Effect of Solute Ta on Grain Refinement of Al-7Si-0.3Mg Based Alloys

Different Ta concentrations together with stochiometric grain refiner (Al-2.2Ti-1B) in Al-Si-Mg based alloys were investigated with the aim to elucidate grain refinement mechanisms. Post-solidification microstructure was characterised using optical microscopy and scanning electron microscopy (SEM), with a special focus on the Ta-rich layer (more likely to be Al3Ta) on the basal planes (0001) of TiB2. A significant grain refinement was observed by using the solute Ta together with stochiometric grain refiner (Al-2.2Ti-1B). In order to further elucidate the formation of Ta-rich layer on the basal planes (0001) of TiB2, the Density Functional Theory (DFT) calculation were also performed to determine the interface energies of different interfaces and sandwich configurations, including Al (111), Al3Ti (112) and Al3Ta (112) at the interface of TiB2 basal plane (0001). It was found that the interface energy for Ti-terminated TiB2 at the interface throughout all configurations involved in this paper is lower than that for B-terminated TiB2, indicating that Ti-terminated TiB2 is more favourable. It was also found that the Al3Ta configuration yields the same interface energies as the Al3Ti configuration. Furthermore, the interface energy of the sandwich configuration also shows nearly identical values along the TiB2 // Al3Ti and TiB2 // Al3Ta interface energy, strongly indicating that the solute Ti can be fully replaced by the solute Ta.

Gold Nanoparticles for Surface-Enhanced Raman Spectroscopy

This work shows comparative analysis of surface-enhanced Raman scattering (SERS) activity of gold nanoparticles fabricated by chemical synthesis and laser ablation methods. The gold nanoparticles prepared by laser ablation (Au-LA) are more effective for SERS than those prepared chemically (Au-citr). The “analyte on Au film” configuration allows obtaining enhancement of Raman scattering up to 104 in case of Au-LA nanoparticles and up to 102 in case of Au-citr. Also the “sandwich” configuration for Au-LA gives additional enhancement of SERS up to two times, and for Au-citr up to one order, that is consistent with theoretical calculations.

Upside-Down Robots: Modeling and Experimental Validation of Magnetic-Adhesion Mobile Systems

In this paper, we present the modeling and validation of a new family of climbing robots that are capable of adhering to vertical surfaces through permanent magnetic elements. The robotic system is composed of two modules, the master and the follower carts, which are arranged in a sandwich configuration, with the surface to climb interposed between them. Thanks to this configuration, the mobile robot can climb even nonferromagnetic and curved surfaces; moreover, the master cart is capable of freely moving on the floor by detaching from the follower. In this paper, we propose the mathematical modeling, simulation, and experimental validation of this kind of robots, with particular focus on the transitions between floor and climbing motion.