Microstructure, smoothening effect, and local defects of alumina 
sol-gel coatings on ground steel

Nofz, Marianne; Dörfel, I.; Sojref, Regine; Wollschläger, Nicole; Mosquera-Feijoo, Maria; Kranzmann, Axel

doi:10.1007/s10971-016-4188-8

Cited by 10 publications

(12 citation statements)

References 32 publications

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“…These surface morphologies were identical for one-, two-, and three-layer coatings. Previous research on alumina sol-gel coating deposited on P92 steels has indicated that the alumina coatings with similar sol formulation and heat treated at 650 • C formed worm-like features when observed using TEM at a high magnification [24]. Based on their study, it is not possible to find a clear distinction between gamma-, delta-, and theta-Al 2 O 3 using electron diffraction, because of the small size of the nano-crystallites stacked in the whole thickness of the TEM samples.…”

Section: Effect Of Coating Thicknessmentioning

confidence: 93%

“…Coatings were applied to X20Cr13 specimens by the sol-gel method, as described by Nofz, et al [24]. Sol was prepared using boehmite (Sasol) stirred in ethanol at room temperature for 20 min.…”

Section: Coating Applicationmentioning

confidence: 99%

“…As reported by Schulz et al and Nofz et. al., Al 2 O 3 sol-gel coatings were able to protect steels in high-temperature flue gas [24,27]. Al 2 O 3 sol-gel coatings were also proven to be protective in NaCl-containing environments [25,28].…”

Section: Introductionmentioning

confidence: 99%

“…Besides the above-mentioned ceramic-based coatings, Al 2 O 3 is considered to be one of the most promising candidates for corrosion protection in various environments because it has excellent wear resistance, corrosion resistance, and high mechanical strength [16]. Various methods have been used to synthesize and apply Al 2 O 3 as coatings, such as chemical vapor deposition [17,18], atomic layer deposition [19,20], plasma spraying deposition [21], magnetron sputtering [22,23], and sol-gel [24,25]. Among these methods, sol-gel is one of the simplest and versatile techniques as it can be applied by dipping, spraying, or spinning [26].…”

Section: Introductionmentioning

confidence: 99%

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Study of Al2O3 Sol-Gel Coatings on X20Cr13 in Artificial North German Basin Geothermal Water at 150 °C

et al. 2021

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Al2O3 has been widely used as a coating in industrial applications due to its excellent chemical and thermal resistance. Considering high temperatures and aggressive mediums exist in geothermal systems, Al2O3 can be a potential coating candidate to protect steels in geothermal applications. In this study, γ-Al2O3 was used as a coating on martensitic steels by applying AlOOH sol followed by a heat treatment at 600 °C. To evaluate the coating application process, one-, two-, and three-layer coatings were tested in the artificial North German Basin (NGB), containing 166 g/L Cl−, at 150 °C and 1 MPa for 168 h. To reveal the stability of the Al2O3 coating in NGB solution, three-layer coatings were used in exposure tests for 24, 168, 672, and 1296 h, followed by surface and cross-section characterization. SEM images show that the Al2O3 coating was stable up to 1296 h of exposure, where the outer layer mostly transformed into boehmite AlOOH with needle-like crystals dominating the surface. Closer analysis of cross-sections showed that the interface between each layer was affected in long-term exposure tests, which caused local delamination after 168 h of exposure. In separate experiments, electrochemical impedance spectroscopy (EIS) was performed at 150 °C to evaluate the changes of coatings within the first 24 h. Results showed that the most significant decrease in the impedance is within 6 h, which can be associated with the electrolyte penetration through the coating, followed by the formation of AlOOH. Here, results of both short-term EIS measurements (up to 24 h) and long-term exposure tests (up to 1296 h) are discussed.

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Section: Effect Of Coating Thicknessmentioning

confidence: 93%

Section: Coating Applicationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Study of Al2O3 Sol-Gel Coatings on X20Cr13 in Artificial North German Basin Geothermal Water at 150 °C

et al. 2021

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“…Detailed preparation of the sol and the coating technique are available in Ref. . The coated samples were dried at 120 °C for 5 min in laboratory air, followed by heating up to 650 °C for additional 30 min.…”

Section: Methodsmentioning

confidence: 99%

Exposition of sol‐gel alumina‐coated P92 steel to flue gas: Time‐resolved microstructure evolution, defect tolerance, and repairing of the coating

Wollschläger

Nofz

Dörfel

et al. 2017

Materials & Corrosion

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Technically relevant P92 steel (9% Cr) was coated with a micron‐thick porous alumina layer prepared by sol‐gel technique and treated with flue gas (60 CO2‐30 H2O‐2 O2‐1 SO2‐7 N2 (mole fraction in %)) at 650 °C to mimic an oxyfuel‐combustion process. Local defects in the coating were marked using focused ion beam (FIB) technique and were inspected after exposition to hot flue gas atmosphere at 300, 800, and 1300 h, respectively. Local defects like agglomerated alumina sol particles tend to spall off from the coating uncovering the underlying dense chromia scale. Re‐coating was found to restore the protection ability from oxidation when repeatedly treated with hot flue gas. Cracks and voids did not promote the local oxidation due to the formation of crystalline Mn/S/O species within and on top of the coating. The protective character of the steel‐coating system is a result of (i) the fast formation of a dense chromia scale at the surface of sol‐gel alumina‐coated P92 steel bars in combination with (ii) the porous alumina coating acting as diffusion barrier, but also as diffusion partner in addition with (iii) fast Mn outward diffusion capturing the S species from flue gas.

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Thin Sol–Gel Alumina Coating as Protection of a 9% Cr Steel Against Flue Gas Corrosion at 650 °C

et al. 2017

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Microstructure, smoothening effect, and local defects of alumina sol-gel coatings on ground steel

Cited by 10 publications

References 32 publications

Study of Al2O3 Sol-Gel Coatings on X20Cr13 in Artificial North German Basin Geothermal Water at 150 °C

Study of Al2O3 Sol-Gel Coatings on X20Cr13 in Artificial North German Basin Geothermal Water at 150 °C

Exposition of sol‐gel alumina‐coated P92 steel to flue gas: Time‐resolved microstructure evolution, defect tolerance, and repairing of the coating

Thin Sol–Gel Alumina Coating as Protection of a 9% Cr Steel Against Flue Gas Corrosion at 650 °C

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