0000000000104424
AUTHOR
P. Perriat
showing 12 related works from this author
Fine grain barium titanate: ferroelectric domains and X-ray diffraction diagram
2002
Through three different studies using various kinds of BaTiO/sub 3/ samples: as a powder while heating over the Curie temperature; as a green ceramic as a function of the forming pressure; as a ceramic while applying a D.C. field. It is shown how X-ray diffraction is able to give information about the evolution of the 90/spl deg/ ferroelectric domain microstructure.
Application of gas separation membranes to detritiation systems
2002
The use of gas separation membranes in tritium removal systems has been studied to develop a new detritiation process. The main advantage of this new process is to reduce the number and/or the size of equipments in comparison to conventional detritiation systems. The objective of this study is to choose the best suited membrane for this application. The hydrogen or its isotopes recovery performance of several commercial hollow fiber organic membranes has been analyzed thanks to three devices. Experiments are performed with small quantities of hydrogen gas or deuterium gas or tritium gas in the range representative of the radioactive contamination level in tritium handling gloveboxes. A math…
Ferroelectric domains in BaTiO3powders and ceramics evidenced by X-ray diffraction
1995
Abstract Through three different studies, using BaTiO3 samples, as a powder while heating over the Curie temperature, and as a ceramic while applying an electric field, it is shown how X-ray diffraction (XRD) is able to give information about the evolution of the ferroelectric domain microstructure. Firstly, the relative intensities of the 002 and 200 lines, as a function of the applied electric field, exhibit the motion of the 90[ddot] domain walls. However, XRD is unable to provide any distinction between two 180[ddot] domains. Secondly, the profile of those two lines and of the other double (hhl), (lhh) lines is particular: the unusual diffracted intensity between such double lines has t…
Oxygen stoichiometry control of nanometric oxide compounds: The case of titanium ferrites
2011
Three techniques have been coupled with an original device, based on H{sub 2}/H{sub 2}O equilibrium, controlling oxygen partial pressure: XRD, TGA and DC conductivity in order to characterize very reactive compounds such as nanometric powders. From XRD, both the structure and the oxygen stoichiometry (thanks to their lattice parameter) were investigated in situ. From TGA, it was the oxygen stoichiometry (thanks to mass gain or loss) which was determined. From DC conductivity, it was both the structure and the oxygen stoichiometry (thanks to the activation energy) which were obtained. The advantages were to determine very rapidly and with a small amount of powder the equilibrium conditions (…
Thermodynamic considerations of the grain size dependency of material properties
1994
Phase transitions which depend on grain size induce very interesting properties in materials such as zirconia or barium titanate. A new and rigorous thermodynamic treatment of this type of phase transition is proposed with consideration of the surface phenomena. An interpretation is given of the observed differences when the material—particularly BaTiO3—under consideration is a fine grain powder or is a fine grain ceramic.
Surface composition analysis during the oxidation of ferrites: A necessity
1998
The cationic composition of a titanium ferrite (Fe 2.5 Ti 0.5 O 4 ) has been followed by XPS during its oxidation in cation deficient phases (without crystallographic transformation) in order to reveal a dynamic segregation phenomenon. Indeed, during this oxidation, an important modification of the chemical composition of the first layers of the material has been revealed: below 350 °C, the titanium ferrites surface becomes richer in iron and poorer in titanium. But, if the reaction is extended above 400 °C, some titanium can move to the surface. This phenomenon has been interpreted on the basis of the differences of mobility of the different ions which are present in the material. Finally,…
Control of grain size and morphologies of nanograined ferrites by adaptation of the synthesis route: mechanosynthesis and soft chemistry
2003
Abstract Nanocrystalline Fe-based spinels with composition Fe 2.5 Ti 0.5 O 4 can be synthesized using two different routes: soft chemistry and high-energy ball milling. This paper is focussed on the fact that each type of synthesis process can lead to powders with a crystallite size of about 15 nm but with significant differences in the grain size distribution and the agglomeration state. Whereas in the case of mechanosynthesis, the ball-milled powders consist of aggregates, those obtained by soft chemistry are very well dispersed. Moreover the chosen investigated nanopowders present a blocked/superparamagnetic transition depending on the grain size. The grain size morphologies obtained by …
Glovebox atmosphere detritiation process using gas separation membranes.
2003
Abstract The use of gas separation membranes in atmospheric detritiation systems has been studied. The main advantage of this new process is to reduce the number and/or the size of the equipment in comparison to conventional tritium removal systems. Owing to the constraints linked to tritium handling, the separation performances of several commercial hollow fiber organic membranes have been analyzed, under various operating conditions, with hydrogen/nitrogen or deuterium/nitrogen mixtures. The experiments are performed with small quantities of hydrogen or deuterium (5000 ppm). The experimental results allow to evaluate the separation efficiency of these membranes and to determine the approp…
Effect of the preparation method and grinding time of some mixed valency ferrite spinels on their cationic distribution and thermal stability toward …
1996
Abstract The reactivity in oxygen of several mixed valency ferrite spinels, namely Fe3O4, FeCr2O4, Fe3 − xTixO4 and Fe3 − xMoxO4 was investigated by derivative thermogravimetry (DTG) analysis as a function of the conditions of preparation and grinding. For all these compounds, low temperature preparation or prolonged grinding time enables small particles ( 0.5 μm), it was observed that oxidation was starting at higher temperature and that the defect spinel phases could not be retained during oxidation. This behaviour was attributed to the presence of stresses induced by the lattice parameter gradient and promoting the formation of nuclei of the α-rhombohedral phase from the superficial γ-de…