Differences between films and monoliths of sol-gel derived aluminas

This work compares thin layers (films) and monoliths prepared from alumina sols with respect to their microstructure, thermal evolution, porosity and specific surface area. After heat treatment at similar temperatures, films and monoliths showed the same qualitative changes in porosity and specific surface area. However, some marked quantitative differences were detected. Film fragments had a lower open porosity, a lower specific surface area and a narrower pore size distribution. Furthermore, the thermal evolution showed a markedly different burnout of organic components between films and monoliths. The observed differences between films and monolith can be explained by the ageing history of the sols during sample preparation.     

热态流变对中间相基炭材料导热性能的影响

以中间相沥青为原料,在变径模具中通过热态高压流变剪切促进分子有序排列制备了中间相有序块体导热炭材料。采用XRD、SEM和偏光显微镜表征了流变收缩比(1∶1、2∶1、2.5∶1和3∶1)对中间相有序排列块体炭材料微观织构及导热性能的影响。结果表明:中间相沥青在高压流变剪切的作用下实现了中间相炭微球之间的融并和有序生长,最终形成了微观有序、类纤维结构特征的块体炭材料。流变收缩比的提高,促进了中间相炭微球之间的融并生长,从而有利于获得更为完美的石墨结构。流变剪切不仅促进了中间相炭微球之间的有序融并在轴向形成了类纤维组织结构,而且能够促进径向不同层面之间中间相炭微球有序融并所形成细棒状纤维结构,正是该结构的存在改善增加了样品的导热系数。当流变收缩比由1∶1增加到3∶1时,样品轴向导热系数由96.88 W/(m.K)增大至131.02 W/(m.K),径向导热系数由140.85 W/(m.K)增大至160.46 W/(m.K)。流变收缩比的提高缩小了样品两维方向上导热特性的差异。     

Porous CS monoliths and their adsorption ability for heavy metal ions

Highly porous chitosan (CS) monoliths were prepared by a unidirectional freeze-drying method and the adsorption performance of the monoliths for metal ions in aqueous solution was evaluated. The porous CS monoliths have excellent adsorption for a range of metal ions. The effect of the amount of porous CS monoliths, the pH, the adsorption time, the amount of the cross-linking agent, and the amount of disodium ethylenediamine tetraacetate (EDTA) on the saturated adsorption efficiency (Ade) were determined. The pH had the greatest influence on the adsorption behavior. Under optimal conditions (C(CU2?) = 800 mg/L, pH 6, and cross-linking agent = 0.15%) for the CS monoliths, the Ade for Cu(2+) exceeded 99%, and the saturated adsorption capacity (Q(s)) reached a value of 141.8 mg/g (2.23 mmol/g) in 4h. Moreover, the addition of EDTA can both increase the Q(s) and shorten the time that achieved the level. If EDTA was added, this level was achieved in 2h. The porous CS monoliths can be regenerated by soaking them in acid and their Ade is maintained.     

High-performance liquid-crystalline polymer films for monolithic “composites”

Highly oriented, free-standing films of a thermotropic liquid-crystalline polymer (LCP) were prepared using a new processing technique, referred to as “foil-spintrusion”. These films underwent solid-state fusion at elevated temperatures to yield homogeneous, self-reinforced monolithic “composites” without the use of additional adhesives. In this study, unidirectional LCP monoliths were evaluated for their mechanical performance. The monoliths exhibited highly anisotropic behavior, with stiffness and tensile strength along the direction of orientation of around 65 GPa and 1.7 GPa, respectively, combined with excellent damping properties in the viscoelastic regime. In addition, experiments showed that the material has a high tensile strength (>2.2 GPa) at high strain rates, indicating promising behavior under high impact conditions. As expected for such highly oriented polymer systems, the monoliths were found to exhibit poor compressive and shear strengths due to low internal coherence of the material itself. However, it was shown that the LCP monoliths could be useful for applications requiring high specific stiffness, for example as facings for composite sandwich panels.     

Interconnect thermal expansion matching to solid oxide fuel cells

A method for the rapid fabrication of homogeneous potential interconnect alloys from metal oxide precursors and evaluation of their thermal expansion mismatch to solid oxide fuel cells is described. Pastes of metal oxide powders were extruded into honeycomb geometries and sintered in hydrogen. Thermal expansion mismatch was evaluated based on heating with a zero-mismatch at room temperature, and on cooling with zero-mismatch temperatures at 600 or 1100∘C. The non-linear expansion behavior of Fe-Ni invar alloys resulted in different compositions being optimum, based on the assumed zero-mismatch temperature.     

聚砜酰胺/聚氨酯纳米复合纤维的制备与表征

将聚砜酰胺(PSA)与聚氨酯(PU)共混制成PSA/PU纺丝液。分别采用静电纺丝工艺以及数显匀胶技术制成复合纤维和复合薄膜。运用布氏粘度计、扫描电镜、傅里叶变换红外光谱、广角X射线衍射、单纤维强力仪等方法表征和分析复合材料的粘度、大分子结构、力学性能、热稳定性。实验结果表明:PSA、PU共混没有改变两者的分子结构和化学组成;不同比例的共混纤维成形良好,直径随粘度而变化;PU明显提高了PSA的强度和断裂伸长,PSA的增加延缓了PU的热分解行为。     

铸态退火2024合金在不同温度下的变形行为

使用MMS-200热力模拟实验机研究了工程用铸态退火2024合金(ϕ247 mm)在不同温度下的变形行为,建立了热变形的本构方程和DMM(Dynamic material model)加工图。分析了铸锭退火态、等温挤压及等温挤压退火实验件的微观组织和力学性能,结果表明：根据DMM加工图确定的热变形温度395~450℃和应变速率0.01~0.1 s^-1工艺,可制备出组织明显细化、力学性能优异的大挤压比2024铝合金等温挤压件。     

Anisotropy of the fatigue behavior of extruded and rolled magnesium alloys

Fatigue tests were conducted using both extruded and rolled magnesium alloys AZ31 to study anisotropy of the fatigue behavior of the alloys. For the above purpose, two types of specimens whose longitudinal axes are parallel (E specimen) and perpendicular (T specimen) to the extrusion direction were prepared for the extruded Mg alloy. For the rolled Mg alloy, three types of specimens, whose longitudinal axes are parallel (R specimen) and perpendicular (T and S specimens) to the rolling direction, were prepared. S–N curves and crack propagation characteristics for both the extruded and rolled specimens with different longitudinal directions were studied to investigate the effects of the texture, microstructures and residual stresses on the fatigue behavior of the magnesium alloy AZ31. Anisotropy of the fatigue behavior was observed for both the extruded and the rolled magnesium alloys. In the extruded Mg alloy, differences in both fatigue lives and fatigue limit exist between E and T specimens. The fatigue resistance for the former is superior to that of the latter. In the rolled Mg alloy, lesser differences were found between R and T specimens. However, fatigue lives of the S specimens were clearly shorter than those of the former at the high stress amplitudes above the fatigue limit. In the extruded Mg alloy, the rod-like microstructure observed is an important factor contributing to the anisotropy of the fatigue behavior of the alloy. While in the rolled Mg alloy, the texture induced during processing is considered to play a dominant role in the anisotropy of the fatigue behavior of the alloy.     

具有三维连通网络结构的多孔SiC/C材料的电磁损耗特征

通过有机泡沫浸渍/高温炭化和热压固化/高温炭化两种工艺分别制备了具有宏观三维连通网络结构的SiC/C泡沫和显微三维连通多孔结构的SiC/C泡沫同质压制块。使用谐振腔微扰法对比测试了2450MHz频率下两种材料的电磁参数随电导率的变化。结果表明:随着电导率的增加,SiC/C泡沫及其同质压制块的介电常数实部εr′均逐渐增加;电损耗tgδe均先增加,达到最大值后逐渐减小;SiC/C泡沫的磁损耗tgδm不断增加,而其同质压制块的tgδm值则先快速增加,达到最大值后缓慢下降。当二者具有相同有效电导率时,SiC/C泡沫的εr′值比其同质压制块约小1/2,tgδe值至少大2倍,而压制块的tgδm值超过SiC/C泡沫4倍多。SiC/C泡沫及其同质压制块是非磁性的,它们的磁损耗均由其特殊结构与电磁场相互作用产生的,是一种非本征磁损耗。     

Effects of extrusion ratio on the ratcheting behavior of extruded AZ31B magnesium alloy under asymmetrical uniaxial cyclic loading

Magnesium alloys are increasingly used in the automotive and aerospace industries for weight reduction and fuel savings. The ratcheting behavior of these alloys is therefore an important consideration. The objective of this investigation was to study the effects of extrusion ratio on the ratcheting behavior of extruded AZ31B magnesium alloy. The experiments have shown that the extruded AZ31B Mg alloy presented the following characteristic behavior with increasing number of loading cycles: first an apparent cyclic softening was observed, then a cyclic hardening occurred, and finally a stable state was reached. This generic behavior can be explained by the fact that the variation trend of the maximum strain with the number of cycles differs from that of the minimum strain. The extrusion ratio did not influence the cyclic softening/hardening behavior or the final ratcheting strain variation trend of the extruded AZ31B Mg alloy with the mean stress and the peak stress. However, the extrusion ratio influenced the final ratcheting strain variation trend of the extruded AZ31B Mg alloy with the stress amplitude. Increasing the extrusion ratio also reduced the ratcheting strain and the effects of the load history on the ratcheting behavior of the extruded AZ31B Mg alloy.     

采用表面喷锌及喷硅扁管的微通道换热器长效特性研究

腐蚀特性是全铝微通道换热器的主要特征之一。对两种不同表面处理方式的挤压扁管：表面喷锌挤压扁管和表面喷硅挤压扁管的长效特性进行了对比研究。对采用这两种不同表面处理方式的挤压扁管的微通道换热器样件,分别进行了7天和14天的盐雾腐蚀实验(SWAAT),对比腐蚀前后两个换热器样品的换热量、空气侧压降和总热阻变化情况。结果表明,采用表面喷硅扁管的微通道换热器的长效特性优于采用表面喷锌扁管。     

Distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans in the landfill site for solidified monoliths of fly ash

One landfill site, which co-treated solidified monoliths of fly ash and bottom ash, was investigated comprehensively to characterize its PCDD/F distribution. The solidified monoliths, soil, banyan leaves, groundwater in the monitoring wells and the treated landfill leachates in this landfill site for solidified monoliths of fly ash were all sampled to clarify their PCDD/F characteristics. Although the PCDD/F leaching concentrations were extremely lower than the Taiwan PCDD/F TCLP regulation of solidified monoliths, the PCDD/F contents in the surface soils of the landfill site are 460 times higher than that of urban soils and the highest value is 2.8 times higher than the Taiwan soil regulation (1000 ngI-TEQkg(-1)). The elevated PCDD/F contents in the soil reveal their potential for causing adverse health risk for humans, including the pathway of resuspension of soil particles and volatilization of PCDD/Fs from soil. The PCDD/F concentrations in the groundwater and the treated landfill leachates of the landfill site for solidified monoliths were both higher than that in the control samples, suggesting its potential to be a PCDD/F source of nearby water environment. Without proper control and management, landfill sites for solidified monoliths of fly ash can seriously hazard the surrounding environment, therefore, are important to consider.     

Preparation of lithium aluminosilicate glass-ceramic monolith from metal alkoxide solution

Glass-ceramic monoliths with a composition of Li₂O·Al₂O₃·4SiO₂ have been synthesized by the sol-gel technique using metal alkoxides as starting materials. Heating dried gel monoliths of about 36 mm diameter and height to appropriate temperatures gave glass-ceramic monoliths of about 20 mm diameter and height without the occurrence of cracks, while a melt-derived glass body of the same composition was cracked or softened on heating. The glass-ceramic monoliths obtained by heating gel monoliths at 1000 C for 40 h were a porous body, whose bulk density and porosity were 1.62 g cm^–3 and 34%, respectively. On heating gel monoliths, -eucryptite crystals were first precipitated around 750 C, followed by precipitation of -spodumene crystals at 830 C. At higher temperatures the latter grew at the expense of the former phase. The crystallized specimens exhibited very low thermal expansion coefficient ranging from –13-12×10^–7 C^–1 at temperatures from room temperature to 700 C depending on the heat-treatment temperature of gels, indicating that a porous glass-ceramic monolith with ultra-low thermal expansion can be prepared using the present sol-gel method.     

Dimensional stability and thermal stress of 6061 Al/SiCw composite during thermal cycles

Abstract

The variations of dimensions and thermal stress of 6061Al/20 vol.-%SiC_w composites were investigated during thermal cycles between 25 and 300°C. Testing results showed that the dimensional stability and thermal stress are mainly related to the whisker distribution in the composite. For the as cast composite, owing to the whiskers being oriented randomly, the temperature cycles hardly affect the dimensions of the specimen, so this material has good dimensional stability. However, for the as extruded composite, owing to whisker alignment, the thermal cycles can evidently affect the dimensions of the specimen, i.e. the dimension is elongated in the alignment direction of whiskers and shortened in another direction. The dimensional stability of the as extruded composite can be improved somewhat by thermal precycles.     

Thermal properties of high-porosity monoliths based on exfoliated graphite

High-porosity monoliths with densities in the range 50 to 300 kg/m³ have been prepared by uniaxial pressing of exfoliated graphite and their thermophysical properties have been investigated both along and across the pressing direction. We have determined strength characteristics of the monoliths: elastic modulus in compression and bending strength. The procedure used to prepare exfoliated graphite is shown to influence the physicomechanical properties of the monoliths.     

挤压Mg-4.5Zn-0.75Y合金的热变形行为

为了研究只含准晶相Mg-Zn-Y合金的高温力学性能并获得其较优的加工参数,本文首先制备了含有I-Phase的挤压Mg-4.5Zn-0.75Y(原子数分数/%,下同)合金,并在Gleeble-3500热/力模拟实验机上对其高温变形行为进行了研究,实验温度为300、350、400℃,应变速率为0.01、0.1、1 s~(-1).在此基础上,建立了该合金的流变应力本构方程及DMM加工图,并结合压缩后的显微组织制定较优的加工工艺参数.结果表明:应变速率和加工温度对流变应力有显著的影响;挤压Mg-4.5Zn-0.75Y合金的平均变形激活能和应力指数分别为107.95 kJ/mol和3.996 6;挤压Mg-4.5Zn-0.75Y合金具有较好的热塑性,在实验条件下并没有发生失稳现象,说明准晶相的存在提高了合金的变形能力;压缩后的显微组织显示,当温度为300~350℃、应变速率0.1~1s~(-1)时,合金压缩后为均匀细小的等轴晶;综合Mg-4.5Zn-0.75Y合金的加工图与压缩后的显微组织图,确定了该合金热加工的较优工艺参数为:θ=300~350℃;ε·=0.1~1s~(-1).     

热处理对挤压变形AM20镁合金疲劳性能的影响

本文研究了固溶处理和固溶＋时效处理对挤压变形AM20镁合金低周疲劳性能的影响。结果表明,不同制度的热处理对挤压变形AM20镁合金循环变形抗力的影响与外加总应变幅的高低有关;不同处理状态的挤压变形AM20镁合金的塑性应变幅、弹性应变幅与疲劳断裂时的载荷反向周次之间的关系可分别用Coffin--Manson和Basquin公式来描述。此外,不同处理状态的挤压变形AM20镁合金的循环应力幅与塑性应变幅之间呈线性关系。     

一步浸渍合成具有多重孔隙的铸型炭体

以多孔块状硅体为模板,通过一步浸渍、炭化、酸处理工艺,制备出结构可控、孔隙联通且具有多重孔隙的铸型炭体。分别采用氮吸附技术、高分辨透射电镜和扫描电镜对模板硅、硅碳复合物及相应炭体进行了结构表征。从微米尺度分析,该炭体是由高度联接的枝状结构单元为骨架构筑而成。与模板硅相比较,此炭体是硅体的正复本。从纳米尺度分析,这种炭体枝状骨架是由分布均匀且相互连接的中孔构成,此中孔及其孔壁对应于模板硅的孔壁及中孔,是多孔硅的负复本。此外构成中孔的炭骨架本体又含有大量炭化过程产生的微孔。因此该法合成的铸型炭具有孔隙高度发达和结构层层嵌套的特点。     

Facile preparation of zwitterionic organic-silica hybrid monolithic capillary column with an improved "one-pot" approach for hydrophilic-interaction liquid chromatography (HILIC)

A simple single-step thermal-treatment "one-pot" approach for the preparation of organic-silica hybrid capillary monolithic columns is described. In this improved method, the cross-linker vinyltrimethoxysilane (VTMS) was replaced by 3-methacryloxypropyltrimethoxysilane (γ-MAPS), which is more active in polymerization reactions, and only one thermal treatment step was required in the preparation of hybrid monoliths. Two zwitterionic organic-silica monolithic columns were successfully synthesized by using [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (MSA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) as the organic monomers. The effects of the tetramethoxysilane (TMOS)/γ-MAPS molar ratio, content of monomer, composition of porogenic solvent, and reaction temperature on the morphologies of the hybrid monoliths were investigated. The MSA-silica and MPC-silica hybrid monolithic columns exhibited good permeability and good mechanical stability. The monolithic columns were used for the separation of polar compounds by capillary hydrophilic-interaction chromatography (cHILIC). A typical HILIC retention mechanism was observed at higher organic solvent contents (>50% ACN). The MSA monoliths were further investigated in the separation of various neutral, basic, and acidic analytes, as well as small peptides, by capillary liquid chromatography (cLC), and high efficiency and satisfactory reproducibility were achieved. In addition, the analysis of a tryptic digest of bovine serum albumin (BSA) by cLC tandem mass spectrometry (cLC-MS/MS) with an MSA monolith further demonstrated its potential in the separation of biological samples.     

粉末粒度对高硅铝合金材料组织及性能的影响

采用空气雾化水冷与真空包套热挤压工艺相结合的方法,制备了Al-40Si高硅铝合金,并利用金相显微镜、扫描电镜、万能电子拉伸机、差热分析仪等设备系统测试和分析了该材料的显微组织、力学和热物理性能.研究表明:当原始粉末粒度较粗时,经热挤压后材料的显微组织中硅相粗大,致密度与气密性较低,抗拉强度较小,导热性能和热膨胀系数较大.