Compiled by A.G.Merzhanov
A.E.Sytschev
About Self-propagating High-temperature Synthesis (SHS)
Short information for the beginners: Self-propagating high-temperature synthesis (SHS) means the synthesis of compounds (or materials) in a wave of chemical reaction (combustion) that propagates over starting reactive mixture owing to layer-by-layer heat transfer. (See photonew window)


Quick Table of Contents

expand1. Starting Systems
expand2. Process and its Characterization
expand3. Products
expand4. SHS Research
expand5. Fundamentals of SHS
expand6. SHS Production Methods
expand7. Applications
expand8. History and State-of-Art
expand9. Useful References (reviews and monographs)
expand10. Glossarynew window
expand11. pdfInformation Brochure about SHS (26.2Mb)new window




Full Table of Contents

shrink1. Starting Systems
1.1. Starting Reagents and their Morphology
1.2. Chemical Classes of Reagents
shrink2. Process and its Characterization
2.1. Combustion in SHS processes (also termed solid flame or solid-flame combustion)
2.2. Initiation
2.3. Modes of Front Propagation
2.4. Combustion Thermograms
2.5. Front, Wave, and Post-Processes
2.6. Process Parameters
2.7. Chemical Classes of SHS Reactions
shrink3. Products
3.1. Morphology and Macroscopic Structure
3.2. Product Composition
3.3. Microstructure of Products
3.4. Chemical Classes of Products
shrink4. SHS Research
4.1. Three levels of experimental diagnostics
4.1.1.Level I: Phenomenology
4.1.2.Level II: Zone structure of the combustion wave
4.1.3.Level III: Mechanism and dynamics of phase/structure transformations behind the combustion front
4.2. Means of Control
shrink5. Fundamentals of SHS
5.1. Thermodynamics
5.2. Chemical Kinetics
5.3. Combustion Theory
5.4. Chemistry and Structural Macrokinetics
5.5. Physical Materials Science
shrink6. SHS Production Methods
6.1 Technological Types of SHS
shrink7. Applications
7.1. SHS Products
7.2. SHS-Based Production
7.3. Effectiveness
shrink8. History and State-of-Art
8.1. Discovery
8.2. SHS in the Former Soviet Union
8.3. SHS in the CIS countries
8.4. SHS all over the world
8.5. Most Important Accomplishments
8.6. Some Important Directions of Research
8.7. Symposia, Workshops, Seminars
shrink9. Useful References (reviews and monographs)
shrink10. Glossarynew window
10.1. General Aspects of Combustionnew window
10.2. Processesnew window
shrink11. pdfInformation Brochure about SHS (26.2Mb)new window




1. Starting Systems

1.1. Starting Reagents and their Morphology

SHS can be performed in fine powders, thin films, liquids, and gases. The most popular are
  • powder mixtures (loose or pelleted)
  • powder (pellet) gas systems
SHS can also be carried out in the
  • powderliquid systems
  • gas suspensions
  • layered systems
  • gas-gas systems
Starting sample morphology must favor chemical reaction.
Green mixture may burn in
  • vacuum
  • open air
  • inert or reactive gas.

1.2. Chemical Classes of Reagents

The elements, individual compounds, and their mixtures that are reactive at high temperatures can be used as reagents while inert compounds, as fillers or diluents.

The most popular reactants are given below:
H2, B, Al, C, N2, O2, Mg, Ti, Nb, Mo, Si, Ni, Fe, B2O3, TiO2, Cr2O3, MoO3, Fe2O3, NiO, etc.

Mineral raw materials and industrial waste can also be used as starting reagents.

SHS reagents must comply with the following requirements:

  • reaction must be exothermic
  • reaction must yield useful solid products
  • process must be technically and cost-effective




2. Process and its Characterization

2.1. Combustion in SHS processes (also termed solid flame or solidflame combustion)

For SHS systems, the most popular are the following modes of combustion:

2.2. Initiation

Reaction is normally initiated from the sample surface with a heat flux (heated wire, electric spark, laser beam, etc.). After initiation, reaction proceeds in the mode of self-propagation. The duration of heating is markedly shorter than the time of reaction (combustion).

In some cases (e.g., low-caloric reactions), reaction may be initiated by bulk heating in a furnace and carried out in the mode of thermal explosionnew window.

2.3. Modes of Combustion Front Propagation

In the simplest and most important case of steady propagationnew window (photoregistrogram of the steady combustionnew window), all of the wave points move at a constant and identical velocity. When the steadiness is upset, the system may undergo
  • planar autooscillations in the front velocity (pulsating combustionnew window)
  • localization of reaction in one or several hot spots that move along the spiral trajectory (spinning wavesnew window)
  • chaotic motion of numerous hot spots (chaotic solid flames)
In case of strong heat losses (small sample diameter, low adiabatic temperature), wave propagation is not sustained altogether.

2.4. Combustion Thermograms

Combustion thermogram gives evolution of temperature at a given point of charge during SHS. A simplest thermogramnew window has an irregular-bell shape. More complicated thermograms exhibit breakpoints, inflexions, and isothermic plateaus. In case of unsteady combustion, thermograms may exhibit temperature oscillations within an ascending portion of the curve.

2.5. Front, Wave, and Post-Processes

Besides heat release, chemical reaction in the combustion wave gives rise to a number of physicochemical processes. The combustion wave is extended and comprised of several zones:
  • heat-affected, or preflame, zone (also zone of heating)
  • reaction zone
  • zone of after-burning
  • zone of secondary (or post-) processes (cooling and structure formation in reaction products)
The combustion wave is a propagating zone of chemical reactions. The front is some imaginary surface that separates the heat-affected and reaction zones. Propagation of the combustion wave is the first stage of SHS. The secondary physicochemical transformations make the second stage of SHS.
SHS = combustion + structure formation

2.6. Process Parameters

The process of wave propagation is characterized by: Typical parameters of SHS
Burning velocity 0.120 cm/s
Combustion temperature 23003800 K
Heating rate 103106 K/s
Igniting fluence 10200 cal/(cm2 s)
Induction time for ignition 0.21.2 s
Ignition temperature 8001200 K
In view of this, SHS can be regarded as an extreme chemical process.

2.7. Chemical Classes of SHS Reactions

For SHS processes, the type of starting reagents is insignificant. Much more important is relation between the heat release in reaction, on one side, and such parameters as the mode of heat release/transfer, state of aggregation for reactants/products, kinetics of phase/structure transformations, etc., on the other.

Therefore, the chemistry of SHS is versatile. The most important examples are given below.

  • Synthesis from the elements Ti + C = TiC
    Ni + Al = NiAl
    3Si + 2N2 = Si3N4
    Zr + H2 = ZrH2
  • Redox reactions B2O3 +3Mg + N2 = 2BN + 3MgO
    B2O3 + TiO2 +5Mg = TiB2 + 5MgO
    MoO3 + B2O3 +4Al = MoB2 + 2Al2O3
    3TiO2 + C + 4Al = TiC + 2Al2O3
    2TiCl4 + 8Na + N2 = 2TiN + 8NaCl
  • Oxidation of metals with complex oxides 3Cu + 2BaO2 + 1/2Y2O3 + 0.5(1.5 - x)O2 = YBa2Cu3O7-x
    Nb + Li2O2 + 1/2Ni2O5 = 2LiNbO3
    8Fe + SrO + 2Fe2O3 + 6O2 = SrFe12O19
  • Synthesis from compounds PbO + WO3 = PbWO4
  • Reaction of the elements with decomposition products 2TiH2 + N2 = 2TiN + 2H2
    4Al + NaN3 + NH4Cl = 4AlN + NaCl + 2H2
  • Thermal decomposition 2BH3N2H4 = 2BN + N2 + 7H2




3. Products

3.1. Morphology and Macroscopic Structure

Solid SHS products may appear in the form of powders, particle conglomerates, foamsnew window, cakes, ingots, films, whiskers, fibersnew window, and crystals. The batch weight depends on charging and the type of process.

In case of premixed green mixtures, the macrostructure of product is normally uniform. For the solidgas systems, the product composition may be expected to vary over the sample cross section.

In some cases, the product macrostructure is intentionally made nonuniform, e.g., multilayer and functionally graded materialsnew window.

3.2. Product Composition

The chemical and phase composition of combustion product depends on green composition, extent of conversion, and cooling conditions.

Product contamination depends not only on the purity of starting reagents but also on the extent of self-purification during combustion. Products synthesized under optimized conditions exhibit low content of unreacted components and contaminants.

3.3. Microstructure of Products

SHS products normally have a polycrystalline structure with a grain size of 15 mm. SHS may also yield nanophase, amorphous or coarse-grained products. The grain size depends on the cooling rate and kinetics of crystallization and recrystllization.

The porosity of products ranges between zero (compact materials) and 9095% (foam materials).

3.4. Chemical Classes of Products

SHS is known to yield the following classes of compounds:




4. SHS Research

4.1. Three levels of experimental diagnostics

Level I: Phenomenology

Detecting a wave propagation mode (steady, pulsating, spinning) and measuring the following readily measurable parameters:
  • burning velocity and combustion temperature (for steady combustion)
  • mean burning velocity and pulsation frequency (for unsteady combustion)
  • mean burning velocity and hot spot velocity (for spinning combustion)
  • chemical and phase composition of end products.
Experimental techniques: motions pictures and video recording, thermometry, pyrometry, chemical analysis, XRD, metallography.

Level II: Zone structure of the combustion wave

Experimental techniques: thermography and time-resolved pyrometry. The obtained temperature profilesnew window shed light on the mechanism of physicochemical transformations in and structure of the combustion wave.

Level III: Mechanism and dynamics of phase/structure transformations behind the combustion front

Experimental techniques:
- time-resolved x-ray diffractionnew window. Example: time-resolved x-ray diffraction patterns for the Ni-Al systemnew window;
- quenchingnew window (arresting) the wave propagation.

4.2. Means of Control

Task objective:

controlling

  • burning velocity, combustion temperature, and extent of conversion
  • composition, structure, and properties of SHS products
Modes of control:
  • green parameters (charge composition, particle size, density, charge volume, initial temperature, type and amount of additives and fillers, etc.)
  • combustion conditions (composition and pressure of ambient gases, external influences)




5. Fundamentals of SHS

SHS is a science-intensive process. Its comprehension requires erudition in thermodynamics, chemical kinetics, general and structural macrokinetics, materials science, and other allied fields of knowledge.

5.1. Thermodynamics

For SHS reactions, thermochemical calculations can be performed either in a concise form for determining only the adiabatic combustion temperature or in the full form for determining both the combustion temperature and product composition.
- Thermodynamics for liquid-flame combustion in "hot" systems of a thermite typenew window
- Thermodynamic analysis for combustion in the Ta-C systemnew window
- Composition diagram for the TiO2-B2O3-Mg systemnew window

5.2. Chemical Kinetics

The kinetics of chemical reactions in SHS systems provides information about the rate of heat release at high temperatures. The latter is normally assessed from the dependence of the burning velocity on combustion temperature as well as from the thermograms of combustion or electrothermal explosion. For reactions of metal with gases, similar data can be assessed from electrothermographic measurements.

5.3. Combustion Theory

Wave propagation and wave structure are readily described in terms of the combustion theorynew window. The latter is based on joint analysis of the equations of heat conduction with nonlinear heat sources (heat release in chemical reaction) and chemical kinetics (ideal solid-flame combustion). Calculations may also take into account the processes of melting and capillary spreading (solid-flame combustion with a melting interlayer), infiltration of a gaseous reagent (infiltration combustion), various heat transfer processes (heterogeneous combustion), etc.

To date, infiltration combustion and have been theoretically analyzed in terms of not only the 1D but also 2Danimation and 3D models
- 3D equations of gasless combustionnew window
- 3D modeling: one-head spinning combustion (dynamics of temperature profile over the cylindrical surface)animation
- 3D modeling: two-head spinning combustion (dynamics of front structure)animation (related paper in PDF-format 347Kbpdf)

Mathematical modeling of SHS was also performed with regard to the constitution diagram.

5.4. Chemistry and Structural Macrokinetics

Investigated is the mechanism of chemical, phase, and structure transformations in SHS reactions by using the experimental techniques specified in Sect. 4.1.3. The routes of chemical reactions have been classified, and the limiting mechanisms of structure formation have been suggested.

5.5. Physical Materials Science

The methods of classical materials science were applied to characterization of SHS products. The effect of cooling rate on equilibrium (nonequilibrium) in SHS products is being investigated. For off-stoichiometric products, the extent of ordering and formation of hyperstructures are being investigated by neutron diffraction.




6. SHS Production Methods

6.1 Technological Types of SHS

SHS productionnew window has much in common with: preprocessing of raw materials/synthesis/product processing. Instead of furnaces and plasmotrons, SHS is performed in reactors.

Six technological types (TTs) of SHS are known:
TT-1new window Chemical synthesis
Preparation of cakes and their grinding to powders
- Industrial reactor SHS-30new window
- Powder of mixed titanium chromium carbidenew window
TT-2new window SHS Sintering
Sintering of preformed pellets
- SHS-produced nitride ceramicsnew window
- Vacuum furnace. Tubular filtrating unitsnew window
- Graded TiC filters prepared by thermal explosionnew window
- Filtrating elements. Assembled filtersnew window
- Graded TiC filtersnew window
TT-3new window Forced SHS Compaction
Consolidation of still hot combustion products by external influence
- Functionally graded materials (SHS FGM)new window
- Graded hard-alloy platesnew window
TT-4new window SHS Technology of High-Temperature Melts (SHS Metallurgy)
Processing the melted products of highly caloric reactions
- Protective coatings by SHS surfacingnew window
- Ceramic-lined steel pipenew window
- Items obtained by SHSnew window
- Inversion of phase separationnew window
TT-5 SHS Welding
SHS reaction in a gap between two items that are to be joined
TT-6 SHS with a Gaseous Mass-Transporting Agent
Deposition of thin coatings onto the surface of items placed into a green mixture

Worth mentioning is also in-line SHS production.




7. Applications

7.1. SHS Products

SHS products find their applicationnew window in mechanical engineering, metallurgy, chemical industry, electrical and electronic engineering, aerospace industry, building industry, etc. SHS products are also used in medicine
- SHS materials with shape memory for use in surgerynew window,
- SHS implantsnew window,

scientific instruments, space experiments
- First microgravity SHS experimentnew window (related paper (in russian)new window, this document in MS Word97 format, zip-compressed, 40Kbarchive),
- Formation of the combustion product in the NiONiAl systemnew window (related paper in PDF-format 489Kbpdf),
- "Contactless" SHS in spacenew window (related paper in PDF-format 467Kbpdf),
- Gasless SHS in Particle Clouds under Microgravity: Experiments Aboard the MIR Space Station,

etc.

7.2. SHS-Based Production

In the former Soviet Unionnew window, SHS was implemented for production of high-temperature heaters (Kirovakan), TiC powders and appropriate abrasive pastes (Baku, Poltava), nitrided ferroalloys (Izhevsk, Chusovaya), silicon nitride (b-phase) and titanium hydride powders (Makeevka; Transcarpathia), high-temperature insulators (Kuibyshev), lithium niobate (Dzerzhinsk), etc.

In Russia, there exist pilot-scale SHS production lines at ISMAN (Chernogolovka, Moscow), at MISISISMAN Research and Educational Center (Moscow), and at SHS Engineering Center (Samara).

In China, SHS is used to manufacture ceramic-lined steel pipesnew window for transportation of ores and coal.

In Japan and the USA, SHS products are reportedly being produced by some companies.

In Spain, a plantnew window for manufacturing silicon nitride (a-phase) and boron nitride powders is operating.

7.3. Effectivenessnew window

The cost-effectiveness of SHS is normally associated with (1) utilization of reaction heat instead of electric power, (2) high combustion temperature and burning velocity, (3) simplicity of facilities, and (4) high quality of products
- Sintering kinetics for Si3N4 powdersnew window,
- Heat-conducting AlN itemsnew window.

SHS is often a material-saving process. It can also be used for net-shape production of finished machine parts. A drawback is a limited range of inexpensive and accessible reagents that react with a sufficient heat release.




8. History and State-of-Art

8.1. Discovery

SHS naturally flew out of the discovery of the solid flame phenomenon. This discovery (officially named as "The Phenomenon of the Wave Localization of Solid-State Autoretarding Reactions"new window) was made (in 1967) by A.G. Merzhanov, I.P. Borovinskaya, and V.M. Shkiro at the Research Center of the USSR Academy of Sciences (Township of Chernogolovka, 30 miles north-east of Moscow).

The very first paper on self-propagating high-temperature synthesis can be seen here new window ( This document in MS Word97 format, zip-compressed, 16.1Kbarchive).

The discovery was made during a search for a model of the so-called gasless combustion (ironaluminum thermite with alumina added as ballast). Another line of this research was synthesis of copper and silver acetylenides that could be expected to burn with no gas evolution.

In the author's opinion, the precursors of SHS are the BeketovGoldschmidt out-of-furnace metallothermy and the SemenovZel'dovich combustion theory.

8.2. SHS in the Former Soviet Union

19671979 Unsupported research in Chernogolovka and then in Tomsk, Yerevan, Kiev, etc.

Basic results: fundamentals, methodology, and ideology of SHS research

19791992 State-supported research and development

Basic results:
- New buildings in Chernogolovka;
- Advisory Board on the Theory and Practice of SHS at the State Committee on Science and Technology;
- State-Governed Program on SHS R&D;
- Interdisciplinary Consortium TERMOSINTEZ affiliated at ISMAN

8.3. SHS in the CIS countries

After collapse of the Soviet Union and economical reforms, the following SHS centers has remained active (in the CIS countries):

8.4. SHS all over the World

1982 Initiation of SHS studies at the US Army Research Center and Lawrence Livermore National Laboratory
Impetus: Crider J.F., Self-propagating high-temperature synthesis: a Soviet method for producing ceramic materialsnew window, Ceram. Eng. Sci. Proc., 1982, vol. 3, nos. 9-10, pp. 519-528.

Initiation of SHS studies in Japan in the beginning of the 80s.

Since the 80s: "Self-propagation" of SHS R&D in Poland, Korea, China, Italy, Spain, France, India, etc. The highest place of advance is achieved in China.

To date, SHS publications have been submitted by researchers from 47 countries all over the world.

Most active in the field are the following institutions:

The worldwide spread of SHS research was prompted by regular (since 1991) International Symposia on SHS and publication (since 1992) of Int. J. SHS by Allerton Press, New York.

8.5. Most Important Accomplishments

  • Original experimental techniques
  • Investigation of combustion in the solidsolid, solidgas, and solidsolidgas systems
  • Theory of solidflame combustion (gasless, infiltration, etc.)
  • Fundamentals of thermal theory for unsteady combustion (autooscillations, spinning waves, etc.)
  • Ideology and methodology of structural macrokinetics
  • Thermodynamic database for SHS processes, pp "Thermo" p p p
  • Synthesis of numerous compounds and high-quality materials
  • New production methods for chemicals, powders, materials, and items; SHS welding and deposition of coatings
  • Applications of SHS products in technology and engineering

8.6. Some Important Directions of Research

  • Phase and structure transformations during SHS
  • Theory of multidimensional SHS modes
  • Mathematical modeling and optimization of concrete SHS processes
  • Synthesis of specialty powders (composite, nanophase, etc.)
  • Preparation and utilization of nonequilibrium materials
  • Mechanochemistry of SHS under the conditions of quasi-static and dynamic (shock) loading
  • In-line production methods (with utilization of evolved heat)
  • Net-shape production of machine parts with required service parameters
  • SHS production methods based on the gasgas and gassuspension systems
  • SHS in organic and elementorganic systems

8.7. Symposia-Workshops-Seminars

All-Union SHS Workshops and Seminars

  • June 512, 1975, Arzakan
  • October 1120, 1977, Arzakan
  • September 1928, 1979, Kirovokan
  • October 26 November 3, 1983, Dilizhan
  • September 1019, 1985, Agavnadzor
  • June 2130, 1988, Chernogolovka
  • June 1118, 1991, Makhachkala

Topical sessions of the Scientific Council of the USSR Academy of Sciences on the
Theory and Practice of Self-Propagating High-Temperature Synthesis

  • SHS processes for producing abrasive tools/May 1416, 1980, Zaporozh'e
  • SHS materials science/October 1315, 1980, Tashkent
  • Chemistry and technology of SHS powders/May 30 June 2, 1981, Baku
  • SHS as a method for producing instrumental materials/September 28 October 2, 1981, Borzhomy
  • Combustion in SHS mode/June 2225, 1982, Odessa
  • Application of SHS products and processes in mashin-building/June 2830, 1983, Kuybyshev
  • SHS metallurgy/May 2931, 1984, Kutaisy
  • Raw materials for SHS/October 46, 1988, Alma-Ata
  • Design of equipment for SHS/April 1920, 1989, Dnepropetrovsk

International Symposia on Self-Propagating High-Temperature Synthesis




9. Useful References (reviews and monographs)

book cover Alexander G. Merzhanov. Self-Propagating High-Temperature Synthesis: Twenty Years of Search and Findings. Chernogolovka: ISMAN, 1989, 91 pp.
book cover SHS-Bibliography (19671995). Int. Journal of SHS, vol. 5, N 4, 1996, 513 pp.
book cover Chemistry of Combustion Synthesis. Ed. M. Koizumi. Moscow: Mir Publ., 1998, 247 pp. (Russian translation).
book cover Combustion Synthesis. Ed. Yin Sheng, Beijing, 1998, 444 pp., (in Chinese).
book cover E.A. Levashov, A.S. Rogachev, V.I. Yukhvid, I.P. Borovinskaya. Physico-Chemical and Technological Foundations of Self-Propagation High-Temperature Synthesis. Moscow: Binom, 1999, 176 pp., (in Russian).
book cover A.G. Merzhanov. Combustion Processes and Materials Synthesis. Chernogolovka: ISMAN, 1998, 512 pp., (in Russian).
book cover Carbide, Nitride and Boride Materials Synthesis and Processing. Ed. Alan W.Weimer, LondonWeinheimNew YorkTokyoMelburneMadras: Chapman & Hall, 1997, 671 pp.
book cover Sharivker, S.Yu. and Merzhanov, A.G. SHS-Produced Powders and Their Processing, Borovinskaya, I.P., Ed., Chernogolovka: Izd. ISMAN, 2000, 123 pp., 21 tables, 30 figs., 273 refs.
book cover Merzhanov, A.G. Solid Flame Combustion (in Russian) Chernogolovka: Izd. ISMAN, 2000, pp. 224, 27 tables, 116 figs., 409 refs book announcement
book cover Self-Propagating High-Temperature Synthesis: Theory and Practice (in Russian). Ed. A.E.Sytschev, Chernogolovka, Territory, 2001, pp.432.book announcement
book cover Self-Propagating High-Temperature Synthesis of Materials, Edited by Anatoli A. Borisov, Luigi De Luca, and Alex Merzhanov Translated by Yury B. Scheck book announcement
book cover c - , Ed. A.G.Merzhanov, Chernogolovka, Territory, 2003, pp.368. Adobe Acrobat document (7.7Mb)
book cover Corbin, N.D., and McCauley, J.W., Self-Propagating High Temperature Synthesis (SHS): Current Status and Future Prospects, MTL MS 86-1, Watertown, MA, May 1986
book cover Frankhouser, W.L., Brendley, K.W., Kieszek, M.C., and Sullivan, S.T., Gasless Combustion Synthesis of Refractory Compounds, Noyes Publications, 1985
book cover Combustion and Plasma Synthesis of High Temperature Materials, Munir, Z.A., and Holt, J.B., Eds., VCH Publishers, 1990
book cover A.G. Merzhanov, A.S. Mukasyan, Tverdoplamennoe gorenie (Solid-Flame Combustion), Moscow: Torus Press, 2007, 336 pp.

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