Thermokinetic model of sample response in nonisothermal analysis

A thermokinetic model for the reaction rates of solids measured in constant heating rate differential thermal analysis is derived from heat transfer and chemical kinetics. An explicit result is obtained for the maximum reaction rate in a constant heating rate experiment in terms of the thermal properties of the solid, the activation energy of the thermal process, the heat of reaction, the sample mass and the heating rate in the test. The theoretical predictions compare well with numerical simulations and experimental data for polyoxymethylene and polystyrene obtained by two different thermal analysis methods using three different instruments over a wide range of sample mass and heating rate. Based on these results, an accuracy criterion for thermal analysis measurements is proposed that is consistent with recommended practices.

► We have developed a thermokinetic model of nonisothermal analysis.
► Thermal diffusion and chemical kinetics are decoupled in the analytic, thermokinetic model.
► Numerical analysis shows that heats of phase change or reaction dominate the temperature profile of milligram samples.
► The thermokinetic model captures experimental data for two polymers using no adjustable parameters.