Question

For metal atoms, the most probable mechanism of diffusion is

	a.	vacancy mechanism
	b.	interstitial mechanism
	c.	direct interchange mechanism
	d.	none of the above

Answer 1

Vacancy mechanism is the most probable mechanism of diffusion in metals. There exists many vacant sites in the metal at thermal equilibrium. During vacancy diffusion, the atoms break its bonds and exchange their position with the vacancy. This can be done with less energy than other mechanisms. So it is the most energetically favourable mechanism in metals. However atoms with small atomic radius such as H, N etc can fit into interstitial sites. Therefore they diffuse by interstitial mechanism. During interstitial mechanism, atoms move from one interstitial site to other.