RESUMEN
Electric field enhanced ultraviolet (UV)-induced nanoparticle colloid jet machining is proposed to improve the material removal efficiency of UV-induced nanoparticle colloid jet machining by applying an external electric field. The influences of TiO2nanoparticle concentration, applied electric field voltage and pH value for the photocatalytic activity of the polishing slurry was investigated by orthogonal experiments. Terephthalic acid (TPA) was used as a fluorescent molecular probe to reflect the relative concentration of hydroxyl radical groups (·OH) in polishing slurry, which directly affects the material removal rate in the UV-induced nanoparticle colloid jet machining process. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and x-ray photoelectron spectroscopy (XPS) were employed to inspect the interaction variations between the TiO2nanoparticles and the SiC workpiece surface. The SEM and XPS results exhibit that the external electric field can enhance the adsorption of TiO2nanoparticles on the SiC workpiece surface, which can create more interfacial reaction active centers in the polishing process. The FT-IR spectra results indicate that TiO2nanoparticles were chemically bonded to the SiC surface by oxygen-bridging atoms in Ti-O-Si bonds. The results of fixed-point polishing experiment show that due to the enhancement effect of external electric field on the photocatalytic activity of the polishing slurry, the material removal efficiency of electric field enhanced UV-induced nanoparticle colloid jet machining is 15% higher than that of UV-induced nanoparticle colloid jet machining, and is 28% higher than that of pure nanoparticle colloid jet machining. Atomic force microscope micromorphology show that an ultra-smooth SiC workpieces with surface roughness of Rms 0.84 nm (Ra 0.474 nm) has been obtained by electric field enhanced UV-induced nanoparticle colloid jet machining.
RESUMEN
Over the past few decades, the research of dissipative chaotic systems has yielded many achievements in both theory and application. However, attractors in dissipative systems are easily reconstructed by the attacker, which leads to information security problems. Compared with dissipative systems, conservative ones can effectively avoid these reconstructing attacks due to the absence of attractors. Therefore, conservative systems have advantages in chaos-based applications. Currently, there are still relatively few studies on conservative systems. For this purpose, based on the simplest memristor circuit in this paper, a non-Hamiltonian 3D conservative system without equilibria is proposed. The phase volume conservatism is analyzed by calculating the divergence of the system. Furthermore, a Kolmogorov-type transformation suggests that the Hamiltonian energy is not conservative. The most prominent property in the conservative system is that it exhibits quasi-periodic 3D tori with heterogeneous coexisting and different amplitude rescaling trajectories triggered by initial values. In addition, the results of Spectral Entropy analysis and NIST test show that the system can produce pseudo-random numbers with high randomness. To the best of our knowledge, there is no 3D conservative system with such complex dynamics, especially in a memristive conservative system. Finally, the analog circuit of the system is designed and implemented to test its feasibility as well.
RESUMEN
Developing novelplatinum (Pt)-based hydrogen evolution reaction (HER) catalysts with high activity and stability is significant for the ever-broader applications of hydrogen energy. However, achieving precise modulation of the ultrafine Pt nanoparticles coordination environment in conventional catalysts is challenging. In this work, we developed a unique "ring-shaped cavity induced" strategy to anchor the Ptx through the ring-shaped cavity of polyoxometalates (POMs) Na33H7P8W48O184 (denoted as P8W48). The NayPtx[P8W48O184] (PtxP8W48) was in-situ converted into abundant Pt/WO3-x heterostructure with Pt (â¼2 nm) and highly depressed Pt-O-W heterointerfaces. Pt/WO3-x nanoparticles supported on highly conductive rGO exhibit superior HER activity. The overpotentials of the catalyst are only 2.8 mV and 4.7 mV at 10 mA·cm-2 in acidic water and seawater, far superior to commercial 20 % Pt/C catalyst. Additionally, the catalyst can be stabilized at a current density of 30 mA·cm-2 for 180 h. This study provides a feasible strategy for rational design of Pt-based catalysts for renewable energy applications.
RESUMEN
Accurately regulating ultrafine molybdenum carbide (MoC)-based catalysts is a significant challenge in the rational design of hydrogen evolution reaction (HER) electrocatalysts. Herein, under the guidance of the first principle calculations, we proposed an in-situ polyoxometalate-confined strategy for creating uniformly distributed ultrafine Co-MoC bimetallic nanoparticles in porous carbon nanostars, with the assistance of precisely designed metal-organic framework (MOF). The Co-MoC@C electrocatalyst has a high specific surface area of 969 m2·g-1 because of the conductive carbon substrate with abundant mesopores, which makes for exposing more active sites of Co-MoC nanocrystals (â¼1.5 nm) and facilitating electron/ion transport. Thus, Co-MoC@C electrocatalyst shows the excellent electrochemical activity with overpotentials of 88.4 mV and 66.6 mV at a current density of 10 mA·cm-2 under acidic and alkaline conditions, respectively. The in-situ polyoxometalate-confined strategy will provide a new guideline for the design and preparation of efficient HER electrocatalysts.