Hot corrosion of materials: a fluxing mechanism?

Rapp, Robert A.

doi:10.1016/s0010-938x(01)00057-9

Cited by 409 publications

(183 citation statements)

References 38 publications

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“…Hot corrosion became a topic of popular interest in the late 1960s as gas turbine engines of military aircraft suffered severe corrosion during the Vietnam conflict when operating over seawater. 6 Metallographic inspection of failed parts often showed sulfides of nickel and chromium, so the mechanism was initially called sulfidation. However, studies by Goebel and Pettit 7 and by Bornstein and DeCrescente 8,9 showed that sulfide formation indeed resulted from the reaction of the metallic substrate with a thin film of fused salt of sodium sulfate base rather than with Na 2 SO 4 vapor.…”

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Hot Corrosion of Na[sub 2]SO[sub 4]-Coated Ti[sub 3]AlC[sub 2] in Air at 700-1000°C

Wang

Zhou

2004

J. Electrochem. Soc.

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Hot corrosion of layered machinable ceramic Ti 3 AlC 2 coated with 3.8 Ϯ 0.2 mg/cm 2 Na 2 SO 4 in air at 700-1000°C has been investigated by means of thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy/ energy-dispersive spectroscopy. The hot corrosion of Ti 3 AlC 2 was slight at low temperatures of 700 and 800°C, while Ti 3 AlC 2 was severely attacked by fused sodium sulfate at 900 and 1000°C. No protective scales were observed on Ti 3 AlC 2 , and sulfur-rich layers were present at the Ti 3 AlC 2 substrate/scale interface. The linear hot corrosion kinetics at 800 and 900°C demonstrated that electrochemical reactions of Ti 3 AlC 2 with sodium sulfate at the substrate/scale interface dominated, while the parabolic kinetics at 1000°C implied that the rate-limiting step involved in the hot corrosion was the diffusion of hot corrosion medium through the scale formed. The hot corrosion behaviors were explained by a mechanism of electrochemistry coupled with basic dissolution-precipitation. Two-layered machinable ternary carbides, Ti 3 AlC 2 and Ti 2 AlC, in the Ti-Al-C system, are of interest as potential high-temperature structural materials due to their high specific strength and excellent high-temperature properties.1,2 Ti 3 AlC 2 and Ti 2 AlC exhibit good oxidation resistance due to the formation of a protective ␣-Al 2 O 3 layer at high temperatures in spite of the low aluminum content. 3,4 Moreover, in contrast to traditional carbide ceramics, they can be readily machined by both conventional tools originating from the relatively weak bonding between sheets of Ti 6 C octahedra and neighboring close-packed Al atoms, 5 and by electrodischarge machining because of its high electrical conductivity. 1,2As a potential high-temperature structural material, Ti 3 AlC 2 will always be exposed to the service circumstance in which hot corrosion occurs. Hot corrosion became a topic of popular interest in the late 1960s as gas turbine engines of military aircraft suffered severe corrosion during the Vietnam conflict when operating over seawater. 6 Metallographic inspection of failed parts often showed sulfides of nickel and chromium, so the mechanism was initially called sulfidation. However, studies by Goebel and Pettit 7 and by Bornstein and DeCrescente 8,9 showed that sulfide formation indeed resulted from the reaction of the metallic substrate with a thin film of fused salt of sodium sulfate base rather than with Na 2 SO 4 vapor. Because corrosion by a thin electrolyte film bears some common features with ''atomospheric corrosion'' by an aqueous film at room temperature, the phenomenon has been renamed ''hot corrosion''. While aqueous atomospheric corrosion is often controlled by the diffusion of dissolved oxygen in the water film, numerous measurements have shown that the soluble oxidant in hot corrosion is SO 3 (S 2 O 7 2Ϫ ) in the fused salt. [10][11][12][13] It is well acknowledged that the subject of hot corrosion can be divided into two subtypes, i.e., hightemperature ...

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Hot Corrosion of Na[sub 2]SO[sub 4]-Coated Ti[sub 3]AlC[sub 2] in Air at 700-1000°C

Wang

Zhou

2004

J. Electrochem. Soc.

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“…La corrosión de estos sistemas de combustión, es el principal obstáculo en la eficiencia térmica de las plantas que queman combustibles fósiles [12,13].…”

Section: • Corrosión Por Sales Fundidasunclassified

Corrosión en sales fundidas de un acero recubierto mediante rociado térmico por llama

2014

prospect

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RESUMENSe evaluó la velocidad de corrosión de un acero laminado en caliente, recubierto con una aleación Ni-Cr, en presencia de sales fundidas con una composición de 80% pentóxido de vanadio (V 2 O 5 ) y 20% Sulfato de sodio (Na 2 SO 4 ), mediante la técnica de pérdida de peso. La evaluación de la velocidad de corrosión se realizó variando la temperatura entre 650-750 °C, durante 1, 7 y 22 horas. El recubrimiento de Ni-Cr obtenido por la técnica de rociado térmico produce una capa que reduce la velocidad de corrosión, sin embargo es susceptible al ataque corrosivo de las sales fundidas a las que se encuentra expuesto dicho recubrimiento. Encontramos que la resistencia a la corrosión del recubrimiento depende de la naturaleza de la capa de óxido, los componentes de la aleación y los constituyentes de las sales.Palabras clave: Corrosión, Sales fundidas, Óxidos, Rociado térmico, Recubrimientos. ABSTRACTWe assessed the corrosion rate of hot-rolled steel coated with a Ni-Cr alloy in the presence of molten salts with a composition of 80% vanadium pentoxide (V 2 O 5 ) and 20% sodium sulfate (Na 2 SO 4 ) by weight loss technique. Evaluating the corrosion rate was done by varying the temperature between 650-750 °C for 1, 7 and 22 hours. The NiCr coating obtained by thermal spraying technique produces a coating that reduces the corrosion rate, however, is susceptible to corrosive attack by the molten salts to which the coating is exposed. Found that the corrosion resistance of the coating depends on the nature of the oxide layer, the components of the alloy constituents and salts.Keywords: Corrosion, Molten salts, Oxides, Thermal spraying, Coatings. INTRODUCCIÓNLa degradación de metales y aleaciones por corrosión en sales fundidas ha sido reconocida como un problema grave para muchas aplicaciones, tales como: calderas, motores de combustión interna, turbinas de gas, incineradores de residuos industriales entre otras. Debido al agotamiento de los combustibles y por razones económicas, se está utilizando aceite residual junto con carbón en los sistemas de generación de energía, los cuales contienen sodio, vanadio y azufre como impurezas. Durante la combustión, el Na y S reaccionan entre sí y para formar Na 2 SO 4 , además, el vanadio reacciona con el oxígeno para formar vanadatos complejos V 2 O 5 entre otros compuestos.Estos compuestos se depositan en la superficie de los materiales, induciendo la corrosión, ya que destruyen las capas de óxido protectoras que forman los materiales durante el funcionamiento [1].

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“…Así, en la corrosión en caliente, los productos de sulfuro no se forman por reacción de los componentes de azufre en la fase gaseosa, pero sí por una interacción metal-sa (Rapp, 2002).…”

Section: Mecanismos De Corrosión En Calienteunclassified

Corrosión a alta temperatura de las aleaciones 9Cr-1Mo modificado, 2,25Cr-1Mo y 304H preoxidadas, en un electrolito de na2So4, mediante técnicas electroquímicas y gravimétricas

et al. 2013

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Corrosión a alta temperatura de las aleaciones 9Cr-1Mo modificado, 2,25Cr-1Mo y 304H preoxidadas, en un electrolito de na 2 So 4 , mediante técnicas electroquímicas y gravimétricas High- ResumenEn el presente trabajo se evaluó la corrosión de tres tipos de aceros, preoxidados y sin preoxidar, en presencia de sulfato de sodio reactivo, empleando técnicas electroquímicas, como resistencia a la polarización, pendientes Tafel e impedancia electroquímica, y técnicas gravimétricas, como ganancia de peso a temperaturas de 600 °C y 650 °C. Se determinó que el acero 304H presenta la menor velocidad de corrosión y además es el más resistente en presencia de Na 2 SO 4 sólido en una atmósfera de aire, debido a que la capa de óxido formada inicialmente se mantuvo aun a altas temperaturas. Para el caso de los aceros ferríticos, existió un ligero incremento de la velocidad de corrosión, con una pequeña difusión de azufre y formación de sulfuros en la interfaz aleación/óxido, puesto que se fracturó dada la diferencia de coeficientes de expansión térmica. En general, un depósito de Na 2 SO 4 sólido sobre los aceros utilizados en sistemas que operan a alta temperatura no es un factor de riesgo que influya en la degradación de los materiales.Palabras clave: Corrosión; altas temperaturas; acero inoxidable; acero ferrítico; preoxidación; electroquímicas; técnicas gravimétricas; sulfato de sodio. AbstractThe corrosion behavior of three types of steels, pre-oxidized and without pre-oxidation, coated with sodium sulfate was evaluated in the present work by using electrochemical techniques, including polarization resistance, Tafel curves, electrochemical impedance, and gravimetric techniques like weight gain, at 600 and 650 °C. It was determined that the steel exhibiting the lowest corrosion rate was 304H, being the most resistant coated specimen with solid Na 2 SO 4 in air atmosphere because its oxide layer formed initially was maintained even at high temperatures. For ferritic steels, a slight increase in corrosion rate was noted, presenting a small diffusion of sulfur and sulfide formation at the alloy/oxide interface, given that it fractured due to the difference in the thermal expansion coefficients. In general, a solid Na 2 SO 4 deposit over the steels used in systems working at high temperatures is not a risk factor that influences material degradation.

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Hot corrosion of materials: a fluxing mechanism?

Cited by 409 publications

References 38 publications

Hot Corrosion of Na[sub 2]SO[sub 4]-Coated Ti[sub 3]AlC[sub 2] in Air at 700-1000°C

Hot Corrosion of Na[sub 2]SO[sub 4]-Coated Ti[sub 3]AlC[sub 2] in Air at 700-1000°C

Corrosión en sales fundidas de un acero recubierto mediante rociado térmico por llama

Corrosión a alta temperatura de las aleaciones 9Cr-1Mo modificado, 2,25Cr-1Mo y 304H preoxidadas, en un electrolito de na2So4, mediante técnicas electroquímicas y gravimétricas

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