Aluminium-gallium substitution in yttrium garnets investigated by NMR

The aluminium-gallium substitution has been studied in the garnet structure of composition Y3Al5-xGaxO12 (x = 0,1,2,3,5) by a local atom observation using both of 27Al MAS and 71Ga static NMR techniques. Each site has been characterised by the isotropic chemical shift (δiso) and the quadrupolar interaction tensor (CQ and ηQ). An important lineshape (quadrupolar parameter) evolution has been observed when the gallium substitution increases which translates as site defonnation, viewed on the whole by atoms with octahedral symmetry. Little electric field gradient variation has been observed for the tetrahedral site. For YGG (Y3Ga5O12), Ga NMR distinguishes two types of octahedron. They are differently affected by substitution

High temperature

27Al NMR spectra have been acquired during the cooling of four liquid samples (12CaO-7Al2O3, CaO-Al2O3, CaO-2Al2O3, CaO-6Al2O3) from 2400 K to supercooled liquid and then glass or crystal. Both CaO-2Al2O3 and CaO-6Al2O3 crystallize and a crystallization rate of 105 g.s-1 can be estimated for the latter. For each compound, the chemical shift values evolve linearly with temperature. The chemical shift/temperaturc slope is minimum for CaAl2O4, the more polymerized liquid of the system. For 12CaO-7Al2O3 (the only observed compound with X(CaO)/X(Al2O3)>1), the slope increases again. The slope evolution with alumina rate is similar to that observed for viscosity at high temperature, signifying a possible relation between both phenomena. For CaO-Al2O3, the study of NMR characteristic time calculated from relaxation measurements and shear correlation time deduced from viscosity in the liquid shows that these two phenomena have the same microscopic origin

High temperature NMR observation of mobile phases up to 1500°C

A new high temperature Nuclear Magnetic Resonance device using double laser heating system has been developed for NMR experiments up to 1500°C. Different systems have been investigated, both of theoritical and applied interest. We report here three examples, where the appearance and the role of mobile species are characterized by 27Al, 23Na and 19F NMR signal evolution with temperature : solid - liquid transition in cryolite Na3AlF6, β-α alumina transformation with fluoride mineralizer, and the effects of mineralizer CaF2 on the high temperature reactions in the clinker formation

The early phyllosoma stages of spiny lobster Panulirus echinatus Smith, 1869 (Decapoda: Palinuridae) reared in the laboratory

The early stages of the Panulirus echinatus were hatched and reared in the laboratory. Ovigerous females were captured in their habitat and carefully transported to the laboratory. Larvae were transferred in a recirculation water tank at a density of 10 larvae.L-1. The larvae were fed on Artemia and gonads of mussel Brachydonts sp. Microalgae Dunaliella viridis was added at a concentration of 150 x 10(4) cell.mL-1. Larvae and exuviae of each zoeal stage were preserved in an alcohol 70% + glycerin (1:1) solution. The phyllosomas moulted eight times; the intermoulting period of each instar averaged about 7 to 10 days. The main morphological changes of each appendage were described in detail, illustrated and compared with previous reports