THE CALCULATION OF ADIABATIC THERMAL-EXPLOSION FROM ISOTHERMAL DSC MEASUREMENTS

The calculation of thermal explosion conditions from results of micro-thermoanalytical measurements is often desirable and sometimes necessary because of the small amounts of material available. Diagrams of isothermal DSC experiments are particularly useful for providing measurements which can be evaluated by calculations of this kind. These calculations are very simple for reactions which proceed according to well-defined nth-order kinetics, as with many reactions used in production processes. The well known theories of Semenov and Frank-Kamenetskii are suitable for this work. The calculation is not so trivial for exothermic decomposition reactions which usually follow an ''autocatalytic'' reaction mode. A method for such calculations is presented here. For the determination of explosion conditions, isothermal DSC diagrams obtained at several temperatures are necessary. The autocatalytic reaction is characterized by two parameters of which at least one is temperature dependent. The differential equation for the adiabatic self-heating is solved numerically for the exothermic decomposition of several substances. The adiabatic induction times calculated are compared with. the results of direct adiabatic measurements. The satisfactory agreement of measured and calculated data show that calculation from isothermal results is a possible method. A small exothermic effect which appears in the first part of the isothermal DSC curve has to be taken into consideration, e.g. as a parallel first-order reaction, in order to get useful results.