Reaction kinetics in Ti3SiC2 synthesis studied by time-resolved neutron diffraction

doi:10.1016/j.jeurceramsoc.2004.09.005

Journal of the European Ceramic Society

Volume 25, Issue 15, October 2005, Pages 3503-3508

https://doi.org/10.1016/j.jeurceramsoc.2004.09.005 Get rights and content

Abstract

The reactive sintering of 3Ti/SiC/C to form the ternary carbide Ti₃SiC₂, previously found to involve the intermediate phases TiC_x and Ti₅Si₃C_x, was investigated by time-resolved neutron powder diffraction. The kinetics of Ti₃SiC₂ formation from the intermediate phases TiC_x, Ti₅Si₃C_x (x ≤ 1) and a small amount of free C was determined. The crystallization rate of the Ti₃SiC₂ phase was determined through quantitative analyses of the diffraction patterns collected at different temperatures and is initially well-described by the Mehl–Avrami–Johnson equation. The activation energy was found to be 380 ± 10 kJ/mol and the Avrami exponent 3.0 ± 0.2. The Avrami exponent decreases to close to 1 when more than half of the crystallization process was completed. This indicates a change in the mechanism of Ti₃SiC₂ crystal growth from unrestricted two or three-dimensional growth in the a–b planes to one-dimensional growth only, due to interaction of the growing disk-like crystals and cessation of growth in the preferred direction.

Introduction

The last few years have seen strong interest in studies of the ternary carbide Ti₃SiC₂ because of its unique combination of properties.1, 2, 3, 4, 5, 6, 7, 8 Ti₃SiC₂ has been prepared using several different methods.9, 10, 11, 12, 13, 14, 15 Among them the reactive sintering of 3Ti/SiC/C to form Ti₃SiC₂ has been extensively studied since, when coupled with hot pressing, this process can produce fully dense near-single phase Ti₃SiC₂ ceramic.1, 11 To understand the reaction mechanism and its time and temperature dependence, we have studied the process using in situ neutron diffraction techniques.16, 17 By conducting the experiments in situ, the microstructural processes and phase transitions occurring in bulk ceramics are revealed in a time-resolved sequence. The reaction paths revealed by in situ neutron diffraction during the heating of 3Ti/SiC/C mixtures at 10 °C/min and reactive sintering at 1600 °C to synthesise Ti₃SiC₂ were discussed in our previous papers.16, 17 There two well-separated reaction stages were observed. In the first stage the two intermediate phases identified by El-Raghy and Barsoum,¹⁸ TiC_x and Ti₅Si₃C_x (x ≤ 1), occurred in the sample according to the overall reaction 9Ti + 3SiC + 3C → 4TiC_x + Ti₅Si₃C_x + C (x ≤ 1). By 1400 °C all of the Ti has been consumed. In the second stage the two intermediate phases plus a small amount of carbon become the only phases in the system prior to the appearance of the product phase. The intermediate phases react to form Ti₃SiC₂ according to the overall reaction 4TiC_x + Ti₅Si₃C_x + C (x ≤ 1) → 3Ti₃SiC₂.¹⁷ Based on the concentrations of the Ti₃SiC₂ phase calculated from quantitative phase analysis of the diffraction patterns, formation of Ti₃SiC₂ is slow at temperatures near 1200 °C and, fairly rapid at higher temperatures.¹⁶ However, the kinetics were not quantified in these earlier continuous heating experiments16, 17—kinetic information is far more readily obtained from isothermal experiments. Knowledge of the reaction kinetics is needed not only for a quantitative description of the temperature-time paths of the reaction, but also for a better understanding of the mechanism of the synthesis process. This paper reports the kinetics of Ti₃SiC₂ formation from the intermediate phases TiC_x, Ti₅Si₃C_x and C in the second sintering stage based upon recent in situ time-resolved neutron diffraction experiments.

Section snippets

Experimental procedure and analysis

The experimental procedure is very similar to that used previously.¹⁷ Ti (Aldrich 99.98%), SiC (Performance Ceramics 99.9%) and C (graphite Fluka Chemika 99.9%) powders were mixed in stoichiometric proportions and hand ground under argon. Cylindrical pellets of 16 mm diameter and 15 mm high were cold pressed to (180 MPa) in a hard steel die. Two pellets were stacked vertically to increase the mass of sample within the neutron beam and thereby reduce data collection times. Time-of-flight (TOF)

Results and discussion

An example of the neutron diffraction data and associated Rietveld refinement fit used for quantitative phase analysis is shown in Fig. 1. The agreement between the calculated and the observed data points is very good. The final plots of ln[−ln(1 − f)] versus ln t at different temperatures after three iterations are shown in Fig. 2. The value of n for the formation of Ti₃SiC₂ from 4TiC_x + Ti₅Si₃C_x + C determined from the measurement of the slopes is 3.0 ± 0.2 and the reaction rate constant K is 1.35 × 10⁻⁴

Conclusion

The kinetics of the growth of Ti₃SiC₂ crystals by solid state reaction of the intermediate phases TiC_x, Ti₅Si₃C_x (x ≤ 1) and a small amount of free C, determined from quantitative analysis of in situ neutron diffraction data collected at different temperatures may be modelled by the by Mehl–Avrami–Johnson equation.

Based on fitting the data with the Avrami equation, the value for the activation energy is 380 ± 10 kJ/mol, and the corresponding Avrami exponent is 3.0 ± 0.2 for the initial stages of

Acknowledgments

The authors are grateful for the support of ISIS technical staff, particularly Chris Goodway. Funding support from the Australian Research Council—Discovery Grants and Linkage Infrastructure Equipment and Facilities Schemes, the Australian Institute of Nuclear Science and Engineering and the Access to Major Research Facilities Program is gratefully acknowledged.

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Reaction kinetics in Ti3SiC2 synthesis studied by time-resolved neutron diffraction

Abstract

Introduction

Section snippets

Experimental procedure and analysis

Results and discussion

Conclusion

Acknowledgments

Mater. Lett.

Mater. Res. Bull.

J. Eur. Ceram. Soc.

J. Eur. Ceram. Soc.

Prog. Solid State Chem.

Synthesis and characterization of a remarkable ceramic: Ti3SiC2

J. Am. Ceram. Soc.

Electronic properties of Ti3SiC2-based solid solutions

Phys. Rev. B

Synthesis and stability of Ti3SiC2

J. Alloy. Comp.

Ti3SiC2 has negligible thermopower

Nature

Experimental investigation and thermodynamic calculation of the titanium–silicon–carbon system

J. Am. Ceram. Soc.

Self-propagating high-temperature synthesis of Ti3SiC2: I: ultra-high-speed neutron diffraction study of the reaction mechanism

J. Am. Ceram. Soc.

Ab initio investigation on the electronic structure and bonding properties in layered ternary compound Ti3SiC2 at high pressure

J. Phys. Condens. Matter

A progress report on Ti3SiC2, Ti3GeC2 and the H-phases, M2BX

J. Mater. Synth. Process.

Preparation of Ti3SiC2 by electron-beam- ignitied solid-state reaction

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Synthesis and characterization of a remarkable ceramic: Ti₃SiC₂

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Self-propagating high-temperature synthesis of Ti₃SiC₂: I: ultra-high-speed neutron diffraction study of the reaction mechanism

Ab initio investigation on the electronic structure and bonding properties in layered ternary compound Ti₃SiC₂ at high pressure

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Preparation of Ti₃SiC₂ by electron-beam- ignitied solid-state reaction