Gd3+掺杂La2Mo2O9的相稳定性及热导率

La2Mo2O9具有极低的热导率,但其在580℃左右会发生α-β相变,严重影响其性能和应用。本实验以Gd203掺杂La2Mo2O9制备了一系列La2-xGdxMo2O9 (x=0.0~0.5)固溶体,研究了掺杂Gd3+对La2Mo2O9相稳定性和热导率的影响。结果表明,随着Gd3+掺杂量的增加,相变得到有效抑制,当x≥0.2时样品以β相存在。样品的热导率随Gd3+掺杂量的增加先减小后增加,室温下在x=0.2时达到最低,此后缓慢上升,但所有样品的热导率均小于1 W/(m·K)。     

7055-T7951铝合金热轧厚板微观组织及非均匀力学行为研究

本文对工业级7055-T7951铝合金热轧厚板的合金成分、室温拉伸性能、显微组织以及织构特征等进行了实验分析,对该板材的微观组织状态、力学性能各向异性与织构特征关系进行了详细研究,结果表明：该板材镁元素含量总体处于下限水平,难溶的合金化合物很少,晶内的析出相主要为h＇相和少量的h相,材料处于轻微过时效状态。板材存在明显的力学性能各向异性,沿轧制方向及横向的屈服及抗拉强度相近且明显优于与轧制方向呈45°方向上的指标。板材中心层各方位上的强度指标均优于表层对应方位上的指标,并且中心层的力学性能各向异性强于表层。该板材中心层有较为强烈的轧制类织构Brass和S,而表层则是以再结晶织构R为主。基于施密特定律研究了板材不同厚度层不同拉伸方向上平均屈服强度与施密特因子间的定性关系,探讨了织构特征对热轧厚板非均匀力学行为的影响规律。     

Plasmon-induced photothermal effect of sub-10-nm Cu nanoparticles enables boosted full-spectrum solar H2 production

Distinguishing the contributions from localized surface plasmon resonance (LSPR)induced photothermal effect is a significant challenge in the study of solar hydrogen production. Herein, a well-defined one-dimensional Cu/TiO₂ heterostructure with Cu size of 3–6 nm is designed to address such issue. Cu nanoparticles present notable LSPR absorption from visible to near-infrared light, while no hydrogen is produced in the presence of simulated light with λ ≥ 700 nm. Interestingly, a remarkable improvement of hydrogen evolution under full-spectrum light was observed which is almost twice of that under only ultraviolet–visible light irradiation, implying the critical yet auxiliary role of LSPR-induced photothermal effect in promoting photocatalytic performance. Significantly, a notable reduction of the apparent activation energy and strengthened charge separation efficiency are observed due to the increased local temperature of catalyst surface caused by the plasmon-induced photothermal effect. The kinetic and thermodynamic changes should be responsible for the enhanced hydrogen production.     

Fabrication of high-fracture-strength and gas-tightness PDC films via PIP process for pressure sensor application

High-fracture-strength and high-gas-tightness thin-film gas-pressure sensors were fabricated using a silicon oxycarbonitride polymer-derived-ceramic (SiCNO-PDC) material via a multiple polymer-infiltration-pyrolysis (PIP) process. To obtain dense SiCNO ceramic films, two types of liquid polyvinylsilazane (PVSZ) precursors were chosen; a high-ceramic-yield precursor with high viscosity (PVSZ-1) was designed to construct the skeleton of ceramic film, whereas a relatively high-ceramic-yield precursor with low viscosity (PVSZ-2) was designed to infiltrate in ceramic defects. The results confirmed that the PVSZ-2 can effectively fill both intergranular and intragranular defects of ceramic films pyrolyzed by the PVSZ-1, and produce the sponge-like structures with nanosized pores. Although the density of the ceramic films only increased by 2.2%-5.2% after PIP process, the gas tightness was fundamentally improved, and all ceramic films after PIP process could keep gas-tight condition without loss of pressure after 72 hours. Similarly, the fracture strengths of the ceramic films after PIP cycles have also been improved, and the value could reach 108 MPa after only three PIP cycles. In addition, because a linear relationship among the load, resonant frequency, and deflection was detected in our ceramic films, the wireless passive gas-pressure sensors with high-sensitivity and high-temperature resistance have been fabricated. It strongly indicates that the ceramic films obtained by our PIP process have real potential to be used as thin-film gas-pressure sensing elements in high-temperature and high-pressure fields.     

Combining effects of TiO6 octahedron rotations and random electric fields on structural and properties in Na0.5Bi0.5TiO3

The structural and dielectric properties of Na_0.5Bi_0.5TiO₃ (NBT) ceramics and crystals have been investigated and are compared to that of Pb(Zr_0.55Ti_0.45)O₃ (PZT55/45) and Pb(Mg_1/3Nb_2/3)_0.72Ti_0.28O₃ (PMNT 72/28) ceramics. X-ray diffraction (XRD) profiles for (100), (110), (111), (200), (220), and (222) (referred to cubic structure) reveal that the monoclinic structure with Cc space group exists both in the NBT single crystal and ceramics. The diffraction profile obtained with high resolution laboratory XRD for the NBT single crystal can be well described, using Cc model instead of R3c model. The dielectric constant of NBT below T_hump shows some similarity to that of PZT45/55 ceramics below 50°C in which oxygen octahedron rotations cause the frequency dispersion of the dielectric constant. The temperature-dependent dielectric constant for NBT can be deconvolved into two independent processes. The lower temperature process shows a typical relaxor characteristic and follows the Vogel-Fulcher relationship. The other process at higher temperature shows less frequency-dependent behavior. Comparing the dielectric constant of NBT with that of PZT55/45 and PMNT72/28 reveals that both oxygen octahedral rotations and random electric fields play an important role in the frequency dispersion of the dielectric constant for NBT relaxor feroelectric.     

Crystallization-induced valence state change of Mn2+ → Mn4+ in LiNaGe4O9 glass-ceramics

Tetra-valent manganese (Mn⁴⁺) has been regarded as an efficient non-rare-earth red-light emitting ion, which has stimulated continued search of robust hosts and efficient synthetic methods to stabilize Mn⁴⁺ centers with strong photoluminescence. In this work, we demonstrate a facile synthetic method for Mn⁴⁺ doped glass-ceramic (GC) based on crystallization-induced oxidation state change in an oxide glass. The parent glass with a formula of LiNaGe₄O₉ is fabricated by melt-quenching and crystallization is induced by thermal treatment in air. Oxidation of Mn²⁺ in glass to Mn⁴⁺ in the GC is confirmed by both optical spectroscopy and electron paramagnetic resonance (EPR) measurements. After thermal treatment, the characteristic reddish photoluminescence (PL) of Mn²⁺ in the glass centered at 611 nm disappears and a strong photoluminescence peak at 660 nm attributed to Mn⁴⁺ is observed. The conversion to Mn⁴⁺ after crystallization in the examined system may have strong implications for synthesis of Mn⁴⁺ doped phosphors which always requires rigorous control of the redox equilibrium during synthesis.     

Larger pore volume tetraphenyladamantane-based hybrid porous polymers: Facile Friedel–Crafts preparation,CO2 capture,and Rhodamine B removal properties

Synthesis of covalently linked porous polymers with high surface area and larger pore volume for two or more task-specific functionalities is always a big challenge. In this article, the facile Friedel–Crafts reaction is employed to construct the hierarchical hybrid porous polymers (HPPs) from tetraphenyladamantane and octavinylsilsesquioxane. The resulting polymers, HPP-1 to HPP-3, possessed the surface areas from 1356 to 1511 m² g⁻¹, and the pore volumes from 2.05 to 2.67 cm³ g⁻¹. All these polymers feature micropores, mesopores, and macropores in nature. The resultant polymers exhibit high CO₂ adsorption capacity up to 2.0 mmol g⁻¹ (8.82 wt %), at 273 K, 1.0 bar, and the maximum Rhodamine B (RB) sorption capacity of 653.6 mg g⁻¹. To illustrate the adsorption process, the effects of factors, contact time, initial concentration, temperature, and pH value on the adsorption capacity of RB were studied. The adsorption equilibrium data displayed a better fitting to the Langmuir isotherm model than the Freundlich model and the adsorption kinetics fitted well with the pseudo-second-order kinetic model. The recycle experiments displayed that the capacity recovery was still higher than 95% after four cycles. Theses polymers are promising to be the adsorbents for capturing CO₂ and removing RB. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 136, 48572.     

A comparison of coagulation and gelation on the structures and stabilization behaviors of polyacrylonitrile fibers

The fiber spinning methods determine the formation of the physical structures of polyacrylonitrile (PAN) fibers which further affect stabilization reactions and the mechanical performances of the resultant carbon fibers. In this study, PAN fibers were prepared by both dry-jet gel spinning (g-PAN) and dry-jet wet spinning (w-PAN), and their stabilization behaviors were compared. While the stabilized w-PAN fibers show sheath-core structures, the stabilized g-PAN fibers exhibit relatively uniform stabilized structures along the radial direction. Additionally, the stabilization reactions of g-PAN fibers occur faster than that of w-PAN fibers, and the cyclization, oxidation, and crosslinking reaction activation energies of g-PAN fibers are lower than that of w-PAN fibers, respectively. Moreover, the carbon yield of g-PAN is higher than that of w-PAN fibers. We believe that above changes are possibly ascribed to the formation of different PAN sheath structures and oriented chain structures during dry-jet wet spinning and dry-jet gel spinning. It is concluded that gel spinning could significantly reduce the sheath-core difference of PAN fibers and the stabilized fibers as compared with wet spinning, which leads to a faster stabilization and more uniform stabilized structures. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48671.     

膜富集-高强UV/SO32-体系高效降解PFOS的研究

工业废水中全氟辛烷磺酸(PFOS)浓度低,直接应用化学法降解能耗较高。采用膜分离与UV/SO3^2-光降解的组合工艺对其进行处理,研究了此组合技术的处理效果,并考察了影响降解率的因素。结果表明,反渗透膜可有效富集PFOS溶液,高强UV/SO3^2-体系可高效降解该富集溶液。提高溶液初始pH、SO3^2-浓度、紫外光强,均有利于PFOS降解率的提高,而PFOS初始浓度的提高会降低其降解率。     

挤出-注塑制备黄麻增强PLA复合材料及其性能

通过挤出共混、造粒、注射成型的方式制备了黄麻纤维填充聚乳酸(PLA)复合材料,研究了复合材料的力学性能以及黄麻与PLA之间的微观界面形貌。结果表明:黄麻的加入,并没有很好地改善黄麻/PLA复合材料的拉伸强度和弯曲强度;碱处理后的黄麻与PLA之间的界面性能有所改善;碱处理黄麻的加入,改善了黄麻/PLA复合材料的断裂伸长率与冲击韧性。