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HPHT Materials Processing


The Warwick Diamond Research Group has installed a High Pressure High Temperature Tetrahedral Diamond Press (HPHT Press) for extreme high-temperature materials processing under stabilising pressures. This HPHT Press can access temperatures up to 3000 deg C and hydrostatic pressures in excess of 10 GPa (equivalent to 1 million atmospheres), which is equivalent to a depth of >300 km. The HPHT Press was constructed by Element Six Ltd for an in-house research project at the Diamond Trading Company (DTC) Research Centre, Maidenhead, which has now finished and the DTC have donated it to the University of Warwick as part of their continued support for UK University research.

An EPSRC research grant (EPSRC Grant Reference: EP/D063027/1) enabled us to relocate the HPHT Press to Warwick, commission the apparatus and initiate a variety of research programmes.  Initially we are focusing on HPHT diamond processing, however the potential of the HPHT Press to impact significantly on the research of other materials is not being overlooked.

If you are interested in utilising the HPHT Press in any collaborative research projects then please contact Mark Newton (

Did you know about the diffusion of nitrogen atoms in diamond? 
Nitrogen is a common impurity in natural and synthetic diamond and is commonly incorporated in the form a single substitutional impurity. At high temperatures and pressures the single substitutional nitrogen impurity can diffuse through the lattice. Upon encountering another substitutional nitrogen impurity a new more stable defect incorporating two adjacent substitutional nitrogen atoms is formed – the so called A-centre. High pressure is required to stabilise the diamond, and prevent conversion to graphite at high temperatures. Both the single substitutional nitrogen impurity and the A-centre have characteristic infrared absorption spectra which allow us to monitor the conversion of single nitrogen to nitrogen pairs. IR absorption spectrum from an as grown synthetic nitrogen doped diamond (blue-solid curve) containing 109 ppm  of single substitutional nitrogen impurity and the same sample recorded after a 30 minute anneal at ~1900°C and 7.2 GPa (red-broken curve). Post anneal 60 ppm of the nitrogen is in the form of single substitutional nitrogen defects and the remaining 49 ppm has converted to A centres. Click here to see the experimental spectra. (ppm = parts per million carbon atoms)