Achieving oxidation protection effect for strips hot rolling via Al_(2)O_(3) nanofluid lubrication

It was discovered the application of Al_(2)O_(3) nanofluid as lubricant for steel hot rolling could synchronously achieve oxidation protection of strips surface.The underlying mechanism was investigated through hot rolling tests and molecular dynamics (MD) simulations.The employment of Al_(2)O_(3) nanoparticles contributed to significant enhancement in the lubrication performance of lubricant.The rolled strip exhibited the best surface topography that the roughness reached lowest with the sparsest surface defects.Besides,the oxide scale generated on steel surface was also thinner,and the ratio of Fe_(2)O_(3) among various iron oxides became lower.It was revealed the above oxidation protection effect of Al_(2)O_(3) nanofluid was attributed to the deposition of nanoparticles on metal surface during hot rolling.A protective layer in the thickness of about 193 nm was formed to prevent the direct contact between steel matrix and atmosphere,which was mainly composed of Al_(2)O_(3) and sintered organic molecules.MD simulations confirmed the diffusion of O_(2) and H_(2)O could be blocked by the Al_(2)O_(3) layer through physical absorption and penetration barrier effect.

Surface quality of cold rolling aluminum strips under lubrication condition

The effects of oil film on the rolled surface, including surface roughness and topography, were investigated during cold rolling of aluminum strips. Various mineral oils with viscosities from 0.10 to 1.6 Pa.s were used to obtain different oil film thicknesses. Results from experiment and calculation show that the thicker oil film protects the initial roughening surface so that it leads to an increase in roughness of the rolled surface, in particular when the surface roughness has the character of direction. The rolled surface roughness was determined by 2, which is the ratio of oil film thickness to the combined surface roughness. When 2 〉 3, the rolled surface roughness increases rapidly with the increase in oil viscosity, whereas the surface roughening has already occurred when 2 〈 3, but the increase of the rolled surface roughness with increasing viscosity is not distinct.

Dynamic optimization analysis of hydraulic pipeline system based on a developed response surface method

When designing a complex pipeline with long distance and multi-supports for offshore platform,it is necessary to analyze the vibration characteristics of the complex pipeline system to ensure that there is no harmful resonance in the working conditions.Therefore,the optimal layout of support is an effective method to reduce the vibration response of hydraulic pipeline system.In this paper,a developed dynamic optimization method for the complex pipeline is proposed to investigate the vibration characteristics of complex pipeline with multi-elastic supports.In this method,the Kriging response surface model between the support position and pipeline is established.The position of the clamp in the model is parameterized and the optimal solution of performance index is obtained by genetic algorithm.The number of clamps and the interval between clamps are considered as the constraints of layout optimization,and the optimization objective is the natural frequencies of pipeline.Taking a typical offshore pipeline as example to demonstrate the effectiveness of the proposed method,the results show that the vibration performance of the hydraulic pipeline system is distinctly improved by the optimization procedure,which can provide reasonable guidance for the design of complex hydraulic pipeline system.

Experimental determination of the Young’s modulus of individual single-walled carbon nanotubes with single chirality

One-dimensional carbon nanotube(CNT)exhibits excellent mechanical properties and is considered to be an ideal candidate material for the space elevator.However,subtle changes in its chirality strongly affect its physical and chemical properties,including mechanical properties(such as Young's modulus,YM).Theoretical studies reveal that the YMs of perfect single-walled carbon nanotubes(SWCNTs)are in the order of TPa and related to their structures.Nevertheless,due to the lack of SWCNTs samples with well-defined structures and the difficulties in mechanical tests on individual SWCNTs,the theoretical correlations between YM and structure of SWCNTs have not been verified and are still in debate,which directly influences the practical utilization of the excellent mechanical properties of SWCNTs.In this work,we have developed an experimental method to measure the YM of an individual micrometer-scale suspended CNT by atomic force microscopy.A distinct regularity is found between the YM and chirality(i.e.,chiral angle and diameter)of SWCNT in the experiment for the first time.By comparing the YMs of SWCNTs with similar diameters and different chiral angles,it manifests that the SWCNT with a near zigzag configuration has a larger YM.This finding suggests that the effect of SWCNT’s structures on the YMs cannot be ignored.The developed method of measuring YMs of SWCNTs will be valuable for further experimental research on the inherent physical and chemical properties of SWCNTs.

Synthesis of N-doped carbon quantumn dots as lubricant additive to enhance the tribological behavioor f MoS_(2)nanofluid

In this study,a novel lubricant additive nitrogen-doped carbon quantum dot(N-CQD)nanoparticle was prepared by the solvothermal method.The synthesized spherical N-CQD nanoparticles in the diameter of about 10 nm had a graphene oxide(GO)-like structure with various oxygen(O)-and nitrogen(N)-containing functional groups.Then N-CQDs were added to MoS_(2)nanofluid,and the tribological properties for steel/steel friction pairs were evaluated using a pin-on-disk tribometer.Non-equilibrium molecular dynamics(NEMD)simulations for the friction system with MoS_(2)or MoS_(2)+N-CQD nanoparticles were also conducted.The results showed that friction processes with MoS_(2)+N-CQD nanofluids were under the mixed lubrication regime.And MoS_(2)nanofluid containing 0.4 wt%N-CQDs could achieve 30.4%and 31.0%reduction in the friction coefficient and wear rate,respectively,compared to those without N-CQDs.By analyzing the worn surface topography and chemical compositions,the excellent lubrication performance resulted from the formation of tribochemistry-induced tribofilm.The average thickness of tribofilm was about 13.9 nm,and it was composed of amorphous substances,ultrafine crystalline nanoparticles,and self-lubricating FeSO_(4)/Fe2(SO_(4))_(3).NEMD simulation results indicated the interaction between S atoms in MoS_(2)as well as these O-and N-containing functional groups in N-CQDs with steel surfaces enhanced the stability and strength of tribofilm.Thereby the metal surface was further protected from friction and wear.

Enhanced exciton diffusion from interlayer charge-transfer transitions in PtSe2/MoSe_(2) van der Waals heterojunction

Artificial van der Waals(vdWs)heterostructures offer unprecedented opportunities to explore and reveal novel synergistic electronic and optical phenomena,which are beneficial for the development of novel optoelectronic devices at atomic limits.However,due to the damage caused by the device fabrication process,their inherent properties such as carrier mobility are obscured,which hinders the improvement of device performance and the incorporation of vdWs materials into next-generation integrated circuits.Herein,combining pump-probe spectroscopic and scanning probe microscopic techniques,the intrinsic optoelectronic properties of PtSe_(2)/MoSe_(2)heterojunction were nondestructively and systematically investigated.The heterojunction exhibits a broad-spectrum optical response and maintains ultrafast carrier dynamics(interfacial charge transfer~0.8 ps and carrier lifetime~38.2 ps)simultaneously.The in-plane exciton diffusion coefficient of the heterojunction was extracted(19.4±7.6 cm^(2)∙s^(−1)),and its exciton mobility as high as 756.8 cm^(2)∙V−1∙s^(−1)was deduced,exceeding the value of its components.This enhancement was attributed to the formation of an n-type Schottky junction between PtSe_(2)and MoSe_(2),and its built-in electric field assisted the ultrafast transfer of photogenerated carriers from MoSe_(2)to PtSe_(2),enhancing the in-plane exciton diffusion of the heterojunction.Our results demonstrate that PtSe_(2)/MoSe_(2)is suitable for the development of broadspectrum and sensitive optoelectronic devices.Meanwhile,the results contribute to a fundamental understanding of the performance of various optoelectronic devices based on such PtSe_(2)two-dimensional(2D)heterostructures.