关键词： Synthesis   Geopolymers   Microstructure   Time   Eight years  

摘要： The main purpose of this study was to perform a microstructural evaluation in geopolymer samples with 28 days of curing (GP28D) and after 8 years of storage (GP8Y). The knowledge on the microstructure of geopolymers in the long run is crucial for the use of these materials, given their great potential appli-cability. Equally important is the use of industrial waste as raw materials for the manufacture of new materials. In this perspective, this study employed two industrial wastes to produce the samples: bottom ash from mineral coal (BA) and residues from white paper recycling industries. The latter was treated to use the kaolin present in composition. The treatment of the paper waste was carried out by burning the cellulose. Then, the resulting material was subjected to chemical reaction in hydrochloric acid (HCl) to separate the CaCO3 from kaolin. In addition to kaolin, calcium chloride (CaCl2) and water were also obtained as reaction products. The kaolin obtained from the paper residue was dehydroxylated at a temperature of approximately 850 degrees C for 2 h to obtain processed metakaolin (PMK). To obtain the geopolymer samples, BA/PMK proportions of 2:1 were activated with NaOH solutions of 5,10 and 15 M mixed with sodium silicate. After the synthesis, the samples were cured for 28 days and subjected to analysis. Then they were stored for more eight years and again underwent microstructural analysis. The results of the analyzes showed significant changes in the microstructure of the materials with 28 days of cure and after eight years. The micrographs obtained in SEM showed a denser structure and the micrographs obtained in TEM showed that the amorphous structure was partially replaced by a crystalline structure. The samples aged for eight years did not show significantly higher mechanical resistance in relation to the samples analyzed with 28 days of cure. It is important to highlight that the results did not show microstructural degradation after eight years.

关键词： Zirconia   Cellular ceramics   Taguchi planning   Suspension emulsification   Ceramic membrane  

摘要： Porous 3 YTZ-Al2O3 membranes were processed aiming controlled cellular microstructures for potential sepa-ration and electrochemical applications. The processing method relies on emulsification of mixed suspensions of Al2O3 and 3 YTZ powders in sunflower oil. Taguchi experimental planning was used to seek guidelines for optimization of microstructural and structural characteristics, including porosity, phase composition and percolation of resulting membranes. Effects of alumina content, oil:suspension ratio, firing temperature and 2 step firing were evaluated by a correlation matrix and multivariate fitting. This analysis provided interpretation for prevailing effects on open and closed porosity, relative porosity loss during firing, and relevant micro structural and structural effects. The results demonstrate that the content of alumina plays key effects on partial transformation of tetragonal to monoclinic zirconia and on cell size. Percolation was analyzed by impedance spectroscopy, revealing that it is determined by series association of resistance to transport across the open cells and internal interfaces, ascribed to interruptions of open cell paths.

关键词： 铁皮石斛   无菌纳米粉   肝损伤   保护作用  

摘要： 目的探讨铁皮石斛无菌纳米粉(DON)的保肝作用及其相关机制。方法建立四氯化碳(CCl4)慢性肝损伤小鼠模型,同时以受试药物灌胃干预,持续8周。昆明种小鼠随机分为正常对照组、模型对照组、DON组以及铁皮石斛普通粉(DOP)组。检测各组小鼠血清丙氨酸氨基转移酶(ALT)、天冬氨酸氨基转移酶(AST)、乳酸脱氢酶(LDH)和过氧化氢酶(CAT)活性;酶联免疫吸附测定(ELISA)检测血清中肿瘤坏死因子-α(TNF-α)和白细胞介素(IL)-6的表达;免疫组织化学法染色检测IL-1β的表达分布情况;苏木精-伊红(HE)染色行小鼠肝脏病理组织学观察;透射电镜观察肝组织超微结构变化。结果与模型对照组比较,DON和DOP干预后,血清ALT、AST、LDH水平均显著下降,CAT活性增强,TNF-α和IL-6的表达下调;免疫组化法显示,肝脏IL-1β的表达被显著抑制;肝脏病理组织学及肝细胞超微结构均有不同程度改善。与DOP组比较,DON组各项指标改善作用更显著。结论DON对慢性肝损伤具有更明显的保肝作用,其机制可能是DOP经过粒径改造后,更易促进机体抗氧化活性,抑制CCl4诱导的氧化应激,并具有抗炎作用。

关键词： Microstructure   Pore size distribution   Thermodynamic calculations   Transport Properties   Modeling  

摘要： A generic modeling framework is presented to relate microstructural changes, i.e. changes in the pore volume distribution and phase assemblage, and mass transport in cement-based materials. The modeling framework accounts for mass transport and chemical equilibrium between ions in the pore solution and solid hydrates by means of an extended version of the Poisson-Nernst-Planck equation, in which the chemical equilibrium is solved by the external geochemical code IPHREEQC. Results of numerical studies concerning carbonation and leaching of a cement-based material indicate significant changes in mass transport properties due to chemical reactions leading to alterations in the microstructure. The resulting highly non-linear (both spatial and temporal) microstructural changes are thereby depending on the exposure and indicate that interactions between chemical reactions, pore structure changes, and mass transport have to be accounted for as a whole.

关键词： anti-oxidation   coatings   microstructure   niobium   spent MoSi2-based materials  

摘要： MoSi(2)coatings are prepared using spent and commercial MoSi(2)powders as raw materials to protect niobium (Nb) substrate by spark plasma sintering (SPS) technique, and the microstructure and oxidation resistance of the coatings at 1500 degrees C are investigated. Results showed that obvious pores are found in MoSi(2)coating using commercial MoSi2(MC coating) after SPS while MoSi(2)coating using spent MoSi2(MS coating) is dense with low porosity. (Mo,Nb)(5)Si(3)diffusion layer is generated between MS coating and the substrate with no gap or cracks, showing excellent metallurgical bonding. After long-term oxidation at elevated temperature, pores and exposed Mo(5)Si(3)can be observed in the oxide scale of MC coating, while dense and complete oxide scale is obtained by MS coating. Lowest mass gain (2.78 mg cm(-2)) is acquired by MS coating after oxidation at 1500 degrees C for 40 h because SiO(2)oxide scale is completely formed on the dense and bentonite-containing coating, blocking the diffusion of oxygen at high temperature. Compared with MC coating, no further oxidation occurs inside the MS coating or substrate, exhibiting better high-temperature oxidation resistance.

关键词： Magneto-active polymers (MAP)   Magneto-mechanics   Lattice model   Magneto-viscoelasticity   Microstructural model   Finite deformations  

摘要： Magneto-active polymers (MAPs) consist of a polymeric matrix filled with magnetisable particles. MAPs may change their mechanical properties (i.e., stiffness) and/or mechanical deformation upon the application of an external magnetic stimulus. Mechanical responses of MAPs can be understood as the combined contributions of both polymeric matrix and magnetic particles. Moreover, the magnetic response is defined by the interaction between magnetisable particles and the external field. Common approaches to model MAPs are based on phenomenological continuum models, which are able to predict their magneto-mechanical behaviour but sometimes failed to illustrate specific features of the underlying physics. To better understand the magneto-mechanical responses of MAPs and guide their design and manufacturing processes, this contribution presents a novel continuum constitutive model originated from a microstructural basis. The model is formulated within a finite deformation framework and accounts for viscous (rate) dependences and magneto-mechanical coupling. After the formulations, the model is calibrated with a set of experimental data. The model is validated with a wide range of experimental data that show its predictability. Such a microstructurally-motivated finite strain model will help in designing MAPs with complex three-dimensional microstructures. (C) 2020 The Authors. Published by Elsevier Ltd.

关键词： 仿生材料   力学性能   微观结构   氧化石墨烯基复合纤维   纺丝工艺  

摘要： 自然界的生物材料经过数亿年的进化已经实现了结构和功能的完美统一,如木材、鱼鳞和贝壳等。在众多的天然生物复合材料中,贝壳珍珠母得益于其内部软硬物质交替叠层排列的精密结构使其同时兼具了刚度、强度和韧性等出色的性能,因而成为研究人员研究和模仿的重点。科学家们常常选用长径比大、力学性能好的材料作为交错叠层结构中的硬质相来制备性能与功能兼具的仿贝壳结构材料。而石墨烯由于其强度高、长径比大、质量轻等优点,因此常被选做制备轻质高强高韧类贝壳结构的理想材料。目前,石墨烯基复合材料已获得了长足的发展。在众多的石墨烯衍生物中,石墨烯纤维因其轻质、高强、柔韧等特性自其2011年被高超小组首次报道以来就引起了极大关注。本文利用贝壳结构的强韧化机理,采用改进的Hummers法制备氧化石墨烯(GO),将其作为“砖-泥”结构中的硬质相,再选用粘结性能较好的聚氨酯(TPU)作为软质相。经湿法纺丝工艺制备了具有类贝壳结构的GO-TPU复合纤维。这些纤维具有不同的微观结构,对它们进行拉伸测试,其强度和韧性随着TPU含量的升高呈现先上升后下降的趋势。结合拉剪链模型和有限元模拟对其力学性能进行分析,结果表明,通过调整氧化石墨烯硬质“brick”与TPU软质“mortar”之间的微观结构,可优化内部应力分布,改善纤维的宏观力学性能。此外,经研究发现,TPU与GO之间的界面结合是影响复合纤维力学性能的又一关键因素。因此,在该层状结构中加入碳纳米管(CNTs)来改善“砖”与“砂浆”之间的界面结合特性和应力传递效率,进一步发挥了GO片层优异的承载特性,从而实现材料抗拉强度和韧性的进一步提高。并对上述氧化石墨烯基复合纤维进行化学还原,进一步提升了其力学性能。此外,经上述研究发现:当TPU与GO在某种特定质量比时,纤维展现出较好的力学性能,而目前工业制造都朝着更为简便环保的方向迈进,因此,采用制备流程更为简便的干法纺丝工艺对这种特定质量比的GO-TPU混合溶液进行纤维纺丝,并且运用ABAQUS仿真模拟软件观测内部缺陷对纤维宏观力学性能的影响。结果表明,干纺纤维由于其内部孔洞缺陷较湿纺纤维更为细微,因此,其力学性能较湿纺纤维展现出了明显的优越性。这可以有效控制纤维的微观结构,改善内部应力分布和载荷传递效率,从而优化其宏观力学性能。综上所述,本文采用湿法纺丝方法制备了GO基复合纤维,并且结合拉剪链模型和有限元模拟对其微观结构和界面结合的强韧化机理进行分析,并对上述GO基复合纤维进行化学还原,大大提升了其力学性能。基于上述工作,进一步采用流程更为简便的干法纺丝方法制备了GO-TPU复合纤维,并且运用ABAQUS对其内部缺陷的失效机制进行分析。这些研究将为氧化石墨烯复合纤维的内部微观结构优化策略和制备工艺的改进提供有益的指导。

关键词： alumina source   calcium hexaaluminate   phase composition   porous material   solid state reaction  

摘要： CA₆ materials have been synthesized by high temperature solid state reaction using CaCO₃ as calcium source combined with Al (OH)₃, uf-Al₂O₃ and industrial Al₂O₃ as alumina sources. Effects of alumina sources on phase composition, microstructure and properties of CA₆ materials were studied. The results show that CA₆ forms at 1 300 ℃ using Al(OH)₃ and uf-Al₂O₃ as alumina sources. Solid state reaction temperature of samples finishes at 1 500 ℃. Further increasing of firing temperature has no effect on the phase composition. The microstructure of CA₆ produced by the reaction is changed with different alumina sources. When Al(OH)₃ is used as the alumia source, the microstructure of CA₆ is mostly platy. However, as used industrial Al₂O₃ as the alumia source, the microstructure of CA₆ is mostly plate-like and granular, but the microstructure of CA₆ is mostly equiaxed grains by using uf-Al₂O₃ as precursor. When used uf-Al₂O₃ as the source, the compressive strength and bulk density of the materials are the highest, and the porosity is the lowest. As used Al(OH)₃ as alumina source, the compressive strength and bulk density of the materials are the lowest, and the porosity is the highest. © 2021 Bulletin of the Chinese Ceramic Society Press. All Rights Reserved.

关键词： 激光冲击成型   塑性变形   模具   纳米微结构   热压印  

摘要： 激光冲击成型是利用脉冲激光照射在吸收层表面产生的高压等离子体冲击波实现材料成型与强化的技术,具有靶材成型精度高,加工尺度小等优点,适合用于微尺度成型工艺制作金属模具。聚合物具有独特的高透光性和生物相容性等特征,通过微纳复制技术将模具表面的微结构转移到聚合物上,可以加工多种用途的功能性表面和光学器件,因此高强度模具是聚合物成型研究的重点之一。本文通过实验和数值仿真方法系统地研究了激光冲击成型制作高精度聚合物热压印模具的成型过程和成型规律,探究了成型微结构强度等性能的改变,结合实验积累和理论分析,逐步从微米尺度模具深入到纳米尺度模具的制作。首先,系统的论述了激光冲击成型加工技术理论,包括激光脉冲与材料间的相互作用、加工原理、冲击波的传播、激光冲击引起的高应变率变形特征和聚合物热压成型机理,为随后的实验和数值仿真提供了理论基础。然后搭建了适用于微米和纳米尺度的激光冲击成型实验平台。针对激光加工的特点,结合高应变率塑性变形理论模型,对本文中不同条件下的激光冲击成型实验建立了数值仿真模型。其次,提出了利用激光冲击成型进行微米尺度金属模具制作的方法。通过对不同材料和不同特征微结构成型的研究发现,在微纳米尺度成型中,靶材屈服强度和微结构型腔尺度对成型效果有显著影响,并分析了接触界面摩擦力对成型的影响。为了得到更高强度模具,提出了成型深度与靶材厚度比值对成型效果影响的理论,通过控制该比值可以实现微结构完全成型,并保证靶材背部不会凹陷变形,结合数值仿真结果进行了不同靶材厚度下成型微结构残余应力分析。采用TEM和EBSD观测了激光冲击前后材料内部的织构和微缺陷变化,并在此基础上揭示了材料的成型和强化机理。然后,结合微米尺度微结构成型的特点和理论研究,成功进行了纳米尺度微结构模具的制作。纳米尺度微结构成型工艺对靶材要求十分严格,因此首先进行了平坦化靶材的制备。通过分析铝箔平坦化实验的参数和靶材特征,最终得出结论,0.25J能量和75%光斑搭接率,是实验效果和实验效率的最优选参数,此参数下制得的平坦化铝箔粗糙度能达到5.71nm。然后为了降低靶材屈服强度,对压平铝箔进行退火并进行纳米压印实验,为了保护靶材和硅母版,通过对实验结果的分析,最终在0.1J能量下进行纳米微结构成型实验,得到了高精度纳米尺度金属微结构模具。最后结合数值仿真分析对压平过程中的脉冲能量对超薄靶材的回弹影响进行了分析。最后,将制得的微米和纳米尺度模具用于热压印实验,检验了模具应用过程中的性能稳定性与聚合物成型效果,研究了模具用于热压印时承受的温度压强条件和脱模阻力对模具强度的影响,并分析了高弹态聚合物流动填充型腔的成型过程。最终得出结论,微米尺度模具热压印前后保持了硬度、弹性模量和形貌的一致性,纳米尺度模具热压印前后形貌、高度分布和表面摩擦学性能也能够保持稳定。该论文共有图61幅,表2个,参考文献95篇。

关键词： Sb2Te3   微结构调控   受主掺杂   力学性能   热电性能  

摘要： 低温(<673 K)废热回收困难限制了能源利用效率的进一步提升。基于Seebeck效应的温差发电技术可以直接实现热能向电能的转换,有希望解决低温废热回收的难题。然而,单一热电材料工作温度区间较窄,难以满足宽温域废热发电的需求。因此,本文采用微结构调控结合元素掺杂的方式,在SbTe材料体系中分别研制出高性能的中、低温热电材料,并使用简单的一步烧结法制备出安全可靠的宽温域级联热电单臂。同时,利用先进的微结构表征技术、热电性能测试设备以及力学性能实验平台系统研究纳米孪晶、第二相和受主掺杂对SbTe合金组织结构、电热输运特性以及力学性能的影响规律及内在机理,进而推动热电材料在低温废热发电领域的发展。研究结果表明,通过调整BiSbTe合金中Te含量,可优化其热电性能同时提升机械强度。增加少量的Te可以优化载流子浓度并抑制本征激发,提高功率因子;同时,因为部分富Te析出相的挥发,材料中形成弥散分布的微孔阻碍声子传输,降低晶格热导率。在Te增加量为0.01时,合金的z T和z T分别达到1.55@373 K和1.39(303～473 K)。另一方面,减小Te含量可在BiSbTe合金中构建高密度的纳米孪晶并在孪晶界内形成间隙原子,起到强化材料的作用。随着Te含量减少,压缩强度先增大,后基本保持不变,在减少0.03的Te时,压缩强度从184.6 MPa提高至248.2 MPa,硬度从102.4 MPa增大至159 MPa。同时,Te含量的减少,有利于带负电的反位缺陷Sb(Bi)形成,从而大幅度增加合金载流子浓度,推迟本征激发出现,进而拓展合金的最佳使用温度区间。随后,通过Bi/Sb比例的调控,在BiSbTe合金中分别获得1.32@423 K和1.2(303～473 K)的z T和z T,实现了机械强度和热电性能的同步提升。通过与n型CuBiTeSe组装成热电器件,转换效率在220～270 K温差下可以达到4.8%。选取宽带隙的In掺杂SbTe合金作为中温热电材料研究对象,采用Mn元素受主掺杂提升载流子浓度,不仅推迟本征激发出现,还驱使费米能级深入价带深处,使得第二价带参与导电,提高费米能级附近的态密度有效质量,实现功率因子全温域提升。同时,使用高能球磨结合放电等离子烧结(SPS)构建高密度晶界和孪晶界,增强声子散射,降低晶格热导率,MnInSbTe合金在673 K时,z T达到0.99。B掺杂可以在不影响InSbTe合金热电性能的情况下,阻碍晶界迁移和变形,抑制高温软化的发生。Cu掺杂可以增大载流子浓度,推迟本征激发出现,并在合金中原位析出纳米富Cu第二相,增强声子散射,降低晶格热导率。同时,少量Cu原子还会进入合金孪晶界间隙处,连接相邻孪晶变体,加速载流子传输,提高功率因子。最终,在B、Cu掺杂量分别为0.05和0.015时,z T达到最大,为1.05@673 K。研究表明,在InSbTe合金中额外加入Mg B实现B-Mg共掺,可以原位析出弥散分布的高硬度第二相,提高合金力学性能。添加1.5 at.%的Mg B可以将合金的压缩强度和维氏硬度分别从183.0 MPa和98.8 MPa提高至230.6MPa和131.8 MPa。并且,高密度的纳米析出相也可以增强声子散射,降低晶格热导率,结合Mg元素的受主掺杂,在673 K时z T达到1.01。选择该合金与低温热电性能优异的BiSbTe合金通过一步烧结法制备宽温域级联单臂,在375 K温差下,实测转换效率达7%,有望应用于低温废热回收。