[en] In this study, we report a facile method to obtain air-stable n-type graphene by plasma-enhanced chemical vapor depositing Si₃N₄ film on the surface of graphene. We have demonstrated that the overlying Si₃N₄ film can not only act as the penetration-barrier against H₂O and O₂ adsorbed on the graphene surface, but also cause an effective n-type doping due to the amine groups at the interface of graphene/Si₃N₄. Furthermore, the studies reveal that the Dirac point of graphene can be modulated by the thickness of Si₃N₄ film, which is due to competing effects of Si₃N₄-induced doping (n-type) and penetrating H₂O (O₂)-induced doping (p-type). We expect this method to be used for obtaining stable n-type graphene field-effect transistors in air, which will be widely used in graphene electronic devices.

[en] This study is concerned with the wear behaviors of the polyurethane rubber (UR) used in the pigging industry under the condition of interference fit. The pin-on-disc tribological tests were conducted to obtain the wear rate of the UR, and the wear mechanisms were identified by observing the worn surface via an optical microscope. Additionally, the relationship between the wear rate and the contact pressure was presented with the method of quadratic fitting. (paper)

[en] Highlights: • The four-element model was rearranged for explaining the variation of the driving force of the bi-directional pig. • A dynamic analytical model of the bi-directional pig was established based on the rearranged four-element model. • The velocity has an obvious effect on the driving force of the bi-directional pig, especially in the launching process. The sufficient driving force is vital for ensuring the operational efficiency of the bi-directional pig. This paper carried out the high-velocity traction experiments by a custom-built experimental device to investigate the driving force of the bi-directional pig which experiences four stages during the running process. The four-element model (Burgers-Frenkel model) was rearranged for explaining the deformation and force condition of the sealing disc in each stage, and then a novel method for analyzing the driving force of the bi-directional pig was first proposed by using a dynamic analytical model which established based on the rearranged four-element model (hereinafter, the four-element model). The friction coefficient was determined with the method of combining the 3D numerical simulation and the experiment, and the model parameters were further extrapolated according to the experimental results. Our results indicate that the proposed analytical dynamic model has satisfying accuracy for predicting the driving force of the bi-directional pigs. The research results of this work are beneficial for avoiding the blockage accident and optimizing the pig design.