Designing the Color of Hot-Dip Galvanized Steel Sheet Through Destructive Light Interference Using a Zn-Ti Liquid Metallic Bath

Abstract

The color of hot-dip galvanized steel sheet was adjusted in a reproducible way using a liquid Zn-Ti metallic bath, air atmosphere, and controlling the bath temperature as the only experi mental parame ter. Coloring was found only for sample s cooled in air and dipped into Ti-containing liquid Zn. For samples dipped 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 ± 22 K (541°C ± 22°C), violet at 847 K ± 10 K (574°C ± 10°C), and blue at 873 K ± 15 K (600°C ± 15°C). With the increasing bath temperature, the thickness of the adhered Zn-Ti layer gradually decreased from 52 to 32 micrometers, while the thickness of the outer TiO 2 layer gradually increased from 24 to 69 nm. Due to small Al contamination of the Zn bath, a thin (around 2 nm) alumina-rich layer is found between the outer TiO 2 layer and the inner macroscopic Zn layer. It is proven that the color change was governed by the formation of thin outer TiO 2 layer; different colors appear depending on the thickness of this layer, mostly due to the destructive interference of visible light on this transparent nano-layer. A complex model was built to explain the results using known relationships of chemical thermodynamics, adhesion, heat flow, kinetics of chemical reactions, diffusion, and optics. The complex model was able to reproduce the observations and allowed making predictions on the color of the hot-dip galvanized steel sample, as a function of the following experimental parameters: temperature and Ti content of the Zn bath, oxygen content, pressure, temperature and flow rate of the cooling gas, dimensions of the steel sheet, velocity of dipping the steel sheet into the Zn-Ti bath, residence time of the steel sheet within the bath, and the velocity of its removal from the bath. These relationships will be valuable for planning further experiments and technologies on color hot-dip galvanization of steel by Zn-Ti alloys.

Synthesis, characterisation and thermal behaviour of Cu-based nano-multilayer

“…It is worth to mention that the Cu crystals on top of the NML seem natural metallic in light microscope, confirming the oxide layer is not too thick on them. Although oxide films might change the visible color of metals [47], but only above a critical thickness [48]. Using Eq.…”

“…Using Eq. (10a) of [48] the smallest thickness of the copper oxide layer of 37 nm is found that ensures the minimum of 400 nm wavelength of destructive interference if the refractive index of the CuO/Cu 2 O taken as 2.7 ± 0.1 (see p. 236 of [44]), where 400 nm is the lowest wavelength of light visible by humans. This means the thickness of the oxide layer on the micron-sized Cu-crystals is surely below 37 nm, which is less than 2 % of the total size of the Cucrystals, explaining why the presence of oxygen on Cu crystals seems negligible in Figs 7,8.…”

Nanoszerkezetű, transzparens bevonatok előállításakolloidkémiai módszerekkel

“…Fémek korrózióvédõ bevonatainak kialakításakor esztétikai szempontok is szerepet játszanak 17,18 . Ezért van jelentõsége átlátszó bevonatok fejlesztésének, melyek nem fedik el a bevonandó fém színét, vagy éppen elõnyösen módosítják azt 12…”

Thermodynamic Stability of Nano-grained Alloys Against Grain Coarsening and Precipitation of Macroscopic Phases

“…NANO-MATERIALS play an increasing scientific and social role. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] In the past, nano-materials were simplified to single nano-particles. However, it has been clear for some decades that the real use of nanomaterials is expected if they form macroscopic articles with nano-structure inside.…”