LIQUID-FLAME COMBUSTION .2. SOME PHYSICAL AND CHEMICAL CHARACTERISTICS OF THE BURNING PROCESS

To gain further insight into the nature of the liquid-flame structure (LFS), which is characteristic of compressed solid mixtures, containin g tetrazole (64 wt%) and sodium tetrazolate monohydrate, a number of p hysical and chemical characteristics of the liquid flame was studied. The temperature distribution on the surface of the LFS and the tempera ture profile in a combustion wave were investigated using optical pyro metry, as well as thermocouples and electrochemical methods. The LFS i s found to be characterized by highly uniform heat radiation; the temp erature on the LFS surface varied from 940 to 1000 K. The small LFSs ( up to 5-6 mm in diameter) are capable of voluminous radiation, while t he LFSs of larger sizes irradiate as hollow envelopes, with a wall thi ckness of similar to 1-2 mm. The temperature and electrochemical measu rements in the combustion wave indicate that the LFS represents a sphe roidal formation, having to a considerable extent a hollow envelope of melt characterized by a relatively even temperature distribution insi de the LFS, the temperature being 1050-1250 K, depending on the LFS si ze. The chemical compositions of the gaseous and condensed products of the thermal decomposition and combustion of pure tetrazole, sodium te trazolate, and a mixture of them were studied by H-1 NMR, IR, mass spe ctrometry, gas chromatography, elemental, and x-ray analyses. The data obtained allow one to identify the chemical reactions in the liquid f lame. The thermal decomposition of sodium tetrazolate results in the f ormation of chemically stable sodium acid cyanamide; this is the basic reaction proceeding in the liquid flame. The fragmentation of the tet razole leads to cyanamide polymer; partial decomposition of sodium tet razolate proceeds in the melt layer below the liquid flame. Both react ions are accompanied by the evolution of considerable heat and gaseous nitrogen. An analysis of all the measurements suggests that the neces sary conditions for an LFS and its development on combustion are a lar ge amount of nitrogen in the initial substances, which must have consi derable thermal stability, along with high positive enthalpies of form ation, together with the presence of definite chemical fragments and i ons of alkali metals in molecules of at least one of the components. I n accordance with these criteria, mixtures of tetrazolates and azides of alkali metals with tetrazole, 1,2,3-triazole, 1,2,4-triazole, guani dine, and some of their derivatives are shown to be capable of forming an LFS on combustion. (C) 1997 by The Combustion Institute.