Question

Alclad is perfectly resistant to corrosion by seawater. The alloy is
A.magnalium coated with aluminium
B.duralumin coated with aluminium
C.duralumin
D.a mixture of magnalium and duralumin

Answer 1

Hint: To answer this question, recall the concept of corrosion. Metal corrodes when it reacts with another substance such as oxygen, hydrogen, an electrical current or even dirt and bacteria.

Complete step by step answer:
The corrosion is a dangerous and extremely costly problem. Corrosion leads to the collapse of metal structures. Various alloys have been developed to overcome this problem of corrosion.
Alclad is an aluminium sheet resistant to corrosion. Alclad is developed from high-purity aluminium which itself is bonded on a high-strength aluminium alloy core material like duralumin.

Therefore, we can conclude that the correct answer to this question is option B.

Note:
The importance of some metals which acquire a natural passivity, or corrosion resistance. Exposure of the metal surface to air results in the formation of an oxide film which further prevents the contact between the metal surface and oxygen. The preventive methods of corrosion include plating with non-corrosive metals, such as stainless steel or aluminium, drying and cleaning of the metal surface, use of drying agents and coatings such as grease, oil, paint or carbon fibre coating and use of electrochemical technology to use a sacrificial anode to provide a cathodic protection system. However, the metals placed higher in the reactivity series such as iron, zinc, etc. get corroded very easily and metals placed lower in the reactivity series like gold, platinum and palladium do not corrode. This is explained by the fact that corrosion involves oxidation of the metals. As we go down the reactivity series tendency to get oxidised is very low. An exception to this fact is that aluminium doesn’t corrode unlike other metals even though it is reactive. When exposed to air aluminium gets covered by a layer of aluminium oxide already. This development of the oxide layer protects it from further corrosion.