含咪唑离子聚乙烯离聚体的合成与性能

利用双(β-二酮单亚胺)钛催化乙烯和5-碘甲基降冰片烯(IMNB)的配位共聚, 高效合成了高分子量、 窄分子量分布和组分可控的烯烃共聚物. 将该含有碘甲基侧基的共聚物与N-甲基咪唑进行亲核取代反应, 然后再与有机金属盐进行离子交换, 制备了一系列带有甲磺酸根(CH₃SO{}_{\mathrm{3}}^{-})、 三氟甲磺酸根(CF₃SO{}_{\mathrm{3}}^{-})或双(三氟甲磺酰)亚胺负离子(Tf₂N^-)的聚乙烯离聚体. 研究表明, 离子基团的引入会破坏聚合物的结晶, 熔融温度和结晶度均随着离子含量的增加而降低. 但离聚体的玻璃化转变温度却高于乙烯/IMNB共聚物, 表明离子基团之间的强相互作用抑制了链段运动.与共聚物前体相比, 聚乙烯离聚体表现出更高的热稳定性、 更好的亲水性和更高的抗拉强度. 当离子含量相同时, 聚乙烯离聚体的抗拉强度顺序为: CH₃SO{}_{\mathrm{3}}^{-}>CF₃SO{}_{\mathrm{3}}^{-}>Tf₂N^-, 而断裂伸长率呈现相反的趋势.     

[100]LiF单晶在60 GPa以内冲击加载下的高压屈服强度特性

获取光学窗口自身的高压强度特性是开展材料高压高应变率冲击响应行为精密测量和数据反演的重要基础。利用平板撞击和双屈服面法,通过冲击-卸载、冲击-再加载原位粒子速度剖面精细测量和数据反演,获得了约60 GPa范围内[100]LiF屈服强度特性随冲击压力的变化规律。结果表明:在实验压力范围内,[100]LiF的屈服强度随加载压力的提高而显著提高,压力硬化效应显著;同时,LiF在冲击加载下的屈服强度高于磁驱准等熵加载结果,应变率硬化效应强于热软化效应。采用Huang-Asay模型确定了可描述冲击加载[100]LiF强度特性的本构模型参数,为LiF在强度、相变、层断裂等加窗测量实验中的深入应用和数据准确解读提供了重要支撑。     

3D X-ray Micro-CT Analysis of Rebar Corrosion in Reinforced Concrete Subjected to a Chloride-Induced Environment

The paper presents experimental investigations of the concrete covers’ protective ability to counteract rebar corrosion in reinforced concrete cubes. The concrete sample was subjected to a chloride-induced environment to get corroded and combined with an un-corroded sample. The chloride-accelerated technique can induce a high degree of corrosion within a controlled time. Moreover, detailed and thorough experimental measurements and analyses of reinforcement loss due to corrosion and its influence on concrete microstructure, were studied through 3D X-ray micro-computed tomography. The rebar outside the concrete was heavily corroded due to the chloride-accelerated test, whereas, only local surface corrosion products appeared inside the concrete. It turned out that the concrete cover showed protective ability to counteract the reinforcing-steel corrosion mechanism despite the accelerated corrosion environment. Moreover, the bond strength between the reinforcement rebar and concrete was not visibly affected since the failure force in the pull-out test and failure mechanisms, observed by 3D X-ray micro-CT, were similar for corroded and un-corroded samples. The failure occurred due to radial cracks with a maximum width equal to approximately 0.25 mm.     

具有高机械强度的掺Er3+∶TeO2-Nb2O5玻璃的光谱性质研究

熔制了掺铒碲铌玻璃样品(100-XTeO2-XNb2O5(X=5,10,15,20 mol%),测试了其密度、折射率、转变温度、析晶温度、维氏机械强度、吸收光谱、荧光光谱、荧光寿命等参量。利用Judd-Ofelt和McCumber理论分别计算了铒离子强度参量Ωt (t=2, 4, 6)和受激发射截面σemi的大小,研究了掺铒碲铌玻璃样品光谱参量对Nb2O5成分的依赖性,并与典型的碲锌钠玻璃（75TeO2-20ZnO-5Na2O）在热学、机械强度、光谱性质和放大品行四个方面进行了比较.     

Self-Compacting Alkali-Activated Materials: Progress and Perspectives

Alkali-activated materials (AAMs) are considered to be alternative cementitious materials for civil infrastructures. Nowadays, efforts have been made in developing AAMs with self-compacting ability. The obtained self-compacting AAMs (SCAAMs) accomplish superior passing and filling properties as well as excellent mechanical and environmental advantages. This work critically revisits recent progresses in SCAAMs including mixture proportions, fresh properties, mechanical strength, microstructure, acid and sulfate resistance, high temperature behaviors, impact resistance and interface shear strength. To facilitate direct comparison and interpretation of data from different publications, mixture proportions were normalized in terms of the content of key reactive components from precursors and activators, and correlation with mechanical behaviors was made. Moreover, special attention was paid to current research challenges and perspectives to promote further investigation and field application of SCAAMs as advanced construction material.     

PVP/CHI交联共混水凝胶的pH敏感性研究

制备戊二醛交联的PVP/CH I共混水凝胶,红外光谱佐证了凝胶网络的生成。pH敏感性实验表明,凝胶的溶胀率在pH=1.0的介质中最大,在pH=4.0的介质中次之,在中性或pH=9.0的碱性介质中最低,表明凝胶具有明显的pH敏感性。CH I含量、交联剂用量、CH I脱乙酰度均对凝胶的pH敏感性有影响,CH I含量40%、交联剂用量0.3%、CH I脱乙酰度99%的PVP/CH I凝胶pH敏感性较显著。介质pH值由1.0到7.0变化时,凝胶拉伸强度随着溶胀率的降低而增大。     

水硬性石灰合成及拉破坏特性试验研究

水硬性石灰在欧洲石质文物修复和加固中获得了很大成功。我国的石质文物主要是砂岩,水硬性石灰的修复效果不好。为满足我国石质文物修复和加固的需求,本文以石灰石和黏土为原料,在950℃煅烧不同时间,制备出水硬性石,对试样的成分、微观形貌、收缩率、抗拉强度和拉破坏过程等进行了研究。结果表明:(1)试样中含有水硬性成分2CaO·SiO2(C2S);煅烧8h时,成分与欧洲水硬性石灰NHL5接近;1.5CaO·SiO2·xH2O(C-S-H)和CaCO3的含量随龄期的增加逐渐增加。(2)龄期1~3d,收缩率较小;龄期4~6d,收缩率以线性规律增加;7d以后,收缩率趋于稳定。(3)局部变形区随拉应力的增加而变大,邻近局部变形区逐渐合并,形成面积更大的应变局部化带;载荷超过峰值后,产生微裂隙;随载荷进一步增加,微裂隙扩展,贯穿整个试件,发展成宏观裂隙,使试件破坏。(4)抗拉强度随龄期的增加而增加,水硬性石灰中C-S-H、CaCO3等相互交织,构成空间致密体,使试件力学强度提高。合成的水硬性石灰物理力学性能与欧洲水硬性石灰NHL5相近,并且成分均匀、可控,在石质文物修复和加固工程中具有良好应用前景。     

基于SVM的固化土无侧限抗压强度模型

为实现较少试验次数下固化土无侧限抗压强度(qu)的准确预测, 提出了基于支持向量机(SVM)的固化土qu的预测模型. 以固化剂各组分掺入比、龄期、初始含水量、固化剂掺量等因素为输入量, 固化土的qu作为输出量, 以径向基为核函数, 采用网格搜索法和交叉验证法进行参数优化, 建立了基于SVM的固化土qu的预测模型. 算例分析表明: 该模型适用于任意条件下固化土qu的精确预测, 且在较小试验成本下实现与响应面法相当的预测精度.     

First-principles prediction of crystal structure and physical properties of ScB3

The crystal structure of ScB₃ is seeked by combining the developed particle swarm optimisation algorithm for crystal structure prediction with first-principles calculations. A new monoclinic phase with the C2/m symmetry is predicted successfully, which is energetically more superior to the early reported R-3m-, P2₁/m-, P6₃/mmc-, P-6m2-, Pnma-, and Pm-3m-type structures in the pressure range from 0 to 100?GPa. The obtained elastic constants and phonon dispersion curve reveal that the C2/m-ScB₃ is mechanically and dynamically stable. The predicted large bulk module, high shear modulus, small Poisson’s ratio as well as the considerable hardness indicate that the C2/m-ScB₃ has outstanding mechanical property. Meanwhile, the dependences of the bulk modulus and Young’s modulus of ScB₃ on the crystal orientation are investigated theoretically. Through applying the strain–stress method, the ideal tensile and shear strengths along different crystal directions are also estimated, and the obtained results confirm that the shear mode dominates the failure mode in the C2/m-ScB₃ structure and it is intrinsically a hard material. The electronic structure calculation and chemical bonding analysis illustrate that the strong covalent B-B and Sc-B bonds are responsible for its structural stability and high hardness.     

Relationship between the radial dynamics and the chemical production of a harmonically driven spherical bubble

The sonochemical activity and the radial dynamics of a harmonically excited spherical bubble are investigated numerically. A detailed model is employed capable to calculate the chemical production inside the bubble placed in water that is saturated with oxygen. Parameter studies are performed with the control parameters of the pressure amplitude, the forcing frequency and the bubble size. Three different definitions of collapse strengths (extracted from the radius vs. time curves) are examined and compared with the chemical output of various species. A mathematical formula is established to estimate the chemical output as a function of the collapse strength; thus, the chemical activity can be predicted without taking into account the chemical kinetics into the bubble model. The calculations are carried out by an in-house code exploiting the high processing power of professional graphics cards (GPUs).The results shown that chemical activity can be approximated qualitatively from the values of relative expansion. This could be helpful in order to optimise chemical output of sonochemical reactors either from measurement data or simulations as well.