Question

Diffusion in metals generally increases with

• A. decreasing temperature
• B. increasing pressure
• C. increasing density
• D. increasing temperature

Hint:

Always relate diffusion rates directly to the exponential temperature term \( e^{-Q/RT} \). Even a small increase in temperature can lead to a massive increase in diffusion rates.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks about the relationship between solid-state diffusion in metals and different environmental/material parameters.

Step 2: Key Formula or Approach:
Diffusion in metals is governed by the diffusivity or diffusion coefficient \( D \), which is related to absolute temperature through the Arrhenius relation:
\[ D = D_0 e^{-\frac{Q}{RT}} \]
This relationship indicates that diffusion is highly sensitive to thermal activation.

Step 3: Detailed Explanation:

• Direct Influence of Temperature: As temperature rises, atoms gain more kinetic energy, which drastically increases the frequency of atomic jumps into adjacent lattice vacancies or interstitial sites.
Thus, the rate of atomic movement (diffusion) increases with increasing temperature.

• Analysis of Other Options:
-

Decreasing temperature (Option A) reduces thermal vibrations, lowering the atomic jump rate and decreasing diffusion.
-

Increasing pressure (Option B) typically decreases the vacancy concentration and increases the activation volume, which hinders diffusion.
-

Increasing density (Option C) reduces free volume and makes atomic motion more difficult, slowing down diffusion.


Step 4: Final Answer:
Therefore, diffusion in metals generally increases with increasing temperature, which is Option (D).