China
Africa
Explore chapters and articles related to this topic
Carbon Allotropes-Based Nanodevices
Published in Shilpi Birla, Neha Singh, Neeraj Kumar Shukla, Nanotechnology, 2022
Sugandha Singhal, Meenal Gupta, Md. Sabir Alam, Md. Noushad Javed, Jamilur R. Ansari
Carbon honeycombs (CHCs), also known as 3D graphene, are the growing interests of researchers, some of which have been theoretically predicted and experimentally synthesized. Pang et al. (2016) theoretically predicted the structure of 3D CHCs. The walls of CHCs have sp2 binding, and its triple junction has sp3 bonding. The two new CHCs exhibited remarkable mechanical as well as thermal properties, along with metallic character [6]. Similarly, Chen et al. (2017) predicted two stable CHCs, Cmcm and Cmmm-CHCn with thermal, dynamic and mechanical stability. The two allotropes had Dirac cones of direction-dependent nature under strain. The energies for the two were lower than previously reported results. Also, physical absorption efficiency is more than CNT and fullerenes [6]. The next category of 3D materials includes superhard materials that possess superior physical properties with exceptional mechanical stability. Thus, they have industrial applications, such as cutting, polishing and drilling tools, as well as coatings in surface protection [22, 23].
Gear Shaper Cutters I: External Gear Machining Mesh
Published in Stephen P. Radzevich, Gear Cutting Tools, 2017
The use of cutting elements made of superhard materials (borazon and others) proved to be useful for machining of hardened surfaces. It is natural to assume that the use of cutting elements made of superhard materials can solve numerous problems that pertain to machining of gears with gear shaper cutters. Unfortunately, the dimensions of the cutting elements are often too small to span over the entire lateral cutting edge of the gear shaper cutter of a standard design. Small dimensions of the cutting elements impose strong constraints in the implementation of the cutting elements made of superhard materials (borazon and others) in the design of gear shaper cutter. This particular problem can be resolved by using gear shaper cutters [118] specifically designed so that the pitch diameter and the outer diameter of the gear shaper cutter are equal to each other (Figure 10.40). When the equality rw.c = ro.c is observed, the lateral cutting edge shrinks to a point [118]. In reality, the generating surface of the gear shaper cutter is reduced to the set of straight lines through the corners of the top cutting edge. All the straight lines are parallel to the axis of rotation Oc of the gear shaper cutter. This makes it possible to place a cutting element of a small size into that point. In such a case, the gear shaper cutter (Figure 10.41) can be used for machining of a gear of any coarse pitch.
Systems Based on BN
Published in Tomashyk Vasyl, Ternary Alloys Based on III-V Semiconductors, 2017
Cubic BC2N was synthesized from graphite-like BC2N at pressures above 18 GPa and temperatures higher than 1930°C (Solozhenko and Novikov 2001, Solozhenko et al. 2001) or using shock syntheses (Komatsu 2004). Nanostructured superhard material bulks have been synthesized at high pressures and high temperatures (Zhao et al. 2002). The starting material for synthesis was a mixture of graphite and h-BN at a 2:1 molar ratio, rendered completely amorphous following 34 h of ball milling in a WC vial. The amorphous form was compressed to 20 GPa and heated to 1930°C for 5 min using a multianvil press. The final product was well-sintered chunks of millimeter size with a grain size of approximately 5 nm and was translucent and yellowish in color. Langenhorst and Solozhenko (2002) used a nanopowder of turbostratic graphite-like (BN)0.48C0.52 solid solution as the starting material for the synthesis of c-BC2N. The precursor was synthesized by simultaneous nitridation of H3BO3 and carbonization of saccharose in molten urea, followed by annealing in N2 at 1500°C. c-BC2N was synthesized by direct solid-state transition of h-BC2N at 30 GPa and approximately 3230°C.
Pressure dependent structural, dynamical, mechanical and electronic properties of magnesium dicarbide
Published in Philosophical Magazine, 2023
HaiYing Wu, YaHong Chen, Zi Jiang Liu, XiangYu Han, PengFei Yin
The calculated Vickers hardness of MgC2 for the Cmcm C2/m and P-3m1 structures under pressures was shown in Figure 6. Superhard materials could be defined as having a Vickers hardness HV > 40 GPa [42]. It was clear that the Cmcm structure had the lowest Vickers hardness and the P-3m1 structure had the highest Vickers hardness and the Vickers hardness for all structures increased with increasing pressure. The Vickers hardness of the P-3m1 structure reached to 37 GPa which was close to the boundary value of superhard material (40 GPa) when the pressure goes up to 150 GPa which also confirmed that MgC2 was hard material. The enhancement of the hardness of the P-3m1 structure probably arose from the sp3 hybridisation in the orbitals of the carbon atoms and these orbitals were available for the strongest covalent bonding in nature with other atoms.
First-principles investigation of the structural, elastic, anisotropic and electronic properties of Pmma-carbon
Published in Molecular Physics, 2021
Zhi-Fen Fu, Zhong-Yi Yang, Qing Cheng, Hai-Ping Chen, Bing Wang, Jian-Ping Zhou
o investigate the hardness of Pmma-carbon, we have calculated the hardness of Pmma-carbon using different empirical models (Chen et al. [46], Tian et al. [47] and Lyakhov-Oganov et al. [48]). All of these models have been successfully employed to predict the hardness of various materials [46, 49–51]. The calculated hardness for Pmma-carbon is 74.4, 71.4 and 71.8 GPa, using Chen et al., Tian et al. and Lyakhov-Oganov et al. models, respectively. For comparison, the hardness of diamond is also calculated to be 80.6, 95.3 and 97.3 GPa using the same models. It can be seen that the hardness of Pmma-carbon is lower than that of diamond (experiment value 96 ± 5 GPa), but is higher than that of the second hardest material c-BN (experiment value 65 GPa). The reason may be attribute to the presence of eight-membered-ring bonding configuration in its structure (all six-membered-ring bonding structure in diamond), which is prone to be compressed. It is general agreement that the materials with a hardness value exceeding 40 GPa are defined as a superhard material. The hardness of Pmma-carbon is much larger than 40 GPa, indicating that Pmma-carbon is a potential superhard material.
Structural, mechanical, electronic and bonding properties of TMB2 (TM = Y, Sc, Ti) under pressure: a DFT investigation
Published in Philosophical Magazine, 2022
MaoLing Zhang, Shi Yin, Jing Chang, NiNa Ge
Superhard materials have been paid high attention by the scientific community and have widespread application in industrial fields due to their high hardness, high melting-point, excellent thermal stability and electronic properties, etc. [1–3]. For the conventional superhard materials, such as diamond and boron nitride, it is not only difficult to synthesise but also it is an expensive process. In addition, the low oxidation temperatures in the air lead them to react easily with black alloys, which limit its application scope [4]. Therefore, searching for new superhard materials with superior mechanical and chemical properties as substitutes for diamond and c-BN have been a subject of continuing efforts.