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Stability,electronic structures,and mechanical properties of Fe–Mn–Al system from first-principles calculations 下载免费PDF全文
The stability, electronic structures, and mechanical properties of the Fe–Mn–Al system were determined by firstprinciples calculations. The formation enthalpy and cohesive energy of these Fe–Mn–Al alloys are negative and show that the alloys are thermodynamically stable. Fe_3Al, with the lowest formation enthalpy, is the most stable compound in the Fe–Mn–Al system. The partial density of states, total density of states, and electron density distribution maps of the Fe–Mn–Al alloys were analyzed. The bonding characteristics of these Fe–Mn–Al alloys are mainly combinations of covalent bonding and metallic bonds. The stress-strain method and Voigt–Reuss–Hill approximation were used to calculate the elastic constants and moduli, respectively. Fe_(2.5)Mn_(0.5)Al has the highest bulk modulus, 234.5 GPa. Fe_(1.5)Mn_(1.5)Al has the highest shear modulus and Young's modulus, with values of 98.8 GPa and 259.2 GPa, respectively. These Fe–Mn–Al alloys display disparate anisotropies due to the calculated different shape of the three-dimensional curved surface of the Young's modulus and anisotropic index. Moreover, the anisotropic sound velocities and Debye temperatures of these Fe–Mn–Al alloys were explored. 相似文献
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实验采用一个内腔布儒斯特双轴锥棱镜,在掺镱多模双包层光纤激光器中实现了径向偏振光振荡,并在长2 m的增益光纤中获得了高达6.2 mW的功率输出.研究揭示了从光纤激光器振荡中获得径向偏振光的新途径.然而,该激光器输出的径向偏振光的光强分布并不很均匀,且偏振消光比较低,需要进一步改进. 相似文献
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2-甲基四氢呋喃(2-MTHF)是极具市场潜力的生物燃料、绿色溶剂和化学中间体.采用浸渍法制备Ni/γ-Al2O3催化剂,在固定床反应器评价其2-甲基呋喃(2-MF)气相加氢合成2-甲基四氢呋喃(2-MTHF)反应性能.通过XRD、N2等温吸附-脱附、H2-TPR、NH3-TPD、TEM、H2吸附和XPS对催化剂结构和表面性质进行表征,研究Ni负载量、焙烧温度和反应条件对催化剂性能的影响规律.结果表明:Ni/γ-Al2O3催化剂的Ni金属面积、晶粒尺寸、反应温度和压力都会影响2-MF的转化率;孔结构、酸量和反应温度是影响2-MTHF选择性的主要原因,平均孔径大、酸量大和适宜的反应温度有利于提高2-MTHF选择性. 400℃焙烧的负载量为15%的Ni/γ-Al2O3催化剂, Ni金属面积大、晶粒尺寸小、总酸量多,催化剂表面的金属活性中心与酸性中心协同作用促进了2-MF呋喃环上C=C加氢生成2-MTHF,性能较优.在2 MPa、100℃、WHSV=2.7 h-1、H2/2-MF=6.4的条件下,该催化剂上2-MF转化率为99.8%, 2-MTHF选择性为98.0%,催化剂可以稳定运行40 h. 相似文献
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Effects of alloying element on stabilities,electronic structures,and mechanical properties of Pd-based superalloys 下载免费PDF全文
The thermodynamic stabilities, electronic structures, and mechanical properties of the Pd-based superalloys are studied by first principles calculations. In this work, we discuss the effect of Pd-based superalloys made from Al, Si, Sc, Ti,V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, Mo, Tc, Hf, Ta, W, Re, Os, Ir and Pt, and we also calculate a face centered cubic(fcc)structure 2 × 2 × 2 superalloy including 31 Pd atoms and one alloying element T M(Pd_(31)TM). The mixing energies of these Pd-Based superalloys are negative, indicating that all Pd-based superalloys are thermodynamically stable. The Pd_(31)Mn has the lowest mixing energy with a value of-0.97 eV/atom. The electronic structures of the Pd-based superalloys are also studied, the densities of states, elastic constants and moduli of the mechanical properties of the Pd-based superalloys are determined by the stress-strain method and Voigt–Reuss–Hill approximation. It is found that Pd_(31)TM is mechanically stable, and Pd_(31)Tc has the largest C_(11), with a value 279.7 GPa. The Pd_(31)Cr has the highest bulk modulus with a value of299.8 GPa. The Pd_(31)Fe has the largest shear modulus and Young's modulus with the values of 73.8 GPa and 195.2 GPa,respectively. By using the anisotropic index, the anisotropic mechanical properties of the Pd_(31)T M are discussed, and threedimensional(3 D) surface contours and the planar projections on(001) and(110) planes are also investigated by the Young modulus. 相似文献