High Pressure Synthesis
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The group has access to several specialised high pressure apparatus, all housed in purpose built safety enclosures in a dedicated lab.
Solid State Press
The solid state press is a commercially available item made by Depths of the Earth Company.
It is a single end piston cylinder design with a hydraulic ram producing the pressure.
Samples are sealed in gold capsules, which in turn are placed inside a furnace assembly.
A furnace assembly as components (left) and assembled (right)
The completed assembly is inserted into the tungsten carbide core of the machine. Pressure is generated between the base block of the assembly, and a piston inserted into the other end of the core. Heat is generated by passing low voltage, high current electricity through the graphite component of the assembly.
Solid State Press
The temperature range is from RT to 1200 degrees centigrade. The pressure achievable depends on which size core is installed. The 0.75" core gives a higher sample volume, but is limited to 10 kBar. The 0.5" core can operate to 25 kBar, but has a smaller sample capacity.
Hydrothermal Rig
The hydrothermal rig was constructed in house. In this case, pressure is generated by the hydraulic action of water.
Samples are sealed into gold capsules. This can be dry powders, or solutions. The capsule is loaded into a bomb, which is filled with water and attached to the rig. A counter-balanced furnace is lowered over the bomb. The whole apparatus is housed inside a steel cabinet for safety.
An initial pressure is set by increasing water pressure with a pump. Heating further increases the pressure in the system, and once at temperature, the pressure can be fine tuned.
Hydrothermal rig with bomb attached and furnace in the raised position
The rig is capable of temperatures to 800 degrees C and pressures to 4 kBar. The system also has a second, identical chamber in the cabinet, allowing two bombs to be run simultaneously.
High Pressure Oxygen Rig
The oxygen rig was again made in house. It allows materials to be annealed under high pressure oxygen gas.
Samples in alumina or gold crucibles are inserted into the inner chamber of a reaction vessel. The inner and outer sections are then purged with high pressure nitrogen gas from a compressor system. A second compressor then provides pressurised oxygen gas to the inner chamber, with a balancing valve in place to equalise pressures between inner and outer chambers. The entire reaction vessel is contained within a furnace.
The reaction chamber of the rig
The temperature can be increased up to approximately 1030 degrees C. The reactions can be carried out under oxygen pressures of up to 700 bar.
Chemistry
Each of the high pressure apparatus can be used for a variety of different experiments with the user selection depending upon required conditions.
The solid state press can be used for a variety of materials such as ceramics and superconductors, as well as geomimetics and synthetic petrology.
The hydrothermal rig is useful for high volume synthesis of materials requiring relatively low pressures, but can also be used with solutions in the capsule to make zeolites and related framework materials under pressure.
The oxygen rig is used to anneal materials such as superconductors, to increase the amount of oxygen in the structure, thus altering oxidation states of the metals.
All of the apparatus are currently being used as part of an Adventurous Chemistry grant, the aim of which is the formation of unknown / rare oxidation states, chemical combinations or environments by synthesis under extreme, high pressure conditions. Systems are being targeted which are known to favour higher oxidation states of metals, such as the pyrochlores.
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