Avrami equation

An equation, describing crystallization kinetics, of the form:
1 − φ c = e − K t n
where φ c is the crystalline volume fraction developed at time t and constant temperature, K and n are suitable parameters. K is temperature dependent. According to the original theory, n should be an integer from 1 to 4, the value of which should depend only on the type of the statistical model; however, it has become customary to regard it as an adjustable parameter that may be non-integral.
Purple Book, p. 85