Oxidatively-heating substance

As stated in Preface, the basic concept of the thermal explosion theory is that whether the thermal explosion or the spontaneous ignition of a chemical of the TD type, including every gas-permeable oxidatively-heating substance, having an arbitrary shape and an arbitrary size, placed in the atmosphere under isothermal conditions, occurs or not is decided, based on the balance between the rate of heat generation in the chemical and the rate of heat transfer from the chemical to the atmosphere at the critical state for the thermal explosion which exists at the end of the early stages of the self-heating process. 

The rate equation in the thermal explosion theory is then expressed with the rate constant, Aa exp[- E/R II. alone. In other words, the rate of the exothermic decomposition reaction, in the early stages of the self-healing process, of a chemical of the TD type, including every gas-permeable oxidatively-heating substance, is thought, in the theory, to depend only on one variable, T, i.e., the temperature of the chemical, included in the rate constant. It is thus seen that the theory is in fact very simple by virtue of the /croth-ordcr assumption. 

Each individual solid chemical of the TD type exists, in reality, in the form of a powder, or of an aggregation of coarse particles. Nevertheless, however, the F-K equation is applicable to the calculation of the T, for a powdery chemical of the TD type, including every gas-permeable oxidatively- heating substance, as well. Individual procedures to calculate the values of T. for these substances are explained in Chapters 6, 7 and 8, respectively. 

For the heat generation data of a chemical of the TD type, irrespective of liquid and powdery, including every gas-permeable oxidatively-heating substance, refer to Sections 2.4. 

Eq. (44) holds between a T, and the time, A t, required for the temperature of a definite quantity of a chemical of the TD type, including every gas-permeable oxidatively-heating substance, charged, or confined, in some one of the open-cup, the draft or the closed cell, in accordance with the self-heating property of the chemical, and subjected to the adiabatic self-heating test, or to the adiabatic oxidatively-heating test, which is started from the T to increase by a definite temperature difference, A T, from the T,. 

As a matter of fact, 2 cm has been used herein as the standard sample volume in the adiabatic self-heating test, or in the adiabatic oxidatively-heating test, performed for a chemical of the TD type, including every oxidatively-heating substance. 

Besides, it is self-evident, as stated in the preceding section, that the spatial distribution of temperature, in particular, in the early stages of the self-heating process, or of the oxidatively-heating process, in a small-scale chemical of the TD type, including every small-scale gas-permeable oxidatively-heating substance, subjected to either of the two kinds of adiabatic tests, is the very ultimate of the Semenov model, because the condition, the Biot number = Ur A = 0, holds strictly in such a chemical. 

The argument made in the present section holds, in principle, in the adiabatic oxidativcly-lieating test, performed for every gas-permeable oxidatively-heating substance, as well. 

A classification of self-heating chemicals is introduced in the present chapter. Treatments of gas-permeable oxidatively-heating substances are made in Chapters 7 anti 8. 

As stated in Preface, each individual self-heating chemical, including every gas-permeable oxidatively-heating substance, is classified into either of the two large groups, i.e., the thermal decomposition or TD type and the autocatalytic reaction or AC type. 

The cross section of the air bath is shown in Fig. 18. The cell assembly including a draft cell is drawn in this cross section, because this was drawn in the early stages of a series of studies described herein, when a series of studies concerning gas-permeable oxidatively-heating substances were predominantly... 

The PID-SCR temperature control technique is adopted for the adiabatic control. Besides, other devices are also adopted to attain as complete an adiabatic control as possible. To cite an instance, a pre-amplifier is incorporated before the PID controller to amplify the A i.e., the temperature difference between the temperature of 2 cm of a chemical of the TD type, including every gas-penneable oxidatively-heating substance, and the T),. A zero suppression circuit is composed of this amplifier to cancel the slight stray-, or pseudo-, Ihermoelcctromotive force of the differential thermocouple. Such a pscudo-ihcmioclcctromolivc force of a differential thermocouple may still appear even if the temperature of 2 cm of the chemical and the r , . are physically the same, and even if the two thermocouples to make up the differential thermocouple are... 

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