Solid-solution interactions precipitation

Specifically, he developed relationships for the free energy of mixing of solvent and solute (polymer) molecules with different solute axial ratios (length/width) and solute interaction parameters. In the absence of interactions between solute molecules, the free energy of the system lowers when rodlike molecules precipitate out of solution and form a separate solid phase. This is due to the fact that small water molecules must order themselves around large rodlike macromolecules in solution and therefore the system is most stable when the water molecules and rodlike molecules are separated in space into different phases, such as liquid and solid phases. 

Silver phosphides.—At 400° C. silver and phosphorus-vapour combine to form the diphosphide, AgP2, a grey, crystalline mass.1 White phosphorus dissolves in molten silver, yielding white, crystalline products containing up to 20 per cent, of phosphorus. They are probably solid solutions of silver and phosphorus. Silver phosphide, Ag2P5, is precipitated as a brown, amorphous substance by the interaction of silver nitrate and a solution in liquid ammonia of rubidium phosphide, Rb2P5.2... 

At half of the solidus temperature on the absolute temperature scale (i.e., 1850°C for tungsten), solid-solution alloys lose much of their strength, and dispersion-strengthened or precipitation-hardened alloys are significantly stronger and creep resistant. This is caused by the interaction between the dispersoids and dislocations, as well as subgrains and grain boundaries. 

Since solubility is the concentration of protein in solution at equilibrium with the solid phase, the state of protein in the solid phase affects the solubility in the solution phase. Theoretical treatment of the protein solubility problem has often ignored solid phase interactions of the protein due to its complexity. A crystalline solid phase is expected to render a lower solubility than the amorphous solid phase. However the complexity and the heterogeneity of the protein in the solid state (e.g. amorphous, gel, or crystalline, or precipitates of native or denatured forms) makes it difficult to directly assess solid state effects. 

An important practical case during SEC is coprecipitation of structurally similar compounds, for example, reaction by-products, chiral molecules, additives, and impurities. Such precipitation is important when the aim is to produce composite crystals or drug xcipient mixtures or, on the contrary, to separate impurities from a solid product. The similarity of molecular structures ensures that such compounds strongly interact with each other, thus increasing the likelihood for solid solutions to form. Strong solid-solid intermolecular interactions typically result in separation problems and in significant variations of the solid state and particulate properties. 

In the literature there are many attempts to describe the interactions between ions in solution and a mineral surface in contact with them. The resulting interactions can be grouped into various phenomena, such as physisorption, chemisorption, co-precipitation, inclusion, diffusion, surface-precipitation, or even formation of solid solutions. 

This is dependent on the amount and distribution of these elements, i. e., whether they are present as precipitates or in supersaturated solid solution, and/or whether they form intermetallic phases. In Fig. 3.1-62 it is clearly apparent that solution treatment reduces the degree of supersaturation and that the range over which tensile strength and 0.2% proof stress decrease rapidly with tenqierature is thus shifted to significantly lower temperatures. Interactions between the various elements present can also affect recrystaUization behavior. 

Numerous studies have attempted to elucidate the role of Mo in the passivity of stainless steel. It has been proposed from XPS studies that Mo forms a solid solution with CrOOH with the result tiiat Mo is inhibited from dissolving trans-passively [9]. Others have proposed that active sites are rapidly covered with molybdenum oxyhydroxide or molybdate salts, thereby inhibiting localized corrosion [10]. Yet another study proposed that molybdate is formed by oxidation of an Mo dissolution product [11]. The oxyanion is then precipitated preferentially at active sites, where repassivation follows. It has also been proposed that in an oxide lattice dominated by three-valent species of Cr and Fe, ferrous ions will be accompanied by point defects. These defects are conjectured to be canceled by the presence of four- and six-valent Mo species [1]. Hence, the more defect-free film will be less able to be penetrated by aggressive anions. A theoretical study proposed a solute vacancy interaction model in which Mo " is assumed to interact electrostatically with oppositely charged cation vacancies [ 12]. As a consequence, the cation vacancy flux is gradually reduced in the passive film from the solution side to the metal-film interface, thus hindering vacancy condensation at the metal-oxide interface, which the authors postulate acts as a precursor for localized film breakdown [12]. 

For precipitation, kinetics are slower with these interactions. The slowdown is too importtint to be related to the small decrease of Zr diffusion in the metastable solid solution at the same temperature. One possibility would be a change of configurational entropy contribution to interface free energy. 

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