Diffusion of solids

Large amplitude motions in molecular crystals such as phase transitions and self-diffusion of solid adamantane have also been treated by a MM method (322). However, the program used in this work is useful only for the calculation of intermolecular interactions. 

There is much more to be said concerning sintering, especially with regard to the role that diffusion plays. Many of the models that describe the sintering processes are based on the diffusivity of solid species, which are addressed in Section 4.3. The practical aspects of the sintering of metals and ceramics are described in Sections 7.1 and 7.2, respectively. 

Dialysis may be described as the fractional diffusion of solids from one side of a semi-permeable membrane to the other side under a concentration gradient Electrolysis is die process of local or spatial separation of the ions of an electrolyte and the transfer of their respective charges, ie the decompn of a compd by an elec current... 

M. Taniguchi and M. Wakihara, Proc. 1st US-Japan seminar on defects and diffusion of solids, Tokyo, 1976. 

The principles of several approaches to measurement have been explained by Hands10. As mentioned in the previous section, several methods are in the process of being standardized for plastics but there does not appear to be any ISO standards for diffusivity published. However, there is an ASTM standard for diffusivity of solids in general using the flash method55. Also as mentioned in the previous section, diffusivity can be calculated from conductivity, and this is specifically mentioned in ASTM E195253. 

ASTM E1461, 2001. Standard test method for thermal diffusivity of solids by the flash method. 

Saiz et al. (1998) considered that in the case of a triple line, the L/V surface can play the role of a grain boundary and the wetting ridge can move either by bulk or surface (or interface) diffusion of solid atoms (Figure 2.14). They treated the case of surface diffusion with n = 4, taking into account the difference of diffusivities at the S/V surfaces and S/L interfaces. In their experiments with Cu and Ni droplets on AI2O3 surfaces (see Section 1.2.4), Saiz et al. maintained the... 

Fat or lipid materials and calcium-lipid complexes also contribute to fouling and flux decline in membrane processing of milk or whey. The transport properties of the feed stream and the changes they undergo as the concentration process proceeds also affect the rate of permeation. At high concentrations, the increased fluid viscosity near the membrane surface limits back-diffusion of solids from the polarized layer to the bulk phase, thereby, depressing flux rate [46]. 

Permeation Molecular diffusion of solid, liquid, or gaseous substances. Permeation of chemicals is a physical process, which can be described as diffusion-controlled movement of molecules through a membrane-like polymer. It depends largely on the type of elastomer and its thickness. 

A method for measuring diffusivity of solid polymers based on this type of boundary condition has been developed by Berlot [49, 50], and by Gehrig et al. [51], A disc sample of thickness 2a is held at a uniform temperature and then a sinusoidal temperature fluctuation of angular frequency ta is imposed on the outer surfaces. The amplitude ratio and phase of the temperature at the center are monitored with a thermocouple. Under these conditions the amplitude ratio A and phase 0 are given by [52]... 

The temperature as a function of time on the back face is usually measured with a radiation pyrometer. Analysis of the results has been discussed by Taylor [58] and by Parrott and Stukes [59]. This is possibly the most accurate method currently available for measuring diffusivity of solid materials. 

Thermal conductivities and diffusivities of solids vary greatly with temperature. Specific heats and densities vary little, except for steels at their phase transition point. The thermal conductivities of solid pure metals drop with increasing temperature, but the conductivities of solid alloys generally rise with temperature. 

Despite the widespread use of these and many other similar correlations, however, they are notoriously unreliable deviations from experimental values as high as 30% are not unusual (Mullin and Cook, 1965). Furthermore, these empirical relationships were devised from diffusion data predominantly on liquid-liquid systems, and there is little evidence to suggest that they are reliable for the prediction of the diffusion of solid solutes in liquid solutions, although an order of magnitude estimation is sometimes possible. For example, the diffusivity of sodium chloride in water at 25 °C is 1.3 x 10 m s , while values calculated from equations 2.23 and 2.24 range from 1.7 to 2.6 x 10 m s . Similarly, for sucrose in water at 25 °C, D = 5.2 x 10 m s , while the predicted values range from 3.6 to 4.2 x 10 m s . ... 

SELECTED METHODS FOR DETERMINING THERMAL CONDUCTIVITY AND DIFFUSIVITY OF SOLID PROPELLANT. FINAL REPORT. 

THE DETERMINATION OF THERMAL DIFFUSIVITY OF SOLID STATE MATERIALS BY A SIMPLIFIED PERIODIC HEATING METHOD. M.S. THESIS. 

A METHOD FOR DETERMINING THE THERAML DIFFUSIVITY OF SOLID PROPELLANTS. QUARTERLY PROGRESS REPT. SEPT. 15, 1963-DEC. 15, 1963. 

INFRARED ABSORPTION SPECTRA AND RAMAN DIFFUSION OF SOLID THIETANE. 

Standard Test Method for Thermal Diffusivity of Solids by the Flash Method, ASTME1461, Am. Soc. Testing and Mater. (Oct, 2,2001)... 

The impact of crushing grapes has already been covered in Section 12.2.2. Energetic crushing increases the diffusion of solid tissue components, bnt, according to a general rule, the corresponding tissue destruction promotes the extraction... 

The diffusion of solid ions, atoms, or molecules through solid matrices, while seemingly not possible, can and does in fact take place. It does so by a mechanism akin to that which described liquid-phase diffusion Local density fluctuations lead to a momentary opening or vacancy into which a neighboring parhcle can displace itself (see Figure 3.1b). Thus, a diffusional flow occurs, which follows Pick s law, as do more conventional diffusional processes. 

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