Jan-Erik Svensson

Influence of Water Vapor and Flow Rate on the High-Temperature Oxidation of 304L; Effect of Chromium Oxide Hydroxide Evaporation

The effect of roman PH2O and flow rate on the oxidation of 304Lat 873 K in oxygen is reported. High concentrations of water vapor and highflow rates result in breakaway corrosion. The mass gain after 168 hrincreased by four to five times, compared to oxidation in dry O2. Inthe presence of H2O, the corrosion products consisted of arelatively thin (Cr,Fe)2O3 oxide plus large oxide islandsconsisting mainly of Fe2O3. A mechanism explaining theeffect of water vapor on marginal chromia formers is proposed.

Indication of Chromium Oxide Hydroxide Evaporation During Oxidation of 304L at 873 K in the Presence of 10% Water Vapor

The oxidation of type 304L stainless steel wasinvestigated at 873 K in the presence of O2and O2 + 10% H2O. Oxidation timevaried between 1 and 672 hr. The oxidized samples wereinvestigated by a number of surface-analytical techniques includinggrazing-angle XRD, SEM/EDX, auger spectroscopy, SIMS andXPS. Oxidation in dry oxygen results in the formation acorundum-type oxide (Me2O3) withadditional formation of spinel oxides after prolonged exposure. Theoxide layer contained mainly chromium, with smalleramounts of Fe and Mn. Oxidation in the presence of watervapor results in an oxide that contains more Fe and less Cr, the outer part of the oxide beingdepleted in Cr. In the presence of water vapor, a massloss is detected after prolonged exposure. We show thatthe mass loss is caused by chromium evaporation. The volatile species is suggested to beCrO2(OH)2.

Evidence for chromium evaporation influencing the oxidation of 304L: The effect of temperature and flow rate

The influence of temperature and flow rate on the oxidation of 304L steel in O2/H2O mixtures was investigated. Polished samples were isothermally exposed to dry O2 and O2+40% H2O at 500–800°C at 0.02–13 cm/sec flow velocity, for 168 hr. The samples were analyzed by gravimetry, XRD, ESEM/EDX, and AES depth profiling. The oxidation of 304L in water vapor/oxygen mixtures at 500–800°C is strongly influenced by chromium evaporation. The loss of chromium tends to convert the protective chromia-rich oxide initially formed into a poorly protective, iron-rich oxide. The rate of oxidation depends on flow rate; high flow rates result in an early breakdown of the protective oxide. The most rapid breakdown of the protective oxide occurs at the highest temperature (800°C) and the highest gas flow (4000 ml/min=13 cm/sec). The oxide formed close to grain boundaries in the metal is more protective, while other parts, grain surfaces suffer breakaway corrosion. The protective oxide consists of a Cr-rich 50–200-nm thick M2O3 film, while the parts experiencing breakaway corrosion form a 10–30-μm thick Fe-rich M2O3/M3O4 scale. The results show that chromium evaporation is a key process affecting the oxidation resistance of chromia formers and marginal chromia formers in O2/H2O mixtures.

Oxidation of 310 steel in H2O/O2 mixtures at 600 °C: the effect of water-vapour-enhanced chromium evaporation

Abstract The oxidation of type 310 stainless steel was investigated at 600 °C in the presence of O 2 and O 2 +10% and 40% H 2 O. The effect of gas velocity was studied. The oxidized samples were investigated by grazing angle X-ray diffraction, SEM/EDX and SAM. The addition of H 2 O to O 2 resulted in a change of oxidation behaviour. A strong dependence on flow rate was observed in O 2 /H 2 O mixtures. At low flow rates a thin (30–50 nm) protective α-(Cr,Fe) 2 O 3 formed, the outer part being depleted in chromium. When the flow rate was increased beyond a critical value the protective oxide failed. Under these conditions ⩾5 μm thick α-Fe 2 O 3 /(Cr,Fe) 3 O 4 , oxide islands formed on the part of the surface corresponding to the centre of the alloy grains. The effect of water vapour is attributed to the water-vapour-assisted evaporation of chromium from the oxide, in the form of a chromium oxide hydroxide, probably CrO 2 (OH) 2 . The oxidation behaviour is rationalized using a qualitative mechanism proposed previously and parallels that of the 304L alloy.

The Influence of Carbon Dioxide on the Atmospheric Corrosion of Some Magnesium Alloys in the Presence of NaCl

The influence of ambient concentrations of carbon dioxide on the NaCl-induced atmospheric corrosion of high purity die-cast MgAl alloys (AM20 and AM60) and MgAlZn alloy (AZ91) is reported. Samples ...

A laboratory study of the initial stages of the atmospheric corrosion of zinc in the presence of NaCl ; influence of SO2 and NO2

Abstract A laboratory study of the NaCl-induced atmospheric corrosion of zinc in air containing sub-ppm concentrations of sulphur dioxide and nitrogen dioxide at 70 and 95% RH is reported. Each sample was exposed individually to synthetic atmospheres with control of pollutant concentrations, relative humidity and flow conditions. NaCl (14–280 μg cm −2 ) was added ex situ either before or periodically during exposure. Mass gain and metal loss results are reported. The corrosion products were investigated with respect to phase composition and sulphur, chloride, nitrite, nitrate and zinc content by a combination of X-ray powder diffraction, ion-chromatography and gravimetry. This results in a detailed knowledge of the corrosion product composition, both quantitatively and qualitatively. Crystalline ZnO(s), Zn 5 (OH) 8 Cl 2 · H 2 O(s), ZnSO 4 3Zn(OH) 2 · 4H 2 O(s) and ZnSO 4 3Zn(OH) 2 NaCl · x H 2 O (s) were detected. In addition soluble (normal) sulphate, nitrite and nitrate, and HNO 2 (g) were found. The deposition of NO x was studied in a time-resolved manner using gas analysers. Evidence was found for NO 2 reduction on zinc. In the presence of sodium chloride, NO 2 was produced, whereas HNO 2 (g) was formed on the clean zinc surface. In the presence of moderate to high concentrations of NaCl(s), sulphur dioxide slowed down the corrosion of zinc somewhat. The weak inhibitive action of sulphur dioxide was connected to the formation of sodium zinc hydroxychloride sulphate, ZnSO 4 3Zn(OH) 2 NaCl · x H 2 O, on the surface. In the presence of NaCl there was no evidence for a synergistic effect of the combination of SO 2 and NO 2 .

Scanning Kelvin probe force microscopy - A useful tool for studying atmospheric corrosion of MgAl alloys in situ

Scanning Kelvin probe force microscopy (SKPFM) is used to study the initial stages of atmospheric corrosion of an AlMg alloy and of physical vapor deposition (PVD) deposited 2 μm Al dots on pure Mg. The latter system is used as a model of a two-phase AlMg alloy. The influence of CO2 was studied in situ in humid air using SKPFM. This method allows for the in situ investigation of the evolution of the Volta potential during exposure, the resolution being in the submicrometer range. The temperature was 22.0°C, and the relative humidity was 85 or 95%. The concentration of CO2 was <1 or 350 ppm. The corrosion products were analyzed by gravimetry, ion chromatography, X-ray diffraction, scanning electron microscopy, scanning Kelvin probe, and Auger electron spectroscopy. We found that the initial stages of atmospheric corrosion on magnesium are influenced by the presence of cathodic PVD-deposited aluminum. A similar effect was seen in the case of AZ91D, the aluminum-rich β-phase forming the cathodic areas. The β-phase is nobler compared to the substrate because of the higher Al content. In the absence of CO2, the corrosion attack is localized in nature whereas the presence of ambient levels of CO2 results in a more general corrosion attack. The inhibitive effect of CO2 on the atmospheric corrosion of AZ91D is explained by the formation of a passivating layer of Mg5(CO3)4(OH)2⋅5H2O. In the absence of CO2, the increase in pH originating from the cathodic reaction results in the dissolution of aluminum in the passive layer. A corrosion mechanism is proposed explaining the behavior in the two environments.

A laboratory study of the effect of ozone, nitrogen dioxide, and sulfur dioxide on the atmospheric corrosion of zinc

The authors report on a laboratory study of the role of O[sub 3], NO[sub 2], and SO[sub 2] in the sub-parts per-million range on the atmospheric corrosion of zinc. Each sample was exposed individually to synthetic atmospheres with careful control of pollutant concentrations, relative humidity, and flow conditions. In addition, they studied the interaction of the pollutants with zinc using time-resolved trace-gas analysis. NO[sub 2] and O[sub 3] accelerate the corrosion of zinc in humid air containing SO[sub 2]. O[sub 3] oxidizes loosely bound four-valent sulfur on the zinc surface to sulfate while NO[sub 2] catalyzes the oxidation of SO[sub 2] on zinc. The increased formation of sulfate and hydrogen ions on the surface leads to the dissolution of solid corrosion products and to an increased rate of metal dissolution. The acceleration of SO[sub 2] oxidation and deposition on zinc by O[sub 3] becomes increasingly important as the concentration of SO[sub 2] and O[sub 3] decreases. The results suggest that O[sub 3] and NO[sub 2] may be important factors in the atmospheric corrosion of zinc.

The atmospheric corrosion of zinc in the presence of NaCl: The influence of carbon dioxide and temperature

The atmospheric corrosion of zinc has been studied at 4, 22, and 38°C. The samples were exposed to synthetic air with careful control of CO 2 concentration, relative humidity, and flow conditions. The relative humidity was 95%, and the concentrations of CO 2 were <1 and 350 ppm, respectively. Sodium chloride was added before the exposures (0, 14, and 70 μg/cm 2 ). Mass gain and metal loss results are reported. As expected, NaCl is corrosive toward zinc giving rise to heavy pitting. In the absence of CO 2 , the rate of the NaCl-induced corrosion was found to increase strongly with temperature. However, in the presence of CO 2 , the corrosion rate of zinc is independent of temperature. In the absence of CO 2 . zincite, ZnO, is the dominant corrosion product, while zinc hydroxy carbonates and simonkolleite, Zn 5 (OH) 8 Cl 2 -H 2 O, dominate in the presence of CO 2 . A mechanism is presented that explains the observations.

Investigation of Chromium Volatilization from FeCr Interconnects by a Denuder Technique

A technique is presented for accurate and time-resolved quantification of chromium volatilization from alloys at high temperature. A denuder tube which is coated with Na2CO3 is placed downstream of the samples. CrO2(OH)(2) that evaporated from the samples is collected on the denuder and converted to the thermally stable Na2CrO4. The chromate is then dissolved in water and determined quantitatively. Three commercially available ferritic 22% Cr steels intended for use as solid oxide fuel cell interconnect materials (Sanergy HT, Crofer 22 APU, and ZMG 232) have been investigated with respect to chromium volatilization and oxidation rate. The effect on chromium volatilization of a submicrometer cobalt coating on the steel surface is reported. Comparisons are made with a conventional thick ceramic coating. The experiments are carried out at 850 degrees C in N-2 - 20% O-2 - 3% H2O atmosphere. The submicrometer Co coatings proved to be very efficient, reducing Cr volatilization by 1 order of magnitude. Microscopic studies show that both uncoated steel and steel coated with a submicrometer cobalt film develop two-layered oxide scales with the bottom part consisting of a Cr-rich corundum-type oxide. The uncoated samples develop a top layer consisting of (Cr, Mn)(3)O-4 oxide, whereas the Co-coated samples exhibit a top layer consisting of Co-rich spinel oxide