Micro‐alloys precipitation in NiO‐ and CoO‐bearing enamel coatings and their effect on adherence of enamel/steel

The effect of CoO and NiO on the adherence between enamel coating and steel is investigated experimentally in this study. Enamel coatings are applied to the steel using a wet process with slurries. A total of five enamels were prepared including three single layer enamels: blank enamel ( BL ), NiO bearing enamel ( MTN i3), CoO bearing enamel ( MTC o3), and two double layer enamels: BL ‐ MTN i3, BL ‐ MTC o3, which consisted an inner layer of BL and an outer layer of MTN i3 or MTC o3. Falling‐weights tests were performed and the cross‐sections at the enamel/steel interface were analyzed with a scanning electron microscopy ( SEM ) coupled with an energy dispersive spectroscopy ( EDS ) and electron probe microanalysis ( EPMA ). Results show that the increases of adherence for MTC o3 and MTN i3 coated steel are attributed to the micro‐alloys precipitation at the enamel/steel interface. These micro‐alloy precipitations grow parallel to the steel/enamel interface for MTN i3, while they are dendritic and perpendicular for MTC o3. Compared with MTC o3, the negative reaction energy between NiO and FeO for MTN i3 causes micro‐alloy precipitations formed far away from the enamel/steel interface, resulting in different morphology and adherence.