Prediction Of New Carbon Materials And Synthesis Of High-strength Carbon Blocks

As science and technology continue to evolve,extreme application scenarios in new technological fields are placing increasingly high demands on the performance of materials,prompting the search for new materials with excellent properties.Carbon atoms have abundant and full-dimensional allotropes,and these diverse forms of crystal structure give carbon materials a unique and rich set of properties that have inspired research into new carbon materials.In this thesis,several new carbon allotropes,including superhard carbon phases,metallic carbon phases,and new orthorhombic carbon phases,are predicted based on first nature principle calculations.It also explores the synthesis of new high-strength carbon bulk materials using nanodiamond phase transition mechanisms through high-temperature and high-pressure techniques and investigates their electrical and mechanical properties.The main research elements are:（1）Superhard carbon phase:CALYPSO software has identified a new sp²-sp³ hybrid superhard carbon,TC12.Its stability was determined by calculating elastic constants,phonon spectra,and enthalpies.TC12 is a semiconductor with an indirect band gap that is smaller than most superhard carbon isotopes.TC12 carbon is incompressible and has a high bulk modulus,Vickers hardness,and tensile strength.When TC12 carbon is stretched in the[100]direction,it can readily change to metallic T6 carbon,suggesting that the TC12 carbon phase may be an intermediate metastable phase between T6 and T12.This fills the gap in the phase transformation path between T6 and T12 carbon.Combined with excellent mechanical and electrical properties,TC12 carbon becomes a potential material for electronic components and industrial tools.（2）Metallic carbon phase:A three-dimensional metallic carbon tetra-C12 carbon with full sp²hybrid hybridization has been discovered by CALYPSO.Its stability was determined by calculations of elastic constants,phonon dispersion curves,and enthalpies.tetra-C12 carbon is a conductor,metallic in nature,with high resistance to compression,good plasticity,and elastic anisotropy.tetra-C12 carbon exhibits structural properties and excellent performance,making it a very promising material for hydrogen storage and the preparation of polymer composites.（3）Novel orthorhombic carbon phases:Two new 3D carbon phases,Cco-C₃₆ and Cco-C₄₀carbon,with mixed sp²-sp³ hybrid hybridization,have been designed based on single-walled carbon nanotubes（SWCNT）.These phases can be regarded as formed by pressure-induced polymerization of（6,0）SWCNT,followed by the formation of（3,0）and（4,0）SWCNT,respectively.Both Cco-C₃₆ and Cco-C₄₀ carbons are indirect band gap semiconductors with elastic anisotropic properties.Both structures are characterized by their low density and large pores,making them potentially useful for shape selection in catalysts,molecular sieves,and absorbers.（4）Synthesis of new high-strength carbon blocks:A series of new high-strength carbon blocks were synthesized using nanodiamond as a precursor and modulating its graphitization at 3 GPa and 1300-1800°C.During the sintering process,the nanodiamond underwent a graphitization transformation,generating disordered sp² amorphous carbon,which was diffusely distributed in the nanodiamond particles,and the samples were gradually transformed into the 2H phase of graphite.Test results show that this new high-strength carbon block has excellent properties of both diamond and graphite,with good nanoindentation hardness and low resistivity.With good mechanical properties as well as excellent electrical properties and a relatively simple synthesis process,it is expected to be used in industrial and commercial applications and will promote the research of high-strength carbon and nanodiamond materials.