International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 2.7, pp. 165-166

Section 2.7.12. High-pressure chamber and gasket in the DAC

A. Katrusiaka*

aFaculty of Chemistry, Adam Mickiewicz University, Poznań, Poland
Correspondence e-mail: katran@amu.edu.pl

2.7.12. High-pressure chamber and gasket in the DAC

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A high-pressure device should be adjusted to the experiments planned, and in particular to the chemical activity of the sample. Gaseous hydrogen penetrates and dissolves in most metals, and therefore special alloys, such as beryllium bronze, have to be used for hydrogen setups. For some experiments non-metallic gaskets can be used, for example amorphous boron, corundum or diamond powders mixed with a resin. Owing to the insulating properties of such a gasket, the pressure dependence of the electric, dielectric and magnetic properties of the sample can be measured. Chemically aggressive samples can interact with the gasket material of the DAC chamber, and even with the diamond anvils, and this effect usually intensifies at high temperature and pressure. Consequently, both the sample and the high-pressure device can be affected. The erosion caused by an aggressive liquid can be considerably slowed down by its crystallization, which freezes the diffusion of molecules into the gasket. For example, in situ crystallization of halogen derivatives of acetic acid could only be performed in a DAC chamber with tungsten gaskets (Gajda & Katrusiak, 2009[link]). In these experiments, the gasket was gradually eroded by the acid, but after its crystallization the measurements could be performed over several days. In order fully to prevent erosion of the gasket, it can be coated with a layer of inert material, for example gold or platinum. Alternatively, a composite chamber can be prepared: after pre-indenting the gasket and drilling a hole at the centre of the indentation, a piece of gold wire can be fitted to the hole, and after pressing into a hole in the DAC again, a smaller hole can be drilled through this inset. A DAC chamber formed in this way has a gold lining and can be resistant to aggressive compounds.

References

Gajda, R. & Katrusiak, A. (2009). Electrostatic matching versus close-packing molecular arrangement in compressed dimethyl sulfoxide (DMSO) polymorphs. J. Phys. Chem. B, 113, 2436–2442.Google Scholar








































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