Corrosion behaviour of inorganic materials in subcritical and supercritical aqueous solutions

The synthesis potential of Supercritical Water Chemistry has been limited o wing to corrosion problems. Until now there is no universal material for re actors or catalysts available, which is stable under the applied conditions (300 to 500 degrees C, 25 to 50 MPa). The subject of this paper is to stud y the corrosion behaviour of some potential oxidation catalysts such as cop per, silver, nickel, palladium ruthenium and cobaltoxide in subcritical and supercritical aqueous solutions (H2O/oxygen and H2O/acetic acid) as a func tion of temperature and pressure. A continuously operating high-pressure te sting-plant with a 250 mi autoclave of Inconel 625 was used for the investi gations. The samples were analysed before and after treatment with SCW-solu tions by using different methods (gravimetric analysis, light microscopy, s canning electron microscopy, energy-dispersive of X-rays spectroscopy and X -ray diffractometry). The effluent of the test reactor was analysed using a tomic absorption spectroscopy. The investigations have shown that all mater ials except of nickel are stable in purl subcritical and supercritical wate r. Treatment in solutions containing acetic acid or oxygen causes corrosion of all materials.