GATE MT 2021 Paper 1 — page 21

Questions 61–63 of 65. Imported answers require review unless explicitly marked reviewed.

A thick steel plate containing 0.1 wt.% C is carburized at 950 °C. The plate’s surface carbon concentration is maintained at 1.1 wt.% C. After 9 hours, the depth (in mm) below the surface at which the carbon concentration is 0.6 wt.% C will be: __________ (round off to 2 decimal places). Given: Diffusivity of carbon in γ-Fe at 950 °C =

m² s⁻¹ Error function table:

z	0.35	0.40	0.45	0.50	0.55	0.60
erf(z)	0.3794	0.4284	0.4755	0.5205	0.5633	0.6039

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At 25 °C, iron corrodes in a deaerated acid of pH 3 with a corrosion current density of 4 μA cm⁻². The corrosion potential (V) is: ________ (round off to 2 decimal places).

Given: βc = 0.1 V per decade of current density Exchange current density of hydrogen on iron surface = 10⁻⁹ A cm⁻² R = 8.314 J mol⁻¹ K⁻¹, F = 9600 C mol⁻¹ All potentials are with reference to standard hydrogen electrode.

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The radius of an interstitial atom which just fits (without distorting the structure) inside an octahedral void of a bcc-iron crystal (in nm) is: ________ (round off to 3 decimal places).

Assume the radius of Fe atom to be 0.124 nm.

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2021 · Paper 1

Question 51

Question 52

Question 53