Time resolved alteration process of oxide glasses

Dissolution of oxide glasses by water has been studied by small angles X-ray scattering. It is shown that the altered residual surface layer due to dissolution and recondensation of Si atoms is a porous material with nanometer size pores. Based on five elements oxide glass (18NaO2-17B2O3-4CaO-yZrO2-(61-y)SiO2 with y=0, 1, 2, 4 and 8) the experiment highlights a strong influence of insoluble element on both the kinetic of alteration and the structure of the altered layer. It is shown that above 2% Zr content, the fraction of porous volume and the surface of exchange in the altered layer pass through a maximum value in the first hours of alteration corresponding to an overshoot of Si lixiviation without recondensation as the saturation limit is not reached. When the saturation limit is reached the porous volume fraction is just below the fraction of volume occupied primarily by the sodium and the boron.     

Time-dependent photoionization of azulene: competition between ionization and relaxation in highly excited states

Pump-probe photoionization has been used to map the relaxation processes taking place from highly vibrationally excited levels of the S(2) state of azulene, populated directly or via internal conversion from the S(4) state. Photoelectron spectra obtained by 1+2(') two-color time-resolved photoelectron imaging are invariant (apart from in intensity) to the pump-probe time delay and to the pump wavelength. This reveals a photoionization process which is driven by an unstable electronic state (e.g., doubly excited state) lying below the ionization potential. This state is postulated to be populated by a probe transition from S(2) and to rapidly relax via an Auger-like process onto highly vibrationally excited Rydberg states. This accounts for the time invariance of the photoelectron spectrum. The intensity of the photoelectron spectrum is proportional to the population in S(2). An exponential energy gap law is used to describe the internal conversion rate from S(2) to S(0). The vibronic coupling strength is found to be larger than 60+/-5 microeV.     

Solvent Extraction: Structure of the Liquid–Liquid Interface Containing a Diamide Ligand

Knowledge of the (supra)molecular structure of an interface that contains amphiphilic ligand molecules is necessary for a full understanding of ion transfer during solvent extraction. Even if molecular dynamics already yield some insight in the molecular configurations in solution, hardly any experimental data giving access to distributions of both extractant molecules and ions at the liquid–liquid interface exist. Here, the combined application of X‐ray and neutron reflectivity measurements represents a key milestone in the deduction of the interfacial structure and potential with respect to two different lipophilic ligands. Indeed, we show for the first time that hard trivalent cations can be repelled or attracted by the extractant‐enriched interface according to the nature of the ligand.     

Einstein’s equations and Clifford algebra

Einstein’s equations of the general theory of relativity are rewritten within a Clifford algebra. This algebra is otherwise isomorphic to a direct product of two quaternion algebras. A multivector calculus is developed within this Clifford algebra which differs from the corresponding complexified algebra used in the standard spacetime algebra approach.     

Electrochemically induced transformations of heteropolyanions: new electroactive metal oxide films studied by the electrochemical quartz crystal microbalance

New oxide films have been electrodeposited from [P₂Mo₁₈O₆₂]⁶⁻ by potential cycling in mildly acidic aqueous media. To obtain an adherent and persistent film, it is necessary that more than six electrons/molecule be fixed on the framework of the heteropolyanion. The film is then studied in pure supporting electrolyte. In this medium, a remarkable current increase is observed during the potential cycling. Whether the film is deposited on a glassy carbon electrode or on the gold electrode of an electrochemical quartz crystal microbalance (EQCM), exactly the same steady current increase up to a maximum is obtained in cyclic voltammetric measurements. The EQCM reveals a steady mass increase during the continuous cycling of the film in the supporting electrolyte. This behaviour is interpreted as featuring an irreversible water and electrolyte intake into the film, up to a maximum, after which the phenomena observed during reduction and oxidation processes are taken as featuring intercalation/deintercalation, respectively. This behaviour is much the same as described in the literature for WO₃ and MoO₃ bronzes, except that the present films seem very stable and have shown no tendency to dissolve or deactivate. Received: 2 December 1998 / Accepted: 26 January 1999     

Zirconium-Based Metal Organic Frameworks for the Capture of Carbon Dioxide and Ethanol Vapour. A Comparative Study

This paper reports on the comparison of three zirconium-based metal organic frameworks (MOFs) for the capture of carbon dioxide and ethanol vapour at ambient conditions. In terms of efficiency, two parameters were evaluated by experimental and modeling means, namely the nature of the ligands and the size of the cavities. We demonstrated that amongst three Zr-based MOFs, MIP-202 has the highest affinity for CO₂ (−50 kJ·mol⁻¹ at low coverage against around −20 kJ·mol⁻¹ for MOF-801 and Muc Zr MOF), which could be related to the presence of amino functions borne by its aspartic acid ligands as well as the presence of extra-framework anions. On the other side, regardless of the ligand size, these three materials were able to adsorb similar amounts of carbon dioxide at 1 atm (between 2 and 2.5 µmol·m⁻² at 298 K). These experimental findings were consistent with modeling studies, despite chemisorption effects, which could not be taken into consideration by classical Monte Carlo simulations. Ethanol adsorption confirmed these results, higher enthalpies being found at low coverage for the three materials because of stronger van der Waals interactions. Two distinct sorption processes were proposed in the case of MIP-202 to explain the shape of the enthalpic profiles.