关键词： compressive strength   high volume slag powder   nano-SiO2   pore structure   resistance to chloride ion penetration  

摘要： Using the strong pozzolanic activity of precipitation method nano-silica (PNS) to improve the early compressive strength and loose internal structure of the high volume slag powder-cement cementitious system. The influence of PNS on the compressive strength and the resistance to chloride ion permeability of high volume slag powder-cement cementing system were studied. The hydration products and pore structure of the system were analysed by XRD, TG-DSC and MIP. Research shows that with the increase of PNS content, the compressive strength of the specimens increases, especially the 7 d compressive strength. The strength of specimens with 5% (mass fraction, the same blow) PNS increases by 20%. The resistance to chlcride ion penetration capacity first increases and then decreaces. When PNS content is 3%, it reaches the optimal level, and its 28 d chloride ion diffusion coefficient is 44.8% lower than that without PNS. PNS can consume a large amount of Ca(OH)₂ in the early stage and generate more hydration products such as C-S-H gel, which makes the pore structure more compact and reduces the porosity. Incorporating PNS within the range also refines the pore size. © 2022 food and fermention indistries. All rights reserved.

关键词： 纳米二氧化硅   大掺量矿粉   抗氯离子渗透   孔结构   抗压强度  

摘要： 利用沉淀法制备的纳米二氧化硅(PNS)极强的火山灰活性,能改善大掺量矿粉-水泥胶凝体系早期抗压强度低、内部结构疏松等缺陷,研究了PNS对大掺量矿粉-水泥胶凝体系抗压强度、抗氯离子渗透性的影响,通过XRD、TG-DSC及MIP对该体系的水化产物与孔结构进行微观分析。研究表明:随着PNS掺量的增加,试件的抗压强度也随之提高,尤其是7 d抗压强度,掺5%(质量分数,下同)PNS试件的强度增幅达到了20%;同时,水泥抗氯离子渗透能力先上升后下降,PNS掺量为3%时,达到最优,其28 d氯离子扩散系数较不掺PNS降低44.8%。PNS在早期能够大量消耗Ca(OH)2,生成更多的C-S-H凝胶等水化产物,使得孔结构更加致密,降低孔隙率,在适宜范围内掺入PNS还可有效细化孔径。

关键词： 艺术鉴赏能力   材料微结构   二维码   仪器使用   微观世界   大赛   培养探索   美轮美奂  

摘要： 材料之美不仅体现在宏观,也表现在其微观组织。为了让更多材料人欣赏到美轮美奂的材料组织,培养探索微观世界的兴趣,提高仪器使用水平与艺术鉴赏能力,特此举办第七届材料微结构大赛。下方展示的是30张入围作品,更多详情可扫描右侧二维码查看。

关键词： 水泥基材料   水化模型   微观结构   孔结构   传输性能   数值模拟  

摘要： 水泥基材料劣化的本质是由于侵蚀性介质通过传输通道进入材料内部生成腐蚀物质,从而对结构造成破坏。因此,结构耐久性与侵蚀介质在水泥基材料中的传输行为密切相关。已有的混凝土寿命预测模型和耐久性评估研究主要基于Fick和Darcy定律,本文从水泥基材料微结构出发,结合最新的国内外研究成果,对孔结构演变及其传输性能的数值模拟研究进展进行阐述,对促进结构耐久性的研究具有一定的指导意义。

关键词： Aging   Conductivity   Dielectric constant   Gamma irradiation   Leakage current  

摘要： Polymer-based Bakelite resistive plate chamber detector samples were exposed to Co-60 gamma source for various irradiation doses. To explore the impact of gamma irradiation induced structural modifications, Positron annihilation lifetime, Fourier transform infrared spectroscopic and X-ray diffraction (XRD) studies were performed. The increased free volume (V-f) for lower irradiation doses is attributed to the scission of polymeric chains. The free volume parameters are in good agreement with XRD and conductivity results. The ac conductivity varies linearly with the applied frequency and obey Jonscher power law. The conduction mechanism is explained on the basis of barrier hopping model.

关键词： adjustable luminescence   CaWO4   Eu3+   incomplete energy transfer   photoluminescence   structural distortion  

摘要： (Ca1-xEux)WO4(x = 0-21 mol%) phosphors were prepared using the classical solid-state reaction method. The influence of Eu(3+)ion doping on lattice structure was observed using powder X-ray diffraction and Fourier transform infrared spectroscopy. Furthermore, under this influence, the luminescence properties of all samples were analyzed. The results clearly illustrated that the element europium was successfully incorporated into the CaWO(4)lattice with a scheelite structure in the form of a Eu(3+)ion, which introduced a slight lattice distortion into the CaWO(4)matrix. These lattice distortions had no effect on phase purity, but had regular effects on the intrinsic luminescence of the matrix and the f-f excitation transitions of Eu(3+)activators. When the Eu(3+)concentration was increased to 21 mol%, a local luminescence centre of [WO4](2-)groups was detected in the matrix and manifested as the decay curves of [WO4](2-)groups and luminescence changed from single exponential to double exponential fitting. Furthermore, the excitation transitions of Eu(3+)between different energy levels (such as(7)F(0)-> L-5(6),F-7(0)-> D-5(2)) also produced interesting changes. Based on analysis of photoluminescence spectra and the chromaticity coordinates in this study, it could be verified that the nonreversing energy transfer of [WO4](2-)-> Eu(3+)was efficient and incomplete.

关键词： Lithium nickel phosphate   cathode materials   XRD   FTIR  

摘要： LiNiPO4 has been the focus of research in developing environmentally friendly, low cost and high performance cathode materials for lithium-ion batteries. The aim of this work is to synthesize LiNi0.5Co0.45Zn0.05PO4 cathode material using solid-state reaction method at 850 degrees C for 20 hours and all the parameters compared with LiNiPO4. The X-ray diffraction (XRD) analysis confirmed that LiNi0.5Co0.45Zn0.05PO4 phase is well crystallized with olivine structure indexed by orthorhombic symmetry with Pnma space group. The phase purity supported by energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM). Local structure of the LiNi0.5Co0.45Zn0.05PO4 phospho-olivine material has been investigated by Fourier transforms infrared spectra (FTIR). All the parameters of LiNi0.5Co0.45Zn0.05PO4 are found in good agreement with XRD, FTIR results of LiNiPO4. Impedance spectroscopy technique has been used to study the cathode materials because it can reveal the relationship between the crystal lattice with the electrochemical properties.

关键词： Alkali-activated materials   Biomass ash   Geopolymers   Microstructure   Mechanical properties   Powder materials  

摘要： The possibility of the application of biomass fly ash (BFA) as a precursor material for the synthesis of alkali activated materials (AAM) is presented in this paper. Glass powder (GP) was tested as an additional substrate in a synthesis process. Different mixtures of samples were produced: four mixtures using only BFA for different NaOH concentrations and nine mixtures where BFA was partially replaced by the GP. Three different NaOH concentrations were applied here. Compressive and flexural strength after 7 and 14 days were performed. The microstructure and the chemical composition of samples were obtained. The results show that the compressive and flexural strength of materials increased with the increase of NaOH concentration and the decrease of the GP content in a mixture. The samples were also characterized by the high porosity with some voids and microcracks. The poorly dissolved BFA particles were also noted in a matrix. (C) 2020 Elsevier B.V. All rights reserved.

关键词： refill friction stir spot welding   aluminum alloy   material flow behavior   precipitate evolution   dislocation configuration  

摘要： In this study, we used the stop-action technique to experimentally investigate the material flow and microstructural evolution of alclad 2A12-T4 aluminum alloy during refill friction stir spot *** are two material flow components, i.e., the inward-or outward-directed spiral flow on the horizontal plane and the upward-or downward-directed flow on the vertical *** the plunge stage, the flow of plasticized metal into the cavity is similar to that of a stack, whereby the upper layer is pushed upward by the lower *** the refill stage, this is process *** such, there is no obvious vertical plasticized metal flow between adjacent *** leads to the coarsening of S(Al2CuMg) in the thermo-mechanically affected zone and the diminishing of S in the stir *** dynamic recrystallization results in the formation of fine equiaxed grains in the stir zone, but this process becomes difficult in the thermo-mechanically affected zone due to the lower deformation rate and the pinning action of S precipitates on the dislocations and sub-grain boundaries, which leads to a high fraction of low-angle grain boundaries in this zone.

关键词： 光致发光   Cr^3+   Eu^3+   能量传递   余辉   荧光粉  

摘要： 同时可作为磁共振成像造影剂与近红外余辉光学成像光学探针双功能的纳米粒子,在生物医学领域具有重要的应用价值。采用自蔓延燃烧法制备了不同掺杂浓度的GdAlO 3∶x%Cr^3+及GdAlO 3∶1%Cr^3+,y%Eu^3+近红外长余辉发光纳米粒子。并采用X射线衍射、扫描电子显微镜、激发和发射光谱及发光动力学分析等技术手段,较系统地研究了其微结构及光学特性。实验结果表明,Cr^3+取代了GdAlO 3中的Al^3+的格位,单掺样品的平均粒子尺寸约为202 nm。GdAlO 3∶x%Cr^3+样品的激发谱显示,激发峰来源于Cr^3+和Gd^3+的跃迁;在583 nm的激发下,在650~750 nm近红外范围内,出现四个近红外光发射峰。其中,725 nm处的发射峰归属为禁戒跃迁2 E到4 A 2的零声子线,700和750 nm处的发射峰则为声子边带的发射。在0.2%~2.0%的掺杂浓度范围内,随着Cr^3+掺杂浓度的增加,这些发射峰的强度先增强后减弱,最优浓度为1%。而位于735 nm处的发射峰强度随Cr^3+浓度增大而增大,其归属于Cr^3+-Cr^3+对的发光。同时,单掺样品可观察到位于725 nm的长余辉发光,其中GdAlO 3∶1%Cr^3+纳米粒子的余辉时间最长,并超过30 s。在上述Cr^3+最优浓度(1%)基础上,通过Eu^3+取代GdAlO 3基质中Gd^3+的格位,实现了Eu^3+/Cr^3+共掺杂。实验发现,在266 nm激发下,在红光区域范围内可观察到以位于614 nm处的发射为主的一系列发射峰。尤其,由于存在Eu^3+到Cr^3+的能量传递,在近红外区出现了位于725 nm处Cr^3+的近红外发射峰。当Eu^3+浓度为13%时,与Cr^3+单掺杂样品相比,其样品的平均粒子尺寸虽然减小到167 nm,但在275 nm紫外光照射5 mi n停止后,发现共掺样品在位于725 nm处Cr^3+的余辉发光强度明显增强。通过比较分析单掺和共掺样品的吸收和发射光谱及发光动力学的结果,验证了由于Eu^3+到Cr^3+的持续能量传递可引起较显著地近红外余辉发光增强的结论。同时,该研究为设计新型的近红外长余辉发光纳米材料提供了新的思路。