Diffusion Of Rb Research Articles

Refractive Index Profiles of KTiOPO4 Ion-Exchanged Waveguides and Effect of Barium Ion

Planar waveguides in KTiOPO4 (KTP) have been fabricated by using molten salts of RbNO3, CsNO3, 80/20 RbNO3/Ba(NO3)2 (molar ratio) and 78/19/3 CsNO3/Ba(NO3)2/KNO3. The increase in the refractive index of the waveguide per mole caused by the replaced Cs+ is one order of magnitude greater than that caused by Rb+. The Ba2+ ion can contribute to both the increase in the refractive index and the promotion of Rb diffusion. A Rb/Ba-exchanged waveguide exhibited an increase in the refractive index three times as large as that in a Rb-exchanged one with the same surface Rb+ concentration. When Ba2+ coexists with Rb+ in the molten salts, the diffusion constants of Rb+ in KTP at 350°C were 2.0 µ m2/min for the TM mode and 2.5 µ m2/min for the TE mode.

Volume self-diffusion of oxygen in biotite, muscovite, and phlogopite micas

The kinetics of oxygen self-diffusion have been measured in natural samples of biotite, muscovite, and phlogopite micas under hydrothermal conditions using both bulk exchange and profiling analyses. All experiments were run at 1000 bars (100 MPa) water pressure except those designed to measure water pressure dependence, which ranged from 200 to 2000 bars. The Arrhenius relations obtained for layer-parallel diffusive transport in the three micas by bulk exchange experiments, fit to an infinite cylinder model, are Mineral biotite muscovite phlogopite Q (kcal mol) 34 ±2 39 ± 5 42 +- 3 D 0 (cm 2 s) 9.1 × 10 −6 7.7 × 10 −5 1.4 × 10 −4 T(°C) 500–800 512–700 600–900. The results of ion microprobe (SIMS) depth profiling perpendicular to the layers (parallel to c-axis) yield diffusion coefficients 3 to 4 orders of magnitude lower than for transport parallel to the layers. A single layer-parallel step profiling experiment yields a diffusion coefficient identical, within uncertainty, to those obtained from bulk exchange experiments. A slight dependence of diffusion rate on water pressure may obtain in phlogopite; however, the difference is approximately within the uncertainty of the measurement. Diffusion rates are similar, within about a half an order of magnitude, for a range of biotite composition from annite 4 to annite 63, as well as for muscovite. Comparison of oxygen diffusion rates in biotite from this study with Ar, K, and Rb diffusion from published data supports the idea that water is the oxygen-bearing species in hydrothermal diffusion experiments. The implication of these results for natural systems is that the micas, especially biotite, will continue to exchange oxygen isotopes via volume diffusion down to temperatures as low as 300 °C. The rapid diffusion kinetics may explain biotite oxygen isotope disequilibrium, which is commonly observed even in rocks where other mineral phases preserve equilibrium compositions.

Time-temperature relation of mineral isochrons: a thermodynamic model, and illustrative examples for the Rb [sbnd]Sr system

We have developed a thermodynamic model for the determination of the closure temperature ( T C ) at which the minerals defining an internal isochron in Rb Sr, or similar, geochronological system were set with a geochronological clock. It is shown that the equilibrium fractionation of 87Rb and 87Sr between a pair of minerals at T C [K D( 87Rb 87Sr) C] is given by the ratio of the quantity ( 87Rb/ 86Sr ) in the two minerals as measured at the present time. K D( 87Rb- 87Sr) , which equals the element distribution coefficient K D(Rb Sr) under equilibrium condition, can be calibrated as a function of temperature, and compared with the retrieved value of K D( 87Rb 87Sr) C in a natural pair to obtain T C . The various mineral pairs defining an internal isochron will yield concordant or discordant values of T C depending on whether or not they closed simultaneously with respect to the diffusion of Rb and Sr. Both types of results are expected, and are important in the analyses of the evolutionary history of the host rocks. Preliminary analyses of the published data in the Rb Sr system suggest a fairly wide range of T C even for the same mineral pair, reflecting differences in the cooling rates and physico-chemical environments of the host rocks.

Ionic equilibria, selectivity and diffusion of cations in soil as influenced by anion additions

Abstract An experiment was carried under controlled conditions to investigate the influence of the anions, H2PO4 ‐. and Cl on the ionic equilibria, selectivity and effective diffusion of Rb, K, Na, Ca, Mg in two Indiana soils. Additon of anions to the soils increased the concentration of cations in soil solution. In both the soils receiving H2PO4 ‐, lower cation concentrations were found in the soil solution than in those receiving Cl‐ . Additon of H2PO4 ‐and Cl‐ reduced the ion selectivity coefficient, k, for various homovalent (Rb/K, Rb/Na, K/Na, Ca/Mg) and mono‐divalent ion pairs (Rb/Ca, Rb/Mg, K/Ca, K/Mg). In Zanesville soil treatments receiving H2PO4 ‐ had lower k values for mono‐divalent cations than treatments receiving Cl‐. However, no such conclusions could be drawn for Raub soil. Soils treated with H2PO4 ‐ had higher k values for homovalent cations than Cl‐ treated soils. The differences in the selectivity of adsorption in these two soils might be attributable to the differences in the type and ...

Diffusion of rubidium ion in pure silver chloride crystals

The diffusion of 86Rb in AgCl has been measured in the temperature range 184-448 degrees C by a tracer-sectioning technique. The transport of Rb+ is found to proceed by a vacancy mechanism. The temperature dependence of the diffusivity follows a linear Arrhenius law with parameters D0=(1.10-0.37+0.56)*102 cm2 s-1 and H=1.20+or-0.02 eV. The data fail to exhibit the continuous positive curvature which is expected on the basis of a non-linear decrease in the Gibbs free energy for Frenkel defect formation with the increase of temperature. It is possible that a strain-induced and temperature-dependent binding energy between the oversized solute ion and a neighbouring vacancy washes out the expected curvature. When the diffusion results of other alkali ions are compared together with the diffusion of Rb+ in AgCl, it seems likely that the temperature dependence of the motion energy is also to be considered along with those of the formation and solute-vacancy association.

ChemInform Abstract: DIFFUSION OF ALKALI IONS IN VITREOUS SILICA

The diffusion of Cs+, Rb+, and K+ ions was measured in three grades of vitreous SiO2 by the radiotracer-sectioning technique or Rutherford, backscattering spectroscopy. The values of the diffusion coefficient, D, at 1000°C decrease strongly with increasing ionic radius, changing by about two and one-half orders of magnitude per row of the periodic table. The difference between DCs and DRb is largely in the preexponential factor Do in the Arrhenius expression rather than in the activation enthalpy Q. The values of D are much smaller than the tracer D values for the alkali metal ion in homogeneous Rb or Cs silicate glasses. Residual metallic impurities in the SiO2 decrease both Q and Do for the diffusion of Rb. The results are analyzed in terms of the interstitial structure of vitreous SiO2.

Observations on anomalous defect parameters in the study of mass transport in silver halides

Abstract The results of the recent experiments on the diffusion of K+ and Rb+ in both AgCl and AgBr are discussed. The diffusion Arrhenius plots for K+ show an anomaly at high temperatures which quantitatively replicates that displayed by the ionic conductivity presumably originating from the nonlinear temperature dependence of the free energy of Frenkel defect formation. However, this “inherent curvature” is not observed in case of the diffusion of Rb+ in both the halides, as it is indeed true for most other diffusions of cations. These results are then compared with the published results of the diffusion study of other impurity cations. It appears that additional temperature dependence of the free energy of migration and association need to be considered to have a unified explanation for the variety of diffusion results.

Diffusion of Alkali Ions in Vitreous Silica

The diffusion of Cs+, Rb+, and K+ ions was measured in three grades of vitreous SiO2 by the radiotracer‐sectioning technique or Rutherford, backscattering spectroscopy. The values of the diffusion coefficient, D, at 1000°C decrease strongly with increasing ionic radius, changing by about two and one‐half orders of magnitude per row of the periodic table. The difference between DCs and DRb is largely in the preexponential factor Do in the Arrhenius expression rather than in the activation enthalpy Q. The values of D are much smaller than the tracer D values for the alkali metal ion in homogeneous Rb or Cs silicate glasses. Residual metallic impurities in the SiO2 decrease both Q and Do for the diffusion of Rb. The results are analyzed in terms of the interstitial structure of vitreous SiO2.

Defect mechanisms for the anomalously high charge and mass transport in silver halides

The defect structure in AgCl and AgBr is Frenkel-type and the ionic transport takes place by vacancy, interstitial and interstitialcy increase of conductivity and silver diffusion is believed due to the increase of defect concentration resulting from the decrease of defect-formation energy at high temperature. The present results of the diffusion of Rb+, a substitutional homovalent ion, in AgCl and AgBr do not show any such anomaly. The high temperature anomaly is also conspicuous by absence in most of the impurity diffusion studied in this system. The mis-match of the ionic radii of the solute and host ions in may lead to a context. The mis-match of the ionic radii of the solute and host ions may lead to a strain induced binding between a solute ion and vacancy. With the observed decrease of elastic modulii at higher temperature, this binding energy will decrease and thus compensate the effect of nonlinear decrease of defect-formation energy.

Cyanide chemistry of rubidium-dosed silver and the use of cyanogen as a titrant for surface alkali

The presence of adsorbed rubidium induces dissociation of cyanogen during chemisorption and leads to a mixed adiayer containing two kinds of cyanide surface species. One of these is weakly bound in an undissociated state and desorbs as (CN) 2 ( E d ⩽ 100 k J mole −1). A second species is the result of dissociation to CN adsand appears to be closely associated with the Rb adatoms. This species desorbs exclusively as RbCN ( E d ~ 165 kJ mole −1) with a kinetic order of between zero and unity depending on the surface coverage. This behaviour, together with the electron impact properties of the Rb + CN overlayer suggest that nucleation and island growth of RbCN occurs above a certain critical coverage. This model can account for the way in which the initially large ESD cross-section for CN loss (~3.5 × 10 −18 cm 2) rapidly decreases towards zero with decreasing coverage. It is demonstrated that the special properties of the Ag-(CN) 2-Rb system permit (CN) 2 to be used as a specific titrant for surface alkali, and the technique is used to obtain a value for the activation energy (30 kJ mole −1) for surface → bulk diffusion of Rb in Ag, as well as the above cross-section to ESD.

Independent yields of Rb and Cs isotopes from thermal-neutron induced fission ofU235

The relative yields of Rb and Cs isotopes from thermal-neutron fission of $^{235}\mathrm{U}$ have been redetermined using the mass separator OSTIS, on-line at a neutron guide of the High-Flux Beam Reactor at the Institut Laue-Langevin, Grenoble, France. The separator ion source was a hot oven containing $^{235}\mathrm{U}$ in a graphite matrix. The neutron beam was pulsed. Alkali fission products diffused out of the graphite and were ionized, thus producing a stepwise increase in the analyzed ion beam proportional to the independent fission yield. The ion beam and the fissions in the source were monitored simultaneously. The diffusion of Rb and Cs from the source was exponential in time with half-lives ranging from 2.8 to 18 sec, depending upon the element and source temperature. The independent fission yields of Rb and Cs are normalized by equating their element yields to each other and to a value computed from the charge distributions observed with the recoil separator LOHENGRIN and well established mass yields. Fractional independent yields are deduced from the independent fission yields, and these compare very well with the EOZ model described by Wahl.NUCLEAR REACTIONS $^{235}\mathrm{U}$($n$,$f$), $E=\mathrm{thermal}$; measured relative abundances; deduced independent fission yields, fractional chain yields, charge displacement and dispersion, odd-even $Z$ effect. Mass separator, fast neutron detector.

The growth and characterization of potassium and rubidium azide single crystals

Large single crystals have been grown of potassium azide from the melt by the Kyropolous technique and rubidium azide from solution by evaporation. These materials have been characterized by the direct observation of dislocations by a new etching technique and preliminary experiments of ionic conductivity and tracer diffusion of Rb in RbN 3.

DIFFUSION AND ABSORPTION OF IONS IN PLANT TISSUE: III. THE ROLE OF THE ROOT CORTEX CELLS IN ION ABSORPTION1

SUMMARY The theoretical aspects of diffusion of Rb+ ions in the free space of young barley roots and their concomitant absorption by the epidermal and cortical cells were studied on the basis of a simplified geometrical model. It is concluded that participation of the cortical cells in the process of Rb+ uptake is irreconcilable with the kinetic features of this process as determined experimentally. Limitation of uptake to the root surface is considered to pertain to other macronutrient ions and other objects as well.

Diffusion and Internal Friction in Na‐Rb Silicate Glasses

The internal friction and self‐diffusion coefficients of sodium and rubidium ions for (l‐X)Na2O‐XRb2O‐3SiO2 glasses were measured. Diffusion was measured by radioactive isotopes and a thin‐sectioning technique at 350° to 500°C. Internal friction was measured at −140° to 500°C and 0.05 to 6000 Hz. The maximum height for the mixed‐alkali internal friction peak occurs at the composition at which the Na and Rb diffusion coefficients are equal. It is concluded that the mechanism responsible for the mixed‐alkali peak is a coupled, cooperative rearrangement of sodium and rubidium ions, with the slower moving ion controlling the rate of rearrangement. This mechanism should also apply to other mixed‐alkali silicate glasses since the internal friction for these systems is similar.

Effect of Al3+ and H+ Upon the Simultaneous Diffusion of 85Sr and 86Rb in Kaolinite Clay

AbstractThe effect of varying concentrations of Al3+ and H+ upon the simultaneous diffusion of 85Sr and 86Rb was measured in salt-free aliquots of clay having different Al:H ratios. The Sr and Rb saturation of the CEC was held constant while the exchangeable Al and H were varied from Al52:H1 to Al12:H34. Aliquots of each clay-treatment were dually tagged with 85Sr and 86Rb. Self-diffusion of Sr and Rb was measured at 4, 24, 48, and 75°C. Radioassay of 85Sr and 86Rb was made with an automatic gamma-detection system equipped with a 400 channel analyzer and card punch unit. The selfdiffusion equation was programmed for the 7040 computer to permit the simultaneous calculation of 85Sr and 86Rb self-diffusion coefficients. Rb diffusion was not significantly altered as the Al3+ concentration was increased from 12 to 52 per cent. The diffusion of Sr was significantly increased as Al3+ increased from 12 to 52 per cent. The faster diffusing Rb ion had a greater energy of activation than Sr (4·8 to 3·6 kcal/mole), however the Arrhenius frequency factor for Rb (a measure of the probability of ion exchange) was much greater for Rb than Sr (28·8 and 0·4 × 10−4, respectively). Altering the Rb and Sr saturation and the complementary ions resulted in changes in the diffusivity, the energy of activation, and the frequency factor for these ions, but not always in the same direction or to the same degree.

COUNTER DIFFUSION OF Rb86 AND Sr89 IN COMPACTED SOIL

SummaryCounter‐diffusion coefficients of Rb86 and Sr89 counter diffusing against H+ ions were measured in Dundee silt loam and Sharkey clay soils at differing soil bulk‐densities. The cation exchange complex of each soil was saturated with either Rb+, Sr++, or H+ and washed free of salts before making diffusion measurements. The water content of the soil on an oven‐dry weight basis was maintained at a constant value for all bulk‐densities; 14.2 and 28.0 per cent for the Dundee and Sharkey soils respectively. These moisture contents correspond to a tension of 2/3 bar for sieved soil. The diffusion coefficients were dependent upon concentration. Average counter‐diffusion coefficients were calculated and related to soil bulk‐density.Soil compaction of Dundee silt loam had little or no effect upon the counter diffusion of Rb86. The average counter‐diffusion coefficients of Sr89 in Dundee silt loam and Sharkey clay were significantly and linearly related to bulk‐density; as bulk‐density increased the average counter‐diffusion coefficients increased. The average counter‐diffusion coefficients were approximately 0.5–0.75 of the corresponding self‐diffusion coefficients measured previously in these soils. The applicability of counter‐ and self‐diffusion data to practical field problems are discussed.

WHOLE-ROCK AGE AND INITIAL 87Sr/86Sr OF VOLCANICS UNDERLYING FOSSILIFEROUS LOWER CAMBRIAN IN THE ATLANTIC PROVINCES OF CANADA

A Rb–Sr whole-rock age study has been carried out on three volcanic groups which underlie fossiliferous Lower Cambrian in the Atlantic provinces of Canada. Isochron ages of these three, and their initial 87Sr/86Sr ratios, are shown below.[Formula: see text]The Harbour Main group unconformably underlies younger formations which include the Bull Arm.The contemporaneity of the Coldbrook, Fourchu, and Bull Arm groups, predicted on field evidence, is confirmed by the age study, as is also the greater age of the Harbour Main. However, the isochron ages (500 m.y, average) of the three younger groups are at least 10% low by current time-scale standards for the base of the Cambrian. As all the data, show considerable departure from strict linearity, it is suggested that small and variable diffusion of Rb into the rocks has occurred, thus scattering the points and lowering the ages.Initial 87Sr/86Sr at the level 0.704—0.707 suggests for these magmas a subsialic source, which if not in the upper mantle, is at least in the lower part of the crust.

Ion Diffusion: II. Comparison of Apparent Self and Counter Diffusion Coefficients

AbstractThe experimental distributions of Rb86 diffusing in soil materials are obtained using a quick‐freeze method. The calculation of apparent diffusion coefficients of Rb from data obtained from these distributions is presented for the following geometries: (1) self diffusion and (2) counter diffusion of Rb diffusing from soil media initially saturated with Rb into the same soil media initially saturated with H+. The distribution of Rb86 counter diffusing from kaolinite clay, montmorillonite clay, Sharkey clay soil and Dundee silt loam soil pastes into H+ saturated kaolinite, montmorillonite, Sharkey and Dundee pastes can be characterized using self diffusion theory.The order of magnitude of apparent self diffusion coefficients is larger than those for counter diffusion in each of the four soil materials. The order of magnitude of the rate of Rb diffusion in the four soil materials is as follows: kaolinite clay > Dundee silt loam soil > Sharkey clay > montmorillonite clay. The values of the diffusion coefficients range from 3.9 × 10−7 cm.2 sec.−1 to 24.3 × 10−7 cm.2 sec.−1.Qualitative apparent counter diffusion coefficients of Rb diffusing from soil media initially saturated with Rb into strong acid exchange‐resin discs initially saturated with H+ are also presented for qualitative comparison purposes.

The Effect of Rubidium‐86 Diffusion on the Uptake of Rubidium‐86 by Corn

AbstractUptake of Rb86 by corn roots was highly correlated with the diffusion of Rb in soil and kaolinite systems. At values of Dp/b above 1 × 10‐6 cm.2 sec.‐1 the relationship was curvilinear whereas it was more nearly linear at rates less than this. The curvilinear relation at the higher rates of diffusion was attributed to the limitations of the rate of absorption of the root.

SELF‐DIFFUSION OF IONS IN SOIL

SummarySelf‐diffusion coefficients for Rb+, K+, and Sr++ have been measured in homoionic soils by determining the quantities of radioactive tracers crossing from labelled to initially unlabelled soil sections through ion‐exchange membrane barriers. Diffusion coefficients were considerably lower than in aqueous solution, and the value for Sr++ was approximately one‐tenth of those for the monovalentions. The diffusion of Rb+ in soils containing both Rb+ and Ca++ was also studied using various compactions and soil solution compositions. The results suggest that cations are able to diffuse along the charged surfaces of soil particles, but at a lower rate than in the free pore solution. Experiments on the effects of temperature suggest that the activation energy for the diffusion of Rb+ in the heteroionic soil was greater at low than at high bulk densities, a result which is interpreted in terms of surface movement.