The focal point of this EEI is tin can corrosion. Therefore dealing with the corrosion between the metals Fe and Sn when a tin can is scratched. Tin cans are Iron or steel cans coated in a thin tin layer and used primarily in the hospitality industry when preserving food and in other cases polyesters or other fabrics. When a tin can is scratched, it's Sn layer is damaged leaving the Fe exposed to the air around itself which contains O. Thus begins the oxidation of the Fe until the both the Fe and Sn metals have corroded away. This EEI will take the path of transforming the Fe and Sn corrosion away from tin can and displaying it as a galvanic cell which contains Fe and Sn metals in solution (this solution will also act as a substitute to organic matter present within tin cans). By looking at the corrosion of the galvanic cell when affected by certain variables, I will be able to test the corrosion rate at which these variable affect tin can corrosion.
Transforming the tin can corrosion into a galvanic cell is a more clear representation of the corrosion and will also allow the experiment to be further controlled and sufficient for recording quantitative and qualitative data.
Below is a list of variables that affect galvanic cell corrosion with the reference
Galvanic Corrosion Factors (Variables)
A collection of factors affecting galvanic corrosion of metals presented by Oldfield (see references below) includes the following:Type of joint: welded, fasteners, separated but with external connection Total geometry: area ratio (see further comments below), distances involved, surface shape, surface condition, number of galvanic cells Bulk solution properties:oxygen content, pH, conductivity, corrosivity, pollutant level Bulk solution environment: temperature, flow rate, volume, height above surface Mass Transport: migration, diffusion, convection Protective film characteristics: dependence on electrolyte conditions and potentials Alloy Composition:major and minor Reaction kinetics: metal dissolution, oxygen reduction overvoltage, hydrogen evolution overvoltage Electrode potentials: galvanic potential between metals, standard electrode potentials (the latter as a "rough" guide only) A listing of factors (and sub-factors) by Hack was broken down into three main categories: Material Properties: composition, processing history, surface condition Environment: composition, temperature, duration, flow Geometry: Further variables were attributed to the above sub-factors, for example conductivity, pH, biological constituents for the environment composition sub-factor. The following have been described as "main factors" influencing galvanic corrosion rates in Skanaluminium's on-line publication"Alubook - Lexical knowledge about aluminium" |
The two variables chosen for this EEI are pH and surface area. Two variables which are already common in tin can corrosion.
Further background research will be done in order to understand the mechanics of galvanic cells thoroughly as well as corrosion which will be seen in later posts.
Below is the current hypothesis and research question for the EEI that have been drafted up.
Research Question
What effect will the pH of the solution within a galvanic
cell and surface area of metals have on the rate of corrosion?
Hypothesis
It was hypothesized that as the pH decreased and the surface
area increased within a Fe and Sn galvanic cell then the corrosion rate of the
Fe would increase when the amount of solution, type of container, multimeter, temperature
and type of joint are kept constant.
- http://www.corrosion-club.com/galvanic.htm
- http://www.doitpoms.ac.uk/tlplib/recycling-metals/tin_cans.php
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