On‐line ultrasonic measurements of methyl methacrylate polymerization for application to reactive extrusion

An ultrasonic measurement system was developed for monitoring the polymerization of methyl methacrylate (MMA) in a model batch reactor and a model twin screw extruder. Conversion of MMA polymerized in a home‐made reaction chamber was compared with results obtained from a differential scanning calorimeter (DSC). The objective is to correlate ultrasonic velocity to extent of reaction based on the model experiments of poly(methyl methacrylate) in solution with MMA. This primary ultrasonic measurement system was applied to the on‐line measurement of the extent of MMA polymerization in a model twin‐screw extruder.     

Tunable Moiré Superlattice of Artificially Twisted Monolayers

Twisting between two stacked monolayers modulates periodic potentials and forms the Moiré electronic superlattices, which offers an additional degree of freedom to alter material property. Considerable unique observations, including unconventional superconductivity, coupled spin‐valley states, and quantized interlayer excitons are correlated to the electronic superlattices but further study requires reliable routes to study the Moiré in real space. Scanning tunneling microscopy (STM) is ideal to precisely probe the Moiré superlattice and correlate coupled parameters among local electronic structures, strains, defects, and band alignment at atomic scale. Here, a clean route is developed to construct twisted lattices using synthesized monolayers for fundamental studies. Diverse Moiré superlattices are predicted and successfully observed with STM at room temperature. Electrical tuning of the Moiré superlattice is achieved with stacked TMD on graphite.     

Synthesis and characterization of nano-sized calcium zincate powder and its application to Ni–Zn batteries

Nano-sized calcium zincate powders used as active materials for a secondary Zn electrode were prepared by a chemical co-precipitation method. The properties were studied by thermal gravimetric analysis (TGA), micro-Raman spectroscopy and nitrogen adsorption–desorption experiments. The secondary Zn electrodes using chemical co-precipitation calcium zincate powders (CP-ZnCa) and ball-milled calcium zincate powders (BM-ZnCa), were examined and compared. The electrochemical performance of the secondary Zn electrodes was systematically investigated by cyclic voltammetry and galvanostatic charge/discharge measurements. It was demonstrated that the electrochemical properties of the secondary Zn-pasted electrode using CP-ZnCa powders were greatly improved, as compared with conventional secondary ZnO electrodes. The results indicated that secondary Ni-Zn batteries using CP-ZnCa powders exhibited a better charge/discharge property and a longer life-cycle performance, compared with those based on ball-milled ZnO + Ca(OH)₂ (BM-ZnCa) powders.     

Stable fuzzy control with adaptive rotor imbalance compensation for nonlinear magnetic bearing systems

Abstract

The six‐DOF nonlinear dynamics and rotor mass‐imbalance induced vibration of a high‐speed magnetic bearing are rather complex. In this paper, an analytical T‐S (Takagi‐Sugeno) fuzzy model with simplified linearly‐parameterized mass‐imbalance model for magnetic bearings is first constructed. Based on the T‐S fuzzy model, a stable fuzzy control including adaptive imbalance compensation is then proposed through robust performance analysis. Simulation validations show that the proposed control law can suppress the rotor imbalance‐induced vibration and has excellent capability for high‐speed tracking and levitation control.     

Plastic Deformation of a Nano‐Precipitate Strengthened Ni‐Base Alloy Investigated by Complementary In Situ Neutron Diffraction Measurements and Molecular‐Dynamics Simulations

In situ neutron‐diffraction experiments at the spallation neutron source, simultaneously illuminating the diffraction of the matrix and the strengthening nano precipitates, allow the determination of their plastic deformation. An irreversible neutron‐diffraction‐profile evolution of the nano precipitates is observed. However, there is no conclusive trend of the nano‐precipitate peak‐width evolution subjected to the greater stress levels. Hence, in the present work, molecular‐dynamics simulations are applied to reveal the deformation mechanisms of the nano precipitate and its interaction with the surrounding matrix. The microstructure size, dislocation content, and structural parameters of the nano precipitates, quantified by X‐ray, transmission electron microscopy, and small‐angle neutron scattering, are used as the simulation input and reference. The simulation results show that there are two competing deformation mechanisms, which lead to the fluctuation of the nano‐precipitate‐diffraction widths, occurring during the higher plastic deformation stages.     

Direct methanol fuel cell based on poly(vinyl alcohol)/titanium oxide nanotubes/poly(styrene sulfonic acid) (PVA/nt-TiO2/PSSA) composite polymer membrane

The high performance poly(vinyl alcohol)/titanium oxide nanotubes/poly(styrene sulfonic acid) (PVA/nt-TiO₂/PSSA) proton-conducting composite membrane is prepared by a solution casting method. The characteristic properties of these blend composite membranes are investigated by thermal gravimetric analysis (TGA), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), micro-Raman spectroscopy, dynamic mechanical analysis (DMA), methanol permeability measurement and AC impedance method. It is found that the peak power densities of the DMFC with 1, 2, and 4 M CH₃OH fuels are 12.85, 23.72, and 10.99 mW cm⁻², respectively, at room temperature and ambient air. Especially, among three methanol concentrations, the 2 M methanol shows the highest peak power density among three methanol concentrations. The results indicate that the air-breathing direct methanol fuel cell comprised of a novel PVA/nt-TiO₂/PSSA composite polymer membrane has excellent electrochemical performance and stands out as a viable candidate for applications in DMFC.     

Quaternized poly(vinyl alcohol)/alumina composite polymer membranes for alkaline direct methanol fuel cells

The quaternized poly(vinyl alcohol)/alumina (designated as QPVA/Al₂O₃) nanocomposite polymer membrane was prepared by a solution casting method. The characteristic properties of the QPVA/Al₂O₃ nanocomposite polymer membranes were investigated using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), micro-Raman spectroscopy, and AC impedance method. Alkaline direct methanol fuel cell (ADMFC) comprised of the QPVA/Al₂O₃ nanocomposite polymer membrane were assembled and examined. Experimental results indicate that the DMFC employing a cheap non-perfluorinated (QPVA/Al₂O₃) nanocomposite polymer membrane shows excellent electrochemical performances. The peak power densities of the DMFC with 4 M KOH + 1 M CH₃OH, 2 M CH₃OH, and 4 M CH₃OH solutions are 28.33, 32.40, and 36.15 mW cm⁻², respectively, at room temperature and in ambient air. The QPVA/Al₂O₃ nanocomposite polymer membranes constitute a viable candidate for applications on alkaline DMFC.