Combustion synthesis

156

Combustion

synthesis

Kashinath C Patil*, Singanahally Many

innovative

(SHS)

self-propagating

techniques

centrifugal

thermite

solid-state

metathesis,

and densification ‘advanced process particle

process,

combustion,

field activated

synthesis the

combustion,

flame synthesis

and simultaneous

have been developed

for the synthesis

materials’. initiated

and mixtures

high-temperature

such as filtration

A novel

gas

producing

at low temperature

has been used

T Aruna and Sambandan

SHS of

self-propagating

using redox compounds

for the

preparation

of fine

oxides.

Addresses Department of Inorganic and Physical Science, Bangalore012, India *e-mail: [email protected] Current 2:156-l

Opinion 65

in Solid

Electronic

identifier:

0 Current

Chemistry

State

Chemistry,

& Materials

Indian institute

Science

of

1359-0266

Abbreviations CH CTPB DFH HC MS ODH SHS SSM T TEA

carbohydrazide carboxy terminated polybutadiene diformyl hydrazine hydrocarbon mass spectroscopy oxalyl dihydrazide self-propagating high-temperature solid-state metathesis adiabatic temperature tetraformal trisazine

number of technologically useful oxide (refractory oxides, magnetic, dielectric, semiconducting, insulators, catalysts, sensors, phosphors etc.) and nonoxide (carbides, borides, silicides, nitrides etc.) materials. To date more than 500 materials have been synthesized by this process, many of which are commercially manufactured in Russia. In recent years, there has been tremendous interest in the combustion synthesis of materials because it is simple, fast, energetically economic and yields high purity products compared to the conventional routes used to prepare these materials. As it is a high-temperature process, only thermodynamically stable phases can be prepared. At the same time, rapid heating and cooling rates provide the potential for the production of metastable materials with new and unique properties.

1997,

1359-0266-002-00156 Ltd ISSN

Ekambaram

synthesis

A number of review articles [2”,3”,4-61 on the combustion synthesis of oxides and nonoxides have been published during the last decade. Merzhanov, one of the pioneers of SHS has periodically reviewed [4,5] the developments in SHS and its applications. His recent article [4] discusses the theory and practice of SHS world-wide along with new directions in the field. A quarterly journal, ‘International Journal of Self-Propagating High-Temperature Synthesis’ devoted to SHS has been published by Allerton Press Inc; New York, since 1992 with Alexander G Merzhanov as the ‘General Editor’. Three International Symposia on SHS have been held, in 1991 (Alma-Ata, Kazakhstan), 1993 (Honolulu, USA) and 1995 (Wuhan, China) and the fourth one is being planned in Spain during October 6-10, 1997.

Introduction The synthesis of solids possessing desired structures, composition and properties continues to be a challenge to chemists, material scientists and engineers. Formation of solids by the ceramic method is controlled by the diffusion of atoms and ionic species through reactants and products and thus requires repeated grinding, pelletizing and calcination of reactants (oxides or carbonates) for longer durations (than soft chemical routes) at high-temperatures. Attempts have recently been made to eliminate the diffusion control problems of solid synthesis by using various innovative synthetic strategies [l]. One such approach is ‘combustion synthesis’ also known as ‘self-propagating high-temperature synthesis’ (SHS) and fire or furnaceless synthesis. The process makes use of highly exothermic redox chemical reactions between metals and nonmetals, the metathetical (exchange) reaction between reactive compounds or reactions involves redox compounds/mixtures. The term ‘combustion’ covers flaming (gas-phase), smouldering (heterogeneous) as well as explosive reactions. The combustion method has been successfully used in the preparation of a large

A two part review [2**,3**] on combustion synthesis of advanced materials by Moore and Feng gives an account of the historical perspectives of SHS; parameters that control the SHS process; and materials that have been prepared and their applications. Various types of SHS reaction and proposed models of reaction are discussed, the thermodynamics and kinetics of SHS reactions are also presented. Important parameters that control combustion synthesis such as the particle size and shape of the reactants, ignition techniques, stoichiometric ratio, processing of reactant particles (green density, i.e. the density of the pellet before sintering) and the adiabatic temperature (Tad) which is a measure of the exothermicity of the reaction, have been discussed in detail [2”,3”,4-61. For this reason no attempt is made here to elaborate on these points. In this article, the recent trends in the SHS, thermite, solid-state metathesis (SSM) and flame syntheses, used in the preparation of inorganic materials will be discussed. The latter part of the article is devoted to the combustion synthesis of oxide materials using redox compounds and mixtures.

Combustion synthesis Patil,

Materials prepared by SHS and related processes

3Fe304

Synthesis of refractory materials: borides, carbides, nitrides, silicides, ceramics, intermetallics, composites and oxide materials continues to be the main thrust of SHS processes. These materials can be prepared by igniting the pellets of respective metals and nonmetals with a suitable heat source. Once ignited, the combustion reaction is self-propagating with an adiabatic temperature (Tad) in the range 1500-3000K. The general chemical equation for the elemental tion reaction can be represented by: mX + nY + X,Y,

combus-

(1)

where X=Ti, Zr, Hf, V, Ta, B, Be, Si act as fuels (metals) and Y = B, C, N, S, Si, Se act as oxidizers (nonmetals). The high ignition temperature (21500°C) required, can be attained by laser radiation, a resistance heating coil, an electric arc, a chemical oven and so on. Innovations in SHS processes are aimed at lowering the ignition temperature and using metal oxides/halides instead of finely divided metal powders.

+ 8Al+

AH&

Aruna and Ekambaram

4A1203 + 9Fe

159

(2)

= -3400 KJmol-’

A modified thermite reaction called a ‘centrifugal thermite reaction’ has been used for coating the inner surface of steel pipes. By coupling SHS with a centrifugal process a surface layer of alumina and an inner layer of Fe is formed in the pipe due to the difference in density between Fe and alumina. The composite pipe will have the strength and toughness of a metal and corrosion and abrasion resistance of a ceramic. Orru et a/. [12] have studied the influence of some of the processing parameters, such as the mass ratio of thermite mixture to substrate pipe and the presence of diluents on the final product distribution, to gain an insight into the mechanism of the centrifugal thermite process. The experimental and modelling studies of product separation during the synthesis of Fe-A1203 materials in a field of centrifugal forces has been investigated [13].

The second type of thermite process involves the reduction of an oxide to the element which subsequently reacts with another element to form a refractory compound. TiOz

+ Bz03

+ 5Mg+

TiBz

+ 5MgO

(3)

To lower the ignition temperature: mechanical activation and field activation processes are used. Mechanical alloying has been successfully used to synthesize Tic, NbC and their solid solutions using Ti, Nb and graphite powders [7]. The alloying was carried out by using steel balls and vials in a SPEX-8000 mixer. Using ball milling it was possible to ignite Ti, Zr, Hf metal powders with C, B, Si or S. Some oxides of Cu, Ni, Fe and Zn were also reduced with Ti, Zr and Hf by ball milling [8*]. A TG-DTA-MS study of self-ignition in SHS of mechanically activated Al-C powder mixtures showed that the disordered C served as the ignition source for the SHS reaction [9]. Field activated (ZOV) combustion synthesis has been used by Munir and co-workers to activate low enthalpy of formation (AHf) (e.g. SIC, B&, WC, WSi2 etc.) reactions. Using this method intermetallics, ceramics and composites (e.g. MoSiz-xNb and MoSiz_yZrOz) have been prepared [lo]. A recent study [ 1 l] on the relationship between the field direction and wave propagation in activated combustion synthesis showed that the field applied in a direction perpendicular to wave propagation resulted in an enhancement of the wave velocity (which helps in the completion of the reaction and results in a decrease in the particle size of the product).

Composites such as MgO-B& [ 141 have been prepared by coupling a highly exothermic Mg-Bz03 thermite reaction with a weakly exothermic B&Z formation reaction. The reaction mechanism of the alumino-thermite reaction in the formation of MoSiz-A1203 has been investigated using DTA and XRD [15]. The effect of reaction parameters such as reactant particle size, use of diluent, and use of reactant preheating during the aluminothermite reduction of TiOz to Tic have been discussed [16]. The structural transformations that take place in all stages of aluminochermic SHS have been studied by performing synthesis under gas pressure, in the field of centrifugal forces, by quenching and so on [ 171. One dimensional mathematical modelling has been used to describe the SHS process for the preparation of TiA13 and NiA13 intermetallics [ 181. Titanium-aluminium-carbon ternary composites with dispersed fine TIC particles having excellent elevated temperature strength compared with that of TiAl intermetallic compounds have been reported [19]. These methods are of great importance in the synthesis of advanced ceramic and composite materials on account of the economic advantages in using cheaper oxide reactants compared with expensive elemental reactants.

Thermite reactions which involve metallo-thermic reduction have been employed in the ceramic coating of pipes as well as in the preparation of composites. There are two types of thermite reactions. The first method involves the reduction of an oxide to the element, for example:

Recently Merzhanov and his associates [20*] have reported the synthesis of electronic engineering materials such as superconductors, ferroelectric and magnetic materials by an SHS reaction using metal oxide and peroxide precursors.

160

Synthesis and reactivity of solids

3Cu The with

+ 2BaOz

+ 1/2YzO3 + YBa2Cu307_x(Y123)

(4)

properties of SHS derived products are compared those prepared by the furnace method. The advan-

tages of SHS process are time and energy increas in the reactivity of the products.

savings

and an

As all the SHS processes yield porous materials, newer techniques combining SHS and densification are being developed to produce dense materials free of pores. Using simultaneous densification and field activated combustion synthesis, hloSi2 with 99.2% theoretical density has been obtained [Zl]. Simultaneous SHS and subsequent densification by an impact forging technique of a TiBz-SiC composite resulted in a density in excess of 96% which is the theoretical value [Z]. Symmetric compositionally gradient materials of the Al20$TiC/Ni/TiC/Al203 and Al203/Cr$Z /Ni/Cr&/AlZOj systems were fabricated by SHS/HIP (hot isostatic pressing) compaction. These materials exhibited outstanding properties such as toughness, hardness and strength compared to conventional alumina ceramics [23]. The density of composite materials can be further improved by deliberately generating an excess of liquid metal in situ with the combustion reaction which infiltrates the pores in the ceramic matrix (e.g. Tic-AIZ03) [3”]. A two dimensional mathematical model of filtration combustion which takes into account the dynamics of changes in the gas temperature and pressure in a SHS reactor, has been proposed [24]. Other applications of SHS are in the field of functionally gradient materials (FGhl’s) (e.g. Ti-C-Ni) which have better mechanical properties and corrosion resistance to oxidation than metals and composites [25].

Materials (SSM)

prepared by solid-state

metathesis

Recently Kaner and his associates have reported [26’,27’] the synthesis of a variety of materials by ‘solid-state metathesis (exchange)’ reactions. Unlike the SHS reactions (elemental or thermite reactions) which employ metals, nonmetals and oxides, this method involves rapid, low temperature initiated solid-state exchange reactions between reactive metal halides with alkali metal main group compounds. The exothermicity of the reaction reaches nearly 1050°C within =300ms. A generalized reaction scheme is hlX,

+ mAY,

ignite + hlY,

+ mAX

Where hl= metal, X= halide, Y = nonmetal or metalloid.

+ [(m.n) -211

A=alkali

metal

(5) and

the precursors changes phase or decomposes enabling increased surface contact. A number of technologically important materials for example, superconductors (NbN, ZrN), semiconductors (GaAs, InSb), insulators (BN, ZrOZ), magnetic materials (GdP, SmAs), chalcogenides (hloS2, NiSz), intermetallics (MoSi2, WSiz), pnictides(ZrP, NbAs), and oxides (Cr203) have been prepared by an SSM reaction. Formation of high-temperature cubic/tetragonal 202 and B-MoSiz is reported by this process. Two possible reaction pathways proposed are (i) Elemental:

hlX3

+ AxY +

hlo

+ Y” + 3AX + hlY

(6)

(ii) Ionic:

hlX3

+ AjY +

M3+

+ y”-

+ 3AX +

h,lY + 3AX

(7)

A serious limitation of this process is the requirement of anhydrous halides which require handling in dry box and storage in presence of inert atmosphere.

Materials

prepared by flame synthesis

Flame synthesis differs from the typical SHS process in that all reactions take place in the gas-phase and form fine powders (often nanoscale as in carbon soot from HC flames, fumed silica, titania etc.). The possible advantages of this process over normal solid/solid, solid/liquid, SHS processes are its continuous rather than batch process of the latter and the higher purities of the products. hlany high purity materials can be synthesized by self-sustaining gas-phase reactions. It is well known that metal halides react spontaneously when their vapours are brought into contact with gaseous or liquid reactive metals such as sodium or magnesium [28]. Sic&)

+ 4Na(g) (Tad

NbC15(R)

+

Si(l) + 4NaCI(r,)

+ Nb(l)

(Tad

+ 512hIg:Clz(g,

(9)

= ZSOOK)

Similarly oxidation and hydrolysis (flame SiCIA, TiCI3 yield fine particle oxides. SiCIJ

(8)

= 24OOK)

+ S/ZhIg(,)

+ 02 +

SiC1.l + 2HzO The SShl reactions can be initiated either by simply mixing/grinding or by a hot filament. Once the SShl reaction is initiated, it becomes rapidly self-sustaining and can reach high temperatures (>lOOO”C) within a short period (~2s). Initiation generally occurs when one of

+ 3AX

+

SiOz(,) SiOz(,)

+

hydrolysis)

ZC12(g)

+ 4HCI(,)

of

(10) (11)

Such gas-phase combustion or flame synthesis has been used to prepare fine particle metal nitrides (Si$KJ), carbides (Sic, BdC, TaC), borides (TiB2, ZrBz), silicides (TiSiz), photovoltaic silicon, advanced fuels (B) and

Combustion synthesis

refractory metals (Ti, Ta, Zr, Hf, and Nb). Nanosize silica, titania, alumina and tialite (Al~Ti05) have been prepared by flame synthesis using the corresponding metal halides and Hz/air or HC/air flames (Rajan TSK, personal communication). Some typical gas-phase reactions are as follows: Sic14 + CzH4 + 302 -+ SiOz(l) + ‘2C0~)

+ 4HCl

(12)

(Tad = 1543K) Tic14 + QH4

+ 302 + TiOz(,)

+ ZCOZ(~) + 4HC1

(13)

(Tad = 1523K) 4AlX3 + 6Hz

+ 302 + ZAl2O3(,) + lZHX(,)

(14)

(Tad = 1393K) High surface area SiO2 having nanosize particles are prepared by the addition of ferrocene to Sic14 [29]. Nanoparticle TiB2 (unagglomerated) has been obtained by the addition of NaCl [30]. Flame synthesis has also been used to prepare nanosize Sic [31], TiB2 [30] and fullerenes [32]. Diamond films which were produced using acetylene earlier, have now been made using two inexpensive fuels: MAPP (a mixture of methyl acetylene, propadiene,and propylene) [33].

Combustion synthesis of oxide materials using redox compounds and mixtures An entirely different approach to the synthesis of simple and complex oxide materials is presented. This approach involves the use of novel combustible precursors (redox compounds) and redox mixtures. It uses low temperature (<5OO’C) initiated gas-producing exothermic reactions which are self-propagating and yield voluminous fine particle oxides in few minutes. Compounds like (NH&$2207 which contain both oxidizing (CrzO& and reducing (NH4+) groups when properly ignited (using KClOx-sucrose-H2S04) decompose autocatalytically to yield voluminous green Cr203 (artificial volcano) [34]. (NH4)2Cr207(s)

2 Cr203(,)

+ N21p) + 4H20(,)

(15)

The exothermicity of the combustion reaction is due to the oxidation of NH4+ to N2 and Hz0 by the dichromate ion which itself is reduced to Cr3+. The combustion is smbuldering type (flameless) and is accompanied by the evolution of gases resulting in fine, voluminous Cr203 powder. Mixed oxides such as spine1 chromites [35], ferrites [36] and cobaltites [37] have been prepared by the pyrolysis of (NH&M(Cr0&.6HzO (M = Mg,Ni), (NH&M(CrO&.ZNH3nX (M = Cu,Zn), MFe2(C20& (NzH4)x (x=5 when M=Mg and x=6 when M=Mn,Ca, Ni,Zn) and MCO~(C~O&(N~H~)X (x = 5 when M = Mg and x = 6 when M = Ni) respectively. However exothermicity of

Patil, Aruna and Ekambaram

161

these precursors is not high enough to sustain combustion and an external heat source is required for the completion of the decomposition. A new class of precursors containing a carboxylate anion, hydrazide, hydrazine or hydrazinium groups were accidentally found to ignite at low temperature (120-350°C) and decompose autocatalytically to yield fine particle, large surface area oxides. The high exothermicity (Tad =lOOOK) of combustion was attributed to the oxidation of strong reducing moieties such as COO-, NzHs- , NzH4 or N2Hs+ (present in the precursors) by atmospheric oxygen to CO2, Hz0 and N2. The preparation, crystal structure and reactivity of various combustible precursors have recently been reported [38]. Table 1 gives a list of these compounds and the oxides formed. The iron containing complexes, Fe(N2H$00)2 (N2H& and N2HsFe(N2H$00)3.H20 and their solid solutions ignite at -12o’C (they can be ignited with a match stick or candle flame) and combust in the presence of atmospheric oxygen like a Pharoah’s snake to yield nanosize Fe203 and ferrites. The smouldering type combustion and the evolution of large amounts of gaseous products (CO2, H20, NH3 etc.) results in the formation of fine oxide products. The surface area of these iron oxides range from 70 to 140mzg1. All the ferrites when pelletized and sintered at 1000°C achieve ~98% theoretical density. Other nanosize oxides obtained by the combustible precursors are Ce02, TiOz and Y2O3. Besides magnetic oxides a few ferroelectric titanates have also been prepared by this route. Fine particle y-Fe203, Fe304 and ferrites find use as recording materials and in the preparation of liquid magnets. Titania, ferrites and cobaltites are all good catalysts. Although the preparation of fine particle oxide materials by the combustion of redox compounds is simple and attractive, it has certain limitations. Firstly, the preparation of the precursors requires several days. Secondly the yield is only =200/o of the precursor. Finally, not all metals form complexes with the hydrazine carboxylate ligand and therefore it is not possible to use this method to prepare high-temperature oxides like chromites, alumina and so on. An alternative method to the combustible redox compounds is the use of the redox mixtures (oxidizerfuel) like gun powder (KNOs+C+S) or solid propellant (NH&l04+CTPB+Al) which when ignited undergo selfpropagating combustion. Since the serendipitous preparation of a-Al203 foam (Fig. 1) by rapidly heating a solution of aluminium nitrate-urea mixture [39], a number of advanced materials [40] (aluminates, aluminosilicates, chromites, ferrites, ferroelectrics and zirconia) have been prepared by the solution combustion process. In addition to urea CH, ODH, DFH, and glycine have been used as fuels in the solution combustion process. Glycine has been used in the preparation of high T, superconductors, manganites and chromites [ 1,41,42].

162

Synthesis and reactivity of solids

Table 1 Metal carboxylate

precursors to fine particle oxides.*

Precursors

WNd-l~C00)&V-Ld2 Zn(N2HsC00)2.(N2H& Ce(N2HsC00),.3HsO Y(N2HsC00)s.3H20 N,HsFe(N2HsC00)s.H20 N2HsM,,aFe2,a(N2HsCOO)s.H20 M=Mg M=Mn M=Co M=Zn M=Cd

_ Oxides

rkP3 ZnO Ce02 y203 -t-Fe203

MPG4 MnFeoO4 CoFe204 ZnFe204 CdFe204

(N~Hs)aNixZnl_xFe~(N~HsC00)a.3H~0 x = 0.2 x = 0.4 x = 0.5 x = 0.6 x = 0.0

Surface area (m2/g) 68 67 90 55 75

Particle size (nm)

17-23

114 140 116 108 93

1O-25

91 86 90 85 91

1 O-20

N~H~M~/~CO~/~(N~H~COO)~H~O M=Mg M=Mn M=Co M=Zn

MnCo204 FeCoz04 ZnCo204

47 24 116 65

MgMg20, ZnMn204 CoMn204 NiMn204 TiO2 ZrTi04 PbTiOs PbZr03 PZT PLZT

28 61 76 20 114 11 23 13 44 30

4@@4

20

35 20

*Reproduced with permission from [38].

Fiaure 1

Solution combustion synthesized c(-A1203 foam. Reproduced with permission from [39].

A recipe [43-l given for the synthesis of oxide materials with the desired composition and structure (spine], perovskite, KzNiF4, garnets etc.) using metal nitrate-oxalyl dihydrazide (C~H~NJO~) illustrates the simplicity and novelty of this technique. During the period of this review, a variety of useful oxide materials such as catalysts [44,45], phosphors [46&S], pigments [49,50], refractories [51,52] and SYNROC (synthetic rock) for nuclear waste immobilization [53] have been prepared. The materials prepared, fuel used and their properties are listed in Table 2. The solution combustion method not only yields nanosize Ti02 [40], ZrOz [54,55] and hexdferrites [56] but it also yields metastable phases like y-Fez03 1571, t-202 [54,55] and anatase TiOz [44]. The process has also been useful in preparing Vq+ doped zircon (blue pigment) without the use of any mineralizer [SO]. The advantages of the solution combustion process over other combustion methods are: firstly, being a solution process, it has control over the homogeneity and stoichiometry of the products; secondly, it is possible to incorporate desired impurity ions

Combustion

mechanism controlling

in the oxide hosts and prepare industrially useful materials such as pigments, phosphors as well as high T, cuprates and SOFC (solid oxide fuel cell) materials; thirdly, the process is simple and fast and does not need any special equipment as in other SHS methods.

synthesis

Patil, Aruna and Ekambaram

163

of the process and the role of the fuel in the combustion process.

Conclusions Almost all known advanced materials (both oxide and nonoxide) in various forms (nanosize, films, whiskers) have been made by a combustion process. The materials arise from the combustion residues (ash) like a ‘Phoenix’, the mythological bird that burnt itself on pyre and arose from the ashes with renewed youth to live again. The combustion process being simple, fast and energetically economic is attracting the attention of material scientists

The advent of the solution combustion method offers a versatile means to synthesize technologically important oxide materials. The future direction of the process will be towards the synthesis of nonoxide materials such as sulfides, nitrides, carbides and so on. There is scope, however, for further investigations to understand the

Table 2 Oxide materials

prepared

by the solution combustion

process during 19951996. Properties

Oxides Catalysts TiO0 Li*M04(M=Co,

Ni,Cu)

Phosphors Y203:Eu3+ CeMgAl”O’a:Tba+ BaMgAlloO’ 7:Eu2+

CHt ODHt TFTA#

Oxidation of methylene blue, ammonia

ODH* U’ U*lDFHl

Emission band k=611 nm h=543nm h=450nm

U’ U’ CHt CHt CHt CHt

Colours pink blue rose blue yellow red

Pigments Al2O3CP+ Al0Os:C02+ Mg2B205:Co2+ ZrSiO4:V4+ ZrSiO4:PI”+ ZrSi04:Fes+ Synroc phases perovskiie, CaTiOs zirconolite, CaZrTi007 hollandite, BaAI,TieO’e Synroc-B

CHt

Nanomaterials Ti02

Applications Oxidation of water and air pollutants fluorescent lamps, colour

Thermal expansion coefficients a=l0.80x10-6K-’ a=9.04 x 1 O-SK-’ a=8.30 x 1 O-SK-’ a=8.72xlOaK-’ Particle size 20 nm

ODH*

Zr02,PSZ BaFe’2O’a

1441

1451

WI

picture tubes

1471 1481

tiles sanitarywares etc.

149,501

nuclear waste immobilization

catalyst, refractory recording tapes

1Onm 70 nm

References

[531

[44,54-561

1561 Magnetic

materials

recording tapes ODH* Tt=fA#

BaFe’2O’a

M,**=29.8-59.0 emu/g Heft-1 925-5375 Oe

Ferroelectrics tan 6@=0.02,

Pb(Zn’,sNb2,s)Os:BaTiOaTFTA Pb(Zn’,aNb&0s:PbTi03 Low thermal expansion coefficient Al’ sB4Oss NaZrpPsO’2 KZr2P30’2 Ca0.5Zr2P3O’

Dm

actuators

[-I

refractories batteries electrochemical

151,591

DI#L=102

materials

2

SOFWmaterials ZrO2:CaO (10 moW0) ZrO2: Y2O3

lU,

tan 6@=0.006,

CGt

U* CHt

a=l.O5x a=1.5Ox

CH’ CHt

a=1 .OO x 1 O-SK-’ a=l.2Ox 1 O-SK-’

ODHt

Resistance

CH4N20; tCH, CHsN4O; *ODH, C0HsN4O2; *DFH, C2H4H202; TFfA, solid oxide fuel cell; ggtan 6, dissipation factor; “D, dielectric displacement.

1 O-SK-’ 1 O-eK-’

sensors

= 112 Kohms

C4H,eHeO2;

Solid electrolyte

** M,, saturation magnetization; ttH,,

1601

coercivity; WOFC,

164

Synthesis

and reactivity

and engineers to prepare special applications under high pressure conditions.

of

solids

new and exotic materials corrosive high-temperature

for and

Acknowledgements l‘hr authors thank CNR Rao for his interest and encouragement. Aruna is grateful to the Council of Scientific and Industrial Research (CSIR), New Delhi, lndla fur the award of a Junior Research Fellowship. Ekambaram is grateful co the hlinistry of Nonconventional Energy Sources (hlNES), New Delhi for funding.

References

and recommended

reading

15.

Deevi SC, Deevi S: In-situ synthesis of MoSi,-Al,O, composite by a thermite reaction. Scr Metal/ Mater 1995, 33:415-420.

16.

Bowen CR, Derby B: The formation of TiC/AI,O, microstructures by a self-propagating high-temperature synthesis reaction. J Mater Sci 1996, 31:3791-3803.

1 7.

Yukhvid VI, Vishnyakova GA, Silyakov SL, Sanin VN, Kachin AR: Structural macrokinetics of aluminothermic self-orooaoatinahigh- temp-synthesis (SHS) processes. ht J Se/;-Propig Hi&Temp Synth 1996, 5:93-l 05.

18.

Sohn HY, Wang X: Mathematical and experimental investigation of the self-propagating high-temperature synthesis (SHS) of TiAIs and Ni,AI intermetallic compounds. J Mater Sci 1996, 31:3281-3288.

19.

Tomoshige R, Matsushita T: Production of titanium-aluminumcarbon ternary composites with dispersed fine TiC particles by combustion synthesis and their microstructure observations. J Ceram Sot Jpn 1996, 104:94-l 00.

Papers of particular interest, published within the annual period of review, have been highlighted as: . l

1.

*

of special interest of outstanding interest Rao CNR:Combustion synthesis. In Chemical Approaches to the Synthesis of inorganic Materials. New Delhi: Wiley Eastern Limited; 1994:28-30.

Moore JJ, Feng HJ: Combustion synthesis of advanced materials: part I. Reaction parameters. frog Mater Sci 1995, 39:243-273. An excellent review covering all aspects of combustion synthesis. Historical perspectives of combustion and various parameters that control combustion are discussed. A list of SHS products and their applications are given.

20. Avakyan PB, Nersesyan MD, Merzhanov AG: New materials for . electronic engineering. Am Ceram Sot Bull 1996, 75:50-55. The synthesis of ferrites, ferroelectrlcs and high T, oxide superconductors by SHS and furnace methods demonstrating the superiority of SHS are described. The use of ferroelectric materials as sensors is also discussed. 21.

Shon IJ, Munir ZA, Yamazaki K, Shoda K: Simultaneous synthesis and densification of MoSi2 by field-activated combustion. I Am Ceram Sot 1996, 79:1875-l 880.

22.

Hoke DA, Kim DK, LaSalvia JC, Meyers MA: Combustion synthesis/dynamic densification of a TiB2-SiC composite. Am Ceram Sot 1996, 79:177-l 82.

2. ..

3. ..

Moore JJ, Feng HJ: Combustion synthesis of advanced materials: part II. Classification, applications and modelling. frog Mater Sci 1995, 39:275-316. Materials prepared by combustion are discussed under different headings and the reactions are classified according to the element/compound or state (solid, liquid or gas) of the reactants. Thermodynamics, kinetics and models of SHS reactions are also discussed. 4.

Merzhanov AG: Theory and practice of SHS: worldwide state of the art and the newest results. Int J Self-Propag High-Temp Synth 1993, 2:113-l 58.

5.

Merzhanov AG: New manifestations of an ancient process. In Chemistry of Advanced Materials: A Chemistry for the 27s’ Century. Edited by Rao CNR. London: Blackwell; 1993:19-39.

6.

Subrahmanyam J, Vijayakumar M: Self-propagating hightemperature synthesis. J Mater Sci 1992, 27:6249-6273.

7.

Liu ZG, Ye LL, Guo JT, Li GS, Hu ZQ: Self-propagating temperature synthesis of TIC and NbC by mechanical J Mater Res 1995, lo:31 29-3135.

highalloying.

8. .

Takacs L: Ball milling-induced combustion in powder mixtures containing titanium, zirconium, or hafnium. J Solid State Chem 1996, 125:75-84. This is an interesting paper on ball-milling induced reactions involving Ti, Zr and Hf metal powders with S, C and metal oxides. 9.

Tsuchida T, Hasegawa T: TG-DTA-MS study of self-ignition in self-propagating high-temperature synthesis of mechanically activated AI-C powder Mixtures. Thermochim Acta 1996, 276:123-l 29.

J

23.

Miyamoto Y, Tanihata K, Kimiaki L, Zenshi, Kang YS, Murakawa H: Development of symmetric gradient structures for hyperfunctional materials by SHSIHIP compaction. Adv Sci Techno/ 1995, 10:87-98.

24.

Grachev W, lvleva TP, Borovinskaya IP: Filtration combustion in a self-propagating high-temperature synthesis (SHS) reactor. Int J Self-Propag High-temp Synth 1995, 4:245-252.

25.

Shcherbakov VA, Shteinberg AS: Macrokinetics of SHS infiltration. Combust Sci Techno/ 1995, 107:21-29.

26. .

Treece RE, Gillan EG, Kaner RB: Materials synthesis via solidstate metathesis reactions. Comment Inorganic Chem 1995, 16:313-337. This article reviews the synthesis of thermodynamically stable inorganic solids (oxides, sulphides, nitrides. intermetallics) by the use of a highly exothermic solid-state metathesis reaction between metal halide and alkali metal main group compounds. 27. .

Gillan EG, Kaner RB: Synthesis of refractory ceramics via rapid metathesis reactions between solid-state precursors. Chem Mater 1996, 8:333-343. This is a detailed article on SSM reactions, its predictive ability and applications in the rapid synthesis of refractory materials such as nitrides is documented. 28.

Glassman I, Davis KA, Brezinsky K: A gas-phase combustion synthesis process for non-oxide ceramics. Twenty-Fourth Symposium (International) on Combustion/The Combustion Institute 1992:1877-l 882.

29.

Fotou GP, Scott SJ, Pratsinis SE: The role of ferrocene synthesis of silica. Combust Flame 1995, 101:529-538.

in flame

10.

Shon IJ, Munir ZA: Synthesis of MoS&xNb and MoSi2-yZrOz by the field-activated combustion. Mater Sci Eng 1995, 202:256261.

30.

Dufaux DP, Axelbaum RL: Nanoscale unagglomerated nonoxide particles from a sodium coflow flame. Combust Name 1995, 100:350-358.

11.

Feng A, Munir ZA: Relationship between field direction and wave propagation in activated combustion synthesis. J Am Ceram Sot 1996, 79:2049-2058.

31.

Keil DG, Calcote HF, Gill RJ: Flame synthesis of high purity, nanosized crystalline silicon carbide powder. Mater Res Sot Symp Proc 1996, 410:167-l 72

12.

Orru R, Simoncini B, Virdis PF, Cao G: Further studies on a centrifugal SHS process for coating preparation and structure formation in the thermite process. Int J Self-Propag High-Temp Synth 1995, 4:137-l 47.

32.

Feldman Y, Wasserman E, Srolovitz DJ, Tenne R: High-rate, gas-phase growth of MO!& nested inorganic fullerenes and nanotubes. Science 1995, 267:222-225.

13.

33. Puszynski JA, Kattamuri DS, Stefansson B, Jagarlamudi S: Simultaneous combustion synthesis and densification with product separation. Adv Powder Metal/ Part Mater 1995, 2:187-l 98.

Shin HS, Goodwin DG, Harris SJ: Alternative fuels for combustion synthesis of diamond. Proc . Nectrochem 1995, 95:231-236.

14.

Wang LL, Munir ZA, Birch J: Formation of MgO-B& composite via a thermite-based combustion reaction. I Am Ceram Sot 1995, 78:756-764.

Sot

34.

Patil KC, Soundararajan R: Pyrotechniques Ind J Chem Edn 1979, 6:29-30/

35.

Wold A, Dwight K: Synthesis of oxides containing transition elements. J Solid State Chem 1990, 88:229-238.

for entertainment.

Combustion synthesis Patil, Aruna and Ekambaram

165

36.

Gajapathy D, Patil KC: Mixed metal oxalate hydrazinites as compound precursors of spine1 ferrites. Mater Chem Phys 1993, 9:423-439.

40.

Kottaisamy M, Jeyakumar D, Jagannathan R, Mohan Rao M: Yttrium oxide: Eu3+ red phosphor by self-propagating high temperature synthesis. Mater Res Buff 1996, 31 :I 013-l 020.

37.

Patil KC, Gajapathy D, Pai &maker VR: Low temperature cobaltite formation using mixed metal oxalate hydrazinite precursor. J Mater Sci Lett 1963, 2~272-274.

49.

Patil KC, Ghosh S, Aruna ST, Ekambaram S: Ceramic pigments: a solution combustion approach. The lndian Potter 1996, 3411-g.

36.

Patil KC, Sekar MMA: Synthesis, structure and reactivity of mete1 hydrazine carboxylates: combustible precursors to fine particle oxide materials. Int J Se/f-Propag High-Temp Synth 1994, 3:181-196.

50.

Muthuraman M, Dhas NA, Patil KC: Preparation of zirconia based colour pigments by combustion route. J Mater Synth Processing 1996, 4:115-l 20.

51.

39.

Kingsley JJ, Patil KC: A novel combustion process for the synthesis of fine particle a-alumina and related oxide materials. Mater Letf 1988, 6:427-432.

Ekambaram S, Dhas NA, Patil KC: Synthesis and properties of aluminum borate (a light weight ceramic). lnt J Self-Propag High-Temp Synth 1995, 4105-93.

52.

Chandran RG, Chandrashekar BK, Ganguly C, Patil KC: Sintering and microstructural investigations on combustion processed mullite. J Eur Ceram Sot 1996, 16:941-949.

53.

Muthuraman M, Patil KC, Senbagaraman S, Umarji AM: Sintering. microstructural and dilatometric studies of combustion synthesized synroc phases. Mater Res Bull 1996, 31:1375-l 361.

54.

Venkatachari KR, Huang D, Ostrander SP, Schulze WA, Stangle GC: A combustion synthesis process for synthesizing nanocrystelline zirconia powders. J Mater Res 1995, 10:746-755.

55.

Venkatachari KR, Huang D, Ostrander SP, Schulze WA, Stangle GC: Preparation of nanocrystelline yttria-stabilized zirconia. J Mater Res 1995. 10:756-761.

56.

Castro S, Gayoso M, Rivas J, Greneche JM, Mira J, Rodriguez C: Structural and magnetic properties of barium hexeferrite nanaostructured particles prepared by the combustion method. J Magn Magn Mater 1996,162:61-69.

57.

Suresh K, Patil KC: A combustion process for the instant synthesis of y-iron oxide. J Mater Sci Lett 1993, 12:572-574.

56.

Sekar MMA, Patil KC: Low-temperature synthesis and propertiesof microwave resonator materials. Mater Sci Eng B 1996, 39:273-279.

59.

Dhas NA Patil KC: Combustion synthesis and properties NASICON materials. J Mater Chem 1995, 5:1463-l 466.

60.

Shukla AM, Sharma V, Dhas NA, Patil KC: Oxide-ion conductivity of celcia- and yttria-stabilized rirconias prepared by a rapid combustion route. Mater Sci Eng B 1996, 40:153-l 57.

40.

Patil KC: Advanced ceramics: combustion synthesis and properties. Bull Mater Sci 1993, 16:533-541.

41.

Honeyboume CL, Rasheed RK: Nitrogen dioxide and volatile sulfide sensing properties of copper, zinc and nickel chromite. J Mater Chem 1996, 6:277-263.

42.

Bates JL, Chick LA, Weber WJ: Synthesis, air sintering and properties of lanthanum and yttrium chromites and manganites. Solid State lonics 1992, 52:235-242.

Suresh K, Patil KC: A recipe for an instant synthesis of fine particle oxide materials. In Perspectives in So/id State Chemistry. Edited by Rao KJ. New Delhi: Narosa Publishing House; 1995:376-369. Gives a ready to use recipe for the combustion synthesis of spin& (aluminates, chromites and ferrites), perovskites (LnM03, M=Al, Fe, Cr), KzNiFd type (La2M04, M=Mn, Co, Ni and Cu) and garnets (Ln3Fe5012 and YIAG [yttrium iron aluminium garnet]). 43. .

44.

Aruna ST, Patil KC: Synthesis and properties of nanosize titenia. J Mater Synth Processing 1996, 4:175-l 79.

45.

Ramesh S, Manoharan SS. Hegde MS, Patil KC: Catalytic oxidation of ammonia over high surface area La2M04 (M-Co, Ni & Cu). J Catal 1995, 157:749-751.

46.

Ekambaram S, Patil KC: Synthesis and properties of rare earth doped lamp phosphors. Bull Mater Sci 1995, l&921 -930.

47.

Ekambaram S, Patil KC: Synthesis and properties of I%*+ activated blue phosphors. J Alloys Compounds 1997, in press.

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