The color of hot-dip galvanized steel sheet was adjusted in a reproducibleway using a liquid Zn-Ti metallic bath, air atmosphere, and controlling thebath temperature as the only experimental parameter. Coloring was found onlyfor sample s cooled in air and dipped into Ti-containing liquid Zn. For samplesdipped into a 0.15 wt pct Ti-containing Zn bath, the color remained metallic(gray) below a 792 K (519 C) bath temperature; it was yellow at 814 K, violetat 847 K, and blue at 873 K. With the increasing bath temperature, thethickness of the adhered Zn-Ti layer gradually decreased from 52 to 32micrometers, while the thickness of the outer TiO2 layer gradually increasedfrom 24 to 69 nm. Due to small Al contamination of the Zn bath, a thin (around2 nm) alumina-rich layer is found between the outer TiO2 layer and the innermacroscopic Zn layer. It is proven that the color change was governed by theformation of thin outer TiO2 layer; different colors appear depending on thethickness of this layer, mostly due to the destructive interference of visiblelight on this transparent nano-layer. A complex model was built to explain theresults using known relationships of chemical thermodynamics, adhesion, heatflow, kinetics of chemical reactions, diffusion, and optics.
展开▼
