How does temperature influence diffusion-controlled phase transformations?

• A. Higher temperature increases diffusion, accelerating nucleation and growth, and shifting transformation times.
• B. Higher temperature slows diffusion.
• C. Temperature has no effect on diffusion rates.
• D. Transformations occur only at low temperatures regardless of diffusion.

Answer: (C)

Temperature strongly controls diffusion rates, and diffusion-driven phase transformations rely on how fast atoms can move to form a new phase. Diffusion is thermally activated: as temperature rises, atoms gain energy to jump between lattice sites, so the diffusion coefficient increases. This faster atomic mobility lets atoms rearrange at the moving phase boundary more quickly, accelerating both nucleation and growth and shortening the overall transformation time. A common way to express this is through an Arrhenius-like relation D = D0 exp(-Q/(RT)); higher T makes D larger, so transformation proceeds faster.

So the idea that temperature has no effect on diffusion is not correct, because diffusion speeds up with heat. Likewise, transformations are not restricted to low temperatures; they typically occur more readily as diffusion becomes easier, though other factors can influence specific systems.