Temperature of initiation—

Curve 2 in Fig. 6.17 corresponds to experiment which we started as usual but reduced the surface of quartz trough treatment by carbon monoxide at 280°C. At this moment emission disappeared and furtiier increase in temperature would not bring it back. The sample was cooled after reaching the temperature of 320°C, oxidized and heated anew. Such subsequent oxidation of quartz resulted in formation and emission of singlet oxygen (see Fig. 6.17, curve 2) but only at temperatures around 320°C, i.e. above the temperature of initial heating. 

In a nutshell, it may be concluded that DTA, DSC and TGA have been used mainly to determine the thermal properties of explosives like melting points, thermal stability, kinetics of thermal decomposition and temperatures of initiation and ignition etc. Further, the properties which can be calculated quantitatively from the experimentally obtained values are reaction rates, activation energies and heats of explosion. DTA data of some explosives are given [46] in Table 3.6. 

The description a(CCH) is probably an oversimplification. The same type of spectrum is also obtained from the thermal dissociation at similar temperatures of initially adsorbed C FLt species. Recent scanning tunneling... 

Assumed, not rigorously established. c Parentheses indicate peak temperature of initial exotherm. d81% n-Ci2OH, remainder other primary C12 alcohols. 

Temperature of initiation of nitroglycerine is 200-205°C (bath temperature), the rate of the temperature increase being 20° per min. Above 180°C a distinct exothermic decomposition of the substance begins, and hence at the moment of explosion the temperature of the nitroglycerine is higher than that of the bath, i.e. 215-218°C (Snelling and Storm [64]). 

Nitrodipenta resembles PETN in its physical and chemical properties. Nitro-dipenta dissolves in acetone more readily than PETN, and this is used to separate the two nitrates. The specific gravity of single crystals of nitrodipenta is 1.630 at 15°C, while pellets prepared under a pressure of 2500 kg/cm2 acquire a specific gravity of 1.589. Nitrodipenta is less sensitive to impact and to friction than PETN and its temperature of initiation is higher. In spite of this, its chemical stability at 100°C is distinctly less than that of PETN. This is the main reason why the presence of nitrodipenta in PETN is undesirable. 

T. Urbanski and Magiera [85] have examined the chemical stability and explosive properties of the ester and conclude that neither the substance itself nor a solution of nitrocellulose in it are sufficiently stable for practical application. Its temperature of initiation is 150°C (whereas nitroglycol is initiated at 220°C), and it is considerably more sensitive to impact than nitroglycol. They also found that an impact energy of 0.91 kgm/cm2 is necessary to ensure a 10% probability explosion of nitroglycol, as compared with barely 0.11 kgm/cm2 for the ester. 

It must be pointed out that experiments intended to attach a nitro group to a nitrogen atom failed. The substance is stable, since it did not undergo decomposition after being maintained for 200 hr at 70°C, and its temperature of initiation is 187°C. Its explosive properties are as follows. At a density of 0.62 g/cm3 it detonates with a rate of 4030 m/sec, the lead block expansion is 325 cm3 and its relatively low sensitiveness to shock is indicated by the fact that it is exploded in a drop test by a 2-kg weight falling from a height of 60 cm. 

Perchlorate of 1 Melt- J ing I point °C Temperature of initiation-explosion within 1 sec at °C Sensitiveness to shock — 10% of explosions from work of kg 1 j Lead block, expansion 1 cm3 i Rate of detonation (glass tube 12 mm dia., density 1.1 g/cm3) m/sec... 

The temperature of initiation is reported by different authors to be 110-130°C. Bircumshaw and F. M. Taylor [49] have examined the thermal decomposition of ammonium permanganate between 96 and 117°C. The activation energy of this decomposition was estimated as 27.9 kcal/mole. Within the temperature range from 70 to 80°C the energy of activation was 26.0 kcal/mole. An explosive decomposition brought about by an initiator procedes according to the reaction ... 

The temperature of initial crystallization of one of the components of a binary system on cooling is not a CST or cloud point. Some confusion exists in the literature from reporting crystallization points as CST. Many such observations have been corrected for use in these tables by placing the prefix < before the temperature. 

Knock resistance has also been correlated with other preflame reaction properties such as the rate of pressure development during adiabatic compression (17), the temperature coefficient of preflame reactions (202), and the pressure developed prior to firing (34). Estrad re (59) made a correlation between the temperature of initial exothermic oxidation in a tube and knock. No quantitative connection exists between apparent activation energy (160) or the total heat (179) of the precombustion reactions and knock. 

The temp at which the sample just began to decomp was named the temperature of initial (or induction) period . For a sample heated in container at atm pressure it was designated as T,0, and for a sample heated in hydraulic press at 2599kg/cm2, as Tj,°... 

The heat resistance of a polymer may be characterised by its temperatures of "initial" and of "half" decomposition. The latter quantity is determined by the chemical structure of the polymer and can be estimated by means of an additive quantity the molar thermal decomposition function. The amount of char formed on pyrolysis can be estimated by means of another additive quantity the molar char-forming tendency. 

FIG. 21.2 Relationships between (A) the activation energy of decomposition, act d and the characteristic decomposition temperature Td)/2 and (B) the characteristic decomposition temperature Td ]/2 and the temperature of initial decomposition Tdo. 

Since a dynamic run described earlier revealed an exothermic polymerization at around 185 to 190 °C, crosslinkers were added in an attempt to lower the temperature for polymerization. The crosslinking agents (10% w/v of resin preparation) used were phthalic anhydride, maleic anhydride, tallow diamine, and p-toluenesulfonic acid. We were unable to lower the temperature of initiation of polymerization by the addition of the first three reagents, but did observe a shift to a lower temperature ( 165 °C) in the presence of p-toluenesulfonic acid. The pH of the mixture prior to heating was around 2.0, whereas, the... 

Cr and Ce compounds reduce the temperature of initiation of the thermooxidative decomposition of the same polymer by 80-100 °C, but the rate of the decomposition itself is lower than that of the unmodified polymer. Thermogravimetric and differential thermal analysis have shown that Me " have no influence on the thermal decomposition of the polymer in the absence of an oxidative atmosphere. 

Material Refractoriness ("C) Temperature of initial deformation under load (°Q Porosity (%) Bulk density (g cm ) Compression strength (MPa) Linear thermal expansion a X lO" (20-1200 )... 

Cherville and associates [44] have examined a number of explosives in a mass spectrograph. Particularly important and reproducible were results at 77K. The formation of NOj was readily established in the spectrograms. The authors introduced a concept of the radiochemical yield of formation of NOj. A considerable difference exists between the values of of nitramines and nitroaromatics. They correlated the values of Gnoj with those of the sensitivity of explosives to impact, friction and high temperature (temperature of initiation f at the rate of heating 5 C/min) Table 9. 

Sensitivity to high temperature was e.xtensively studied [124]. Chaudhriand Field Il2 ) recently described a dependence on temperature of initiation of a lead azide on crystal thickness, wliUe studying individual single crystals of known size. There was a drop in the explosion temperature from 415 to 385 C for an increase in crystal thickness from 4 to 30 pm. Crystals of less than 3 pm thickness did not explode even up to 450 C. They did not melt at this temperature. 

Figure 3.30. Dependence of tangent of dielectric losses angle on temperature of initial and modified PETP - samples 1 - initial PETP 2 - PETP + 0,1% of HC-2 3 - PETP + 0,5% of HC-2 4 - PETP + 3,0% of HC-2.

In the simplest case, the distillation method involves use of a standard round-bottom distillation flask of 250-ml capacity attached to a water-cooled condenser. The thermometer bulb is placed at the opening to the side arm of the flask. One hundred milliliters of sample are placed in the flask and heated by a small gas flame so as to produce ten milhliters of distillate every 4 or 5 min. The temperature of initial distillation is recorded the temperature at which each further 10 ml distils and the final boiling point are also recorded. 

Td.max Temperature of maximum rate of decomposition (weight loss), in degrees Kelvin. Td,o Temperature of initial decomposition (weight loss), in degrees Kelvin. 

---