10.3.1 Introduction

A kinetic study thus involves measurement of ? either as a function of time, t, at constant temperature, or as a function of temperature, T, which is increased according to some heating programme (usually linear), ? = d T/d t. The isothermal method, ? against t, corresponds to the conventional curve of concentration against t familiar from homogeneous kinetics, while the dynamic method, i.e. measurement of or ? against T, is the basis of thermal analysis, see Figures 10.2, and 10.3.

Figure 10.1: Formation and growth of nuclei of product in the decomposition of solids: (a) nucleation sites; (b) first nuclei formed; (c) growth and further nucleation; (d) overlap of nuclei; (e) ingestion of a nucleation site; (f) continued growth.

The reproducibility of the sets of ?, t or ?, T data under fixed conditions of isothermal temperature, or at a constant heating-rate, needs to be examined, including any influence of the sample mass on the data. Some experimental techniques may produce relatively noisy ?, t or ?, T traces and some smoothing of the data may be advisable. The extent of mathematical smoothing can always be monitored, while the smooth experimental traces from other measurement techniques may contain an unknown amount and type of instrumental damping.

Kris and Sest k ^[14] have pointed out that both ? and T