Neutron and X-ray experiments at high temperature
2014 Advanced technologies, like for instance aerospace or nuclear engineering require the most exhaustive information on the behaviour of materials used at very high temperature such as ceramics, refractory alloys or molten metals. Among high temperature techniques, X-rays and more recently neutron scattering have appeared as powerful tools to get information, mainly structural, on these materials in their working conditions. High temperature devices (above 2 000 K) developed for that purpose, based on various heating techniques (induction, imaging furnaces, lasers, gas-flame heaters and principally Joule heated devices) are reviewed. Some crucial points are particularly emphasized such as : 2014 the determination of the real temperature (thermocouples and optical pyrometry) in the scattering zone hardly accessible partly due to the unavoidable thermal gradients, 2014 the chemical reactivity of the sample with its surrounding, i.e. atmosphere and sample holder. Neutrons, mainly because of their low absorption by matter, allow the work on real bulky materials and give a greater freedom in the conception of high temperature scattering devices compared to X-rays. At the present time thermal neutron high flux reactors offering a wide range of neutron wavelengths are available, and a new generation of more and more efficient multidetectors has emerged in the last decade; the data acquisition and consequently the high temperature exposure time have been notably reduced, opening a way for precise and reliable experiments in the 3 000 K range. This very high temperature domain already studied by a few other techniques can also be investigated by neutron scattering. Revue Phys. Appl. 19 (1984) 649-662 SEPTEMBRE 1984, PAGE (*) The author’s personal work has been done at the ILL (HFR Grenoble). Now with the Equipe de Physico-Chimie Moleculaire, CENG-DRF, 85X, 38041 Grenoble Cedex, France. REVUE DE PHYSIQUE APPLIQUEE. T. I9, N° 9, SEPTEMBRE 1984 45 Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:01984001909064900
Quadrupole Lamp Furnace for High Temperature (up to 2050 K) Synchrotron Powder X-ray Diffraction Studies in Air in Reflection Geometry
A four-lamp thermal image furnace has been developed to conduct high temperature x-ray diffraction in reflection geometry on oxide ceramic powder samples in air at temperatures ⩽2050K using synchrotron radiation. A refractory crucible made of Pt20%Rh alloy was used as a specimen holder. A material with well characterized lattice expansion properties was used as an internal crystallographic thermometer to determine the specimen temperature and displacement. The performance of the apparatus was verified by measurement of the thermal expansion properties of CeO2, MgO, and Pt which were found to be within ±3% of the acceptable values. The advantages, limitations, and important considerations of the instrument developed are discussed.
OM4 Tetrahedra linkages and the cationic group (M0)nn+ in rare earth oxides and oxysalts
Abstract Consideration of the coordination of the oxygen atoms in rare-earth oxide and oxysalt structures shows that these are generally surrounded by a tetrahedron of metal atoms. All known structures can therefore be described as tri-dimensional or bi-dimensional packing of such OM4 tetrahedra sharing edges. In A-M2O3, B-M2O3, and the oxysalts, the packed tetrahedra appear as an infinite polymeric complex cation (MO)nn+. Possible implications for the unknown structures of nonstoichiometric oxides are discussed. The results suggest that the oxygen atoms are involved in a directional bonding.