In this communication two novel orthorhombic allotropes trig-C12 with trigonal C(sp 2) and tetr-C12 with tetrahedral C(sp 3) are proposed from crystal engineering and unconstrained geometry optimizations to ground state structures using calculations based on the quantum density functional theory DFT. The two allotropes in space group P212121 were identified with original topologies 3,3,4T2 and cai-4,4-Pnma respectively. Both are metastable with respect to diamond and present super hard properties with a larger density and hardness for tetr-C12. Electronic band structures reveal conductive trig-C12 and semiconducting tetr-C12.
The structure formation features and mechanical properties of the AlN–С–TiB2 ceramic composite containing 2 wt
The chemical interactions between components and high-pressure high-temperature (HPHT) reaction sintering processes (p = 7.7 GPa, T = 2200°C) were studied for superhard composites of groups BH and BL in the cBN–Me and cBN–TiCN–Me systems (where Me = Ni, Co, W with a content of 30 vol
The etching behavior, mechanism, and efficiency of diamond were systematically compared for the silicon-thermal method and direct etching using pure Fe powder or Fe2O3₂O₃ alone. XRD, SEM, and thermodynamic analyses showed that the silicon-thermal reaction system (Fe2O3–Si), owing to its strong exothermic effect (ΔH ≈ –1070 kJ mol–1), generated an active high-temperature etching medium in situ, dominated by Fe and FeO and accompanied by the formation of silicates. Together, they created a dynamic etching environment described as “high-enthalpy-driven multiphase coupling catalysis-dissolution-migration”. The introduction of CaO further led to the formation of Ca2SiO4, which significantly enhanced the etching effect by stabilizing the FeO phase and improving mass transport, particularly inducing complex and deep etch morphologies on the diamond (111) planes and grain boundaries. Experiments demonstrated that the etching efficacy of the silicon-thermal method was significantly superior to the mild etching achieved by pure Fe or Fe2O3 alone. This research provides a new strategy based on silicon-thermal reduction for the efficient and deep surface processing of diamond.
Based on an investigation of the scattering behavior of sludge nanoparticles and wear nanoparticles originating from the polishing powder during the polishing of copper optical components using a dispersed system of micro- and nanopowders of copper metaborate in kerosene, as well as the formation of a deposit composed of copper oxide nanoparticles on the polished surface, it was established that the dependence of the total scattering cross section of sludge nanoparticles on the radius of the circular zones of the component is characterized by maximum values at radii of 10, 15, 17.5, and 20 mm. These maxima correspond to the highest probability of deposit formation on the processed surface, specifically within these circular zones. Investigation of the influence of the emergent properties of quantum sludge nanoparticles and polishing powder wear nanoparticles on their collective behavior, self-organization, and assembly during motion within an optical resonator of variable length formed by the surfaces of the workpiece and the polishing lap demonstrated that a deposit composed of sludge nanoparticles forms on the processed surface of the copper component. Fragments of this deposit are discretely distributed along concentric circles whose radii coincide with the values calculated using the quantum theory of nanoparticle scattering. It was further shown that, during the polishing of copper optical components using micro- and nanopowders of copper metaborate dispersed in kerosene, the material removal rate reaches 28.6 × 10–13 m3/s, which is in good agreement with the experimentally determined polishing productivity of 1.5 ± 0.1 mg/min, or 7.3 ± 0.4 μm/h, or (28 ± 1) × 10–13 m3/s, with a deviation of 5–6
