Soldering of Mg Joints Using Zn-Al Solders

Magnesium has applications in the automotive and aerospace industries that can significantly contribute to greater fuel economy and environmental conservation. The Mg alloys used in the automotive industry could reduce mass by up to 70 pct, providing energy savings. However, alongside the advantages there are limitations and technological barriers to use Mg alloys. One of the advantages concerns phenomena occurring at the interface when joining materials investigated in this study, in regard to the effect of temperature and soldering time for pure Mg joints. Eutectic Zn-Al and Zn-Al alloys with 0.05 (wt pct) Li and 0.2 (wt pct) Na were used in the soldering process. The process was performed for 3, 5, and 8 minutes of contact, at temperatures of 425 °C, 450 °C, 475 °C, and 500 °C. Selected, solidified solder-substrate couples were cross-sectioned, and their interfacial microstructures were investigated by scanning electron microscopy. The experiment was designed to demonstrate the effect of time, temperature, and the addition of Li and Na on the kinetics of the dissolving Mg substrate. The addition of Li and Na to eutectic Zn-Al caused to improve mechanical properties. Higher temperatures led to reduced joint strength, which is caused by increased interfacial reaction.     

Innovation and the growth of service companies: the variety of firm activities and industry effects

This paper examines the relationship between innovation performance and employment growth in firms by taking a closer look at specific innovation activities and industry effects in the context of the services sector. Firm-level CIS data on Polish services firms in 2004–2009 are analysed using robust M-estimation. The results indicate that the effects of product, process and organisational innovations depend strongly on the level of technological opportunities in the industry in question. Given the widely acknowledged role of marketing innovations in services, possible synergies between innovations in the form of new products and new marketing techniques are also analysed. We demonstrate that marketing innovations are conducive to firm growth if they complement product innovations, but they are less likely to foster growth when applied in isolation.     

Design and fabrication of miniature compliant hinges for multi-material compliant mechanisms

Multi-material molding (MMM) enables the creation of multi-material mechanisms that combine compliant hinges, serving as revolute joints, and rigid links in a single part. There are three important challenges in creating these structures: (1) bonding between the materials used, (2) the ability of the hinge to transfer the required loads in the mechanism while allowing for the prescribed degree(s) of freedom, and (3) incorporating the process-specific requirements in the design stage. This paper presents the approach for design and fabrication of miniature compliant hinges in multi-material compliant mechanisms. The methodology described in this paper allows for the concurrent design of the part and the manufacturing process. For the first challenge, mechanical interlocking strategies are presented. For the second challenge, the development of a simulation-based optimization model of the hinge is presented, involving functional and manufacturing constrains. For the third challenge, the development of hinge positioning features and gate positioning constraints is presented. The developed MMM process is described, along with the main constraints and performance measures. This includes the process sequence, the mold cavity design, gate selection, and runner system development. A case study is presented to demonstrate the feasibility of creating multi-material mechanisms with miniature hinges serving as joints through MMM process. The approach described in this paper was utilized to design a drive mechanism for a flapping wing micro air vehicle. The methods described in this paper are applicable to any lightweight, load-bearing compliant mechanism manufactured using multi-material injection molding.     

Effect of the design parameters on the in vitro wear performance of total shoulder arthroplasties

The loosening of the glenoid component is the main reason for the failure of a total shoulder arthoplasty. It may be caused either by high tensile stresses or by osteolysis of the surrounding bone in response to the presence of particle debris. This failure might be associated with the wear of the implant as occurs with replacement hip and knee joints.The paper reports the findings of a study of the in vitro performance of the currently used total shoulder prostheses to determine the effects of implant geometry on the wear of the polyethylene components and the friction conditions operating within the shoulder prosthesis.The wear performance of the implants was evaluated using a self-developed tribotester, simulating the physiological conditions of a shoulder joint. This study revealed that significantly different wear occurred with conforming and non-conforming articulation and revealed the influence of the thickness of the polyethylene glenoid on the wear and friction occurring in the joint. In this preliminary study significant wear of the polyethylene glenoid component occurred, estimated to be up to 19 mm³/year, which is similar to that found in retrieved implants. The conforming implants demonstrated significantly greater wear than the non-conforming implants (p < 0.05). A significantly lower friction factor, about 0.05 ± 0.01 (p < 0.05), was obtained for the less conforming implants.     

Redox doping behaviour of poly(3,4-ethylenedithiothiophene) - The counterion effect

Poly(3,4-ethylenedithiothiophene) - PEDTT, an alkylene sulphur derivative of PEDOT, presents itself as an interesting polymer with a number of disparate redox and chromic properties compared to its close analogue - PEDOT. In this study we present the results of an investigation into the electrochemical doping process of PEDTT, using four different electrolyte solutions, differing in anion content of the chosen salt. The results show that the anion identity plays a key role in the redox reactions accompanying these processes in what could be interpreted as anion ionochromism. In situ UV-Vis spectroelectrochemical experiments reveal an intriguing double electrochromic transition of PEDTT films during their oxidative doping, going from golden-yellow through green to pomegranate - a quality not so common within the family of electroactive conjugated polymers. The evolution of each UV-Vis spectrum over a potential range indicates that different redox states of the polymer are responsible for the chromatic changes. In the reduction half-cycle, the dedoping process of PEDTT appears to follow a path dissimilar to the p-doping one, featuring only one, direct electrochromic transition of the film’s colour, bypassing the green state, and a distinct two-step bleaching process of doping-induced charge carrier bands. The observed electrochemical and spectral phenomena have been accredited to the specific redox behaviour of doping-induced radical cation and cationic defect states interacting with the dithioalkylene sulphur atom.     

Wetting Behavior and Reactivity of Molten Silicon with h-BN Substrate at Ultrahigh Temperatures up to 1750 °C

For a successful implementation of newly proposed silicon-based latent heat thermal energy storage systems, proper ceramic materials that could withstand a contact heating with molten silicon at temperatures much higher than its melting point need to be developed. In this regard, a non-wetting behavior and low reactivity are the main criteria determining the applicability of ceramic as a potential crucible material for long-term ultrahigh temperature contact with molten silicon. In this work, the wetting of hexagonal boron nitride (h-BN) by molten silicon was examined for the first time at temperatures up to 1750 °C. For this purpose, the sessile drop technique combined with contact heating procedure under static argon was used. The reactivity in Si/h-BN system under proposed conditions was evaluated by SEM/EDS examinations of the solidified couple. It was demonstrated that increase in temperature improves wetting, and consequently, non-wetting-to-wetting transition takes place at around 1650 °C. The contact angle of 90° ± 5° is maintained at temperatures up to 1750 °C. The results of structural characterization supported by a thermodynamic modeling indicate that the wetting behavior of the Si/h-BN couple during heating to and cooling from ultrahigh temperature of 1750 °C is mainly controlled by the substrate dissolution/reprecipitation mechanism.