The effect of wet milling on the hydriding properties of magnesium based mixture has been investigated. To prepare these mixtures, magnesium was ball milled with different weight percent of graphite (5, 10 and 25), at 300 rpm under air, for various duration using a ball miller apparatus Retsch S100 (R=12). Different solvents have been used such as benzene, heptane, styrene, DMSO. The hydriding properties were studied using a manual Sievert-type apparatus, at different temperatures (25°C, 100°C, 150°C and 200°C). The mixture Mg + 5wt% graphite milled during 6 hours in presence of 5mL heptane has shown the best hydriding properties at 150°C. The improvement of these properties has been related to the dielectric constant of the solvent and to the small size of the particles. The different mixtures have been analysed by means of scanning electron microscopy and laser granulometry.
Spectroscopic properties of mixed aggregates of the guest/host : tetracene/chrysene and tetracene/dibenzo(a,h)anthracene were studied in n-alkane colloidal solutions in water and crystallized mixed films at low temperature. Low guest concentration resulted in the observation of sensitized fluorescence., whereas at high guest concentration, emission of a new exciplex type was seen. The theoretical work of Stevens concerning the correlations of donor-acceptor molecular orbitals was considered in order to interpret the structure of the newly observed exciplex.
The utility of fine-grained iron metal in the remediation of water contamined with Atrazine and Parathion was investigated. Batch procedures under water treatment conditions (ambient temperature and pH of ∼7) indicated that these pesticides degrade rapidly in the presence of iron powder (40–60 mesh, 40 g/l). The decline in the concentration of pesticide was monitored by HPLC. Experiments with unbuffered solutions showed a steady increase in pH values during the reactions. Therefore, experiments were run in buffered solutions. Different buffered solutions resulted in different degradation rates indicating that the buffer plays an important role in enhancing the degradation process. Tests were also performed on an industrial effluent solution containing a variety of pesticides. Although the products of degradation were not characterized, our HPLC results indicated the disappearance of all the parent pollutants.
Several examples of exciplex-type emissions observed in mixed aggregates of polycyclic aromatic hydrocarbons prepared in frozen n-alkane solutions and as colloidal suspensions in water are reported for the first time. Crystallization conditions and structural defects are shown to play a major role in the formation of the complexes responsible for these emissions. A predictive rule for their observation based on the crystallographic structure of the host and guest molecules is proposed. Because their emissions differ on several points from those of regular exciplexes on the one hand, and on the other hand because they were found in two cases to exist in the ground state, these complexes are tentatively assigned as “contact complexes”.
Concentrated frozen solutions of dibenzofuran in n-heptane and pyrene in n-hexane were investigated by both fluorescence and absorption specroscopy. At extremely high concentrations or relatively high concentrations and diminished crystallization rates, the “normal” quasiline spectra are replaced by “new” spectra that exhibit quasiline character and that are not due to the formation of microcrystals of the solute. Intensity distribution chanfes among the vibronic lines involving non totally symmetric vibrational modes in the first electronic transition of the new spectrum have been interpreted as a result of weak interactions between oriented solute molecules. A model of the centers from which these spectra are originating is proposed. It is suggested that the model may provide an alternative interpretation for the occurrence, only at high solute concentration, of quasiline spectra, in the case of aromatics in “unsuitable” frozen n-alkanes.
Une hétéroassociation particulière entre les molécules des hydrocarbures aromatiques polynucléaires (HAP) à l’état fondamental est mise en évidence (hétéromère). Les conditions qui favorisent ces associations en l’influence de la concentration relative de ces aromatiques sont étudiées. Les hétéromères sont caractérisés par des spectres d’absorption électroniques et par des émissions particulières.