P. Tissot

Thermodynamic considerations in constructing energy balances for cellular growth

A review with 48 refs. The topics discussed include mass and energy balances for open and non-steady state systems, calcn. of reaction enthalpies, and enthalpy balance in aerobic and anaerobic growth. [on SciFinder (R)]

β phase and γ-β metal-insulator transition in multiferroic BiFeO3

We show that epitaxial (001) thin films of multiferroic bismuth ferrite BiFeO3 are monoclinic at room temperature instead of tetragonal or Rhombohedral as reported earlier . We report a orthorhombic order-disorder beta-phase between 820C and 950C contrary to the earlier report. The transition sequence monoclinic-orthorhombic phase in (001)BiFeO3 thin film (rhombohedral-orthorhombic transition in single crystal) resembles that of BaTiO3 or PbSc1/2Ta1/2O3. The transition to the cubic

Pseudo-binary Pb(Mg13Nb23)O3-PbO phase diagram and crystal growth of Pb(Mg13Nb23)O3 [PMN]

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Specific heat capacity and Debye temperature of zirconia and its solid solution

-phase causes an abrupt collapse of the bandgap toward zero (insulator-metal transition) at the orthorhombic-cubic beta-gamma transition around 950C. This transition is similar to the metal-insulator transition in Ba0.6K0.4BiO3.

Anodic oxidation of cyanide on a reticulated three- dimensional electrode

Abstract A pseudo-binary phase diagram between the perovskite Pb(Mg 1 3 Nb 2 3 ) O 3 and PbO has been established by D.T.A.. The melting point of PMN was found at 1320°C and the eutectic temperature at 830±2°C with the eutectic composition of 74% PbO 26% PMN (in wt%). On the basis of the determined phase diagram single crystals of the perovskite phase have been grown by the high temperature solution technique by using 30wt% PbO as solvent. The obtained crystals show pseudo-cubic form with (100)cub. growth steps or degenerated forms. Size (∼ 1cm) and quality of the obtained crystals are adequate for physical characterizations.

The characterrization of high temperature solution-grown single crystals of Pb(Fe1/2Nb1/2)O3

Specific heat CP of zirconia and yttria stabilized zirconia doped or not with erbia and ceria was measured from 128 to 823 K and of yttria stabilized zirconia doped with erbia and plutonia from 443 to 1573 K. The new determined data were modelled using Debye theory. Data for the tetravalent oxide and for the studied solid solutions show that the extended Dulong and Petit law in Neumann–Kopp rule is verified for zirconia and the quaternary compounds. The Debye temperature of zirconia (590 K) and its yttria, erbia and ceria doped solid solutions (575–625 K) derived from these CP measurements between 150 and 823 K is discussed and compared with that reported for other tetravalent metal oxides.

Determination of the thermal conductivity in zirconia based inert matrix nuclear fuel by oscillating differential scanning calorimetry and laser flash

The preparation of a three-dimensional electrode suitable for the oxidation of dilute solutions of cyanide, by the electrodeposition of Pb02 on a reticulated vitreous carbon substrate is described. The electrode obtained (RVC-Pb02) is corrosion resistant and allows the oxidation of less than 5 p.p.m. of CN− with a faradaic yield estimated at 50%. The mass transfer coefficient for the oxidation of the potassium ferrocyanide and the specific surface area of the RVC-Pb02 electrode has been determined.

Electrical conductivity in uranium doped, modified lead zirconate pyroelectric ceramics

Polarization microscope studies on single crystal samples of Pb(Fe1/2Nb1/2)O3 (PFN) have been made. Thin platelets (<60 μ) show large, homogeneous ferroelectrics domains, and optical characterization shows that PFN is trigonal at room temperature and optically negative. Birefringence measurements between 4.2 and 400 K reveal that the transition to the cubic structure takes place at 383 K, in accordance with earlier work, but they also locate a previously undetected structural modification at 354 K, accompanied simultaneously by a reorientation of the index ellipsoid; both transitions manifest themselves by endothermic reactions on heating in DTA experiments. The new phase is very likely monoclinic.

Polarization Optical, Electric and Neutron Scattering Studies of the Perovskite Pb2CoWO6

The performances of oscillating differential scanning calorimetry (ODSC) and laser-flash technique in determining the thermal conductivity and the specific heat of zirconia-based materials, analogous to a potential nuclear fuel, were compared. The tested materials were (Zr1−x−y−z,Yx,Ery,Mez)O2−(x+y)/2, with Me=Ce or Th. The measured specific heats were around 0.4 J K−1 g−1 and the thermal conductivities ranged from 2 to 3 W K−1 m−1. The ODSC measurements resulted in cp values. The thermal conductivity was derived from two complementary measurements, one with a thin and the other with a thick sample. The laser-flash technique directly delivered the thermal diffusivity of the sample; consequently, the specific heat capacity cp has to be known for determining the thermal conductivity. The ODSC measurements were affected by the position of the sample on the support. This, consequently, influenced the reproducibility of the measurements. The reproducibility of the scans by laser flash was excellent. Thermal conductivity decreased with increase in the stabilizer (Y, Er) concentration. This trend was justified on the basis of a model including concentration and size of the oxygen vacancies.

Electrochemical reduction of 2-chloro-2-cyclohexenones

Abstract A number of ceramic compositions in the PbZrO3-Pb2FeNbO6-PbTiO3 system have been developed for use in pyroelectric ‘point-detectors’. It has been found that it is highly desirable for the pyroelectric ceramic to possess a controllable electrical resistivity in the range of 109 to 1011Ωm to allow the detector elements electrical time constant to be simply determined. The effects of the addition of up to 1 mole % UO3 and the inclusion of up to 3 mole % excess PbO during the fabrication of selected compositions in the PbZrO3 - Pb2FeNbO6 - PbTiO3 ceramic system were investigated. Measurements of electrical resistivity, pyroelectric coefficient, dielectric constant and loss, and grain size were carried out. Two distinct activation energies were measured for the conduction process. Evidence suggests that both electron and hole conduction may be observed, depending upon the uranium concentration and PbO excess. Significant reductions in dielectric constant and loss, brought about by uranium doping, are...