P-4-01: Perforation of Steel Plate by Steel Ampoule with SHS Mixture

A.N. Gryadunov, E.A. Dobler, S.A. Bostandjiyan,V.A.Gorelski, S.A. Zelepugin

A stoichiometric mixture of titanium powders and carbon black was used as an active mixture. The final product, titanium carbide, was used as an inert analog. The experimental results showed that introduction of highly exothermic SHS mixtures (Ti+C, Ti+2B) as a filling material resulted in a 5-7 % increase in the weight of a fuse beaten out from the barrier as well as in the diameter of the aperture formed in the steel plate.

The numerical modelling of the process of interaction of a cylindrical ampoule filled with a reactive exothermic mixture and a steel plate was performed. The calculations showed that the change in the shock wave characteristics of the filling material during the chemical interaction did not influence the process of punching. The observed effect could arise due to various factors (not taken into account by the model), which distinguished the reacting filling material from the inert.

The experiments showed that the presence of a liquid phase (liquid titanium) in the zone of the dynamic contact could be the factor essentially influencing the process of interaction of the bullet and the barrier in the case of a reactive mixture. It should cause the increase in the rate of the crack growth in the punched barrier (the Rebinder effect).

From experiments and calculations it is evident that under the conditions of a shock wave titanium carbide is synthesized during interaction of the ampoule filled with the SHS mixture of the titanium powders and carbon black with the steel plate. It is shown that the presence of the liquid phase formed (liquid titanium) leads to a considerable change in the nature of the interacting materials deformation. It is well confirmed by the increase in the diameter of the punched aperture.

The work was supported by the Russian Foundation for Basic Research (grants № 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 № 47, Decree 272, of July 13, 1998).
 
 

P-4-02:Gravity-Induced Effects in the Microstructure Formation

of SHS-Products

It is known that product formation in the SHS process often occurs through nucleation and growth of solid grains in a matrix melt. Gravity-driven processes, such as convection of the melt and buoyancy/sedimentation of the grains may effect the process of final structure formation. The present work is aimed to better understanding of the role of gravity-induced processes on the microstructure of SHS materials. We have studied ceramic-metal compositions TiC+30% Ni, TiC+30% Co, and Ti₅Si₃+30% Cu (wt.), obtained by SHS at different conditions of artificial gravity. Centrifugal machine was used to provide acceleration up to 20 G. All these materials consist of ceramic grains distributed in the metal matrix, boundaries of the grains and metal binder are very sharp, which allowed us to apply methods of quantitative image analysis to characterize microstructure.

The results have shown that centrifugal acceleration intensifies plastic flow of hot products and deformation of the samples. Pore structure obtained at increase gravity consists of coarser pores with more rounded shape, as compared to normal gravity conditions. An average ceramic grain size and size distribution are also disturbed by the centrifugal force. Variations of grain sizes lays within 20% of initial value obtained at normal conditions. Decreasing of the grain size was observed when acceleration increased from 0 to 5 G. With the further rise of acceleration, grain size increases or remains approximately the same.

The obtained dependencies can be explained on the base of “dissolution - precipitation” model of microstructure formation during SHS, taking into account convection, buoyancy (or sedimentation) and plastic flow of the material. Simplified mathematical model is suggested to describe the main features of the structure formation process.
 
 

P-4-03: Gravitational Effects on Liquid Flame Forming Gas-Liquid Suspension

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.
 
 

P-4-04: On Interaction of Heterogeneous and Homogeneous Chain-Branched

Mechanisms in Catalytic Combustion Reactions

For check of a put forward hypothesis about gas-phase started chain continuation for of the catalytic acts in reactions about catalytic combustion on platinum it was decided carry out series of experiments in considerably other to experimental conditions - in reactor with single catalytic wire gauze, described minimum possible from time to time of contact (milli & micro second). Received results (preservation of constant characteristic of switching threshold, practically, complete conversion at extremely small times of contact) have created the new basis for confirmations justice of representations, advanced on a basis data of a mass-spectrometer measuring technique.Transition from catalytic Pt-wire gauze elements to silica fiber glass vowen catalysts (change of Pt-content in it about on 2-3 order, radical change of geometry and structure of the woven catalytic elements) has not caused essential changes earlier measured dynamic characteristics of investigated reactions, that has strengthened arguments for the benefit of developped of the non-traditional concepts.

Put forward representations about the special nonequillibrium state of gas reactionary environment near to a surface of the catalyst have made an ideological basis for arising absolutly recently and causing great technological interest directions: -realization of processes selective oxidation of light alkanes on platinum in conditions of extremely small times of contact; - catalytic activation of furnace's atmospheres in processes of nitriding of details from metals and alloys.

The work has carried out under the support of RFBR(Project 97-03-32606a )
 
 

P-4-05: On the Possibility of Shock Initiating Detonation in SHS-Mixtures

S.N. Buravova

Institute of Structural Macrokinetics and Materials Science,

Russia Academy of Science, Chernogolovka, 142 432 Russia,

Initiation of detonation processes in exothermical systems, which have a small amount of gaseous components, is connected with large difficulties and needed of using of special methods for stimulating of chemical reaction proceeding.

During initiating detonation regimes in SHS – system by detonation of condensed explosive charge there shock wave is creating which have a falling profile. The estimation of shock-wave action duration shows that it only slightly exceeds the passing time of detonation wave through explosive charge.

The solution of problem of proceeding of nonstationary heat explosion in reaction mixtures showed strong dependence of induction period from duration of shock – wave action.

The critical condition of the possebility of explosiveproceeding of chemical reaction is
 
 

d /t _o > G _o*U_o*E / (R_*T_o*C_o)
 
 

where d is duration of shock – wave action, t _o is iduction period of adiabatic explosion, G _o – Gruneisen coefficien, U_o – mass velosity, T_o – is temperature behind of shock – wave front and E – the activation energy.
 
 

P-4-06: Effect of a DC Electrical Field on SHS of Ferroelectrics

Russia Academy of Science, Chernogolovka, 142 432 Russia,

An effect of applied dc electric field on the parameters of combustion and specific properties of some ferroelectric systems was discovered. General experiments in the longitudinal electric field were carried out for the Nb-R₂O₂-Nb₂O₅ (R=Li, Na, etc.) systems. The compact samples of elemental powder mixture after initiation showed auto oscillating combustion wave propagation. During SHS the bipolar e.m.f. of combustion above 1 V was detected. The e.m.f. and its variation in time depended on the field strength, orientation of the field respect to wave front propagation direction and the product composition. It is shown that in electrical field with strength up to 0,3 kV/cm, applied to a reactionary zone, the dependence of e.m.f. of combustion in area the post - process from time appreciably differs from the case of the non-disturbing process. No significant dependence of combustion parameters on the field strength and its orientation were found.

The LF dielectric permeability of the products at different temperatures was studied. Electric polarization of the ferroelectric ceramics was found related with combustion conditions. A successful attempt to study in situ polarization of synthesized ferroelectrics was done. The effect of electric field on the composition and microstructure of reaction products tentatively explained the observed change in combustion characteristics.
 
 

P-4-07: A Versatile Method of Modification of Magnetic

Properties of SHS Ferrites

Yu.G.Morozov, M.V.Kuznetsov

Institute of Structural Macrokinetics and Materials Science,

Chernogolovka, 142432 Russia
 
 

The method of modification of magnetic parameters of SHS ferrites based on combination of partially replacement of iron by chromium before and application of a dc magnetic field during the synthesis is developed. Magnetic characteristics of a wide class of SHS ferrites, synthesized in a combustion mode both in the applied magnetic field, and in its absence are investigated. The smooth maximum in dependence of coercive force of hard ferrite from the chromium content is found. The effect of “softening” for all the samples synthesized in the magnetic field, both hard ferrite, and soft ferrite is established. It is shown that the presence of a magnetic field at synthesis in most cases results in essential increase maximal and residual magnetization and decrease of coercive force of the samples. It is shown that by synthesis in a magnetic field the Curie temperature and ferritization degree of the final products is increased. The experimental results are interpreted within the framework of representations about influence of replacement of ions on the thin magnetic structure of ferrite and reorganization of a material at the initial synthesis stage on the magnetic texturing. The received results allow using the SHS method for modification of ferrite materials with the purpose to finish their magnetic parameters up to values necessary for the special applications.
 
 

P-4-08: Fabrication of a Diamond-Dispersed Cemented Carbide by

Because of the low value of the enthalpy of formation of WC (– 40.5 kJ/mol), stoichiometric W-C reactants with 10 wt% Co cannot sustain an SHS reaction without some form of activation. When compacts of these reactants are covered by carbon foil and placed inside a high frequency induction coil, a reaction can be initiated and sustained. The resulting combustion wave propagated radially towards the center. The role played by the induction process in the field-activated synthesis of this cermet is two fold: (1) the preheating of the reactant compacts by heat conducted from the carbon foil, and (2) Joule heating by the inducted current in the combustion zone. In this work, the combustion synthesis was carried out under a static pseudo isostatic compaction through the use of commercial casting sand as a pressure-transmitting medium. With this approach, simultaneous synthesis and densification of WC-Co cermets can be achived in one step. The fabrication of diamond highly-dispersed WC composites by a combination of these techniques was shown to be feasible.
 
 

P-4-09: Experimental Investigation Shock-Wave Properties

of CuO/B Pirotechnical Mixture

The work was supported by Russian Foundation for Basic Research (grants № 96-03-32703а, № 98-03-32201а, № 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).
 
 

P-4-10: The Autowave Modes at Solid Phase Polymerization in Composition

210 ± 7° C. Apparently, the metal nature determined C=C bond reactivity, thus for I, II, III, values of the front-propagation rate were 0.42 mm/s, 0.14 mm/s, and 0.70 mm/s, respectively.

Kinetic lows of the solid-phase polymerization in one-component systems and fiberglass matrices were compared. Front traveling was stabilized even by small content of the filler. Meanwhile, realization of a layer-by-layer process became impossible with increase of a glass powder content (up to 30%) in the monomer matrix.

Front polymerization was performed on flat of glass fabric appreted by complex 1. For the given composites, the autowave mode of prepreg design yielded essential enhance of mechanical characteristics of the fiberglass composites being promising in the fabrication technology. Also, thermolysis of the appreted composites resulted in formation of organic synthesis catalysts, transition-metal nanoparticles, immobilized on matrices.
 
 

P-4-11: Self-Propagating Synthesis of Iron(III) Acetylacetonate after

Mechanical Activation of a System “FeCl₃ - NaC₅H₇O₂”

The mixture of reagents turns amorphous after several minutes of mechanical loading with vibration ball mill. Then its grey colour turns dark brown, and, finally, it gains bright red colour of iron acetylacetonate. Physico-chemical investigations of the reaction mixtures have shown that simultaneous formation of final products (sodium chloride and iron acetylacetonate) and intermediate activated mixture occurs in the course of mechanical loading. The amount of the activated mixture, determined by the intensity of the exothermic event at DTA-curves, at first increases in the course of mechanical loading, then decreases and, finally, it completely turns to products.

The action of local thermal impulse on an end face of a specimen pressed from the activated mixture causes the appearance of bright red zone which propagates along the brown specimen up to a full exhaustion of the material. Depending on conditions of the mechanical loading and organization of the process, the rate of propagation can reach ~5 mm/sec and temperature in the reaction zone can rise up to ~200° C.

Temperature of external thermal initiation of self-propagating process (~50-90° С) is equal to the temperature of beginning of exothermic event on DTA curves. However, temperature profiles of the process measured by thermocouples immersed into the block are rather unusual. Sharp jump from ambient temperature to ~50-90° С occurs at the first stage indicating extremely small breadth of a warm-up zone. Then it is replaced by slower exothermic process. Such low temperature of initiation and very fast growth of temperature at the initial stage against a background of rather small its magnitude allows to assume that not only heat transfer process can take part in the self-propagation. The mechanism of this phenomenon is under study.

Support from RFBR (grants 99-03-32253; 99-03-32900) is greatly acknowledged.
 
 

P-4-12: Mechanical Activation (MA) of Silicon and its Influence on SHS of

Niobium Dicilicide

O.G. Terehova, O.A. Shkoda, Yu.M. Maksimov, L.D. Chaluh

Experimental results on MA of silicon as well as joined activation of silicon and niobium in order to realize SH synthesis of niobium dicilicide are presented in the work. Experiments on MA were carried out in planetary mill with water cooling with acceleration of % g. Steel containers and steel balls with the diameter of 0,5-0,7 sm were used. The MA conditions of KP-1 type silicon are as follows: medium - air, argon; simass: mass balls relation 1:20. Activation duration was from 3 to 120 min. It was shown that the size of silicon particles decreases from 100 m m to < 1m m with the increase in duration of mechanical activation, accumulations of defects of various types (II and III type) occurs simultaneously.

To determine MA efficiency the parameters of crystal lattice were calculated and the value of microdistortions (?) was defined, using activated silicon as on example. It was shown, that the value of microstresses decrease approximately 3-fold with the increase in activation time from 3 to 120 min. Simultaneously crystallites size decreases by the same value. The result of radiographic analysis of jointly activated silicon and niobium powders showed, that the formation of niobium dicilicide is already beginning in MA after 5 min of grinding in argon. At the same tome the traces of Ni and Si oxides, Ni and small amount of SiO₂ are present. After 120 min of MA only NbSi₂ is fixed on X-ray patterns of Ni and Si. After MA, Si and Ni mixture was pressed and ignited and SH synthesis was carried out in argon. The combustion is observed for the charge, being activated in argon for more then 120 min. X-ray analysis of SHS product confirmed the formationof niobium dicilicide.

Thus, it was shown, that preliminary MA of charge (Si and Ni) allows to realize SH synthesis of weakly exothermal NbSi₂ without preheating.
 
 

P-4-13: MASHS process applied to the Cu₃Si phase formation

P-4-14: SHS Long-Sized Rods Produced from the in Samples in Combustible

The study was supported by the Russian Academy of Sciences and the Russian Foundation for Basic Research.
 
 

P-4-15: Method of Mould free SHS-Compaction and Measurement of

formation Performance Data

The possibility for mould free SHS-compression technique could be put to producing the macrolayer metalloceramic materials and coating is described. A variety of techniques for producing the macrolayer materials type of metal-composite, metal-composite-metal are tested.

The study by means this technique concerns itself with the peculiarites of rheological behaviour of the materials based on titanium carbide and titanium boride with nickel binder. The above-mentioned systems have the layers with clearly defined transition zones, as this takes places, a strong bonds are between material layers. The features of phase and chemical compounds of transition zone between metal and ceramic layers has been investigated. The gradient contribution of the metal binder content with height has been found. It is shown, that it is possible to product materials of different microstructure with experimental conditions, but of chemical compounds in common.

This work was supported by FCP “Integration” №0099.
 
 

P-4-16: Exothermic Welding with Transient Eutectic Liquid

A method is described for the welding of these materials with the use of a transient eutectic liquid phase. The use of an eutectic phase in this method enables to initiate the exothermic welding reaction before the melting point of the matrix materials is reached. As an example the use of the Al-Cu eutectic is discussed in this paper. In addition, further examples of the welding process include; welding of composite layers on unreinforced alloys to improve wear resistance, and the use of gradient welds. Preliminary results in these areas will also be dealt with.
 
 
 
 

P-4-17: Calculation of Equilibrium Temperature in the Ideal

Detonation Wave in the Zn--S SHS System

P-4-18: Feasibility of Synthesis of Dense Nanomaterials from Mechanically

Activated Powders.

F.Charlot^1,2, Ch.Gras^1,2, E.Gaffet¹, F.Bernard², J.C.Niepce², Z.A.Munir³

Although the SHS reaction retains the nanostructure obtained by the mechanical activation step, the densification is weak. Indeed, during the combustion, some sources of porosity are activated [4]. this low density is the major hurdle to development of these nanomaterials obtained by MASHS. The purpose of this work is to investigate the feasibility of forming dense Fe/Al or Mo/Si nanomaterials by the use of the Field Activated Pressure Assisted Synthesis Apparatus (FAPASA) developed by Z.A.Munir. Mechanically activated reactant powders were enclosed in a graphite die. The die is then maintained under uniaxial pressure while an electric field flows through the die and ignites the combustion. After reaction, samples exhibit a relative density greater than 95%. Following mechanical activation conditions, sample are one intermetallic phase with little or no secondary phases. The microstructure is investigated by XRD. The first results are encouraging and suggest that this technique may open a new route to obtain dense nanomaterials, where the consolidation step is the same time as the synthesis step.
 
 

References:

1. F.Charlot, F.Bernard, E.Gaffet, B.Zeghmati, J.C.Niepce. Mater. Sci. Eng. A, 1999, on press.

2. F.Charlot, F.Bernard, E.Gaffet, D.Klein, J.C.Niepce. Acta Mater., 1999, v.47, N 2, p. 619-629.

3. M.Abdellaoui, E.Gaffet. Acta Mater., 1993, v.44, N 2, p. 275.

4. Z.A.Munir. J. of Materials Synthesis and Processing, 1993, v. 1, p. 387-394.
 
 

P-4-19: The Investigation of Porous Structure Characteristics for Capillary

In the work the investigation results on superporous structures characteristics are presented for the purpose of production of capillary pumps for contour heat conduction pipes.

Nitride alloys, obtained by powder methods and SHS were used as the material for porous structure.

The result investigation analysis showed that the SHS capillary materials can be successfully used in contour heat pipes.
 
 

P-4-20: Shs Method for Research of Boiling

P-4-21: Investigation on Field Effects during SHS Reactions in Multilayer

Systems

N. Bertolino^1,2, F.Maglia², U. Anselmi-Tamburini², Z. A. Munir¹

The geometry of the reactants was simplified [17-19] using foils instead of powders, but still utilizing the field-activated combustion synthesis (FACS) method. Each multilayer sample was placed between spring-loaded graphite plates that acted as electrodes for field application. All the experiments were carried out inside a stainless-steel chamber under argon gas at 1 atm pressure. The samples were combusted in two different ways. In the first method, ignition and reaction is effected only by the passage of an AC current. In the second method ignition and combustion is effected by radiative heat. For each set of experiments, the temperature was the same in both methods. The combustion process was investigated with different applied voltages and times.

In both cases, the reactions are rapid, with high rates of heating and cooling. The systems investigated are Ni-Al, Fe-Al, and Ti-Al. Preliminary results indicate that phase formation is not affected by the current, but there is evidence that the field has an effect on the convective heat and mass transport during synthesis.
 
 

References:

1. A.Feng and Z.A.Munir, Metallurgical Transaction 1995, v.26B, p.587

2. Z.A.Munir, Zeitshrift fur Physicalische Chemie 1998, v.207(PT1-2), p.39

3. L.M.Klinger,X.Chu,W.W.Mullins,C.L.Bauer, Scripta Met.Mat.1993, v.29, p.579

4. L.Klinger,L.Levin, J. Appl. Phys.1995, v.78, N 3, p.1669

5. A.Onuki, Physica A 1995, v.217, p.38

6. M.Shimojy,T.Itami, Diffusion and Defect Data 1987, v.43, N 1

7. P.S.Ho,T.Kwok, Rep.Prop.Phys,1989, v.52, p.301.

8. J.H.Zhao, Electromigration and Electronic Device 1994, N 6, p.167

11. P.Asoka-Kumar,K.O’Brien,K.G.Lynn,P.J.Simpson,K.P.Rodbell, Appl.Phys.Lett. 1996,

12. T.Kouno,M.Osaka,H.Niwa,M.Yamada, J.Appl.Phys.1998, v.84, N 2, p.742

13. A.K.Misra, Metal.Trans.A 1985,v.16A, p.1354

14. A.K.Misra,Metal.Trans.A 1986, v.17A, p.360

15. S.Ahmed,R.Bond,E.C.McKannan, Adv.Mat.Proc.1991, v.10, p.30

16. A.Prodhan,J.Mat.Sci.Lett. 1997,v.16, p.958

19. A.S.Rogachev,V.A.Shugaev,I.Khomenco,A.Varma, Combust.Sci.Technol.1995, v.109, p.53