Lu Wang,Shengdong Sun,Huajie Luo,Yang Ren,Hui Liu,Xianran Xing,Jun Chen
The realization of high piezoelectric performance and excellent temperature stability simultaneously in Pb-free ceramics is the key for replacing Pb-containing perovskites in the industry. In this study, large piezoelectric performance (d33 = 354 pC N−1) was achieved in a wide temperature sinterable potassium-free NaNbO3–BaTiO3–BaSnO3 system, which is twice more than the piezoelectricity found in NaNbO3–BaTiO3 binary ceramics. Structural refinement of high-energy synchrotron powder diffraction data suggests a single tetragonal structure with P4bm symmetry for the studied NaNbO3-based Pb-free ceramic. The results indicate that the small axial ratio favoring polarization reorientation benefits strong piezoelectricity, while the large oxygen octahedron tilt enhances the stability of the P4bm structure during the changing temperature according to the in situ high-energy synchrotron X-ray diffraction measurements and provides the foundation for the excellent thermal stability (20–100 °C) of the piezoelectric properties. A single tetragonal phase with a tiny axial ratio and large oxygen octahedron tilt effectively balances the piezoelectricity and thermal stability in Pb-free systems.
A new preparation method for a filter material with an inclined modification pattern is described herein. The effects of the inclination angle of the strips, the composition and the number of layers on the performance of the filter materials were analysed systematically. On this basis, the optimal structure and parameters of the filter materials were determined. The performance of this filter material was verified by preparing an industrial filter cartridge. The results demonstrated that the filter materials achieved the highest comprehensive filtration performance when the inclination angle of the modification strips was 75°. The steady-state quality factor improved by up to 137.1 % compared to the original filter materials with uniform wettability. The double-layer filter had the best filtration performance when the front and back layers were both modified filter materials and the strips were overlapped. In terms of the impact of layers, the seven-layer composite filter material achieved the optimal comprehensive filtration performance for oil mists of different sizes (1.18 and 2.60 kPa −1 for sub-micro and micro droplets respectively). After the modified filter material and the original filter material were processed into a filter cartridge, the modified filter cartridge showed significant advantages of ‘pressure drop and efficiency improvement’ under different superficial gas velocities compared to the unmodified filter cartridge.
Li Dong,Wang Chaoyu,Su Yishi,Zhang Di,Ouyang Qiubao
The inclination angle of the flake particle has a significant impact on the in-plane thermal conductivity of composites. The graphite flake/Al composites (50 vol%) with different inclination angles were fabricated via flake powder metallurgy, and the results show that with increasing the size of Al particle from 25.6 to 50.7 μm, the inclination angle of graphite flake decreases from 7.3° to 4.4°, while the in-plane thermal conductivity of composites increases from 473 to 555 Wm −1 K −1 . Based on the rules of mixture, an effective model was established to qualify and quantify the relation between the inclination angle and the in-plane thermal conductivity of the corresponding composites. This model can also be applied to other flake particle-reinforced composites.
This work designs a fractal latent heat storage (LHS) unit with tree-shaped fins for enhancing heat exchange efficiency. The melting/solidification processes inside a fractal LHS unit are experimentally studied by visualization observation, focusing on the role of inclination angles. Comparative studies on fractal LHS and traditional LHS units are conducted by assessing the temperature response, phase change behavior, liquid fraction variation, and thermal storage/release performance. The experimental results indicate that the inclination angle presents a more significant impact on melting processes than solidification processes, especially for thermal characteristics in the axial direction. Variations in the onset and duration of natural convection determine the main difference in the melting/solidification mechanism of fractal LHS units. Large inclination angle is not conducive to convection development, thus prolonging the late conduction-dominated stage and diminishing the overall thermal performance. Therefore, the thermal characteristics of fractal LHS units are less affected by orientations than traditional LHS units. Moreover, the overall thermal performance of fractal LHS units is more superior to traditional LHS units irrespective of orientations. Particularly, the vertical fractal LHS unit has a maximum reduction of 52.6% in the complete melting duration, and the heat storage/release rate of horizontal fractal LHS units augments by 94.7% and 101.5% when compared with traditional LHS units.
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