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

Abstract

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 (MTNi3), CoO bearing enamel (MTCo3), and two double layer enamels: BL-MTNi3, BLMTCo3, which consisted an inner layer of BL and an outer layer of MTNi3 or MTCo3. 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 MTCo3 and MTNi3 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 MTNi3, while they are dendritic and perpendicular for MTCo3. Compared with MTCo3, the negative reaction energy between NiO and FeO for MTNi3 causes micro-alloy precipitations formed far away from the enamel/steel interface, resulting in different morphology and adherence. K E Y W O R D Sadhesion, characterization, coatings, diffusion N160205001.

Exploring the hindering mechanism of element Ti on the adherence of CoO‐bearing one‐coat enamel/steel

“…The firing process of the titanium‐free OCE has been described in detail in previous studies, and a brief summary is made here for the convenience of understanding: Firing stage I: enamel powders are not completely fused to cover the metal, and the substrate is rapidly oxidized, evenly forming an iron oxide layer on the surface of the steel. Firing stage II: enamel powders are melted and the rapid oxidation of iron stops.…”

“…The nominal composition of OCE and TBE is shown in Table . The preparation method of enamel powder has been previously described in detail elsewhere . All the powder passes through the 200 mesh sieve.…”

“…Adherence measurement was conducted using a falling‐weight method, which has been described in detail elsewhere . Photos of samples after hitting were taken by a SLR camera (Canon 550D) and fraction of metal‐exposed area was determined using the ImageJ (imagej.nih.gov/ij) analysis program.…”

“…Previous study has reported a titanium‐free one‐coat enamel (OCE for short) with good adherence performance . During the firing process of the OCE, a lot of Fe–Co/Fe–Ni alloy anchors were formed at interface between the steel and the enamel, accordingly, the coating and steel were closely combined by mechanical interlocking.…”

Thermal shock and sulfuric acid corrosion behavior of enamel–nano‐Ni composite/enamel–nano‐nickel composite coating

“…By melting and quenching, the raw materials, the enamel frits, were obtained, and then the enamel powder was obtained by milling the frits. The preparation method of enamel powder has been previously described in detail elsewhere 18 . Mixing of enamel and nano‐Ni powder (~100 nm) was carried out in a ball‐milling machine for 1 hour, where enamel and nickel powders and agate balls were all sealed in an agate container.…”