Liquid chemical of the TD type

The above condition is the formal definition of the Semenov model. The Semenov equation becomes effective under the condition above referred to and defines the Tf for an arbitrary volume of a self-healing fluid (a sclf-hcating liquid chemical, in general) of the TD type charged, or confined, in an arbitrary container and placed in the atmosphere under isothermal conditions. The Semenov equation is thus appropriate for the calculation of the TV for every liquid chemical of the TD type. ... 

As commented in I rcface, the self-healing behavior of every self-healing liquid chemical, with the exception of liquid high explosives, such as nitroglycerin, of the true AC type, is ofthc TD type, so tltat a sclf-hcating liquid chemical of the TD type or self-heating liquid chemicals of the TD type are described hereafter simply as a liquid or liquids. 

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. 

Each molecule of liquid chemicals of the TD type decomposes as a free one in the liquid phase. On the other hand, each molecule of powdery chemicals of the TD type decomposes while it remains fixed within the cage composed of the surrounding crystal lattice in the solid phase. Therefore, once innumerable molecules decompose almost simultaneously throughout each individual crystal, it appears that the whole sample collapses in a moment to form fine particles or gaseous products, with the result that this phenomenon is recorded as an... 

Both the Semenov and the F-K equation are in fact the same in the sense that each of them describes the balance between the rate of heat generation per unit volume per unit time in a liquid chemical, or a solid chemical, of the TD type, having an arbitrary shape and an arbitrary size, placed in the atmosphere under isothermal conditions, and, the rate of heat transfer per unit volume per unit time 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. 

Some heat loss, therefore, necessarily occurs from a chemical of the TD type, irrespective of liquid and powdery, having an arbitrary shape and an arbitrary size, placed in the atmosphere under isothermal conditions, to the atmosphere. 

When a small-scale chemical of the TD type, irrespective of liquid and solid, including every small-scale gas-permeable oxidatively-heating substance, the diameter of which is of the order of, say, 10 mm, is 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 either of the above-mentioned two kinds of adiabatic tests, the spatially uniform distribution of temperature is effected necessarily in the chemical so it is done, while the selfheating process is, in particular, in the early stages. 

It will, thus, be necessary here for us to confirm a posteriori, with reference to some concrete example, the validity of the linear approximation of the selfheating process or curve, in the early stages, of 2 cm of a chemical of the TD type charged in the open-cup cell, or confined in the closed cell, in accordance with the self-heating property of the chemical, and subjected to the adiabatic self-heating test started from a 7. The confirmation illustrated below is performed with reference to the experimental data which are determined for the ten organic liquid peroxides and are listed in Table 8 in Subsection 5.7.1. 

It is obvious that the absence of the melting point is characteristic of the DTA curve of a powdery chemical of the TD type. That is, a powdery chemical of this type decomposes prior to melting. The self-heating behavior of a powdery chemical, such as 98 % O, a -azobis(isobutyronitrile) (AIBN), which decomposes explosively prior to any remarkable exothennic decomposition reaction, is also of the TD type, so that the F-K equation is applied to calculate its 1. When confined in the closed cell and subjected to the adiabatic selfheating test started from a in the range of 65 to 74 C, 2 cm of AIBN shows such a self-healing behavior, which is typical of liquid, or powdery, chemicals of the TD type, as exemplified in Fig. 15. 

An air bath is adopted instead of a liquid bath, considering that the heat capacity of the former is much smaller than that of the latter. That the heat capacity of the bath is small means that it is possible to heat the atmosphere in the adiabatic jacket, which is set in the air bath, at a rate high enough to follow a rapid increase in temperature of 2 cm of a chemical of the TD type, including every gas-permeable oxidatively-heating substance, in the two kinds of adiabatic tests. 

As a matter of fact, however, the experimental procedure explained in the present section is, in principle, in common with (1) the procedure for 2 cm of a non-volatile liquid or powdery chemical of the TD type charged in the open-cup cell, which is explained in Section 5.4, and (2) the procedure for 2 cm of a gas-permeable oxidatively-heating substance charged in the draft cell, which is explained in Section 7.4 and in Subsection 8.4.1, as well as (3) the procedure... 

It has already been confirmed well that it is possible, in principle, to calculate the 7). for a powdery 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, by applying the F-K equation, i.e., Eq. (29) derived in Section 1.3. On the other hand, the method to calculate the T. for an arbitrary volume of a liquid charged in an arbitrary container and placed in the atmosphere under isothermal conditions has so far been left unresolved. 

In order to compare the values of Tc calculated each for the ten organic liquid peroxides charged each in the container and placed each in the atmosphere under isothermal conditions with one another, however, it is required to calculate the individual values of T assuming that these peroxides are each placed under the same conditions of shape and size. The same is true of powdery chemicals of the TD type and of gas-permeable oxidatively-heating substances. 

The Semenov model holds for a chemical of the TD type, irrespective of liquid or powder, charged in the Dewar flask used in the BAM test. For further details, refer to Section 6.8. 

As commented in a footnote in (2) of Subsection 6.4.3, only MNTS, in the ten powdery chemicals of the TD type tested herein, is powdery at room temperature but self-heats as a liquid at temperatures higher than its melting point. It is, therefore, required to calculate the Tc for MNTS by applying the Semenov equation. This calculation is performed in Section 6.8 for the ten powdery chemicals of the TD type, including MNTS, assuming that 400 cm each of these powdery chemicals of the TD type are each charged in the 500 cm Dewar flask, which is used in the BAM test, and to which the Semenov model applies, and are each placed in the atmosphere under isothermal conditions. 

The result of the above calculation suggests that the condition, UKK A, may hold for 400 cm each of average organic powdery chemicals of the TD type charged each in the 500 cm Dewar flask used in the BAM test and placed each in the atmosphere under isothermal conditions as well and therefore, the spatially uniform distribution of internal temperature may be effected in each of them in the early stages of the self-heating process, with the result that each of them may take the same values of qj and Tuq - Tset-up) as 400 cm of a liquid charged in the Dewar flask and placed in the atmosphere under isothermal conditions (For matters relevant to this subject, refer to Subsection 5.5.1). 

At all events, an important and useful proposition obtained in the present section is that there is a prospect that it is possible to calculate the value of the BAM test for an arbitrary powdery chemical of the TD type as well as an arbitrary liquid in other words, there is a prospect that it is possible to compare the individual values of Tc for various chemicals of the TD type, irrespective of liquid or powder, with one another under definite conditions of the BAM test, without performing actually the test. 

The draft cell and the touch-flow cell, in the four kinds of cells, are used exclusively in the adiabatic oxidatively-heating test. In this regard, the open-cup cell, one of the three kinds of open cells, is used only in the adiabatic selfheating test performed for a non-volatile liquid chemical, or powdery chemical, of the TD type at atmospheric pressure. 

Since the 1980 s, people called the chemicals safety circles appeared and attempted to calculate the so-called SADT for each individual self-heating chemical. They, however, attempted to do so by applying a few equations, which appear in the initial stages of the derivation process of the Semenov equation, to every self-heating chemical, irrespective of whether it is of the TD type or of the AC type, or, irrespective of whether it is liquid or solid. We have, therefore, no choice but to say that, theoretically speaking, their approach to the subject was almost meaningless. 

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. 

Figure 31. 2.2 g of silica powder, the volume of which is about 2 cm, is charged in a closed cell, i.e., the cell with which the reference cell is prepared. In this photograph, however, the cell is filled with milk in place of silica powder for the convenience of photography. It has been made a rule in the adiabatic scIf-heating test performed for every chemical, irrespective of liquid and powdery, of the TD type to use silica powder as the reference material. In this connection, silica powder is used as the reference material in the isothermal storage test as well. 

As a matter of fact, however, there is a subtle difference between a liquid of the TD type and a powdery chemical of the quasi-AC type in terms of the interx al between the endothermic peak and the exothermic peak in the DTA curve which each chemical affords (see Fig. 147). 

Figure 147. The subtle difference between the DTA curve of a liquid of the TD type and that of a powdery chemical of the quasi-AC type.

A chemical which is powdery at room temperature and shows a large interval between the two peaks of the DTA curve is, in principle, a liquid of the TD type. In case of a powdery chemical of this type, the melting is isolated, as a perfectly separate phase transition, from the exothermic decomposition reaction of the resultant liquid. In other words, the resultant liquid of this type decomposes exotliermically, independent of the melting process, so that the Semenov equation is applied to calculate the T. For instance, the DTA curve of MNTS is a case in point (see Fig. 12 in Section 3.3). 

In Chapter 3, a classification of self-heating chemicals, except gas-permeable oxidatively-heating substances, is introduced. Treatments of gas-permeable oxidatively-heating substances are made in Chapters 7 and 8. Self-heating chemicals are divided into two large groups, i.e., the thermal decomposition or TD type and the autocatalytic reaction or AC type. The TD type is subdivided into liquid chemicals, for each of which the Semenov equation is applied to calculate the Tc, and, solid (powdery, in reality) chemicals, for each of which the F-K equation is applied to calculate the Tc. On the other hand, the AC type is subdivided into high explosives of the true AC type and powdery chemicals of the quasi-AC type. 

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