Shipwrecks help ~~ (1 Viewer)

[pc_wizz]

for my assignment i need to answer 6 dot pts ... i have done three and there are three remaining, which all suprisingly have to do with cathodic protection, can ppl help as much as they can, thanx

4.2.3 – Outline the process of cathodic protection, describing examples of its use in both marine and wet terrestrial environments.

4.2.4 – Describe the process of cathodic protection in selected examples in terms of the oxidation/reduction chemistry involved.

4.3.4 – Gather and process information to identify applications of cathodic protection, and use evidence to identify the reasons for their use and the chemistry involved.

 

[gbong]

1. galvanising: a layer of zinc covers iron so that the iron acts as a cathode. instead of Fe(2+) reacting with OH- to form rust, Zn(2+) reacts with OH- giving Zn(OH)2, thereby protecting the iron from corrosion. the thin foil of moisture between on the surface serves as the electrolyte

anodic site: Zn ---> Zn (2+) + 2e-
cathodic site: O2 + 2 H2O + 4e- -----> 4 OH-

oh yeh. zinc is also moderately passivating so yeh its oxide layer reforms when it cracks.

used in marine environments - galvansed nails etc.
also in wet terrestrial environments - underground pipes etc.

2. sacrificial anodes: a block of magnesium or zinc is bolted to the hull of a ship or underground pipes. similar concept to above, where magnesium is oxidised in place of the iron.

3. applied voltages: an inert electrode is used. a negative voltage is applied on the electrode thereby forcing electrons into places of stress in the ship's hull etc. the electrode is separated from the hull by an insulator

hope dat helps..... u beta check it all

 

[xiao1985]

gbong summaries most of them... but do remember that two metals need to have electrical contact, or it will not work...

 

[pc_wizz]

thanx ...