Understanding the friction behavior of sulfur-terminated diamond-like carbon films under high vacuum by first-principles calculations

Renhui Zhang,Juan Zhao,Yingchang Yang,Wei Shi,Zhibin Lu,Junjun Wang 한국물리학회 2018 Current Applied Physics Vol.18 No.3

Generally, the repulsive force was a key factor account for superlow friction of H or F doped diamond-like carbon (DLC) films under high vacuum. As we known, H or F doped DLC usually exhibited superlow friction under high vacuum. However, the superlow friction of S doped DLC under high vacuum was not found so far. This phenomenon was desirable to be well investigated. In this work, S-terminated diamond interfaces also exhibited strong repulsive force, however, the estimated friction coefficient was variable for S-terminated diamond interfaces. The lowest and largest friction coefficient was about 0.003 and 0.4 respectively, which indicated that the superlow friction of S doped DLC could achieve in theory. In order to well probe the unusual friction behavior of S doped DLC under high vacuum, using first-principles method, the repulsive interaction between sliding surfaces was well investigated in order to understand the unusual friction behavior of S doped DLC films.

First-principles investigation of the monoclinic NaMnO2 cathode material for rechargeable Na-ion batteries

Renhui Zhang,Zhibin Lu,Yingchang Yang,Wei Shi 한국물리학회 2018 Current Applied Physics Vol.18 No.11

Using first-principles calculations, we successfully investigate the electrochemical performance of the monoclinic NaMnO2 for the sodium ion batteries. NaMnO2 possesses a voltage window of 3.54–2.52 V and theoretical reversible capacity of 136 mAh g−1. Besides, we find that the metallicity of the monoclinic NaMnO2 gradually increases during Na extraction. Moreover, the computational Na migration energy barrier in the monoclinic NaMnO2 is 0.18 eV, ensuring ideal conductivity and reversible capacity. Although the Jahn-Teller distortion effects limit the enhancement of the reversible capacity of the monoclinic NaMnO2, it is still a right cathode material for the sodium ion batteries. The computational results are well in consistent with the experimental investigations.

Gas-liquid two-phase flow in the axial clearance of liquid-ring pumps

Renhui Zhang,Lei Tian,Guangqiang Guo,Xuebing Chen 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.2

In this study, the leakage flow in the axial clearance of a 2BEA-203 liquid-ring pump has been modeled through numerical simulation using the renormalization group k-ε turbulence model and the multiphase volume of fluid method. Numerical results show that the axial leakage flow reduces the inlet vacuum and efficiency of the liquid-ring pump. The gasliquid two-phase flow within the axial clearance region is completely separated. Several droplets are scattered outside the suction region, some of which flow back into the low-pressure suction region along the wall of the suction port. Given the axial asymmetry of the flow passage, the phase distribution within the impeller region is non-uniform along the axial direction. The numerically simulated pressure distribution within the axial clearance region accords well with the vortex distribution caused by the leakage flow. The leakage flow interacts with the impeller flow, and forms a corner vortex near the pressure side and a leakage vortex near the blade suction side. As the relative coordinate of the cross planes to the blade (sc −1 ) decreases from tip to hub, the corner vortex near the blade pressure side gradually weakens while the leakage vortex near the suction side gradually strengthens. These vortices mostly form in the suction and compression zones of the clearance region and significantly affect the overall pump efficiency. Findings of this study reveal the flow structure in the axial clearance of the liquid-ring pump and the interaction between the leakage and main flow.

Investigation on the effect of slot pulse jet on centrifugal pump performance

Renhui Zhang,Lichen Yun 한국유체기계학회 2018 International journal of fluid machinery and syste Vol.11 No.2

To improve centrifugal pump cavitation performance, the slot pulse jet pump is proposed. The slot is designed directly on the impeller shroud near the suction side of the blade leading edge. The slots are alternately blocked by the cambered prominence, which is designed at the impeller front side chamber along the circumferential direction. The leakage flow from the front side chamber flows into the slot alternately, and the pulse jet is formed near the blade inlet. Because of the strong shear, the pulse jet is more efficient than steady jet in terms of energy transmission. Based on the numerical simulation, the hydraulic performances of the slot pulse jet pumps with two different pulse frequencies are compared with the slot steady jet pump. The calculation result shows that with the increase of flow rate, the head and efficiency of the three kinds of pumps are basically the same. The cavitation performance of slot pulse jet pump is better than that of slot steady jet pump, especially for slot pulse jet pump Ⅱ. The distribution of pressure difference acted on the slot appears to be jagged, and the pulse frequency is consistent with shaft frequency or its harmonic frequency. The amplitude of the pressure fluctuation on slot jet pump Ⅱ is much higher than that of the slot pulse jet pump Ⅰ. The vapor volume distribution in the middle span of the impeller for slot pulse jet pump is less than that of slot steady jet pump. So, the pulse jet is an effective way to further improve the cavitation performance of slot steady jet pump, and NPSHr is significantly decreased, especially at design condition.

Akebia trifoliate koiaz peels extract as environmentally benign corrosion inhibitor for mild steel in HCl solutions: Integrated experimental and theoretical investigations

Mengqin Zhang,Lei Guo,Mengyue Zhu,Kai Wang,Renhui Zhang,Zhongyi He,Yuanhua Lin,Senlin Leng,Valentine Chikaodili Anadebe,Xingwen Zheng 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.101 No.-

In this account, pectin components were obtained from akebia trifoliate koiaz peels with the acid extractiontechnology. The chemical constituent of the akebia trifoliate koiaz peels extract (ATKPE) was analyzedand its anti-corrosion performance for mild steel in HCl medium was investigated byelectrochemical methods, surface analysis and theoretical calculations. Experimental results show thatATKPE exhibits excellent corrosion inhibition characteristic, and its inhibition efficiency can be as highas 90% when the concentration of ATKPE is 800 mg/L. Electrochemical measurements show that ATKPEis a mixed-type corrosion inhibitor consisting with Langmuir adsorption model. In addition, SEM, AFMand contact angle observations suggests that the ATKPE may attach firmly to the metal surface by forminga barrier film. XPS and ATR-FTIR results further verify the bonding interaction between the functionalgroups and steel substrate. Meanwhile, quantum chemical calculations and molecular dynamics (MD)simulations were performed to reveal the inhibition mechanism at molecular/atomic level. In brief, ourfindings demonstrate a novel environmentally benign, efficient corrosion inhibitor for steel protection inacidic media.

Core–Shell Grain Structure and High Energy Storage Performance of BNT-Based Relaxor Ferroelectric Ceramics

Zixin Zhang,Renhui Tan,Fangfang Wan,Kang Yan 대한금속·재료학회 2023 ELECTRONIC MATERIALS LETTERS Vol.19 No.2

Bismuth sodium titanate (Bi0.5Na0.5TiO3, BNT) based ferroelectric ceramic is one of the important lead free dielectric materialsfor high energy storage applications due to its large polarization. Herein, we reported a modified BNT based relaxor ferroelectricceramics composited with relaxor Sr0.7Bi0.2TiO3(SBT) and ferroelectric BaTiO3(BT), which exhibits a high recoverableenergy density of 5.59 J/cm3 and a high energy storage efficiency of 84.0% under large breakdown electric strengthof 420 kV/cm. A core–shell grain structure is observed in the BNT-SBT-BT ceramics with high content BT additive, whichplays crucial role on the enhancement of the energy storage performance. This ceramic also exhibits superior temperaturestability with small energy density variation of less than 6.5% in wide temperature range from room temperature to 180 °C. The impedance spectroscopies show that the ceramics have good insulation properties at high temperature. These characteristicsdemonstrate that the BNT-SBT-BT ceramic is a promising candidate for high-power energy storage applications.