Research Article

Facile Synthesis of Ti₂SC Powder with Super-Fine Grains using Iron Monosulfide as a Sulfur Source with Microwave Hybrid Heating

Lian Tan¹ and Chunlong Guan²*

¹School of Electric Power, North China University of Water Resources and Electric Power, China

²Engineering Laboratory of High Temperature Resistance-wear Materials, Henan University of Technology, China

Submission: January 01, 2018; Published: January 23, 2018

*Corresponding author: Chunlong Guan, Engineering Laboratory of High Temperature Resistance-wear Materials, Henan University of Technology, China, Email: chunlong_guan@haut.edu.cn

How to cite this article: Lian T, Chunlong G. Facile Synthesis of Ti2SC Powder with Super-Fine Grains using Iron Monosulfide as a Sulfur Source with Microwave Hybrid Heating. JOJ Material Sci. 2018; 3(5): 555624. DOI: 10.19080/JOJMS.2018.03.555624

Abstract

A novel method is presented for the synthesis of Ti₂SC powder by heating FeS/Ti/TiC mixtures. The results indicated that Ti₂SC powder was synthesized at a temperature 300 oC lower and required only 10% of the heating time compared to the conventional method. It was confirmed that the Ti₂SC phase was obtained with only trace impurity of TiC impurity obtained after acid treatment by microwave hybrid heating of 1FeS/1Ti/1TiC mixtures at 1300 oC for 3 minutes. The super-fine powder was mainly composed of flake-like particles with a mean diameter of ~700nm.

Keywords: Ti₂SC; Powder; Microwave hybrid heating; Acid treatment

Introduction

MAX phases are a new family of layered ternary ceramics that have attracted much attention due to their unique physio- chemical properties [1,2]. Compared with other MAX phases, Ti₂SC has two distinctive structures, firstly one with the lowest c/a ratio known to date (c/a ≈3.5) of all MAX phases and a second structure with a stronger M-A bond strength. These features result in high hardness (~8 GPa) [3], good thermal conductivity at room temperature (~60 Wm^-1 K^-1) [3], high modulus and stable structure under about 50GPa [4]. Furthermore, our work also indicated that tribological performance can be improved greatly with a suitable additive of Ti₂SC powder in base oil [5]. Therefore, Ti₂SC is expected to be promising candidate to be used as high-temperature lubrication material.

Commonly, most of bulk Ti₂SC ceramics were obtained by pressureless sintering or hot pressing of Ti₂SC raw powders [2-4]. However, the fabrication of high purity Ti₂SC powder is difficult because of the evaporation of S at 433.6^oC, the complex reaction between S and Ti, and the decomposition of Ti₂SC at elevated temperature [3]. Until recently, Li et al [6] synthesized Ti₂SC powders using elemental S as sulfur source by combustion synthesis. Results showed a large amount of TiC and Ti₃S₄ impurities existed and the grain size of Ti₂SC was shown to be very large. Zhu et al [7] adopted TiS₂ as a sulfur source instead of S to synthesize high purity Ti₂SC at temperatures as high as 1600 ^oC using the conventional method.

In previous work from our laboratory, high purity Ti₂SC powder was successfully synthesized by microwave hybrid heating of a Ti-TiS₂-C system at a low temperature of 1100 ^oC [5]. Nevertheless, the sulfur source TiS₂ is difficult to synthesize and very expensive and so is not favorable for industry applications [5,7] . In this study, we introduce a novel method for the synthesis of Ti₂SC powders using FeS as a sulfur source. The evolution and morphology of Ti₂SC phase were also investigated.

Experimental Procedures

Commercial powders of Ti (99%, 200 mesh), FeS (99%, 200 mesh), and TiC (99%, ~3|im) were used as starting materials. The FeS, Ti, and TiC powders with different molar ratios were mixed and then compacted using a cylindrical steel die (8mm diameter). The green compacts were put in a self-designed solid- state reactor. A schematic diagram of illustrating this process can be found elsewhere [8]. The reactor containing the reactant- loaded crucible was heated at temperatures ranging from 550 ^oC to 1300 ^oC (>100 ^oC min^-1) in a 2.45GHz multimode microwave furnace (BoDa, maximum power of 3kW) for 3min in a flowing Ar atmosphere. An infrared thermometer was used to measure the temperature of the samples which could be controlled automatically during the heating process. Finally, the as-received products were pulverized and immersed in H₂SO₄ solution (1 mol L^-1) to remove the Fe impurity.

The as-prepared powders were characterized by X-ray diffraction (XRD, M18X-AHF, Japan) to identify the phase compositions. A scanning electron microscope with an energy dispersive spectroscopy (SEM, F50-FEI, USA) was used to investigate the morphology and the compositions of the powders.

Results and Discussion

The phase evolution from the 1FeS/1Ti/1TiC reactant system at different temperatures for 3min is shown in Figure 1. Fe and TiS phases were detected with continuous consumption of FeS and TiC in the temperature range of 500 ^oC-700 ^oC. Discrepancies existed in comparison with the results reported by Chen et al., who suggested the Fe and TiS phases began to form at temperatures as high as 800 ^oC [9]. In our present work, the Ti₂SC phase appeared at 900 ^oC which was comparable with the formation temperature of 1200 ^oC by the Pulse-Electric-Current-Aided sintering as previously reported [9]. When the heating temperature reached 1300 ^oC, the Ti₂SC phase could be synthesized successfully, being accompanied with the disappearance of the FeS phase and the residue the Fe and TiC phases in the final product. The present synthesis temperature decreased by 300 ^oC and by one-tenth of the heating time of the conventional method [7]. Furthermore, the synthesis temperature using this approach was at least 200^oC lower than that of the Pulse-Electric-Current-Aided sintering technique (also called SPS) [9]. Compared with the previous methods mentioned above, the current method has the distinct advantages of a lower reaction temperature and shorter reaction time, which can be attributed to the combination of FeS adoption and microwave hybrid heating technique [10]. Based on the above observation, the reaction route of Ti -FeS-TiC system can be described as follows:

FeS + Ti = TiS + Fe (500 ^oC-900 ^oC) (1)

TiS + TiC = Ti₂SC (900 ^oC-1300 ^oC) (2)

Thus, it can be concluded that the optimum conditions for synthesizing Ti₂SC were using a 1FeS/1Ti/1TiC system sintered by microwave hybrid heating at 1300 ^oC for 3 minutes. Nevertheless, some impurities were left in the final products. To improve the purity, the as-obtained powders were treated with H₂SO₄ solution (1mol L^-1).

XRD patterns of the products synthesized at 1300 ^oC for 3mins before and after H₂SO₄ solution treatment are shown in Figure 2. The results indicated that the Fe impurity could be completely dissolved after acid treatment, which could be confirmed by the disappearance of Fe peaks in Figure 2b. Although the TiC phase could not be removed by acid treatment, it could be used as a reinforced phase in further composite sintering. Figure 3 shows the microstructure of powders after H₂SO₄ solution treatment. It can be seen that the crystals showed a flake-like morphology and were tightly linked together. The high magnification image of the area I in Fig.3a is shown in Fig.3b. The ratio of Ti to S in the region (marked by I) was close to that of 2 (Figure 3a), indicating that the Ti₂SC phase further existed in these regions. The C content obtained from EDS was not precise due to the limitations of this method. The as-received Ti₂SC particles were fine, uniform and regular with a mean diameter of less than 700 nm, which was much finer than that of achieved using other methods (5~10|im] [3,7] . The very fine particles could be ascribed to the rapid heating rate, low synthesis temperature and short dwelling time of the microwave hybrid heating method [10].

Conclusion

FeS as the sulfur sources was used to synthesize Ti₂SC powder with superfine grain (~700 nm) successfully via the microwave hybrid heating method at 1300 ^oC for 3 mins. The synthesis temperature and time required by this approach were at least 300 ^oC lower and 3 hours shorter than those of the traditional method.