I am not sure which density value should be used. Density of steel or density of metal coating
Iron can be coated with an active metal zinc. It stands in the series of standard oxidation-reduction potentials above iron. If there is a hole in the zinc to the iron, then the iron will not corrode. It will corrode zinc until it all dissolves in the corrosive environment. For tin standard oxidation- reduction potential is lower. If there is a hole in the tin to the iron, then the iron will corrode. Therefore, for your experiments it is necessary to choose a galvanic pair of the second type and determine the loss of weight of a tin-type coating.
The rate of corrosion is the speed at which any given metal deteriorates in a specific environment. The rate, or speed, is dependent upon environmental conditions as well as the type, and condition, of the metal.
Corrosion rates in the US are normally calculated using mpy (Mils per year). In other words, the corrosion rate is based on the number of millimeters (thousandths of an inch) it penetrates each year.
In order to calculate the rate of corrosion, the following information must be collected:
- Weight loss (the decrease in metal weight during the reference time period)
- Density (density of the metal)
- Area (total initial surface area of the metal piece)
- Time (the length of the reference time period)
The corrosion rate can be calculated in millimeter per year, (mm/yr) on the basis of the apparent surface area using equation.
Corrosion Rate (mm/yr) = Weight loss x K/Density x Area Time = W.K/𝜌 x A x T
Where W = Weight loss in milligrams, 𝜌 = metal density in g/cm3, A = Area of sample in cm2, T = Time of exposure of the metal sample in hours, K = constant = 87500(Depends on the nature of test sample)
To can obtain density of the test sample from its mass ans volume. Mass by direct weighing and volume by water displacement method.
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