Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Nucleation Ostwald limit

Hydrate nucleation and growth may have direct analogies in crystallization processes such as the precipitation of salt from solution. Metastability in salt crystallization was hypothesized to occur through supersaturation by Ostwald (1900). (A supersaturated solution is one in which the liquid [solvent] contains more dissolved solute than can be ordinarily accommodated at that temperature the greater the degree of supersaturation, the greater number of crystal nuclei that will form in solution.) Miers and Isaac (1907) experimentally proved metastability and postulated that for each solute-solvent pair, a concentration-temperature relationship exists that defines the metastable limit, formally called the thermodynamic spinodal. [Pg.121]

The model is essentially that of Ostwald which emphasized a cycle of supersaturation, nucleation and depletion of co-precipi-tates to explain Liesegang bands [9] However this theory, especially as formulated mathematically by Prager [10] emphasizes the presence of a gap between bands. This occurs in the model presented here as a special limit of parameter values but is not required. The model presented here as well as teh Ostwald-Prager theory are designed with phenomenon (i) in mind. They clearly cannot explain the other phenomena, however. [Pg.291]

The classical analysis of nucleation and growth phenomena (see Section 2.3) involves the concentration of precursor of the solid phase as the main parameter controlling the particle size, because it regulates the relative importance of each reaction step and their possible overlap.. During Ostwald ripening, the system reaches thermodynamic equilibrium, However, for a given concentration of the solution, the particle size decreases as the difference between PZC and the precipitation pH of the cation increases. Under such conditions, Ostwald ripening is almost non-existent. The fact that the divided state of the solid may be limited permanently makes the thermodynamic stability of oxide particles a reality from a dimensional point of view. [Pg.311]

Until now we have limited ourselves to planar interfaces. In fact the free enthalpy of a system is dependent on size and curvature in several ways. First of all, on account of the greater surface area, an ensemble of smaller crystals has a greater surface energy than an ensemble of larger crystals of the same total mole number, same composition and comparable shape. For this reason large crystals grow at the expense of small ones (Ostwald ripening) and for the same reason there is an activation threshold to be overcome (nucleation) in the process of phase formation... [Pg.148]


See other pages where Nucleation Ostwald limit is mentioned: [Pg.254]    [Pg.255]    [Pg.445]    [Pg.234]    [Pg.273]    [Pg.146]    [Pg.65]    [Pg.504]    [Pg.504]    [Pg.146]    [Pg.318]    [Pg.155]    [Pg.391]    [Pg.1375]    [Pg.5585]    [Pg.504]    [Pg.504]    [Pg.26]    [Pg.106]    [Pg.146]    [Pg.2390]    [Pg.362]    [Pg.208]    [Pg.1438]    [Pg.138]    [Pg.306]    [Pg.207]    [Pg.22]    [Pg.110]   
See also in sourсe #XX -- [ Pg.134 ]




SEARCH



Ostwald

© 2024 chempedia.info