Luminescent downconversion is a promising way to harvest ultraviolet sunlight and transform it into visible light that can be absorbed by solar cells, and has potential to improve their photoelectric conversion efficiency. In this work, the uniform hollow spheres and well dispersed CaF2 phosphors doped with rare-earth Ce3+ and Tb3+ ions are prepared by a one-step hydrothermal synthesis method. Benefiting from the stronger ability of absorption and emission and excellent transparency property, we demonstrate that the application of the doped nanocrystals can efficiently improve visible light transmittance. The chosen phosphors are added in the SiO2 sols so as to get the anti-reflection coatings with wavelength conversion bi-functional films, promoting the optical transmittance in the visible and near-infrared range which matches with the range of the band gap energy of silicon semiconductor. Optimized photoelectric conversion efficiency of 14.35% and the external quantum efficiency over 70% from 450 to 950 nm are obtained through the silicon solar cells with 0.10 g phosphors coating. Compared with the pure glass devices, the photoelectric conversion efficiency is enhanced by 0.69%. This work indicates that fluorescent downconversion not only can serve as proof of principles for improving photoelectric conversion efficiency of solar cells but also may be helpful to practical application in the future.
Ultra high molecular weight polyethylene (UHMWPE) fibers possess outstanding properties such as high tensile strength and low density. However, their low surface polarity and poor heat resistance restrict the application of UHMWPE fibers as a reinforcing material for high performance composites. These shortcomings of UHMWPE fibers can be overcome by ultraviolet (UV) assisted grafting treatment and hybridization with aramid fibers. Results show that UHMWPE fibers could firstly be modified by means of an UV radiation assisted one step grafting process with acetone as solvent and acrylic acid as monomers, then the mechanical properties of composites of epoxy resin with the modified UHMWPE fibers was greatly enhanced; with the increasing monomer content in the acetone solvent, the tensile strength of UHMWPE fibers/epoxy resin composites increased obviously, while there was no significant change of flexural strength and impact strength. In order to further improve the heat resistance of UHMWPE fibers/epoxy resin composites, UHMWPE fibers were hybridized with aramid fibers and then the hybrid fibers were used as reinforcing material to produce hybrid fibers/epoxy resin composites. As a result, the deformation of the hybrid fibers/epoxy resin composites decreased by 66.7% at 90°C compared to that of UHMWPE fibers/epoxy resin composites. The result proves that the pre-hybridization of UHMWPE fibers is an effective means to enhance the heat resistance of UHMWPE fibers/epoxy resin composites .
Abstract This article mainly tested and evaluated the carbonation resistance of sprayed concrete mixed with different liquid accelerators, and thus attempted to establish a prediction model for the carbonation depth of sprayed concrete. Firstly, the influence of alkaline liquid accelerator based on sodium aluminate (AR), alkaline-free liquid accelerator based on aluminum sulfate (AS), and alkali-free liquid accelerator based on fluoroaluminate (AF) on carbonation resistance of sprayed concrete was explored. In addition, the porosity and pore structure distribution of ordinary sprayed concrete (OSC), sprayed concrete with AR (SC-AR), sprayed concrete with AS (SC-AS), and sprayed concrete with AF (SC-AF) were analyzed by the mercury intrusion porosimetry. The carbonation depth and compressive and splitting tensile strength also were tested. Furthermore, the scanning electron microscopy was employed to observe the micromorphology of hydration products. The experimental results indicated that the carbonation depth order of sprayed concrete was as follows: SC-AR > SC-AF > SC-AS > OSC. After analyzing the disparity of SC-AR, SC-AS, and SC-AF carbonation depth caused by AR, AS, and AF dosage, the influence coefficients of sprayed concrete carbonation depth were introduced. Finally, the carbonation depth prediction models of SC-AR, SC-AS, and SC-AF were preliminarily established.
Monodisperse Fe3O4 nanoparticles modified by oleic acid were synthesized by a solvothermal method and dispersed into mineral transformer oil to prepare Fe3O4 nanofluids. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis indicated that the obtained nanoparticles are single crystals with an average diameter of 15 nm. The test results indicate that the nanoparticles exhibited good dispersibility in the nanofluids at a wide range of concentrations. Moreover, the positive impulse breakdown strength of nanofluids was greatly improved by 36.6% at the optimum concentration of nanoparticles.
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