Authors:P. Thomas, P. Šimon, A. Smallwood, and A. Ray
The dehydration of an opal specimen was investigated
by thermogravimetric analysis (TG) in powder and bulk forms. The change in
geometry resulted in a significant difference in the temperature range in
which dehydration occurred with peak temperatures in the differential TG (DTG)
curve for the hand ground opal at 203°C and for the bulk opal at 340°C.
This difference was attributed to time taken for diffusion of free water in
the bulk opal to the specimen surface prior to evolution as a registered mass
loss. A model was proposed to account for the diffusion of water and was used
to estimate the diffusion coefficient.
Authors:Y. Kobayashi, K. Hirata, Y. Ujihira, and K. Itoh
Diffusion coefficients of positronium (Ps) in polycarbonate (PC) have been determined at temperatures between 20 and 300 K by means of positron lifetime spectroscopy. 2,2-dinitrobiphenyl (DNB) was added to the polymer as a Ps quencher and the diffusion coefficients were determined from measured Ps quenching rate constants, assuming that the reaction between Ps and DNB is completely diffusion-controlled.
Authors:S. Osaki, E. Inoue, S. Sugihara, and Y. Takashima
The diffusion coefficients of Sr in gelled silica gel layers have been measured at various porosities. They decreased with the second power of porosity. At constant porosity, the diffusion coefficients of Sr and Co were measured at various pHs. They were dependent on the distribution coefficients (K) of the species between silica gel and pore water as a function of 1/(1+K). Gelation of the porous layer enables a stable measurement of diffusion coefficients under various conditions and facilitates the analysis of the distribution of ions after the diffusion experiments.
A thermogravimetric method has been used for the determination of the oxygen chemical diffusion coefficients in La1–xSrxMnO3+δ; x=0; 0.05; 0.10; 0.15 (LSM).
A temperature range of 700–1000C was studied.
The chemical diffusion coefficient varies between 1.6⋅10–13 and 1.8⋅10–10cm2s–1 for the samples in the temperature range studied. The activation energy for oxygen chemical diffusion was determined to be
190–280 kJ mol–1 for the LSM samples. The magnitude of the chemical diffusion coefficients of the LSM samples does not depend on the strontium
site occupation factor.
Authors:G. Bozhikov, G. Bontchev, P. Ivanov, A. Priemyshev, O. Maslov, M. Milanov, and S. Dmitriev
The electrophoretic method was recently developed for the determination of diffusion coefficients of ions in aqueous solution. By solving the Fick's second law in the presence of unlimited media and constant quantity of diffusing species we obtain a relationship between the diffusion coefficient and the standard deviation of the distribution profile. The diffusion coefficients of Cd(II), In(III), Zr(IV), Hf(IV), Pu(VI) and [InDTPA]2– in nitric acid solution were determined as well as the effective charge of In-DTPA complex at pH 4.50.
Soil samples were collected at the site of a 1951 leak from an underground storage tank of 6.7 liter of an aqueous solution
of irradiated uranium. Laboratory simulations were conducted using irradiated and non-irradiated natural uranium metal, dissolved
in acidic aqueous solutions and added to soil columns. Contaminant transport experiments were conducted for a period of 12
to 14 months, followed by sample analysis employing gamma-spectroscopy, neutron activation analysis and liquid scintillation
counting. The concentration distributions of U, Cs and Sr found from the experiments were used to derive diffusion coefficients.
The measured diffusion coefficients from the field samples were: for 137Cs, 3.0E-04 cm2·s−1; for 238U, 1.8E-09 cm2·s−1; and for 90Sr, 2.6E-09 cm2·s−1. Corresponding values for the laboratory simulations were 5E-06, 3E-05 and 1.9E-05 cm2·s−1, respectively.
Self-diffusion coefficients D of the trivalent aquo ion Cm3+ have been determined in aqueous Nd(ClO4)3–HClO4 solutions (pH 2.5) at 25°C, by the open-end capillary method (O. E. C. M.). The variation of D versus the square root of the concentration of inactive solution is an exponential form in the studied range of concentration. The limiting value D0 at zero ionic strength is 6.0·10–6 cm2·s–1. The curve
relating to Cm3+ can be compared to those of241Am3+ and153Gd3+ obtained under similar conditions. We find a similar ionic structure of Cm3+ with Am3+ and Gd3+. They have the same hydration as a tripositive of 5f and 4f ions in the absence of hydrolysis, complexing, or pairing at pH 2.5. The present study contributes to show the analogy of the solvation structure of trivalent actinide ions in aqueous solution at pH 2.5 with that of the trivalent lanthanide ions as a help for predicting the thermodynamic properties.
Measurements have been made of radon (222Rn), release from diverse quaternary samples collected from different sediment deposits in the Errachidia and Beni-Mellal areas (Morocco). The radon diffusion coefficient as one of some important parameters of radon transport in the soil has been measured using solid state nuclear track detectors (SSNTD). Radon -activity, uranium content and radon exhalation rate have been determined in the studied samples. Uranium concentrations were found to vary from 0.14 to 9.52 ppm whereas the radon exhalation rate varied from 0.003 to 0.145 Bq.m-2.h-1. A positive correlation has been found between radon exhalation rate and uranium content in the studied samples. The average radon diffusion coefficients were found to vary from (1.26±0.09).10-6 m2.s-1 to (4.3±0.36).10-6 m2.s-1. Furthermore, the correlation between 222Rn diffusion coefficient and porosity are also discussed.
Cation self-diffusion studies have been carried out by using the radiochemical technique for strontium ion in both hydrated ceria and zirconia. The particles of these exchangers are shown to behave as variable capacity ion exchangers. Self-diffusion coefficients for strontium ion were measured as a function of the variable capacity for that ion in solutions of varying acidity. The results are shown to be in qualitative agreement with the absolute rate theory. Also, it is shown that the measured self-diffusion coefficients are dependent only upon the total strontium ion capacity.
Radioanalysis, more particularly the use of radiotracers, enables measurement of coefficients of mass- and self-diffusion
by simple benchtop experiments. They are related to environmental inquiries and materials science mainly Current procedures
are surveyed here.