High-temperature Powder Diffraction Study Research Articles

Laser heating setup for diamond anvil cells for in situ synchrotron and in house high and ultra-high pressure studies

The diamond anvil cell (DAC) technique combined with laser heating is one of the major methods for studying materials at high pressure and high temperature conditions. In this work, we present a transferable double-sided laser heating setup for DACs with in situ temperature determination. The setup allows precise heating of samples inside a DAC at pressures above 200 GPa and could be combined with synchrotron beamline equipment. It can be applied to X-ray diffraction and X-ray transmission microscopy experiments. In the setup, we use high-magnification and low working distance infinity corrected laser focusing objectives that enable us to decrease the size of the laser beam to less than 5 µm and achieve the maximum optical magnification of 320 times. All optical components of the setup were chosen to minimize chromatic and spatial aberrations for accurate in situ temperature determination by multiwavelength spectroscopy in the 570–830 nm spectral range. Flexible design of our setup allows simple interchange of laser sources and focusing optics for application in different types of studies. The setup was successfully tested in house and at the high-pressure diffraction beamline ID15B at the European Synchrotron Radiation Facility. We demonstrate an example of application of the setup for the high pressure–high temperature powder diffraction study of PdH and X-ray transmission microscopy of platinum at 22(1) GPa as a novel method of melting detection in DACs.

In situ high-temperature powder diffraction studies of solid oxide electrolyte direct carbon fuel cell materials in the presence of brown coal

Direct carbon fuel cells are an attractive alternative for conventional power generation; however, there is almost no information on the stability of conventional fuel cell materials in direct carbon fuel cell environments, in particular when exposed to realistic fuels and the contaminants contained within these fuels. Similarly, there is little information on the structure and phase assemblage of solid fuels exposed to typical environments found in direct carbon fuel cells. In this paper, we use in situ high-resolution synchrotron powder diffraction on conventional high-temperature fuel cell materials and untreated brown coal to assess the stability and reactivity of these materials at various temperatures up to 850 °C. Materials investigated include nickel metal (Ni), gadolinium-doped ceria (GDC) and yttria-stabilised zirconia (YSZ). The phase stability, crystallite size, lattice parameters and associated linear coefficient of thermal expansion were determined. The phase stability of all fuel cell materials was found to be good with no additional phase formation noted either during heating or after prolonged periods at temperature. An increase in the crystallite size was observed for both GDC and Ni. Non-linear thermal expansion observed in these materials was related to partial reduction of cerium ions (GDC) and due to a Curie point transition (Ni). A wide range of mineral phases were observed in the coal samples and these phases were found to change significantly with temperature. Mineral phases consistent with the ash composition and existing literature on Victorian brown coal were assigned to phases observed.

High temperature powder diffraction study of (Zn,Cd)S and ZnxCd1−xS nanopowders

Nanocrystalline powders of cubic (Zn,Cd)S and ZnxCd1−xS were synthesized by the chemical precipitate method from the aqueous solution of sodium sulphide, zinc nitrate and cadmium nitrate at 277 K without any capping agent. High temperature X-ray diffraction (HTXRD) has been performed to test the stability of the nanopowders. We observed, ZnS is more structurally stable than CdS even at high temperature. The systematic shift in peak position towards the higher angles revealed the changes in the lattice parameter of ZnS and ZnxCd1−xS with an increase in the temperature. The environmental impact on ZnS during HTXRD has also been observed. We observed a significant change in the particle size as the temperature increases. Results of the high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAD) are in accordance with the XRD data.

P-V and T-V Equations of State of natural biotite: An in-situ high-pressure and high-temperature powder diffraction study, combined with Mossbauer spectroscopy

The P - V and T - V equations of state of a natural biotite sample (Mg/Fe ratio ≈ 1) have been studied using in-situ high-pressure (0.0001–11 GPa) synchrotron radiation powder diffraction at the European Synchrotron Radiation Facilities (ESRF) in Grenoble, France, and in-situ high-temperature (298–610 K) laboratory X-ray powder diffraction. A third-order Birch-Murnaghan model [ V = 498.7(1) A3, measured value] provides the following elastic parameters: K = 49(1) GPa, K ’ = 8.1(5). The volume thermal expansion is satisfactorily described by a constant value resulting in 37(2) 10−6 K−1. Mossbauer spectroscopy proves that REDOX reactions have occurred upon heating, presumably 2(OH− + Fe2+) → 2O2− + 2Fe3+ + H2↑ and/or 4Fe2+ + 2OH− + O2 → 4Fe3+ + 3O2− + H2O. On the basis of the elastic and thermal parameters measured we have modeled the deformation contribution ( G deform) to the Gibbs energy. The third-order Birch-Murnaghan model with V fixed at its experimental value and the model with refined V do not significantly differ from one another in terms of G deform. A comparison based on G deform between biotite and phlogopite shows a better compliance to P of the former, though balanced in mineral reactions by a difference of molar volume, i.e., V (biotite) > V (phlogopite).

Physical and physicochemical processes accompanying powder synthesis, growth of PbMoO4 crystals, and their annealing in various media: I. Solid-state mechanism of the formation of the Pb2MoO5 microheterogeneous phase in PbMoO4 crystals

In this study, the first of the proposed cycle, the conditions and the mechanism of nucleation and formation of particles of the Pb2MoO5 phase in PbMoO4 crystals, which are due to the physicochemical features of the heating, melting, and solidification of PbMoO4, are considered. It is shown that preferred evaporation of one of the composite components of this compound, MoO3, leads to the violation of the initial stoichiometry and formation of excess PbO in a charge at the synthesis stage and in a melt during the crystal growth. The formation of the Pb2MoO5 phase in crystals with excess PbO occurs during their postgrowth cooling at temperatures below 930°C (eutectics between PbMoO4 and Pb2MoO5). The results of the differential thermal analysis, X-ray diffraction analysis, high-temperature powder diffraction study, and annealing of crystals in specific media confirm the solid-state mechanism of the formation of the Pb2MoO5 phase in PbMoO4 crystals.

Reduced magnesium titanate electrodes for solid oxide fuel cells

The solid solution series Mg2−yTi1+yO4,0<y<0.5 with average Ti oxidation state, x (3.3<x<3.9), has b een investigated as a possible high temperature anode for fuel cell and electrochemical reactor application. Reduced magnesium titanate spinels, have been shown to have good stability in reducing atmospheres and to resist oxidation in air up to 500°C. Good electronic conductivity is exhibited, with room temperature conductivities in the range 10−4 to 0.5 S cm−1. On increasing temperature, conductivity increases and Arrhenius conductivity dependence is observed, activation energies vary from 50–400 meV from x=3.3 to x=3.9. Thermal expansion coefficients obtained from high temperature powder diffraction studies, ≈1×10−5K−1, demonstrate structural compatibility with 8% yttria-stabilised zirconia electrolytes. Some evidence was found for chemical reaction between (Y2O3)0.08(ZrO2)0.92 and reduced spinel powders at very high temperatures. The product of this reaction was found to be electronic ally conductive; indicating that problems at the electrode/electrolyte interface would not be encountered.