Measurement of diffusion of pyridine in Çayirhan lignite

The aim of this study is to measure the diffusion coefficients of pyridine in Turkish Çayirhan lignite (C: 57.1 wt %, dmmf) at temperatures about 20-27 C and determine the type of transport mechanism of diffusion. The raw coal sample was demineralized with HCl and HF by standard methods, and the raw and demineralized coal samples were extracted with pyridine. To investigate the diffusion of pyridine vapor in coal samples, the mass of pyridine uptake per mass of coal sample (Mt/M) was calculated as a function of time. The diffusion coefficients were measured from the slope of graphs of Mt/M versus t1/2. The diffusion coefficient of pyridine in the raw coal increased from 10.0 × 10-15 to 11.9 × 10-15 m2/s when the temperature was elevated from 21.1 to 26.9 C, respectively. The diffusion coefficients of pyridine raw coal and of those treated with HCl and HF were 11.9 × 10-15, 4.3 × 10-15, and 4.8 × 10-15 m2/s at 26.9 C, respectively. The studies in the present work on pyridine vapor diffusion in raw coals have generally indicated that the diffusion obeyed the Fickian diffusion mechanism the temperatures 20.0-27.0 C. Generally, the diffusion exponent values increased when the temperature elevated from 20.0 to 27.0 C, but this raise placed the diffusion of pyridine between the Fickian diffusion and Case II diffusion mechanisms

The use of solid angle for alpha detector efficiency in 226Ra analyses of soil samples

In the frame of proficiency tests organized by IAEA and IRMM, the specific activity concentration of radium-226 in soil has been measured. The BaSO4 co-precipitation technique has been used. Normally, in this method, the detector efficiency of the alpha spectrometer is determined by using a 226Ra source with known activity. As an alternative to using a 226Ra standard, we calculated the detector efficiency from the relative solid angle subtended by the detector on the soil samples. The accuracy of this method depends on the uncertainty on geometrical properties and the distribution of activity within the source. An uncertainty budget is provided. The method was applied successfully in the intercomparisons.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Diffusion of solvents in coals: 1. measurement of diffusion coefficients of pyridine in Elbistan lignite

The aim of the present report is to measure the diffusion coefficients at temperatures about 20-27 degreesC, the activation energies of diffusion, and to determine the type of transport mechanism of diffusion of pyridine in macromolecular structure of Turkish Elbistan lignite (C: 53.0 wt %, dmmf). The raw coal sample was demineralized with HCl and HF by standard methods. The raw and demineralized coal samples were extracted with pyridine. Pyridine uptake of the coal samples was recorded at temperatures 20-27 degreesC in an adiabatic setup until a constant weight was attained. The extent of swelling of original and treated coal samples in pyridine were measured. Pyridine extraction created a fraction of enlarged particle size due to irreversible solvent swelling. The diffusion coefficients were measured from the slope of graphs of M-t/M-infinity versus t(1/2) The diffusion of pyridine in the raw coal seemed to be less, compared to those of the treated coal samples. Extraction of the raw coal with pyridine extended the pyridine diffusion in the coal very little. The formation of new carboxylic acid groups in acid-washed samples enhanced diffusion of pyridine. In all of the samples the diffusion constants increased linearly with an increase in the temperature. The greater diffusion coefficients are encountered with the coal samples which swelled more in pyridine. It seemed that the diffusion coefficients increased with swelling and acid washings as a result of structural variations decreasing the activation energy of diffusion of the solvent to the coal. The transport mechanism of pyridine in the macromolecular coal network of Elbistan lignite was not relaxation controlled. The diffusion of pyridine in the low rank Elbistan lignite obeyed generally Fickian mechanism or an intermediate case of Fickian-anomalous mechanism