Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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strate was plated with 1.5 µm nickel (followed by 0.3 µm gold). The non-treated sample showed close to 100% complete wetting effect after activation. These same samples after post-dip treatment provided a contact angle of 76°. The results from all these tests highlight the strong hydrophobic properties of Betatec post-dip for both pure metal surfaces and electrodeposited nickel/gold. Figure 5: Process sequence for the plating of copper-based samples. CORROSION RESISTANCE STUDY Reference standards were used to assist corrosion inspection and sample assess- ment.15 Typical laboratory corrosion test conditions utilize an artificial atmos- phere provided by a climate chamber. The atmosphere can be carefully controlled with respect to humidity, temperature, and the desired concentration of corrosive gas or gas mixtures (e.g., sulphur dioxide, chlorine, nitric acid, etc.).16–18 Salt spray tests are also widely used, partic- ularly the "neutral salt spray test," which simulates the high salt content found in seawater or that used on highways during cold winter periods.19 In general, the choice of test was dictated by the application and the expected corrosion severity. NITRIC ACID VAPOR (NAV) TEST The ASTM B-735 standard uses the "nitric acid vapor test" to evaluate porosity, and the extent of corrosion is microscopically measured by a quantitative pore count per surface area. Test requirements include: • Temperature: 20–25°C • Air humidity of approximately 55% (never exceeding 60%) Figure 6: Corrosion inhibitor comparison (as corroded area after NAV testing) for Betatec and conventional products. • Acid vapor provided from 70% w/w nitric acid reagent. The procedure involves placing nitric acid into a dry chamber or desiccator, fol- lowed by a delay period of approximately 30 minutes prior to introduction of the corrosion test samples. The ASTM standard specifies a duration of 60 min for gold thickness to 2 µm. Required test time as a function of gold deposit thickness20: 60 ± 5 min for Au = 0.6–2.0 µm 75 ± 5 min for Au = 2.0–2.5 µm The actual duration used for this study was extended to 120 minutes to pro- vide an increased severity of two times the ASTM standard. The gold thickness used throughout this study was fixed at 0.3 µm (well 150

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