Melts, diffusion

Hervig RL, Moore G (2003) Fractionation of boron (and lithium) between hydrous fluid and silicate melt diffusion, contamination, and orphaned experiments. EOS Trans, Am Geophys Union 84 F163 Hoefs J (1997) Stable Isotope Geochemistry, 4 ed. Springer-Verlag, Berlin... 

The diffusion behavior of components that are not the principal equilibriumdetermining component is difficult to model because of multicomponent effect. Many of them may show uphill diffusion (Zhang et al., 1989). To calculate the interface-melt composition using full thermod3mamic and kinetic treatment and to treat diffusion of all components, it is necessary to use a multicomponent diffusion matrix (Liang, 1999). The effective binary treatment is useful in the empirical estimation of the dissolution distance using interface-melt composition and melt diffusivity, but cannot deal with multicomponent effect and components that show uphill diffusion. 

It was possible to obtain an excellent fit of Eq. (8) with Eq. (9) to the combined M and T dependence of D and extract of value VE - 13.7 0.2 cm3/mol, slightly more in a similar polymer having one terminal —OH group. The constants P and fg had to be fitted as well, the latter assuming the value fg = 0.023 0.001. This interpretation of melt diffusivity was confirmed in separate experiments in which diffusion of the smaller oligomers was measured in a high molecular weight cispolyisoprene host (see below). Data and fitted theory in the melts are shown in Fig. 4. 

One possibility that would lead to larger inferred porosities for the U-series was introduced by Qin (1992, 1993), who proposed that the retained melt was only in complete equilibrium with the surface of minerals and that solid-state diffusion limited the re-equilibration of the retained melt with the solid. In other respects, this model is identical to the ACM model of Williams and Gill (1989). Qin introduced a specific microscopic melting/diffusion model for spherical grains and coupled it to the larger-scale dynamic melting models. The net affect of this... 

Scheubel (1989) characterized the sintering processes of two raw materials, one with silica distributed as clay minerals and the other with coarse quartz. With the former material, the reaction that forms the silicates in the short sintering zone with a steep temperature profile was said to be dependent primarily on the physical parameters of the melt (diffusion constant) and the mean path length for elemental migration. With the raw material containing coarse quartz and burned with a shallow temperature profile, coarsely crystalline belite which had formed... 

Dai et al. further demonstrated the potential application of PAFs in the electrochemical field. By the melting diffusion of sulfur into the framework of JUC-Z2, PAF-S was obtained with sulfur highly dispersed inside JUC-Z2. As a cathode material, the PAF-S composite shovt 1083 mA g reversible capacity and excellent stability in 1.0 M LiPFg-MiPS. In the ion liquid electrolyte N-methyl-N-propyl pyrrolidinium bis-(trifluoromethanesulfonyl)imide (MPPY TFSI), an 830 mA h g reversible capacity is achieved and 83% is retained after 50 cycles (Figure 8.7). The authors pointed out that once sulfur is loaded into the aromatic framework, the poor cycle stability of the sulfur electrode can be partially mitigated because of the confinement effect of the porous framework. Though the electronic conductivity of PAFs is low, this research does demonstrate the potential application of PAFs in batteries. 

This example illustrates how the thermal diffusivity can be measured and how it is used to describe heat conduction problems. For amorphous polymers and polymer melts, diffusivity is approximately linear with the velocity of sound v the proportionality constant is about 6E-13 [41] ... 

With polymer melts, devolatilisation is normally diffusion controlled. Within the bulk of the polymer melt, diffusion rate depends on a volatile concentration gradient existing... 

The dynamics of structure development during the experiment may be observed in the contour plots in Figure 11. SAXS and WAXS contours are in arbitrary levels of I(q) and 1(26) respectively. The peak position in the SAXS pattern has been marked vnih a bold line, q, and remains constant up to 120 °C after which the structure starts to change continuously by lamella thickening. This process involves melting, diffusion and some recrystaUisation and is manifest as a shift in q to lower values of q the weak WAXS pattern is relatively insensitive to these dynamic processes. Eventually the hard segments melt ( 210 °C) and mix with the soft segment, the SAXS peak... 

The polymer melt diffusion experiments were done in collaboration with Dr. Stephen J. Mumby, visiting scientist at IBM Research Laboratory, and with Dr. Edward T. Samulski and Li-Ping Yu of the Chemistry Department, University of Connecticut, Storrs, CT. 

Most kinetic studies have been carried out on diluted solutions when the reaction is carried out in the melt, diffusion may control the kinetics. 

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