Radio tracer measurements

The PBD technique probes concentration gradients near the electrode surface. However it is not possible to distinguish between a concentration gradient produced by ion transfer or solvent transfer in the opposite direction. In practice additional experiments with differing electrolyte concentrations or techniques, such as the EQCM or radio tracer measurements, are necessary to evaluate solvent transfer contributions to the total beam deflection. 

Measurements of the adsorption of inhibitors on corroding metals are best carried out using the direct methods of radio-tracer detection and solution depletion measurements . These methods provide unambiguous information on uptake, whereas the corrosion reactions may interfere with the indirect methods of adsorption determination, such as double layer capacity measurements", coulometry", ellipsometry and reflectivity Nevertheless, double layer capacity measurements have been widely used for the determination of inhibitor adsorption on corroding metals, with apparently consistent results, though the interpretation may not be straightforward in some cases. 

Early studies on oxide films stripped from iron showed the presence of chromium after inhibition in chromate solutionand of crystals of ferric phosphate after inhibition in phosphate solutions. More recently, radio-tracer studies using labelled anions have provided more detailed information on the uptake of anions. These measurements of irreversible uptake have shown that some inhibitive anions, e.g. chromateand phosphate are taken up to a considerable extent on the oxide film. However, other equally effective inhibitive anions, e.g. benzoate" pertechnetate and azelate , are taken up to a comparatively small extent. Anions may be adsorbed on the oxide surface by interactions similar to those described above in connection with adsorption on oxide-free metal surfaces. On the oxide surface there is the additional possibility that the adsorbed anions may undergo a process of ion exchange whereby... 

Experimental data measured by the radio tracer quenching technique at 75°C. 

Stone and Tilley have shown that the spectral changes which occur on spinel formation can be related to the extent of reaction of the component oxides, although the kinetics were also followed by chemical analysis. Keyser et have studied the reaction of zirconium silicate with calcium oxide by a radio tracer method. Wagenblast and Damask have used internal friction measurements to study the rate of precipitation of carbon in iron. The rate of decrease of the Snoek peak can be related to the growth kinetics of the iron carbon precipi-... 

A laboratory membrane brine electrolysis cell, designed for automated operation, was constructed ( 1,2). This system enables the measurement of the sodium ion transport number of a membrane under specific sets of conditions using a radiotracer method. In such an experiment, the sodium chloride anolyte solution is doped with 22Na radio-tracer, a timed electrolysis is performed, and the fraction of current carried by sodium ion through the membrane is determined by the amount of radioactivity that has transferred to the sodium hydroxide catholyte solution. The voltage drop across the membrane during electrolysis is simultaneously measured, so that the overall performance of the material can be evaluated. 

Li and DeBruyn (19) measured the adsorption density of Na on ground Brazilian optical quartz (using radio-tracer methods) and zeta potential, both as functions of pH and NaCl concentration. 

Surface self-diffusion is the two-dimensional analogue of the Brownian motion of molecules in a liquid bulk. Measurements of self-diffusion have to be performed in complete absence of any Marangoni flow caused by surface tension differences. Such experimental conditions are best established in an insoluble monolayer where one part consists of unlabelled and the other of radio-tracer labelled molecules. The movement of molecules within the surface monolayer can be now observed by using a Geiger-Miiller counter. There are possible effects of liquid convective flow in the sublayer which was discussed for example by Vollhardt et al. (1980a). With e special designed apparatus Vollhardt et al. (1980b) studied the self-difihision of different palmitic and stearic acid and stearyl alcohol and obtained self-diffusion coefficients between l-i-4 lO cm /s. 

As an example of a radio-tracer method, the measurement of sulfate reduction rates using according to Jorgensen (1978) Fossing and Jorgensen (1989) Kallmeyer et al. (2004) is described in brief (Fig. 5.14). The is... 

Because Dqq oc [V(5o]then if one measured the radio tracer diffusion of cobalt in CoO, the isothermal oxygen pressure dependence should exhibit a one-quarter dependence. This is exactly what Carter and Richardson ( ) did. Their results are shown in Figure 5. The electronic conductivity, o,... 

The flow distribution in a model soil column (length 1 m, diameter 10 cm) with defined disturbing inserts (Fig. 2.1) was studied to demonstrate the feasibility of PET-studies. The measurements were carried out with a commercial PET-camera (Siemens ECAT EXACT HR (3D)). Kaliumfluoride, marked with the positron emitting isotope F-18 (half life time 110 min), was applied as hydrodynamic tracer. Fluorides of two-valent cations are only slightly soluble. The radio tracer would be absorbed in the col-... 

The main problem of the in situ radio-tracer study of electrosorption phenomena originates from the very nature of the method, because the radiation measured consists of two main parts. The first one is that coming from the solution phase or from the solution layer contacting the electrode. The second radiation component is the radiation coming from the adsorption... 

The diffusion of zinc in n- and p-type aluminium antimonide was measured at 660 to 860C by using a radio-tracer technique. At high donor concentrations, the diffusion constant was found to decrease. The diffusion was described by ... 

With optimized reaction parameters the recovery of the metals in the eluate is around 80 %. Variations of 5-22 % of the analytical results determined by radio tracer experiments are higher than the 1-14 % achieved for the yields relative to the internal standard (95 %) obtained by TXRF measurements. If the relative yields are based on an internal standard for TXRF, variations in the recovery do not have any significant effect, as long as all elements display uniform behaviour during the sample preparation procedure. That this applies was shown by Prange et al. (1983). Thus, effects of incomplete precipitation, adsorption or elution are eliminated by the internal standard used for quantification. 

Modern methods for the measurement of moisture profiles lead to diffusivity measurement methods. Such methods discussed in the literature are radio-tracer methods, nuclear magnetic resonance (NMR), electron spin resonance (ESR), and the like. 

This form of the Gibbs fundamental equation demonstrates the importance of surface and interfacial tension measurements of interfacial layers out of the adsorption equilibrium. These methods are the most frequently used techniques to follow the time-dependence of the adsorption process. However, for very slow processes, which occurs in systems with extremely small amounts of surfactants, other methods such as the radio-tracer technique and ellipsometry, or the very recently developed technique of neutron reflectivity, can be used to directly follow the change of surface concentration with time. 

The choice of tracer gas for the measurements is Kr-85 It has a long half-life so that it can be stored for application when needed. It is a noble gas which is chemically inactive giving a low radio toxicity as it is readily removed in case of accidental contamination. 

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