Chris Goodway

Experimental arrangements suitable for the acquisition of inelastic neutron scattering spectra of heterogeneous catalysts

Inelastic neutron scattering (INS) is increasingly being used for the characterization of heterogeneous catalysts. As the technique is uniquely sensitive to hydrogen atoms, vibrational spectra can be obtained that emphasize a hydrogenous component or hydrogen-containing moieties adsorbed on to an inorganic support. However, due to sensitivity constraints, the technique typically requires large sample masses (∼10 g catalyst). A reaction system is hereby described that enables suitable quantities of heterogeneous catalysts to be appropriately activated and operated under steady-state conditions for extended periods of time prior to acquisition of the INS spectrum. In addition to ex situ studies, a cell is described which negates the need for a sample transfer stage between reaction testing and INS measurement. This cell can operate up to temperatures of 823 K and pressures up to 20 bar. The apparatus is also amenable to adsorption experiments at the gas-solid interface.

A high temperature cell for simultaneous electrical resistance and neutron diffraction measurements

An in situ cell that allows the electrical resistance of a sample pellet to be measured while performing neutron diffraction experiments has been developed at the ISIS pulsed neutron source. The sample is held between two spring loaded platinum electrodes embedded in a boron nitride clamp assembly with the resistance measured using the four-probe method. An outer quartz glass jacket allows the atmosphere within the sample enclosure to be controlled, and the entire device can be accommodated within a standard ISIS neutron furnace for measurements at temperatures up to 1270 K. The operation of this cell is illustrated using data for the structural, magnetic, and electrical properties of chalcopyrite CuFeS(2) collected over the temperature range of 398-873 K on the Polaris powder diffractometer at ISIS.

Sample environment issues relevant to the acquisition of inelastic neutron scattering measurements of heterogeneous catalyst samples

Refinements to established sample handling issues connected with the acquisition of inelastic neutron scattering (INS) spectra of heterogeneous catalyst samples are described. This involves modification of a reactor and improvements to gas handling apparatus. The latter includes provision of laboratory space and ventilation facilities that are suited to the increasingly wide range of catalytic samples being examined. INS measurements for CO hydrogenation over an iron-based Fischer-Tropsch catalyst recorded using the MARI spectrometer are presented to illustrate the applicability of the new arrangements.

Hydrogen gas sample environment for TOSCA

The idea of using hydrogen as a fuel has gained immense popularity over many years. Hydrogen is abundant, can be produced from renewable resources and is not a greenhouse gas. However development of hydrogen based technology is impossible without understanding of physical and chemical processes that involve hydrogen sometime in extreme conditions such as high pressure or low and high temperatures. Neutron spectroscopy allows measurement of a hydrogen atom motion in variety of samples. Here we describe and discuss a sample environment kit developed for hydrogen gas experiment in a broad range of pressure up to 7 kbar and temperatures from 4 K to 473 K. We also describe para-hydrogen rig which produces para-hydrogen gas required for studying the rotational line of molecular hydrogen.

A non-destructive experimental investigation of elastic plastic interfaces of autofrettaged thick-walled cylindrical aluminium high pressure vessels

Positions of elastic plastic interfaces play a vital role in safe design and safe use of high pressure vessels. The ENGIN-X neutron diffractometer at the ISIS facility was used to measure the residual strain profiles in a series of aluminium vessels which had been subjected to different pressure levels. The positions of elastic plastic interfaces of the autofrettaged pressure vessels were identified. The results revealed that the residual strain magnitude and the depth of the plastic region will increase with increasing autofrettage pressure level. When autofrettage pressure produces an elastic-plastic boundary at a greater depth than the geometric mean position of the vessel wall, reverse yielding will occur, hence the loss of the vessels’ elastic ability to its subsequent loading. The neutron experimental results agreed well with both the suggestions from existing literatures and the results from FE simulations.

Large volume Bridgman seal cell for neutron scattering experiments at ultralow temperatures

A pressure cell (maximum working pressure of 100 bars) has been developed for neutron scattering experiments at ultralow temperatures (T<100 mK) which makes use of a Bridgman seal design more usually seen in higher temperature experiments in the kilobar range. The large volume of the cell ( approximately 18 cm3) and its construction from a high-strength aluminum alloy make it suitable for inelastic neutron scattering experiments. The cell has been proof tested in operando in search for the supersolid state of helium-4.

Robust measurement of para-ortho H2 ratios to characterise the ISIS hydrogen moderators

We discuss an experimental approach to determine the concentration of para-H2 in the hydrogen moderators serving the Target Stations 1 and 2 at ISIS. The outcome of the measurements based on this approach is crucial for the Target Station 1 project, where a detailed characterisation of the present performance is needed to test neutronics simulations. The approach described here is based on the measurement of neutron transmission spectra over a wide energy range of samples extracted from the moderators. Pilot experiments were performed on the VESUVIO spectrometer at ISIS and were combined with measurements of thermal conductivity of the same samples using the ISIS para-H2 rig.

Development of high pressure gas cells at ISIS

High-pressure research is one of the fastest-growing areas of natural science, and one that attracts as diverse communities as those of physics, bio-physics, chemistry, materials science and earth science. In condensed matter physics there are a number of highly topical areas, such as quantum criticality, pressure-induced superconductivity or non-Fermi liquid behaviour, where pressure is a fundamental parameter. Reliable, safe and user-friendly high pressure gas handling systems with gas pressures up to 1GPa should make a significant impact on the range of science possible. The ISIS facility is participating in the NMI3 FP7 sample environment project supported by the European Commission which includes high pressure gas cell development. In this paper the progress in designing, manufacturing and testing a new generation of high pressure gas cells for neutron scattering experiments is discussed.

High-resolution neutron-diffraction measurements to 8 kbar

ABSTRACT We describe the capability to measure high-resolution neutron powder diffraction data to a pressure of at least 8 kbar. We have used the HRPD instrument at the ISIS neutron source and a piston-cylinder design of pressure cell machined from a null-scattering titanium zirconium alloy. Data were collected under hydrostatic conditions from an elpasolite perovskite LaNiMnO; by virtue of a thinner cell wall on the incident-beam side of the cell, it was possible to obtain data in the instruments highest resolution back-scattering detector banks up to a maximum pressure of 8.5 kbar.