Use of glow discharge in fluidized beds

Static charges and agglomerization of particles in a fluidized bed systems are minimized by maintaining in at least part of the bed a radio frequency glow discharge. This approach is eminently suitable for processes in which the conventional charge removing agents, i.e., moisture or conductive particle coatings, cannot be used. The technique is applied here to the disproportionation of calcium peroxide diperoxyhydrate to yield calcium superoxide, an exceptionally water and heat sensitive reaction

Process for the preparation of calcium superoxide

Calcium superoxide is prepared in high yields by spreading a quantity of calcium peroxide diperoxyhydrate on the surface of a container, positioning said container in a vacuum chamber on a support structure through which a coolant fluid can be circulated, partially evacuating said vacuum chamber, allowing the temperature of the diperoxyhydrate to reach the range of about 0 to about 40 C; maintaining the temperature selected for a period of time sufficient to complete the disproproriation of the diperoxyhydrate to calcium superoxide, calcium hydroxide, oxygen, and water; constantly and systematically removing the water as it is formed by sweeping the reacting material with a current of dry inert gas and/or by condensation of said water on a cold surface; backfilling the chamber with a dry inert gas; and finally, recovering the calcium superoxide produced

Magnetic properties of the honeycomb oxide Na2_2Co2_2TeO6_6

We have studied the magnetic properties of Na$_2$Co$_2$TeO$_6$, which features a honeycomb lattice of magnetic Co$^{2+}$ ions, through macroscopic characterization and neutron diffraction on a powder sample. We have shown that this material orders in a zig-zag antiferromagnetic structure. In addition to allowing a linear magnetoelectric coupling, this magnetic arrangement displays very peculiar spatial magnetic correlations, larger in the honeycomb planes than between the planes, which do not evolve with the temperature. We have investigated this behavior by Monte Carlo calculations using the $J_1$-$J_2$-$J_3$ model on a honeycomb lattice with a small interplane interaction. Our model reproduces the experimental neutron structure factor, although its absence of temperature evolution must be due to additional ingredients, such as chemical disorder or quantum fluctuations enhanced by the proximity to a phase boundary.Comment: 9 pages, 13 figure

Anisotropic interactions opposing magnetocrystalline anisotropy in Sr3_3NiIrO6_6

We report our investigation of the electronic and magnetic excitations of Sr$_3$NiIrO$_6$ by resonant inelastic x-ray scattering at the Ir L$_3$ edge. The intra-$t_{2g}$ electronic transitions are analyzed using an atomic model, including spin-orbit coupling and trigonal distortion of the IrO$_6$ octahedron, confronted to {\it ab initio} quantum chemistry calculations. The Ir spin-orbital entanglement is quantified and its implication on the magnetic properties, in particular in inducing highly anisotropic magnetic interactions, is highlighted. These are included in the spin-wave model proposed to account for the dispersionless magnetic excitation that we observe at 90 meV. By counterbalancing the strong Ni$^{2+}$ easy-plane anisotropy that manifests itself at high temperature, the anisotropy of the interactions finally leads to the remarkable easy-axis magnetism reported in this material at low temperature

Magnetic order in the frustrated Ising-like chain compound Sr3_3NiIrO6_6

We have studied the field and temperature dependence of the magnetization of single crystals of Sr3NiIrO6. These measurements evidence the presence of an easy axis of anisotropy and two anomalies in the magnetic susceptibility. Neutron powder diffraction realized on a polycrystalline sample reveals the emergence of magnetic reflections below 75 K with magnetic propagation vector k ~ (0, 0, 1), undetected in previous neutron studies [T.N. Nguyen and H.-C zur Loye, J. Solid State Chem., 117, 300 (1995)]. The nature of the magnetic ground state, and the presence of two anomalies common to this family of material, are discussed on the basis of the results obtained by neutron diffraction, magnetization measurements, and symmetry arguments

Domain Wall Spin Dynamics in Kagome Antiferromagnets

We report magnetization and neutron scattering measurements down to 60 mK on a new family of Fe based kagome antiferromagnets, in which a strong local spin anisotropy combined with a low exchange path network connectivity lead to domain walls intersecting the kagome planes through strings of free spins. These produce unfamiliar slow spin dynamics in the ordered phase, evolving from exchange-released spin-flips towards a cooperative behavior on decreasing the temperature, probably due to the onset of long-range dipolar interaction. A domain structure of independent magnetic grains is obtained that could be generic to other frustrated magnets.Comment: 5 pages, 4 figure

Effects of a Dispersed and Undispersed Crude Oil on Mangroves, Seagrasses and Corals

The primary objective of this study was to evaluate the application of dispersant to spilled oil as a means of reducing adverse environmental effects of oil spills in nearshore, tropical waters. The results of numerous laboratory and field studies have suggested that dispersants may play a useful role in reducing adverse impacts on sensitive and valued environments such as mangroves, seagrasses, and corals. However, the use of dispersants has not been allowed thus far in most situations because of a lack of direct experimental data on the various effects of dispersants and the environmental trade-offs presumed to occur as a result of their application to crude oils. To accomplish this objective, a 21/2- year field experiment was designed in which detailed, synoptic measurements and assessments were made of representative intertidal and nearshore subtidal habitats and organisms (man-groves, seagrass beds, and coral reefs) before, during, and after exposure to untreated crude oil and chemically dispersed oil. The results were in-tended to give guidance in minimizing the ecological impacts of oil spills through evaluation of trade-offs in the relative impacts of chemical dispersion to tropical marine intertidal and subtidal habitats