Sulfonated polyimide (SPI) and ZrO 2 are blended to prepare a series of novel SPI/ZrO 2 composite membranes for vanadium redox flow battery (VRFB) application. Results of atomic force microscopy and X-ray diffraction reveal that ZrO 2 is successfully composited with SPI. All SPI/ZrO 2 membranes possess high proton conductivity (2. ). SPI/ZrO 2 -15% membrane is determined as the optimum one on account of its higher proton selectivity and improved chemical stability. The VRFB with SPI/ZrO 2 -15% membrane presents higher coulombic efficiency and energy efficiency than that with Nafion 117 membrane at the current density, which ranged from 20 to 80 mA cm À2. Cycling tests indicate that the SPI/ZrO 2 -15% membrane has good operation stability in the VRFB system.

No abstract

No abstract

No abstract

A series of fluorine‐containing branched sulfonated polyimide (Fb‐SPI) membranes with different degrees of branching (0–12 %) were synthesized through polycondensation. The chemical structure of Fb‐SPI‐10 membrane was confirmed using ATR‐FTIR and 1H NMR spectroscopy. The physico‐chemical properties of Fb‐SPI membranes were systematically investigated and compared to linear SPI (l‐SPI) and Nafion 117 membranes. The vanadium‐ion permeabilities of Fb‐SPI membranes (2.45–0.99×10−7 cm2 min−1) are much lower than that of Nafion 117 (17.1×10−7 cm2 min−1) membranes. Besides, the chemical stability of Fb‐SPI membranes is superior to that of l‐SPI membranes. During 500‐time continuous cyclic charge‐discharge measurements, the VRFB assembled with a Fb‐SPI‐10 membrane shows higher coulombic efficiency (98.4–99.7 %), higher or close energy efficiency (69.0–79.7 %) from 40 to 80 mA cm−2, and higher or close capacity retention (52.8–100 %) from 40 to 70 mA cm−2 compared with a device using a Nafion 117 membrane. All of these results demonstrate that the as‐selected Fb‐SPI‐10 membrane has promising potential for VRFB applications.

The initial reaction mechanism of energetic materials under impact loading and the role of crystal properties in impact initiation and sensitivity are still unclear. In this paper, we report reactive molecular dynamics simulations of shock initiation of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) crystals containing a cube void. Shock-induced void collapse, hot spots formation and growth, as well as spalling are revealed to be dependent on the shock velocity. The void collapse times are 1.5 and 0.7 ps, for the shock velocity of 2 and 4 km·s –1 , respectively. Results indicate that the initial hot spot formation consists of two steps: one is the temperature rise caused by local plastic deformation and the other is the temperature increase resulting from the collision of upstream and downstream particles during the void collapse. Whether hot spots will continue to grow or quench depends on sensitive balance between energy release caused by local physical and chemical reactions and various heat dissipation mechanisms. In our simulations, hot spot would grow for U p = 4 km·s –1 ; hot spot is weak to some extent for U p = 2 km·s –1 . The tensile wave reflected by the shock wave after reaching the free surface causes the spalling, which depends on the initial shock velocity. Typical spalling occurs for the shock velocity 2 km·s –1 , while the tensile wave induces the microsplit region in RDX crystals in the case of U p = 4 km·s –1 . Chemical reactions are studied for Rankine–Hugoniot shock pressures P s = 14.4, 57.8 GPa. For the weak shock, there is almost no decomposition reaction of the RDX molecules near the spalling region. On the contrary, there are large number of small molecule products, such as H 2 O, CO 2 , NO 2 , and so forth, around the microsplit regions for the strong shock. The ruptures of N–NO 2 bond are the main initial reaction mechanisms for the shocked RDX crystal and are not affected by shock strength, while the microsplit slows down the decomposition rate of RDX. The work in this paper can shed light on a thorough understanding of thermal ignition, hot spot growth, and other physical and chemical phenomena of energetic materials containing voids under impact loading.

Accurate and efficient monitoring of electrical machine (EM) operating parameters, including temperature, mechanical vibration, torque and rotating speed and others that can indicate the EM health conditions is becoming ever more important in the world of electrical drives. The traditional methodology of one sensor per parameter can be theoretically replaced by a "one sensor measures all" technology, which can be achieved through the use of fibre-optic sensors (FOS). In this paper, several FOSs, which use different optical sensing principles for multiple physical parameter measurements of EMs, are reviewed. This paper also provides an insight into the major developments, and discusses the engineering challenges of FOS used for EM monitoring over the last few decades, and compares the advanced features of FOS with those of conventional sensors in use. Finally, a novel FOS-EM observer system scheme employing the Fibre Bragg Grating technique for multiparameter monitoring of EM health is proposed, after discussion of the preceding industrial and academic FOS cases for EM applications.

No abstract