A micro-Raman cell for studying aqueous solutions at high temperatures and pressures

The wetted surfaces of the high-temperature, high-pressure Raman cell (400 °C and 1 kbar) were constructed of inert materials (i.e., sapphire or quartz and platinum with gold seals) and designed to allow spectroscopic measurements to be made with small volumes (<0.5 cm3 at temperature) of corrosive solutions. This design permits solution to be forced slowly through the cell at experimental temperatures and pressures for cases where the solute may be unstable thermally over prolonged periods of time. The entire pressure-generating equipment, temperature controller and readout, solution separation vessels, and cell can be mounted on a cart for convenient transport to various laboratories. Raman spectra of bichromate/dichromate solutions were obtained from ambient conditions to 300 °C and 1 kbar in order to test the capabilities of this apparatus and to allow comment on the controversy surrounding the existence of HCrO−4 raised by recent Raman studies of the aqueous chromate system at ambient conditions.