STATION 16.4
Energy Dispersive Powder Diffraction at High Temperature and Pressure

Energy Dispersive Powder Diffraction

White radiation is used to produce diffraction peaks from a crystalline sample. The energy of any given peak is related to a d spacing in the sample that generated it and to the 2 theta angle of the detector system collecting it. The data is analysed using an energy discriminating detector that bins data into an MCA. With this technique all data is measured simultaneously minimising data collection times and making the technique ideally suited to the real time study of chemical reactions and phase transitions using time slices of ~ 1 minute.

Angle Dispersive Powder Diffraction

Use of the Laue-Bragg monochromator produces photons at 60 keV which generate powder patterns detected by a MAR 300 image plate.

Functional Description

This station is designed primarily for the study of chemical reactions and phase transitions of materials held at high pressures and temperatures using Energy Dispersive Powder Diffraction (EDPD).

The combination of a very intense, high energy white beam from the 6T Wiggler and the EDPD technique provides an ideal means for tracking such processes over timescales ranging from < 1 second to several hours.

The recent introduction of a Laue-Bragg monochromator combined with a MAR 300 image plate system provides the capability to record angle dispersive powder patterns from samples held in the Large Volume Press.

Technical Description

Front end containing pinhole assembly, slits and monochromator. 10000 kN Large Volume Press with Walker multianvil high P/T cell. Adjustable diffraction table for EDPD detector and cell positioning. Energy Dispersive Powder Diffractometer with 3 element liquid nitrogen cooled Ge solid state detector system for extended d space range. Removable image plate table and MAR 300 system. Several hydrothermal cells, ovens and an xyz stage.

The EDPD detector can be positioned on the diffraction table in two places. Front position for use with the Large Volume Press. Back position for use with other cells mounted on the diffraction table.

This consists of four cells on a rotating stage. Each cell has its own Eurotherm temperature controller and stirrer magnet. Cell position and temperature is controlled from the computers in the user area. The cells can be operated in parallel using the 4cellscan macro on the station computer.

This cell operates over a temperature range of -20 to 95 degrees Centigrade using a circulating glycol bath and additional electric heaters. It also has the capability of crash cooling using a bypass system operated by a solenoid controlled from the user area.

The recent installation of the Laue-Bragg monochromator amd Image Plate system provides the capability of collecting angle dispersive powder patterns from samples held in the Large Volume Press.

Proposed Development

Intended to replace existing stage with one of greater range and better   precision.

As part of a Lab. wide development of high energy bent monochromators it is intended to install a bent Laue monochromator on 16.4 to increase the flux and thus shorten data collection times.

Turnaround Times

Hydrothermal to Large Volume Press mode - a few hours

Installation of Image Plate Table and MAR 300 for angle dispersive work - a full day

Typical Scientific Studies on 16.4.

• Cement related minerals during solidification
• Microporous materials such as zeolites during hydrothermal synthesis crystallisation from solution, polymorphic transformations etc.
• systems that absorb heavy metal pollutants such as Cd
• Fast solid state combustion reactions (t < 1s)
• Topographic Energy Dispersive Diffraction Imaging (TEDDI)- maps an extended object, used for non-destructive studies on such things as archaelogically significant items.
• intercalation studies on gas/liquid going into framework structures
• X-ray fluorescence detection - used for monitoring liquid diffusion in rocks Studies on the chemistry of the earth's mantle using the Walker cell.

Experimental Cells

• Hydrothermal bombs (20-250 C, 0-300psi)
• Glycol Cold Cell (-20-95 C, 0-300psi)
• Several furnaces (0-1200 C)- often user brought
• xyz stage
• Specialist user cells for crystallisation, gas/liquid flow etc
• Walker Multianvil Cell ( 0-25 GPa, 0-2000 C)