Deformations inside burning specimens

Proskudin, V. F.; Голубев, В. А.; Berezhko, P. G.

doi:10.1007/bf02671839

Combust Explos Shock Waves

1997

DOI: 10.1007/bf02671839

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Deformations inside burning specimens

V. F. Proskudin¹,

В. А. Голубев²,

P. G. Berezhko³

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Cited by 3 publications

(6 citation statements)

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“…The latter circumstance allows us to propose a hypothetical model of combustion of the Al + Ni system in a loose state, which explains approximately identical values of the temperature T e and combustion temperature. The impurity gas released in the combustion wave and passing toward the combustion products is expected, by analogy with the data of [21,26], to loosen the system in a loose state and to form a quasi-fluidized bed. Because of the beginning of sporadic interactions of Al and Ni particles accompanied by their melting and coalescence, individual clusters are formed, which do not yield closed electrical circuits because the porosity of the system in the loose zone is higher than the critical value.…”

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confidence: 99%

“…3 The Al + Ni chemical reaction continues and, apparently, finalizes in these individual clusters. Behind the combustion wave, the system now consisting of combustion products becomes compacted again (by analogy with other condensed systems [26]) and forms closed electrical circuits, which ensures electrical conductivity of the system at a temperature close to the combustion temperature.…”

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“…of combustion of the Co + S system obtained in [9] (above 110 V for the pulsed e.m.f.) can be caused by origination of the electrostatic difference in voltage [27] between the cobalt and sulphur particles separated from each other by mechanical displacements in the combustion wave, which are accompanied by loosening [26] or cracking [28] of the burning system (e.g., in the zone of the hole for the probe [9]). Indeed, if a metallic particle is separated from a nonelectroconducting surface, there appears a difference in voltage between the particle and the surface, which can reach several kilovolts [29].…”

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“…If the description of formation of electromotive forces of solid-flame combustion is supplemented by information on displacements of matter in the combustion wave [21,26,28], i.e., changes in density (including origination of cracks, gaps, and quasi-fluidized bed) and porosity of the system in the course of combustion and associated changes in electrical conductivity of the system, the description will inevitably become more complicated but will allow much better understanding of the examined processes and the mechanism of origination of electromotive forces of heterogeneous combustion.…”

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Electromotive force for solid-flame combustion of heterogeneous systems in loose and pressed states

Proskudin

2006

Combust Explos Shock Waves

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By an example of condensed 3Zr + 2WO 3 and Al + Ni systems, it is demonstrated that the electromotive force of solid-flame combustion measured by probing in loose systems is significantly higher than that in the same systems in a pressed state. An explanation for this phenomenon is offered, based on the difference in electrical conductivity in different zones of the combustion wave in loose and pressed condensed systems.Key words: solid-flame combustion, electromotive force of combustion, condensed systems, electrical conductivity in the combustion wave.Electrical phenomena in combustion have attracted researchers' attention for a long time [1][2][3][4]. Many papers deal with studying the electromotive force (e.m.f.) of combustion in condensed systems. These papers describe the general ideas on the nature of origination of the combustion-induced e.m.f. in condensed systems [5][6][7][8][9][10][11][12][13] and show that the e.m.f. of combustion can be used as a tool for studying combustion properties [14][15][16]. It should be admitted, however, that the detailed mechanism of combustion-induced e.m.f. formation in condensed systems has not been clearly understood yet. In particular, it is not clear which mechanism is responsible for the influence of the initial density of the condensed system on the e.m.f. of solid-flame combustion.Loose systems display rather high values of the combustion-induced e.m.f., which reaches ≈900 mV in some individual systems [5][6][7]10]. At the same time, the e.m.f. values registered for pressed systems in [11,12] were lower approximately by an order of magnitude (less than 100 mV). We should recall that the constant component of the e.m.f. obtained in [9] in measuring the e.m.f. in the combustion wave in the pressed Co + S system reached 5 V, and the value of the variable and pulsed e.m.f. exceeded 110 V. The results of [9] seem to be anomalous, and their alternative interpretation will be presented below. It is also of interest to note that the amplitude of the e.m.f. induced by combustion of a mixture of tetrazole and sodium tetrazolate monohydrate in a pressed state is ≈900 mV [17].Of particular interest is to compare the results obtained for the Al + Ni system in [5,6,[10][11][12]. Typical values of the combustion-induced e.m.f. in this system in a loose state are 560-570 mV [5,6,10], and the corresponding values for the same system in a pressed state are less than several millivolts [11,12]. Though these data were obtained by different authors for different mixtures of Al and Ni powders and with the use of different measurement electrodes (which can affect the results obtained [18]), the main reason for the difference in the values of the combustion-induced e.m.f. seems to be the difference in initial densities of the burning systems.To check this assumption, we performed experiments to estimate the combustion-induced e.m.f. on a setup (Fig. 1), which allows experimentation with condensed systems in a loose state with the use of the same measurement electrodes and powder mixtures...

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confidence: 99%

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Electromotive force for solid-flame combustion of heterogeneous systems in loose and pressed states

Proskudin

2006

Combust Explos Shock Waves

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“…The material displacement dynamics during combustion is conveniently studied using flash radiography [7,8] for specimens in a rigid shell and by measuring the specimen height change Δl in time with a mechanical sensor for unconfined specimens. The latter method was used in the present study.…”

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Combustion of pressed specimens of heterogeneous systems subjected to a constant axial mechanical load

Proskudin

Belyaev

2007

Combust Explos Shock Waves

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The growth dynamics of the height of burning pressed specimens with the specimen ends subjected to a compressive force of constant magnitude is studied using the heterogeneous Ti + C + 20% TiC system as an example. It is found that in the examined range of compressive forces 0.1-2 kg/cm 2 , the growth of the height of the burning specimens with time obeys a linear law; under a compressive force of ≈0.1 kg/cm 2 , the specimen height increases by ≈100%, and under a force of ≈2 kg/cm 2 , it increases by about 25%. The method used to measure the growth dynamics of the specimen height during combustion proved a useful tool for the experimental determination of both the burning time of the specimens and the delay in the transfer of combustion through an obstacle.Key words: combustion, elongation of specimens, burning rate, transfer of combustion through an obstacle.It is known that solid-flame combustion is frequently accompanied by the displacement of the material in the burning specimen. In the absence of a rigid shell, the variation in the specimen dimensions during combustion can be referred to one of the two types (type II or type III) described in [1]. For type II, the shape of the burning specimen is preserved as its dimensions, in particular, length, vary significantly while the diameter does not change (the displacement of material of type II was for the first time observed in studies of the combustion of the Ti + 2B system [2][3][4]). Type III is characterized by changes in both shape and dimensions of the burning specimen.During combustion of specimens in a rigid halfclosed shell, a situation can arise where the dimensions and shape of the burning specimens do not vary (type I [1]) and displacement of the material occurs only within the burning specimen [5]. Furthermore, material displacement can be observed both at the combustion front and behind and ahead of the front [6-10].The displacement (deformation) of the material in a burning specimen changes not only the combustion parameters, in particular, burning rate [2-4] but also the parameters of combustion transfer through an obstacle [7,9,10], which should be taken into account in experiments. In addition, deformation of burning specimens is allowed for in computational and theoretical papers devoted to the combustion of heterogeneous systems [11][12][13][14][15][16].The material displacement dynamics during combustion is conveniently studied using flash radiography [7,8] for specimens in a rigid shell and by measuring the specimen height change Δl in time with a mechanical sensor for unconfined specimens. The latter method was used in the present study. A heterogeneous Ti + C + 20% TiC mixture prepared in a ball mill was used [6]. This mixture was pressed into specimens of diameter 8 mm and height l equal to 4 or 7 mm using the procedure described in [17], which involves the formation of a paper ("blue ribbon" decalcified filter paper) shell on the cylindrical surface of the specimens. The ends of the specimens remained opened. The specimens were pressed...

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Proskudin

Belyaev

Tarakanov

et al. 2002

Combustion, Explosion, and Shock Waves

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Deformations inside burning specimens

Cited by 3 publications

References 4 publications

Electromotive force for solid-flame combustion of heterogeneous systems in loose and pressed states

Electromotive force for solid-flame combustion of heterogeneous systems in loose and pressed states

Combustion of pressed specimens of heterogeneous systems subjected to a constant axial mechanical load

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