Zn–Ni Alloy Plating with Trivalent Chromate: Effects of NaF Additive Concentration and Treatment Time on Film Color, Thickness, and Electrochemical Properties

Abstract

Zn–Ni alloy plating is widely applied in manufacturing of automobile and construction material components because it provides better corrosion resistance and wear resistance than Zn plating. Furthermore, chromate coating treatment is gaining attention with respect to improving the corrosion resistance of Zn–Ni alloys. In this study, we investigated the effects of NaF additive concentration and treatment time on trivalent chromate coating, which has been developed as an alternative to hexavalent chromate coating. The chromate post-treatment solution used in this study comprises Cr(NO3)3·9H2O (360 g/L), CoSO4·7H2O (40 g/L), and HNO3 (35 mL/L), to which NaF is added in the concentration range of 0–30 g/L. The as-formed coating films at 1.6 pH and 60 °C treatment temperature for deposition times ranging from 30 to 120 s demonstrated a decreasing corrosion rate as the NaF concentration increased. The electrochemical and morphological analyses inferred that NaF acted as a catalyst, enhancing the rate of film formation. Furthermore, the film thickness increased with the treatment time, and the film color changed in the order of yellow, purple, and green.

Examining the Oxidation States of Metals in Aerosols Emitted by Electronic Cigarettes

“…However, under 60 W, the Cr2p 3/2 core level could be deconvoluted into three peaks at 579.4, 576.9, and 572.6 eV. The latter peak can be attributed to the presence of different oxidation states associated with chromium compounds or ligands, or it can be attributed to noise caused by Zn, whereas the former peak indicates the presence of about 15% of Cr (VI) species. , The power setting of the device directly influences the temperature reached by the heating coil. , At higher power settings (60 W), the presence of 15% Cr (VI) suggests that the high coil temperature, and potentially the contribution of other ions such as alkali, is sufficient to trigger Cr (VI) oxide formation . This aligns with the temperature-dependent nature of chromate formation.…”

Concentration Influence of Complexing Agent on Electrodeposited Zn-Ni Alloy

“…The variables of chromate conversion coating, such as duration, temperature, and pH, directly affect the growth, bonding strength, and corrosion resistance of the passivation film. Our group reported adding a chromate coating as a post-treatment to increase the corrosion resistance of Zn-Ni coatings [24]. The combination of NaF additive concentration and eco-friendly trivalent chromate treatment time was investigated.…”