多孔材料在三向载荷作用下的力学模型

为更全面掌握三维网状多孔材料在工程应用中的安全承载问题,分析了各向同性的该类材料在三向载荷(多向载荷)作用下的力学性能.在其结构简化的基础上,提出了该类材料在三向载荷作用下相应的承载力学模型,其中三向载荷中的任何一个载荷都可以任意为拉伸和压缩.运用这一模型,可以判断当该类材料在承受上述载荷条件时是否会发生破坏,其用来判断的材料固有指标即是多孔体的孔率,该指标是多孔材料最基本的参量.     

多孔吸声材料发展现状与展望

吸声降噪在人们日常生活、设备安全以及军事领域具有重要意义，多孔材料是一类重要的吸声材料。介绍了多孔材料的吸声原理、多孔吸声材料的种类及其特性、影响多孔吸声材料吸声性能的因素等。综述了多孔吸声材料的发展现状，并对吸声材料的发展趋势做了展望。     

氢溢流在多孔材料储氢性能研究中的应用

多孔材料的储氢性能研究是氢能经济发展的重要课题之一,然而其室温下的储氢性能还不能满足氢存储系统的所有要求。氢溢流被证明是提高多孔材料在室温下储氢性能的有效方法。主要从氢溢流产生的方法及其优缺点,氢溢流在碳基纳米材料、沸石、金属有机骨架和共价有机骨架等多孔材料储氢性能研究中的最新动态进行了详细综述,并指出了当前存在的问题和今后的发展方向。     

A micromechanical model of distributed damage due to void growth in general materials and under general deformation histories

We develop a multiscale model of ductile damage by void growth in general materials undergoing arbitrary deformations. The model is formulated in the spirit of multiscale finite element methods (FE ²), that is, the macroscopic behavior of the material is obtained by a simultaneous numerical evaluation of the response of a representative volume element. The representative microscopic model considered in this work consists of a space‐filling assemblage of hollow spheres. Accordingly, we refer to the present model as the packed hollow sphere (PHS) model. A Ritz–Galerkin method based on spherical harmonics, specialized quadrature rules, and exact boundary conditions is employed to discretize individual voids at the microscale. This discretization results in material frame indifference, and it exactly preserves all material symmetries. The effective macroscopic behavior is then obtained by recourse to Hill's averaging theorems. The deformation and stress fields of the hollow spheres are globally kinematically and statically admissible regardless of material constitution and deformation history, which leads to exact solutions over the entire representative volume under static conditions. Excellent convergence and scalability properties of the PHS model are demonstrated through convergence analyses and examples of application. We also illustrate the broad range of material behaviors that are captured by the PHS model, including elastic and plastic cavitation and the formation of a vertex in the yield stress of porous metals at low triaxiality. This vertex allows ductile damage to occur under shear‐dominated conditions, thus overcoming a well‐known deficiency of Gurson's model. Copyright © 2012 John Wiley & Sons, Ltd.     

新型聚合物多孔材料的制备研究进展

介绍了超浓乳液的形成及其特点,综述了超浓乳液作模板制备聚合物多孔材料的方法、机理和化学改性等方面的研究进展,并对其发展前景进行了展望.     

泡沫金属多向承载行为的研究意义

泡沫金属具有优良的物理性能和综合力学性能,在很多场合都可用作轻质结构材料.在简要介绍该类材料用途的基础上,指出了多向载荷研究对于泡沫金属应用的实际意义,分析了以往工作在该类材料力学性能研究方面的不足,以期推进相关领域的研究者在该方面的突破.在此基础上,提出了一条研究该类材料在多向载荷作用下有关数理关系的思路.     

含镁环境治理材料研究现状

针对含镁治理材料在国内外环保领域的研究进行了评述。对环保级氢氧化镁,含镁无机盐复合材料,含镁天然高分子复合材料,含镁多孔性吸附材料特征及应用现状进行了介绍。     

静水压力下高分子材料黏弹性动力学参数测量

提出测量静压下高分子材料黏弹性动力学参数方法。分别制作均匀实心覆盖层及圆柱空腔覆盖层样品,测量实心覆盖层复反射系数计算复纵波波数,测量圆柱空腔覆盖层复反射系数,结合圆柱空腔结构变形,利用圆柱管中轴对称波特征方程计算复剪切波波数,综合复纵波波数与复剪切波波数计算静压下复杨氏模量及复泊松比。对橡胶材料进行声管测试,分析、总结静压对黏弹性动力学参数影响规律。测量某吸声覆盖层静压下反射系数,并与用实测材料参数计算的反射系数进行比较,验证方法的可靠性。     

Characterization of SiNx/a-Si:H crystalline silicon surface passivation under UV light exposure

One of the most promising solution for crystalline silicon surface passivation in solar cell fabrication consists in a low temperature (< 400 °C) Plasma Enhanced Chemical Vapor Deposition of a double layer composed by intrinsic hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon nitride (SiN_x). Due to the high amount of hydrogen in the gas mixture during the double layer deposition, the passivation process results particularly useful in case of multi-crystalline silicon substrates in which hydrogenation of grain boundaries is very needed. In turn the presence of hydrogen inside both amorphous layers can induce metastability effects. To evaluate these effects we have investigated the stability of the silicon surface passivation obtained by the double layer under ultraviolet light exposure. In particular we have verified that this double layer is effective to passivate both p- and n-type crystalline silicon surface by measuring minority carrier high lifetime, via photoconductance-decay. To get better inside the passivation mechanisms, strongly connected to the charge laying inside the SiN_x layer, we have collected the Infrared spectra of the SiN_x/a-Si:H/c-Si structures and we have monitored the capacitance-voltage profiles of Al/SiN_x/a-Si:H/c-Si Metal Insulator Semiconductor structures at different stages of UltraViolet (UV) light exposure. Finally we have verified the stability of the double passivation layer applied to the front side of solar cell devices by measuring their photovoltaic parameters during the UV light exposure.     

The charge transport properties of a-Si:H thin films under hydrostatic pressure

Time resolved thermoelectric effects (TTE) were used to simultaneously determine trap levels and trap state density differences in amorphous (a-Si:H) samples. In particular, the trap state density differences are obtained from the decay of the ambipolar charge distribution, i.e. stage 2 of the TTE transients. The trap state difference density is measured under hydrostatic pressures, up to 2.2 kbar. The trap state density difference changes from a negative peak to a positive peak with increasing hydrostatic pressure, suggesting a significant pressure induced shift of the electron and hole trap levels.     

An equation of state for porous materials under shock loading

Based on the physical interpretation of the linear equation of state (EOS) of dense solids under shock loading, which relates particle and shock speeds asU _s=C _b+gU _p, the EOS for porous solids has been developed and is expressed asU _s*=ΨC _b*+g*U _p whereC _b* andg* are effective bulk sound speed and effective inverse ultimate volume strain respectively. Ψ is a pore collapse function introduced specially to differentiate loading and unloading behaviour.C _b* andg* are derived theoretically whereas Ψ is established empirically as Ψ=f(U _p,C _b). This EOS does not call for any experimentally established material constant to describe the effect of porosity. Also its ability to describe the unloading behaviour distinguishes it from the presently available equations of state.     

高效纤维-石膏功能复合吸声材料的研制

以高强石膏为胶凝材料,内掺玻璃纤维,制备出一种新型多孔吸声材料.实验发现,孔隙率、平均孔径大小、玻璃纤维含量、发气剂含量对材料吸声性能有显著影响.采用驻波管法测试材料的吸声系数.结果表明材料的平均吸声系数和降噪系数分别达0.58和0.60,且材料的中低频吸声性能优良.     

基于数值-解析方法测量静压条件下阻尼材料动态力学参数

建立了一种测量静压条件下阻尼材料动态力学参数的数值-解析方法。首先,分别制作两种空腔半径不同的圆柱空腔覆盖层样品,测量两种样品在静压力下的复反射系数。其次,采用有限元法仿真静压力下的空腔结构变形,在此基础上同样采用有限元法计算复反射系数。以实测复反射系数和计算复反射系数建立二元非线性方程组,利用牛顿迭代法求解方程组可获得复弹性模量和复泊松比等黏弹性动态力学参数。对聚氨酯材料制作的样品进行了复反射系数测量,分析了静压力对聚氨酯材料动态力学参数的影响规律。最后,测量了某不同结构吸声覆盖层静压下的反射系数,并与采用实测材料参数计算的反射系数进行了比较,验证了该方法的正确性。     

Preparation and performance of shape-stable phase change materials based on carbonized-abandoned orange peel and paraffin

Phase change materials (PCMs) require an excellent matrix support material such as porous carbon materials. Orange peel, a discarded, readily available raw material, could potentially be used to prepare biological porous carbon material (BPCM) with abundant pores of uniform size and strong loading capacity through a vacuum freeing method and a carbonization process under nitrogen atmosphere. Herein, paraffin (PA) was encapsulated into BPCM by vacuum impregnation method to obtain environmentally friendly; recyclable PA/carbonized-abandoned orange peel (CAOP) shape-stable PCMs (PA/CAOP SS-PCMs). CAOP was composed of amorphous carbon and a certain degree of graphitization occurred, the best of which was observed following carbonization at 1000?°C. Further, at this temperature, the pores were abundant and PA loading was sufficient. PA/CAOP SS-PCMs were shown to undergo simple physical loading with no chemical interactions and to have good thermal stability and a maximum loading percentage of 88.46%; the calculated maximum loading percentage was of 88.07%. The temperature and latent heat during the melting of PA/CAOP SS-PCMs were 47.68?°C and 180.25?J/g, respectively, and the solidification process occurred 34.47?°C and 177.55?J/g, respectively. The composite exhibited excellent thermal stability and reliability after 200 thermal cycles. Therefore, it has very broad application prospects and value in the fields of energy saving and emission reduction, including solar energy, air conditioning storage cooling systems, and building cladding.     

Application of BIB polishing technology in cross-section preparation of porous,layered and powder materials: A review

For the accuracy of experimental results, preparing a high quality polished surface and cross-section of the materials for further analysis using electron backscattered diffraction (EBSD), electron probe microanalysis (EPMA), and scanning probe microscopy (SPM) is extremely important. Broad ion beam (BIB) polishing, a method based on the principle of ion bombardment, has irreplaceable advantages. It makes up for the drawbacks and limitations of traditional polishing methods such as mechanical polishing, electrochemical polishing, and chemical polishing. The ions will not leave the bombardment area during polishing, which makes the BIB method suitable for porous materials. The energy of the ion beam can be adjusted according to the sample to reduce the deformation and strain of the polishing area, especially for fragile, soft, and hard materials. The conditions that need to be controlled during BIB polishing are simple. This paper demonstrated the unique advantages of BIB polishing technology in porous, layered and powder materials characterization through some typical application examples, and guided more researchers to understand and utilize BIB polishing technology in the development of new applications.     

边界条件对多孔材料声学参数测试的影响研究

多孔材料声学特征参数测试前需要采用机械切割方法和样品容器匹配,然而切割后的材料边缘不能完全和样品容器匹配,因此采用加环的方式进行处理。以三聚氰胺泡沫为例,通过控制测试材料的边界条件,测试材料的流阻率,在软件中选用合适的声学模型计算得出该材料的声学特征参数。最后将阻抗管测试得到的吸声系数与AMDesigner仿真得到的吸声系数进行比较。结果显示,加两个环后仿真得到的值与测试值吻合效果较好,加一个环在低频区吻合效果较好,而直接将切割得到的材料进行测试效果最差。该研究可以为今后的声学材料测试研究提供指导。     

两次离心挂浆工艺制备网眼多孔陶瓷

以具有三维网状结构和贯通气孔的聚氨酯泡沫体为载体,采用两次离心挂浆工艺制备了高气孔率、无堵孔且结构均匀可控的氮化硅网眼多孔陶瓷.借助TG-DSC分析了泡沫体的热分解过程,确定了排胶工艺.借助流变测量和光学显微镜观察了挂浆工艺及浆料粘度对泡沫体挂浆量和多孔结构的影响,并对制品材料的微观结构和性能进行了表征.结果表明,与传统辊压工艺相比,采用两次离心挂浆工艺后,改善了多孔结构的均匀性,显著提高了材料强度,为高强度、结构可控、网眼多孔陶瓷的制备提供了一个有效途径.     

云母和页岩对铁尾矿基多孔保温材料微观性能的影响

为了高附加值地利用铁尾矿,实验以铁尾矿、页岩和云母为基材并添加适量的长石和发泡剂,通过烧结的方法制备铁尾矿基多孔保温材料。采用TGA法分析云母和页岩掺量对粉料低共熔温度和烧成温度的影响,利用XRD、SEM研究云母和页岩比例的变化对铁尾矿基多孔保温材料矿物组成和形貌的影响。结果表明云母-页岩二元体系中云母含量的增加会降低试样的低共熔温度和烧成温度;页岩含量的增加能促使更多的石英参与反应生成斜长石,试样中斜长石的含量略有增加,石英则有所降低;试样内部含有大量分布均匀的气孔,最大孔的孔径约为2mm,在大气孔之间和内部存在许多小气孔。     

Determination of the crystallinity of cephalexin in pharmaceutical formulations by chemometrical near-infrared spectroscopy

Background: Near-infrared (NIR) spectroscopy has gained wide acceptance in the pharmaceutical industry as a rapid and non destructive method for drug identification and the determination of the drug content of preparations. Aim: The crystallinity of cephalexin (CEX) in microcrystalline cellulose (MCC) was determined using a nondestructive NIR reflectance spectroscopic technique. The molecular interaction of a ground amorphous solid of CEX was investigated by the method. Method: Six kinds of standard material with various degrees of crystallinity were prepared by the physical mixing of crystalline, amorphous CEX, and MCC. X-ray powder diffraction profiles and NIR spectra were recorded for standard samples. A chemometric analysis of the NIR spectral data sets was conducted using principal component regression (PCR). Results: The correlation between the actual crystallinity of CEX and that predicted using the conventional X-ray diffraction method showed a straight line with a slope of 1.000, an intercept of ?2.071 × 10^?5 and a correlation coefficient of determination (R²) of 0.974. The NIR spectrum of amorphous CEX showed significantly different peaks at 1176 and 1206 nm because of the CH₃ group from those of CEX. PCR was performed on various kinds of pretransformed NIR spectral data sets of standard samples of CEX. To minimize the SE of cross-validation (SECV), the spectral data sets were subjected to the leave-one-out method. The second derivative treatment in the range of 1176–1206 nm yielded the lowest SECV values. Based on a two-component model, a plot of the calibration data between the actual crystallinity of CEX and that predicted by the NIR method was obtained. The plot showed a straight line (Y = 0.995X + 0.117 and R² = 0.994; n = 18). The mean bias for the NIR and X-ray powder diffraction methods was calculated to be 1.52% and 2.26%, and mean accuracy was 3.06% and 7.14%, respectively. Conclusion: NIR spectral changes of crystalline CEX during grinding suggested that the intermolecular hydrogen bonds between the amino and carboxyl groups are destroyed and the binding of methyl groups is heightened by the resonance effect of carboxyl groups, and the crystals are transformed into amorphous CEX.     

聚硅氧烷型交联剂的制备及其在聚合物多孔材料中的应用

为了获得性能优异的聚合物多孔材料,首先,在封端剂六甲基二硅氧烷(MM)的存在下,通过硅酸钠与甲基丙烯酰氧基丙基三甲氧基硅烷(MPS)的水解缩聚反应制备了含甲基丙烯酰氧基丙基官能基团的MTQ有机硅树脂;然后,以MTQ硅树脂为交联剂,丙烯酸异辛酯(EHA)为单体,利用高内相比乳液模板法制备了MTQ硅树脂/聚丙烯酸异辛酯(PEHA)聚合物多孔材料;最后,对该多孔材料的孔结构、压缩性能和热稳定性进行了研究。结果表明:采用MTQ硅树脂作为交联剂制备得到的MTQ硅树脂/PEHA聚合物多孔材料的泡孔孔径介于4~10μm范围内,毛孔孔径分布于0.3~2.0μm区间内;泡孔之间紧密相连,毛孔均匀分布且通道较窄。MTQ硅树脂含量对MTQ硅树脂/PEHA聚合物多孔材料的比表面积和孔容的影响较小,但可显著提高聚合物多孔材料的热稳定性和压缩强度;在氮气氛围下,聚合物多孔材料的最大热分解速率温度可达411.5℃。