Metal Finishing Guide Book

2012-2013

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Tridur Finish 300 Post-dip Solution Base Layer/Passivate Concentration Temperature pH Corrosion Protection (ISO 9227) Zinc/Tridur Zn H1 100 ml/l 45��C (40���50��C) pH 4.5 (4���5.5) >72 h to wc Zinc���iron/Tridur ZnFe H1 200 ml/l 45��C (40���50��C) pH 5.5 (5���6.5) >240 h to wc Zinc���nickel/Tridur ZnNi H1 200 ml/l 45��C (40���50��C) pH 5.5 (5���6.5) >300 h to wc Table 1: Application Parameters and Corrosion Results of the Post-dip (Tridur Finish 300) the passivate or the passivate with post-dip system. The conversion coating���like composition is confirmed by an XPS depth profile, recorded on a sample of Tridur ZnNi H1 with Tridur Finish 300 (20% v/v) applied (Fig. 8). Significant carbon concentrations are only found on the surface, likely due to adsorption of CO2 from the air or surface contaminaFigure 16: Log plot of polarization experiments of an tions. Within about 10 nm, the carexperimental black zinc passivate formulation. bon concentration falls to a very low level, not changing significantEcorr /mV icorr /��A/cm2 ly with increasing sputter depth. Sample The composition of the post-dip Experimental black zinc layer and the passivate���s conversion ���1,059 89 passivate without final finish coating appear almost identical. A change in nickel concentration indiExperimental black zinc ���1,055 40 passivate + Tridur Finish 300 cates a diffuse transition between the more post-dip-like and the more Experimental black passivate ���1,050 16 passivate-like layers. Therefore, the + Corrosil Plus 501 post-dip contributes to an increase Table 2: Corrosion Potential (E ) and Corrosion Current in thickness of about 0.2 ��m in this Densities (i ) from Tafel Analysis: Potentials vs. Ag/AgCl application. (3M KCl) However, the lack of sharp transitions is also due to the fact that the post-dip penetrates deeply into the passivate layer, effectively filling up micro cracks. Both the passivate layer and the post-dip layer Figure 17: Tridur Finish 300 applied to Tridur ZnNi H1 on bear reactive sites with regard to Zn/Ni (14% Ni, 8 ��m) after 1,008 h in neutral salt spray coordination chemistry. During testing according to DIN EN ISO 9227. No voluminous the deposition at elevated temperwhite corrosion products were produced. ature, and especially in the subsequent hot-air drying process, the chromium(III) present in the passivate layer reacts with the post-dip solution���s components, finally building up the enhanced corr corr 391

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