Microstructural evolutions of the Ag nano-particle reinforced SnBiCu-xAg/Cu solder joints during liquid aging

Ag nano-particle reinforced Sn30Bi0.5Cu-xAg (x = 1 wt%, 2 wt% and 5 wt%) solder pastes were prepared and reflowed on Cu substrates at 523 K. Then, the solder joints were liquid aged at 473 K for 6 and 12 h. Microstructural evolutions of these solder joints were observed by scanning electron microscopy (SEM). The results show that Bi-rich phase was refined in the as-reflowed Sn30Bi0.5Cu-xAg composite solder matrices. With the increase of the liquid aging time, Bi-rich phase was refined both in the Sn30Bi0.5Cu solder and in the Sn30Bi0.5Cu-xAg composite solders. The addition of Ag nano-particles changed the growth rate of the IMC layers during liquid aging due to the absorption effect of the Ag₃Sn micro-particles.     

Effect of Suspension Plasma-Sprayed YSZ Columnar Microstructure and Bond Coat Surface Preparation on Thermal Barrier Coating Properties

Suspension plasma spraying (SPS) is identified as promising for the enhancement of thermal barrier coating (TBC) systems used in gas turbines. Particularly, the emerging columnar microstructure enabled by the SPS process is likely to bring about an interesting TBC lifetime. At the same time, the SPS process opens the way to a decrease in thermal conductivity, one of the main issues for the next generation of gas turbines, compared to the state-of-the-art deposition technique, so-called electron beam physical vapor deposition (EB-PVD). In this paper, yttria-stabilized zirconia (YSZ) coatings presenting columnar structures, performed using both SPS and EB-PVD processes, were studied. Depending on the columnar microstructure readily adaptable in the SPS process, low thermal conductivities can be obtained. At 1100 °C, a decrease from 1.3 W m^?1 K^?1 for EB-PVD YSZ coatings to about 0.7 W m^?1 K^?1 for SPS coatings was shown. The higher content of porosity in the case of SPS coatings increases the thermal resistance through the thickness and decreases thermal conductivity. The lifetime of SPS YSZ coatings was studied by isothermal cyclic tests, showing equivalent or even higher performances compared to EB-PVD ones. Tests were performed using classical bond coats used for EB-PVD TBC coatings. Thermal cyclic fatigue performance of the best SPS coating reached 1000 cycles to failure on AM1 substrates with a β-(Ni,Pt)Al bond coat. Tests were also performed on AM1 substrates with a Pt-diffused γ-Ni/γ′-Ni₃Al bond coat for which more than 2000 cycles to failure were observed for columnar SPS YSZ coatings. The high thermal compliance offered by both the columnar structure and the porosity allowed the reaching of a high lifetime, promising for a TBC application.     

Six sigma-based approach to optimize deep drawing operation variables

The six sigma approach has been increasingly adopted worldwide in the manufacturing sector in order to enhance the productivity and quality performance and to make the process robust to quality variations. This paper deals with one such application of six sigma methodology to improve the yield of deep drawing operations. The deep drawing operation has found extensive application in producing automotive components and many household items. The main issue of concern of the deep drawn products involves different critical process parameters and governing responses, which influences the yield of the operation. The effects of these parameters are analysed by the DMAIC (Define, Measurement, Analyse, Improve, Control)-based six sigma approach. A multiple response optimization model is formulated using the fuzzy-rule-based system. The functional relationship between the process variables and the responses is established, and thereafter their optimum setting is explored with the aid of response surface methodology (RSM). Rigorous experimentations have been carried out, and it is observed that the process capability of processes is enhanced significantly, after the successful deployment of the six sigma methodology.     

Simultaneous removal of organic and inorganic pollutants in tannery wastewater using electrocoagulation technique

Tannery wastewater can cause severe environmental problems related to its high chemical oxygen demand, high biochemical oxygen demand, high total suspended solids, high oil and grease contents together with the elevated chromium concentration and objectionable color. The one-step electrocoagulation process was carried out to simultaneously remove chromium and various pollutants from tannery wastewater at ambient temperature in the laboratory scale. Low-cost commercial iron plates were employed in this study as anodes and cathode materials. Effects of various parameters were investigated including types of electrode configuration, initial pH of wastewater (7–9), current density (15.7–24.6 Am⁻²) and circulating flow rate of wastewater (0–3.67 lmin⁻¹). The optimum condition was found by applying the mono-polar electrode in a parallel connection at the current density of 22.4 Am⁻², flow rate of wastewater of 3.67 lmin⁻¹ and 20 min electrolysis time. The initial pH of wastewater ranging from 7–9 provided the similar removal efficiency. At optimum condition, more than 95% of chromium and pollutants except TKN and TDS were eliminated from the wastewater and the properties of the treated wastewater met the standard and permitted to discharge into the environment. The required energy consumption at optimum condition was less than 0.13 kWhm⁻³ wastewater. In addition, the COD reduction was fit very well with the first-order kinetics model.     

Lift force on bubbles in a bubble column reactor: Experimental analysis

The lift force acting on bubbles in a swarm has been estimated by analyzing the instantaneous velocity-time data obtained using LDA in a cylindrical bubble column. Phase distinction was achieved through the multiresolution analysis of the velocity-time data. Several important issues related to the transverse motion of bubbles subjected to a shear field have been discussed quantitatively. The actually measured bubble sizes, the respective slip velocity values in transverse and axial directions and the local shear rates (γ) enabled the verification of known formulations for the lift coefficient (C_L) for bubbles. At many locations in the column the radial flux of the gas phase by turbulent dispersion and the radial slip were estimated. The radially inward movement of bubbles from low to high axial velocity (from column wall to center, i.e., C_L<0) was observed at most of the measurement locations. The local lift coefficient was estimated using the transverse drag force and the values support the results from the material balance approach. The estimated C_L values showed a wide variation over the column cross-section.     

燃烧室形状对柴油机缸内气流运动影响的数值模拟研究

为了研究燃烧室形状对柴油机缸内气流运动的影响,利用AVLFire软件对三种不同凸台形状的缩口型燃烧室内的气流运动进行数值模拟。研究表明,凸台形状对缸内气流运动有较大的影响。锥形凸台和球形凸台比平底凸台更有利于挤气涡流的形成和发展,平底凸台燃烧室具有更好的涡流强度保持性和更合理的湍动能分布。     

用椰壳制活性炭吸附去除三价铋离子(英文)

In present study,we report the preparation of coconut shell activated carbon as adsorbent and its appli-cation for Bi(Ⅲ) removal from aqueous solutions.The developed adsorbent was characterized with scanning elec-tron microscope(SEM),Fourier Transform Infrared(FTIR),C,H,N,S analyzer,and BET surface area analyzer.The parameters examined include agitation time,initial concentration of Bi(Ⅲ),adsorbent dose and temperature.The maximum adsorption of Bi(Ⅲ)(98.72%) was observed at 250 mg·L-1 of Bi(Ⅲ) and adsorbent dose of 0.7 g when agitation was at 160 r·min-1 for 240 min at(299±2) K.The thermodynamic parameters such as Gibb’s free energy(△Gθ),enthalpy(△Hθ) and entropy(△Sθ) were evaluated.For the isotherm models applied to adsorption study,the Langmuir isotherm model fits better than the Freundlich isotherm.The maximum adsorption capacity from the Langmuir isotherm was 54.35 mg?g?1 of Bi(Ⅲ).The kinetic study of the adsorption shows that the pseudo second order model is more appropriate than the pseudo first order model.The result shows that,coconut shell ac-tivated carbon is an effective adsorbent to remove Bi(Ⅲ) from aqueous solutions with good adsorption capacity.     

Dynamics in self-assembled organic monolayers at the liquid/solid interface revealed by scanning tunneling microscopy

The liquid/solid interface provides an interesting medium for molecular self-assembly and scanning tunneling microscopy is the preferred technique to analyse the structural features of the surface-supported self-assembled monolayers in this medium. An interesting aspect is the phenomenon of molecular dynamics at the liquid/solid interface. In this mini-review, we report on our efforts and strategies to investigate and even induce molecular dynamics at the liquid/solid interface, bringing insight to various kinds of processes such as conformational, translational and adsorption/desorption dynamics.     

Stability of Pt–Co/C and Pt–Pd/C based oxygen reduction reaction electrocatalysts prepared at a low temperature by a combined impregnation and seeding process in PEM fuel cells

The stability of Pt–Co/C and Pt–Pd/C electrocatalysts relative to that of a commercial Pt/C catalyst was measured in terms of the loss of the electrochemical surface area (ESA). The electrocatalytic activity was investigated in an acidic solution (0.3 M H₂SO₄) and in a single PEM fuel cell under H₂/O₂ conditions. In the acidic solution, the ESA of the catalyst decreased as the number of repeated potential cycles increased, which is likely to be due to dissolution of the different metals contained within the catalyst structure. In the fuel cell environment, the deterioration of the cell performance increased as the number of repeated potential cycles increased. Thus, the loss of cell performance may be related to the loss of the ESA. In addition, the loss of the catalyst’s ESA affected the cell performance at low-, medium-, and high- current densities, indicating a loss of either the activation potential or an ohmic loss. Among the three electrocatalysts evaluated, the Pt–Co/C based one exhibited the highest electrocatalytic activity in both the acidic solution and in the fuel cell environment.     

LED照明产品寿命测试评价方法研究进展

本文在调研LED照明产品国际和国家标准有关寿命评价考虑的基础上,介绍了目前针对LED寿命测试的相关研究工作,对LED照明产品的寿命评估方法做了探索性研究。经分析可知,采用寿命测试推算方法,IESTM21和边界函数法均存在一定的问题。研究表明,采用试验条件加速的方法来测试推算LED照明产品的寿命存在较高的可行性,且此评价方法可显著缩短产品的寿命评价周期。