Aplication of Corncob-Based Activated Carbon as Electrode Material for Electric Double-Layer Capacitors

To investigate the influence of expansion pretreatment for materials on carbon structure, activated carbons （ACs） were prepared from corncob with/without expansion pretreatment by KOH activation, the structure properties of which were determined based on N2 adsorption isotherm at 77 K. The results show that the expansion pretreatment for corncobs is beneficial to the preparation of ACs with high surface area. The specific surface area of the AC derived from corncob with expansion pretreatment （AC-1） is 32.5% larger than that without expansion pretreatment （AC-2）. Furthermore, to probe the potential application of corncob-based ACs in electric double-layer capacitor （EDLC）, the prepared ACs were used as electrode materials to assemble EDLC, and its electrochemical performance was investi- gated. The results indicate that the specific capacitance of AC-I is 276 F/g at 50 mA/g, which increases by 27% com- pared with that of AC-2 （217 F/g）. As electrode materials, AC-1 presents a better electrochemical performance than AC-2, including a higher voltage maintenance ratio and a lower leakage current.

Microstructural characteristics of cold-rolled Zr-2.5Nb alloy annealed near the monotectoid temperature

A dual-phase Zr-2.5 Nb alloy was rolled at room temperature to 50% reduction and then annealed at two temperatures(560 and580°C) near the monotectoid temperature. X-ray diffraction, electron channeling contrast imaging and electron backscatter diffraction techniques were jointly used to characterize microstructural characteristics developed in the as-rolled and annealed specimens. Results show that plastic deformation occurs in both bulk α-Zr grains and thin β-Zr films during rolling, allowing large lattice strains to be accumulated in β-Zr and active dislocation slip(especially the prismatic áa?slip) to be initiated in α-Zr. During subsequent annealing at 580°C, the prior β-Zr films are transformed into submicron β-Zr particles, which lose coherency(the Burgers orientation relationship) with surrounding α grains. In the specimen annealed at 560°C, however, the prior β-Zr films are found to be decomposed into nanoscale β-Nb particles. In both the annealed specimens, the β-Zr and the β-Nb particles appeared to be linearly distributed along the rolling direction. Two types of α structures, i.e., small equiaxed crystallites formed by recovery of dislocation structures and coarse bamboo-like recrystallized grains, are revealed in the annealed specimens. Effective boundary pinning due to the dense β-phase particles is demonstrated to play a key role in forming such unusual bamboo-like grains.

Incrusting structure of nanosized Fe_(3)O_(4) particles in magnetic fluids

High-performance nanosized Fe3O4 magnetic fluids are prepared by chemical co-pre- cipitate method. The microstructure of magnetic fluids is characterized using a transmission electron microscope (TEM) and high-resolution electron microscope (HREM). The results are satisfactory. The nanosized magnetic particles have diameter of 8—10 nm and the minimum diameter is 4 nm, belonging to super-paramagnetic material. The nanosized magnetic particles crystallized completely and have clear crystal boundary. The surfactant used in the test coats the magnetic particles homogeneously and forms a uniform and complete elastic spherical shell of amorphous phase around the magnetic particles. The study proves that the incrusting layer of surfactant has the protective effect and stable effect on the magnetic particles. These effects can enhance and maintain the magnetic properties of the magnetic fluids effectively.