Influence of fluoride ions on the amorphous phosphating of aluminium alloys

Burokas, V.; Martušienė, A.; Girčienė, O.

doi:10.1016/j.surfcoat.2007.05.034

Cited by 14 publications

(9 citation statements)

References 8 publications

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“…The results presented here differ from results of the phosphating of Al alloys at pH ∼4.5, where SiF 6 2− has been found to yield layers with larger weight than NH 4 HF 2 . 21 These differences are consistent with the reported higher stability of SiF 6 2− at lower pH. 40 An important difference to Al alloys investigated in the literature is the lack of intermetallic particles in the AS coatings.…”

Section: Discussionsupporting

confidence: 73%

“…For this reason, at the pH ∼2.5 used here, the addition of SiF 6 2− effectively suppresses phosphating, in contrast to behavior at higher pH. 21 While the role of phosphating in industrial processes is likely to dwindle in the coming years, due to its large environmental impact, the complex colloid, surface, and possible solution chemistry during activation and initial stages of the growth process still presents a number of challenges.…”

Section: Discussionmentioning

confidence: 95%

“…2 Different fluorides on Al alloys lead to different conversion. 21 The role of the activation has been studied on Al alloys, 13 as have initial stages of the phosphating process itself. 22 Experiments have been performed using a rotating disk electrode to control transport to the interface and to show transport limitation of the phosphating process.…”

Section: Introductionmentioning

confidence: 99%

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Activation and Fluoride-Assisted Phosphating of Aluminum-Silicon-Coated Steel

Schneider

Sigel

Lange

et al. 2013

ACS Appl. Mater. Interfaces

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Phosphating is a crucial process in the corrosion protection of metals. Here, activation and fluoride-assisted tricationic phosphating is investigated on aluminum-silicon (AS) coated steel surfaces. Dynamic light scattering results from the activation bath show a bimodal size distribution, with hydrodynamic radii of ~400 nm and ~10 μm. For the smaller particle fraction, static light scattering results are consistent with the interpretation of disklike particles as scattering objects. Particles of the larger fraction sediment with time. In the presence of electrolyte, the scattering intensity from the larger particle fraction increases. Coagulation with time is suggested to be related to the decrease in activity of the activation bath. Scanning Auger microscopy (SAM) shows a higher phosphorus concentration after titanium phosphate activation in the Al-rich areas compared to the Si-rich areas of the AS coatings. There is no correlation between the size of the species in the activation bath, and the size of the phosphate-containing regions on the activated surface. Phosphating was performed in the presence of hexafluorosilicic acid, H2SiF6, ammonium hydrogen difluoride, NH4HF2, and both, at an initial pH of 2.5. The absence of crystals after phosphating with H2SiF6 is an indication that SiF6(2-) is the final product of the oxide dissolution in the presence of fluoride. In the presence of NH4HF2, the Si-rich regions of the surface are phosphated before the Si-poor (Al-rich) regions. Hence, the phosphate distribution after activation and after phosphating are opposite. These results show that a high surface concentration of phosphate after activation is not sufficient for a high coverage with phosphate crystals after phosphating.

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Section: Discussionsupporting

confidence: 73%

Section: Discussionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Activation and Fluoride-Assisted Phosphating of Aluminum-Silicon-Coated Steel

Schneider

Sigel

Lange

et al. 2013

ACS Appl. Mater. Interfaces

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“…, which would otherwise poison the coating process. 4,[18][19][20] Hence, deposition of manganese phosphate coating enriched with iron and manganese hureaulites on Al by chemical conversion method appears to be a difficult proposition.…”

Section: àmentioning

confidence: 99%

A facile electrochemical approach for the deposition of iron–manganese phosphate composite coatings on aluminium

et al. 2015

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“…8). This may be ascribed to the formation of sodium cryolite, Na 3 AlF 6 , which is known to have a very poor solubility in water (2 mmol L −1 at 20 • C) [50,51].…”

Section: Tablementioning

confidence: 99%