Ultrasound influence upon calcium carbonate precipitation on bacterial cellulose membranes

The effect of ultrasonic irradiation (40 kHz) on the calcium carbonate deposition on bacterial cellulose membranes was investigated using calcium chloride (CaCl₂) and sodium carbonate (Na₂CO₃) as starting reactants. The composite materials containing bacterial cellulose-calcium carbonate were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The polymorphs of calcium carbonate that were deposited on bacterial cellulose membranes in the presence or in the absence of ultrasonic irradiation were calcite and vaterite. The morphology of the obtained crystals was influenced by the concentration of starting solutions and by the presence of ultrasonic irradiation. In the presence of ultrasonic irradiation the obtained crystals were bigger and in a larger variety of shapes than in the absence of ultrasounds: from cubes of calcite to spherical and flower-like vaterite particles. Bacterial cellulose could be a good matrix for obtaining different types of calcium carbonate crystals.     

The application of the boundary element method to the magnetohydrodynamic duct flow

A boundary element method is developed in order to investigate the flow of viscous, incompressible, electrically conducting fluids in cylindrical ducts having arbitrary cross-sections. The numerical results obtained for the circular duct with insulating wall are very close to the results obtained by means of analytical formulas.     

Hexachlorantimonate(V) mit Nitroverbindungen als Liganden, 1. Mitt.: Komplexverbindungen mit einwertigen Metallen

Hexachloroantimonates with nitroderivatives as ligands on the cations are formed in a double complexation reaction of a mono-valent metal chloride (LiCl, NaCl, KCl, CuCl) with SbCl₅, and a nitroderivativeL (nitromethane, nitrobenzene, α-nitronaphthalene). Solid complexes of the typeML(SbCl₆) andML ₂(SbCl₆) were isolated. Synthesis, analytical results andi.r. spectra are discussed.     

Study of drip line nuclei through two-step fragmentation

We have studied the structure of light neutron-rich nuclei around N = 16 by employing the in-beam -ray spectroscopy technique using the fragmentation of secondary beams of ^25,26Ne, ^27,28Na and ^29,30Mg isotopes. This secondary-beam cocktail was obtained by the fragmentation of a ³⁶S beam at 77.5 MeV by the SISSI/GANIL facility. By a second-step fragmentation, we have measured -ray-residue coincidences in ^17-20C and ^23,24O and described the obtained levels in the framework of the shell model.Received: 31 October 2002, Published online: 24 February 2004PACS: 23.20.Lv transitions and level energies - 21.60.Cs Shell model - 27.20. + n - 27.30. + t