O-4-01: Electroexplosion of Metastable Metal Powders with Stored Energy

Energy that is 1.5-2.0 times higher than sublimation energy is input in metals in 1 m sec as wires are electroexploded. The metal overheated to 20,000 – 40,000 ° C broadens in shock waves in aerosol form and cools at a speed of 10⁶ – 10⁸ deg/sec. Aerosols deposited (the installation productivity is to tens kilograms per month) represent electroexplosion powders (EEP) of a size less than 100 nm. They are stable at storage on air in open jars. The powders possess some unusual physicochemical properties:

Their excessive stored energy is 2-5 times higher than metal melting heats. This energy is released in the heat waves mode at the temperatures much lower than melting temperatures (400 ° C for Al, Cu, 150 ° C for Ag, Sn, 120 ° C for In) [1]. Al EEP reacts with water similar to alkali metals at 50-70 ° C with the release of hot hydrogen [2]. In standard calorimetric bombs Al EEP reacts with nitrogen in SHS mode at the pressures of 20 atm. at a 100 % AlN yield. Nitrides not oxides are formed in mixtures with lead and barium nitrides at burning.

Aluminium boride is formed in mixtures with commercial boron in SHS mode. Al EEP - amorphous boron pellets were put on an electrically heated plate. The process begins at 730 ° C and occurs at a speed of 5 mm/sec, at a self-sintering to 1,000 ° C. Brass is formed in SHS mode in mixtures of a commercial Zn powder and Cu EEP, at the temperatures within 170-200 ° C and self-heating to 800 ° C.
 
 

References:

1. G.V. Ivanov, B. G Ivanov, V.P. Kuznetsov. Formation of heat waves in dispersed metal media at the metastable state relaxation. 1^st All-Union Symposium on Macrokinetics and Gas Dynamics. Abstracts, Alma-Ata, 1984.

2. B. G Ivanov., S.N Leonov., G. L. Savinov et al. Burning of ultrafine aluminium with gel-like water. Physics of Burning and Explosion, 1994, N 4, p. 167.
 
 

O-4-02: Near Net-Shaped Alkaline-Earth-Bearing Ceramics

O-4-03: Influence of Anti-Combustibles Additive on the Inflammability

of Foam Polymer

Two ways of foam-polymers inflammability reduction have been shown as the most perspective. The first way consists in drawing fire-protective layer on the material surface . However this layer can be destroyed at further use of the product. The second way consists in addition in the foam-polymers the various chemical compounds, which will create some kind of obstacle to access the material surface oxidation as a result of thermal decomposition. The present paper were guided by the second direction. The additive for foam-polyuretan and foam-polysterol on the basis of urea-formaldehyde pitch (UFP) and diammonium phosphate (DAP) has been developed as anti-combustibles additive. These substances were added in polymers in frothing process in various percentage ratio. The advantages of these additives are cheapness, insignificant influence on frothing process and complete ecological safety. Solid UFP which has been used as the additive is a waste production and was not suitable for all industrial applications.

The tests of the synthesized material have been carried out on installations " Fire pipe " and " Oxygen index ". The obtained results have shown increase of the foam-polyuretan and foam-polysterol oxygen index more than twice. Now we may consider the received materials as not light igneous but hard igneous under the given inflammability characteristics (GOST 12.1.044-84). The found results are compared to the world analogues.

These days work on foam-polyuretan and foam-polysterol production with proposed anti-combustibles additive is conducted in industrial scale.
 
 

O-4-04: Microstructure and Mechanical Properties

of the SiO₂-- Al₂O₃--Li₂O--MgO--ZrO₂--TiO₂ Glass Ceramic

The objective of this study is to investigate the two aspects:

1. the microstructural evolution from glass to glass ceramic state during heat treatment.
2. The mechanical behaviour corresponding to each state.

1. the first stage corresponds to a precipitation of small particles of ZrTiO₄.The maximum particle size of ZrTiO₄ observed is about 55 A° .
2. The second stage corresponds to the nucleation of crystalline phase from the ZrTiO₄ nuclei. The crystalline phase is identified as the Virgilite (LiAlSi₄O₈).
3. The last stage corresponds to the growth of the Vrigilite according to an Oswald ripening mechanism.

O-4-05: Heat Explosion in a Heterogeneous Medium

We consider the square geometry and assume that the side walls are heat isolated while the temperature at the upper and lower walls is equal to the ambient temperature. We study first the thermal model [1,2] of heat explosion (stationary solutions of (1) - (4) with zero velocity), relevant to condensed medium. Dependence on the coefficient of heat exchange, critical conditions of heat explosion, continuous branches of solutions were obtained as well as complete results on stability for a general positive and convex rate. These results can be applied to the case of heat explosion in a homogeneous medium. We study numerically the influence of natural convection on behavior of the two-phase system. If the Rayleigh number is sufficiently small, then the pure thermal regime [1,2] is stable and the medium is unmovable. If the Rayleigh number exceeds a critical value, then this solution losers its stability and convective structure appear. We study critical conditions of

convective instability and the interaction with convection.
 
 

Referenses:

1. C. Barillon, G.M. Makhviladze, V. Volpert, Existence of solutions for an elliptic-algebraic

2. C. Barillon, G.M. Makhviladze, V. Volpert, Stability of solutions for a model of heat explosion in

a two-phase medium. Submitted.

3. S. Goroshin, J.H.S. Lee, D.L. Frost, Combustion synthesis of ZnS in microgravity, 26h

International Symposium on Combustion, The Combustion Instotute, pp. 1651-1657, 1994.

4. A.G. Merzhanov, E.A. Shtessel, Free convection and thermal explosion in reactive systems,

Astronautica Acta, 1973, v.18, N 3, p.191-199.
 
 

O-4-06: Dynamics of thermal explosion in the post-induction period.

Development of problems of self-propagating high-temperature synthesis (SHS) intensified interest to thermal explosion as a synthetic method in inorganic media. Due to conservation of hard mixture during all time of process one can investigate the dynamics of complete thermal explosion by means of the uniform macrokinetic mathematical model - model of gasless combustion.

In present report by computing simulation the dynamics of thermal explosion was considered in the post-induction period and the complete nonstationary analysis was realized. The depth of the volume of medium and the depth of conversion in frontal regime were investigated in the induction period.

Two mechanisms of the front propagation in the post-induction period were defined. We showed that SHS in conditions of thermal explosion ( samples in kiln or in the grafhite press-form ) has essential stage of self-propagating front. Therefore it is more correct to considere thermal explosion like way of the front synthesis initiation together with changing the initial temperature of mixture. The investigation were carried out for the wide diapason of changing parameters Fk, Bi, Td, Ze and for the different macrokonetic laws of chemical conversion.

Supported by Int’l. Sci. & Tech.Ctr. Grant 355-97.
 
 

O-4-07: Electrothermal Explosion and Gasless Combustion in

SHS Systems Containing a Melting Reagent

A.S. Shteinberg, K.V. Popov

In this connection, some data on SHS in layered samples obtained by PVD (material widely applied in semiconductor industry) are considered. Good agreement of theoretical and experimental results testifies that joint application of kinetic method of ETE and SHS research is an exceptionally promising direction for study of layered samples with limiting layer thickness (down to 100 Е).
 
 

O-4-08: Modeling of Reactive Synthesis in Consolidated Blends of

B₄C-Ti and BN-Ti

O-4-09: Computer Simulation of Electrothermal Explosion in the Ni-Al System

O-4-10: Effect of Shock Waves on SHS

Yu.A. Gordopolov, R.M. Shikhverdiev

O-4-11: Modeling of Solid-Phase Detonation

O-4-12: Detonation Type Autowave in Phase and Chemical Transformation

Processes in Condensed Matter (Gasless Detonation)

Our investigation shows that supersonic autowaves exit in this gasless model (so as classical detonation). In the absence of a dissipation factor (losses), continuum of travelling wave solutions is found. In the presence of one( for example, diffusion) a steady state supersonic wave solution is found.
 
 
 
 

O-4-13: Application of Explosive Shock Compacting to Functionally Graded

Materials Produced by SHS Reaction

R. Tomoshige¹, H. Tanaka ¹, A. Kato¹, K. Imamura², A. Chiba²

In this study, the hot-shock compaction technique was also applied to the production of FGMs. The study shows it to be possible to readily fabricate the dense TiC/Ti₄Al₂C₂/TiAl and TiB₂/TiNi/Cu FGMs by the hot shock compaction method. Especially, TiNi shape memory alloy was utilized in the TiB₂/TiNi/Cu system FGMs as an effective material, in order to reduce the thermal thermal stress produced between both end materials by a reversible shape change of the alloy, so-called pseudo-elastic effect. The FGMs were evaluated on their microstructural characteristics and thermal properties. The particles in the FGMs bonded strongly with each other. EDS analysis revealed that each element was graded smoothly. Thermal shock tests revealed that the as-compacted FGMs had high interlayer bonding strength, no exfoliation and no microcracks. Thus, the SHS reaction had the potential to easily overcome the difficulties in FGM fabrication
 
 

O-4-14: Optimum Choice of Three-Parameter Expression to Approximate

Dynamic Adiabatic Curves of Shs Systems and other Condensed Media

V.S.Trofimov

Analysis of shock and detonation adiabatic curves thermodynamic equations was carried out at additional as sumption that was not used till now at the present context. Namely, it was assumed that Grtneisen coefficient monoto-nously approaches to its limit corresponding infinite increase in pressure at constant volume. It turned out, that this assumption essentially restricts type of expressions describing dynamic adiabatic curves of condensed media. As a result it is succeed to describe uniformly equations of state (dependence temperature of volume and pressure) and caloric equations of state (dependence specific energy of volume and pressure) of various condensed media. On this basis new simple methods of shock and detonation waves parameters calculation in SHS-systems are proposed.
 
 

O-4-15: About Possibility of Gasless Detonation in Some Pyrotechnic Mixtures

E.A. Dobler, A.N. Gryadunov, S.A. Bostandjiyan, A.V. Utkin, V.E. Fortov

Q_PV<0 (1),

where Q_PV is the heat of the reaction at constant volume and pressure. This demand can be easily satisfied for reacting systems produces gases. But condition (1) holds and for some systems which are not producing gases systems. Most energy of the reaction in such systems are revealed in the form of the heat rather then in the form of the mechanical work and all work produced are performed by heat expansion of condensed products. So, detonation in such systems can be designated as gasless or heat detonation.

Satisfaction of (1) means that detonation can occur at some (may be infinite) diameters of reactive substance greater then some critical value. To provide detonation in the reasonable amount of substance the second demand must be satisfied: the time of reaction must be extremely small-a some microseconds (condition 2).

Current report devoted to the evaluation of possibility of the gasless detonation in metal - metal oxide pyrotechnic mixtures. Theoretical modelling of shock adiobates of reacting powders and detonation adiobates of products was used to test the possibility of the detonation regimes in some systems at different initial porosity’s. Necessary conditions for satisfying of (2) are discussed on the base of the experimental dates. As a result, the list of some perspective for gasless detonation systems with parameters of the possible detonation regime is presented.

The work was supported by Russian Foundation for Basic Research (grants № 96-03-32703a, № 98-03-32201a, № 99-03-32262a) and the Russian Academy of Sciences (within the competition of the young scientists projects in the field of chemistry, physical chemistry, chemical physics and chemical engineering initiated by the RAS Presidium, Project No.47, Decree 272, of July 13, 1998).
 
 

O-4-16: Liquid Flame in Gravitational Field

K.G. Shkadinsky¹, G.V. Shkadinskaya¹, B.J. Matkowsky²

Multiple experiments on centrifuges, in the microgravity conditions and on earth showed existence (or absence) of separation in liquid products due to difference of the component densities. However the gravity separation begins after the solid matrix destruction (where components receive freedom of relative motion), i.e. in the preheat zone of the combustion front. Distribution of concentration and temperature is changed in the reaction zone. That influences on the front propagation velocity. In the present report the influence of the gravity fields on the propagation of liquid flame is investigated. We formulated a nonstationary mathematical model of liquid flame in the gravitational force fields. We carried out numericalsimulation and the analitical approximations of the model and compare to the experimental results. We studied the factors increasing (or decreasing) the combustion velocity with increase of the gravity acceleration. We showed that increase of the gravity acceleration can change the adiabatic temperature of combustion and the product structure. As for solid flame there are instability and nonuniqueness of the front propagation of liquid flame.

Supported in part by NASA Grant NAG3-1608, Int’l. Sci. & Tech. Ctr. Grant 355-97.
 
 
 
 
 

O-4-18: Combined Effect of Magnetic Field and Gravity on SHS

Final products exhibited magnetization and coercive force whose value were strong dependent on the orientation of attractive magnetic field with respect to the direction of gravity. (i) samples have greater magnetization and strong reduced values of coercive force compared to (ii) and convenient SHS condition samples. The most obvious effect of magnetic suspension took place when the combustion temperature was below the Curie point of both the raw material and final product (Li_0.5Fe_2.5O₄). It is assumed that the observed increase in the magnetization and decrease in coercivity are caused by difference in magnetic particles separation phenomena in the gravity and magnetic field.
 
 

O-4-19: Gasless SHS in Microgravity

In our experiments, we used spherical particles of AI cladded with Ni (the thickness of a Ni coating corresponded to a ratio of Ni/A1=1/1 for each cladded particle). Two types of samples were used: (a) cylindrical pellets of cladded powder and (b) loose powders with a different bulk density.

The pressed samples burnt in space and on the ground retained their cylindrical shape and size. According to the data of electron probe microanalysts and X-ray diffraction, the chemical and phase compositions are identical (NiAl). As follows from ESM analysis, the NiAl grains are larger in the space-produced material. For this material, the intercrystalline fracture is prevailing. Meanwhile, the ground-produced material exhibits marked transcrystalline fracture. Apparently, microgravity affects the crystallization process due to the absence of convection.

Burning of the loose powder at normal gravity proceeds without volume change. The space-produced product (NiAl) exhibits higher porosity and acquires the shape of the ampoule. Combustion velocity in the loose powder (under terrestrial condition) is about 1.5 cm/s. At microgravity, for the first time we observed the propagation of gasless SHS wave in the particle cloud in vacuum. The space-produced material exhibits a high-porosity skeleton (bound) structure.

The experimental results shown that space-produced pressed samples of NiAl possess more perfect microstructure with larger crystal grains. Gasless combustion of the vacuum particle clouds is the most interesting result in the present work. A mechanism of this process must be studied. High-porous continuous structure is formed due to change in the shape and size of particles during combustion.
 
 

O-4-20: Effect of Microgravitation on Structure Formation of Refractory

In the work our attention was focused on the effect of amount of a liquid phase in final and intermediate combustion products on gravitational sensitivity SHS processes and structure of resultant products. The detailed investigation of differences in course of SHS process and formation of final products in space and terrestrial conditions was carried out. The accuracy of the forecasting interpolated diagnostics was analyzed.
 
 

O-4-21:Self-Propagating High-Temperature Synthesis of Foam Cermet in Space

A.G. Merzhanov, V.A. Shcherbakov

O-4-22: Investigation of Effects of Electric Field on the Combustion Behavior in

the SHS Process by Use of the Heterogeneous Theory

O-4-23: A Splitting Model for Interaction between Intense HF

Radiation and SHS Systems

The model involves (1) the constitutive relations of the Maxwell equation for a green mixture (nonquasi-stationary approach), (2) specially transformed Maxwell equations (suggested for the first time), and (3) formal scheme for nonstationary energy dissipation in SHS systems. The model was applied to a real SHS system taken as an example. In view of complexity of the processes taking place in real SHS systems, predictions of the model are only qualitative in their character. Instead of existing "refined" modifications of the splitting technique, the model utilizes a more rough approximation based on the Laplace–Karson operational calculus. By its simplicity and physical clearness, the suggested technique was found to be comparable with macrokinetic modeling. The model has two advantages important for practical applications of SHS: (1) it is based on simple mathematics (convenient for experimental checking of results) and applicable to both direct and reverse problems of energy dissipation and (2) it provides new convenient approaches to classification of the electrical properties of SHS systems.
 
 

O-4-24: On the Field-Activated Combustion Synthesis of Titanium Aluminides

The reaction mechanism of the field-activated combustion synthesis (FACS) of the phase Ti₃Al from elemental powders is also investigated. Intermediates of the reaction leading to final product are identified by performing X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) of "quenched" samples obtained by turning off the applied field during wave propagation. The combustion reaction is preceded by the melting of aluminum, which then spreads over the titanium particles. A reaction between liquid aluminum and titanium results in the formation of a layer of TiAl₃ which grows around the original Ti particles until the aluminum disappears completely. Subsequently, the remaining (unreacted) Ti interacts with TiAl₃. At this stage, the particles consist of Ti cores surrounded by a layer of Ti₃Al which in turn is surrounded by another layer of TiAl. This interaction further proceeds leading to a shrinkage of the Ti cores, the gradual disappearance of the TiAl layer, and the simultaneous increase of the Ti₃Al content. A single Ti₃Al phase product is finally obtained.
 
 
 
 

O-4-25: Induction Field-Assisted SHS of AlN-SiC Solid Solutions

In this work we describe another modification of the field-activated process: the use of an induced current. Samples covered with sheets of carbon foil are placed inside an induction coil. Depending on the electrical conductivity of the reactants, the induced current will be localized in the foil or in both foil and the outer sample layer. Analogous to the case of regular field-activation, two sources of energy can be present inside the reaction zone: chemical and electrical. Moreover, the use of the induction field-activation facilitates post-combustion annealing of the product. In this paper we describe the results of an investigation on the induction field-activated synthesis of AlN-SiC solid solutions and compare these results with those obtained under normal field-activation.
 
 

Referenses:

1. Z. A. Munir, W. Lai, and K. Ewald, , U. S. Patent No. 5,380,409, January 10,

(1995); A. Feng, and Z. A. Munir, J. Appl. Phys.,1994, v. 76, p.1927..

2. H.Xue and Z.A.Munir, Ssripta Mater., 1996, v. 35, p.979; J. Euro. Ceram. Soc.,1997,v. 101, p.1787
 
 

O-4-26: SHS in an External Magnetic Field (1.1T, 2T, 4T, 6T, 10T, 12T, 16T,

20T); Preparation and Characterization of Ferrites.

O-4-27: Mathematical Modeling of Frontal Polymerization

We develop mathematical models of FP and determine the structure of the polymerization wave and its propagation velocity as well as their dependence on the parameters of the problem. Our analytic results are in good quantitative agreement with both numerical simulations of the model and experimental data.
 
 

O-4-28: The Autowave Modes of Solid Phase Polymerization in

Two- and Three-Dimensional Composition Matrixes on the

Base of Fiberglass Fillers Appreting by Metal-Containing Monomers

V.V. Barelko, A.D. Pomogailo, G.I. Dzhardimalieva,

S.I. Evstratova, A.S. Rozenberg, B.M. Zuev

O-4-29: Organoelemental Synthesis in an SHS Mode

The important task of the subsequent researches is increasing of number of reactions classes, in which organic SHS is possible. In this connection, the attempts to organize autowave modes of reactions in organoelemental synthesis systems triphenylphospin/chloramine "B"and ferrozen/phtalic anhydrid/AlCl₃ were undertaken.

The thermogravmetric research has shown existence of exothermic interaction near to melting point of low-melting reagent. In equimolar mixes of powders was a success to organize the SHS wave. The main schemes of chemical interaction are offered on the basis of the analysis data:

                                                                                                                                                         | ---------->  (C₆H₅)₃ PNSO₂C₆H₅+NaCl+3H₂O
                                                                                                                   |
                                                                                (C₆H₅)₃ P + C₆H₅SO₂NNaCl· 3H₂O---- |
                                                                                                                                                          |
                                                                                                                                                          | ----------> (C₆H₅)₃PO+C₆H₅SO₂NH₂+NaCl+2H₂O
 
 

(wave velocity u @ 4,0 mm/sec, max temperature Tm @ 190⁰C, conversion a = 100 %, output of a target product triphenyl-(phenylsulfonamide)phospinimide b@ 40 %);

(u @ 1 mm/sec, Tm @ 190 C, a = 100 %, output of a target product o-carboxybenzoilferrozene b @ 16 %).

The results on study of the various factors influence on the processes macrokinetics and structure of products, microstructure of synthesized substances, date on DTA, NMR, X-ray analysis are discussed.
 
 

O-4-30: Frontal polymerization under conditions of weak convection

Referense:

1. Briskman V.A., Kostarev K.G., Lyubimova T.P. et al. Polymerization under different gravity conditions. Acta Astronautic, 1996, v.39, N 5, p.395-402.