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V Correcher J Garcia-Guinea FJ Valle-Fuentes 《Journal of Thermal Analysis and Calorimetry》2006,83(2):439-444
In
this paper, novel results on the blue thermally stimulated luminescence (TSL)
emission of ulexite (NaCaB5O6(OH)6·5H2O)
have been studied. The four maxima appearing at 60, 110, 200 and 240°C
on the TSL glow curves of this borate could be respectively associated to:
(i) the first dehydration (NaCaB5O6(OH)6·5H2O→NaCaB5O6(OH)6·3H2O),
(ii) the creation-annihilation of the three-hydrated
phase, (iii) the Na-coordinated chains
dehydroxylation and the starting point of the alkali self-diffusion through
the lattice and (iv) the amorphisation
of the lattice. These results are fairly well correlated with the differential
thermal analyses (DTA), in situ thermal observations under environmental scanning
electron microscope (TESEM) and thermal X-ray diffraction (TXRD) techniques. 相似文献
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Prof. Dr. Begoña García Dr. Francisco J. Hoyuelos Dr. Saturnino Ibeas Dr. María S. Muñoz Dr. Ana M. Navarro Dr. Indalecio A. Peñacoba Prof. Dr. José M. Leal 《化学:亚洲杂志》2010,5(12):2530-2540
The mechanisms for the hydrolysis of organopalladium complexes [Pd(CNN)R]BF4 (R=P(OPh)3, PPh3, and SC4H8) were investigated at 25 °C by using UV/Vis absorbance measurements in 10 % v/v ethanol/water mixtures containing different sulphuric acid concentrations in the 1.3–11.7 M range. In all cases, a biphasic behavior was observed with rate constants k1obs, which corresponds to the initial step of the hydrolysis reaction, and k2obs, where k1obs>k2obs. The plots of k1obs and k2obs versus sulfuric acid concentration suggest a change in the reaction mechanism. The change with respect to the k1obs value corresponds to 35 %, 2 %, and 99 % of the protonated complexes for R=PPh3, P(OPh)3, and SC4H8, respectively. Regarding k2obs, the change occurred in all cases at about 6.5 M H2SO4 and matched up with the results reported for the hydrolysis of the 2‐acetylpyridinephenylhydrazone (CNN) ligand. By using the excess acidity method, the mechanisms were elucidated by carefully looking at the variation of ki,obs (i=1,2) versus ${c_{{\rm{H}}^ + } }$ . The rate‐determining constants, k0,A‐1, k0,A‐2, and k0,A‐SE2 were evaluated in all cases. The R=P(OPh)3 complex was most reactive due to its π‐acid character, which favors the rupture of the trans nitrogen–palladium bond in the A‐2 mechanism and also that of the pyridine nitrogen–palladium bond in the A‐1 mechanism. The organometallic bond exerts no effect on the relative basicity of the complexes, which are strongly reliant on the substituent. 相似文献
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Peñacoba IA García B Navarro AM Hoyuelos FJ Leal JM 《Journal of colloid and interface science》2010,352(2):465-469
The decomposition reaction of the purple dye murexide in acidic media is used as a probe indicator for protons in nonionic microemulsions. The reaction kinetics primarily rely on the proton concentration and permit assessment of the proton activity in the nonionic microemulsions of water/cyclohexane/Igepal and water/heptane/Igepal. The experiments performed in the two microemulsions covered a wide range of water-to-oil mass fraction for the two systems. The kinetic runs were monitored under pseudo-first order conditions by the stopped-flow technique. The equilibrium constants for the formation of purpuric acid and the kinetic constants for the ensuing decomposition reaction fulfill a trend consistent with the micro compartmentalized nature of the multicomponent medium, and support the use of murexide as an indicator of the proton activity in microemulsions. 相似文献
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Fernández-Ibáñez P de las Nieves FJ Malato S 《Journal of colloid and interface science》2000,227(2):510-516
Electron transfer between a titanium dioxide/electrolyte solution interface has been studied. As found by other researchers of similar interfaces (TiO(2)- and ZnO-electrolyte solution), a slow consumption of OH(-) ions takes place in this type of interface. A theoretical model has been developed for calculating the change in the Fermi energy of both electrolyte solution and semiconductor, showing that ion consumption from the solution is favoured by the decrease of the difference between their Fermi energies. A kinetic constant (upsilon) is found to characterise the consumption process, its value increasing with electrolyte and semiconductor mass concentrations. Furthermore, this process may be used to estimate the point of zero charge of a titanium dioxide colloidal dispersion. Copyright 2000 Academic Press. 相似文献