Coefficient of interdiffusion

The coefficient of interdiffusion of two liquids must be considered as depending on all the physical properties of the mixture according to laws which must be ascertained only by experiment. 

An inversion of these arguments indicates that release agents should exhibit several of the following features (/) act as a barrier to mechanical interlocking (2) prevent interdiffusion (J) exhibit poor adsorption and lack of reaction with at least one material at the interface (4) have low surface tension, resulting in poor wettabihty, ie, negative spreading coefficient, of the release substrate by the adhesive (5) low thermodynamic work of adhesion ... 

Interdiffusion of bilayered thin films also can be measured with XRD. The diffraction pattern initially consists of two peaks from the pure layers and after annealing, the diffracted intensity between these peaks grows because of interdiffusion of the layers. An analysis of this intensity yields the concentration profile, which enables a calculation of diffusion coefficients, and diffusion coefficients cm /s are readily measured. With the use of multilayered specimens, extremely small diffusion coefficients (-10 cm /s) can be measured with XRD. Alternative methods of measuring concentration profiles and diffusion coefficients include depth profiling (which suffers from artifacts), RBS (which can not resolve adjacent elements in the periodic table), and radiotracer methods (which are difficult). For XRD (except for multilayered specimens), there must be a unique relationship between composition and the d-spacings in the initial films and any solid solutions or compounds that form this permits calculation of the compo-... 

Silver coatings may blister above 200°C because of oxygen diffusion. A nickel undercoat stops interdiffusion with a copper substrate above 150°C. Alloying with antimony, selenium, sulphur or rhenium increases hardness—the coefficient of friction is also much reduced in the last case. ... 

The resolution of infra-red densitometry (IR-D) is on the other hand more in the region of some micrometers even with the use of IR-microscopes. The interface is also viewed from the side (Fig. 4d) and the density profile is obtained mostly between deuterated and protonated polymers. The strength of specific IR-bands is monitored during a scan across the interface to yield a concentration profile of species. While in the initial experiments on polyethylene diffusion the resolution was of the order of 60 pm [69] it has been improved e.g. in polystyrene diffusion experiments [70] to 10 pm by the application of a Fourier transform-IR-microscope. This technique is nicely suited to measure profiles on a micrometer scale as well as interdiffusion coefficients of polymers but it is far from reaching molecular resolution. 

Tominaga, T. and Matsumoto, S. Limiting interdiffusion coefficients of some hydroxylic compounds in water from 265 to 433... 

Unfortunately, the interpretation of Giletti et al. (1978) does not solve the problem of differential diffusivities of 0 and To do this, their experimental results should be interpreted in terms of interdiffusion of 0 and O. Application of Pick s first law to interdiffusion of the two species would in fact lead to the definition of an interdiffusion coefficient/), so that... 

This quantity is called the coefficient of self-diffusion. Equation (87) also describes the interdiffusion of ortho- and para-forms. 

In view of the lack of interdiffusion in the course of multiple-layer formation at the A-B interface and because of complicated mechanism of this process, calculation of integrated diffusion coefficients seems in most cases meaningless. 

As we have commented previously for metals, the diffusion in concentration gradients is described with the chemical diffusion coefficient, or interdiffusion coefficient. In this case, it is possible to consider that the interdiffusion and the intrinsic diffusion coefficients are equivalent, since we have only the movement of one species, that is, oxygen, by the vacancy mechanism. Subsequently, applying the Einstein relation... 

With the help of Equation 5.107, as was previously done with Equation 5.86, we obtain a transport or chemical diffusion coefficient that is a result of Fick s laws. We now interpret the meaning of this coefficient if we consider diffusion in a microporous solid, as a special case of binary diffusion, where A is the mobile species and the diffusivity of the microporous framework atoms is zero, then, the frame of reference are the fixed coordinates of the porous solid consequently, we have a particular case of interdiffusion where the diffusion coefficient is simply the diffusivity of the mobile species [12,20],... 

Transmission Electron Microscopy (TEM) has been used to characterize aluminum thin films thermally evaporated (vacuum around 10 4 Torr) on Polyethyleneterephtalate (Mylar) and to correlate the crystallographic structure of the system Al/Mylar and the adhesion of the aluminum films. The adhesion of these films has been measured by a Peel test technique. For the polymer, an amorphous layer (t=12 nm) followed by a crystalline film have been observed on a Corona treated film and the opposite configuration has been found on a bi-axially stretched film. Some spherical precipitation ana interdiffusion zones have also be observed in the Mylar for the films which have the lower coefficient of adhesion (100 g/inch). The main conclusion is the augmentation of the adhesion of the aluminum film as the size of the grains decreases and/or as the microroughness of the Al/Mylar interface increases. 

Such excellent or at least adequate capillary behaviour is also typical of the process variant known as eutectic bonding in which the transient creation of a liquid phase is caused by the interdiffusion of two chemically different metal alloy component materials. In the laboratory variant process known as partial transient liquid phase bonding, (Shalz et al. 1992), a coated interlayer is used for ceramic-ceramic or ceramic-metal joints. In this process the interlayer is a ductile metal or alloy whose surface is coated with a thin layer of a lower melting temperature metal or alloy, for example Ni-20Cr coated with 2 microns of Au. The bonding temperature is chosen so that only the coating melts and the ductility of the interlayer helps to accommodate mismatches in the coefficient of thermal expansion of the component materials. 

Interdiffusion coefficients of gases are much larger than those of liquids. The diffusion coefficients of most gases are of the order of a few tenths of a square centimeter per second, cm /s, at the standard temperature and pressure, whereas diffusion coefficients of liquids are less than 10 cm /s. The diffusion coefficient D at pressure p (torr) and temperature T (ZT) can be derived from the diffusion coefficient Z)o at the standard temperature and pressure (po = 760 torr, ro = 273K) by... 

The application of ion-exchange dynamics for the determination of HETP or HTU values should be studied in ion-exchange systems characterized by invariable static and kinetic parameters such as ion-exchanger swelling, electrolyte sorption, separation coefficient, and interdiffusion coefficients in solution and resin phases over experimentally investigated ranges of component variation. 

Solid-phase interdiffusion coefficient of counterions i and j Scale diffusion coefficient (cmVs )... 

In the two-component system gas + zeolite, in parallel with a general two-component system, one may consider 5 diffusion coefficients Dab (interdiffusion coefficient of sorbate and zeolite) Da, Db (intrinsic diffusion coefficients, respectively, of sorbate and zeolite) and Da, Db (tracer diffusion coefficients, respectively, of sorbate and zeolite). However, because Db and Db are effectively zero, as for a nonswelling crystal. 

In addition, a model has been formulated to predict the self-diffusion coefficient of diffusing species, which are hydrogen and aluminum ions. The interdiffusion coefficient value for the coupled transport of these two ions is also determined for the two types of membranes. 

It was seen that in the experiments performed hydrogen ion was the trace species. Therefore, for coupled Al -H transport, the interdiffusion coefficient approached the self-diffusion coefficient of the faster-diffusing ions. This conclusion appears counterintuitive, but explains the good kinetics of the process. 

Diffusion coefficients for sorbed solvent and ions in Nafion have been estimated using several techniques. Yeo and Eisenberg [53] studied the sorption of water by a dry slab of Nafion (EW 1155) and estimated the interdiffusion coefficient of water in the membrane over the temperature range 0-99 °C from the water uptake dynamics. Diffusion coefficients from these measurements increased with increasing temperature over the range (1-10) x 10 cm /s with a reported activation energy of 4.5 kcal/ mol (18.8 kJ/mol). The method used to estimate the diffusion coefficients by Yeo and Eisenberg [53] was based on the dependence of the uptake in the initial portion of the uptake curve and is probably not fully appropriate [82]). 

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