Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA) , Los Angeles, California 90095, United States.
Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
J Am Chem Soc. 2017 Nov 29;139(47):17120-17127. doi: 10.1021/jacs.7b08706. Epub 2017 Nov 15.
Tungsten tetraboride is an inexpensive, superhard material easily prepared at ambient pressure. Unfortunately, there are relatively few compounds in existence that crystallize in the same structure as tungsten tetraboride. Furthermore, the lack of data in the tetraboride phase space limits the discovery of any new superhard compounds that also possess high incompressibility and a three-dimensional boron network that withstands shear. Thus, the focus of the work here is to chemically probe the range of thermodynamically stable tetraboride compounds with respect to both the transition metal and the boron content. Tungsten tetraboride alloys with a variable concentration of boron were prepared by arc-melting and investigated for their mechanical properties and thermal stability. The purity and phase composition were confirmed by energy dispersive X-ray spectroscopy and powder X-ray diffraction. For variable boron WB, it was found that samples prepared with a metal to boron ratio of 1:11.6 to 1:9 have similar hardness values (∼40 GPa at 0.49 N loading) as well as having a similar thermal oxidation temperature of ∼455 °C. A nearly single phase compound was successfully stabilized with tantalum and prepared with a nearly stoichiometric amount of boron (4.5) as WTaB. Therefore, the cost of production of WB can be decreased while maintaining its remarkable properties. Insights from this work will help design future compounds stable in the adaptable tungsten tetraboride structure.
四硼化钨是一种廉价的超硬材料，在常压下很容易制备。不幸的是，目前存在的具有与四硼化钨相同结构的化合物相对较少。此外，由于四硼化物相空间的数据有限，限制了任何具有高不可压缩性和三维硼网络的新超硬化合物的发现，这些网络能够承受剪切。因此，这里工作的重点是从化学角度探测热力学稳定的四硼化物化合物的范围，包括过渡金属和硼的含量。通过电弧熔炼制备了具有可变硼浓度的四硼化钨合金，并研究了它们的力学性能和热稳定性。通过能谱和粉末 X 射线衍射确认了纯度和相组成。对于可变硼 WB，发现金属与硼的比例为 1:11.6 至 1:9 的样品具有相似的硬度值（在 0.49 N 载荷下约为 40 GPa），并且具有相似的热氧化温度约为 455°C。通过成功地用钽稳定了几乎单相化合物，并以近乎化学计量的硼（4.5）制备了 WTaB。因此，在保持其显著性能的同时，可以降低 WB 的生产成本。这项工作的见解将有助于设计未来在适应性强的四硼化钨结构中稳定的化合物。
