Corrosion General theory

1. Define the term electrolyte.

Answer----It is a substance when in solution , usually water or in its fused state will conduct electricity and be broken down by it .

2.How does corrosion of steel occur .

Answer----Corrosion of steel occurs due to electro chemical process which results from an anodic reaction & at least one cathodic reaction .

3.Is the corrosion circuit AC or Dc.

Answer----DC

4.Where does corrosion occur anode or cathode.

Answer----Anode.

5.Which three factors are required for corrosion current to to exist.

Answer----Electrolyte & anodic reaction & cathodic reaction.

6.In a corrosion circuit , which way do electrons flow.

Answer----Negative to positive.

7.Name four external factors which can accelerate corrosion .

Answer----millscale , electrolyte , acid & alkali.

8.Which is more noble steel or zinc.

Answer----Steel.

9.Which is more electrically negative copper or steel .

Answer----Copper

10.If steel or zinc were coupled in series , which metal would corrode first .

Answer----Zinc.

11.If magnesium and zinc were coupled in series , which would corrode first .

Answer----magnesium.

12.When the potentials of metals are known , by what other name could we call the galvanic series.

Answer----Electrochemical series.

13.What is the approximate thickness of millscale.

Answer----25 to 100 microns .

14.What are three compounds which together form millscale

Answer ---- Fe O, Fe3o4 & Fe2o3

15. In which environments are chloride salts likely to be found .

Answer----Marine.

16.In which environments are sulphate salts likely to be found .

Answer----Industrial.

17.Name three metals which could be used as anodes on a steel pipeline .

Answer----Magnetite , graphite & silicon iron .

18. Name the two hygroscopic salts commonly found on substrates.

Answer----Soluble iron & soluble chlorides.

19.Which gas is released during ionisation at the cathode.

Answer----Hydrogen.

20.What is polarization

Answer----When electrons have circuits through which they can travel resulting in one area of a component being anodic and one area being cathodic .

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