Decompositions with melting

The thermal decomposition process of HMX was studied by time-of-flight mass spectrometry (Model Zhp-6 spectrometer) [71]. It is suggested that the decomposition of HMX involves three stages, i.e. initial decomposition of the solid phase at about 160 C, decomposition with melting and decomposition of the liquid phase. The products which have been confirmed are NOj, NO, HCN and CHO. 

Sintering Melting Sublimation Decomposition I Melting with l decomposition... 

Following three phase transformations [951] (>298 K), NH C decomposition begins [915] in the solid phase at 423 K but only becomes extensive well above the melting point ( 440 K). Decomposition with the evolution of N20 and H20 from the melt is first order [952,953] (E = 153—163 kJ mole-1), the mechanism suggested involving intermediate nitramide formation. Other proposed schemes have identified NOj [954] or the radical NH2NO [955] (<473 K) as possible participants. Studies [956,957] have been made of the influence of additives on NH C decomposition. 

On heating S9O decomposes at 32-34 °C with melting and SO2 evolution. At 20 °C the solid oxide decomposes quantitatively within 2 h to SO2 and a polymeric sulfuroxide (S 0)x with n>9. Even dissolved in carbon disulfide S9O decomposes within 20 min to a large extent with formation of SO2 as can be seen from the decrease of the infrared absorption intensity at 1134 cm (S9O) and the intensity increase at 1336 cm (SO2). The solubihty of S9O in CS2 (>21 g r at 0 °C) is much higher than in CH2CI2 (260 mg at 0 °C) while the substance is practically insoluble in n-pentane, n-hexane and tribromomethane. At -80 °C, S9O can be stored for longer periods of time without decomposition. 

Decomposition methods are usually classified as melt decompositions, wet decompositions (with liquid decomposing agents) and dry decompositions by combustion. Sample decomposition methods are varied, and involve open and closed systems (at low and high pressure), UV and thermal activation, low or high temperature, and use of conventional convective or microwave heating. Table 8.4 lists the main sample decomposition methods for trace-element determination. 

The polymerization proceeds under photo- [49,50],X-ray [51], and y-ray [52] irradiation in the dark in vacuo, in air, or even in water or organic solvent as the dispersant (nonsolvent) for the crystals, similar to the solid-state polymerization of diacetylene compounds [ 12]. The process of topochemical polymerization of 1,3-diene monomers is also independent of the environment surrounding the crystals. Recently, the thermally induced topochemical polymerization of several monomers with a high decomposition and melting point was confirmed [53]. The polymer yield increases as the reaction temperature increases during the thermal polymerization. IR and NMR spectroscopies certified that the polymers obtained from the thermally induced polymerization in the dark have a stereoregular repeating structure identical to those of the photopolymers produced by UV or y-ray irradiation. 

It attacks glass at a red heat, giving silicon tetrafluoride and sulphur trioxide. Carbon and boron are without action on the gas at a red heat, but sodium at a temperature considerably above the melting-point causes gradual decomposition with absorption. Hydrogen sulphide, aided by heat, attacks both thionyl and sulphuryl fluorides, inducing decomposition.1... 

At very high temperatures the sulphates of metals such as copper, zinc, iron, aluminium and chromium tend to lose sulphur trioxide (largely in the form of sulphur dioxide and oxygen) and to give residues of the corresponding oxides.7 Calcium sulphate is stable up to 1300° C., above which temperature it melts and immediately undergoes almost complete decomposition with abundant evolution of fumes.8 Very slight decomposition has been observed with barium sulphate at 1300° C.9... 

Triphenyl selenium bromide, (C6H5)3SeBr, is formed when the foregoing chloride is dissolved in boiling ethylene dibromide. It is crystallised from methyl ethyl ketone and melts with decomposition at 236° C., heating at this temperature causing decomposition with formation of diphenyl selenide and bromobenzene. 

Reduction by zinc dust yields an oil iodine in chloroform has no action, but chlorine in the same solvent gives selenium tetrachloride and chloroacetylacetone, and bromine yields lachrymatory products and a colourless crystalline substance of melting-point 180° C. Aqueous hydrogen sulphide causes slow decomposition, with liberation of sulphur and selenium. Potassium metabisulphite and sodium hydrogen sulphite transform selenium acetylacetone quantitatively into alkali selenodithionates, a reaction which affords the best known means of preparing these salts. 

Thermotropic polymers require no solvent for formation of a liquid-crystalline phase, which occurs instead within a defined temperature range. The chemical units useful for thermotropic polymer formation are generally those already exemplified in Figs. 1 and 2, but these units in homopolymer form give rise to crystalline polymers with melting points above their decomposition temperatures. The problem of polymer design is to reduce the melting temperature in order to obtain a liquid-crystalline phase at a temperature below that of decomposition. Whereas the lyotropic systems are... 

The abbreviations and symbols used in the Tables are Ac, acetyl Bz, benzoyl Ms, methylsulfonyl Ns, p-nitrophenylsulfonyl Ts, p-tolylsulfo-nyl Bzd, benzylidene Ipd, isopropylidene Et, ethyl Me, methyl Ph, phenyl -0-, anhydro d. 338, decomposes (without melting) at 338° 153 d., melts at 153° with decomposition l , compound is dimorphous, with melting points at 166° and 177° amorph., amorphous cryst., crystalline trans. 192, transition in crystal form at 192° , racemic and active, asymmetric, but [< ]d not recorded. 

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