Time spinodal decomposition

ALnico 5, with added ductihty. The very Low Co alloys, however, require extremely long he at-treatment times because of the decreased kinetics of the spinodal decomposition. Deformation aged 23%Cr—23%Co—2%Cu exhibits (BH) of 78 kJ/m (9.75MG - Oe) (85). 

Short-time Brownian motion was simulated and compared with experiments [108]. The structural evolution and dynamics [109] and the translational and bond-orientational order [110] were simulated with Brownian dynamics (BD) for dense binary colloidal mixtures. The short-time dynamics was investigated through the velocity autocorrelation function [111] and an algebraic decay of velocity fluctuation in a confined liquid was found [112]. Dissipative particle dynamics [113] is an attempt to bridge the gap between atomistic and mesoscopic simulation. Colloidal adsorption was simulated with BD [114]. The hydrodynamic forces, usually friction forces, are found to be able to enhance the self-diffusion of colloidal particles [115]. A novel MC approach to the dynamics of fluids was proposed in Ref. 116. Spinodal decomposition [117] in binary fluids was simulated. BD simulations for hard spherocylinders in the isotropic [118] and in the nematic phase [119] were done. A two-site Yukawa system [120] was studied with... 

Bruder and Brenn (1992) studied the spinodal decomposition in thin films of a blend of deuterated polystyrene (dPS) and poly(styrene-co-4-bromostyrene) (PBrxS) by TOF-ERDA. They examined the effect of different substrates on the decomposition process. In one series of experiments, a solution of the polymers in toluene was spread on a silicon wafer to form a film of thickness 550 nm which was then heated in vacuum at 180°C for various times. 

The results for the glass crystallization of PET annealed at 80 °C as before are shown in Fig. 8. In the early stage of spinodal decomposition up to 20 min, the characteristic wavelength A remains constant at a value of 15 nm, which agrees with the theoretical expectation that only the amplitude of density fluctuations increases whilst keeping a constant characteristic wavelength. In the late stage from 20 to 100 min it increases up to 21 nm just before crystallization. Such a time dependence of A in nm can be represented by... 

Fig. 25 Annealing time evolution of the difference SAXS intensity in the induction period (a) and the crystallization period (b) for the melt crystallization of PET at 244 °C [18]. This system corresponds to crystallization from the metastable state where a nucle-ation and growth type of primary phase separation first occurs followed by the spinodal decomposition type secondary phase separation...

The systems undergoing phase transitions (like spinodal decomposition) often exhibit scaling phenomena [ 1—4] that is, a morphological pattern of the domains at earlier times looks statistically similar to a pattern at later times apart from the global change of scale implied by the growth of L(f)—the domain size. Quantitatively it means, for example, that the correlation function of the order parameter (density, concentration, magnetization, etc.)... 

Figure 17. Different stages of the spinodal decomposition in a symmetric mixture (4>0 = 0.5) r is the dimensionless time. The Euler characteristic is negative, which indicates that the surfaces are bicontinuous. The Euler characteristic increases with dimensionless time. This indicates that the surface connectivity decreases.

Equations (10) and (16) indicate that a plot of the logarithm of the scattering intensity vs. time will behave quite differently for spinodal decomposition than for nucleation and growth, even though both mechanisms undergo an increase in the scattering intensity with time. 

Therefore, we expect the scattered intensity /(q, t), proportional to ( /q(t)) to be exponential in time, 7(q, t) exp(2fiqr), with the rate Oq = q AT — q with both lower and upper cutoffs in q. If these arguments are valid, flq/ should rise sharply with q, reach a maximum, and then decrease at higher q values. These predictions are fully consistent with the experimental [10] and simulation [57] observations on /(q, t) and Oq. If the mechanism is simply a spinodal decomposition into two liquid phases, then D. /q should show a monotonic linear decrease from a finite positive value at q 0 with a slope independent of quench depth, which is not experimentally observed during... 

Furthermore, for A = l/2-Amin, the term in brackets in Eqn. (12.30) has a maximum. Therefore, after a sufficient time of continuous spinodal decomposition, zones with the Amax periodicity will predominate. With other words, the decomposed solid solution exhibits periodicity in the direction, and the period length is Amax- min and max increase with strain, as can be seen from Eqns. (12.29) and (12.31). If the strain energy is high enough, Amax may become sufficiently large so that spinodal decomposition does not take place any more. 

According to Eqn. (12.30), r = [ ]mi n is the characteristic relaxation time of the decomposition process ([ ] represents the term in brackets). Let us assume D, = (ibj/RT) to be on the order of 10 10 cm2/s. r is then on the order of a second or less. This means that in-situ observations of the spinodal process are hardly possible. If the sample has been quenched to room temperature, the decomposition has often already reached its final stage. The continuous spinodal decomposition for which the early stages are the pertinent ones cannot be verified in this way. 

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