Mechanical and thermal characterizations of nanoporous two-dimensional boron nitride membranes

Abstract

Hexagonal boron nitride (h-BN) is a promising 2D material due to its outstanding mechanical and thermal properties. In the present study, we use molecular dynamics simulations to investigate the influence of porosity and temperature on the mechanical characteristics of h-BN based on uniaxial and biaxial tensions. Meanwhile, the progression of the microstructure of h-BN up to fracture is studied in order to clarify its fractures mechanism during the tension process. Our results reveal that depending on the porosity and tensile direction, the phase transition occurs more or less. The strength, and Young's modulus of h-BN membranes reduce as increasing porosity. Due to the presence of the pores, the most substantial stresses will be centred around the pores site in the tensile test. Then the fracture starts on the pore edge and spreads preferentially along the zigzag direction of h-BN. Furthermore, fracture strain, strength, and Young's modulus decrease when the temperature rises. In addition, the non-equilibrium molecular dynamics (NEMD) simulations are performed to investigate the influence of various porosities and temperatures on the thermal conductivity of h-BN membranes. The results reveal that the thermal conductivity is greatly reduced by nanoporous. The higher the porosity, the lower the thermal conductivity. The vibration density of states of h-BN membranes is calculated; the result suggests that the defects might reduce the phonon mean free path because of the high collision of the phonons. These alterations represent the scattering influence of defects on phonons, which reduces phonon life and considerably lowers thermal conductivity. Moreover, the findings also proved that as temperature increases, the intrinsic thermal conductivity of h-BN decreases. The thermal conductivity and mechanical properties of the pristine h-BN thin film are interestingly equivalent in the zigzag and armchair orientations.

Mechanical Properties and a Brittle-to-Ductile Fracture Transition in 3D Boron Nitride Foams

“…Integrating nanomaterials into functional systems requires that we thoroughly understand their fracture behavior, both theoretically − and experimentally. − However, to date, the fracture behavior of BNF has not been investigated. A previous theoretical analysis of the fracture behavior of 2D BN and of BN nanotubes indicates that atomic-scale defects induce local stress concentration sites, from which cracks initiate and propagate. ,− A study of graphene foam (GF), whose 3D network structure is similar to that of BNF, found that the formation of fractures is highly influenced by the sliding motion of the graphene layers . A similar sliding motion of graphene layers was observed in GFs subjected to an electrostatic tension force and in multilayer carbon nanotubes subjected to torque .…”

“…Boron nitride (BN) has recently emerged as a new two-dimensional (2D) material and has attracted immense scientific attention because of its outstanding physical properties, including its wide energy band gap, high mechanical strength, − electromechanical coupling, excellent lubrication, tunable wavelength emission, high thermal conduction, thermomechanical coupling, and ultraviolet light emission . The recent synthesis of BN as a three-dimensional (3D) foam (abbreviated here as BNF) has opened new frontiers for this material since first reported by Yin et al in 2013 …”

Mechanical characteristics and thermal conductivity of defect single-layer buckled honeycomb germanene

“…Based on the relationship between the temperature and kinetic energy (equation ( 5)), the atoms will be more oscillate at the higher temperature leading to the bond between atoms becoming weaker causes mechanical characteristics to decrease [70,71]. Besides, as the temperature rises, the temperature-induced softening causes mechanical characteristics to decrease [72]. The chaotic movement of atoms creates a high collision of the phonons, which reduces atoms' life and significantly lowers thermal conductivity [73,74].…”

Role of nanofiller porosity in monitoring streamer and phonon dynamics in Transformer oil

“…This contradictory variation of k is due to the increase in porosity in PBN 1050 compared to PBN 950. Increased porosity, presence of non-uniform pores along with short spatial extent of PBN 1050 led to the increase in phonon-pore scattering and heat flux localization and heat losses at the pore edges [50][51][52][53]. As a result, effective mean free path for phonons decreased and k is reduced.…”

“…With crystalline nanofillers, ballistic transfer of phonons occurs both via the nanofiller as well as the oil-nanofiller interface due to low phonon collision and scattering [52]. The ballistic phonon movement via a nanofiller depends on its type, phase and aspect ratio [50,52].…”