Tracer-sectioning technique diffusion measurement

The tracer-sectioning technique was employed for the diffusion measurement. The distribution of specific activity C of a radioactive tracer at fixed temperature and oxygen partial pressure is expressed as... 

Sharma and Laskar [129] measured the self-diffusion of potassium in melt-grown potassium azide using a radioactive tracer sectioning technique. The diffusion coefficient in the range 85-254°C was found to be (0.19 0.03) exp [(- 0.80 0.06) eV/kT] cm sec. They concluded that the cation is the predominantly mobile species, with diffusion occurring by a vacancy mechanism. The value of 0.80 0.06 eV (77 kJ/mole) for the enthalpy of migration agrees well with the results of Maycock and Pai Verneker [127]. 

The impurity diffusion of Fe in CoO was measured in air by using the tracer-sectioning technique. The results, at 1001 to 1600C, could be described by ... 

An extremely valuable technique for research that has been developed in recent years is the use of both radioactive and nonradioactive isotopes as. tracers. By the use of these isotopes an element can be observed in the presence of large quantities of the same element. For example, one of the earliest uses of tracers was the experimental determination of the rate at which lead atoms move around through a crystalline sample of the metal lead. This phenomenon is called self-diffusion. If some radioactive lead is placed as a surface layer on a sheet of lead, and the sample is allowed to stand for a while, it can then be cut up into thin sections parallel to the original surface layer, and the radioactivity present in each section can be measured. The presence of radioactivity in layers other than the original surface layer shows that lead atoms from the surface layer have diffused through the metal. 

The diffusion of Ce was measured by using tracer and serial sectioning techniques. It was found that the diffiisivity obeyed ... 

The self-diffusion of C in hyperstoichiometric UC was measured in the single-phase region, using a radioactive tracer and sectioning technique. The diffusion equations were ... 

The diffusion of uranium was measured using radioactive tracers and sectioning techniques. The diffusion in stoichiometric material as a function of temperature was described by ... 

The tracer diffusion of Ag in dense polycrystalline specimens was investigated. The concentration profiles were measured by using radiotracer plus serial-sectioning techniques. The bulk diffusivity of H Ag in Cu3(Bi,Pb)2Ca2Sr20x could be described by ... 

The diffusion of Fe was measured parallel to the c-axis of single crystals at 708 to 1303C, at an O activity of unity. The tracer penetration profiles were determined by using sectioning techniques. At above 900C, the tracer diffusion could be described by ... 

The neutron activation technique mentioned in the preceding paragraph is only one of a range of nuclear methods used in the study of solids - methods which depend on the response of atomic nuclei to radiation or to the emission of radiation by the nuclei. Radioactive isotopes ( tracers ) of course have been used in research ever since von Hevesy s pioneering measurements of diffusion (Section 4.2.2). These techniques have become a field of study in their own right and a number of physics laboratories, as for instance the Second Physical Institute at the University of Gottingen, focus on the development of such techniques. This family of techniques, as applied to the study of condensed matter, is well surveyed in a specialised text... 

This section is concerned with measurement techniques of the diffusivity and solubility from which the permeability can easily be calculated. In the following analysis we restrict ourselves to the measurement of constant values of D. Concentration- and position-dependent diffusivities are analyzed in Crank and Park (1968) and Crank (1975). Generally, the techniques are for permeability, steady-state and time lag techniques and for diffusivity, sorption and desorption kinetics and concentration-distance curves. For self-diffusivity in polymer melts the techniques are (Tirrell, 1984) nuclear magnetic resonance, neutron scattering, radioactive tracer, and infrared spectroscopy. 

---