Unit 5: Corrosion - Practice Quiz

1 Corrosion is best defined as the:

2 The reddish-brown deposit formed when iron corrodes in moist air is commonly called:

3 Corrosion generally occurs because most metals in nature tend to:

4 Direct chemical corrosion is also known as:

5 Which of the following is an example of direct chemical (dry) corrosion?

6 In dry oxidation corrosion, a protective oxide film is one that is:

7 Electrochemical corrosion requires the presence of:

8 During electrochemical corrosion, oxidation of the metal takes place at the:

9 In the oxygen absorption mechanism of electrochemical corrosion, which ion is formed at the cathode?

10 The hydrogen evolution mechanism of electrochemical corrosion generally occurs in:

11 Galvanic corrosion occurs when:

12 When zinc and copper are connected together in an electrolyte, which metal corrodes preferentially?

13 A concentration cell corrosion arises due to differences in the:

14 In differential aeration corrosion, the region exposed to a lower oxygen concentration behaves as the:

15 Differential aeration corrosion is caused mainly by differences in the amount of:

16 In a steel tank partly filled with water, water-line corrosion occurs:

17 Pitting corrosion is characterized by:

18 Intergranular corrosion takes place mainly:

19 Which factor generally increases the rate of corrosion of a metal?

20 In cathodic protection using a sacrificial anode, the metal to be protected is connected to a metal that is:

21 Rusting of iron in a moist environment is best classified as which type of process, considering that it involves loss of metal to its surroundings?

22 Corrosion is often described as the reverse of extraction metallurgy. What does this statement imply thermodynamically?

23 According to the Pilling–Bedworth rule, a metal forms a protective oxide layer when the ratio of oxide volume to metal volume is:

24 Alkali metals like Na and K, and alkaline earth metals like Mg, form porous non-protective oxide films. This is because their Pilling–Bedworth ratio is:

25 Which of the following gases is responsible for the formation of a metal chloride during direct chemical (dry) corrosion of a metal at high temperature?

26 In the hydrogen evolution mechanism of electrochemical corrosion, what reaction occurs at the cathode in an acidic medium?

27 In the oxygen absorption mechanism of corrosion in a neutral aerated solution, the cathodic reaction produces:

28 During electrochemical corrosion, where does the actual loss (dissolution) of metal always occur?

29 When zinc and copper are electrically coupled and exposed to an electrolyte, which metal corrodes and why?

30 A steel bolt used to join two copper plates in a marine structure corrodes rapidly. The main reason is:

31 In a concentration cell formed by a single metal dipped in electrolyte of two different metal-ion concentrations, corrosion occurs at the electrode in contact with:

32 In differential aeration corrosion, which region of the metal surface becomes anodic?

33 A metal partly immersed in water and partly exposed to air corrodes most severely just below the waterline. This is because:

34 In pitting corrosion, once a small pit forms under a dirt or scale deposit, why does corrosion accelerate within the pit?

35 Water-line corrosion is commonly observed in steel water storage tanks. The line of attack forms because:

36 Intergranular corrosion in welded stainless steel (weld decay) occurs mainly because:

37 Which factor generally increases the rate of soil corrosion of buried metal pipelines?

38 In the sacrificial anode method of cathodic protection for a buried iron pipeline, a suitable anode metal is:

39 Galvanising protects iron even if the zinc coating is scratched, whereas tinning fails at a scratch. This difference arises because:

40 Ceramic coatings are widely used to protect metals in high-temperature environments mainly because they:

41 A metal spontaneously reverts to its combined (oxide) state during corrosion. From a thermodynamic standpoint, why is corrosion of most engineering metals a spontaneous process?

42 The Pilling–Bedworth ratio (PBR) predicts protective behavior of oxide films. For a metal whose oxide has , what corrosion behavior is expected?

43 In high-temperature oxidation following a parabolic rate law, the weight gain relates to time as . If the oxide layer thickness after 1 hour is , what is it after 4 hours (assuming ideal parabolic kinetics)?

44 During electrochemical corrosion of iron in a neutral aerated solution, the anodic reaction is . What is the corresponding cathodic reaction that consumes the liberated electrons?

45 In acidic, oxygen-free (deaerated) media, corrosion of iron proceeds by which mechanism, and what characteristic evidence appears at the cathodic sites?

46 Two dissimilar metals are coupled in an electrolyte. In a Zn–Cu galvanic couple and an Fe–Sn couple (tin coating on iron), which combination protects the base metal and which accelerates its corrosion when the coating is scratched?

47 A concentration cell forms when identical copper electrodes are placed in solutions of and . Which electrode acts as the anode?

48 In differential aeration corrosion, which region of the metal becomes anodic and undergoes attack?

49 A steel bolt fastens two plates, leaving a tight crevice. Why does crevice corrosion, driven by differential aeration, tend to be autocatalytic and self-accelerating?

50 In a partially filled steel water tank, corrosion is most severe just below the waterline. What is the correct explanation based on differential aeration?

51 Pitting corrosion is considered more dangerous than uniform corrosion despite low overall metal loss. What is the primary reason?

52 A dust particle sits on a stainless steel surface exposed to a chloride solution, initiating a pit. Why does the area covered by the particle become anodic?

53 Intergranular corrosion (weld decay) in austenitic stainless steel arises from sensitization. What microstructural change makes the grain-boundary regions anodic?

54 Which practical measure does NOT effectively prevent intergranular (weld decay) corrosion in stainless steel?

55 A buried steel pipeline runs through alternating sandy and clay soils. Why is the section in clay more likely to become anodic and corrode?

56 Regarding the effect of the anode-to-cathode area ratio on corrosion rate, which condition produces the most rapid, dangerous localized attack?

57 In impressed current cathodic protection (ICCP) of a buried steel tank, the structure is connected to the negative terminal of a DC source with an inert anode. How does this differ fundamentally from sacrificial anode protection?

58 Anodic (passivation) inhibitors such as chromates and phosphates are described as "dangerous" inhibitors. Why can insufficient dosing be worse than adding none?

59 Ceramic coatings (e.g., oxides, carbides, nitrides) protect metals in aggressive high-temperature environments. Which property mismatch is the most critical failure risk to control when applying a ceramic coating on a metal substrate?

60 In an electroplating operation, a current of is passed for seconds through a copper sulphate bath. Using Faraday's laws (, atomic mass , ), what mass of copper is deposited?