A new type of hydrothermal diamond-anvil cell with cooling system

A new type of hydrothermal diamond-anvil cell (HDAC-VII) and its accompanied cooling system were designed. The design of HDAC-VII in which the three posts work simultaneously as guideposts and screw posts greatly shortened the horizontal size of HDAC compared with older types. It provides more open space and shorter distance to analyze and observe the sample chamber from side access. Moreover, four ports were used to connect the upper and lower spaces between windows and anvils, so mixed gas (Ar + H₂) can pass through both of them. In the heating experiments, the mixed gas prevents diamond anvils and other parts from being oxidized as well as cooling the observing windows. Dry gas can be passed through those spaces during cooling, preventing condensation on the table faces of anvils and the observing windows. The cooling system can cool the sample chamber to -170 °C with an accuracy of ±0.5 °C by using a nitrogen stream cooled through a stainless steel coil immersed in a liquid nitrogen Dewar. The heating rates while reheating a frozen sample can be controlled to be 0.1 °C/min with a temperature fluctuation of 0.1 °C. These improvements extend the HDAC applications especially in low temperature conditions. For example, (1) we measured the salinities of NaCl-H₂O loaded in the sample chamber, (2) we observed the ice I and VI-melting process and correspondingly calculated the density of water in the sample chamber, and (3) we performed lepidolite crystallization in an aqueous solution with 10 wt. % NaCl to simulate its natural forming conditions.