High-temperature oxidation and electrochemical studies related to hot corrosion. Final report, Nov 85-May 92

Technical Report · Fri Jul 24 04:00:00 EDT 1992

OSTI ID:7039699

Reidy, R; Kim, D H; Patton, J; Simkovich, G

This research has examined the transport mechanisms relevant to hot corrosion. Three different approaches were used to elucidate this problem: an examination of the corrosion of the base metal, an exploration of the transport properties in Na2SO4, and an investigation in the role of defects in the transport behavior of a protective coating. The transport properties of molten Na2SO4 have been investigated to aid further understanding of hot corrosion processes at 1 1 73 K. Tests were conducted to determine: the effect of height of Na2SO4 melts, the effect of electronic short circuiting the Na2SO4 melts with gold wires, and the effect of presaturating the salt melt with corrosion products in the hot corrosion process. Basically, these tests showed that neither ionic nor electronic transport in the bulk melt controls the hot corrosion process. However, the amount of Na2SO4 present, which is directly proportional to the height of the melt, does affect the rate of corrosion. This was demonstrated by the decrease in rate observed when the melt was presaturated with the corrosion products. An A.C. impedance technique for the total electrical conductivity, the potentiostatic polarization method for ionic transport numbers, and the steady state polarization method of Wagner and Hebb for the electronic conductivity were employed as a function of Na2O activity in the melt by controlling the gas atmosphere. These results showed that the conductivities of the pure Na2SO4 were of the order of 0.232 (ohm-cm)-l and varied only slightly with Na2SO4, activity changes. From the polarization measurements, on the pure Na2SO4, it was found that electron conductivity was much higher than electron hole conductivity. The transport numbers were = 7.Oxl0-3 and = 5.7x

• Research Organization: Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering
• OSTI ID: 7039699
• Report Number(s): AD-A-254435/1/XAB; CNN: N00014-91-J-1528
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
ALKALI METAL COMPOUNDS
ALLOYS
ATMOSPHERES
CERIUM
CHARGED PARTICLES
CHEMICAL REACTIONS
CHEMISTRY
CHROMIUM ALLOYS
COATINGS
CONTROL
CORROSION
DIMENSIONS
ELECTRICAL PROPERTIES
ELECTROCHEMISTRY
ELECTRONS
ELEMENTARY PARTICLES
ELEMENTS
FERMIONS
FUNCTIONS
GOLD
HEAT RESISTANT MATERIALS
HEAT RESISTING ALLOYS
HEIGHT
IMPEDANCE
IONS
LEPTONS
MATERIALS
METALS
NICKEL ALLOYS
OXIDATION
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POLARIZATION
PROTECTIVE COATINGS
RARE EARTHS
RESEARCH PROGRAMS
SALTS
SODIUM COMPOUNDS
SODIUM SULFATES
STABILITY
SULFATES
SULFUR COMPOUNDS
TRANSITION ELEMENTS
ZIRCONIUM