Use Of Detonation Research Articles

Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects.

The goal of the protocol described in this article is to prepare aluminothermic compositions (nanothermites) in the form of porous, monolithic objects. Nanothermites are combustible materials made up of inorganic fuel and an oxidizer. In nanothermite foams, aluminum is the fuel and aluminum phosphate and tungsten trioxide are the oxidizing moieties. The highest flame propagation velocities (FPVs) in nanothermites are observed in loose powders and FPVs are strongly decreased by pelletizing nanothermite powders. From a physical standpoint, nanothermite loose powders are metastable systems. Their properties can be altered by unintentional compaction induced by shocks or vibrations or by the segregation of particles over time by settling phenomena, which originates from the density differences of their components. Moving from a powder to an object is the challenge that must be overcome to integrate nanothermites in pyrotechnic systems. Nanothermite objects must have both a high open porosity and good mechanical strength. Nanothermite foams meet both of these criteria, and they are prepared by dispersing a nano-sized aluminothermic mixture (Al/WO3) in orthophosphoric acid. The reaction of aluminum with the acid solution gives the AlPO4 "cement" in which Al and WO3 nanoparticles are embedded. In nanothermite foams, aluminum phosphate plays the dual role of binder and oxidizer. This method can be used with tungsten trioxide, which is not altered by the preparation process. It could probably be extended to some oxides, which are commonly used for the preparation of high performance nanothermites. The WO3-based nanothermite foams described in this article are particularly insensitive to impact and friction, which makes them far safer to handle than loose Al/WO3 powder. The fast combustion of these materials has interesting applications in pyrotechnic igniters. Their use in detonators as primers would require the incorporation of a secondary explosive in their composition.

Distinctive features of galloping detonation in a supersonic combustible-mixture flow under an inert gas layer

The problem of detonation initiation in a supersonic flow of a stoichiometric propane-air mixture occupying partially or completely the cross-section of a plane channel is considered. The initiation in the flow is produced by a step or a wall completely cutting off the flow. The study is conducted within the framework of one-stage combustion kinetics. A numerical method based on the Godunov scheme is employed. The critical conditions for detonation formation are determined in terms of the oncoming flow velocity. A previously unknown mechanism of detonation propagation is found; it is related with the presence of the combustible mixture in the wall layer under an inert gas layer. It is due to the formation of a complicated wave structure of the flow characterized by the penetration of a shock wave formed in the inert gas layer into a combustible mixture layer ahead of the detonation wave with the result that the latter layer is heated and ignited. The process as a whole is periodic in nature, as distinct from the conventional cellular detonation in a homogeneous fluid. Many problems arise in connection with the use of detonation in engines and other power plants. The most important among them are detonation excitation and stabilization in combustion chambers. The detonation initiation within a layer under conditions of unbounded space and a fluid at rest was experimentally investigated in [1]. In the case of a combustion chamber bounded in the transverse direction, some new effects accompanying the detonation might be expected.

Formation of detonation in rotating channels

308 For estimating the possibility of detonation initia� tion during rotation, we considered the gasmixture flow inside and outside the rotating elliptic cylinder included in the circular cylinder. The values of critical parameters at which the detonation is formed were determined. We presented the analogy to the detona� tion initiation in the gasmixture flow in the channel of a special helical shape. The investigation is carried out by the numerical method based on the scheme of S.K. Godunov with a mobile calculation grid within the framework of the singlephase kinetics of burning of a stoichiometric propane-air mixture. A detailed flow pattern is obtained enabling us to reveal the fea� tures of the detonation initiation during the motion of boundaries of the region containing the gas mixture. Attempts at practical use of detonation in engines and other various power devices placed a number of problems in front of researchers. The problem of det� onation initiation in a limited space seems to be the most important among them. At present, we know of no experimental and theoretical results on the detona� tion initiation due to the combustionchamber rota� tion. The onedimensional problem on the detonation initiation by a piston (1) has a certain relation to the case under consideration.

Use of gas detonation in a controlled frequency mode (review)

Research problems arising in the development of various devices with the use of detonation in a controlled frequency mode (pulsed detonation) are considered. The frequency of cycles can be varied by independent initiation of detonation by a controlled system of ignition. Problems of detonation initiation concerning the frequency mode are considered: direct initiation, deflagration-to-detonation transition, and transition of a detonation wave formed in a narrow channel into a wide channel. The possibility of using thermochemical conversion in devices with pulsed detonation is considered. Examples of practical applications of devices with pulsed detonation are given (pulsed detonation engine, using pulsed detonation for drilling and crushing of rocks, and removal of metal cord from rubber in worn tires).

Use of detonation in gases for coating application

Use of detonation in gases for coating application

Exothermic reaction zone in one-dimensional shock waves in gases

In principle, ~he exper imenta l ly determined d i s t r i bution of density, p r e s s u r e o r t empera tu re in the chemical reac t ion zone behind a shock front can be made to yield important information about the fundamental cha r ac t e r i s t i c s of h ightempera tu re chemical reac t ions . However, the use of detonation p rocesses to invest igate exothermic reac t ions is ser ious ly l imited by so-ca l led "spin" effects, which r e su l t in deformation of the shock front and the appearance of a complex th ree -d imens iona l react ion zone. In [1, 2] D. R. White succeeded in conducting chemica l -k ine t ic studies in incident waves both under nonstat ionary conditions in a section with a two-dimensional nozzle and in exper iments with highly r a r e f i ed mixtures . In both oases the gas flow is cons iderably different f rom the se l f sus ta in ing detonation r eg ime . In the exper iments descr ibed below we made a quantitative study by optical methods of both "sustained" s ta t ionary shock waves and complete ly se l f sustaining detonation waves. In the la t te r case, to c rea t e one-dimensional quas i s t a t iona ry detonation conditions, the mixture was preheated to a t e m p e r a ture of 650-856 ~ K by means of a shock wave [3]. Apar t f rom the independent value of a study of the hydrodynamic s t ruc tu re of the exothermic reac t ion zone, these exper iments a re of in te res t in that they also pe rmi t a compar ison with the reac t ion-k ine t ics data obtained f rom analogous measu remen t s in re f lec ted shocks.