Cooling rate dependence

To interpret the cooling rate dependence of the glass transition temperature, one can use the Vogel-Fulcher law discussed in the section on the... 

Applying this prediction to the cooling rate dependence of a break points in the specific volume curves, one obtains a Vogel-Fulcher temperature of To = 0.35 that agrees well with that determined from the temperature dependence of the diffusion constant in this model, which is T = 0.32. 

Molecular-Weight and Cooling-Rate Dependence of Simulated Tg for Amorphous Polystyrene. 

Note 2 A cloud point is heating rate- or cooling rate-dependent. 

Experiments indicate that the smooth variations of thermodynamic properties (e.g., V, Ky, and the specific heat at constant pressure Cp) with temperature are intermpted by the kinetic process of glass formation, leading to cooling rate dependent kinks in these properties as a function of temperature. In our view, these kinks cannot be described by an equilibrium statistical mechanical theory, but rather are a challenge for a nonequilibrium theory of glass formation. Nonetheless, some insight into the origin of these kinks and the qualitative... 

Using this expression which refers to definite conditions and knowing how the cooling rate depends on these conditions (dimensions of the vessel, pressure, composition of the explosion products), we can compute the yield of nitric oxide in any case. Tm and [NO] are computed thermodynamically, kmrl by formula (8.8) we take into consideration the difference between r under the conditions of the given experiment and in the series of experiments on which the derivation of (8.8) was based. Then from the curve of Fig. 14 we find NO/[NO] corresponding to the new (because of the different t) value of UNO]r. 

Solidification of weld metal takes place at high cooling rates. Depending on process parameters, such as the size of the weld pool, rates have been reported to vary between 20 and 200°C/s, [10, 11],... 

The similarity between the calculated isobaric excitation profiles shown in Fig. 14 and the isochoric profiles obtained by molecular simulation (Sastry et al., 1998a) is remarkable. The isobaric excitation profiles have a discontinuity (not shown) at T for T < Tk the system remains trapped in the unique (ideal glass) basin, and Ai/a is constant. The discontinuity is absent in the simulated isochoric profiles, because the system gets trapped kinetically in a cooling rate-dependent basin and is not able to access the deepest amorphous basin. 

As 64% of the total water in the apical meristems of embryos in recently collected seeds was freezable, freezing injuries are able to occur, the extent of damage being cooling-rate dependent. In fact, both LM and TEM revealed different degrees of cellular injuries in the apical meristems of frozen embryos (Figures 42.3 and 42.4). 

Figure 4. Cooling rate dependence of freeze-thaw inactivation of seeded catalase solutions. After seeding at —2°C, samples were cooled at the rate noted to —25°C or below, held at — 78°C, then warmed at 0.6°C/min from —25 to...

Figure 6. Cooling-rate dependence of catalase inactivation in lOmM neutral KHPO solutions containing various concentrations of NaCl. All solutions were seeded, cooled at stated rates to —50°C or lower, and then warmed at 0.5°C/ min from —50°C. Mean and SE are shown for four to six samples in each case...

This conclusion raises an additional question. In our classical molecular dynamics simulations, the excess kinetic energy was uniformly added to all heme atoms. Does the observed simulated heme cooling rate depend upon the mode of excitation No dependence on the mode of excitation was observed in the classical simulations. In addition to the V4 and V7 modes, other modes, including iron out-of-plane motions, are initially excited, leading to a broad excitation of heme atoms in the initially excited state. It is reasonable to assume that, ignoring coherence, that state of excitation is similar to our uniform heating protocol. 

De Guire, M. R., O Handley, R. C. Kalonji, G. (1989). The cooling rate dependence of cation distributions in CoFc204. Journal of Applied Physics, 65, 3167-72. 

The quench rates quoted in the previous section encompass cooling times which range from 2.5 x 10 MCS s to 2.5 x 10 MCS s. Whereas these times are much larger than the structural relaxation time of a polymer, the Rouse time tr, at infinite temperature (tr(oo) 5380 MCS s), the cooling process must reach a temperature, at which tr(T) Fq Then the melt freezes on the time scale of the simulation. The present section discusses the properties of this cooling rate dependent freezing by some representive examples. 

The essence of cryomicroscopy lies in the ability to vitrify the sample using the thermal fixation technique that alters the sample microstructure to the least extent. Cooling rate estimates of 10 K/s [14], 10 K/s [15], and 10 K/s [16] are quoted as necessary to vitrify water or dilute aqueous suspensions. The ability to achieve the desired cooling rate depends on the sample, the cryogen, and the fixation technique. 10 K/s is probably the most accurate estimate. This evaluation is based on estimates of the cooling rate in freezing techniques that are known to produce vitreous specimens. 

Hashimoto and co-workers have prepared a novel cyano-bridged bimetallic complex composed of Sm(H20)5[W(CN)g] (Figure 34), showing, on cooling, rate dependent ferromagnetism. The crystal structure of this compound consists of a two-dimensional cyanide-bridged network. 

Equation (1.29) permits the determination of the cooling-rate dependence of the glass-transition temperature for metallic glasses that have viscosities given by the modified VFT relation with the free volume given by eq. (1.13), rather than exhibiting an Arrhenian dependence. Thus,... 

Kanai, T., H. Ishibashi, Y. Hayashi, T. Ogawa, S. Furukawa, R. West, T. Dohmaru, and K. Oka. 2000. A new cooling-rate dependent thermochromism of polyjdioctylsilane). Chem Lett 6 650. 

Non-isothermal crystallization during cooling is a cooling rate-dependent process. Ozawa extended the isothermal crystallization analysis to the non-isothermal case of controlled cooling rate [20,21]. This method accounts for the effect of cooling rate,, on crystallization from the melt by replacing t in equation (A) with T/ as Equation (5) ... 

Suppose we combine 0.60 mol A and 0.40 mol B (zb = 0.40) and adjust the temperature so as to put the system point at b. This point is in the one-phase liquid area, so the equilibrium system at this temperature has a single liquid phase. If we now place the system in thermal contact with a cold reservoir, heat is transferred out of the system and the system point moves down along the isopleth (path of constant overall composition) b-h. The cooling rate depends on the temperature gradient at the system boundary and the system s heat capacity. 

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