Slow Burning

Studies of slow thermal decomposition, when combined with the hot-spot theory, proved to have particularly interesting consequences for understanding the sensitivity of the azides and their troublesome and seemingly temperamental response to some stimuli. 

within the thermal or hot-spot theory, there existed a rationale for describing not only how azides respond to various stimuli, but considering the many possible parameters involved in the energy transfer from an external stimulus to the molecules of a crystal, a basis for the erratic behavior of samples. 

with respect to the initiation of reaction, early work demonstrated the usefulness of a macroscopic, thermal model of the process and enabled the response of the more sensitive azides to be rationalized in a qualitative and sometimes semiquantitative way. The more difficult task of understanding the phenomena on an electronic or a molecular basis began to bear fruit, and gross, quantitative predictions of slow decomposition by heat or light became possible. However, unless their sensitivities had been first empirically established by statistical experiments, it remained impossible to predict the response of samples to different stimuli or to induce reaction with finesse or precision. Spontaneous initiation and explosion, such as encountered with crystals growing in solution, could not be explained by any mechanism, thermal, photochemical, or tribochemical. 

The growth of the decomposition reactions to burning or detonation has not been studied with the intensity devoted to the initiation of reaction. The speed of the transition and the rate of detonation in azides make detailed studies difficult deflagration has been studied more commonly with slower-burning substances such as ammonium perchlorate. 

A recent review of detonation theory is given elsewhere [12]. Models of the phenomenon envisage a detonation wave propagating into unreacted material with a sharp discontinuity in temperature and pressure at the detonation front. A reaction zone of a millimeter or smaller dimensions and yielding the equilibrium quantities of reaction products at high temperature and pressure abuts the up-stream side of the front. Using macroscopic hydrodynamic-thermodynamic theory, the energy released, and an equation of state for the assumed products, detonation velocities, pressures, and temperatures may be calculated in certain cases. 

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D. Price, J. E. Wehner, and G. E. Robertson, Transition from Slow Burning to Detonation Kole of Confinement, Pressure Eoading and Shock Sensitivity, TR68-138, Naval Surface Weapons Center (NSWC), White Oaks, Md., 1968. 

Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

Flammability. The fire hazard associated with plastics has always been difficult to assess and numerous tests have been devised which attempt to grade materials as regards flammability by standard small scale methods under controlled but necessarily artificial conditions. Descriptions of plastics as selfextinguishing, slow burning, fire retardant etc. have been employed to describe their behaviour under such standard test conditions, but could never be regarded as predictions of the performance of the material in real fire situations, the nature and scale of which can vary so much. 

Schwelung, /. low-temperature carbonization slow burning, smoldering. 

Releasing fusion energy on a human scale requires fusion fuels that react vith each other more rapidly than the slow-burning basic fuels of stars. 

A deflagration is a slow burning exothermic reaction similar to the combustion explosion, but which propagates from the burning gases into the unreacted material at a velocity that is less than the speed of sound in the unreacted material. Most (not all) explosions are deflagrations. 

Ethyl vinyl acetate Slow burning 0.93-0.95. 01-.02 Transparent... 

Polyethylene low density Slow burning. 910-.925. 01-03 Transparent to opaque... 

Polyethylene high density Slow burning 0.94-0.98. 01-.04 Translucent to opaque... 

Phenoxy Slow burning, Self-ext. 1.17-1.34. 003-.004 Transparent to opaque... 

H. Muraour G. Aunis, CR 196, 478—80 (1933) CA 27, 2301 (1933) (Laws of combstn of mixts of slow fast burning proplnts are the same as for the slow burning proplnt alone, ie, if /Pdt is plotted vs time, the values fall on the same straight line in both cases) 5) H. Muraour, BullFr 9, SI ]-16 (1942) CA 37,6526(1943) (Rate of combstn of colloidal proplnts as a func-tion of the press temp of emitted gases)... 

Red P is used in burning-type munitions mainly for signaling purposes. Compns consisting of red P and certain oxidants or fuels are relatively slow-burning and are sometimes used in sea markers. The chemical reactions may be quite involved. For example, the main reaction for a burning mixt of Ca sulfate and red P appears to be ... 

Obviously, there are many combinations and variations of the use of primers and detonators. There are instances where primers are used to ignite detonators, the output of which is then used either to cause directly the operation of a main expl charge or to ignite a slow-burning... 

Pyroclok. Trademark for a slow-burning delay train which furnishes a 5-minute delay time in about 10 inches of column length Refs 1) H. Ellern D.E. Qlander USP 2954735 (1960) 2) Ellern (1968), 199... 

An important example of the first type is the oil smoke pot which is powered by a slow burning, gassy pyrotechnic mixt such as amm nitrate and amm chloride with a small amount of carbonaceous fuel. The resulting gas jet pulls a stream of oil from a reservoir and injects it into a venturi where the formation of the aerosol takes place... 

At the CISE Laboratories in Milan, where the phenomenon of fast and slow burn-out was first noted, the onset of random temperature oscillations has in itself been assumed to signify burn-out, the implication being that temperature oscillations always occur [Bertoletti et ah (BI9) and Alessandrini et al. (A5)]. However, the CISE experiments have in the past been carried out with preformed mixtures of steam and water at entry to a heated test channel, and it is possible that this feature, which is known to produce flow disturbances (see Section III), may be the reason for the fact that temperature oscillations always occur. 

Slow burn-out tends to be associated with high-quality burn-out conditions and to produce a not unduly excessive wall-temperature rise. In fact, there appears to be an extreme condition in which the temperature rise may hardly be noticeable, and it becomes difficult to say whether burn-out has occurred. These circumstances probably coincide with the jump discontinuity in Fig. 3 ceasing to exist for certain values of system parameters. The condition is effectively one in which, at the burn-out point, the heat-transfer coefficient is the same whether the surface is vapor-blanketed or liquid-wetted. 

Group 5 Slow burning/heating Burn slowly Small fireworks in primary Slow single-item... 

Special slow burning cool propellants can be used to generate gas under pressures suitable for the operation of mechanical devices. Perhaps the most important of these applications is in cartridge starting of jet engines for aircraft. The principles involved in this application of propellent explosives are illustrated in Fig. 19.7. 

Safety fuse. A fuse which propagates by slow burning. 

Sustainer. In rocketry, a slow burning motor to produce a continued thrust. 

The explosive decomposition of the solid has been studied in detail [6], The effect of moisture upon ignitibility and explosive behaviour under confinement was studied. A moisture content of 3% allowed slow burning only, and at 5% ignition did not occur [7], Thermal instability was studied using a pressure vessel test, ignition delay time, TGA and DSC, and decomposition products were identified [8], The presence of acyl chlorides renders dibenzoyl peroxide impact-sensitive [9], There is a further report of a violent explosion during purification of the peroxide by Soxhlet extraction with hot chloroform [10], Residual traces of the peroxide in a polythene feed pipe exploded when it was cut with a handsaw [11]. The heat of decomposition has been determined as 1.39 kJ/g. The recently calculated value of 69° C for critical ignition temperature coincides with that previously recorded. 

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