Epoxy resin-impregnated insulation paper (RIP) composites are used as the inner insulation of dry condenser bushing in the ultra-high voltage direct current (UHVDC) power transmission system. To improve the dielectric properties and heat conductivity of RIP, hexagonal boron nitride (h-BN) nano-flakes are added to the insulation paper at concentrations of 0–50 wt % before impregnation with pure epoxy resin. X-ray diffraction (XRD), scanning electron microscopy (SEM) observations, thermal conductivity as well as the typical dielectric properties of direct current (DC) volume conductivity. DC breakdown strength and space charge characteristics were obtained. The maximum of nano-h-BN modified heat conductivity reach 0.478 W/(m·K), increased by 139% compared with unmodified RIP. The DC breakdown electric field strength of the nano-h-BN modified RIP does not reduce much. The conductivity of nano-h-BN modified is less sensitive to temperature. As well, the space charge is suppressed when the content is 50 wt %. Therefore, the nano-h-BN modified RIP is potentially useful in practical dry DC bushing application.

The water molecule migration and aggregation behaviors in oil-impregnated pressboard are investigated by molecular dynamics simulations in combination with Monte Carlo molecular simulation technique. The free energy and phase diagram of H₂O-dodecylbenzene (DDB) and H₂O-cellulose mixtures are calculated by Monte Carlo technique combined with the modified Flory-Huggins model, demonstrating that H₂O molecules can hardly dissolved with infinitesimal content in cellulose system at temperature lower than 650 K, based on which the oil/cellulose layered structure with water impurity representing three-phase coexistence in oil-impregnated pressboard are modeled and performed for molecular dynamics. The molecular dynamics of H₂O/DDB/cellulose three-phase mixture simulating oil-paper insulating system with H₂O impurity indicates that DDB molecules can thermally intrude into the cellulose-water interface so as to separate the water phase and cellulose fiber. The first-principles electronic structure calculations for local region of H₂O/DDB interface show that H₂O molecules can introduce bound states to trap electrons and acquire negative charges, so that they will obtain sufficient energy from applied electric field to break DDB molecular chain by collision, which are verified by subsequent molecular dynamics simulations of H₂O⁻/DDB interface model. The electric breakdown mechanism under higher than 100 kV/m electric field is presented based on the further first-principles calculations of the produced carbonized fragments being dissolved and diffusing in DDB phase. The resulted broken DDB fragments will introduce impurity band between valence and conduction bands of DDB system, evidently decreasing bandgap as to that of conducting materials in their existence space. The conductance channel of these carbonized DDB fragments will eventually be formed to initiate the avalanche breakdown process by the cycle-feedback of injected charge carriers with carbonized channels.

The complex configuration, H₂ adsorption binding energy, magnetic, and optical properties of FAU zeolites with Ag cations loaded by ion exchange in the vacant dielectric cavities were investigated by employing the first-principles calculations with all-electron-relativistic numerical atom-orbitals scheme and the Metropolis Monte Carlo molecular simulations. The visible absorption spectrum peaked at distinct wavelengths arranging from red or green to blue colors when changing the net charge load, due to the produced various redox states of Ag cations exchanging at multiple Li⁺-substituted sites. The spin population analyses indicate the ferrimagnetic coupling between Al–O–Si framework and Ag cations originates from the major ferromagnetic spin polarization in Ag cation cluster coordinating with sodalite cages, with the net spins appreciably depending on the Ag content and exchange site. The H₂ adsorption capacities and binding energies represent significant dependence on the content, location, and electronic property of Ag cations introduced into the FAU zeolites. The evident decrease of H₂ adsorption binding energy with increased loading concentration demonstrates repulsive interaction between H₂ molecules and heterogeneous adsorption configuration on Ag cations. The adsorption sites of H₂ sorted by the binding energy with different adsorption configurations were correlated with exchange sites of Ag cations under different Ag loading to comprehend the H₂ adsorption mechanism.

Scale effect and topological frustration can form magnetic order in the finite graphene structures (graphene nanoflakes (GNFs)). In this paper, the GNFs that can generate large net electron spin or electron spin antiferromagnetic coupling between local regions of net electron spins are classified reasonably. Representative special GNF configurations are proposed to be effectively used as fundamental logic gate devices for ultra-fast high density spintronics, and theoretically investigated by the first-principles electron structure calculations based on spin-polarized density functional theory. The first-principles calculations are performed by utilizing all-electron numerical-orbital scheme in the M11-L form of meta-GGA exchange-correlation functional. The energy spectrum of singly occupied states and the isodensity surface of total spin distribution indicate evidently that spin-single-state electrons are localized on two sides of a representative double-triangle GNF and the spin polarizations of two GNF segments are in opposite directions, resulting in antiferromagnetic coupling, which is consistent with the results derived from the graph theory and Lieb theorem. The energy of antiferromagnetic spin-coupled state is 55 meV lower than that of ferromagnetic spin-coupled state, which is obviously higher than the thermodynamic threshold of the minimum energy dissipation at room temperature. The spin coupling energy of the double triangle GNF increases with the scaling of GNF dimension increasing. The magnetic coupling strength of the double triangle GNF with and without mirror symmetry approach to the maximum stable values of 50 meV and 200 meV respectively, which are remarkably higher that of quantum dots and transition metal atom systems. Due to the fact that the spin coupling strength of the GNF logic gate spin device can reach 200 meV, it can operate normally at ambient temperature with an error rate of 0.001 which can be easily improved by an error correction technique. The calculation results demonstrate that the proposed GNF logic gate can finely operate at ambient temperature with significantly low and correctable error rate. Recent experimental studies show that graphene nanodevices on a scale of only a few nanometers can be successfully fabricated by etching technique of electron beam and scanning probe. Furthermore, the properties of GNF spin logic devices are not sensitive to intrinsic defects. The triangular GNF with n carbon rings has only (n+2)2-3 carbon atoms, while it can endure n-1 internal defects, thus persisting in non-bond states and local magnetic moments. It is suggested that the full spin logic gate devices based on GNF can be realized by using the current advanced nano-processing technology.