Types and microstructures of pores in shales of the Ordovician Wulalike Formation at the western margin of the Ordos Basin, China

Shale samples from the Ordovician Wulalike Formation at the western margin of the Ordos Basin are studied to define the types, microstructures and connectivity of pores as well as the relationships between the pore structures and gas content of the samples by using experimental techniques such as high-resolution field emission scanning electron microscopy (FESEM), mercury injection capillary pressure (MICP), low-temperature nitrogen adsorption (LTNA), CO_(2) adsorption, and focused ion beam scanning electron microscopy (FIB-SEM). The results show that the shale has 10 different lithofacies, typical mixed sedimentary characteristics, and poorly developed pores. The reservoir space mainly consists of intercrystalline pores, dissolution pores, intergranular pores, and micro-fissures, with organic pores occasionally visible. The pore size is mostly within 0.4–250 nm range but dominated by micropores and mesopores less than 20 nm, with pore numbers peaking at pore sizes of 0.5 nm, 0.6 nm, 0.82 nm, 3 nm, and 10 nm, respectively. The pores are poorly connected and macropores are rarely seen, which may explain the low porosity and low permeability of the samples. Samples with high content of organic matter and felsic minerals are potential reservoirs for oil and gas with their favorable physical properties and high connectivity. The pores less than 5 nm contribute significantly to the specific surface area and serve as important storage space for adsorbed gas.

Comprehensive Model Construction and Simulation for Superconducting Electrodynamic Suspension Train

With the advantages of levitation/guidance self-stability,large levitation gap,and high lift-to-drag ratios,superconducting electrodynamic suspension(SC-EDS)train is becoming a viable candidate for the high-speed and ultra-high-speed rail transportation.In order to provide the basis for designing the optimization and control strategy,this paper establishes a comprehensive model for the SC-EDS train,which considers the dynamics of the bogie and car body in all directions.The obtained model reveals the complex coupling and feedback relationships among the variables,which cannot be described by the existing local models of the SC-EDS train.Simulation examples under different parameters and initial conditions are presented and discussed to demonstrate the potential use of the model given in this paper.

In situ real-time study buckling behavior of boron nitride nanotubes with axial compression by TEM

Boron nitride nanotubes(BNNTs)were treated as brittle materials and could be used to enhance the composite mechanical properties.Many approaches were used to verify the theoretical prediction experimentally,but how to in situ real-time characterize nanomechanical properties of BNNTs was still interested to the researchers.An in situ transmission electron microscopy(TEM)equipped with a force transducer holder had been used to study the structure evolution behavior of BNNTs with axial compression.Real-time video and the force transducer had been used synchronously to record the whole force loading process where the mechanical deformation of BNNT began,buckled and ended with fracture.An in dividual ultrathin BNNT was employed to con duct the loading test.The results showed that the elastic deformation happened on the BNNT.Young's modulus?1.05-1.37 Tpa and elasticity coefficient?198.7-255.9 N/m of BNNT were calculated by Euler formula and Hooker's law,respectively.

Enhanced tribological properties of aligned graphene-epoxy composites

The random distribution of graphene in epoxy matrix hinders the further applications of grapheneepoxy composites in the field of tribology.Hence,in order to fully utilize the anisotropic properties of graphene,highly aligned graphene-epoxy composites(AGEC)with horizontally oriented structure have been fabricated via an improved vacuum filtration freeze-drying method.The frictional tests results indicated that the wear rate of AGEC slowly increased from 5.19x10^(-6)mm^(3)/(N-m)to 2.87x10^(-5)mm^(3)/(N-m)with the increasing of the normal load from 2 to 10 N,whereas the friction coefficient(COF)remained a constant of 0.109.Compared to the neat epoxy and random graphene-epoxy composites(RGEC),the COF of AGEC was reduced by 87.5%and 71.2%,and the reduction of wear rate was 86.6%and 85.4%at most,respectively.Scanning electron microscope(SEM)observations illustrated that a compact graphene self-lubricant film was formed on the worn surface of AGEC,which enables AGEC to possess excellent tribological performance.Finally,in light of the excellent tribological properties of AGEC,this study highlights a pathway to expand the tribological applications of graphene-epoxy composites.

Deformation mechanism and in-situ TEM compression behavior of TB8βtitanium alloy with gradient structure

Severe plastic deformation is known to induce grain refinement and gradient structure on metals’surfaces and improve their mechanical properties.However,the fundamental mechanisms behind the grain refinement and micromechanical properties of materials subjected to severe plastic deformation are not still well studied.Here,ultrasonic surface rolling process(USRP)was used to create a gradient microstructure,consisting of amorphous,equiaxed nano-grained,nano-laminated,ultrafine laminated and ultrafine grained structure on the surface of TB8βtitanium alloy.High energy and strain drove element co-segregation on sample surface leading to an amorphous structure during USRP processing.In situ transmission electron microscope compression tests were performed in the submicron sized pillar extracted from gradient structure and coarse grain,in order to reveal the micromechanics behavior of different grain morphologies.The ultrafine grained layer exhibited the lowest yield stress in comparison with single crystal and amorphous-nanocrystalline layers;the ultrafine grained layer and single crystal had an excellent strain hardening rate.The discrepancy among the grain sizes and activated dislocation sources led to the above mentioned different properties.Dislocation activities were observed in both compression test and microstructure evolution of USRP-treated TB8 alloy.An evolution of dislocation tangles and dislocation walls into low angle grain boundaries and subsequent high angle grain boundaries caused the grain refinement,where twinning could not be found and no phase transformation occurred.

Quantitatively investigating the self-attraction of nanowires

The self-attraction of nanowires(NWs)would lead to NWs bunching up together when fabricated in high density and the short circuit of NW-based devices during service.However,the underlying mechanism of the self-attraction of NWs remains debatable due to the lack of in situ characterization of the attraction.In this study,a versatile method of in situ investigating the self-attraction of NWs was developed.The attractive force between two NWs and their distance can be determined quantitatively in the process of attraction under an optical microscope,eliminating the influence of electron beam in electron microscopes.With this approach,the self-attraction of SiC NWs was investigated and a two-stage mechanism for the self-attraction was proposed.The electrostatic force between two individual SiC NWs increased as their distance decreased,and acted as the initial driving force for the attraction of NWs.SiC NWs remained in contact under van der Waals force until they separated when external force exceeded van der Waals force.The charge density and the Hamaker constant of SiC NWs were determined to be 1.9×10^(-4)C·m^(-2)and 1.56×10^(-19)J,which played an important role in the attraction of NWs.The results shed light on the mechanism of selfattraction among NWs and provide new insights into fabricating high-quality NWs and developing high-performance NW-based devices.