Amorphous supersaturated solid solution

Cocco et al. [54] discuss the preparation of metallic glass, while copper-titanium, aluminum-titanium, and palladium-titanium systems in particular are prepared under a controlled atmosphere with hydrogen and argon. Components of Nb-Ni and Nb-Y have also been described [55]. Amorphous Ni-Ti alloys have been prepared by Schwarz et al. [56], while Ni-Ga, Ni-Ge, Ni-In, and Ni-Sn has been synthesized in supersaturated solid solutions [57]. Fe, Co, Ni-Ta-alloys are described by Lee and Yang [58], while FeSi2 doped with Co or Al for thermoelectric material is also mentioned [59]. 

Mo are single phase, supersaturated solid solutions having an fee structure very similar to that of pure Al. Broad reflection indicative of an amorphous phase appears in deposits containing more than 6.5 atom% Mo. As the Mo content of the deposits is increased, the amount of fee phase in the alloy decreases whereas that of the amorphous phase increases. When the Mo content is more than 10 atom%, the deposits are completely amorphous. As the Mo atom has a smaller lattice volume than Al, the lattice parameter for the deposits decreases with increasing Mo content. Potentiodynamic anodic polarization experiments in deaerated aqueous NaCl revealed that increasing the Mo content for the Al-Mo alloy increases the pitting potential. It appears that the Al-Mo deposits show better corrosion resistance than most other aluminum-transition metal alloys prepared from chloroaluminate ionic liquids. 

In polymorphous crystallization, an amorphous solid crystallizes into a single crystalline phase with different structure but with same chemical composition as the amorphous phase. This reaction can only occur in concentration ranges near to those of stable compounds (Ci in Fig. 2) or pure elements (C2) and needs only single jumps of atoms across the crystallization front. The polymorphous crystallization reaction (reaction (1) or (2)) may produce a single compound phase (P) or a supersaturated solid solution phase (a), as shown... 

In primary crystallization, amorphous phase crystallizes into a phase with different composition (C4 in Fig. 2) in the first step (this can be either a supersaturated solid solution... 

Recent advances in the scientific understanding of the in vivo performance, the role of supersaturation, and advanced manufacturing technologies will likely render solid solutions and solid dispersions more commercially successful. Excipients used in solid solutions and solid dispersions include polyvinylpyrrolidone, PEG 4,000, PEG 8,000, Gelucire 50/13, and Gelucrie 44/14. Solid solutions are molecular mixtures of a drug dissolved in a solid at a concentration below supersaturation and are thus thermodynamically stable, compared to solid dispersions, which are thermodynamically unstable amorphous drug dispersed within a solid matrix susceptible to crystallization. 

The Ostwald step rule, or the mle of stages, postulates that the precipitate with the highest solubility (i.e., the least stable solid phase) will form first in a consecutive precipitation reaction. This mle is very well documented mineral formation via precursors and intermediates can be explained by the kinetics of the nucleation process. The precipitation sequence results because the nucleation of a more soluble phase is kinetically favored over that of a less soluble phase because the more soluble phase has the lower solid-solution interfacial tension (7cw) than the less soluble phase (equation 50). In other words, a supersaturated solution will nucleate first the least stable phase (often an amorphous solid phase) because its nucleation rate is larger than that of the more stable phase (Figure 13.26). While the Ostwald step mle can be explained on the basis of nucleation kinetics, there is no thermodynamic contradiction in the initial formation of a finely divided precursor. 

It seems likely that, amorphous phase formation by mechanical alloying of the mixture of elemental metal powders occurs in four stages (i) formation of very fine composite powder whereby particles my be understood as diffusion couples (ii) formation of solid solution (ii) collapse of supersaturated solution to the amorphous phase and (iv) gradual dissolution of residual crystallites (dispersoids) into the amorphous matrix. 

Nickel deposits have unique magnetic properties, except deposits containing more than 8 percent phosphorus are essentially nonmagnetic. In Ni-P coatings, phosphorus is present as supersaturated solution in fine microcrystalline solid solution, bordering on amorphous or liquid-like (glass-like) metastable structure, and this phosphorus is... 

As shown in Fig. 2 [37], and also in the work of Barraclough and Hall [34], moisture uptake onto sodium chloride as a function of relative humidity is reversible as long as RH0 is not attained. This is evidence that actual dissolution of water-soluble crystalline substances does not occur below RH0. This is consistent with thermodynamic rationale that dissolution below RHo would require a supersaturated solution (i.e., an increased number of species in solution would be necessary to induce dissolution at a relative humidity below that of the saturated solution, RH0). In this regard, one should only need to consider the solid state properties of a purely crystalline material below RH0. As will be described, other considerations are warranted for a substance that contains amorphous material. 

Large concentrations of Fe + develop in the soil solution in the weeks following flooding, often several mM or tens of mM (Figure 4.5). Calculations with chemical equilibrium models show that the ion activity products of pure ferrous hydroxides, carbonates and other minerals are often exceeded 100-fold (Neue and Bloom, 1989). Evidently precipitation of these minerals is inhibited, probably as a result of adsorption of foreign solutes, such as dissolved organic matter and phosphate ions, onto nucleation sites (Section 3.7). However, once a sufficient supersaturation has been reached there is a rapid precipitation of amorphous solid phases, which may later re-order to more crystalline forms. Only a small part of the Fe(II) formed in reduction remains in solution the bulk is sorbed in exchangeable forms or, eventually, precipitated. 

When supersaturated fresh gallbladder bile (or model bile) is centrifuged to remove solid crystalline and amorphous precipitates, and supernatant vesicles, and the resultant isotropic (one phase) solution maintained in a dust-free environment at 37 °C and examined daily by light microscopy, cholesterol crystals can be observed to precipitate. The time taken for these solid cholesterol... 

---