Fullerenes. Nanotubes. and Carbon Nanostructures. 13: 121-129 2005 Copyright C Taylor Francis, Inc. SN 1536-383X print/1536-4046 online DOI:10.1081/FST-200039233 Common Features of the Formation Mechanism of carbon filaments Nanotubes, and Silicon Carbide Whiskers on Metal Catalysts V. L. Kuznetsov, A. N. Usoltseva, and L. N. mazon Boreskov Institute of Catalysis, Novosibirsk, Russia Abstract: The formation mechanisms of carbon deposits and silicon carbide whiskers on metal surface catalysts have some common steps. The most important are:(1)the formation of metal particle alloys oversaturated with carbon or silicon and carbon atoms and (2)the nucleation of corresponding deposits on the metal catalyst surface A thermodynamic analysis of the carbon and or silicon carbide nucleation on the metal surface was performed. The master equations for the dependence of critical radius of carbon or SiC nucleus on reaction parameters, such as reaction temperature, supersaturation degree of catalyst particles with C(or Si and C), work of adhesion of metal to carbon(or metal to SiC)were obtained. These equations combined with the phase diagram approach can be used for the description of different scenarios of arbon and or SiC deposits formation and for the development of the main principles of catalyst and promoters design. Keywords: Nucleation, carbon filaments, nanotubes, Sic whiskers, formation mechanis INTRODUCTION Carbon deposition from metal-carbon mixtures is a key step for many important process, namely, catalyst deactivation, carbon filaments, and nanotubes formation(here we limit our consideration with carbon filaments Address correspondence to V.L. Kuznetsov, Boreskov Institute of Catalysis, Lavrentieva 5, Novosibirsk 630090, Russia. E-mail: kuznet @catalysis nsksu
Common Features of the Formation Mechanism of Carbon Filaments, Nanotubes, and Silicon Carbide Whiskers on Metal Catalysts V. L. Kuznetsov, A. N. Usoltseva, and I. N. Mazov Boreskov Institute of Catalysis, Novosibirsk, Russia Abstract: The formation mechanisms of carbon deposits and silicon carbide whiskers on metal surface catalysts have some common steps. The most important are: (1) the formation of metal particle alloys oversaturated with carbon or silicon and carbon atoms and (2) the nucleation of corresponding deposits on the metal catalyst surface. A thermodynamic analysis of the carbon and/or silicon carbide nucleation on the metal surface was performed. The master equations for the dependence of critical radius of carbon or SiC nucleus on reaction parameters, such as reaction temperature, supersaturation degree of catalyst particles with C (or Si and C), work of adhesion of metal to carbon (or metal to SiC) were obtained. These equations combined with the phase diagram approach can be used for the description of different scenarios of carbon and/or SiC deposits formation and for the development of the main principles of catalyst and promoters design. Keywords: Nucleation, carbon filaments, nanotubes, SiC whiskers, formation mechanism INTRODUCTION Carbon deposition from metal –carbon mixtures is a key step for many important process, namely, catalyst deactivation, carbon filaments, and nanotubes formation (here we limit our consideration with carbon filaments Address correspondence to V. L. Kuznetsov, Boreskov Institute of Catalysis, Lavrentieva 5, Novosibirsk 630090, Russia. E-mail: kuznet@catalysis.nsk.su Fullerenes, Nanotubes, and Carbon Nanostructures, 13: 121–129, 2005 Copyright # Taylor & Francis, Inc. ISSN 1536-383X print/1536-4046 online DOI: 10.1081/FST-200039233
V.L. Kuznetsov, A. N. Usoltseva, and L. N. Mazon and nanotubes formation)(1). Selective methods of synthesis of these (2). Silicon carbide, which has many superior properties, such as hardness ind strength, high resistance to oxidation and corrosion, low coefficient of thermal expansion, and high thermal conductivity (3), can be also produced he form of whiskers using metallic cataly CARBON AND SIC DEPOSITS' FORMATION ON METAL CATALYSTS ACCORDING PHASE DIAGRAM APPROACH The careful analysis of catalytic methods of production of carbon products and Sic whiskers allows to find a lot of similarities and common steps of these very different processes at a fist glance. Fig. I demonstrates the carbon(A) nd Sic(B)deposition in terms of phase diagrams. Mention that the influence of the carbon and /or Si-C precursors'nature on the yield of final products can be discussed in terms of equilibrium concentrations of reaction products and intermediates along with kinetic stability of different products. However. these factors are not considered here Carbon deposits formation on metal catalysts can occur at high(higher than metal-carbon eutectic temperature) and moderate temperatures(from 500C up to metal-carbon eutectic temperature)(see Fig 1A). High-tempera ture route bases on the preliminary evaporation of carbon and metal sources (using arc discharge, laser ablation, and solar ovens) with the forthcoming vapor+solid c solution liquid+solid c d. solid M+solid Figure 1.(A) Metal-carbon phase diagram. Lines a'-b'-c'-d and a-b"-c"show the high temperature and moderate temperature routes of carbon deposits formation respectively(13).(B)Ni-C-Si phase diagram at 1633 K(data from Ref (14)), L, region of formation of liquid phase: A, region of coexistence of Sic and liquid hase(1); B, region of coexistence of Sic enriched with carbon and liquid phase: c, region of coexistence of solid carbon and liquid phase
and nanotubes formation) (1). Selective methods of synthesis of these products are highly desirable due to wide perspectives of their utilization (2). Silicon carbide, which has many superior properties, such as hardness and strength, high resistance to oxidation and corrosion, low coefficient of thermal expansion, and high thermal conductivity (3), can be also produced in the form of whiskers using metallic catalysts. CARBON AND SIC DEPOSITS’ FORMATION ON METAL CATALYSTS ACCORDING PHASE DIAGRAM APPROACH The careful analysis of catalytic methods of production of carbon products and SiC whiskers allows to find a lot of similarities and common steps of these very different processes at a fist glance. Fig. 1 demonstrates the carbon (A) and SiC (B) deposition in terms of phase diagrams. Mention that the influence of the carbon and/or Si –C precursors’ nature on the yield of final products can be discussed in terms of equilibrium concentrations of reaction products and intermediates along with kinetic stability of different products. However, these factors are not considered here. Carbon deposits formation on metal catalysts can occur at high (higher than metal –carbon eutectic temperature) and moderate temperatures (from 5008C up to metal –carbon eutectic temperature) (see Fig. 1A). High-temperature route bases on the preliminary evaporation of carbon and metal sources (using arc discharge, laser ablation, and solar ovens) with the forthcoming Figure 1. (A) Metal–carbon phase diagram. Lines a0 –b0 –c0 –d0 and a00 –b00 –c00show the high temperature and moderate temperature routes of carbon deposits formation respectively (13). (B) Ni –C–Si phase diagram at 1633 K (data from Ref. (14)), L, region of formation of liquid phase; A, region of coexistence of SiC and liquid phase (l); B, region of coexistence of SiC enriched with carbon and liquid phase; C, region of coexistence of solid carbon and liquid phase. 122 V. L. Kuznetsov, A. N. Usoltseva, and I. N. Mazov
Mechanism of Formation of Filaments, Nanotubes, and whiskers condensation leading to the formation of metal-carbon particles(region between a-b points of Fig. 1A). Deposition of carbon starts when the particle temperature drops below the values corresponding to the liquid line f metal-carbon phase diagram(point b). Carbon atoms from the metal ulk diffuse through the metal particle to the surface and form primary nucleus. Carbon atoms for the forthcoming growth can be also supplied fter dissolution of amorphous carbon deposits. For this temperature interval the equilibrium concentration of carbon in metal particle is deter mined by the points on the liquid line. The process stops after dramatic decrease of the carbon diffusion rates at low temperatures(below the tempera ture corresponding points c-d). Moderate temperature route attributes with CVD methods of carbon filaments and nanotubes production(carbon concen- tration varies along the line a-b-c). It occurs at the temperature region below eutectic temperature line of phase M-C phase diagram. Formation of metal-carbon particles proceed via the decomposition of hydrocarbons, alcohols, or carbon monoxide on the surface of primary metal catalyst particles. So, for the case, when the carbon deposition occurs on low dis- persion metal catalyst and catalyst metal particles exist in a solid state, the equilibrium concentration of carbon is determined by point b". After reaching the high degree of metal particle saturation with carbon, the process of carbon formation begins (in the region of point c").However, highly dispersed metal particles and especially metal-c car forming in situ can exist in a liquid-like state, even at temperatures below eutectic temperature. Metal-carbon particles can be produced also in situ via the decomposition of volatile organometallic compounds in a reaction gas flow containing hydrocarbon or Co (4-7)or via the in situ reduction of metal oxide solid solutions (8-10). Carbon deposition starts after metal particle supersaturate with carbon(somewhere near point c") According to our literature and experimental data, catalytic SiC whisker formation proceeds on liquid metal particles at 1,300-1, 700K(11). Metal catalysts activate Si and C precursors(SiO2, Sio, graphite, hydrocarbons, anosllane lese processes lead to the metal-silicon-carbon particle formation. SiC whisker growth starts after the nucleation SiC on the metal surface. Steady whisker growth requires the stable flow of carbon and silicon through the metal particle. Fig. IB shows a schematic isothermal section of the Ni-Si-C ternary phase diagram at T=1633 K. According to am,when pure Ni comes into contact with Si-and C-containing initial products, dissolution of Si and C atoms occurs. Thus, Ni is continuously enriched with Si and C and the composition of the metallic phase varies following one of the lines A, B, or C. Complete melting of the metal particle occurs at region L, after which metal is significantly saturated with Si and C atoms and forms the liquid alloy. Due to the different ratio of si and C in the regions A, B, and C formation of different products occur. In the A region, deposition of Sic proceeds, while in the B and C regions
condensation leading to the formation of metal –carbon particles (region between a0 –b0 points of Fig. 1A). Deposition of carbon starts when the particle temperature drops below the values corresponding to the liquid line of metal –carbon phase diagram (point b0 ). Carbon atoms from the metal bulk diffuse through the metal particle to the surface and form primary nucleus. Carbon atoms for the forthcoming growth can be also supplied after dissolution of amorphous carbon deposits. For this temperature interval the equilibrium concentration of carbon in metal particle is determined by the points on the liquid line. The process stops after dramatic decrease of the carbon diffusion rates at low temperatures (below the temperature corresponding points c0 –d0 ). Moderate temperature route attributes with CVD methods of carbon filaments and nanotubes production (carbon concentration varies along the line a00 –b00 –c00). It occurs at the temperature region below eutectic temperature line of phase M–C phase diagram. Formation of metal –carbon particles proceed via the decomposition of hydrocarbons, alcohols, or carbon monoxide on the surface of primary metal catalyst particles. So, for the case, when the carbon deposition occurs on low dispersion metal catalyst and catalyst metal particles exist in a solid state, the equilibrium concentration of carbon is determined by point b00. After reaching the high degree of metal particle saturation with carbon, the process of carbon formation begins (in the region of point c00). However, highly dispersed metal particles and especially metal –carbon particles forming in situ can exist in a liquid-like state, even at temperatures below eutectic temperature. Metal –carbon particles can be produced also in situ via the decomposition of volatile organometallic compounds in a reaction gas flow containing hydrocarbon or CO (4 – 7) or via the in situ reduction of metal oxide solid solutions (8 – 10). Carbon deposition starts after metal particle supersaturates with carbon (somewhere near point c00). According to our literature and experimental data, catalytic SiC whisker formation proceeds on liquid metal particles at 1,300– 1,700 K (11). Metal catalysts activate Si and C precursors (SiO2, SiO, graphite, hydrocarbons, CO, organosilanes); these processes lead to the metal – silicon –carbon particle formation. SiC whisker growth starts after the nucleation SiC on the metal surface. Steady whisker growth requires the stable flow of carbon and silicon through the metal particle. Fig. 1B shows a schematic isothermal section of the Ni–Si –C ternary phase diagram at T ¼ 1633 K. According to this diagram, when pure Ni comes into contact with Si- and C-containing initial products, dissolution of Si and C atoms occurs. Thus, Ni is continuously enriched with Si and C and the composition of the metallic phase varies following one of the lines A, B, or C. Complete melting of the metal particle occurs at region L, after which metal is significantly saturated with Si and C atoms and forms the liquid alloy. Due to the different ratio of Si and C in the regions A, B, and C formation of different products occur. In the A region, deposition of SiC proceeds, while in the B and C regions, Mechanism of Formation of Filaments, Nanotubes, and Whiskers 123
V. L Kuznetsov. A.N. Usoltseva, and L.N. mazon formation of SiC enriched with carbon and pure carbon deposits occur. THERMODYNAMIC ANALYSIS OF CARBON AND/OR SIC DEPOSITS NUCLEATION ON METALS The consideration of phase diagrams demonstrates that for both processes in addition to the activation of initial reagents, metal catalyst takes part as media for carbon and /or Si and C dissolution providing the dramatic decrease of temperature solidification of carbon(or SiC). Catalyst also forms the metal- carbon (or M-Sic) interfaces responsible for the formation of different carbon(or SiC) deposits. Thus, for any type of carbon or Sic deposits, their formation occurs via the common steps including metal-carbon and /or metal-silicon-carbon particle formation and subsequent nucleation of corre- sponding deposits. The consideration of thermal stability of nanocarbons (namely, single walled carbon nanotubes (SWNT), fullerene-like species on diamond surface, small graphite blocks in the graphitization processes] either with the possibility of formation of very long SWNT ropes lead us to the conclusion that once formed the nanosize carbon nuclei are stable enough and the nuclea- tion step can determine the type of carbon deposit. Thus, the conditions of formation, at least they can influence the size and polytype of Sic C whileoo rimary nucleation are the most important for selective production specific types of carbon deposits. They are also important for Now, we summarize the data on the thermodynamic analysis of carbon nd or SiC nucleation on metal surfaces to estimate the influence of eaction parameters on the nucleation step, which is a crucial stage for the formation of different carbon deposits. The flat form of carbon nucleus was proved in Ref. (1). The form of Sic nucleus was chosen on the base of obser- vation of flat metal-whisker interfaces. It was found SiC-catalyst interface is crystal face [11 1) for cubic modification and 1000 1) for hexagonal one. According to experimental data we consider the change in Gibbs free energy using the simplest model of carbon(and /or SiC) deposit nucleation where a flat, round nucleus with radius r and height h is bonded to the metal surface(see Fig. 2). In this case the variation in Gibbs free energy may be written as Eq (1) △Gpre+△ esrf+△E where AGprec represents the change of free energy following the precipitation of C (SiC)in the bulk part of nucleus, AEsurface reflects the change in surface free energy, AEedge is the change of edge free energy
formation of SiC enriched with carbon and pure carbon deposits occur, respectively. THERMODYNAMIC ANALYSIS OF CARBON AND/OR SIC DEPOSITS’ NUCLEATION ON METALS The consideration of phase diagrams demonstrates that for both processes in addition to the activation of initial reagents, metal catalyst takes part as media for carbon and/or Si and C dissolution providing the dramatic decrease of temperature solidification of carbon (or SiC). Catalyst also forms the metal– carbon (or M–SiC) interfaces responsible for the formation of different carbon (or SiC) deposits. Thus, for any type of carbon or SiC deposits, their formation occurs via the common steps including metal–carbon and/or metal–silicon–carbon particle formation and subsequent nucleation of corresponding deposits. The consideration of thermal stability of nanocarbons [namely, singlewalled carbon nanotubes (SWNT), fullerene-like species on diamond surface, small graphite blocks in the graphitization processes] either with the possibility of formation of very long SWNT ropes lead us to the conclusion that once formed, the nanosize carbon nuclei are stable enough and the nucleation step can determine the type of carbon deposit. Thus, the conditions of primary nucleation are the most important for selective production of specific types of carbon deposits. They are also important for SiC whisker formation, at least they can influence the size and polytype of SiC. Now, we summarize the data on the thermodynamic analysis of carbon and/or SiC nucleation on metal surfaces to estimate the influence of reaction parameters on the nucleation step, which is a crucial stage for the formation of different carbon deposits. The flat form of carbon nucleus was proved in Ref. (1). The form of SiC nucleus was chosen on the base of observation of flat metal –whisker interfaces. It was found SiC –catalyst interface is crystal face f111g for cubic modification and f0001g for hexagonal one. According to experimental data we consider the change in Gibbs free energy using the simplest model of carbon (and/or SiC) deposit nucleation, where a flat, round nucleus with radius r and height h is bonded to the metal surface (see Fig. 2). In this case the variation in Gibbs free energy may be written as Eq. (1): DGS ¼ DGprec þ DEsurface þ DEedge ð1Þ where DGprec represents the change of free energy following the precipitation of C (SiC) in the bulk part of nucleus, DEsurface reflects the change in surface free energy, DEedge is the change of edge free energy. 124 V. L. Kuznetsov, A. N. Usoltseva, and I. N. Mazov
Mechanism of Formation of Filaments, Nanotubes, and whiskers carbon nucleus =1.767Jm2 a=0.718Jm metal-carbon particle Figure 2. Form of nucleus of graphite-like carbon(A)and silicon carbide(B) Table 1 represents the terms of Eq. (1)for the nucleation of graphite-like carbon and SiC Where Na is the Avogadro constant, AHi are the enthalpies of formation of corresponding single bonds(M-C, Si-C, C-C, Si-H, C-H), Q is a constant for curved edge of graphite-like nucleus following from the elas city theory, xo and x are the saturated and actual molar content of carbon and or silicon in metal particle, Ai represents the exchange energy of the binary i-j solution, oi is the corresponding specific surface energy, and w is the work of adhesion of metals to C(graphite)and Sic The maximum of AGs as a function of corresponds to the critical size of the nucleus d(AGs/dr=0, from which we easily deduce the equations of rcrit for graphite-like carbon deposits, Eq. (2) △HM-C-AHcc,Q)「RT·h rcrit A 45)w10+(Wwa-20v and for SiC whiskers, Eq (3) 2AHs;-c-AHcH-△Hsi-H h The details of getting these equation were published elsewhere(for carbon deposits see Refs. (1, 11)and for Sic (12) Eqs. (1)and(2)express the dependence of the critical radius on the different reaction parameters. The analysis of the influence of different reaction par- ameters on the critical radius of the carbon nucleus allows us to draw th following conclusions. The radius of critical nucleus decreases with increasing temperature(D), with increasing saturation coefficient of the metal-carbon
Table 1 represents the terms of Eq. (1) for the nucleation of graphite-like carbon and SiC. Where NA is the Avogadro constant, DHij are the enthalpies of formation of corresponding single bonds (M –C, Si –C, C –C, Si –H, C –H), Q is a constant for curved edge of graphite-like nucleus following from the elasticity theory, x0 and x are the saturated and actual molar content of carbon and/or silicon in metal particle, lij represents the exchange energy of the binary i–j solution, si is the corresponding specific surface energy, and Wad is the work of adhesion of metals to C (graphite) and SiC. The maximum of DGS as a function of r corresponds to the critical size of the nucleus d(DGS/dr ¼ 0, from which we easily deduce the equations of rcrit for graphite-like carbon deposits, Eq. (2): rcrit ¼ DHMC DHCC 2NA rCC þ Q 4:5h RT h VM ln x x0 þ ðWad 2sgraphiteÞ 1 ð2Þ and for SiC whiskers, Eq. (3): rcrit ¼2DHSiC DHCH DHSiH 4rCCNA h Vmolar RT ln x x0 C x x0 Si þ X i=j lijxixj ( )þ ð2sSiC WadÞ " #1 : ð3Þ The details of getting these equation were published elsewhere (for carbon deposits see Refs. (1, 11) and for SiC (12). Eqs. (1) and (2) express the dependence of the critical radius on the different reaction parameters. The analysis of the influence of different reaction parameters on the critical radius of the carbon nucleus allows us to draw the following conclusions. The radius of critical nucleus decreases with increasing temperature (T), with increasing saturation coefficient of the metal–carbon Figure 2. Form of nucleus of graphite-like carbon (A) and silicon carbide (B). Mechanism of Formation of Filaments, Nanotubes, and Whiskers 125
Table 1. The terms of Eq (1)for the graphite-like carbon and SiC nucleation () Tr(2 graphite-Wad △HM-C-△Hc-c,Q h △Hc-H+△Hsi-H-2MHsi RT In +∑Ax 4NArC-C
Table 1. The terms of Eq. (1) for the graphite-like carbon and SiC nucleation DGprec DEsurface DEedge C pr2h VM RT ln x x0 C pr2(2sgraphite 2 Wad) 2pr DHMC DHCC 2NArCC þ Q4:5h SiC pr2h Vmolar RT ln x x0 C xx0 Si þXi=j lijxix j ( ) pr2(2sSiC 2 Wad) 2pr DHCH þ DHSiH 2DHSiC 4NArCC V. L. Kuznetsov, A. N. Usoltseva, and I. N. Mazov 126
Mechanism of Formation of Filaments, Nanotubes, and whiskers solution(x/xo), and with increasing work of adhesion(Wad). Note that this criterion gives us a minimal value for the radius of the carbon nucleus Nuclei with smaller radii are not stable, but nuclei with larger sizes can continue to row. The comparison of calculated data of the size of carbon nucleus critical radii with the smallest size of observed carbon nanotubes and carbon filaments demonstrate reasonable coincidence of calculated and experimental data (1, 11). It was shown that the increase of reaction temperature leads to the formation of smaller nuclei, and finally to the formation of SWNTs. The usage of metals characterized by a higher metal-carbon energy bond leads to nanotubes with smaller diameters. SWNT growth is likely to proceed on liquid metal particles. Elements that decrease the melting point of the catalyst carbon mixture and do not form stable compounds with carbon at the reaction temperature also promote the formation of SWNTs. The values of rert (30-40 A)calculated for SiC nucleus according to Eq (3) are also very close to the smallest size of experimentally observed whiskers'tips. So Fig. 3 demonstrates the tip of Sic whisker, which was produced with iron catalyst at 1470K, with the smallest flat part close to 65a 65 2,51 风 Figure 3. HR TEM image of the tip of SiC whisker(see insert) produced on Fe catalysts at 1470 K using SiO2 and carbon soot as precursors in hydrogen atmosphere. One can see 3C polytype of SiC on end of the tip following numerous stacking fault dislocation
solution (x/x0)i, and with increasing work of adhesion (Wad). Note that this criterion gives us a minimal value for the radius of the carbon nucleus. Nuclei with smaller radii are not stable, but nuclei with larger sizes can continue to grow. The comparison of calculated data of the size of carbon nucleus critical radii with the smallest size of observed carbon nanotubes and carbon filaments demonstrate reasonable coincidence of calculated and experimental data (1, 11). It was shown that the increase of reaction temperature leads to the formation of smaller nuclei, and finally to the formation of SWNTs. The usage of metals characterized by a higher metal–carbon energy bond leads to nanotubes with smaller diameters. SWNT growth is likely to proceed on liquid metal particles. Elements that decrease the melting point of the catalyst– carbon mixture and do not form stable compounds with carbon at the reaction temperature also promote the formation of SWNTs. The values of rcrit (30 – 40 A˚ ) calculated for SiC nucleus according to Eq. (3) are also very close to the smallest size of experimentally observed whiskers’ tips. So Fig. 3 demonstrates the tip of SiC whisker, which was produced with iron catalyst at 1470 K, with the smallest flat part close to 65 A˚ . Figure 3. HR TEM image of the tip of SiC whisker (see insert) produced on Fe catalysts at 1470 K using SiO2 and carbon soot as precursors in hydrogen atmosphere. One can see 3C polytype of SiC on end of the tip following numerous stacking fault dislocation. Mechanism of Formation of Filaments, Nanotubes, and Whiskers 127
V. L. Kuznetsov, A. N. Usoltseva, and l N. mazo Eqs.(2)and (3)combined with the phase diagram approach can be used for the description of different scenarios of carbon (11)and/or SiC(12) deposit formation and for the development of the main principles of catalyst and promoter design ACKNOWLEDGMENTS inancial support by INTAS (01-254, YSF 03-55-1816), RFBR(02-03- : 96), and CRDF and Department of Education of RF(No. -008-X1)under REFERENCES 1. Kuznetsov. V L. Usoltseva. A.N. Chuvilin. A L. Obraztsova. E D. and Bonard, J -M.(2001)Thermodynamic analysis of nucleation of carbon deposits on metal particles and its implications for the growth of single-wall carbon nanotubes. Phys. Rev. B. 64: 5401-5408. 2. 2004)Special issue on Advances in Nanotubes. MRS Bulletin, 4: 237-285 3. Chrysanthou, A and Grieveson, P(1991) Formation of silicon carbide whiskers and their microstructure. Mater. Sci.. 26: 3463-3476 4. Satishkumar, B. C, Govindaraj, A, Sen, R, and Rao, C N.R. (1998)Single-walled nanotubes by the pyrolysis of acetylene-organometallic mixtures. Chem. Phys 5. Cheng, H M.Li, F. Su, G, Pan, H.Y., He, L.L., Sun, X, and Dresselhaus, M.s. (1998)Large-scale and low-cost synthesis of single-walled carbon nanotubes by the catalytic pyrolysis of hydrocarbons. Appl. Phys. Left, 72: 3282-3284 6. Nikolaev, P, Bronikowski, M, Bradley, R, Rohmund, F, Colbert, D, Smith, K and Smalley, R E.(1999) Gas-phase catalytic growth of single-walled carbon nanotubes from carbon monoxide. Chem. Phys. Lett., 313: 91-97 7. Zhou, W Ooi, Y, Russo, R, Papanck, P, Luzzi, D, Fischer, J, Bronikowski, M Willis, P, and Smalley, R E.(2001)Structural characterization and diameter dependent oxidative stability of single wall carbon nanotubes synthesized by the catalytic decomposition of CO. Chem. Phys. Leff, 350: 6-14 8. Bacsa, R.R., Laurent, Ch, Peigney, A, Vaugien, T, Flahaut, E, Bacsa, w.S., and Rousset, A.(2002)(Mg, Co)o solid solutions precursors for the large-scale synthesis of carbon nanotubes by catalytic chemical vapor deposition. J. Am Ceram. soc.,85:2666-2669 9. Govindaraj, A, Flahaut, E, Laurent, Ch, Peigney, A, Rousset, A, and ao, C.N.R.(1999)An investigation of carbon nanotubes obtained from the decomposition of methane over reduced Mg,O4 (M=Fe, Co, Ni) spinel catalysts. J. Mater. Res, 14: 2567-2576 10. Flahaut, E, Govindaraj, A, Peigney, A, Laurent, Ch, Rousset, A,and Rao, CNR.(1999) Synthesis of single-walled carbon nanotubes using binary (Fe, Co, Ni) alloy nanoparticles prepared in situ by the reduction of oxide solid
Eqs. (2) and (3) combined with the phase diagram approach can be used for the description of different scenarios of carbon (11) and/or SiC (12) deposit formation and for the development of the main principles of catalyst and promoter design. ACKNOWLEDGMENTS Financial support by INTAS (01-254, YSF 03-55-1816), RFBR (02-03- 32296), and CRDF and Department of Education of RF (No.-008-X1) under marked grants is gratefully acknowledged. REFERENCES 1. Kuznetsov, V.L., Usoltseva, A.N., Chuvilin, A.L., Obraztsova, E.D., and Bonard, J.-M. (2001) Thermodynamic analysis of nucleation of carbon deposits on metal particles and its implications for the growth of single-wall carbon nanotubes. Phys. Rev. B, 64: 5401– 5408. 2. 2004) Special issue on Advances in Nanotubes. MRS Bulletin, 4: 237– 285. 3. Chrysanthou, A. and Grieveson, P. (1991) Formation of silicon carbide whiskers and their microstructure. J. Mater. Sci., 26: 3463– 3476. 4. Satishkumar, B.C., Govindaraj, A., Sen, R., and Rao, C.N.R. (1998) Single-walled nanotubes by the pyrolysis of acetylene – organometallic mixtures. Chem. Phys. Lett., 293: 47 – 52. 5. Cheng, H.M., Li, F., Su, G., Pan, H.Y., He, L.L., Sun, X., and Dresselhaus, M.S. (1998) Large-scale and low-cost synthesis of single-walled carbon nanotubes by the catalytic pyrolysis of hydrocarbons. Appl. Phys. Lett., 72: 3282– 3284. 6. Nikolaev, P., Bronikowski, M., Bradley, R., Rohmund, F., Colbert, D., Smith, K., and Smalley, R.E. (1999) Gas-phase catalytic growth of single-walled carbon nanotubes from carbon monoxide. Chem. Phys. Lett., 313: 91– 97. 7. Zhou, W., Ooi, Y., Russo, R., Papanck, P., Luzzi, D., Fischer, J., Bronikowski, M., Willis, P., and Smalley, R.E. (2001) Structural characterization and diameterdependent oxidative stability of single wall carbon nanotubes synthesized by the catalytic decomposition of CO. Chem. Phys. Lett., 350: 6 – 14. 8. Bacsa, R.R., Laurent, Ch., Peigney, A., Vaugien, T., Flahaut, E., Bacsa, W.S., and Rousset, A. (2002) (Mg, Co)O solid solutions precursors for the large-scale synthesis of carbon nanotubes by catalytic chemical vapor deposition. J. Am. Ceram. Soc., 85: 2666– 2669. 9. Govindaraj, A., Flahaut, E., Laurent, Ch., Peigney, A., Rousset, A., and Rao, C.N.R. (1999) An investigation of carbon nanotubes obtained from the decomposition of methane over reduced Mg1-xMxAl2O4 (M ¼ Fe, Co, Ni) spinel catalysts. J. Mater. Res., 14: 2567– 2576. 10. Flahaut, E., Govindaraj, A., Peigney, A., Laurent, Ch., Rousset, A., and Rao, C.N.R. (1999) Synthesis of single-walled carbon nanotubes using binary (Fe, Co, Ni) alloy nanoparticles prepared in situ by the reduction of oxide solid solutions. Chem. Phys. Lett., 300: 236– 242. 128 V. L. Kuznetsov, A. N. Usoltseva, and I. N. Mazov
Mechanism of Formation of Filaments, Nanotubes, and whiskers 11. Kuznetsov, V L, Usol'tseva, A N, and Butenko, Yu. V.(2003)Mechanism of carbon deposition formation on the metal catalyst surface. Kin. Catal. (Egl.), 44: 726-734 2. Kuznetsov, V L. and Mazov, I.N. Specific aspects of silicon carbide whiskers nucleation on the surface of the metal particle, in pres 13. Leu, I.C., Lu. Y.M., and Hon. M. H.(2002) Nucleation behavior of silicon carbide whiskers grown by chemical vapor deposition. J Cryst. Growth, 236: 171-175 14. Rado, C, Kalogeropoulou, S, and Eustathopoulos, N(1999)Wetting and bonding of Ni-Si alloys on silicon carbide. Acta Mater, 47: 461-473
11. Kuznetsov, V.L., Usol’tseva, A.N., and Butenko, Yu.V. (2003) Mechanism of carbon deposition formation on the metal catalyst surface. Kin. Catal. (Egl.), 44: 726– 734. 12. Kuznetsov, V.L. and Mazov, I.N. Specific aspects of silicon carbide whiskers nucleation on the surface of the metal particle, in press. 13. Leu, I.C., Lu, Y.M., and Hon, M.H. (2002) Nucleation behavior of silicon carbide whiskers grown by chemical vapor deposition. J. Cryst. Growth, 236: 171– 175. 14. Rado, C., Kalogeropoulou, S., and Eustathopoulos, N. (1999) Wetting and bonding of Ni –Si alloys on silicon carbide. Acta Mater., 47: 461–473. Mechanism of Formation of Filaments, Nanotubes, and Whiskers 129
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