Diffusion data, radiotracer

Diffusion experiments at surfaces are designed to measure self-diffusion or the diffusion of adsorbates. The techniques used [49-55) may provide atomic-scale diffusion data or macroscopic diffusion parameters. The techniques that provide atomic-level information include (a) field ion microscopy, which can be used to observe the surface migration of isolated adatoms or clusters of atoms, (b) field electron microscopy, and (c) scanning tunneling microscopy (for descriptions of the techniques, see references [56-68]. Macroscopic mass transport along the surface can be monitored by the use of radiotracers or by techniques that monitor the restructuring of surfaces as a function of time. 

Mercury radiotracer diffusion data were presented for bulk and epitaxial Hgi xCdxTe at temperatures ranging from 254 to 452C. This was believed to be the... 

The simultaneous diffusion of 210pb and l Cd into ion-exchange purified single crystals was studied by using the serial sectioning radiotracer technique. It was found that the diffusion data, for 347 to 569C, could be described by ... 

In order to test the feasibility of a Cr barrier layer, a submonolayer of Cr with a nominal thickness of 0.1 nm was deposited onto the DIP film prior to evaporation of the Ag radiotracers. In Figure 19.10(a) the depth profiles for DIP films with and without Cr barrier are shown. In Figure 19.10(b) the data are normalised with respect to the activity on the surface of each sample. As for TMC-PC, the deposition of Cr leads to a reduced Ag concentration in the film. However, the reduction of the Ag diffusion is not as effective as observed... 

Table 8.2 Role of methane as a carbon source for sulfate reduction in marine sediments. The compiled data show cumulative sulfate reduction rates measured by radiotracer technique, either over the entire sulfate zone, or in the upper 0-15 cm combined with modeling below that depth. The contribution of methane was calculated from the diffusion flux of methane up into the lower sulfate zone. In other data sets where sulfate reduction rates are determined only by modeling, or where also methane oxidation was measured by radiotracer technique, the calculated % of SRR from CH is higher than shown here. (SRR = sulfate reduction rate). ...

Self-diffusion measurements were carried out under an excess Cd vapor pressure, by using radiotracer and serial sectioning techniques, and the results were combined with previous data. It was found that the Arrhenius plot could be divided (at 780C) into 2 separate straight-line sections with differing slopes. The data could be described by ... 

The diffusion of Ni in P-doped Czochralski monocrystals was studied by using Ni radiotracer, autoradiographic and sectioning techniques. It was found that the data for 220 to 540C were described by ... 

The diffusion of carbon was determined at 1338 to 1772K. A simple radiotracer technique was used which monitored the change in surface activity as a function of annealing time. A single expression represented the data over the entire range of temperatures ... 

Self-diffusion was measured in single crystals of the a-phase, at 1540 to 1697C, by using 26a1 as a radiotracer. It was found that 2 diffusion mechanisms were involved. These were a lattice diffusion mechanism and a sub-boundary mechanism. The latter data could be described by ... 

Self-diffusion was determined directly, using a 127mxe radiotracer, in polycrystalline and dislocated single-crystal samples. The data for grain boundaries between 280 and 390C could be represented by ... 

Separation procedures are based on the principles of volatilization, liquid-liquid distribution, adsorption, diffusion, chromatography, ion exchange, electrophoresis, precipitation, coprecipitation, and electrodeposition. In all of these, radio-tracers provide the best tool for methodological investigations, determination of equilibrium constants, kinetic data, and optimization of applied analytical data (yield, interference levels, etc.) [54], Use of radiotracers in complex multielement separation schemes is reviewed in [4], [17], [20]. [41], [54], radiochromatography is reviewed in [551. [61], [93], 197],... 

The diffusivity is related to the radiotracer diffusion ooeffident by the correlation factor or, more generally, the Haven ratio. If one knows or can assmne a value for this qirantity, the tracer diffusion coefficient may be determined. Alternatively, if tracer data are available, information about the diffusivity provides a value of the Haven ratio, which is related to the mechanism of the ion jumps. 

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