The GATE Grind

GATE 2023 MT – Question 20

Physical Metallurgy · Diffusion in solids · 1 mark · Multiple choice

For self-diffusion in polycrystalline copper, let $D_L,D_{GB},D_S$ denote lattice, grain-boundary, and surface diffusion coefficients. The correct relationship is

  1. $D_S>D_{GB}>D_L$
  2. $D_L>D_S>D_{GB}$
  3. $D_{GB}>D_S>D_L$
  4. $D_{GB}=D_S=D_L$

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) $D_S>D_{GB}>D_L$

Explanation

Less constrained surface atoms have low diffusion barriers. Grain boundaries provide disordered fast paths, while lattice diffusion has the largest barrier. The usual order is $D_S>D_{GB}>D_L$, **A**.