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81.
Site-selective spectroscopy of Eu-doped orthorhombic lanthanum and monoclinic yttrium polyphosphates
Riadh Ternane Mokhtar Ferid Grard Panczer Malika Trabelsi-Ayadi Georges Boulon 《Optical Materials》2005,27(12):1832-1838
In order to study the influence in the change of the coordination environment of the cationic sites on the luminescent properties of rare-earth ions doping polyphosphates Ln(PO3)3 (Ln = La, Y) with two different structures, the time-resolved luminescence of the Eu3+ ion, used as structural probe, is reported. La(PO3)3 has an orthorhombic structure in which only one position with eight coordination is available for the cation, while Y(PO3)3 adopts the Yb(PO3)3 structure in which four slightly different octahedral sites are available for the trivalent rare-earth ion. Site-selective excitation of the 5D0 level was performed and luminescence decay times of each Eu3+ site were measured at 77 K. The spectroscopic results are discussed and correlated with the structural data. 相似文献
82.
Hassan El Attaoui Malika Saâdaoui Jérôme Chevalier Gilbert Fantozzi 《Journal of the American Ceramic Society》2005,88(1):172-178
Grain bridging degradation behind a crack tip is the main cyclic fatigue mechanism in nontransforming ceramics. In this work, a compliance function is used to quantify the shielding capacity of grain bridges during cyclic loading of alumina ceramics with different grain sizes. This allows to identify the different stages occurring during cyclic loading. Significant degradation is observed in the coarse grain material and a marked sensitivity to the loading level is outlined. At moderate loads, bridging degradation occurs prior to fatigue crack growth during an incubation period which can reach several million cycles. At low cyclic loads, the shielding capacity can be entirely degraded, leading to a cyclic fatigue threshold equivalent to that of the fine grain material. 相似文献
83.
Malika Ouagued Abdallah Khellaf Larbi Loukarfi 《International Journal of Hydrogen Energy》2018,43(6):3451-3465
The potential of hydrogen production by thermochemical cycle in Algeria using solar radiation as heat sources is estimated under the climate conditions of the country. The study analyzes an integrated copper–chlorine (Cu–Cl) thermochemical cycle with solar parabolic trough system for hydrogen production. In order to determine the most promising solar sites available for deploying the integrated system, the direct normal solar irradiance (DNI) for horizontal tracking system oriented in North-South has been estimated and compared for different locations. Heat gain from parabolic trough collector model is evaluated under Algerian conditions. To describe the different steps of the Cu–Cl cycle for hydrogen production, we perform a thermodynamic analysis accounting for relevant chemical reactions and including the determination of the energy necessary to the cycle. A parametric study is conducted to investigate the effect of heat gain from the parabolic trough collector (PTC) on the hydrogen production rate. Furthermore, the rate production of hydrogen by the Cu–Cl cycle is analyzed and compared for performance improvement of the system for different climatic regions in Algeria. Simulation results reveal great opportunities of hydrogen production using Cu–Cl cycle combined with solar PTC in the south of Algeria with annual hydrogen production exceeds 84 Tons H2/year (around 0,30 kg/m2/day). 相似文献
84.
Sana Hraiech Fathia Chehimi-Moumen Mokhtar Ferid D. Ben Hassen-Chehimi Malika Trabelsi-Ayadi 《Materials Research Bulletin》2005,40(12):2170-2179
Synthesis and single crystal structure are reported for a new gadolinium acid diphosphate tetrahydrate HGdP2O7·4H2O. This salt crystallizes in the monoclinic system, space group P21/n, with the following unit-cell parameters: a = 6.6137(2) Å, b = 11.4954(4) Å, c = 11.377(4) Å, β = 87.53(2)° and Z = 4. Its crystal structure was refined to R = 0.0333 using 1783 reflections. The corresponding atomic arrangement can be described as an alternation of corrugated layers of monohydrogendiphosphate groups and GdO8 polyhedra parallel to the () plane. The cohesion between the different diphosphoric groups is provided by strong hydrogen bonding involving the W4 water molecule.
IR and Raman spectra of HGdP2O7·4H2O confirm the existence of the characteristic bands of diphosphate group in 980–700 cm−1 area. The IR spectrum reveals also the characteristic bands of water molecules vibration (3600–3230 cm−1) and acidic hydrogen ones (2340 cm−1). TG and DTA investigations show that the dehydration of this salt occurs between 79 and 900 °C. It decomposes after dehydration into an amorphous phase. Gadolinium diphosphate Gd4(P2O7)3 was obtained by heating HGdP2O7·4H2O in a static air furnace at 850 °C for 48 h. 相似文献