Gérard Demazeau

The aim of this work was to develop a high-pressure decontamination and sterilization process for pharmaceutical treatments as was developed in food processing in the late eighties. The lack of normalized biological indicators able to validate sterilizing treatments under high pressure led us to select representative pathogenic strains from flora and the European Pharmacopoeia. We selected the following four bacterial strains: Candida albicans (ATCC 10231), Psuedomonas aeruginosa (ATCC 9027), spores of Aspergillus niger (ATCC 16404) and Staphylococcus aureus (ATCC 6538). This present study is focussed on S. aureus. Successive pressurization and depressurization cycles appeared to be more efficient than a continuous high-pressure treatment. Importantly, these pressure conditions, temperature and process duration are perfectly compatible with current industrial plants. These results show that HHP technology is a new alternative to inactivate pathogenic strains in accordance with pharmaceutical requirements.

Purpose. According to the development in the last decade of industrial processes using high hydrostatic pressure (HHP) for preservation of several commercial food products, novel sterilization or...

Pd L-edge XANES and Pd K-edge XANES/EXAFS have been studied to investigate the electronic configuration and local structure of Pd in a new perovskite LaPdO₃, which was prepared under high pressure. A white line in the Pd L-edge XANES for LaPdO₃ is positioned just in the middle of those for divalent (Pd^IIO) and tetravalent (Zn₂Pd^IVO₄) palladates. The peak intensity for LaPdO₃ is also in-between those for PdO and Zn₂PdO₄. Pd K-edge XANES spectra for PdO is characterized by a shoulder in the threshold edge due to the planar square coordination of Pd. The absence of such a shoulder in Pd K-edge XANES spectra for LaPdO₃ and Zn₂Pd^IVO₄ suggests a nearly regular octahedral symmetry of (PdO₆) in both structures. These XANES results underline that the palladium ions with an oxidation state of III are stabilized with the electronic configuration, t_2g ⁶σ*¹ in LaPdO₃. The Pd K-edge EXAFS analysis confirms that (PdO₆) octahedra in LaPdO₃ are nearly isotropic and the average Pd^III–O bond distance is 2.06₄ Å, which is compatible with the average Pd^III–F bond distance (2.00 Å) estimated from a recent EXAFS study on trivalent palladium fluoride.

An evolution of local structure of Ni and chemical bonding, Ni(III)-O in perovskite lattice with strongly distorted structure is investigated with 57 Fe Mössbauer spectroscopy. The Mössbauer spectra for 57 Fe-doped TlNiO 3 were resolved to two quadrupole doublets with different isomer shifts, which underlines a partial charge disproportionation phenomenon: 2Fe 3+ M Fe 3+ f +Fe 3 m f . This result supports the existence of two different crystallographic sites for Ni in the distorted perovskite lattice.

Gallium nitride can be synthesized by a solvothermal route using ammonia as solvent and a nitriding additive (such as hydrazine hydrochloride NH 2 NH 3 Cl or sodium azide NaN 3 ) encapsulated in melt gallium as chemical reagents. The involved temperature and pressure are respectively 600 °C and 150 MPa. The synthesized products are then characterized by X-Ray Diffraction and Scanning Electron Microscopy. The synthesis parameters influence the powder morphology and purity.

A new Ni(III) compound, TlNiO₃ has been prepared under high oxygen pressure. The pressure and temperature domain required to prepare pure TlNiO₃ was found to be very narrow (P ≥ 7.5 GPa, 650 ≤ T ≤ 700 °C). TlNiO₃ crystallizes in the GdFeO₃-type perovskite structure with the following lattice parameters: a = 5.2549(1), b = 5.3677(1) and c = 7.5620(2) Å. The corresponding unit cell volume of 213.3 ų is somewhat larger than the value expected from a plot of unit cell volume vs. ionic radius of the A cation for the analogous ANiO₃ series (A = rare earth metal or yttrium). According to the structural analysis, the twelve Tl–O bonds in TlNiO₃ can be classified into three approximate groups (four short, four medium and four long distances), while, in the other ANiO₃ compounds, the A–O bonds are divided into two groups of eight short and four long distances. The large unit cell volume of TlNiO₃ is surely due to the different coordination of the Tl(III) ion in the perovskite lattice. The average Ni–O–Ni bond angle (147.6°) in TlNiO₃ is very similar to that observed in YNiO₃ (147.3°). However, the Néel temperature (T_N = 105 K) in antiferromagnetic TlNiO₃ is significantly lower than that observed in YNiO₃ (T_N = 145 K), which has a comparable Ni–O–Ni angle. The magnetic properties could be explained by the competing effect of the Tl(III)–O bond on the covalency of Ni(III)–O bond.