Kota Sankalp, Zapata-Solvas Eugenio, Ly Alexander, Lu Jun, Elkassabany Omar, Huon Amanda, Lee William E, Hultman Lars, May Steve J, Barsoum Michel W
Drexel University, Department of Materials Science &Engineering, Philadelphia, Pennsylvania 19104, United States.
Centre for Nuclear Engineering, Department of Materials, Imperial College London, London, SW7 2AZ, United Kingdom.
Sci Rep. 2016 May 25;6:26475. doi: 10.1038/srep26475.
The 'MAlB' phases are nanolaminated, ternary transition metal borides that consist of a transition metal boride sublattice interleaved by monolayers or bilayers of pure aluminum. However, their synthesis and properties remain largely unexplored. Herein, we synthesized dense, predominantly single-phase samples of one such compound, MoAlB, using a reactive hot pressing method. High-resolution scanning transmission electron microscopy confirmed the presence of two Al layers in between a Mo-B sublattice. Unique among the transition metal borides, MoAlB forms a dense, mostly amorphous, alumina scale when heated in air. Like other alumina formers, the oxidation kinetics follow a cubic time-dependence. At room temperature, its resistivity is low (0.36-0.49 μΩm) and - like a metal - drops linearly with decreasing temperatures. It is also a good thermal conductor (35 Wm(-1)K(-1) at 26 °C). In the 25-1300 °C temperature range, its thermal expansion coefficient is 9.5 × 10(-6 )K(-1). Preliminary results suggest the compound is stable to at least 1400 °C in inert atmospheres. Moderately low Vickers hardness values of 10.6 ± 0.3 GPa, compared to other transition metal borides, and ultimate compressive strengths up to 1940 ± 103 MPa were measured at room temperature. These results are encouraging and warrant further study of this compound for potential use at high temperatures.
“MAlB”相是纳米层状的三元过渡金属硼化物，由过渡金属硼化物亚晶格与单层或双层纯铝交错组成。然而，它们的合成和性质在很大程度上仍未被探索。在此，我们使用反应热压法合成了一种此类化合物MoAlB的致密、主要为单相的样品。高分辨率扫描透射电子显微镜证实了在Mo - B亚晶格之间存在两层铝。在过渡金属硼化物中独一无二的是，MoAlB在空气中加热时会形成致密的、大多为非晶态的氧化铝层。与其他形成氧化铝的材料一样，其氧化动力学遵循立方时间依赖性。在室温下，它的电阻率很低（0.36 - 0.49μΩm），并且——像金属一样——随着温度降低呈线性下降。它也是一种良好的热导体（在26℃时为35Wm⁻¹K⁻¹）。在25 - 1300℃温度范围内，其热膨胀系数为9.5×10⁻⁶K⁻¹。初步结果表明该化合物在惰性气氛中至少稳定到1400℃。与其他过渡金属硼化物相比，在室温下测得其维氏硬度值适中，为10.6±0.3GPa，极限抗压强度高达1940±103MPa。这些结果令人鼓舞，值得对该化合物在高温下的潜在应用进行进一步研究。
