The influence of alkali‐degreasing on the chemical composition of hot‐dip galvanized steel surfaces

Abstract

The influence of dipping temperature and time on the surface chemistry of hot-dipped galvanized steel sheets during the alkaline degreasing process is investigated. The surface chemistry was monitored with scanning Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The results show high Al concentrations on the untreated surfaces, which are significantly reduced during alkaline degreasing. The same conclusions could be drawn for the carbon compounds that accumulate on the surface during storage. The measurements reveal a gradual reduction in surface Al as the alkali solution temperature and/or degreasing time are increased. When degreasing was conducted at 70°C for 30 s the surface was practically free from Al, which was present only in small islands. Furthermore, the experiments showed that the thickness of the oxide film covering the surfaces before and after alkaline degreasing is approximately 20Å. The main constituents of the film varied from ZnAl hydroxide/oxide to Zn hydroxide/oxide, before and after degreasing, respectively.

Effect of Hot Dip Galvanized Steel Surface Chemistry and Morphology on Titanium Hexafluoride Pretreatment

“…The Al/Zn atomic ratio decreased rapidly already at low concentrations of the cleaning solution. Similar trends have been obtained by increasing the treatment time and temperature [19]. In this study, the concentration of aluminum decreased much slower than the Al/Zn ratio.…”

“…During the alkaline cleaning, the surface is also activated by dissolving some of the inert Al 2 O 3 [18] [19]. Removal of aluminum oxide as a function of alkaline cleaning solution concentration is shown in Figure 2.…”

Convenient extraction method for quantification of thin zinc patina layers

“…The FTIR spectrum for sample 1 was typical for metallic zinc with no specific bands. The natural thin oxide layer that typically occupies the outermost few nanometers of galvanized coatings showed no absorption . In the FTIR spectrum of the scCO 2 ‐treated sample (sample 2), the bands that are typically associated with zinc hydroxy carbonates were present.…”

Dissolution-Induced Nanowire Synthesis on Hot-Dip Galvanized Surface in Supercritical Carbon Dioxide

“…The aluminum from the galvanizing bath reacts with oxygen in air to form aluminum oxide (Al 2 O 3 ) on the surface of the HDG sheet [ 30 ]. Residual aluminum can also be detected after alkaline cleaning treatment [ 31 ]. The presence of aluminum in the scCO 2 treated sample confirms the uneven surface coverage by the nanowire structure.…”