Midterm #3 Questions 3-6 - Stony Brook University ESG 332

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3) a) Tin and zinc are used to coat steel to prevent the corrosion of steel. The coatings operate in theoretically different ways. Explain fully and give examples. (15pts) The way by which tin... and zinc are used to prevent corrosion of steel is through galvanizing. Galvanizing is a form of cathodic protection where a layer of zinc is applied to the surface of steel by way of hot dipping. The zinc when exposed to the atmosphere and most aqueous environments is anodic and will cathodically protect the steel from surface damage. Zinc is more reactive than steel and will act as a sacrificial anode Tin is used to coat the inside of tin cans made of steel because it will protect the steel from corrosion by food products in the same manner that zinc reacts, by being anodic in most environments and cathodically protecting the steel. Tin is more noble than steel and will act as a protective coating cathodic protection. Cathodic protection uses externally supplied electrons to add to metal, which causes the reversing of corrosion (reduction). One specific process is called a galvanic couple – where the metal to be protected is connected to a sacrificial anode- a more reactive metal (usually magnesium or zinc). The sacrificial anode will be oxidized and will provide electrons that will be used for the first metal. 3) b) How does the relative ratio of anion and cation defects affect the diffusional processes involved in the oxidation of metals? (10pts) [Show More]

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