A high-temperature high-pressure optical cell for general-purpose spectrometers designed for supercritical water experiments

We have developed a compact size high-temperature high-pressure optical cell that can be mounted on a commercially available general-purpose spectrometer. A small electric furnace heats the high-pressure optical cell while a water-cooled thermal shielding jacket protects the spectrometer. This cooling device works quite effectively to eliminate undesirable heating of spectrometer optics and thus makes it possible to take spectra at temperatures up to 600 °C with an ordinary spectrometer. The optical cell is made of Hastelloy-X and equipped with two optical windows of synthetic sapphire. The length and the diameter of the optical path are 10 and 6 mm, respectively. As the optical cell is combined with a flow system, which allows the quick replacement of the sample solution with the reference water, the reference signal can be taken immediately after the measurement of the sample signal. The developed cell can be operated up to 60 MPa and 600 °C without any special modification to the spectrometer. The NiBr2 absorption spectra were taken under the supercritical water condition to demonstrate the efficiency of the optical cell.