Physical Chemistry
Questions & Answers
Mechanics of Materials Lab Experiment #1: Galvanic Corrosion Experiment Objective The object of this experiment is to demonstrate the importance of proper material selection. Various situations will be investigated to determine factors that affect galvanic corrosion.
Problems 1. The following electrode potentials were observed after a 1-year immersion period in natural seawater of pH 8.0 [20]:
2. Suppose that an acid flux is inadvertently left on the surface of a silver contact and that in the presence of a thin film of condensed moisture, the acid residue has a pH of 5.0. Under what range of electrode potentials could the corrosion of silver occur in the thin-film electrolyte?
3. Palladium (like gold and platinum) is a noble metal. However, the Pourbaix diagram for pal-ladium (Fig. 6.14) contains a region where palladium is subject to corrosion. Can palladium corrode by the following reaction:
4. The electrode potential of titanium immersed in a sulfuric acid solution of pH approximately 1 was measured to be -0.70 V vs. SCE [21]. (a) Confirm that titanium undergoes active corrosion under these conditions and (b) consult the Pourbaix diagram to suggest three different means to provide corrosion protection.
5. In the interpretation of Pourbaix diagrams, corrosion is considered to occur when the concentration of dissolved metal ions attains a minimum concentration of 1.0 x 10-6 M. Suppose that a 0.50-cm² sample of aluminum immersed in 1.0 L of an aqueous solution corrodes at a constant current density of 100 μA/cm². How long will it take to produce a concentration of 1.0 x 10-6 MAI³+?
Q4: If zinc surface is corroding at a current density of 2 x 105 0.2 mA/cm², what thickness of metal would corrode in 8 months? The atomic weight of zinc is 65.38 g/mol.
Q2: A tin can immersed in seawater shows a current density of 2.45 x 10-6 A/cm². What is the rate of corrosion in mg/dm²/day (mdd)? Atomic weight of tin is 118.69 g/mol.
Q3: Calculate the penetration rate for 304 stainless steel (71.75% Fe, 19% Cr, 9.25% Ni) in mils per year (mpy) and mm/yr. The density of steel is 7.9g/cm³. The atomic weight of Fe, Cr, and Ni are 55.85 g/mol, 52 g/mol, and 58.71 g/mol respectively.
