S.M. Clark

An Apparatus for the study of the kinetics and mechanism of hydrothermal reactions by in situ energy dispersive x-ray diffraction

The design and implementation of a pressure cell for the study of hydrothermal reactions by in situ energy dispersive x‐ray diffraction is described. The cell permits the study of both the kinetics and mechanism of formation of a wide range of important solid‐state compounds such as zeolites and other microporous solids. Reactions can be studied over a wide range of temperature (5–230 °C) and autogenous pressure [0–400 psi (gauge)] conditions. The use of this apparatus is illustrated by a study on the synthesis of a microporous tin chalcogenide phase performed on Station 9.7 of the UK Synchrotron Radiation Source.

A new energy-dispersive powder diffraction facility at the SRS

Abstract A new energy-dispersive powder diffraction facility has been constructed on the 6 T wiggler beam line of the Daresbury Laboratory Synchrotron Radiation Source. This paper describes the facility, in particular the beam definition apparatus (front end), the detector positioning system (back end), a 10 000 kN loading frame and high pressure cell and the counting and control electronics. Some recent results are presented including a study of the compressibility of talc and the phase I → II transition of ammonium chloride.

Energy-dispersive powder diffraction at the SRS

Abstract A new energy-dispersive powder diffraction facility has been constructed on the wiggler beam line of the synchrotron radiation source (SRS) at the Science and Engineering Research Councils Daresbury Laboratory. This paper describes the facility, in particular the beam definition apparatus (front end), the diffractometer (back end), and the counting and control electronics. Some recent results are presented including a high pressure study of La 2 CuO 4 .

Letter to the editorA new three-angle energy-dispersive diffractometer

Abstract A novel energy-dispersive diffractometer has been designed in which diffraction patterns can be collected simultaneously at three angles. This results in a much wider overall coverage of reciprocal space and a matching of the X-ray source and detection system to chosen regions of a pattern so that quantitative analysis is considerably enhanced. We predict a wide acceptance of the technique for in situ studies and multi-phase analysis.

Development of large volume reaction cells for kinetic studies using energy-dispersive powder diffraction

Abstract Two novel sample chambers for the energy-dispersive powder diffraction study of chemical reactions are presented. One for air sensitive samples and the other for hydrothermal synthesis. The use of these vessels is illustrated with data collected during a study of the intercalation of cobaltocene into SnS2.

The equation of state of lawsonite to 7 GPa and 873 K, and calculation of its high pressure stability

Abstract The volume of lawsonite, CaAl2Si2O7(OH)2 · H2O, has been measured up to 7 GPa and 873 K using in situ energy dispersive powder diffraction and a multi-anvil high pressure-temperature cell at the Synchrotron Radiation Source, Daresbury Laboratory, U.K. Measurements were made on isotherms at 298, 323, 373, 473, 573, 673, 773, and 873 K within the pressure range. Sample pressure was measured from a NaCl standard mixed with the sample; the unit-cell volume of lawsonite was taken from the same diffraction pattern. The data gave an ambient temperature isothermal bulk modulus of K298 112 ± 6 GPa, similar to previous values. This value overestimates the temperature stability of lawsonite in thermodynamic calculations. A fit of the Birch-Murnaghan equation of state to the whole high pressure and temperature data set gave an isothermal bulk modulus of K298 = 125 ±5 GPa and a dK/dT of -0.01 ± 0.01/K, with K1 set to a value of 4 and the expansivity set to 3.16 × 10-5/K. Using these values to calculate the pressure-temperature positions of three of lawsonite’s dehydration reactions improved the agreement between observed and calculated positions of the lawsonite dehydration reactions to within experimental and calculation error. This work shows that the ambient temperature bulk modulus and ambient pressure expansivity do not adequately describe the volume behavior of lawsonite at combined high pressure and temperature.

Apparatus for the in situ kinetic study of reactions involving air sensitive materials using energy‐dispersive powder diffraction

A novel sample chamber has been developed for the study of chemical reactions involving air sensitive samples using energy‐dispersive powder diffraction. The apparatus consists of a reaction vessel, automatic reactant dispensing system, heating jacket, stirrer, and gas purge system. The use of this apparatus is illustrated with data collected on station 9.7 of the UK Synchrotron Radiation Source during a study on the intercalation of cobaltocene into tin disulfide.

Thermal decomposition of rhombohedral KClO3 from 29–76 kilobars and implications for the molar volume of fluid oxygen at high pressures

Abstract KClO3 thermal decomposition has been studied from 29-76 kilobars using a multianvil highpressure device and in-situ energy-dispersive X-ray diffraction and off-line quenching experiments. The rhombohedral form of KClO3 was found to decompose to the B2 form of KCl and O2 via an orthorhombic KClO4 intermediate over this pressure interval. The decomposition temperature was found to vary only slightly with pressure. The online experiments gave decomposition temperatures between 500 and 580 °C. Further off-line quenching experiments using sealed gold tubes determined the equilibrium decomposition boundary to be 550 ± 15 °C over this pressure range. Unit-cell parameters and volumes were determined for the high-pressure phases of KClO3 and KCl from the diffraction data. The partial molar volume of O2 was calculated from the difference in the solid volumes. Oxygen fluid volumes were then calculated along the decomposition boundary and vary from 10.6 ± 0.2 cm3/mol at 29 kbar to 9.6 ± 0.1 cm3/mol at 76 kbar. These volumes are 30 to 50% less than previous estimates determined from shock wave data, and imply that oxygen can be more easily stored in Earth’s mantle and core than previously believed. The thermal equation of state of the B2 form of KCl was investigated online using NaCl as an internal pressure standard. KCl was then used as an internal pressure calibrant for the online KClO3 decomposition experiments. The mechanical behavior of the multianvil high-pressure device was also studied and load vs. force characteristics are presented here.

In situ EXAFS, X-ray diffraction and photoluminescence for high-pressure studies

A new facility for simultaneous extended X-ray absorption of fine structure (EXAFS), X-ray diffraction and photoluminescence measurements under high pressures has been developed for use on station 9.3 at the Daresbury Laboratory Synchrotron Radiation Source. This high-pressure facility can be used at any suitable beamline at a synchrotron source. Full remote operation of the rig allows simultaneous collection of optical and structural data while varying the pressure. The set-up is very flexible and can be tailored for a particular experiment, such as time- or temperature-dependent measurements. A new approach to the collection of high-pressure EXAFS data is also presented. The approach significantly shortens the experimental times and allows a dramatic increase in the quality of EXAFS data collected. It also opens up the possibility for EXAFS data collection at any pressure which can be generated using a diamond cell. The high quality of data collected is demonstrated with a GaN case study. Particular attention will be paid to the use of energy-dispersive EXAFS and quick-scanning EXAFS techniques under pressure.

Rapid methods for the calibration of solid-state detectors

A complementary pair of rapid methods for the energy calibration of solid-state detectors have been developed. Each method requires only a single measurement from either (i) a glass sample containing elements chosen to produce fluorescence lines over a suitable energy range when exposed to a polychromatic beam of X-rays, or (ii) a powder diffraction standard in the presence of diffraction slits. The fluorescent glass method has the advantage of allowing simultaneous energy calibration of a number of detectors without requiring diffraction slits. There is the potential for the glass material to be incorporated into virtually any sample holder to allow a continuous in situ calibration. Complementary observations of a powder diffraction standard allow simultaneous calibration of diffraction 2theta and monitoring of the detector for drift.