In this research, the possibility of production of TiC powder from inexpensive raw materials via simple methods has been investigated. Impure Ti chips, carbon black and Al powder were activated by a highenergy ball mill. Then they were synthesized by the method of self propagating high-temperature synthesis (SHS) at various temperatures. XRD study indicated that TiC within 1000 °C to 1300 °C temperature range has been synthesized where the temperature in a sample containing Al was less than 1000 °C. From the broadening of the diffraction lines in the XRD patterns, it was concluded that the TiC crystallites were nanosized and the lattice parameter had deviated slightly from the standard size. The existence of Al increased the lattice parameter of TiC and the strain in the process

Mansour Razavi

Mohammad Reza Rahimipour

Eurasian Chemico-Technological Journal

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Printed in Kazakhstan© 2008 al-Farabi Kazakh National University*corresponding  authors. E-mail: m-razavi@merc.ac.irEurasian ChemTech Journal  10 (2008) 31-35Synthesis of Nano-Crystalline TiC Powder from Active Impure Ti Chips via Self Propagating High-Temperature Synthesis and the Effect of Al on the Synthesis TemperatureMansour Razavi* and Mohammad Reza RahimipourMaterials and Energy Research Center, P.O. Box 14155-4777, Tehran, IranAbstractIn this research, the possibility of production of TiC powder from inexpensive raw materials via sim-ple methods has been investigated. Impure Ti chips, carbon black and Al powder were activated by a high-energy ball mill. Then they were synthesized by the method of self propagating high-temperature synthesis (SHS) at various temperatures. XRD study indicated that TiC within 1000°C to 1300°C temperature range has been synthesized where the temperature in a sample containing Al was less than 1000°C. From the broadening of the diffraction lines in the XRD patterns, it was concluded that the TiC crystallites were nano-sized and the lattice parameter had deviated slightly from the standard size. The existence of Al increased the lattice parameter of TiC and the strain in the process. IntroductionTitanium carbide (TiC) with the cubic structure of NaCl has desirable properties as reinforcing phase in composites [1]. Lattice parameter of this mate-rial is 0.4327±0.0001 nanometers [2]. In compari-son to other carbides such as tungsten carbide (WC), TiC has 33% higher hardness than WC, less weight and higher temperature stability [3]. TiC can be used as a reinforcing phase in composites or can be used alone. In case of using TiC, other materials such as SiC, TiN, NbC, TiC, TiB2, WC and C to reach the required toughness along with the needed hardness, should be added (because toughness of TiC is low) [4-6]. In the industry, SiC, Al2O3 and TiC respective-ly are highly used as reinforcing phases for produce composites currently [7].One of the synthesis methods of TiC is self-prop-agating high-temperature synthesis (SHS). Mer zha-nov first developed this method in 60's [8]. In this process the temperature was increased to a certain degree and then reaction starts and the necessary heat for continuation of the reaction will be obtained from the heat reaction [9]. High purity of products, easily method and inex-pensive equipments, saving time and energy, pos-sibility of producing unstable phases in one step, reducing the separation between matrix and rein-forcing phases, reaching to near-net shape and high mechanical properties of materials, are the advan-tages of SHS method [9-12]. For performance a self-propagating reaction, the following conditions should be satisfied [8,11]: Reaction should be exothermic (1. ∆Hreaction < –167 kJ/g⋅mol). The heat loss rate should be less than the rate of 2.produced heat.In this research, the feasibility of producing TiC from cheaper materials by SHS method and the ef-fects of Al on the synthesis temperature and grain size has been studied.ExperimentalThe titanium used in this research was commercial pure. The X-ray Fluorescence Spectrometry (XRF), Synthesis of Nano-Crystalline TiC Powder32Eurasian ChemTech Journal  10 (2008) 31-35used to analyze the Ti, revealed that it contained im-purities with the composition of 0.32 wt.% Al, 0.37 wt.% Si and 0.41 wt.% V. To produce titanium its profile was used. The titanium crushed chips were ball milled for 5 hours to achieve the particle size <50 mesh. Carbon black was used as carbon source. Carbon black size is < 250 mesh. Also 99.9% purity aluminum powder with <250 mesh size was used.The materials were mixed according to stoichio-metric ratio along with 10 wt.% Al in a full ener-gized planetary ball mill for 5 hours. Three similar balls with the diameter of 20 mm were used. In or-der to protect the materials from oxidation, the ar-gon gas was charged with the purity of 99.99% and pressure of 2.5 atm. Subsequently, disc specimens with 20 mm diameter and 5mm thickness were pro-duced in a steel die using 1000 kg load. Because the high temperature rate plays a ma-jor role in the SHS method, the muffle furnace tem-perature was increased and then tables were put in at once. Furthermore in order to control inner fur-nace atmosphere and prevent oxygen from mixing with the material, these were buried under 5 cm of active coke. The samples were kept in the furnace for 10 minutes with various temperatures. After cool-ing down the specimens in the furnace, they turned to powder and were prepared for further examinations. In order to identify the produced phases and com-pounds, the XRD analysis was performed with Cu Kα (λ = 1.54 Å) radiation with the voltage and cur-rent of 30 kV and 25 mA respectively. The crystallite size and strain were evaluated through Williamson-Hall method [13] and the lattice parameter was also obtained by Nelson-Riley method [14] with follow-ing equations: θη+λ=θ sin29.0cosdb Williamson-Hall eq.θθ+θθ=θ22 cossincos21)(F Nelson-Riley eq.Where b is full width of peak at half intensity (rad), θ is position of peak in the pattern (rad), λ the wavelength of X-ray (nm), η microstrain in the powder and F(θ) is the Nelson-Riley function.Results and DiscussionTi-C Binary SystemXRD pattern of sample containing Ti and C which has been exposed to 1300°C temperature by SHS methods, is presented in Fig. 1a. The acquired dominant phases at 1300°C were TiO2 and TiC. Although the materials had been buried under coke but titanium oxide peaks still was found in the com-pound, which is the outcome of existence of oxygen in the mentioned system. In Figure 1b XRD pat-tern of sample, which were synthesized at 1000°C, is shown. In this temperature, TiC was not synthe-sized and the identified phases were limited to Ti and TiO2. Therefore TiC was synthesized at 1000°C to 1300°C in this system (Ti-C).Fig. 1. XRD patterns of samples that were synthesized by the SHS method in Ti-C system (a) 1300°C (b) 1000°C TiC (*), Ti (+), TiO2(^).The synthesis mechanism of TiC from Ti and C elements starts by diffusion of C into Ti forming TiC layer. The diffusion coefficient of C in TiC is three times higher than diffusion coefficient of Ti in TiC. As the reaction temperature increases, Ti start to melt and TiC layers are dissolved in it, then C pe ne trate into open porosities and cover the layer. There after, C diffusion in the TiC dissolution layer for reaching Ti to form TiC nucleus which growth. Obviously, carbon morphology effects on final carbide struc-tures, speed and mechanism of reaction [11,15].The grain size of TiC produced by SHS technique at 1300°C temperature was calculated according to the Williamson-Hall equation as Fig. 2 illustrates. The result of this calculation is presented in Table 1. In Table 1, η and d are strain and grain size respec-tively. According to this calculation the crystal size of TiC is in nanometer order (about 50 nm).The lattice parameter of TiC can be calculated in accordance with Nelson-Riley equation. In Figure 3 the variations of the lattice parameter are plotted based on F(θ). By extrapolation of the curve in Fig. 3 and determination of the best fitted curve intersect at x = 0 abscissa, the lattice parameter of TiC can be M. Razavi and M.R. Rahimipour 33determined. The lattice parameter was estimated to be 0.4312 nm, which is far from ideal. The deviation from the standard of lattice parameter of TiC syn-thesis is 0.0015 nm. It is believed that this deviation was caused by high rate temperature in SHS meth-od. Of course the nonexistence of calibration in the instruments and not considering the exact stoichio-metric ratio of the produced TiC, also effect the de-viation [2,16].Ti-C-Al Ternary SystemXRD pattern obtained in the sample containing Ti, C and Al produced at 1300°C by SHS method is shown in Fig. 4b. It can be observed a consider-able amount of Al2O3 and TiO2 produced with TiC at 1300°C. Figure 4a shows the XRD pattern for the same sample at 1000°C. The dominant phases at this temperature were Al, Ti, their oxides and also very weak TiC peaks.From Figure 4, the temperature of synthesizing for TiC via SHS method from Ti, C and Al should be less than 1000°C. Because the oxidation of alumi-num is very exothermic reaction; therefore, as it was expected the existence of Al decreases the produc-tion temperature of TiC. The synthesis mechanism of TiC from Ti, C and Al elements was explained re-garding the following steps [17]:On initial heating, the aluminum melts and 1. spreads over the titanium particles. At this stage, TiAlx compounds form at the interface between the aluminum melt and the titanium particles. Thus: 2Ti + 2C + xAl = TiAlx + Ti + 2C + Q1As the temperature further increases, the dis-2. solved titanium in aluminum covers carbon par-ticles and titanium diffuses into the carbon which lead to formation TiC.  Thus: TiAlx + Ti + 2C = TiAlx + TiC + C + Q2When the temperature increases more, TiAl3. x compound gradually diminishes and Ti dissolves in the mixture.  Thus: TiAlx + TiC + C = TiC + Ti + xAl + C – Q3When the temperature reaches the melting point 4. Ti, the molten Al and Ti enters into carbon po-Table 1The mean size of the particles and the strain caused by SHS in accordance to Williamson-Hall equation in Ti-C and Ti-C-Al systems 1300°C temperatureFig. 2. Calculations of strain and crystal size by Williamson-Hall method in Ti-C and Ti-C-Al systems at 1300°C temperature.  R2 = 0.9431   R2 =  0.9634  0.002 0.0025 0.003 0.0035 0.004 0.0045 0.005 0.0055 0.4 0.6 0.8 1 1.2 1.4 2sinθ bcosθ Ti-C-Al Ti-C Systembcosθ = 2asinθ + b dTiC, nmηTiC, % R2a bTi-C 0.0020 0.0028 49.52 0.20 0.9634Ti-C-Al 0.0025 0.0019 72.97 0.25 0.9431 R2 = 0.8138 R2 = 0.9619 0.4302 0.4304 0.4306 0.4308 0.431 0.4312 0.4314 0.4316 1 1.5 2 2.5 3 Nelson Riley Function Lattice Parameter, nm Ti-C Ti-C-Al Fig. 3. Determination of TiC lattice parameter in Ti-C and Ti-C-Al systems using Nelson-Riley method at 1300°C temperature.Fig. 4. XRD patterns for samples synthesized by the SHS method in Ti-C-Al system 1000°C (b) 1300°C Al (#), Ti (^), TiO2 (+), Al2O3 (v), TiC(*).Eurasian ChemTech Journal  10 (2008) 31-35Synthesis of Nano-Crystalline TiC Powder34rosity and TiC dissolve in this molten mixture. Therefore, TiC is produced and starts growing. Thus: TiC + Ti + xAl + C = 2TiC + xAl + Q4However, very little oxygen in the mixture could create Al2O3 and as a result the speed of the reaction increases. Without oxygen the reaction has the fol-lowing from [18]: 2Ti + 2C + xAl = 2TiC + xAl + Q (Q = Q1 + Q2 – Q3 + Q4).The grain size of synthesized TiC at 1300°C was calculated from Williamson-Hall method as Fig. 2 illustrates. A summary of the results for the particle size is presented in Table 1. Due to existence of Al and an excess amount of heat, the crystal size were found to be larger than the TiC synthesized from Ti-C system (about 73 nm but still nanosized). In Figure 3 the Nelson-Riley function curve for determining synthesized TiC lattice parameter is shown. According to the mentioned figure, lattice parameter is found to be 0.4302 nm which has a 0.0025 nm deviation from the standard of lattice pa-rameter of TiC. This value is more than the lattice parameter of Ti-C system. Since the generated heat of Al2O3 is very high, the rate of heat in this process is relatively higher, it causes more defects and that affects the lattice parameter. Also the existence of strain in the each system can be caused by milling and SHS process may be the cause for the lattice pa-rameter deviation (Table 1).ConclusionsIt was shown that it is possible to produce nano •	TiC crystals from impure Ti chips, carbon black and Al by mechanical activation and SHS methods.The synthesizing temperature of TiC in Ti-C sys-•	tem was found to be 1000°C to 1300°C, which temperature in a sample containing 10 wt.% of Al was decreased under 1000°C.TiC crystal sizes in both procedures were in the •	range of nanometer. This value for Ti-C system was found to be 50 nm and for Ti-C-Al was 73 nm. Lattice parameter in both systems deviated from •	the standard value. It was shown that the devia-tion was higher in sample containing Al, which is suggested to be caused by defects and strain. In addition, non-stoichiometric ratio and non-cal-ibrated apparatus could be the other two reasons for such deviation.ReferencesV.K. Rai, R. Srivastava, S.K. Nath, S. Ray, 1. Wear in cast titanium carbide reinforced ferrous composites under dry sliding, Wear 231 (1999) 265-271.J.B. Holt, Z.A. Munir, Combustion synthesis of 2. titanium carbide theory and experiment, Journal of Materials Science 21 (1986) 251-259.J.M. Panchal, T. Vela, T. Robisch, Ferro-TiC 3. metal matrix composites for high performance tooling and engineering application, ASM International (1990) 245-260.Q. Fan, H. Chai, Role of iron addition in the 4. combustion synthesis of TiC-Fe cermet, Journal of Materials Science 32 (1997) 4319-4323.G.M. Song, Q. Li, G.W. Wen, Y. Zhou, Me cha-5. nical properties of short carbon fiber-reinforced TiC composites produced by hot pressing, Materials Science and Engineering A326 (2002) 240-248.G.M. Song, Y. Zhou, S.J.L. Kang, Experimental 6. description of thermomechanical properties of carbon fiberreinforced TiC matrix composites, Materials and Design 24 (2003) 639-646.A. Evans, C.S. Marchi, A.Mortensen, Metal 7. Mat rix Composites in Industry, Kluwer Aca-demic Publishers, (August 2003).S.C. Tjong, Z.Y. Ma, Microstructural and me-8. chanical characteristics of in situ metal matrix composites, Materials Science and Engineering, 29 (2000) 49-113.A.K. Bhattacharya, Temperature-enthalpy ap-9. proach to the modeling of self-propagating combustion of materials, Journal of Materials Science 27 (1992) 3050-3061.J. Subrahmanyam, M. Vijayakumar, Review self-10. propagating high-temperature synthesis, Journal of Materials Science 27 (1992) 6249-6273.W.C. Lee, Sh.L. Chung, Ignition phenomena 11. and reaction mechanisms of the self-propagat-ing high-temperature synthesis reaction in the Ti + C system, Journal of Materials Science 30 (1995) 1487-1494.K. Das, T.K. Bandyopadhyay, S. Das, A review 12. on the various synthesis route of TiC reinforced ferrous based composites, Journal of Materials Science 37 (2002) 3881-3892.G.K. Williamson, W.H. Hall, X-ray line broad-13. ening from filed aluminium and wolfram, Acta Metall.1 (January 1953) 22-31.Eurasian ChemTech Journal  10 (2008) 31-35M. Razavi and M.R. Rahimipour 35B.H. Lohse, A. Calka, D. Wexler, Effect of 14. starting composition on the synthesis of nano-crystalline TiC during milling of titanium and carbon, Journal of Alloys and Compounds 394 (2005) 148-151.Q. Fan, H. Chai, Z. Jin, Microstructural evo-15. lution in the combustion synthesis of titanium carbide, Journal of Materials Science 31 (1996) 2573-2577.Metals Handbook, Alloy Phase Diagrams, 16. ASM, Vol. 3, 1989.W.C. Lee, Sh.L. Chung, Ignition phenomena 17. and reaction mechanisms of the self-propagat-ing high-temperature synthesis reaction in the titanium-carbide-aluminum system, Journal of American Ceramic Society 80 (1997) 53-61.Y. Choi, Sh.W. Rhee, Effect of aluminum ad-18. dition on the combustion reaction of titanium and carbon to form TiC, Journal of Materials Science 28 (1993) 6669-6673.Received  7 October  2007Eurasian ChemTech Journal  10 (2008) 31-35

Synthesis of Nano-Crystalline TiC Powder from Active Impure Ti Chips via Self Propagating High-Temperature Synthesis and the Effect of Al on the Synthesis Temperature

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Synthesis of Nano-Crystalline TiC Powder from Active Impure Ti Chips via Self Propagating High-Temperature Synthesis and the Effect of Al on the Synthesis Temperature

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