The Experts below are selected from a list of 204 Experts worldwide ranked by ideXlab platform
Ian Farnan - One of the best experts on this subject based on the ideXlab platform.
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investigation of the maximum dissolution rates and temperature dependence of a simulated uk nuclear waste glass in circum neutral media at 40 and 90 c in a dynamic system
Applied Geochemistry, 2017Co-Authors: Tajudeen M Iwalewa, Ian FarnanAbstract:Abstract This study investigates the influence of temperature on the dissolution of MW25, a non-radioactive simulant of UK Magnox glass. A single-pass flow-through (SPFT) system was used to measure the forward dissolution rate of MW25 at 40 and 90 °C and circum-neutral pH. The forward dissolution rate was found to be approximately one order of magnitude higher at 90 °C than at 40 °C. A similar release was observed for Si, Mg and Al at 40 °C and 90 °C, whereas the B, Cs, Na, Li and Mo showed an order of magnitude increase when the temperature was increased from 40 to 90 °C for low q/S values. The temperature dependence of the dissolution rates was determined using the Arrhenius rate law and the resultant activation energy (E a ) shows that the dissolution process is a Surface Phenomenon. At 90 °C, the net effect of the processes governing MW25 dissolution led to preferential release of boron and alkali metals relative to the release of Si during the transient dissolution stage, accompanied by an increase in the concentration of silicic acid. This suggests that the solution activity of silicic acid at higher temperature has a weak influence on the release of the mobile elements. This study features a new method for estimating the Surface area of reacted glass powder more accurately than the geometric Surface area estimate, which is the preferred standard method among researchers.
Jongsoo Jurng - One of the best experts on this subject based on the ideXlab platform.
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Surface Phenomenon of ceo2 added v2o5 tio2 catalyst based chemical vapor condensation cvc for enhanced selective catalytic reduction at low temperatures
Chemical Engineering Journal, 2016Co-Authors: Woojoon Cha, Sheryl H Ehrman, Jongsoo JurngAbstract:Abstract In this study, our purpose was to investigate and research in depth the different physico-chemical properties and the Surface Phenomenon mechanism of the CeO2-added V2O5/TiO2 catalyst prepared via the chemical vapor condensation (CVC) and impregnation method for enhanced NH3-selective catalytic reduction activity. In addition, we performed Surface analyses of the materials using various techniques, such as X-ray photoelectron spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy, and electron energy loss spectroscopy, and used some data from previous research. CeO2 on the Surface of V2O5-CeO2/CVC-TiO2 contained a higher ratio of Ce3+ ions. This was because many free carriers on the Surface of the CVC-catalyst moved toward the Surface of the loaded material that had higher binding energy (eV). Secondly, V2O5-CeO2/CVC-TiO2 had very little amorphous-phase CeO2 because of the inherent physical and structural properties. Finally, the CVC-catalyst showed higher reducibility and acidity when V2O5 and CeO2 were loaded onto CVC-TiO2 because of a higher number of oxygen species and hydroxyls on the catalyst Surface.
Jonathan D. Mayer - One of the best experts on this subject based on the ideXlab platform.
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Challenges to understanding spatial patterns of disease: Philosophical alternatives to logical positivism
Social science & medicine (1982), 1992Co-Authors: Jonathan D. MayerAbstract:Most studies of disease distribution, in medical geography and other related disciplines, have been empirical in nature and rooted in the assumptions of logical positivism. However, some of the more newly articulated philosophies of the social sciences, and of social theory, have much to add in the understanding of the processes and mechanisms underlying disease distribution. This paper represents a plea for creative synthesis between logical positivism and realism or structuration, and uses specific examples to suggest how disease distribution, as a Surface Phenomenon, can be explained using deeper analysis.
S. Schumacher - One of the best experts on this subject based on the ideXlab platform.
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Forward dissolution rate of silicate glasses of nuclear interest in clay-equilibrated groundwater
Chemical Geology, 2012Co-Authors: P. Jollivet, Stéphane Gin, S. SchumacherAbstract:Abstract This study describes the influence of neutral or slightly basic clay-equilibrated groundwater on the forward dissolution rate of nuclear borosilicate glasses. The forward rate measured for the SON68 glass, a 26-oxide glass of nuclear interest, is about five times higher in clay-equilibrated groundwater than in deionized water. The corresponding apparent activation energy, measured between 30 °C and 90 °C, is similar for both media, indicating that glass dissolution is likely controlled by the hydrolysis of Si–O bonds in both solutions. The specific effect of clay-equilibrated groundwater appears to be related to a Surface Phenomenon; aluminum–oxygen and zirconium–oxygen bonds appear to be less impacted by clay-equilibrated groundwater than silicon–oxygen bonds. More particularly, this work shows that the influence of clay-equilibrated groundwater on the forward dissolution rate is due to its ionic strength with cations predominating over anions, although not all tested cations have the same effect. The effect is due mainly to calcium ions, although the concentration of sodium ions in the clay-equilibrated water tested was four times higher than that of calcium ions. The specific influence of alkali metal (Li + , Na + , K + , Rb + , Cs + ) and alkaline earth (Mg 2 + , Ca 2 + , Sr 2 + , Ba 2 + ) ions shows that all cations do not have the same effect on the forward glass dissolution rate and that the rate increases with the mole fraction of Surface metal sites. The presence of calcium in the glass does not prevent this particular effect.
Tajudeen M Iwalewa - One of the best experts on this subject based on the ideXlab platform.
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investigation of the maximum dissolution rates and temperature dependence of a simulated uk nuclear waste glass in circum neutral media at 40 and 90 c in a dynamic system
Applied Geochemistry, 2017Co-Authors: Tajudeen M Iwalewa, Ian FarnanAbstract:Abstract This study investigates the influence of temperature on the dissolution of MW25, a non-radioactive simulant of UK Magnox glass. A single-pass flow-through (SPFT) system was used to measure the forward dissolution rate of MW25 at 40 and 90 °C and circum-neutral pH. The forward dissolution rate was found to be approximately one order of magnitude higher at 90 °C than at 40 °C. A similar release was observed for Si, Mg and Al at 40 °C and 90 °C, whereas the B, Cs, Na, Li and Mo showed an order of magnitude increase when the temperature was increased from 40 to 90 °C for low q/S values. The temperature dependence of the dissolution rates was determined using the Arrhenius rate law and the resultant activation energy (E a ) shows that the dissolution process is a Surface Phenomenon. At 90 °C, the net effect of the processes governing MW25 dissolution led to preferential release of boron and alkali metals relative to the release of Si during the transient dissolution stage, accompanied by an increase in the concentration of silicic acid. This suggests that the solution activity of silicic acid at higher temperature has a weak influence on the release of the mobile elements. This study features a new method for estimating the Surface area of reacted glass powder more accurately than the geometric Surface area estimate, which is the preferred standard method among researchers.
