Electrically conductive aluminosilicate/graphene nanocomposite

Highly electrically conductive ceramic material based on aluminosilicate/graphene nanocomposite has been prepared by high pressure (400 MPa) compaction of montmorillonite intercalated with polyaniline followed with the high temperature (1400 °C) treatment in argon atmosphere. Tablets pressed from polyaniline/montmorillonite intercalate exhibits strong texture due to the disk-shaped montmorillonite particles and, consequently, the high anisotropy in conductivity. The high temperature induced phase transformation of montmorillonite into cristobalite and mullite preserved the aluminosilicate layered structure and created good conditions for formation of graphene sheets from polyaniline layers intercalated in montmorillonite. Therefore, the texture and anisotropy in conductivity remain preserved in resulting aluminosilicate/graphene tablets, while the in-plane conductivity in aluminosilicate/graphene tablets is 23,000× higher than the conductivity of uncalcined polyaniline/montmorillonite tablets. Simple fabrication method of aluminosilicate/graphene tablets is very promising for the manufacturing of the electrically conductive and tough ceramic material, which can be exposed to corrosive environment as well as to high temperatures.     

Conduction mechanism of polyaniline: Effect of moisture

It has recently been shown that the emeraldine base polymer form of polyaniline undergoes a transition from an insulating to a metallic state upon protonation with HCl. The conductivity of the protonated polymer is sensitive to the moisture content of the polymer, varying by as much as a factor of five upon pumping the samples. We report here the temperature-dependent microwave-frequency (10¹⁰ Hz) conductivity and dielectric constant as a function of environmental history. The results are consistent with the effect of moisture on the barriers between small metallic polymer grains. Texture of granular metal particles and localization within metallic islands are decisive in the frequency- and temperature-dependence of the conductivity and dielectric constant.     

Solid state characterization and x-ray crystal structure of a 1:1 complex of tetrathiafulvalene and meta-dinitrobenzene (TTF-mDNB)

A crystalline 1:1 complex of tetrathiafulvalene and meta-dinitrobenzene has been prepared in high yield and characterized by i.r. and u.v. spectroscopies, e.s.r. and bulk magnetic susceptibility data, four-probe d.c. conductivity and single-crystal X-ray analysis. It is a neutral complex with low conductivity, σ_rt = 2.7 × 10⁻⁹ S cm⁻¹, and has a mixed stack structure.     

Open-circuit corrosion as the origin of the electrical instability arising from the dissolved metal content in insulating oils in EHV current transformers

It is proposed that the source of dissolved copper in the oil within a transformer is the open-circuit corrosion of the copper parts in contact with the oil; the magnitude of this corrosion is proportional to the concentration of dissolved oxygen gas in the oil, based on data for six transformer units.     

Point contact abrasive wear behavior of MAX phase materials

The room temperature abrasive wear behavior of three selected MAX phases, Ti₃SiC₂, solution strengthened Ti_2.7Zr_0.3SiC₂ and Cr₂AlC, is investigated by low velocity scratch testing using a diamond conical indentor with a final radius of 100 μm and a cone angle of 120° and applied loads of up to 20 N. All three materials showed a relatively low wear resistance in comparison to most engineering ceramics such as Al₂O_3, Si₃N₄ and SiC. For all three materials, the wear rate scaled more or less linearly with the applied load. The softer Ti₃SiC₂ with a hardness of 2.8 GPa showed the lowest wear resistance with extensive ploughing and grain breakout damage, both within and outside the direct wear track, in particular at the highest load. The hardest material, Ti_2.7Zr_0.3SiC₂, with a hardness of 7.3 GPa, showed a 5 times better wear resistance. The Cr₂AlC with a hardness of 4.8 GPa showed a wear resistance equal to or even better than that of the Ti_2.7Zr_0.3SiC₂. The wear mechanism depends on the applied load and the microstructure of the MAX phase materials tested. For the Ti₃SiC₂ sample, a quasi-plastic deformation behavior occurs below a point load of 10 N, resulting in grain bending, kink band formation and delamination, grain de-cohesion, as well as trans-and intra-granular fracture near the scratch groove. At this load, the Ti_2.7Zr_0.3SiC₂ and Cr₂AlC MAX samples display plastic ploughing, grain boundary cracks and material dislodgments.     

Transportation interface facilities design using interactive high-level computer graphics

A prototype pedestrian facilities design system is described. The design system exploits the capabilities of an intelligent high-resolution vector graphics workstation which features a highly interactive computer graphics environment. A summary of historical developments in pedestrian facility design and graphics workstation architecture is presented, followed by a discussion of the stochastic model and interactive computer graphics features utilized by a prototype facilities design system. Potential applications of such a design system are discussed, and promising areas of future development are outlined.     

X-ray focussing for synchrotron radiation microprobe analysis at the SRS,Daresbury (UK)

A toroidal bent Si (111) crystal has been made and used to obtain a spot size reduction and therefore an increased flux density of synchrotron radiation for microprobe trace analysis. Measured beam profiles and fluxes are compared with the results of a ray tracing program, used to simulate the experimental situation. It is shown, that the spotsize has been reduced by a factor of 50 horizontally, and by a factor of 11 vertically, which is in good agreement with the calculations. It indicates a good shape accuracy of the doubly bent crystal. The measured photon flux density of 200 photons/(smA μm²) is shown to be sufficient to detect trace elements of ppm concentration in an organic matrix with a detection volume of the order of 10 μm diameter.     

Enhancement of the luminous efficiency of a ceramic phosphor plate by post-annealing for high-power LED applications

Currently, phosphor-converted white light-emitting diodes offer low energy consumption, good environmental stability, and a long lifetime. Hence, they are widely utilized in high-power light-emitting diode (LED) applications such as those in the automotive headlamp industries. However, obtaining high luminous efficiency of such diodes is challenging because of their internal structural properties such as micropores. Herein, we developed phosphor-in-glass (PiG) plates by mixing a blue LED chip and yellow phosphor to create high-power white LEDs (w-LEDs). In addition, the influence of post-annealing on the prepared PiG plates at different temperatures (350°C-550 °C) was investigated. Post-annealing, a treatment that facilitates the mobility of the ceramic matrix encapsulating the phosphor powder, decreases an LED's porosity, thereby enhancing its overall luminous efficiency. Results show that PiG plates post-annealed at 450 °C exhibit superior optical performance and effective color properties than PiG plates that were non-annealed or post-annealed at 350 °C, 400 °C, 500 °C, and 550 °C. Therefore, post-annealed PiG plates are more suitable potential materials for application in the high-power LED industry.     

Structure-design strategy of 0–3 type (Bi0.32Sr0.42Na0.20)TiO3/MgO composite to boost energy storage density,efficiency and charge-discharge performance

A novel 0–3 type (Bi_0.32Sr_0.42Na_0.20)TiO₃/MgO composite is investigated in this work, which possesses a high stored energy storage density w_s˜2.50 J/cm³, recoverable energy storage density W_R˜2.09 J/cm³ with high efficiency η˜84% under low electric field (20 kV/mm). The excellent performance is owning to the increase of breakdown strength (BDS) value and the intrinsic mechanism for enhanced BDS value by MgO incorporation is disclosed by numerical simulations (COMSOL). Moreover, the studied composite exhibits excellent charge-discharge performance, the current density (C_D) and power density (P_D) are 1671 A/cm² and 150 MW/cm³, respectively, which are much superior to that of other ceramics. Besides, most of the stored energy is discharged within ˜0.15 μs via charge-discharge tests. This work not only provides a novel technique to designing bismuth-based ceramic capacitors with simultaneously high W_d, η and excellent charge-discharge performance, but also deepens the understandings of the role for the metallic oxide in the composite.