Extended sampling , equilibrium phase

The phenomenon of vacancy ordering is often observed in the transition metal carbides. " While in the group 4 carbides the tendency towards carbon ordering is weak and can be observed only by extended annealing of 5-TCi samples at comparably low temperatures (<800 °C), the tendency becomes more pronounced in the group 5 and 6 carbides. By the ordering of vacancies at low temperatures, even the metal atom positions are affected. In some cases, however, such ordered structures probably cannot be regarded as equilibrium phases nor can an impurity influence on the stabihty of the structures be ruled out. 

The rate experiments were carried out in 3.5 liter glass jars covered with a plexiglass lid. Two baffles of 2 cm width extended from the lid to 1 cm from the bottom of the reactor. Agitation was provided by a stirring motor with polyethylene stirrers, and the speed of the motor was controlled with a variac. Three liters of solution without the adsorbent particles was agitated, and allowed to reach equilibrium with the vessel before withdrawing the initial sample for analysis. At time t - 0, a measured quantity of activated carbon was introduced into the reactor and agitated. Samples, 10 ml each were withdrawn periodically, until equilibrium was reached, and analyzed for the solute concentration in the liquid phase. The numerical procedure developed earlier was adjusted to allow for the volume reduction due to the withdrawal of samples at discrete time Intervals. 

True thermodynamic equilibrium refers to the phase in their most stable state, and for the crystalline polymer phase the most stable conformation is the fully extended one. The equilibrium melting temperature, T , corresponds to the melting of perfect crystals of infinite size with fully extended chains. The value of for a polymer is unique. Since the crystalline samples of polymers are made up of crystals of finite size in which the chains are folded and not fully extended, the experimentally determined melting temperature, is always lower than There is a strong dependence of T on the thickness of the crystalline lamella, / always increases with /. 

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