玻璃纤维增强材料在土木工程结构中的应用

本文综述了玻璃纤维增强复合材料（GFRP）的物理力学性能,及其在土木工程各类结构中的多种应用形式,基于许多国内外的工程实例分析了各种应用形式从理论到工程实践的可行性,供科研、设计和GFRP产品管理、开发人员参考。     

Upconversion Luminescence in Yb/Ln (Ln = Er,Tm) Doped Oxyhalide Glasses Containing CsPbBr3 Perovskite Nanocrystals

Yb/Ln (Ln=Er, Tm) doped TeO₂-based glasses containing CsPbBr₃ perovskite quantum dots were successfully prepared via in-situ glass crystallization. The nanocomposites yield typical green downshifting luminescence attributing to CsPbBr₃ exciton recombination under UV excitation, and produce Er³⁺ green, Er³⁺ red and Tm³⁺ blue upconversion emissions under 980 nm laser excitation. Impressively, specific Ln³⁺ emissions will be quenched with the precipitation of CsPbBr₃ in glass, enabling to finely tune upconversion emitting color. Spectroscopic characterizations evidence that the luminescence quenching is originated from non-radiative reabsorption effect induced by the precipitation of CsPbBr₃ rather than energy transfers from Ln³⁺ to CsPbBr₃. Finally, these nanocomposites are demonstrated to exhibit superior water resistance due to the effective protecting role of dense structural glass, particularly, about 95% downshifting luminescence of CsPbBr₃ and upconversion luminescence of Er³⁺ related to pristine ones are retained after immersing the products in water up to 30 days.     

Domestic Micro-Environments

In the following works, Mathieu Lehanneur readdresses our understanding of domestic spaces through the environmental systems that control and condition them. Such spaces are generally conditioned by centralised heating, cooling and ventilation systems that lump together many sensory qualities, including primary thermal controls as well as by-products of scent and sound, into a singular, mechanical system that fails to engage any of them fully. Lehanneur's projects look to separate these senses into systems distributed throughout the home, engaging each one specifically and locally, in an attempt to redefine the domestic spaces they are located within. Copyright © 2009 John Wiley & Sons, Ltd.     

Cuticle and cortical cell morphology of alpaca and other rare animal fibres

The null hypothesis of the experiments reported is that the cuticle and cortical morphology of rare animal fibres are similar. The investigation also examined if the productivity and age of alpacas were associated with cuticle morphology and if seasonal nutritional conditions were related to cuticle scale frequency. Cuticle and cortical cell dimensions and ellipticity of the fibre cross section were investigated in 32 samples of cashmere, alpaca, mohair, bison, qiviut and vicuña from various origins. In addition, 24 Peruvian alpaca samples from animals ages 2–6 years and of varying fleece productivity were examined. Cuticle scale frequency, cuticle thickness and cortical cell dimensions (length, diameter, volume and ratio of length to diameter) and ellipticity differed between fibres and cuticle scale frequency also varied with mean fibre diameter. For Peruvian alpaca fleece samples, cuticle scale frequency varied with the age of alpaca and fleece productivity. Fibre ellipticity increased with increasing fibre diameter. Cortical cell length was strongly related to cortical cell diameter. The cuticle scale morphology of these rare animal fibres did not have fixed dimensions. Using cuticle scale morphology as a diagnostic tool to positively identify rare natural animal fibres needs to standardize measurements for fibre diameter but will still be affected by differences in animal productivity.     

Signature of rigidity percolation effect in dielectric behavior of germanium containing multi-component chalcogenide glasses (ChGs)

To develop new chalcogenide glasses (ChGs) as dielectric materials having a high dielectric constant and low dielectric loss, some quaternary glasses have been prepared from a novel third-generation Se–Te–Sn-Ge (STSG) system. This study reveals the effect of Ge addition on the dielectric relaxation and thermally activated a.c. conduction in a ternary ChG of Se–Te–Sn (STS) system. The compositional variation of the various dielectric and electrical parameters in the present STSG chalcogens rich non-oxide glasses Se_78-yGe_yTe₂₀Sn₂ (0 ≤ y ≤ 6) has been investigated. The results show that Ge plays a potential role in improving the dielectric properties of the parent STS glass.The dielectric relaxation and thermally assisted a.c. conduction have been investigated by examining the frequency/temperature dependence of dielectric constant/loss. The absence of the dielectric relaxation for the higher concentration of Ge indicates that the relationship of microstructure and dielectric properties can be explained in terms of the stiffness transition followed by the self-organization of the corner sharing and the edge-sharing arrangements of GeSe₄ phase.     

Influence of the Material and the Surface Roughness of the Drying Support on the Self‐detachment of Maltodextrin Films

The influence of four different materials (glass, stainless steel, polytetrafluoroethylene – PTFE and polyamide) used as a paste drying support on the detachment conditions of dried maltodextrin films was investigated. The tests were accomplished in a drying chamber that allows the spreading of a uniform film of pastelike material over solid plates and the visual observation of the instant of the detachment from the surface. The chamber temperature and the water content of the dried film were compared with the corresponding glass transition temperature curve. The effect of the material roughness on the detachment of the dried maltodextrin film was evaluated comparing glass plates with two different surfaces (smooth and sand‐blasted glass). Results indicate that the higher the surface roughness, the drier should the film be, in order to promote self‐detachment at the same temperature conditions. The chemical and physical interactions between the support material and the dried film also influence the process. The PTFE support required less severe detachment conditions than solids with lower surface roughness.     

A Novel Glass Membrane for Low Temperature H2/O2 Fuel Cell Electrolytes

A novel structure for an H₂/O₂ fuel cell with a proton conducting glass electrolyte and a Pt/C catalyst was developed. The performance of the fuel cell, which was impregnated with a glass electrolyte and a gaseous hydrogen–oxygen feed at low temperature in a humidified atmosphere was significantly improved by introducing membrane electrode assemblies (MEAs) consisting of heteropolyacids (HPAs) (phosphotungstic acid, PWA and phosphomolybdic acid, PMA) doped with a P₂O₅‐SiO₂ glass electrolyte. The HPAs containing porous glass electrolytes show promise for applications in low temperature H₂/O₂ fuel cells. The electrochemical behaviour of these materials was studied by measuring the current–voltage profile from polarisation curves. A maximum power density of ≈ 35 mW cm^–2 was obtained at 30 °C and 30% RH (relative humidity) using a PMA/PWA‐P₂O₅‐SiO₂ glass electrolyte membrane. The impedance measurements displaying the total cell ohmic resistance for 12 h at 0.5 V were evaluated at 30 °C. The resistance value was 3.5 Ω for an operating time of 12 h. This MEA showed the best and the most stable performance for use in an H₂/O₂ fuel cell.     

A study on lithium/air secondary batteries—Stability of NASICON-type glass ceramics in acid solutions

The stability of a NASICON-type lithium ion conducting solid electrolyte, Li_1+x+yTi_2−xAl_xP_3−ySi_yO₁₂ (LTAP), in acetic acid and formic acid solutions was examined. XRD patterns of the LTAP powders immersed in 100% acetic acid and formic acid at 50 °C for 4 months showed no change as compared to the pristine LTAP. However, the electrical conductivity of LTAP drastically decreased. On the other hand, no significant electrical conductivity change of LTAP immersed in lithium formate saturated formic acid-water solution was observed, and the electrical conductivity of LTAP immersed in lithium acetate saturated acetic acid-water increased. Cyclic voltammogram tests suggested that acetic acid was stable up to a high potential, but formic acid decomposed under the decomposition potential of water. The acetic acid solution was considered to be a candidate for the active material in the air electrode of lithium-air rechargeable batteries. The cell reaction was considered as 2Li + 2 CH₃COOH + 1/2O₂ = 2CH₃COOLi + H₂O. The energy density of this lithium-air system is calculated to be 1477 Wh kg⁻¹ from the weights of Li and CH₃COOH, and an observed open-circuit voltage of 3.69 V.     

Interface effect of oxygen doping in polythiophene

Long-time evolution of the electrical characteristics for two-terminal and transistor of poly(3-hexylthiophene) film with various gate dielectric interfaces are measured. The oxygen doping is found to depend sensitively on the amount of hydroxyl groups of the interface and irreversible after long time in vacuum except for quartz. For a given interface, dip-coated film always has a higher doping level and slower de-doping than spin-coated films because of higher porosity. With careful control of the oxygen level transistor with mobility of 0.12 cm²/V s and on–off ratio of 29,000 are obtained for dip-coated film on glass substrate.     

Acoustic emission for monitoring the mechanical behaviour of natural fibre composites: A literature review

In recent years, natural fibres are increasingly used as reinforcements for the production of low-cost and lightweight polymer composites: other advantages include non-abrasive nature, high specific properties, and biodegradability. However, their limitations, including moisture absorption, poor wettability and large scattering in mechanical properties, and the not sufficient understanding of mechanisms controlling their mechanical behaviour and failure modes, still confine the use of natural fibre reinforced composites in non-structural applications. Acoustic emission (AE) proved useful for its capability of real-time monitoring over the whole material volume and high sensitivity to any process generating stress waves.This paper presents a literature review of AE applications in studies on natural fibre composites. The following fields of application are covered: (1) interface studies in single fibre composite (SFC) tests, (2) damage evolution and failure mechanisms detection and (3) crack propagation, including also current limitations of existing literature and future work.