Abstract
A molten-salt and microwave co-facilitated boro/carbothermal reduction methodology was developed for low temperature high-efficiency synthesis of TiB2 powders. By using relatively inexpensive titanium oxide (TiO2), boron carbide (B4C) and amorphous carbon (C) as raw materials, single-phase TiB2 powders were prepared after 60 min at as low as 1150 °C or after only 20 min at 1200 °C. Such synthesis conditions were remarkably milder than those required by the conventional reduction routes using the identical reducing agent. As-synthesized TiB2 powders exhibited single-crystalline nature and well-grown hexagonal-platelet-like morphology. The achievement of low temperature high-efficiency preparation of high-quality TiB2 microplatelets in the present work was mainly attributable to the synergistic effects of molten-salt medium and microwave heating.
Highlights
As one of the most important ultra-high temperature ceramics (UHTCs), titanium diboride (TiB2 ) exhibits many useful properties, including a high melting point (3225 ◦ C), low density (4.52 g·cm−3 ), good corrosion resistance, and high hardness (25–35 GPa) [1,2,3,4]
Phases in raw materials and product samples were analyzed by an X-ray diffractometer (XRD, Figure 1 presents X-ray diffraction (XRD) patterns of samples prepared by MSM-boro/carbothermal reduction method (BCTR) at 1150 ◦ C
Morphologies and sizes of TiB2 product powders were examined using a field-emission scanning just extending the dwelling time at 1150 ◦ C from 20 to 60 min, TiC disappeared and only TiB2 was electron microscope (FE-SEM, 15 kV, Nova400NanoSEM, PHILIPS, Amsterdam, The Netherlands) formed, indicating the high efficiency of the conversion reaction from TiC to TiB2 equipped with an energy dispersive spectrometer (EDS, IET 200, Oxford, UK), and a transmission (Reaction 3), and the completion of the overall reaction (Reaction 1) after a short time period at such a electron microscope (TEM, 200 kV, JEM-2100UHRSTEM, JEOL, Tokyo, Japan)
Summary
As one of the most important ultra-high temperature ceramics (UHTCs), titanium diboride (TiB2 ) exhibits many useful properties, including a high melting point (3225 ◦ C), low density (4.52 g·cm−3 ), good corrosion resistance, and high hardness (25–35 GPa) [1,2,3,4]. The introduction of molten-salt medium combined with microwave heating showed crucial positive effects on the overall synthesis process, as well as on the crystalline degree and morphology of the powder product [29,30] In this work, such a molten-salt and microwave heating co-facilitated boro/carbothermal reduction method (MSM-BCTR), was adopted to prepare TiB2 powders with high crystalline degree and anisotropic morphology by using inexpensive TiO2 , B4 C and amorphous C as raw materials, while avoiding using any costly B or active metal (Mg or Al) reducing agents. The influence of processing parameters including temperature, dwelling time, microwave/salt medium conditions and the amount of reducing agent on the phase composition and microstructure of powder product was systematically investigated, so as to confirm the superiority of MSM-BCTR over the conventional methods in the preparation of high-quality TiB2 powders as well as a broad range of UHTCs
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