Synthesis and Property Characterization of Ternary Laminar Zr2SB Ceramic

Abstract

In this paper, Zr2SB ceramics with high relative density (99.03%) and high purity of 82.95 wt% (containing 8.96 wt% ZrB2 and 8.09 wt% zirconium) were successfully synthesized from ZrH2, sublimated sulfur and boron powder by spark plasma sintering at 1300 ℃. The reaction mechanism, microstructures, physical properties and mechanical properties of Zr2SB ceramic were systematically studied. The results show that Zr2SB was obtained by the reaction of zirconium sulfide, zirconium and boron, and ZrB2 coexisted in the sample as a symbiotic impurity phase. The average grain size of Zr2SB was 12.46 μm in length and 5.12 μm in width, and the mean grain sizes of ZrB2 and zirconium impurities were about 300 nm. In terms of physical properties, the measured thermal expansion coefficient was 7.64 × 10-6 K-1 from room temperature to 1200 ℃, and the thermal capacity and thermal conductivity at room temperature were 0.39 J·g−1·K−1 and 12.01 W∙m−1∙K−1, respectively. The room temperature electrical conductivity of Zr2SB ceramic was measured to be 1.74 × 106 Ω−1∙m−1. In terms of mechanical properties, Vickers hardness was 9.86 ± 0.63 GPa under 200 N load, and the measured flexural strength, fracture toughness and compressive strength were 269 ± 12.7 MPa, 3.94 ± 0.63 MPa·m1/2, and 2166.74 ± 291.34 MPa, respectively.

Extension of MAX phases from ternary carbides and nitrides (X = C and N) to ternary borides (X = B, C, and N): A general guideline

“…Figure 7 shows the lattice constants a and c of M 2 AX phases (X = B, C, and N) versus VEC. The recent experimentally discovered Zr 2 SB, Hf 2 SB, Nb 2 SB, Zr 2 SeB, Hf 2 SeB, Zr 2 TeB, and Hf 2 TeB are included 34–38 . To enrich the data, the lattice constants of the theoretically predicted Zr 2 PB, Hf 2 PB, Nb 2 PB, Zr 2 AsB, Hf 2 AsB, Nb 2 AsB, Zr 2 SbB, Hf 2 SbB, and Nb 2 SbB are also included.…”

“…Recent discovery on layered ternary borides M 2 AB (M = Nb, Zr, Hf, A = S, Se, and Te) by Rackl et al 34,35 . and Hu et al 36,37 . shed some light on this issue, which also fueled the research activities in this field 38,39 …”

“…If stable rock salt-structured MB exists, it is conceivable that MAX phases with X = B can be formed by proper selecting of A-group element. Recent discovery on layered ternary borides M 2 AB (M = Nb, Zr, Hf, A = S, Se, and Te) by Rackl et al 34,35 and Hu et al 36,37 shed some light on this issue, which also fueled the research activities in this field. 38,39 To give an insight into the formation mechanism and stability of MAX phase borides M 2 AB and some guidelines for the discovery of new MAX phases, the electronic structure, chemical bonding, and elastic properties of M 2 AX (X = B, C, and N) phases (Hägg phases or 211 phases, which were first discovered in 1960s by Nowotny et al 40 ) were investigated in this work as model materials of MAX phases.…”