KCl induced corrosion of a 304-type austenitic stainless steel at 600 degrees C; The role of potassium

• The influence of KCl on the oxidation of the 304-type (Fe18Cr10Ni) austenitic stainless steel at 600 degrees C in 5% O-2 and in 5% O-2 + 40%H2O is investigated in the laboratory. The samples are coated with 0.1 mg/cm(2) KCl prior to exposure. Exposure time is 1-168 h. Uncoated samples are exposed for reference. The oxidized samples are analyzed by ESEM/EDX, XRD and AES. The results show that small additions of potassium chloride strongly accelerate high temperature corrosion, the oxide thickness being up to two orders of magnitude greater after exposure in the presence of KCl. The rapid corrosion is initiated by the formation of potassium chromate through the reaction of KCl with the protective oxide. Chromate formation is a sink for chromium in the oxide and leads to a loss of its protective properties. The resulting rapidly growing scale consists of an outer hematite layer with embedded K2CrO4 particles and an inner layer consisting of spinel oxide, (Fe,Cr,Ni)(3)O-4. Little or no chlorine is found in the scale or at the scale/metal interface.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering (hsv//eng)

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

oxidation

11-percent

breakaway corrosion

high-temperature corrosion

fired boilers

oxide hydroxide evaporation

KCl

deposits

chromate

alloys

chromium steel

water-vapor

oxidation

deposit

304L

chloride

flow-rate

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