The Effect of Cu Addition on the System Stability and Thermoelectric Properties of Bi2Te3

Cu-doped Bi₂Te₃ nanopowders with nominal composition Cu _x Bi₂Te₃ (x = 0, 0.01, 0.025, and 0.05) were synthesized by a gas-induced-reduction method using TeO₂, Bi(NO₃)₃·5H₂O and Cu(NO₃)₂·3H₂O as raw materials and then hot-pressed into bulk materials. x-Ray diffraction (XRD) analysis indicates that, when x ≠ 0, pure Cu _x Bi₂Te₃ phase was obtained, and that when x = 0, Bi₂Te₃ mixed with a small amount of Bi₂TeO₅ was obtained. Field emission scanning electron microscopy observation reveals that Cu addition significantly reduces the grain sizes of the materials. First-principle calculations show that the order of the free energies of the materials is: Cu-doped Bi₂Te₃ (substitution of Cu for Bi) < Cu intercalated Bi₂Te₃ < Bi₂Te₃. The electrical and thermal conductivities decrease and the Seebeck coefficient increases with Cu addition. The maximum figure of merit, ZT, reaches 0.67 at 500 K for a Cu_0.05Bi₂Te₃ sample.     

Analysis of bending region physics in determining electrospun fiber diameter: effect of relative humidity on evaporation and force balance

This paper explores the role of the bending region and relative humidity (RH) in determining the resulting electrospun fiber diameter through a combined experimental and modeling analysis. Analysis of experimental measurements on PEO/water and PVP/alcohol solutions indicates that the bending region is significant in determining the final fiber diameter. A model is developed, to determine the dominant process physics of the bending region, predicting the final fiber diameter to be within 6% of experimental observations. The experimental analysis reveals that stretching in the bending region accounts for 40–60% of the stretching in the electrospinning process and the significant impact that RH has on fiber diameters. Our modeling analysis reveals the role of both evaporation and stretching in the bending region, and how RH influences both the jet length (stretching time) and force balance to determine the final fiber diameter.     

Development and Validation of Processing Maps for Ti-6Al-4V Alloy Using Various Flow Instability Criteria

Based on the flow stress data obtained from the isothermal hot compression tests, the processing maps of Ti-6Al-4V alloy were developed based on the instability criteria of Prasad, Malas, and Murty. The validation of the processing maps was achieved by investigating the microstructures of compressed Ti-6Al-4V alloy specimens. The results showed that the power dissipation maps obtained using the criteria of Prasad and Murty exhibited similar distribution, whereas the instability domains obtained by various instability criteria had great differences. Microstructure analysis showed that the instability domains determined by Murty’s criterion were more accurate than those determined using other criteria.     

Friction and wear properties of high-velocity oxygen fuel sprayed WC-17Co coating under rotational fretting conditions

Rotational fretting which exist in many engineering applications has incurred enormous economic loss. Thus, accessible methods are urgently needed to alleviate or eliminate damage by rotational fretting. Surface engineering is an effective approach that is successfully adopted to enhance the ability of components to resist the fretting damage. In this paper, using a high-velocity oxygen fuel sprayed(HVOF) technique WC-17 Co coating is deposited on an LZ50 steel surface to study its properties through Vickers hardness testing, scanning electric microscope(SEM), energy dispersive X-ray spectroscopy(EDX), and X-ray diffractrometry(XRD). Rotational fretting wear tests are conducted under normal load varied from 10 N to 50 N, and angular displacement amplitudes vary from 0.125° to 1°. Wear scars are examined using SEM, EDX, optical microscopy(OM), and surface topography. The experimental results reveal that the WC-17 Co coating adjusted the boundary between the partial slip regime(PSR) and the slip regime(SR) to the direction of smaller amplitude displacement. As a result, the coefficients of friction are consistently lower than the substrate's coefficients of friction both in the PSR and SR. The damage to the coating in the PSR is very slight. In the SR, the coating exhibits higher debris removal efficiency and load-carrying capacity. The bulge is not found for the coating due to the coating's higher hardness to restrain plastic flow. This research could provide experimental bases for promoting industrial application of WC-17 Co coating in prevention of rotational fretting wear.     

Strain-Induced Surface Dynamics of Aluminum Studied by <Emphasis Type="Italic">In Situ</Emphasis> Photoelectron Emission

In situ photoelectron emission in high-purity aluminum deformed under uniaxial tension while exposed to pulsed excimer laser radiation (248 nm) is reported in this paper. The effect of various surface treatments, including polishing, air oxidization, carbon coating, and gold coating, on photoelectron emission was investigated. The photoelectron emission signals are sensitive to strain-induced surface structure changes, such as slip lines and slip bands. In the case of aluminum with oxide of 4.5 nm thickness, the photoelectron emission increases gradually in a nonlinear fashion at the early stage of deformation (strain ≤0.05). Then the photoemission grows linearly until the accumulated strain reaches about 0.17. In the final stage, the photoelectron intensity increases parabolically until failure. The transition of photoelectron emission from linear to parabolic growth correlates with the onset of strain localization. The strain-induced microstructural change was also analyzed by scanning electron microscopy (SEM). The photoelectron emission signals from aluminum during tension were interpreted in the light of surface treatment, surface electron work function, and surface microstructural change.     

Preparation and cupric ion release behavior of Cu/LDPE porous composites with tunable pore morphology for intrauterine devices

Copper/low-density polyethylene (Cu/LDPE) porous composites are novel materials for copper-containing intrauterine devices (Cu-IUDs). Here we report a method, i.e., by changing the mass ratio of two kinds of porogens that have different melting points through the combined techniques of injection molding and particulate leaching, to prepare the Cu/LDPE porous composites with tunable pore morphology. After these Cu/LDPE porous composites with different pore morphologies were obtained, the influences of pore morphologies on their cupric ion release behaviors were studied. The results show that the pore morphology has great influence on the cupric ion release behavior of Cu/LDPE porous composites. This phenomenon is caused by the different influences of different pore morphologies on the effective porosity and the surface hydrophilicity. And those results can be applied to guide the fabrication of Cu/LDPE porous composite Cu-IUDs with minimal weight at an appropriate cupric ion release rate.     

电极阻抗控制器对电弧炉冶炼电耗的影响

通过对电极阻抗控制器阻抗参数的研究,结合超高功率电弧炉变压器的特点,摸索出合适的供电级数,降低了冶炼电耗。     

建筑门窗节能工程的施工技术探讨

若要门窗节能工程能够顺利地进行，并达到良好的节能效果，就需要专业工程方案的支持。本文主要介绍门窗节能工程中的门窗节能材料选用，产品加工、运输及其施工要求。     

Study on air flow dynamic characteristic of mechanical ventilation of a lung simulator

As an important life support treatment, mechanical ventilation is usually adopted in clinics. With the development of the res-piratory diagnostic and treatment technologies, air flow dynamics of mechanical ventilation is usually referenced in the evaluation of pulmonary status and assessment of respiratory therapy. In order to improve the ventilation efficiency and provide a reference for pulmonary diagnostics, in this paper, a new mathematical model of mechanical ventilation system was set up. Furthermore, a prototype mechanical ventilation system for an artificial simulating lung was designed and experimentally studied. Lastly, in order to improve the ventilation efficiency and provide a reference for pulmonary diagnostics, the air flow dynamics of the mechanical ventilation system was illustrated through simulation and experimental studies. The study can be helpful to the optimization of the mechanical ventilation system.     

一起透平膨胀机管路断裂的分析

天科气体6500 m3/h空分设备配套的一台增压透平膨胀机,在正常运行时管道突然发生断裂。分析了故障原因,并阐述了处理措施。