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Correct OPTION is (a) True

Easy explanation: Every METAL MICROSTRUCTURE CONSISTS of grains and GRAIN boundaries. Grain boundaries are high energy areas, formed due to the mismatch between the grains during the solidification.

The correct option is (a) True

To EXPLAIN I WOULD say: It is the second statement in the mixed potential theory that the number of electrons generated and CONSUMED are same. Anode produces the same number of electrons that REQUIRE for the cathode.

Right CHOICE is (b) False

Explanation: Concentration polarization refers to the electrochemical reaction that is controlled by the diffusion of ions in an ELECTROLYTE. This occurs in the low concentration of electrolyte. It is neglected in the CASE of anodic reaction (metal dissolution) because there is a sufficient supply of metal atoms in a metallic PIECE and there is no NEED for diffusion.

Right option is (d) W/At = [(I × am) / (N × F)] and W/At = [(I × am) / (d × n × F)]

The explanation: W/At denotes the CORROSION rate, I= CURRENT density, am=molecular weight, n=number of electrons transferred, F=faraday constant (96500), d=density of a specimen. [(I*am) / (n*F)] is used to calculate the MDD WHEREAS the [(I*am) / (n*d*F)] is used to calculate the MPY.

The correct option is (a) True

Best explanation: Preventive action involves the replacement of partially corroded or failed equipment. It avoids plant shutdowns and CONTAMINATION of a PRODUCT. HENCE, the process become more ECONOMICAL.

The correct answer is (d) Both loss of APPEARANCE and effect of safety

The explanation: Restaurants and in MANY other public places, the main CONCERN about the corrosion is that the loss of appearance and effect of safety. Badly CORRODED and RUSTED products would leave a poor impression on the observer.

Right option is (d) Stainless steel

Explanation: Corrosion resistant material is the material which has less corrosion rate in a PARTICULAR atmosphere without much DEGRADATION. Stainless steel (an alloy of iron, chromium, nickel) is CONSIDERED as corrosion resistant material. This is because it forms CHROMIC oxide layer over its surface to avoid physical contact with the OUTSIDE environment.

Correct answer is (a) True

For explanation I would SAY: Temperature increases the rate of ALMOST all the reactions because it increases the kinetic energies of atoms or ions. This increase in kinetic ENERGY makes them react to each other to get stable products. It also increases the MOBILITY of ions in the electrolyte.

The correct choice is (a) 18Cr–8Ni in HNO3

For explanation I would say: Stainless steel (18Cr–8Ni) in the HNO3 medium will have a negligible effect on the corrosion rate with the increase in temperature. It forms a STABLE oxide layer and avoids the EXPOSURE of a corrosive atmosphere to the metallic SURFACE. It is stable up to very high TEMPERATURES.

Correct choice is (a) Oxidation

Easy EXPLANATION: The DIRECTION of current flow is exactly OPPOSITE to the movement of electrons. We know electrons starts at the anode and travels towards CATHODE WHEREAS current will flow from anode to electrolyte. This results in oxidation or corrosion on that electrode.

Correct CHOICE is (a) Stability of a metal ion

The best EXPLANATION: Negative or LESS Gibbs free energy of the metal ions is the reason for corrosion whereas passivation and use of COATINGS decreases the extent of corrosion.

The correct CHOICE is (a) HOMOGENOUS alloys

Best EXPLANATION: Homogenous alloys are highly corrosion resistant alloys than other ALLOY types. Since the GALVANIC effect is not present in homogenous alloys because of its single phase.

The CORRECT answer is (C) 423

The explanation is: We know MDD = W/At = (I*am) / (n*F). We should convert the given unit values in milligrams/sq. Decimeter/day.

Given, I = 1.69*10^-4 amp/cm^2

Atomic weight of IRON = am = 55.86 g/mol

n = number of ELECTRONS = 2 [Fe ==> Fe^+2 +2e^–]

F = faraday’s constant = 96500 coulombs

= (1.96×10^-4 coulombs/sec*cm^2) × (55.86) ÷ (2×96500 coulombs)

= [(1.96×10^-4)*(60*60*24)*(100)*(55.86 *10^3)] / [2*96500]

= 422.53 MDD.

Correct ANSWER is (d) Bolts and nuts METAL joining’s, piping arrangements and MACHINERY of a different metal combinations

The explanation is: The GALVANIC effect is due to the contact of two dissimilar METALS in a conductive solution. The corrosion caused due to galvanic effect is known as galvanic corrosion. It can be usually observed at bolts and nuts metal joining’s, piping arrangements and machinery of different metal combinations.

The correct OPTION is (B) Fe2O3

For explanation I WOULD say: Corrosion of Iron is generally known as rusting. The CHEMICAL REACTION can be represented as 4Fe + 3O2 ==> 2Fe2O3.

Right answer is (a) Face centered cubic STRUCTURE

Best explanation: Austenitic stainless steel is an alloy of iron, CHROMIUM, and nickel. Due to the HIGH content of chromium, the resultant stabilizes in the austenitic phase. AUSTENITE USUALLY exists in the FCC (Face centered cubic) crystal structure.

Correct choice is (a) Active region

The explanation: Copper will act as an active METAL in sulfuric acid, the CORROSION rate increases with an increase in oxygen CONCENTRATION. And the PASSIVITY is not achieved irrespective of the OXIDIZER added.

The correct option is (a) Ecell=E^ocell–RT/nF ln(K)

Explanation: Ecell=E^ocell–RT/nF ln(K) is the Nernst equation. E^ocell is the potential of a CELL in the standard state, R is Universal GAS CONSTANT, n is the valency of ion, T is absolute TEMPERATURE, F is Faraday’s constant and K is the reaction QUOTIENT, Ecell is the cell potential.

The correct choice is (b) MPY=(534*W)/DAT

To explain I would say: W = weight loss in milligrams, D=Density of a specimen (g/cm^3), A=Area of specimen(sq.in), T=time of EXPOSURE in hours and 534 is a conversion FACTOR. MPY means MILS PENETRATION per YEAR I.e. milli inches penetration per year.

Right answer is (a) Corrosion of metal in the water

Best explanation: Wet corrosion occurs when the LIQUID is present. This usually involves aqueous solutions or electrolytes as CORROSIVE mediums. Corrosion of iron in the PRESENCE anhydrous calcium CHLORIDE, by furnace gases and by dry chlorine are CLASSIFIED under dry corrosion.

Right choice is (B) 77

Easy explanation: We KNOW MDD = W/At = (I*am) / (d*n*F). We should convert the GIVEN UNIT values in milli inches per year.

Given, I = 1.69*10^-4 amp/cm^2

Atomic weight of iron = am = 55.86 g/mol

n = number of electrons = 2 [Fe ==> Fe^+2 +2e^–]

F = FARADAY’s constant = 96500 coulombs

d=density of iron = 7.875 g/cm^3

= [(1.96×10^-4 coulombs/sec*cm^2) × (55.86)] ÷ [(7.874 g/cm^3×2×96500 coulombs)]

= [(1.96×10^-4 coulombs/sec*cm^2) × (55.86)] ÷ [(7.874 g/cm^2*cm×2×96500 coulombs)]

= [(1.96×10^-4 1/sec) × (55.86)] ÷ [(7.874 g/cm ×2×96500)]

= [1.69×10^-4 × (60*60*24*365) × (55.86) × 10^3] / [2 × 96500 × 7.875 × 2.54]

= 77.117 MPY.

Correct CHOICE is (d) PROTECTION of metals by the surficial oxide layer and Zn-carbon electrochemical reactions in the battery

To elaborate: Initially passivating metals undergoes corrosion in order to form oxide layer. These thick, dense oxide layer acts as a strong barrier and protects the inner metal against corrosion. The Zn-carbon batteries WORKS on the principle of galvanic corrosion. It INVOLVES conversion of chemical energy into electrical energy by these electrochemical reactions.

The correct OPTION is (b) Return on investment

For EXPLANATION I would say: ROI means Return on investment.

 ROI=[(Oa+Ia/na)–(Ob+Ib/nb)/Ib–Ia]*100 where O = ANNUAL costs including maintenance cost, I=Investment, n=anticipated life in years, and subscripts a and b refer to the present and proposed installations, RESPECTIVELY.

The CORRECT OPTION is (a) True

For explanation I would say: Grain BOUNDARIES are the high energy area and are more active chemically. Hence, grain boundaries are highly prone to corrosion than the grain faces. This is used to develop a contrast between grain and grain boundaries in the inspection of MICROSTRUCTURE.

Correct OPTION is (d) Crystalline, amorphous and semi-crystalline

Easiest EXPLANATION: The atoms in the crystalline materials are regularly arranged with the same REPEATING UNIT in a long-range order. EXAMPLES of crystalline materials are metals.

The atoms in which the atoms are not regularly arranged over a long-range are called amorphous materials. Example: Glass, rubbers.

Whereas semi-crystalline is the combination of both crystalline and amorphous materials.

The correct CHOICE is (d) Salt BRIDGE

Best explanation: Salt bridge is a connection between two half CELLS USED to neutralize the ions with respective opposite charged ions. USUALLY, strong electrolytes such as KCl along with agar-agar gel are used.

The correct answer is (a) True

Easiest explanation: Mixed potential THEORY states that any electrochemical reaction can be divided into two or more partial reactions (anodic and cathodic reactions). DISSOLUTION of an alloy in pure acid involves more than one anodic reaction. Corrosion of pure METAL in oxygenated IMPURE acid involves more than one cathodic reaction.

Right OPTION is (d) Faraday’s law

The explanation is: Faraday’s law is used in ORDER to DERIVE the corrosion rate expression [W/At=I*am/n*F]. W/At denotes the corrosion rate, I=current density, am=molecular weight, n=number of electrons TRANSFERRED, F=faraday constant (96500).

Right OPTION is (a) thinner

Easy explanation: Uniform CORROSION is the most common form of corrosion. It is characterized by an electrochemical REACTION that PROCEEDS uniformly over the entire exposed SURFACE. Thus, the metal becomes thinner.

Right option is (d) both petroleum and PAPER

Explanation: The operating conditions in both the petroleum and paper industry are MAINLY in aqueous state with various chemicals in it. Hence these are LIKELY prone to various electrochemical reactions which causes corrosion. Maintenance works include periodic inspection and replacements of partially corroded parts. It minimizes COSTLY catastrophic failures, unscheduled down time, RESULTING in increased production and revenue.

Correct ANSWER is (d) Destruction of materials involving in the conversion of metal ATOMS into metal ions

To elaborate: Corrosion is a DESTRUCTIVE or deterioration of a material because of reaction with its environment. It occurs due to the HIGHER stability of metal ions than the metal atoms.

The CORRECT option is (c) A1≠a2≠a3 and α=β=\(\ddot{\gamma}\)=90

Explanation: Crystal structures are divided into 14 different types based on the STRUCTURE of the unit cell and arrangement of atoms in it. These 14 different types are called Bravais lattice. And the conditions for ORTHORHOMBIC crystal structure is a1≠a2≠a3 and α=β=γ̈=90

, where a1, a2, a­3 are unit vectors in three directions and α, β, γ̈ are angles between them.

Correct choice is (c) Concentration polarization

Explanation: Concentration polarization REFERS to the electrochemical REACTION that is controlled by the diffusion of ions in an ELECTROLYTE. With an increase in the velocity or AGITATION of the electrolyte the contact of ions with metal interface increases.

Right option is (d) Both stainless steel and TITANIUM

Explanation: Stainless steel and titanium are EASILY passivating MATERIAL and easily GET passivated in high-velocity mediums. These metals form a stable oxide layer that can resist high velocities of CORROSIVE medium.

Right choice is (a) True

Explanation: Mixed potential THEORY STATES that any ELECTROCHEMICAL reaction can be divided into two or more partial reactions (OXIDATION and reduction reaction). Presence of oxidizing impurities such as Fe^+3 INCREASES the number of reduction reactions. It correspondingly increases the oxidation rate or corrosion rate.

Right answer is (B) Net present value

To explain I would say: NPV provides the most accurate basis for analyzing business COSTS and can be directly APPLIED to the ECONOMICS of corrosion control. But it needs EXTENSIVE calculations.

Correct answer is (a) High carbon steel

The best EXPLANATION: HETEROGENOUS alloy is the alloy in which the components are partially DISSOLVED in each other and it has two or more phases. High carbon steel consists of alpha iron, CEMENTITE phase, and lamellar STRUCTURE.

Correct answer is (b) False

Easy explanation: Usually mils per year is USED to MEASURE the PENETRATION rate. Penetration is the average depth of METAL loss in the specimen. MPY is usually used for pitting corrosion. MDD (milligrams/sq. Decimeter/day) is used to measure the WEIGHT loss per unit area.

Right choice is (a) AgCl

Easy explanation: SILVER on reaction with chlorine forms silver chloride. It ACTS as a protective layer and prevents chlorine to CORRODE further. Here SnCl2 and CaO are volatile in nature whereas Fe2O3 is POROUS in nature. HENCE, they can’t act as protective layers.

Correct answer is (d) Relative surface area of an anode and cathode, nature of oxide layer and purity of metal

To EXPLAIN I would say: As the CATHODIC to anodic area increases, the more oxygen REDUCTION, or more corrosion can occur. The corrosion resistance of aluminum can be attributed to the formation of the thick, dense oxide layer. IMPURE metals undergo corrosion at a faster rate than the pure metals.

The correct choice is (d) Anode, Cathode and Electrolyte

For EXPLANATION: Corrosion OCCURS by the creation of ELECTROCHEMICAL cell which includes a cathode, an anode and an electrolyte. A high REDUCTION potential will act as cathode and other will acts as anode preferentially and electrolyte is needed to transfer ions between these two electrodes.