You are to select the material for a rod to be used in an aqueous environment an

Question

You are to select the material for a rod to be used in an aqueous environment and your main concern is corrosion. You have three choices for your selection: 1) annealed Cu - 20% Zn alloy 2) 30% cold worked Cu - 20% Zn alloy 3) annealed Cu - 50% Zn alloy bl) What kind of corrosion this material can be subjected to? b2) Which of these three materials would you use for this particular application? Justify your choice. c) Corrosion is observed at the root of threads on bolts and in other areas with sharp corners. Explain this phenomenon.

Explanation / Answer

SOLUTION:-b1)

Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and stopping corrosion

TYPES:-

1) Environmental Cracking:

Environmental cracking is a corrosion process that can result from a combination of environmental conditions affecting the metal. Chemical, temperature and stress-related conditions can result in the following types of environmental corrosion:

2)

General Attack Corrosion:

Also known as uniform attack corrosion, general attack corrosion is the most common type of corrosion and is caused by a chemical or electrochemical reaction that results in the deterioration of the entire exposed surface of a metal.

Ultimately, the metal deteriorates to the point of failure.

General attack corrosion accounts for the greatest amount of metal destruction by corrosion but is considered as a safe form of corrosion, due to the fact that it is predictable, manageable and often preventable.

3)

Galvanic Corrosion:

Galvanic corrosion, or dissimiliar metal corrosion, occurs when two different metals are located together in a corrosive electrolyte. A galvanic couple forms between the two metals, where one metal becomes the anode and the other the cathode. The anode, or sacrificial metal, corrodes and deteriorates faster than it would alone, while the cathode deteriorates more slowly than it would otherwise.

Three conditions must exist for galvanic corrosion to occur:

b2)

1)Low brass is a copper-zinc alloy containing 20% zinc with a light golden color and excellent ductility;

it is used for flexible metal hoses and metal bellows

2)Cartridge brass is a 30% zinc brass with good cold working properties. Used for ammunition cases

3)( a)Beta brasses, with 45–50% zinc content, can only be worked hot, and are harder, stronger, and

suitable for casting

(b)White brass contains more than 50% zinc and is too brittle for general use. The term may also refer to certain types of nickel silver alloys as well as Cu-Zn-Sn alloys with high proportions (typically 40%+) of tin and/or zinc, as well as predominantly zinc casting alloys with copper additive

c) Corrosion is possible when two metal and water are contact at present of water

so, we can say root of thread of bolts and sharp corners are direct contact of atmosphere

and we know that atmosphere has water and metals are present at bolt

so, we can say corrosion is easiet at  root of thread of bolts and sharp corners.

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