Evaluation of 316L stainless mill additives on microstructure and alkali corrosive behavior of enamel coatings

Abstract

Excellent chemical stability, good corrosion resistance, and compositional controllability make vitrified enamel promising coating materials. The corrosion resistance of the [–Si–O–]/[–Si–O–Al–]‐based enamel coatings decreases in alkaline environments, whereas can be improved by incorporating metal oxides, such as ZrO2 and SnO2. The introduction of these oxides results in an increase in the sintering temperature and a decrease in the toughness of the coatings. It was observed that the corrosion resistance of the coatings in an alkaline medium could be improved using metal powder‐based additives without increasing the sintering temperature and affecting the mechanical properties of the coatings. We used powdered 316L stainless steel as the mill additive, and the effects of this additive on the structure and alkali corrosion resistance of the vitrified enamel coatings were studied. Results indicate that the addition of an appropriate quantity of the additive (4 wt.%) improves the extent of gas consumption during the enamel sintering, decreases the degree of porosity and the size of the pores. Furthermore, the mechanical properties of the skeleton formed between the pores could be improved, because blocklike corrosion products are not peeled off, which increases the corrosion resistance of the coatings. The corrosion products, such as Ca‐based compounds, block the corrosion holes, resulting in a decrease in the corrosion rate also.

Enamel coatings mill additives optimization for sulfuric acid corrosion

“…The PE coating had a few pores but with large diameters, whereas the QE, FE, and ME coatings had lots of pores with small diameters. The increase of viscosity in enamel would be attributed to the mill additives, for the nucleation sites for pores that are provided during the high‐temperature sintering, 14 because of the high‐temperature chemical reaction between the enamel glass frits and the substrate steel (as shown in Reactions and ) 15,16 . Hydrogen was produced during the reaction between the substrate steel and water vapors, which caused pores in enamel coatings, as shown in Reaction 15,17 …”

“…The increase of viscosity in enamel would be attributed to the mill additives, for the nucleation sites for pores that are provided during the high-temperature sintering, 14 because of the high-temperature chemical reaction between the enamel glass frits and the substrate steel (as shown in Reactions 1 and 2). 15,16 Hydrogen was produced during the reaction between the substrate steel and water vapors, which caused pores in enamel coatings, as shown in Reaction 3. 15,17 NiO (enamelslurry) +Fe 3 C (substrate) As the partially enlarged view from SEM cross-sectional images shown in Figure 2, many island-like dendrites dissolution were separated from the substrate steel.…”

Porcelain Enamel Coatings for Building Façades

“…In the architectural sector, materials are frequently in contact with alkaline concrete matter and concrete products. Enamel coatings suffer in the presence of a basic pH [38], even if adjustments in the type and/or amount of mill additives were shown to improve the resistance of this type of material toward an alkaline pH [39,40]. The EN 12206-1 standard [28] was thus followed to test the resistance of the enamel coatings to basic concrete by evaluating variations in the color and gloss of the samples after contact with concrete matter.…”