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(self-propagation) characteristics of these reactions are presented.
exothermic reaction which involves a metal reacting important examples of their utilizations.
tant oxides. the elemental c o m p o n e n t s c o r r e s p o n d i n g to the reac- cussed later. the adiabatic temperatures.1/2A1203 4181 1495 II. b u t conditions. as shown in Fig. 2. Formation of nuclear metals AI + 3/-16U308--+9/16U + 1/2A1203 2135 1405 A1 + 3/4PuO/--* 3/4Pu + 1/2A1203 796 913 The calculation of T. Both a l u m i n i u m a n d the p r o d u c t phases with the a s s u m p t i o n of adiabatic z i r c o n i u m have c o m p a r a b l e reducing tendency. The heat released thermite reactions were calculated a n d are presented from the reaction heats up the p r o d u c t to the in Table I. I n m a n y cases..3/2Ni + 1/2A12Oa 3524 1726 A1 + 3/4TIO2 --* 3/4Ti + 1/2A1203 1799 1943 A1 + 3/8Co304 ~ 9/8Co 4. Nb O. Formation of refractory metals ' AI + 1/2Cr203 --*Cr + 1/2A1203 2381 2130 A1 + 3/10VaOs ~ 6/10V + 1/2A1203 3785 2175 AI + 3/10TaaOs ~ 6/10Ta + 1/2A1203 2470 3287 A1 + 1/2MOO3---. ] [ ~... These a l u m i n i u m .. Tad. Figure 2 Free energy of thermite reactions with aluminium as the reducing agent.-~TiO2 & -1oo / j. for these micity of the thermite reactions..b a s e d its oxides are more suitable for the requirements of thermite reactions result in p r o d u c t i o n of A1203 a n d several metallurgical applications . b Tmpof A1203 is 2315 K.~ddoes not take into account vaporization of the product phases. 91]. 3/4Pb + 1/2A1203 > 4000 600 A1 + 3/4MNO2 ~ 3/4Mn + 1/2A1203 4178 t517 A1 + 3/4SIO2 ~ 3/4Si + 1/2AIzO3 1760 1685 IV.J_. -160..o 2000 I I _ _ 3000 Temperature (K) Figure I Free energy of formation for oxides.l/2Mo + 1/2A1203 4281 2890 A1 + 1/2WO3 ~ 1/2W + 1/2A120a 4280 3680 A1 + 3/10Nb2Os --*6/10Nb + 1/2A1203 2756 2740 III. because it is more by a l u m i n i u m up to relatively high temperatures readily available. Fe + 1/2A1203 3622 1809 AI + 3/2NIO ---. a n d thus are less desirable for adiabatic temperature which can be calculated from certain applications because of high reaction pressure the enthalpy of the reaction a n d the heat capacity of a n d v a p o r i z a t i o n losses . as will be dis. [90. 0 t " L] I ~ ~ I [ ~Fe203 1000 NiO~-- oo.. }iii 0 1000 2000 Temperature (K) zO3 3000 "~ 00. the adiabatic temperature TAB L E I Adiabatic combustion temperatures and melting points of the product metals Reaction Ta(K) a Tmpof metal (K) b I.. (at 1 arm pressure). Formation of other metals and non-metals AI + 1/2B203 ~ B + 1/2AlzO3 2315 2360 AI + 3/4PBO2 --. Formation of common structural metals A1 + 1/2Fe203 --. A large n u m b e r of oxides can be reduced a l u m i n i u m is more c o m m o n l y used. Its physical properties a n d those of (2500 K).. 3694 . U s i n g the usual t h e r m o d y n a m i c a p p r o a c h A n o t h e r factor is the consideration of the exother.
suitable to use thermodynamic calculations igniter for pyrotechnical uses [36. the information of T~a also provides some insight mentally [21-24]. From this study. In self-propagation.g. Combustion of thermites A1203. MnO/. 97]. based on minimization of the total Gibbs free energy The electrical energy required to ignite thermite of the system to obtain equilibrium distribution of mixtures has been investigated . TiOz. Finally. 2.03 J. NiO. play a significant role in initiating the combustion These include reactions that reduce Fe203. This for the systems A1-Cu/O. product phases and the corresponding reaction tem. the oxidation of aluminium by reactions and. in Fig. It may also hinder ignition in air by eliminating the influence of the external oxygen. with the Class 4 oxides. if the rate of where P is the vapour pressure of the most volatile chemical interaction of the aluminium with the liquid component (or dissociation pressure of the products) oxides is low. it was found that the oxides which fall under Class 1 (e. NiO. unstable oxides that undergo further oxidation. Intrinsic and materials parameters the moment of ignition. More. As a rule.exceeds both melting points of the product phases. which is initiated by the exothermicity of the reaction. Finally. the reaction proceeds lished in a variety of methods. whether in solid.g. and the heat liberated from this is the adiabatic temperature below the melting point reaction can heat the specimen to the ignition point of of both product phases. The Fe203-A1 thermite mixture ides can become the step that initiates ignition. V203. The ignition process of reactants are consumed. 87]. In this multiple reducing metals are present. 37]. For example. niter) [21-25].  classi. Striking an aluminium smear thermite mixtures . The high reac. (2) chemi. The investigation of this ignition to the possible states of interaction. WO3. respectively sible product phases in more complicated starting . The initiation of thermite reactions can be accomp- propagate. to proceed as a gasless combustion . The criterion for defin- WO3. 95]. Li202. or a combination of these. such as in the choice of optimum composition of the therefore. but also a quick deter. but also for a number of practical applications. while the reaction to reduce B203 170~ which is the decomposition temperature of reaches the melting point of A1203. Cr203. They can be ignited by in a combustion form in which the heat generated a combustion wave from a chemical reaction (or ig- from the locally ignited region can subsequently trig.60. sibility of achieving equilibrium conditions. mixture can occur at as low a temperature as about and Nb2Os. the laser impingement on the samples is simultaneously coupled with measurement of the tem- perature distribution in the sample by a high-speed 3. BaO2). and Nb2Os) are essentially inert up to 4. plosions in chemical plants  and mines . (3) chemically this case. Using a laser as the ignition source has also been thermite mixtures in which multiple oxides and/or attempted on the AI--Fe203 system [96. Ignition of t h e r m i t e reaction thermographic method. ternal gas pressure. the ignition of the CrO3-A1 C0304. Al-Si-Cu/O. radiation ger the reaction in the adjacent reactant layer. Chernenko et al. mination of the propensity of the reaction to self. further oxida- cases (e. Moreover. problem of the interaction between two reactive sys- tion temperatures of thermite systems ensure the pos. both theoretically and experi- over. and (4) chemically stitutes an industrial fire hazard. at the combustion temperature To. tems. gas. It is. most intensely studied. BzO3 make many thermite systems examples of reactions in which melts at 450~ MoO3 which sublimes. A1-Mg-Cu20 as 6. reaction. The adiabatic temperature the thermite reaction. reduction of TiO2 and PuOz by aluminium) tion takes place in air. As illustrated the ignition process is more complex because the oxy. the condensed nature of the atmospheric oxygen initiates the combustion of the reactants and products at the reaction temperature mixtures. In cally stable but physically unstable oxides. thus the energy from a heat source or a laser beam [96. Cr203. which also sublimes) the appearance of a liquid ing gasless combustion is  oxide phase may increase the rate of the oxida- tion-reduction reaction and thus enhance system igni. Only in a few CrO3. in general. and Po is the ex- the reaction between aluminium and the gaseous ox. When such thermite reactions The high exothermic energy associated with thermite are carried out in air. MoOa. VzO3. and the gasless combustion regime.g. it has also been dem- The physical and chemical stability of the reactant onstrated that a thermite reaction can be initiated by oxides has important effects on the ignitability of the mechanical means . 92]. investigation. process is not only of great interest as a theoretical liquid. P(Tr ~ Po (2) tion. PbO2. the time-independent ignition energies were obtained perature under adiabatic conditions [38. the reaction can a thermite reaction by a combustion wave has been self-propagate if the Taa exceeds 2000 K . In their experimental study. CrO~. 97]. In the diluted with the end product (A1103) has been shown case of Class 3 oxides (e.1. 4. reaction of FeO with oxygen to form a higher oxide. and analysis is especially applicable in predicting the pos. 3. In the case of Class 2 oxides (e. the occurrence of thermite reactions con- unstable oxides that decompose.g. the combustion rate of the Fe203-A1-A1203 gen liberated from the decomposition of the oxide can system is independent of the inert gas pressure (up to 3695 . Ta2Os. with volatile reactant oxides. on a piece of rusty mild steel with a hammer can create fied the oxides according to the following criteria: a spark which has been blamed for initiating ex- (1) chemically and physically stable oxides. an electrical current [94. An example of such a case is the provides not only a quantitative measure of the ignition of FeO-A1 in air.81 and 3. or reaction zone moves in the form of a wave until all the by mechanical impact [86.
This can be mite systems react with gas evolution resulting from related to the difference in the thermophysical proper- the decomposition of oxides or the vaporization of ties (e. 4 . 104]. MgF2). Figure 5 Mass combustion rate versus compact density (average (3) CaO . Addition of salts of alkali metals (e. Balakir et al. 3 3O 2 2 3 I I 20 SS v 20 40 60 10 Inert diluent(wt%) 1 2 3 Compact density (g cm3) Figure 4 Dependence of the mass combustion rate. 102]. 5. diluents ..(2) CaFz. However. particle size of iron ore. and cryolite (NaA1F6) can effectively increase the mass combustion rate of a thermite mixture as 4 40 . the mass combustion of thermite systems. thermal conductivity and heat capacity) of the reactants. crushed iron ore (89. low-density range. pre-combustion compact density . In these cases. A1F3. lain: (1) 57. as indicated above.g.  conducted an comes more complicated because mass diffusion is no extensive study of the effect of compact density and longer negligible when compared with the thermal particle size on the mass combustion rate of diffusion. The combustion rate can be significantly aluminothermic compositions which are mixtures of affected by pressure. NaF. the mixture as a function of the bulk density of the Numerous experimental studies have been conduc. (2) 50. Addition of inert diluents also effectively reduces the combustion rates [28. 3696 . tances between reactants. Vrn. 3 '. The theoretical model for the SiO2).--. the combustion rate decreases as salt addition . ambi. of the Co304-A1 systemon the type of diluent added: (1) A1203. In general.g.4 u~ u n 0 0 0 u 0 the combustion rate [100-102]. For a fixed bulk density. Dubrovin et al. as will be seen in some thermite Cr203. In the [25. Dubrovin et al.. and aluminium. 102]. consistent size of reactants [100-102].7 wt% systems discussed below. 107]. 102] because of the Figure3 The combustion velocity of (2AI+Fe203): 30wt% production of less heat and the longer transport dis- A1203 system as a function of the inert ambient gas pressure . bulk density increases reaching a minimum and then ent inert gas pressure [99.2 I o 20 40 60 80 100 initiation of the thermite reactions (A1-CoaO4 and P (atm) A1-NiO). centrifugal force [103.. Different types of inert dilu- ent also produce different degrees of reduction in the ~100 arm). 28.g. and chemical stability of oxide reactants [102. The mass combustion rate of partial gas evolution cases is not well studied .7 wt% Fe203:8. (3) 40) . alkaline earth metals (e. combustion rate as shown in Fig.  observed that increasing the aluminium particle size I I I I to larger than 100 gm can result in difficulty in the 0. addition of inert diluent with the observations of others [100. some ther. 106].  related this behaviour of the combustion rate to the effective ther- mal conductivity of pressed mixture which has been found to exhibit a similar bulk density dependence . 5 NaC1 and KC1). decreasing the reactant particle size increases 0 0. mixture for different iron ore particle sizes is shown in ted to determine factors affecting the combustion rate Fig. KF. These factors included particle rate increases with decreasing particle size. the combustion model be. and the physical increases again. 105.
6 0. by thermite-based systems. Karataskov et al.80 0. The effect of pressure and centrifugal force The effect of centrifugal force. In this range. to the gravitational 0 acceleration. C r O 3 . 6 . It is proposed that salt ad. a.O3 thermite . 8 . and consequently. 0.16 0. but with a further increase in the the influence of a centrifugal force on the two acceleration force. graphite the velocity first increased slowly at low ac- More recently. the ignition temperature of the thermite mixture with salt addition l0 / is notably reduced . and studied the effect of centrifugal force in the range of 0-895 a/g. in rate as a result of the application of a centrifugal gal force on combustion rate in these two systems has force is attributed to the forced penetration of the 3697 .4 ditives reduce the temperature at which the reaction between the oxide and the aluminium commences.a/g Serkov et al.). can be disintegrated by the alkali metal or alkaline earth metal salts at a tem- / perature significantly lower than the ignition temper- ature of the thermite. as seen in Fig.5 be due to the presence of molten aluminium. The increase in burning rate was suggested to taining carbon black increased by a factor of 1:5-2. 7.3 0. O and the highest combustion rate was found in the / compositions containing aluminium fluoride (A1F3) and cryolite (NaA1F. As in the previous study. reported as the ratio of the centrifugal acceleration.3 0.) / 4.C r 2 0 3 . Centrifugal force. The effect of salt addition is 30 most prominent with the addition of small amounts. are in the molten state at the combustion temperature. 104J. S w t % A1203 which 9~Tgure 7 Combustion velocity of ferro-aluminium thermite as yields a condition that all components (start and end) a function of centrifugalforce . the increase C r O 3 .A I .  investigated celeration forces. 20 J The oxide film on the aluminium particle. g.0 0. .32 0.C . for the compounds containing still unreacted substance ahead of the wave . the burning rate was found a strong dependence on the nature of the carbon used. on the combustion rates of several 0 400 800 thermite systems has been investigated [103.N i O .C r a O 3 . the velocity increased sharply. The combustion rate of the mixture con- Fig.00 0.. to increase by a factor of approximately 6. which acts as a barrier to the interaction.A 1 .0 0. which is with an increase in the acceleration force (0-800 a/g). shown in Fig.2. The effect of the centrifu.C and a factor of 7-12. . driven by the acceleration force into the pores of the On the other hand.24 ~oE 0.  used the thermite system 815 wt% ( 2 0 w t % A l : 8 0 w t % F e O ) : t 8 .9 0.6 Amount of salt added (tool) Figure 6 Influenceof the addition of various salts on the mass combustion rates of the 2AI + Cr.
attempted to explain this anomalous pressure depen- duct is significantly higher than that without nickel dence of the combustion rate on the basis of the and is consistent with the proposed role of a centrifu. in vacuum range. liquid into pores of the unreacted materials [-104]. 9 . A 84 1 4 . while BaO2 has a low melting point (450 ~ ciated with vaporization of the starting components at and liquid BaO2 can readily decompose at a lower the temperature reached in the combustion front temperature as the pressure decreases. and P b O 2 . 3698 . Combustion under vacuum proceeds in the presence of a gas phase (aluminium vapour). this regard it is worth noting that the increase in M o O a . as the pressure decreases. as shown in 61. In certain thermite systems. the boiling point of aluminium is 1148 ~ Combus- 12 tion rate of this thermite system at low ambient gas pressure was found to depend on the level of pressure. Ivanov et al. reaching a maximum.0 0 0. low normal boiling points (1107 and 906 ~ respec- pends on the ambient pressure. The combus- tion of this mixture has been shown earlier to be independent of inert gas pressure for pressures higher than 1 atm . For all three .g. Carbon black J 0 I I I I I 0 100 200 300 400 0 200 400 600 800 (a) ~/g (b) o/x Figure8 Influence of the centrifugal force and the nature of the carbon used on the combustion velocity for (a) 37% CrO3 + 27% Cr203 + 27% A1 + 9% C mixture. because of the high volatility of pressure. the combustion rate in- creases with pressure.Z n [-99]. physical properties of the reactants and the selective gal force. tively). - I # I ! . 10.-e i _ '~ 2 'm 4 Graphite /. mixtures: (1) BaO2-Zr. 1-99] velocity of the reaction containing nickel in the pro. and then decreases with further pressure increase. Both magnesium and zinc h a v e the pores and reacts with aluminium. low melting points (650 and 417 ~ respectively) and For some thermite systems the burning rate de. 10 for three thermite systems: BaO2-Zr. (3) PbO2-Zn [99J. However.0 I I I 200 400 600 0 40 80 P (nun Hg) P (atm) Figure 9 Pressure dependence of combustion velocity of (2A1+ Figure 10 Effectof pressure on the combustion velocityof thermite Fe203): 30 wt% A1203 system under vacuum .M g . R o m o d a n o v and Pokil  studied the effect systems shown in Fig. the molten nickel penetrates wetting of the liquid. and (b) 33% CrO3 + 24% Cr203 + 9% NiO + 27% A1 + 8% C mixture (the percentages are wt%) 1-104].% 2. Fig. Presumably. In Fig.0 f 1. (2) MoO3 Mg. on the combustion of the thermite mixture. 14 the boiling point of aluminium can become lower than the combustion temperature (e. FezO3-A1-A1203. This has been asso. at P = 10 -2 m m Hg.
vapours are formed resulting from the 0. The pres- system software. thus lowering the driving force for the propagation of the ~o 0. and C0304-A1 and found that oxidizers Figure 11 The dependence of the combustion velocity of various with high vapour pressure (e. Cr203-A1.of reactants. in the report . 12. The rise of combustion rate at the low range of pressure is associated with the rise in the 0. (3) CrO3-AI-B. This is consistent (3) CrOa-A1-B. Nb2Os-A1.0 0. As the argon gas pressure increases. The stron- it is possible to form gaseous product phases at high gest dependence of Vo on Po was observed for the temperatures as demonstrated by the equilibrium cal.6 (the subscripts refer to the reactions as stated above). the greatest rates of combustion. of all five systems were found to Figure 12 The effectof ambient pressure on the calculatedadiabatic increase with increase in the argon pressure. WOs sublimes. and CrO3 and sure while the total product gas concentration de- CrO2 easily decompose to 0 2 and Cr203. with the results shown in Fig. account of increase in combustion temperature and tively) was repeated by using CSIRO thermochemistry the reduction in the gas Volume generated.6 2. Po. is described by the formula efficientsare weight fractions).182 and 0.124. thus lowering the combus- tion velocity. and total product gas concentration shown in Fig.4 systems: WO3-A1. mixture NiO + Ti and may be attributed to the dis- culation of the final product compositions . The effect = 9 0. WO3 and MOO3)gave thermite reactions on pressure:(1) WOa-CoO-AI-C. (2) NiO-Ti. Po.A I . 11.28 formed in the combustion process can selectively wet 3000 ~ the pores resulting in inhibition of reaction.r 5 4. In general.  and low-pressure range (1-13 atm).182A1 + 0.124CoO + 0. The Pressure (atm) combustion rates.24 tures: (1) WO3-CoO-A1-C.0 combustion front.C o O .4 amount of heat loss to the surrounding argon gas also increases due to an increase in the density and thermal conductivity of the argon gas. Moreover. Vo = B P u. (2) NiO-Ti. and decreased with a further increase in the argon pressure (200-1020 atm). on pressure. However. Vo. creased with an increase in the argon pressure in the tively with those obtained by Yukhvid et al. remained relatively show significant amounts of gaseous products mainly constant in the mid-pressure range (30-150 atm).g. The pressure dependence of the combustion rate in- dicates the presence of gas phase in the combustion CO. the calculated theoretical combustion 0.22 I I I I I 2800 20 40 60 80 100 temperatures are high and exceed the melting points of the initial components and final products . The dissolved gases are liberated into the reac- gas concentrations was not specified. and the melt 0. u2 = 0. in effect. creases as the ambient pressure decreases.32 3200 heat of combustion.8 1. I I investigated for a variety of thermite systems [102. MoO3-A1. A120. solved hydrogen and nitrogen gas in titanium particles Because. as combustion temperature. decreases the temperature gradient in the combustion front. been observed .66 WO3 + 0. Vo.034. 2 o. The calculated results agree qualita. 0.3. As ature increases with an increase in the ambient pres- discussed previously. where u3 = u4 = us = 0. T h e role of o x i d e stability The dependence of the combustion rate on the phys- -0. and (5) C r O 2 . In all five systems. The calculated adiabatic combustion sure dependence of the combustion velocity of the temperature and the total product gas concentration stoichiometric 6Mg + 2B2Oa + C system has also (in mole fraction) as a function of pressure are pres.4.C r 2 0 3 . (4) WO3-A1 C. The combustion velocity in- ented in Fig. T d. 2900 0. The combustion temper- process: this is evident from the nature of oxides. (5) CrO2 Cr203-A1 C . significant amounts of the reactant loss due to vaporization decreases the combustion temperature.A 1 C system (in increase in Vo with increasing Po may occur on the weight fractions: 0.  studied the following thermite 0. Balakir et al. (4) WO3 AI-C.30 extent of the vapour phase penetrating the pores as the 3100 ambient pressure increases.4 -- ical and chemical stability of the oxides has been z.66. the unit of the product . calculation for the W O a . At low pressure. respec. 0. at a higher pres- sure the gas formation is suppressed. and some Co. 11 in which the mixtures 3699 . of the 0. The dependence of combustion velo. ul = 0. the 0.26 of pressure on combustion rate was also investigated 6 on the following thermite and thermite-based mix. AI. This. Log P o (atm) W205 A1. the equilibrium ting melt and then form a gas phase. 107].034C system(the co- city.2.C .
continuation of the thermite reaction. and with further increases in pressure. t w o other experimental approaches have been adiabatic temperature exceeds the melting point of attempted. (2) finely dispersed FeO particles on the presented in Fig.g. (3) fine particles of FeAI204 with traces of FeO on stoichiometric 2A1 + Fe203 system. containing WO3 exhibited higher combustion velo. i.5 wt ~ AI ~. tion proceeds primarily with the participation of the however. In sition of FezOa (Fe2Oa ~ Fe304 --* FeO) precedes the the study by Shidlovskii and Gorunov . for systems in which the temperature diffraction electron microscopy permits oxide does not dissociate or undergo a phase trans. M e c h a n i s t i c i n v e s t i g a t i o n s dissociation. there 4 ~ 3 2 1 is a strong tendency for the liberated nickel to react with aluminium to form the intermetallic compound AINi. and the other em- involves the reaction between the molten oxide and ployed a programmed heating method . as well with the binding energy of the resulting oxides seen in Fig. the vaporization of aluminium at 4 MPa the step is sufficiently suppressed.4. decomposition of Ni203 to oxygen and NiO. 26. Obviously. MgO and AlzO3). the detection of (ZrO2. the interaction between iron oxide and aluminium.4 MPa. the study of the structure and composition of the formation (e. defined as the product of density and wave propagation velocity (g cm-2 s-i). where the oxide is stable relative to 4. of the interaction of Fe203 particle on aluminium film The combustion rates of CrzO3-M (where M = Zr. thermite system Co304-A1. For In the area of mechanistic studies of thermite combus- example. 13 along with results for the aluminium film. 38 wt %AI ~ 2 5 wt~/o~ ~ ~ 9~ . The higher combustion rate of NizO3-A1 and NiO-A1 2Co304 --* 6CoO + O2(g ) (4) relative to FezO3-Al at all pressures was suggested to The next step then involves the reaction of the oxygen be the result of the additional contribution of the gas with aluminium to form additional A1203 and the interaction of aluminium and the product nickel. The mass burning velocities. 3700 . pressure range 0 . the mass burning velocity of cities. In the nitrogen the aluminium film. whereas the and as it reaches 900 ~ the reactant oxide becomes combustion of NizO3-A1 continues t o involve the unstable with respect to dissociation. in the case of the of Ni2Oa-A1 was observed to increase with pressure. (4) FeAI204 layer 1-109]. Examination between a solid oxide and the liquid aluminium. the tion. all three thermites increases with increasing pressure.5 wt % AI 0 0 I I 0 4 8 0 4 8 (a) P (MPa) (b) P (MPa) Figure 13 Influenceof the pressure on the mass combustion rate of the mixtures(a) A1-NizO3 and (b) AI-NiO containingvarious amounts (wt%) of aluminium in the reactants . the reactions of NiO-A1 and Fe/O3-A1 take 3Co304 § 8A1 ~ 9Co + 4A1103 + AH (3) place in the gasless regime so that their combustion The liberated heat raises the temperature of the system velocities are independent of pressure. The combustion rate was traces of Fe304 led to the proposal that the decompo- found to decrease with decreasing binding energy. other factors may play a role. the thermite process is products being formed at the interface. but now as 3CoO + 2A1 ~ A1203 + 3Co (5) In other systems. For example. One involved using high-temperature dif- Nb205 (1783 K) and thus at least part of the process fraction electron microscopy . even at 570 K. Cr/O3-A1). revealed that three intermediate reaction zones exist Mg. of NizO3-AI and NiO-A1 thermite mix- Figure 14 Interaction zones between Fe203 and aluminium films: tures with varying amounts of starting aluminium are (1) pure aluminium film. and A1) thermites  were found to correlate between the ferric oxide and the aluminium film. 14 . In this study. It is concluded that in these systems the interac. in the case of the Nb2Os + A1 thermite. Also.'~ wt ~A! If" '\ 19.e. above 4 MPa only the mass burning velocity gas phase . High- liquid aluminium. and it decomposes with the formation of NiO. The combustion of the Ni/O3-AI and NiO-A1 thermites presence of FeO leads to the formation of FeAI204 was studied and compared with that of Fe203 A1 for the following reasons: Ni203 is less stable than Fe203 (the more common oxidizer used). the mechanism begins by Presumably.
associated with thermite reactions. Utilization of t h e r m i t e reactions alkali metals (Group IA) are often done by reduction 5. that can be used in thermite reactions (see Sec. 91]. different calcium and magnesium. a cylindrical sample of the thermite stable silicides and carbides. 1.or small-scale in- gasless systems. Tw. As pointed out elsewhere [111. must be One of the early industrial applications of thermite sufficiently high to melt both phases. alloys (Pu-A1. Aluminium during which the oxide is in the liquid state. 3] reported using CaO can be added to the mixture to form lower aluminium as the reducing agent for thermite reac. iron. To. which has a higher speci.38 RT2/E (9) to steel. have been adequately described process of preparing metals and alloys is to achieve elsewhere [39. perature. Ferroalloys are obtained where R is universal gas constant. Ca-AI. a n d ferro- 658 kJmol-1. or the mixture can be preheated prior to phase (commonly referred to as slag). ATm = To . U-A1) by aluminothermic reduction ment for ignition of the thermite reaction and its high process has also been investigated in several studies reaction rates. Preparation of nuclear metals (Pu. V. once ignition has occurred. phase. which typically involve the use of The important requirement for effective thermite metallic reactants. W. nobium and ferroalloys. ried out at elevated temperature and in vacuum. Such reactions. Although aluminium is more heating conditions can result in different controlling expensive than silicon and carbon. Mg-Si) instead of aluminium as reducing agents in tion 2). 2Fe304 + 1/202 (6) CaO is 2580~ and magnesium (Trap of MgO is Fe304 + 2/3A1 --. For less energetic reactions is in the preparation of metals and alloys. Ferroalloys. This high activation energy value was boron.1. thermal boosters (such as sodium Because of the large amount of heat generated from chlorate (NaC104) and potassium nitrate (KNO3) the reaction. Another reducing agent in metal and alloy preparation because important criterion regarding separation is the time of several important advantages [53. Ta.Tw. by using intermetallic reactants (Ca-Si. Thus.g. melting slags (e. and E is the activation energy. the oxide of aluminium (A1203) has a lower melting point (2051 ~ than those of calcium (Tmp of 3Fe203 --. Ti) [4-8]. The interest here is primarily generated by the desire to develop stable nuclear fuels. such as calcium and magne. does not require pressure-tight reaction vessels. which react exothermically with aluminium) can be and thus the metallic phase. 2CaO. Preparation of metals and alloys mic reductions are mostly endothermic and are car- The use of self-propagating high-temperature syn. This reduction method to study the gasless thermite reaction process can proceed to form such important commer- 3Cu20(s) + 2Al(s)~ A12Oa(s) + 6 Cu(s) + 2406 Jg-1. the use of aluminium.Pure (thermal explosion). cial alloys as ferrotitanium. < 1400 ~ considerably lower than the melting point vanadium. Thermite reactions that mixture is heated at a constant rate up to the point at use aluminium as the reducing agent are commonly which the entire sample proceeds to react all at once called aluminothermic reduction reactions . and sample wall tem. As early as 1898. [114. nium produces purer metals and alloys because silicon In the programmed-heating method developed by and carbon can react with the product metals to form Miller . as shown in Fig. can be very different from that in the combustion From a cost standpoint. To is the initial by co-reducing the oxides of the desired alloying ele- temperature. of one or more additional elements for use as additives AT m = 1.1. This time provides a good reducing potential. 112]. common structural metals (Fe. and because they do not include an good separation of the metallic phase from the oxide oxide phase. Based on the thermal explosion metals that have been produced by aluminothermic theory developed by Frank-Kamenetskii  for reduction processes in either large. just prior to the reac. thermite reactions. the products are often in the liquid state. which are alloys of iron containing a sufficient amount tion is given by . they do not fit the general exothermic criterion pounds has been demonstrated relatively recently. U) and rationalized in terms of the high-temperature require. ferromolybdenum. 1. Using this ments with iron ore by aluminium. 3FeO + 1/3A1203 (7) 2800 ~ This lower melting point facilitates phase separation of metal from the oxide. Although preparation of alkaline earth metals (Group IIA) and 5. Aluminium also FeO + A1203 --+ FeAI204 (8) has lower vapour pressure and when reacted at 1 atm Although this approach provides a direct examination does not usually boil at the reaction temperature. Alternatively. can be controlled by both the reactant particle size 3701 . ignition [5-]. first of all. aluminium is cheaper than process. manganese. The reaction temperature.according to Moreover. Nb) and sample centre temperature. can be separated from the lighter oxide evolution. Although there of A1203). of the structure and chemical composition changes.A1203 which melts at tions to prepare chromium. they will not be covered in this review. ferroniobium. added to the thermite mixture to increase the heat fic gravity. there- thesis (SHS) reactions to synthesize intermetallic com. fluxing additives such as Goldschmidt and co-workers E2. the use of alumi- mechanisms. aluminium is still by far the most preferred order to form lower melting compounds . fore. Goldschmidt had employed this approach are other reducing agents. Mo. and sium. the maximum difference between the clude refractory metals (Cr. ferrovanadium. 115]. unlike calcium or magne- the heat-transfer condition of the sample examined sium. ferrotun- Miller  obtained an activation energy of gsten. these aluminother- 5. are produced principally by aluminothermic reduction processes [5-83. Metallurgical applications of their oxides by aluminium .
1. mite reactions have the advantage over these elemen- mite reactions is welding. 15 . With a to the electrode to add additional heat to the arc and medium-fine aluminium powder. Welding components to form the refractory compounds. 117. In an arc welding process using a con- (depicted by the dashed line) above the temperature sumable electrode. With a coarse powder. 1183. solidifies. :~ 50 typically by burning magnesium . '~. the molten metals formed settle to the 0 100 200 300 400 Median aluminiumparticle size (gm) bottom and are allowed to flow by gravity to the gap between the metal pieces. Synthesis of materials separation is not as good as with a medium-fine pow- The use of thermite-based reactions to synthesize der. The thermite mixture is packed in the crucible and ignited. Therefore. has been heat generation and heat loss are occurring simultan. for a highly fluid slag is longer.2. These reaction processes can be classified under smaller surface area to volume ratio of the larger the materials synthesis method commonly referred to mixture charge.2. it joins the two metal pieces together. Fine powder Mediumpowder Coarse powder slag aould Time Time Time Figure 15 Schematic illustration of the effect of aluminium particle size on temperature time profile during aluminothermic reduction [61 Figure 17 Schematic representation of the thermite welding process U0]. and metal-slag 5. 203. 20. 19. Because ybdenum yield in the aluminothermic reduction of MoO3 . another common form of welding. Instead of reaction is completed before appreciable heat is con. 39]. the reaction is provide additional filler metal [19. thermite mixtures are often bound required for a highly fluid slag is short. shown to improve the speed of welding and the rate of eously. The viscosity of molten high field-welding process for rails [11. 118]. Ther- The other important metallurgical application of ther. Many SHS reactions start with elemental 5. Goldschmidt also demonstrated the use of 90 the metal produced from thermite reactions for "-6 welding metal parts . the temperature drops rapidly and the time join the metals. of the relatively low cost of the equipment and mater- ials used. Increasing the batch size of the thermite mixture ceramic and composite materials under self-propagat- also increases the separation yield of the metal product ing conditions has gained attention in recent years because of the smaller heat loss resulting from the . 18]. thermite welding is still the most widely used and the batch size . the reducing agents in some cases [16. Most thermite alumina slags does not vary linearly with temPerature. Arc slower so that the peak temperature is lower because welding. The effects of aluminium particle size as self-propagating high-temperature synthesis (SHS). Reaction Thermite mixtures with copper oxides as the principal with a fine aluminium powder is so rapid that the oxidizing agents are also employed [17. but the time above the temperature required metal deposition [19. is achieved additional heat is generated after all the aluminium is by using an electric arc as the heat source to melt and oxidized. 17 . Arc a high peak temperature is produced. 20. molten duration is illustrated in Fig. Once the reac- 40 I I I tion is complete. welding processes use iron produced from the alumi- but decreases abruptly with relatively small increases nium-iron oxide mixtures [13-16] or alloys of iron in temperature only slightly above their melting points from the aluminium-iron oxide mixture with addition . As illustrated in Fig. 12]. The method is an energy- A1 M o O 3 system is shown in Fig. The effect of aluminium particle size on this of other oxides such as NiO  and MnO2 . but because no welding. with the use of a thermite mixture. 80 the apparatus for thermite welding is relatively simple and consists of a reaction crucible and a heated mould 60 in which the workpieces to be welded are placed. and batch size on the product metal yield for the or combustion synthesis. As the thermitic metal Figure ]6 Effect of aluminium particle size and batch size on mol. reaction is so slow that the temperature is never much higher than the required temperature. 16 . titanium and magnesium are also used as ducted away to the colder reaction vessel. aluminium. 100 1000g century. At the beginning of this tal reactions in that they start with naturally occurring 3702 . efficient way of synthesizing many refractory materials E38.
(K) Trap.1000. r. The use of an alternative To : 800 K) . for various systems. The magnitude of dc was found to decrease with increasing centrifugal acceleration and increasing initial temperature.g. 43] and BaC [44-46] powders. carbides. (1) Mo2C. solidification of the preforms of thermite mixtures in the furnace to the 3703 . a/9 = 1000. produce composite materials with phases uniformly tions exceed the melting points of both product distributed in the materials [47. and MC-A1/O3 a specific centrifugal acceleration. (3) WC. are presented in Table II ~ The phases in the thermite-based reactions. the diameter of the reaction volume. In this case. therefore. (2) WC + Co. With d > de. d. a/9 = 1000. a partial list of these is given in Table III. the crystalliza- tion may be unidimensional or in all directions. These pro- duction of the oxides to form the element. Calculation was performed in the approximation of complete suppression of vaporization of volatile components for the given composition of products. the cast refractory and oxide phases in the combustion products will be completely separated. of the melt. TABLE II Examples of thermite-based reactions for synthesis of refractory phases  System Original mixture Desired T~. a (in 9). m. They also demonstrated the feasibility of produ- vessel diameter. (6) W. aluminium is (5) WC. Taa. magnesium. The first Critical conditions for phase separation were found known composite material synthesisapplication was with respect to the vessel diameter. which done by Walton and Poulos  in 1959 to produce presents the completeness of phase separation (yield of ceramic-metal composites (e. ni. uniformity in grain size is typically found. 18. is used. the grain size increases from the periphery to the centre. The extremely high temperatures listed for Systems 1 and 2 are evidently very difficult to realize. and the com- bustion product consists of a fused but unseparated 1 . a/9 = 1. there are two sequential chemical refractory phases is readily achieved by dissolving the reactions in thermite-based synthesis reactions: (1) re. Fig. m) as a function of mets. of these reac. In the reactions presented in Table II. Trap= 2300 K. as a function of blisters and cracks . It is. the phase separation time is shorter than the time of thermal relaxation of the combustion products. With a (cm) d < L. various investigators have used thermite- compounds which can be separated from the lighter based reactions to produce composite materials. L. and (2) cesses with magnesium as the reducing agent have interaction of the reduced element to form the desired been applied to synthesis of submicrometre SiC [42. cing MSi A1103. M g O phase with a dilute acid solution. A1203-Cr). Examples of this type of synthesis of inor. reducing metal. Depending on the ratio between 0 . ganic refractory phases. forming a clean boundary between the layers.(K) product (calculated) (of desired product) 1 2MOO3 + 4Al + C Mo2C 5200 2573 2 3CrO3 + 6AI + 2C Cr3C 2 6500 2168 3 WO3 + 2A1 + C WC 3800 3058 4 3V205 + 10AI+ 6C VC 3400 2921 5 2MOO3 + 6AI + B/O3 MoB 3800 2823 6 CrO3 + 4AI + BzO3 CrB2 4100 2473 7 2WO 3 + 6A1 + B203 WB 3600 3073 8 3V20 5 + 22A1 + 6B203 VB2 3500 2673 9 3MoO 3 + 14A1+ 6SIO2 MoSi2 3200 2293 10 3CRO3 + 14AI + 6SIO2 CrSi2 3600 1748 11 3WO3 + 14AI+ 6SIO2 WSi2 3000 2433 12 3V2Os + 10AI + 3N2 VN 3400 2323 Note: Reducing agent aluminium. For each system. a/9 = 1000. (To = 300 K for all except (5) where used as the reducing metal. (4) VC. MB-AlzO3. separation of the desired Generally. or cer- cast refractory phase in the ingot. Over the past phases. on the other hand. possible to form cast refractory three decades. Zr and Ti) by heating the With d < dc (critical diameter). mass. a/9 .JJJ oJ 5 6 the diameter and height. it is possible to adiabatic combustion temperatures. composites (M = Cr. product phases. and in the central part there are shrinkage Figure 18 Yield of cast refractory compounds. compound. 48]. system is faster than phase separation. and oxide (A1203) by gravity or with use of a centrifuge. With the simultaneous production of multiple trides and silicides. With 0 2 4 6 d > L. a/9 = 1. such as borides. often results in product phases (MgO and the refractory phases) of solid forms because the adiabatic combus- oxides which are less expensive and more readily tion temperature is less than the melting points of the available than elemental reactant powders . In this case. By-product A1203. d.
3704 . SiC. Holt . AI + SiO2 + C + N 2 --.sNo. MozC + 2A1203  9. AI203.C). TiO2 + B203 + 10/3A1~ TiB2 + 5/3A1203 [47. In the latter mixture.s + 2A1203 + 1. attempts have been made to simultaneously hot- strated the possibility of forming A1203-B4C and press  or hot-roll  the mixture during the M g O B4C composites by a combustion process (Re. The predicted phases were found in the ucts under the self-propagating process are often por- products.ignition temperature. 49] 4. SiO2 + A1~ Si + AI203 + N2 + heat ~ 13-sialon. B4C + 2A1203 [42.5NaCN --. 46] 12. 2B203 + 4AI + C -. 46] 8. reaction in order to densify the product.5No. TAB L E I I I Reactions for synthesizing composite materials Reaction Reference 1. 3Fe304 + 8A1 ~ 4A1203 + 9Fe  6. A1203  Note: All reactions are balanced assuming the given starting compositions on the left side of the equations.5) + 2A1203  10. Park et al. A I 2 0 3 . and aluminium.  Figure 19 Spatial distribution of (1) A1203 and (2) B4C in the Figure 20 Spatial distribution of (1) MgO. noticeable amounts of magnesium borate phase were thesizing composites by thermite reactions include the also found in the combusted product. B203. 15R-sialon. Holt and W a n g and co-workers demon. and L o g a n and co-workers of studies to understand the reaction process of form- 1-49 53]. 2ZrO2 + 2SIO2 + 16/3A1~ 8/3A1203 + ZrSiz + Zr  3. Other recent studies of syn. Cutler et al. A1ON.M o 2 C . 1020 atm (secondary electron image) . Cr203 + 2AI -~ 2Cr + AI203 [97. preform is then infiltrated with aluminium. 3TiOz + 4A1 + 3/2C + 3/4N2 ~ 3Ti(Co. (2) B4C and 4A1 + 2B203 + C samples combusted at 1 atm (secondary electron (3) Mg3(BO3)2 in the 6Mg + 2B203 + C samples combusted at image) . al. AIN  13.5 3 ] began a series co-workers [40. The ture (4A1 + B 2 0 3 q. uniformly distributed product phases. R u s a n o v a et actions 7 and l 1 in Table III). metallurgy methods in producing finely dispersed and ture (6Mg + 2 B 2 0 3 + C) . 6Mg + 2B103 + C ~ 6MgO + B4C [45. This pro- bution of the M g O and B4C phases in the combustion cess is deemed advantageous over equivalent powder product starting with the stoichiometric reactant mix. except Reactions 12 and 13.  developed a process for producing bution of the A1203 and B~C phases in the combusted A1203 Cr A1 composites by first using A1-Cr203 product starting with the stoichiometric reactant mix. Because the TiB2-A1203 prod- composites. Since the early work done by Cutler et al. L o g a n and co-workers [ 4 9 .T i C x N I _ x the reactant particles. . Their studies resulted in (Reactions 6-10 in Table III) to synthesize A1203-SiC. AIN. and A 1 2 0 3 . 46]. 54] 2. 3TIO2+ 4A1 + 1. 2MoO 3 + 4A1 + C -. TiO2 + 4/3A1 + C ~ TiC + 2/3A1203  5. thermite reaction to form A1203 Cr preform. 20 shows the distri. ous. Fig. explored the possibilities of ing TiB2-A1203 composites starting with a mixture of using self-propagating thermite reaction processes TiO2. a qualitative model describing the interaction between A1203 B4C.5Na  11. SiO2 + 4/3A1 + C ~ SiC + 2/3A1203  7. 45. and Fig. W a n g and 1980s. 19 shows the distri. 3TiCo.
heated to 1853 K). and C. The centrifugal force assists the speed found to depend on the nitriding temperature. it is possible to regulate the the layer in the radial direction. B. and subsequently reached the highest temperature when all the packed 5. can undergo separation due to the difference in materials. The microstructure of the duce industrial products is the centrifugal thermite composite lining is dictated by the thermal history of process (C-T) of lining metal pipes with a ceramic the cooling process .3. The centrifugal thermite process. combination with a subsequent nitriding process. and gas pressure (Fe203-A1 or Fe203-Mg). Lisachenko et the pipe. and the additives to thermite powders . By chang. At of separation and also the effective expulsion of trap- lower nitriding temperatures (1400-1600~ a mix. The result is the formation of ture of 13-sialon. ped and impurity gases. Using thermite during the centrifugal thermite reaction process is reactions to synthesize materials can also be carried shown in Fig. It induce the thermite reaction 3SIO2 + 4 A l ~ 3Si + then dropped rapidly when the fume generated was 2A1203 . methods studied were by: (1) a thermite reaction environmental gas content . the product phases are in the liquid state and. Several process parameters that SiOz-A1 mixture either with or without the addition affect the composites were investigated. The three ignition cluded thermal insulation . Schaffer and McCormick creased around the point of ignition (1) and then  demonstrated that it is possible to form 1~' brass decreased as the reaction proceeded to propagate in by ball milling a mixture of CuO. 21. Si-A1203 mixture was then nitrided at elevated tem. 1600 =4> Time Figure 22 Schematicillustration of the temperature profile of the hollow surface measured by an infrared radiation thermometer during the centrifugalthermite process: (1) ignition. Hida and Lin observed that grinding can acutely when the whole interior surface had reacted.  investigated the effect of initial composition Much of the research and development work of the and the ignition method on the phase composition of process has been carried out by Odawara and co- the combustion product obtained by reacting the workers [58. which bonds to the inside of 15R-sialon were found in the product. A1203) [58 61]. form ceramic layer. then followed (Stage C). Many industrial appli. It to self-combustion (i. abrasion-resistant. the com. The phase composition of the product was their densities.synthesized sialon materials by first reacting the the pipe is being rotated about its axis. is obtained. ZnO and calcium the longitudinal direction. and the composi. The temperature first in- out by mechanical means. being blown off (2). and then into tion of the atmosphere. cooling cess . AlzO3 and A1N results. A. inner surface of the hollow body first. The temperature rose powders. and (3) heating . molten state becomes longer. and heat-resistant ce.g. Coating by centrifugal thermite process thermite powder had reacted. (2) plasma. 70]. 3705 .~ 2200 FezO3+ 2A1 A1203+ 2Fe + 836 ld 2000 / 1800 <. It involves first packing a powdery thermite mixture. against the inner surface of the - pipe and then igniting the mixture at one point while . was confirmed by temperature measurements along ing the method of initiating the combustion. The reaction proceeded to propa- gate in the radial direction (Stage B). 15R-sialon. The cooling process An interesting utilization of thermite reaction to pro. it is The schematic illustration of temperature at a hollow then possible to obtain various nitride-containing or surface measured by an infrared-radiation thermometer sialon-containing ceramic materials. 61 70]. is illustrated in Fig. which provides a rapid and econ- omical method for producing such metal-ceramic composite pipes. 22 [63. process . the pipe length that the reaction proceeds along the position of the batch composition.(2) blow-offof fumes. propagation of reaction along the hollow surface. a denser and more uni- cations require pipes and vessels with a corrosion. al. At bonded low-porosity layers of A1203 on top of the a higher temperature (1750~ only 13-sialon and higher density iron layer. such as the 2400 A1-FezO3 mixture. Figure 21 Schematicrepresentationof the centrifugal-thermitepro. As the duration of metal in the molten state becomes ramic bonded to the metallic body. As the duration of ceramic material (e. there- perature for an extended period of time to form sialon fore. resulting in a homo- phase composition of the combustion product. and these in- of carbon in a nitrogen atmosphere. The large amount of heat released by the thermite reaction. resistant. but with larger grains.e. Because of the A1-SiO2 thermite to form silicon and A1203. centrifugal force . propagation of reaction in the radial direction. and in geneous quality in the direction of pipe length .
This longer molten metal dura. .  involves first In addition to utilizing the heat generated by the mixing radioactive wastes into a thermite mixture and thermite reaction. mixture . momentarily. The principal thermite reaction for this process is Thermite compositions such as Si-MoO3-WO3 can be incorporated into the starting powder mixture used 4Fe203 + 3Si ~ 3Fe/SiO4 + 2Fe (12) to produce thin-layer passive electronic components with a heat of reaction of -245 cal. economically suitable initiates the following sequential reactions for large-scale industrial processing. The heat of thermite reac- the mould. be formed by irradiation of CO2 laser on a thin pow- quired to preheat the mixture before ignition. which has a higher density. For example. Conclusion The high energy generated from the thermite reac. applications where. ZrO2. The product mixture is melted by the ventional powder metallurgy approach . Another application was demonstrated fore. only relatively these components. results in slower cooling. reaction to achieve certain overall material properties. and has comparable leaching mite reactions can be used to provide the oxide characteristics as the glass from the conventional hardeners (such as A1203. Such com. According to this study. Lastly. surface . once reacted. Such a process has been shown to metal oxides generated from nuclear power plants is provide finer dispersion hardeners ( < 1 lam) and more mixed with aluminium powder and ignited to reduce uniform distribution of these hardeners over the con- the metal oxides. Because this outer ceramic layer tion. heat generated from the thermite reaction and thus can be cast into shape. the thermite reaction tions involving a metal and an oxide. In ThO2) in the process of making dispersion-hardened the third method . production of high- posites are demonstrated by the following reactions pressure and high-velocity gases is required. however. and possibly many electronic applications [122. The circuit . able energy that can be released by a thermite reaction tion. der layer of MoO3-A1 mixture applied on the wafer over. This method reduces the baking the heat required for the formation of molten silicates temperature and time typically needed to produce is derived from the chemical reaction.longer. method developed by Spector et al. and this thermite layer in the solid product from thermite reactions have can be ignited by electrical current to self-destruct the been developed by several investigators [71-73]. This centrifugal mixture (2A1 + 3CuO) to develop small torches for thermite process has also been extended to forming applications where the amount of space is limited. The reducing (8A1 + 3Fe/O3 ~ 4Al103 + 9Fe) has been considered tendency and the physical properties of the metal as the fuel for heating the motive fluid in a gas turbine and the physical properties of its corresponding oxide 3706 . tions has also been applied to sintering ceramic pow- ders [79. 6. causing pactness of the thermite mixture. many other interesting applications then igniting the mixture to form highly water insol. which has a lower density. In ceramic-ceramic composite pipes 1-69]. the a solid electrolyte. 80] and for relieving localized stress in welds.4. resistors) . The thermite mixture A1-WO3 can be vacuum 5. radioactive waste-containing ferrous alloys.  involves using aluminium as the reducing agent to react with Mo + xSi -* MoSix (14) metallic oxidants (Fe/O3 and/or MnO2). [-81]. which in molten form is conductive. 123]. thus thermal at a high rate for a limited period of time. The product Metal silicides have low resistivity. Other novel applications deposited as thin layer on a substrate underlying or Cost-effective methods of storing radioactive wastes overlying a thin-film circuit. 77]. of the thermite reaction make it suitable for such an sulting in microcrack formation in this layer. There. can generate sufficient heat to melt does not wet the inner surface of the mould. the thermite reac- as the outer layer. They employed a thermite obtain a desirable microstructure. In this application. The method is reported to reduce the waste volume with low cost. both silicon and Fe203 are readily available. application. and the quietness the product ceramic layer to compress more and re. wetting between the product metal and the to be used for torpedo propulsion . a balance of these two stages is needed in order to by Mohler et al. as the inner layer reaches above the ignition temperature of the thermite and the carbide or boride. good thermal and of the thermite reaction is reported to be a solid chemical stability. ther- also vitreous phases. also use the substances produced by the thermite uble polysilicates which fix the radioactive materials. A MoSi film on a silicon wafer can low-temperature furnace facilities (600~ are re. A thermal cell employing a ther- The process results in the formation of the oxide mite reaction can be activated when the external gas (A1103).g. Because part of (e. thermite mixtures with MoO3 + 2A1 + 1/2C --+ A1203 + 1/2Mo2C (10) additions of substances that decompose into gases at MoO3 + 2A1 + B --* A1203 + MoB (11) high temperature can be ignited to result in such a condition [76. SiO2 and vitrification process for storing radioactive waste. This paper presents a general review of thermite reac- tion is an excellent heat source for many other special tions which are exothermic oxidation-reduction reac- applications. Another thermite MoO3 + 2A1 --* Mo + A1203 (13) method proposed by Rudolph et al. and are desirable materials for containing several crystalline phases. the com- shrinkage of the outer metal pipe will be larger. such as in the demolition of concrete. More. TiO2. the CO2 laser relatively inexpensive and thus. The consider- outer pipe improves. ceramic composite pipe could be easily removed from thus completing a circuit.
Acad. BARESKOV. Y. Munir and J. DARPA/ARMY SHS Symposium Proceed- CHIGAREV. Vol. in "Combustion and Plasma Synthesis of High-Temperature Phys. IL. edited by Z. D. Illinois Institute of Techno. J. Sci. A. G. H. 1982) pp. 1987 ) pp. 40. 41. 1973) pp. LYUBCHENKO and G. TARLINSKI. B. ERMAKOV. A. Ceram. Daytona Beach. ibid. MERZHANOV. E R M A K O V . US Pat. Transl. LOGAN.) 21 (1985) 421. OH. Gabriel. Weld. (Amer.V. J. J.A. Holt (VCH. NJ. Z. J .  (1980) 26. chemical reaction. 2.Shock Waves (Engl. V. E. A. 26. J. Holt (VCH. ature Synthesis". V. loterm. NEIFELD. electrical current. in "Advances in Ceramics". W. 4. A. propagation. edited by Z. 895 628 (1908). I. S. J. ial-related inventions based on thermite reactions. H. Materials". J. 6 (1985) 715. VIRKAR and J. R. 2t. cermets. V A U T I N . M. inar" (liT Research Institute. USSR (Phys. Combust.E. STRUNINA. Nater.A. ibid. 22. ldem. PRICE and W.) 255 (1980) 503. GUPTA. LOGAN. nia.L. Wax and 19. Explos.  (1985) 39. 47. 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