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 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 c0 –d0 ). Moderate temperature route attributes with CVD methods of carbon filaments and nanotubes production (carbon concen￾tration 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 dis￾persion 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