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Right choice is (a) True

To explain I would say: Metals that FOLLOWS linear oxidation KINETICS at low temperature tend to oxidize CATASTROPHICALLY at high temperatures. It is due to the rapid exothermic REACTIONS at the SURFACES at high temperatures.

The correct choice is (d) Titanium, NIOBIUM, and Zirconium

To elaborate: Titanium, Niobium, Zirconium, Hafnium, and Tantalum are the metals that produce metal OXIDES at the metal-scale INTERFACE. It is DUE to the predominant diffusion of oxygen-ion rather than metallic cation.

The correct option is (b) CORROSION products precipitate in the metal matrix and metals such as Fe, NI, and Co are highly prone to internal corrosion

Easy explanation: Internal corrosion is due to the one or more dilute ALLOYING ELEMENTS form more STABLE oxides than the base metal and preferentially forms corrosion in the metal matrix. Iron, nickel, and cobalt are the base metals that are prone to internal corrosion.

Correct OPTION is (d) The stress required to cause a rupture in short-term high-temperature applications at a predetermined time is known as stress rupture and it is an IMPORTANT mechanical property for GAS turbines and rocket engines

The BEST I can explain: Stress rupture is defined as the amount of stress that is required to cause a rupture in short-term high-temperature applications at a predetermined time. It is an important mechanical property for gas turbines and rocket engines.

Right choice is (d) Linear, parabolic, CUBIC and logarithmic law

To explain I would say: Oxidation rate laws are CLASSIFIED based on the variation of oxidation rate in DIFFERENT metals. They are linear, parabolic, cubic, and logarithmic laws.

Correct option is (c) Al2O3, CdO2, and TiO2

The best I can explain: Semiconducting OXIDES such as CdO2, Al2O3, CdO, TiO2, Ta2O5, and SiO2 are n-type SEMICONDUCTORS. It CONTAINS an excess of NEGATIVELY charged electronic current carriers I.e. ELECTRONS.

Correct option is (c) Hastelloy C-276, Inconel 718 and Hastelloy HX

Easy explanation: Superalloys or high-performance alloys are the alloys that can resist extreme conditions such as high temperature, high stress, high WEAR, and corrosive ATMOSPHERES. Nickel-based alloys are WIDELY USED as superalloys that include Hastelloy C-276, Inconel 718, and Hastelloy HX.

The correct choice is (b) ALUMINUM

To explain: Linear oxidation law states that an INCREASE in weight PER unit area of metal is directly proportional to the time of exposure. Metals such as SODIUM, potassium, tantalum, and niobium follow linear oxidation law WHEREAS aluminum follows the logarithmic oxidation law.

The correct option is (a) True

For explanation I would say: High-temperature metal-OXYGEN interaction can’t be separated electrically whereas diffusion of EITHER cation or oxygen ions usually controls the REACTION rate of high-temperature metallic OXIDATION.

Correct answer is (d) Tensile strength, Yield strength, Ductility, and FRACTURE TOUGHNESS

Best EXPLANATION: Mechanical properties that are important in STRUCTURAL applications of METALS are:

i. Tensile strength

ii. Yield strength

iii. Ductility

iv. Fracture toughness.

Correct answer is (B) High stress-rupture strength, low creep rate, and high fracture TOUGHNESS

To ELABORATE: Low creep rate, high stress-rupture strength, and high fracture toughness are the adequate high-temperature MECHANICAL PROPERTIES to avoid fracture.

The correct choice is (d) Weight gain per unit area of metal is directly PROPORTIONAL to EXPOSURE TIME, it is characteristic of porous or cracked SCALE and sodium follows LINEAR oxidation law

The explanation: Linear oxidation law:

Weight gain per unit area of the metal is directly proportional to the exposure time

It is characteristics of porous or cracked scale

Sodium follows linear oxidation law.

The correct option is (c) WELDABILITY, less resistance to THERMAL shock, LACK of ductility and formability

The EXPLANATION is: Limitations of high-temperature non-metallic materials are:

i. Lack of ductility

ii. Less resistance to thermal shock

iii. Lack of ductility

iv. Formability

v. Weldability.

Correct option is (C) OSMIUM, tungsten, molybdenum, and Vanadium

The best explanation: Volatile oxides are the oxides that get EVAPORATE within the fractions of seconds after their formation. Metals that form volatile oxides include osmium, tungsten, molybdenum, and vanadium.

Correct choice is (c) Weight GAIN PER UNIT area of metal is the MEASURE of the rate of oxidation

To elaborate: Rate of oxidation is usually measured and expressed in TERMS of weight gain per unit area of metal. As oxidation results in the conversion from metal M (x gms) to metallic oxides MOn (x+n*16 gms).

The correct answer is (a) True

For explanation I would say: Dilute alloying elements of base metals exhibiting a RELATIVELY HIGH solubility and diffusivity for atomic oxygen are subject to INTERNAL CORROSION. It is due to the formation of preferential STABLE oxides than the base metals.

The correct option is (a) True

For explanation I WOULD SAY: In general, all OXIDES are nonstoichiometric in nature their COMPOSITIONS VARY from an ideal molecular formula. It is due to the excess or deficiency in metallic ions or equivalent oxygen ions.

Correct ANSWER is (B) True

Explanation: diffusion-controlled oxidation can be MINIMIZED by decreasing the CONCENTRATION of ionic defects in the scale. These defects include Frenkel defect, Schottky defect, and many crystallographic defects.

The correct ANSWER is (d) Gas turbines, rocket engines, and furnaces

The EXPLANATION is: High-TEMPERATURE systems such as gas turbines, rocket engines, and furnaces are prone to high-temperature CORROSION due to high working temperature and petrochemical corrosive atmosphere around it.

Right option is (a) GRAIN GROWTH, PHASE changes, precipitation dissolution and precipitation over aging

Best explanation: Metallurgical changes that affect the structural stability of METALS at high temperature are:

i. Grain growth

ii. Phase changes

iii. Precipitation dissolution

iv. Precipitation over aging.

The correct option is (c) Unprotective and insufficient oxide

For explanation: If PILLING and Bed WORTH ratio of a metal oxide is less than 1 then it is an unprotective and insufficient oxide, if it is near to 1 then it is protective and adherent and if it is GREATER than 1 then it is unprotective.

The correct option is (C) Good adherence, high MELTING point, low VAPOR PRESSURE, and low electrical conductivity

To explain: Ideal characteristics of passive metal OXIDES layer are:

Good adherence

High melting point

Low electrical conductivity

Low vapor pressure

Low diffusion coefficient.

Right choice is (c) It was PROPOSED by C. Wagner which states that SQUARE of weight loss is DIRECTLY proportional to the time of EXPOSURE and it resembles non-steady-state diffusion-controlled reactions

The explanation is: True statements regarding parabolic oxidation rate LAW:

It was proposed by C. Wagner

It states that square of weight loss is directly proportional to the time of exposure

It resembles non-steady-state diffusion-controlled reactions.

The correct answer is (d) SODIUM, MAGNESIUM, and NIOBIUM

Easy explanation: If the rate of heat transfer from metal to SURROUNDINGS is less than heat evolution from OXIDE formation then it increases the surface temperature of metals. This leads to the ignition of metals and it includes sodium, magnesium, and niobium.

Correct ANSWER is (d) Large compressive stresses in the oxide, cracking and spalling

To explain I would say: Metal oxides with a value GREATER than 1 Pilling and Bed worth ratio have poor OXIDATION RESISTANCE due to large compressive stresses in the oxide, cracking, and spalling.

The correct OPTION is (c) It is the continuous plastic elongation of metal under CONSTANT load at high temperature and it can be MINIMIZED by the fraction of grain boundaries

The explanation is: It is defined as the continuous plastic elongation of metal under constant load at high temperatures. Creep rate is then expressed as PERCENT elongation in a GIVEN time. It can be minimized by reducing the fraction of grain boundaries.

The correct option is (b) 3.40

Explanation: Pilling and Bed WORTH RATIO is DEFINED as the volume ratio of oxide and metal per grams atom of metal. The Pilling and Bed worth ratio of TUNGSTEN is around 3.40 and it is unprotective in nature.