Carbon Contamination in Diamond Anvil Cell

The high pressure induced carbon transport from diamond anvils into pressure chamber of diamond anvil cells (DAC) for various samples were studied with micro-Raman spectroscopy. Depending on experimental conditions, different carbon phases including the amorphous carbon, micro- or nano-crystalline graphite, and diamond, are observed. Compression at room temperature and pressures above 40 GPa results in the formation of disordered graphite phase(s) on the surface of samples (at diamond-sample interface). Various heating with both electrical and laser techniques are employed. The temperature induced graphite phase formation was observed in situ in external heated DAC at pressure about 15 GPa and temperature 690 K. In the case of laser heating at pressure above 6 GPa the pure diamond or microcrystalline diamond and graphite phases were obtained on the surface of samples and inside pressure medium on the metallic pieces as well. The common phenomenon of carbon diffusion inside the pressure chamber of a DAC is very important for high-pressure studies with DAC. The presence of carbon around or inside the samples in pressure chamber can significantly change the kinetics of phase transformation and conditions of chemical reaction. For example, the melting temperature obtained from laser-heating experiments in DAC should be corrected by taking into account possible influence of the carbon layer that could significantly changes the melting conditions. It also could be a source of discrepancy in experimental data on melting temperatures obtained for the same material in the difference experiments and methods (shock wave, multi-anvil and DAC). Physical-chemical phenomena studied in DAC, such as elements partitioning, phase transformations, chemical reactions, resistivity, at high pressure and high temperature conditions should be analysed considering possible presence of carbon phases.