Federal University of Sгo Carlos, Dept. of Materials, Via Washington Luiz, km 235, CEP 13565-905,Sгo Carlos, Spain-Brazil, E-mail: morelli@power.ufscar.br
 
 

¹ Department of Materials, Yunnan Polytechnic University

Kunming 650051,P.R.China, E-mail:Јєkyzhao@ynpu.edu.cn

² Department of Materials,Kunming University of Science and Technology, Kunming 650093,P.R.China

P-2-23: Chemical Stimulated Combustion in (Zr+SiO₂+C) System and Synthesis

of (Zro₂+SiC) Composite Powder Containing SiC Whiskers

In this work SHS process has been developed for the synthesis of (ZrO₂+SiC) composite powder containing SiC whiskers. Zr powder, silica and carbon black were used as the reactants. The addition of chemical activators was found necessary for self-propagation of reaction zone. The minimum content of fluorine containing activator - polytetrafluorethylene (FT-4) necessary for realization of combustion wave propagation is 0.3% mass. In this case the combustion temperature is equal 1500K. Maximum combustion temperature to be achieved at 3% mass. content of FT-4 is 2000K. The average rates of combustion are not high - 0.15-0.25 cm/s.

It was established that combustion wave propagates mainly non-stationary with oscillations. The parameters of combustion front oscillations and microstructural peculiarities of product caused by oscillations were determined. Addition of FT-4 was found not only make the combustion reaction possible but also to enable SiC whiskers to be formed. Thus, the additives used have bifunctional effect. On the other hand - the addition of gas-generated agents to initial mixture was found useful for increasing of SiC whiskers content in combustion products. The obtained materials are being currently characterized by SEM and EPMA microanalysis. Effects of various experimental parameters (ratio of initial reagents, content and type of additives, gas pressure, gas type etc.) on the combustion rate and temperature, phase composition and microstructure of product, as well as on SiC whiskers content in combustion products were investigated. The optimization of initial mixture and combustion parameters for synthesis of ZrO₂/SiC composite powder with maximum content of SiC whiskers were performed.

The work has been carried out under financial support of INTAS (Research Grant No.1613)

P-2-24: The Results of High-Speed High-Temperature Exothermic Reactions

Russia Academy of Science, Chernogolovka, 142 432 Russia
 
 

In ISMMS RAS an original method for research of high-speed high-temperature reactions in condensed systems, based on fast uniform bulk heating of sample by direct passing of an electrical current through it with a subsequent intensive selfheating, stipulated by an exothermic reaction, is developed.

The sample heating by an electrical current is executed up to a moment of an intensive chemical reaction begins, then by program the heating is interrupted, and the further growth of temperature is registered with high speed in seven points on a sample surface. The distinction of a behaviour of thermit mixes from quantity of atoms of a oxygen in oxide component of a mix under study is found out. The characteristic thermograms of processes and the dependence of heat release speed from temperature for researched systems are indicated.

The given results present exclusive interest as for the researchers of processes of burning, explosion and detonation in condensed systems, as for a wide range of applied problems.
 
 

P-2-25: Study on the Reaction Models of SHS in Al-TiO₂-C System

Zeng Songyan, Zhang Erlin, Yang Bo

P-2-26: Thermal Explosion in the Intermetallic Systems

The sample heated by an electrical furnace up to the point self-ignition. The sample temperature was registered with thermocouples Thermocouples were pressed into sampes at two end. Test channels of thermocouples is 1000 times per one second. In experiments varied composition, density, the heat rate of samples and was observed the dependence of kinetics on these parameters.

For system Cu-Al the sharp heat release begins at temperature of eutectic - 524єC. And for system Nb-Al thermal explosion occured at temperature 880єC, when low-melter reactant (Al) already melting (660єC).

Time-resolved X-rays difraction analysis (TRXD) of sinthesis of intermetallics we study. The main purpose of the work was to detirmine the sequence of phases transformation, i.e. destruction initial composition, formation of intermediate and final phases.

For system Nb-Al after melting aluminium, but before the basic exothermal reaction phase NbAl₃ is formed.

For composition 3Cu+Al at a stage of cooling we observed that the high-temperature phase Cu₃Al disintegrates on two phases - Al₄Cu₉ and solution a -Cu. The amount of the broken phase the is more, than below speed of cooling.
 
 

P-2-27: Thermal Explosion in B4C - Ti , BN - Ti and SiC-Ti Powder Blends in

Restrained Dies: Measurement of Kinetic Combustion

Parameters and Modeling

M.Shapiro¹, I.Gotman², V. Dudko¹

¹ Laboratory of Transport Processes in Porous Materials, Faculty of Mechanical

Engineering,

² Faculty of Materials Engineering, Technion - Israel Institute of Technology,

Haifa 32000, Israel
 
 

Kinetic parameters characterizing the combustion rate were measured in B4C-Ti, BN-Ti and SiC-Ti in porous and dense compacted blends and were used to identify and investigate the optimal thermal conditions for production of fully dense ceramic matrix composites. Towards this goal heat transfer and combustion in compacted blends were investigated during monotonous heating at a constant rate. This process is modeled using an one dimensional heat transfer-combustion model with kinetic parameters determined from the differential thermal analysis of the experimental data.

The kinetic burning parameters and the model developed are further used to describe synthesis of in situ composites via the thermal explosion mode of SHS in a restrained die under pressure. It is shown that heat removal from the reaction zone affects the combustion process and the final phase composition.

It was shown that the SiC -Ti blends have characteristic combustion constants which are about ten times larger and time to explosion shorter than their BN-Ti powder blends. Accordingly the former have lower minimal explosion temperature, as per the model predictions. In all cases the residence time before explosion was found to be below 45 seconds in accordance with the measurement data collected from the resrained dies.
 
 

P-2-28: Estimation of Carbon-Containing SHS-Systems Reactivity by Using

Electrothermal Explosion

K.V.Popov, V.T.Popov, V.A.Veretennikov

References:

1.Veretennikov V.A., Popov V.T., Popov K.V. A procedure for selecting reactive gasless carbon-containing detonable systems. Fiz. Goreniya Vzryva, in press.

2.Knyazik V.A., Denisenko A.E., Chernomorskaya E.A., Steinberg A.S. Automated setup for kinetyc investigating of SHS reactions. Prib. Tekh. Eksp. 1991, N 4, p.164–167.

3.Tyurkin Yu.V., Zenin A.A., Korolev Yu.M., Popov V.T. The effect of carbon strukture on rection between carbon and metals under nonisothermal conditions. VIII All-Union symp. on combustion and explosion, Chernogolovka, 1986, p. 18-22.

P-2-29: Self-Propagating High-Temperature Synthesis (SHS) of Silicon

¹ NASA Center of Applied Radiation Research Prairie View A&M University

Prairie View, TX 77446, USA. E-mail: sclin@uh.edu

² Bell Helicopter Textron Inc.Fort Worth, TX 76101, USA

³ Chemical Engineering Department University of Houston, Houston, TX 77204, USA
 
 

Silicon carbide-Silicon Nitride micro-composite materials may be used as high temperature structural ceramics due to their superior mechanical properties and chemical stability at high temperatures. We synthesized these micro-composite materials via high-pressure Self-propagating High-temperature Synthesis (SHS). The impact of the standard SHS variables on the product quality was investigated using pellets with different diameters and densities, and various nitrogen pressures. The local stoichiometry, phases and microstructure of the product were determined by EMPA, XRD and SEM, respectively. The thermal behavior of the reactants at high temperatures was determined by TG/DTA. The reaction network and kinetics were deduced from the temperature history during the combustion. The mechanical properties of consolidated SHS powders, such as hardness, fracture toughness, compressive yield strength, modules of elasticity, Poison's ratio, and density were measured.
 
 

P-2-30: Combustion Synthesis of TiO₂-Al-C System Modulated by Nanometric

Particles

² Institute of Iron and Steel, Kunming Iron and Steel Co., Kunming 650302

³ University of Science and Technology Beijing, Beijing 100083, China
 
 

Self-propagating High-temperature Synthesis (SHS) is a typical non-equilibrium process with instantaneously high temperature and very short duration. It is very hard to control or modulate the process for obtaining high quality products.

In the present work, we attempt to modulate the combustion kinetic process and the formation of microstructure of combustion products by means of addition of special nanometric ceramic particles in the raw materials. Nanometric ZrO₂ powders are selected as the modulation agent. TiC-Al₂O₃-ZrO₂ composite powder was synthesized by SHS process. The thermodynamics and kinetics of combustion synthesis of TiO₂-Al-C-ZrO_2(n) system are studied. It is found that the addition of tetragonal ZrO₂ nanometric particles has a strong impact on the combustion behaviour of TiO₂-Al-C system. With the increasing amount of ZrO₂ additive up to10wtЈҐ, the combustion temperature of TiO_{2-Al-C-ZrO2 system keeps constant which is the melting point of Al2O3, and then decreases with the higher ZrO2 amount. The combustion rate of the system increases with the increasing content of ZrO2} up to 7.5wtЈҐ, and then decreases with the higher ZrO_{2 content. The combustion products of TiO2-Al-C-ZrO2(n) system are mainly TiC, Al2O3. The addition of nanometric ZrO2 particles can help to restrain the growth of Al2O3 grains, and therefore eliminate the particle size of Al2O3 and improve the homogeneity of the composite. This work is of great significance for the manufacture of tough composite ceramics.}
 
 

P-2-31: The Effect of Nanometric SiC Particles on the Combustion Synthesis

of TiO₂-Al-C System

Tang Qing¹, Zhang Dengjun¹, Li Fan¹, Zhu Zhenqi², Li Wenchao², Wang Fuming²

¹ Institute of Chemical Metallurgy, CAS, Beijing 100080, P.R.China,

² University of Science and Technology Beijing, Beijing 100083, P.R.China
 
 

Self-propagating high-temperature synthesis (SHS) or combustion synthesis is a recently developed technology for producing high-performance materials.

In the present paper, the effect of SiC nanometric additive on the thermodynamics and kinetics parameters of combustion synthesis process and microstructure of the products are studied. In the view of thermodynamics, possible products are analyzed and the adiabatic temperature T_ad is calculated . The effect of SiC nanometric particles on the combustion rate v and the mass combustion rate M_t is also analyzed.

Theoretical analysis shows that SiC may take part in the reaction and finally convert into Si and titanium silicide . By ignoring the side reactions, when the content of SiC is in the range of 0.8~ 4.8wt.% , the adiabatic temperature T_ad keeps constant at 2323K which is the melting point of Al₂O₃. When the content of SiC is more than 4.8wt.% , the adiabatic temperature T_ad falls continuously.

XRD and SEM assisted with EDS analysis show that when the content of SiC is lower than 10wt%, no SiC but titanium silicide such as TiSi₂ is found. The combustion temperature T_c approximately keeps constant, and the combustion rate v and the mass combustion rate M_t decrease with the increasing amount of SiC .
 
 

P-2-32: Use of SHS Reactions in Refractory Alloy Fabrication

P-2-33: Evolution of Microstructures in Thermal Explosion of

Equiatomic Ni-Al Mixture

A.Biswas¹, S.K.Roy¹, J.B.Singh¹, K.R.Gurumurthy², S.Banerjee¹

¹Materials Science Division

²Atomic Fuels Division Bhabha Atomic Research Centre Mumbai 00085 India, E-mail : abiswas@apsara.barc.ernet.in

Synthesis of B2 NiAl was studied in thermal explosion mode using three different nickel particle sizes and a constant aluminium particle size at varying heating rates, both under vacuum and in argon atmosphere. Finest nickel always led to complete conversion to B2 NiAl, whereas coarse nickel particles gave rise to multiple phase porous product. Detailed microstructural analysis was carried out using SEM, TEM and EPMA which yielded valuable insight into the possible mechanism of synthesis.
 
 

P-2-34: Features of Synthesis Silicides and Carbides of

Transition Metals From Oxides in the Oxygen Reactor

V.A.Grygorian, A.V.Pavlov, A.E.Semin

Moscow Steel and Alloys Institute, Leninsky prospect,4,Moscow 117936, Russia

The synthesis of junctions of transition metals with carbon and silicon at use as initial substances of metals oxides, silicon oxide and carbon is strongly endothermic process. In the oxygen reactor the obtaining of a part of necessary heat is realised by oxidation of carbon of a charge by gaseous oxygen inside a stratum of a charge. The post-combustion of carbon oxide up to carbon dioxide is realised in under arch space of the reactor by oxygen give atop of a level of solid charge. It ensures the process with all necessary amount of heat. Through a hole in arch of the reactor filling of a blend from lump carbon fuel and ore-coal briquettes consisting from compact mixture of dispersible oxides and carbons powder. In zone of maximum heat release on a surface solid carbon checker there is a fast heating of initial materials and formation of condensed target products of synthesis (liquid carbides or silicides) and accessory products (slag). Metal and slag are filtered through a layer of carbon checker and accumulate on hearth of the reactor, he periodic release of products of the process whence is made.

In laboratory conditions are carried out synthesis of mutual solutions of technical carbides of iron, manganese, chromium, nickel, vanadium (carbon ferroalloys), complicated silicides of iron, nickel, chromium (ferrosilicon, ferrochrome silicon, nickelsilicon, nickelchrome silicon) with use of an electrical heating reactionary volume up to 1000 iN for compensation heat lost. On the pilot oxygen reactor with a minor diameter of 400 mm are smelted without use of additional power sources carbon ferr nickel, ferrochrome and steelmaking pig iron. The given process is new and has not analogues in production of pig iron and ferroalloys. The special attractiveness to it attach that circumstance, that under it such classical metallurgical aggregates as the blast furnace, blast cupola or open-hearth furnace can be rather simply converted. The test of the process on an aggregate of an industrial scale with a minor diameter of 1200 mm has confirmed functionality of the process and its large economic efficiency.
 
 
 
 

P-2-35: Combustion Synthesis of the Silicides of Chromium, Tantalum,

Vanadium, and Zirconium

F. Maglia¹, N. Bertolino^1,2, U. Anselmi-Tamburini¹, Z. A. Munir²

¹ Department of Physical Chemistry and C.S.T.E./CNR, University of Pavia,

V.le Taramelli, 16, 27100 Pavia, Italy

² Department of Chemical Engineering and Materials Science,

University of California, Davis, CA 95616-5294, USA
 
 

Silicides have received a great deal of attention during the past two decades due to their technologically attractive properties [1]. The combustion synthesis of several silicides has been investigated and the results reported in the literature [2-7]. In few cases, some aspects of the microscopic reaction mechanism have been clarified. More recently details on the reaction mechanism have been obtained using time resolved X-ray diffraction technique and particle-foil experiments [8-10]. The role of pre-combustion solid-state reactions in determining the reaction path has been investigated by Trambukis and Munir [11].

In this work we present a contribution to the study of the combustion synthesis of silicides through an investigation of the following systems: Cr-Si, Ta-Si, V-Si and Zr-Si. Little information is available in the literature regarding the formation of these silicides through combustion synthesis. The synthesis of the silicides was investigated using different approaches, including SHS, volume combustion experiments, solid-liquid interaction. Diffusion couples experiments were also used to investigate the lower temperature interactions.

When the reaction enthalpy was low for the reaction to be initiated and/or sustained, as for some Cr, V, and Ta silicides, the field-activated combustion synthesis (FACS) method [12-15] was used. The melting of Si has been identified as the triggering step for all the combustion processes. Once initiated the reactions proceed through solid-liquid or liquid-liquid interactions depending on the system and on the starting composition. The phase formation sequence was shown to be controlled by kinetic parameters rather then thermodynamic considerations.

The role of the applied field in the combustion parameters and its effect on the product phase formation have also been investigated.
 
 

1. Murarka, S.P. Silicides for VLSI Application, Academic Press, New York, 1993.,p. 200.

2. Itin, V.I., Naiborodenko, Y.S., Bratchikov, A.D., Butkevich, N.P., Korostelev, S.V., and Sholokova, L.V., Sov. Phys. J. (Engl. Transl.),1976, v. 3, p. 408-409

3. Sarkisyan, A.R., Dolukhanyan, S.K., Borovinskaya, I.P., and Merzhanov, A.G., Comb. Expl. Shock Waves (Engl. Transl.) , 1978, v.14, p. 310.

4. Zhang, S., and Munir, Z.A., J. Mater. Sci., 1991, v.26 , p. 3685-88

5. Bhaduri, S.B., Radhakrishnan, R., and Quian, Z.B., Scripta Metall. et Mater., 1993, v.29,

6. Subrahmanyam, J., J. Mater. Res.,1994, v. 9, p. 2620-26

7. Deevi, S.C., Mater. Sci Eng., 1992, A149, p. 241-51.

8. Kachelmyer, C.R., Khomenko, I., Rogachev, A.S., and Varma, A., J. Mater. Res., 1997, v. 21,

9. Rogachev, A.S. Shugaev, V.A., Khomenko, I., Varma, A., and Kachelmyer, C.R., Combust. Sci. Technol.,1995, v. 109, p. 53

10. Varma, A., Kachelmyer, C.R., and Rogachev, A.S., Int. J. SHS, 1996, N 5

11. Trambukis, J., and Munir, Z.A., J. Am. Ceram. Soc, 1990, v. 73, p. 1240

12. Feng, A., and Munir, Z.A., J. .Appl. Phys., 1994, v.76, p. 1927

13. Gedevanishvili, S., and Munir, Z.A., Mater. Sci. Eng., 1996, A211 , 1-9

14. Gedevanishvili, S., and Munir, Z.A., J. Mater. Res., 1995, v.10, p. 2642

15. Shon, I.J., Munir, Z.A., Yamazaki, K., Shoda, K., J. Am. Ceram. Soc., 1996, v.79, p. 1875

P-2-36: Zirconia-Based Metastable Solid Solutions through SHS:

Synthesis Characterization and Mechanistic Investigations

In the present work we report on the self-propagating high-temperature synthesis of cubic Zr_1-xMe_xO_y (Me = Fe, Co, Ni, Cu) metastable solid solutions with metal contents significantly higher than equilibrium levels. Thermite reactions between metallic zirconium and the transition metal oxides CoO, Fe₂O₃, CuO, and NiO have been used because of their high DH_r values. For the case of iron, a metal content, i.e., x of up to 9 mol% was obtained. Copper and nickel showed a much lower tendency for the formation of metastable solid solutions. Both reaction temperature and cooling rate play a controlling role in product formation. Monophasic products were obtained when the highest synthesis temperature is coupled with rapid quenching of the products.

The stability and mechanism of formation of metastable solid solutions of cubic zirconia with transition metals were also investigated. The zirconia-based solid solutions obtained through SHS are metastable in nature. Heating to temperatures above 800° C causes a partial or total decomposition. The product of such decomposition is a mixture of monoclinic zirconia plus the transition metal oxide. The detailed mechanism of this decomposition has been investigated by in situ XRD analysis.

Several possible mechanisms for the formation of the metastable cubic solid solution during the SHS process were considered and investigated. Results of auxiliary experiments strongly suggest that the formation of the solid solution takes place behind the combustion front by a reaction between zirconia and the metal.
 
 

Referenses:

1. Stevens, R.An Introduction to Zirconia;Twickenham, England,Magnesium Elektron Ltd.:1983;

p. 1-22

2. A.D. Neuimin, A.G. Kotlyar, S.F. Pal’guev, V.N. Strekalovskii, and N.A. Batrakov, “Structures and Electrical Conductivity and its Nature in the Zirconium Dioxide-Vanadium Sesquioxide System with Additives of Iron, Manganese, Cobalt, and Nickel Oxides," Tr. Inst. Elektrokhim. Ural. Fil. Akad. Nauk SSSR, 1969, v.12, p. 92-113

3. H. J. Stocker, “The Properties of Zirconia-Based Solid Refractory Solutions and the Stabilization of Cubic Zirconia,” Ann. Chim., 1960, v.5, p. 1459-503

4. I. B. Inwang, F. Chyad, and I. J. McColm, “Crystallization of Iron (III) Zirconia Co-gels,” J. Mater. Chem., 1995, v.5, N 8, p. 1209-13

5. P. Li, I.-W. Chen, and J. E. Penner-Hahn, “Effects of Dopants on Zirconia Stabilization – an X-Ray Absorption Study: I, Trivalent Dopants,” J. Amer. Ceram. Soc., 1994, v.77, N 1, p. 118-28.

6. P. Li, I.-W. Chen, and J. E. Penner-Hahn, “Effects of Dopants on Zirconia Stabilization – an X-Ray Absorption Study: II, Tetravalent Dopants,” J. Amer. Ceram. Soc., 1994, v.77, N 5, p. 1281-88.

7. P. Li, I.-W. Chen, J. E. Penner-Hahn, J. Amer. Ceram. Soc., 1994, v.77, N 5, p. 1289-95.

P-2-37: SHS Ferrites: Technology, Production, Efficiency

A number of technological approaches developed to manufacture high-quality ferrite powders and items as well as techniques for SHS products disintegration into powders are described. Influence of treatment conditions (sintering) on structure formation and functional characteristics of items were studied. SHS ferrite items were proved to meet all the requirements of modern industry.

Some results of developing high-efficiency production method of industrial scale and absolutely unique (no analogs in the world) equipment for ferrites manufacturing are presented.

Taking into consideration high consumption of ferrites in the world (more than 150000 t/year), comparative analysis of SHS and furnace production methods is performed.
 
 

P-2-38: Formation of Composition and Structure in Shs of Carbide-Aluminide

Systems

The main attention was given to influence of ratio of carbides and metal binder in combustion products and so nickel and aluminum in the metal binder on particulars of chemical and phase composition of composite materials and its structures and microstructure.

The influence of the scale factor on sputtering process, completeness of phase separation and extraction of target elements from a mixture was studied. The uniformity degree of distribution of elements in an ingot, change macro and microstructure in horizontal and vertical section of an ingot was investigated.