Raman spectroscopy sheds new light on TiC formation during the controlled milling of titanium and carbon

doi:10.1016/j.jallcom.2006.08.216

Journal of Alloys and Compounds

Volumes 434–435, 31 May 2007, Pages 405-409

https://doi.org/10.1016/j.jallcom.2006.08.216 Get rights and content

Abstract

A magneto ball mill was used to mill titanium and carbon elemental powder mixtures with compositions of Ti₅₀C₅₀ and Ti₆₀C₄₀ under a helium atmosphere. Previous studies on the milling of titanium and carbon powder mixtures have reported a sudden increase in the temperature of the milling vial, which occurs after a specific milling interval, referred to as t_ig [Z.G. Liu, J.T. Guo, L.L. Ye, G.S. Li, Z.Q. Hu, Appl. Phys. Lett. 65 (1994) 2666–2668; G.B. Schaffer, J.S. Forrester, J. Mater. Sci. 32 (1997) 3157–3162; N.Q. Wu, S. Lin, J.M. Wu, Z.Z. Li, Mater. Sci. Technol. 14 (1998) 287–291; Z. Xinkun, Z. Kunyu, C. Baochang, L. Qiushi, Z. Xiuqin, C. Tieli, S. Yunsheng, Mater. Sci. Eng. C 16 (2001) 103–105; C. Deidda, S. Doppiu, M. Monagheddu, G. Cocco, J. Metastable Nanocryst. Mater. 15/16 (2003) 215–220]. This sudden temperature increase has been found to correspond to the formation of TiC via a rapid, highly exothermic reaction. In these cases, XRD analysis did not detect TiC in powder sampled before t_ig. These results, combined with those from studies suggested that the milling period prior to t_ig represents an incubation period during which the powders become mechanically activated and that no reaction between the starting powders occurs during this time [L. Takacs, J. Solid State Chem. 125 (1996) 75–84; B.K. Yen, T. Aizawa, J. Kihara, J. Am. Ceram. Soc. 81 (1998) 1953–1956; M. Puttaswamy, Y. Chen, B. Jar, J.S. Williams, Mater. Sci. Forum 312–314 (1999) 79–84; G.B. Schaffer, P.G. McCormick, Metall. Transact. A 23A (1992) 1285–1290; M. Mingliang, L. Xinkuan, X. Shenqui, C. Donglang, Z. Jingen, J. Mater. Process. Technol. 116 (2001) 124–127].

In the current investigation a sudden increase in the temperature of the milling vial was also observed after a specific milling duration of t_ig. XRD analysis of powder sampled before t_ig did not detect TiC, whilst for powder sampled after t_ig, XRD analysis indicated that the powder had almost completely transformed into TiC. However, Raman spectroscopy showed the formation of non-stoichiometric TiC in Ti₅₀C₅₀ and Ti₆₀C₄₀ powders sampled before t_ig. It is believed that the current, and many previous XRD analyses did not detect the formation of TiC prior to t_ig either because the TiC grain size was too small and/or the phase represented too small a volume fraction of the powder samples to be detected by the XRD method employed. These Raman spectroscopy results suggest that a significant component of the heat generated at t_ig may be due to a combination of growth of TiC accompanied by consumption of unreacted Ti and carbon, and/or recrystallisation of the TiC formed prior to t_ig, rather than the direct formation of TiC.

Introduction

Titanium carbide (TiC) is suited to a number of commercial applications, such as abrasives, cutting tools, grinding wheels and coated cutting tips because it exhibits very high hardness, high melting temperature and excellent thermal and chemical stability [1], [11], [12], [13], [14]. Recent studies have shown that high-energy milling of titanium and carbon powders may be a viable synthesis method for the production of TiC powder [1], [2], [3], [4], [5], [6], [12], [13], [14], [15], [16]. However, the process by which titanium and carbon react to form TiC during milling is not yet well understood. The aim of this study is to further the understanding of this reaction through the use of Raman spectroscopy to characterise the milling products.

Very little has been reported on the use of Raman spectroscopy to study TiC. The literature states that stoichiometric TiC has no Raman active vibrational modes and that Raman scattering in TiC is due to disorder induced by carbon vacancies [17], [18]. Klein et al. [17] produced Raman spectra of TiC_x where x = 0.97, 0.90 and 0.80, whilst Amer et al. [18] published a Raman spectrum of TiC_0.67.

Section snippets

Experimental

Titanium powder of particle size <250 μm and minimum purity of 99.9% was mixed with high purity activated carbon powder to give compositions of Ti₅₀C₅₀ and Ti₆₀C₄₀. Controlled ball milling was performed using a magneto ball mill (Uni-Ball-Mill 5) operating in impact mode under a high purity helium atmosphere. Samples were taken using a glovebag to prevent contamination of the powders. The external temperature of the milling vial was monitored during milling using an infrared thermometer.

X-ray

XRD analysis of as-milled Ti–C powders

An abrupt increase in the temperature of the milling vial was observed after milling for a specific duration, referred to as the ignition time, t_ig. The average ignition time for Ti₅₀C₅₀ was approximately 71 h, whilst that for Ti₆₀C₄₀ was approximately 41 h. Typical plots of the milling vial temperature versus milling time are shown in Fig. 1. The ignition time was repeatable within ±2 h of the average ignition time.

The XRD patterns for samples taken before and after t_ig are shown in Fig. 2, Fig. 3

Discussion

When milling Ti₅₀C₅₀ and Ti₆₀C₄₀ elemental powder mixtures, a sudden increase in the temperature of the milling vial was observed after a milling duration of t_ig. XRD analysis of powder sampled before t_ig revealed only peaks corresponding to titanium. For powder sampled after t_ig, XRD analysis revealed strong peaks corresponding to TiC and a very weak peak corresponding to a small amount of unreacted titanium. These results suggest that the sudden temperature increase detected during milling is

Conclusions

Raman spectroscopy detected the formation of TiC well before it was detected by XRD analysis. For Ti₅₀C₅₀ and Ti₆₀C₄₀ elemental powder mixtures, the combined results of external mill temperature monitoring and X-ray diffractommetry indicated that, after a milling duration of t_ig, TiC formed rapidly via a mechanically induced reaction which resulted in sudden heating of the milling vial. However, Raman spectroscopy clearly showed the formation of non-stoichiometric TiC prior to t_ig. This is a

Acknowledgements

The authors wish to thank Dr. Peter Innis from the Intelligent Polymer Research Institute and ARC Centre for Nanostructured Electromaterials at the University of Wollongong for his help and advice with the Raman spectroscopy. The authors also gratefully acknowledge financial support from the Australian Research Council, under ARC-Large Grant No. A00103022 and ARC-Discovery Grant No. DP0451907. The Reviewer is also acknowledged for valuable suggestions for improvements to the article.

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Raman spectroscopy sheds new light on TiC formation during the controlled milling of titanium and carbon

Abstract

Introduction

Section snippets

Experimental

XRD analysis of as-milled Ti–C powders

Discussion

Conclusions

Acknowledgements

J. Solid State Chem.

J. Mater. Process. Technol.

Nanostruct. Mater.

Appl. Phys. Lett.

J. Mater. Sci.

Mater. Sci. Technol.

Mater. Sci. Eng. C

J. Metastable Nanocryst. Mater.

J. Am. Ceram. Soc.