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  • 21
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    Influence of sulfurization time on two step grown SnS thin films (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): M. Gurubhaskar, Narayana Thota, M. Raghavender, G. Hema Chandra, P. Prathap, Y.P. Venkata Subbaiah SnS thin films were prepared using a simple two-stage process. The two-stage process involved in sputtering of Sn over glass substrate followed by sulfurization of sputtered Sn at 350 °C. The sulfurization process was carried out in the ambience of sulfur for different time lengths, 10–120 min and its influence on physical properties are reported. XRD study showed that the films sulfurized at 10 min were poor in crystallinity with reflections of un-reacted tin and sulfur. As the sulfurization time (S t ) is increased to 60 min, a single phase orthorhombic SnS was observed with (111) preferred plane. Four distinct Raman modes at 95, 163, 190 and 220 cm −1 confirms the formation of SnS for S t  > 30 min, however, S t  〈 30 min treated Sn films had extra Raman peak at 489 cm −1 related to S x phase. The ratio of Sn/S was found to be 2.92 for 10 min and reached stoichiometric ratio with densely packed grain morphology for 60 min. The optimized films showed a direct band-gap of 1.35 eV. The XPS oxidation states of Sn and S were found to be (+2) and (−2), indicating the formation of SnS. The S t dependent electrical measurements are also reported and discussed.
    Print ISSN: 0042-207X
    Electronic ISSN: 1879-2715
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 22
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    Study of the metal-semiconductor contact to ZnO films (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Yu Yan, Wei Mi, Jinshi Zhao, Zhengchun Yang, Kailiang Zhang, Chongbiao Luan High resistance Zinc oxide (ZnO) films have been prepared on Si (100) substrates using magnetron sputtering method. Structure analysis revealed a clear out-of-plane orientation of ZnO (001) || Si (100). The metallic composition of the contact is a critically important parameter for making ohmic contacts to ZnO films. Al/Ti metal contacts show linear I-V characteristics indicative of ohmic behavior, while other metal contacts such as Al and Ti show nonlinear characteristics with rectification, that reveal the presence of schottky barriers.
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    Electronic ISSN: 1879-2715
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 23
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    The strength-ductility balance of Al0·4CoCu0.6NiTix (x≤1.0) and Al0·4CoCu0·6NiSi0.2Tix (x≤0.5) high entropy alloys by regulating the proportion of Ti and improving the cooling rate (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Yongxing Chen, Sheng Zhu, Xiaoming Wang, Baijun Yang, Zhiqiang Ren, Guofeng Han, Shu Wen The work prepared Al 0·4 CoCu 0·6 Ni(Si 0.2 )Ti x (Si 0 Ti x (x ≤ 1.0) and Si 0.2 Ti x (x ≤ 0.5)) high entropy alloys (HEAs) with high strength and excellent plasticity by optimizing the added ratio of Ti and rapid cooling, discussed the effects of Ti and cooling rate on HEAs' microstructures and mechanical properties. The results showed that arc melted and copper injected Si 0 Ti x HEAs' phase structures changed gradually from “fcc + L1 2 (Si 0 Ti 0.25 )” to “fcc + L1 2 +minor bcc (Si 0 Ti 0.5 )” and finally to “fcc + L1 2 +bcc + Ni 3 Ti-type phase (Si 0 Ti 0.75 , Si 0 Ti 1.0 )”. But they transformed from “fcc + L1 2 +bcc + Ni 16 Ti 6 Si 7 -type phase (Si 0·2 Ti 0.25 )” to “fcc + L1 2 +bcc + AlNi 2 Ti-type + Ni 16 Ti 6 Si 7 -type phase (Si 0·2 Ti 0.5 )” for Si 0.2 Ti x HEAs. The micro-hardness of arc melted and copper injected HEAs gradually increased compared with Si 0 Ti 0 matrix HEA and that of copper injected HEAs were larger than arc melted HEAs (except Si 0 Ti 0.5 ). The compressive properties of Si 0 Ti 0.25 , Si 0 Ti 0.5 and Si 0·2 Ti 0.25 HEAs were relatively better, in which, the yield strengths of copper injected Si 0 Ti 0.25 , Si 0 Ti 0.5 and Si 0·2 Ti 0.25 HEAs were 2.7, 2.9 and 4.8 times than that of arc melted Si 0 Ti 0 matrix HEA (295 MPa), the fracture strain rates of the corresponding HEAs were 47.1%, 22.4% and 13.5% respectively. It introduced three strengthening mechanisms of solid solution strengthening, trace phase transformation and fine grain strengthening and realized HEAs' strength-ductility balance.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 24
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    Prediction of vacuum deterioration caused by vacuum accident in the beamline (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): S. Takahashi, M. Sano, A. Watanabe Vacuum deterioration at the most upstream of the front-end was predicted quantitatively under the assumption that a rupture of windows and subsequent inrush of air might occur in the SPring-8 beamline. A 10-m-long shock tube was employed to simulate an inrush of air into a region with rarefied gas dynamics. The shock Mach number ( Ma ) and pressure increase were measured with the fast-closing shutter (FCS) system both activated and de-activated. Actual front-end components as well as plain pipes having various lengths and another pipe with baffle plates inside were inserted into the shock tube by arranging various combinations in tandem. Although it could be observed that an increase in the number of repetitions of the cross-sectional change decreases Ma , the pressure increase essentially depends on the total internal volume of the shock tube. Besides, for the other internal structure, which has a gently tapered cross-sectional change, the pressure increase are suppressed as well as the decrease of Ma . The effective leak rate of the FCS at the inrush of air could be presented as a function of the total internal volume; thus, the number of gas molecules flowing into the most upstream of the front-end could be estimated.
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    Electronic ISSN: 1879-2715
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 25
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    Effect of multilayered CoO-CoAl2O4 films on improving solar absorptance of Co-WC solar selective absorbing coatings (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Xuemin Zhang, Xiaobo Wang, Xiong Zhang, Yongjia Li, Xudong Cheng The multilayered CoO-CoAl 2 O 4 solar selective films were prepared on Co-WC coatings with different mole ratio of Co and Al by sol-gel process. The thin film has high and low refractive indices, respectively. The inner layer can improve surface condition of Co-WC coating as a high absorbing film and buffer lay, annealed at 650 °C in vacuum. The outer layer was annealed at the same condition. The absorptance ( α ) of the multilayer structure coating increased from 0.873 to 0.932. The properties of the sols were characterized by thermogravimetry-differential scanning calorimetry (TG-DSC). The phase compositions and structure of samples annealed at 650 °C were analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The microstructure and elements distribution of thin films were investigated by field emission scanning electron microscopy (FE-SEM) and energy dispersive spectrometer (EDS), respectively. The absorptance of coatings indirectly indicate the binding force between the Co-WC substrate, durability, long-time stability and corrosion resistance are fine. The results illustrated that defects on surface of the Co-WC coating gradually decrease with the deposition of sol films. And the good element gradients in multilayer structures and the structure of thin films might be the reasons for its improvement in absorptance.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 26
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    Microstructure and mechanical property of Ni-based thick coating remelted by gas tungsten arc (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Li Ya-long, Dong Tian-shun, Li Guo-lu, Wang Hai-dou, Fu Bin-Guo, Zheng Xiao-dong, Zhou Xiu-kai Herein a NiCrBSi coating with 800 μm thickness was fabricated via plasma spraying on AISI 1045 steel, whereupon gas tungsten arc welding (GTA) process was employed to remelt the coating. The microstructure and mechanical properties of the coating before and after remelting were investigated. The results indicate that microstructural inhomogeneity in the as-sprayed coating were almost completely eliminated by GTA remelting. The main phases in the as-sprayed coating are γ-Ni, Cr 7 C 3 and Cr 2 B. While, the remelted coating is mainly composed of fine dendrite γ-(Ni,Fe,Cr) and thin interdendritic lamellar eutectic (Fe,Cr) 23 C 6 . Moreover, there are some submicron particles Ni 3 B, CrB and Ni 3 Si in the grain interior of γ-(Ni,Fe,Cr), and a large number of nanocrystallines in the grain boundary of γ-(Ni,Fe,Cr). After remelting, a compact and complete solid solution γ-(Ni,Fe,Cr) is formed at the interface between the remelted coating and substrate, hence the interface is transformed from mechanical bonding to metallurgical bonding. In addition, remelting the coating was found to induce a 84.4% increase in the elastic modulus, a 18.5 times increase in the fracture toughness, and a 42.8% increase in the microhardness. Therefore, GTA remelting is found a feasible method to significantly improve the microstructure and mechanical properties of the coating.
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  • 27
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    Study of rarefied gas flows in backward facing micro-step using Direct Simulation Monte Carlo (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Abhimanyu Gavasane, Amit Agrawal, Upendra Bhandarkar A backward facing micro-step is a building block for many microfluidic devices. Due to micron sized characteristic dimensions, the gas flow in such a geometry is rarefied in nature. Such rarefied gas flows are widely solved using the Direct Simulation Monte Carlo (DSMC) technique. Flow separation, circulation and re-attachment are some of the basic characteristics of step flows. The objective of this study is to analyze the effect of rarefaction on the flow properties and the separation of the flow. The range of selected Knudsen number (Kn) covers the slip and transition regime from a value of 0.0311–13.25. The pressure ratios employed are 3 and 5. It is observed that the slip velocity continuously increases while the centre-line velocity first decreases, then remains constant and finally increases with increase in Kn. At the step, separation of the flow is seen for Kn 〈 0.1325 while no such separation is observed in the range of Kn from 0.198 to 13.25. The corresponding Re for these ranges are 6.43 to 0.67 and 0.392 to 0.012 respectively. The re-attachment length decreases with increase in Kn whereas it increases with increase in Re. A stronger pressure force and a weaker diffusion effect leads to flow separation in the slip regime whereas stronger diffusion and weaker pressure force lead to an absence of flow separation in the transition regime. Finally, this work presents for the first time the existence of the Knudsen minimum for such a backward step geometry.
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  • 28
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    The facility effects of a Hall effect thruster's relative exhaust direction in ground tests (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Zhe Zhang, Junxue Ren, Haibin Tang, Jinbin Cao, Shuai Cao, Zhiyuan Chen, William Yeong Liang Ling, Rikang Zhao This research focuses on understanding how the relative pumping orientation and backpressure of a vacuum facility affects the measured performance and plasma plume parameters of a Hall-effect thruster (HET). A HET was operated in two opposite directions: plume ejection towards the vacuum pump and plume ejection away from the pump. The HET plume for each orientation was individually characterized at three vacuum facility operating pressures to study the effect of the facility pumping orientation and backpressure on the measured plume parameters and thruster performance. The ion current density, divergence angle, beam current, and ion energy distribution were measured using a Faraday probe and a retarding potential analyzer (RPA). The variation in the direction of the plume with respect to the pumping orientation leads to a clear difference in the measured performance of the HET when operating at an elevated backpressure. These are the first experiments that take the effect of the pumping orientation of a vacuum facility with respect to the thruster's exhaust direction into consideration. The results here will aid future research in selecting an adequate thruster exhaust direction when performing different Hall thruster ground tests such as plume diagnostics, lifetime tests, and erosion tests.
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  • 29
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    Theoretical parametric investigation of plasma sustained by traveling electromagnetic wave in coaxial configuration (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-16
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): T. Bogdanov, E. Benova The electromagnetic wave traveling along a dielectric–gas interface can produce and sustain gas discharge in various geometrical configurations. We propose a parametric study of surface-wave-sustained plasma in coaxial configuration at low pressure based on stationary 1.5D (1D for plasma density and 2D for the wave electromagnetic field components) model. At this configuration the plasma is produced outside a dielectric tube in a low pressure chamber when at the tube axis a metal antenna is arranged. The model gives the phase diagrams and the axial distribution of the plasma density, wave power, wave number, and wave field components, as well as the radial distribution of the wave field components. The dependence of wave and plasma characteristics on the geometry parameters (the plasma radius, the dielectric tube thickness, and the metal antenna radius) and on the dielectric tube permittivity is investigated and shown in this paper. The discharge conditions at which it is possible to sustain plasma by an azimuthally symmetric wave are obtained. Comparison with the cylindrical plasma in corresponding conditions and with experimental data is also presented.
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  • 30
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    Hot corrosion behavior of Ba2DyAlO5 exposed to calcium-magnesium-alumina-silicate at 1300 °C and 1350 °C (2018)
    Elsevier
    In: Vacuum
    Details
    Publication Date: 2018-06-15
    Description: Publication date: September 2018 Source: Vacuum, Volume 155 Author(s): Jianxing Yu, Caimei Wang, Lei Guo, Yang Yu, Yan Zhao, Qiwei Yuan, Huakun Wang, Zhiqiang Feng Calcium-magnesium-alumina-silicate (CMAS) attack has been considered as one of the significant failure mechanisms for thermal barrier coatings (TBCs). In this study, CMAS corrosion behavior of Ba 2 DyAlO 5 is investigated at 1300 °C and 1350 °C for 0.5 h, 4 h, 12 h and 24 h. The results indicated that Ba 2 DyAlO 5 had high resistance to CMAS infiltration for prolonged durations (24 h), ascribed to the rapid formation of crystallization phases by chemical reaction between Ba 2 DyAlO 5 and CMAS. The corrosion products with a main constitution of Ca 2 Dy 8 (SiO 4 ) 6 O 2 , Ba 1.31 Ca 0.69 SiO 4 , BaAl 2 O 4 and Dy 2 O 3 phases formed a sealing layer on the sample surfaces, which can effectively suppress further penetration of the molten CMAS. The associated mechanism was discussed.
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