Quasi-AC type

As will be explained hereafter in the present chapter, the self-heating behavior of a powdery chemical of the quasi-AC type is also of the AC type. 

Derivation of an empirical formula, nAt = alT, + b, Le., Eq. (59), which is used to calculate the SADT for a chemical of the AC type, including every powdery chemical of the quasi-AC type, having an arbitrary shape and an arbitrary size, confined in an arbitrary closed container of the corresponding shape and size, and placed in the atmosphere under isothermal conditions... 

The SADT for a high explosive of the true AC type depends on the induction period of the autocatalytic reaction however, the autocatalytic reaction does not depend, in principle, on the quantity of the high explosive. On the other hand, as will be explained hereafter in the present chapter, the SADT for a powdery chemical of the quasi-AC type depends on the phase transition, the melting however, it does also not depend, in principle, on the quantity of the chemical. 

In addition to chemicals of the TD type and those of the true AC type, there exist chemicals refeired to as powdery chemicals of the quasi-AC type. 

When confined in the closed cell and subjected to the isothermal storage test performed at a T 2 cm of a powdery chemical of the quasi-AC type warms slowly up to the T, but the temperature remains near the T, over a long time, because a phase transition, the endothermic melting, of the chemical occurs almost simultaneously with the exothermic decomposition reaction all through this time. Once, however, the chemical finishes melting in the course of time, an apparently sudden quasi-autocatalytic reaction of the resultant liquefied chemical starts. 

Figure 7. The induction period, of the quasi-autocatalytic reaction, of 2 cin of a powdery clicmical of the quasi-AC type confined in the closed cell and subjected to the isothermal storage test performed at a T, on the high temperature side, recorded for the time. At, from the insertion of the cell into the isothennal storage testing device till the start of the quasi-autocatalytic reaction occurring simultaneously with the finish of melting of the chemical at the T,.

Correlation among the pattern of the TG-DTA curve of a self-heating powdery chemical, the two types of self-heating behaviors, Le., the TD type and the quasi-AC type, and the two equations of the thermal explosion theory... 

The type of the self-healing behavior of a self-healing powdery chemical is closely related to the pattern of the thermogravimctry-diffcrcntial thermal analysis (TG-DTA) curve which the chemical affords. In other words, it is possible, in principle, to infer the self-healing behavior of a self-healing powdery chemical to be either of the TD type or of the quasi-AC type by glancing over the TG-DTA cuiwe of the chemical, so that it is also possible to infer the equation of the thermal explosion theory applied to calculate the of the chemical to be either the Semenov equation, i.e., Eq. (17) presented in Section 1.2, or the F-K equation, i.e., Eq. (29) presented in Section 1.3, or neither equation. 

On the other hand, individual TG-DTA cuiwcs, which are also each recorded with the glass open-cup cell, 5 mm in diameter, 2.5 mm in depth, at the same value of 0 of 2.5 K/min in air at atmospheric pressure, of four of the live powdery chemicals of the quasi-AC type, which are listed in Table 26 in Subsection 10.4.1, are presented in Fig. 9. 

Figure 9. Individual TG-D l A curves of the four powdery ehennleals of the quasi-AC type.

It is obvious in Fig. 9 that one characteristic of the DTA curve of a powdery chemical of the quasi-AC type is the presence of the melting point [22]. Another characteristic of the DTA curve of a powdery chemical of this type is that the curve shifts successively from the endothermic peak caused by melting... 

The property of each individual powdery chemical of the quasi-AC type varies in a continuous fashion with the interval between the cndothcnnic peak and the exothermic peak in the DTA curve which the chemical affords. Both peaks arc in particular close together in the case of ABCN or AMVN, as shown in Fig. 9. The pattern of the DTA curve of a typical powdery chemical of the quasi-AC type, such as ABCN or AMVN, is thought to reflect the fact that, when heated, a phase transition, the endothermic melting, takes place in parallel with a chemical reaction, the exothermic decomposition reaction, in it, as shown diagrammatically in Fig. 10. 

Figure 10, Simultaneous occurrence of a phase transition, the endothermic melting, and a chemical reaction, the exothermic decomposition reaction, in ABCN as a representative of powdery chemicals of the quasi-AC type.

In addition to liquid chemicals of the TD type of the kind above referred to, once cither a powdery chemical of the TD type or that of the quasi-AC type is dissolved in some solvent at room temperature, it also becomes a liquid to which the Semenov equation is applied to calculate the T. In this connection, it is a matter of course that a chemical which is liquid at room temperature has its freezing point at a temperature far lower than room temperature. 

However, a powdery chemical, such as 98 % l-nilroso-2-naphthol (IN2N), which affords an endothermic peak far smaller than the subsequent exothermic peak in the DTA curve (see Fig. 13), also self-heats as a powdery chemical of the TD type at temperatures lower than its melting point, although the DTA curve as a whole is similar, in pattern, to that of a powdery chemical of the quasi-AC type. 

As explained already, with the exception of powdery high explosives of the true AC type, powdery chemicals of Group I, powdery chemicals of Group II and chemicals which are liquid themselves or dissolved in any solvents at room temperature are said to be of the TD type, and, powdery ehcmicals of Group m are said to be of the quasi-AC type. 

On the other hand, when confined in the closed cell and subjected to the isothermal storage lest performed at a T, on the low temperature side, the time interval up to the start of the quasi-autocatalytic reaction occumng simultaneously with the finish of melting of 2 cm of a powdery chemical of the quasi-AC type becomes naturally far longer, and the temperature decrement caused by melting also becomes of the order of 0,1 0.2 K only. In the meantime, the rate of increase in temperature of the chemical after the start of the quasi-autocatalytic reaction also becomes so slow, as shown in Fig, 16, that it becomes somewhat uncertain to locate the point of time b on the chart of the strip-chart recorder (see Fig. 143 in Subsection 10.2.5, as an example). The same is true of the induction period of the autocatalytic reaction of a high explosive of the tnie AC type (see Fig. 125 in Subsection 9.3.5, as an example). 

The temperature of 2 cm of a chemical of the AC type, including every powdery chemical of the quasi-AC type, confined in the closed cell and subjected to the isothermal storage test at a 7, is recorded by means of an analog/digital temperature recorder. The digital output of the recorder is read to 0.1 K and is printed out every 30 min on the other hand, the analog signal of the recorder is recorded continuously with a T pen on the strip chart of the... 

It is, thus, clear that it is indispensable to assign a due safety margin to the value of SADT calculated for each high explosive of the true AC type tested herein. It is for this reason that it is stated at the final paragraph of Section 9.5 that the upper limit temperature for the safe handling of a high explosive of the true AC type will be a temperature 30 K lower than the SADT calculated herein. Similarly, it is stated in Chapter 10 as well that the upper limit temperature for the safe handling of a powdery chemical of the quasi-AC type will be a temperature 30 K lower than the SADT calculated herein. 

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