Question

URGENT

In each of the following configurations, identify the anode and rank in terms of approximate corrosion rates of the anode (fast to slow). All are 50 mm thick in seawater:

1 meter square titanium plate with a single 50 mm aluminum bolt in the center

1 meter square Brass plate with a single 50 mm silver plated bolt in the center

1 meter square aluminum plate with a 70 x 70 cm square titanium hatch bolted to it with titanium bolts.

Answer 1

Before going to the given assignment, we will see the metal to metal galvanic corrosion. Metals from passive to anodic are in the following order

Copper

Bronze

Brass

Nickel

Tin

Lead

Steel

Aluminium

Zinc

Magnesium ( more anodic)

Metals from passive to most noble are in the following order,

Stainless steel

Silver

Gold

Platinum

Now the given cases, we can conclude the corrosion as mentioned below.

Case 1. Here anode will be aluminium. And 50 mm aluminium has to protect 1 square metre titanium, hence the corrosion rate for aluminium is more.

Case 2: here brass plate will be the anode. In this case 1 square metre brass plate has to protect 50 mm silver plated bolt, hence corrosion rate of anode will be slower.

Case 3: Here anode will be aluminium plate. Now 1 square metre of aluminium as anode has to protect 70 square cm of titanium, so the cathodic surface which is to be protected is relatively more than case 2. So this case rate of corrosion is more than case 2 and less than case 1.

Hence ranking of approximate corrosion rate of the anode from fast to slow is in the following order,

Case 1 > case 3 > case 2.