Question

In comparison to lattice diffusion, the activation energy for diffusion along surfaces and grain boundaries is

• A. higher
• B. lower
• C. almost negligible
• D. infinite

Hint:

Grain boundary and surface diffusion dominate at lower temperatures, while lattice diffusion is significant at higher temperatures.

Answer 1

The Correct Option is B

Diffusion in solids occurs via different pathways, including lattice diffusion, grain boundary diffusion, and surface diffusion. The activation energy required for diffusion varies depending on the pathway: 

Step 1: Comparing Activation Energies - Lattice Diffusion: Occurs through the bulk crystal structure and requires high activation energy due to strong atomic bonds. - Grain Boundary Diffusion: Occurs along grain boundaries where atomic packing is less dense, requiring lower activation energy. - Surface Diffusion: Takes place on the outer surfaces of materials, having the lowest activation energy due to minimal atomic constraints. 

Step 2: Conclusion Since atomic bonding is weaker along surfaces and grain boundaries compared to the bulk lattice, diffusion along these regions requires lower activation energy. Hence, the correct answer is (B) lower.