphosphate crystal structure, but forms an amorphous phase between the crystals of polyphosphate. The amorphous phase is not detected by x-ray. 3. The excess phosphorus pentoxide does not enter the crystal structure of the polyphosphate, but forms as an ultraphosphate between the crystalline polyphosphate crystals as a eutectic phase. (This latter case is precisely what happens in the calcium sodium ultraphosphate system from which calcium phosphate fibers are grown (21) and the phase diagram of Hill et. al. is obeyed as it should be.)... 

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