低密度TMPTA泡沫的制备及表征

低密度聚合物泡沫在惯性约束聚变靶及电磁内爆靶中应用十分广泛。以三羟甲基丙烷三丙烯酸酯(TMP-TA)为聚合单体,安息香甲基醚为引发剂,通过紫外光引发生成凝胶,经超临界干燥得到TMPTA泡沫材料。通过红外光谱仪和元素分析仪确定了TMPTA单体中官能团转化率及泡沫纯度的表征。实验结果表明,聚合反应过程中,在1636cm-1附近碳碳双键(C=C)的转化率为40.48%,泡沫为高纯度的低密度TMPTA泡沫,机械强度可满足核磁内爆靶(Z-pinch)靶装配的需求。     

超低密度CHO泡沫结构与力学性能研究

基于溶胶-凝胶技术,通过不同的干燥方式,制备了3种10 mg/cm~3的CHO泡沫,并对泡沫的显微形貌、孔结构分布以及力学性能进行了测试分析。结果表明,通过超临界干燥技术制备得到的三乙酸纤维素(TAC)泡沫力学性能最佳,其弹性模量为3.50×10~4 Pa,冷冻干燥制得的TAC泡沫弹性模量为3.38×10~4 Pa,冷冻干燥获得的TMPTA(聚三羟甲基丙烷三丙烯酸酯)泡沫力学性能最差,其弹性模量仅为0.36×10~4 Pa。超临界干燥TAC泡沫中的孔径较小(数纳米至十几纳米量级),孔径分布较为均匀。冷冻干燥的TAC泡沫孔径增大(几十纳米量级),孔径分布较宽。冷冻干燥的TMPTA泡沫孔径最大(百纳米量级孔洞大幅增加),孔径分布最宽。     

静压箱作用半径及送风口密度对送风均匀性的影响

地板送风系统以其布置与调节方式灵活、节能和为活动区创造良好的空气品质等诸多优点,得到越来越广泛的应用.本文运用Fluent建立地板送风系统静压箱模型,分析作用半径和送风口密度对静压箱送风均匀性的影响,为工程设计提供一定的参考.     

基于沥青混合料各组分密度的内部结构均匀性分析

为了有效地测试和评价沥青混合料内部结构均匀性,应用X-ray CT技术和数字图像处理方法,考虑粗集料、砂浆和空隙各组分的作用,提出了一种基于沥青混合料各组分密度的内部结构均匀性识别方法,选用4组不同油石比的沥青混合料试件,利用该方法对其内部结构均匀性进行了分析。结果表明:基于该方法提出的均匀性评价参数可以识别单一或一组沥青混合料试件的内部结构均匀性,并且通过分析计算得到沥青混合料的最佳油石比与室内试验获得的相差0.21%,这表明均匀性识别方法的有效性。     

不同密度聚酰亚胺泡沫的制备与性能

制备了基于3,3’-4,4’-二苯甲酮四酸二酐(BTDA)、多苯基多亚甲基多异氰酸酯(PAPI)及二苯甲烷二异氰酸酯(MDI)的聚酰亚胺泡沫,通过改变发泡时的环境压力,制备了不同密度的泡沫;利用红外光谱和扫描电镜对所制备的聚酰亚胺泡沫进行了结构与形貌表征,并对泡沫热性能和压缩强度行了表征。结果表明,所制备的泡沫密度随着制备压力的增大而增加,泡沫密度为7.3~160kg/m~3,红外光谱确认了目标聚合物的合成,泡沫T_g不低于250℃,且具有良好的热稳定性,经过250℃处理的泡沫的T_g达到270℃,T_(d5%)达到404℃,均高于230℃处理得到的泡沫的性能。压缩性能测试表明所制备泡沫压缩强度随着密度增加而增加,当密度为160kg/m~3时,压缩强度达到1.88 MPa。     

全息涂料涂布均匀性影响因素分析及其数学描述

研究了工艺参数对全息涂料涂布均匀性的影响规律,给出了涂膜光学密度变化的数学表达式,以及定量评价涂布不均匀度的方法,为涂布工艺参数的优化设计,提供了理论依据.     

增韧改性酚醛泡沫的烟密度和宏观燃烧行为探究

针对酚醛泡沫的脆性、易粉化性、吸水性等问题,通过物理和化学结合方式在酚醛结构中引入柔性分子链,并复配适量的短玻璃纤维和有机蒙脱土.实验结果表明:改性酚醛泡沫的力学强度、粉化性、吸水性等都有较为显著提高,同时改性酚醛泡沫的热解燃烧性能得到一定程度的改善.本文还对增韧改性酚醛泡沫的烟密度和宏观燃烧行为进行系统描述,为酚醛泡...     

活性炭和活性炭纤维的能量不均匀性

活性炭和活性炭纤维的能量不均匀性Ｍ．ＪａｒｏｎｉｅｃＲ．Ｋ．ＧｉｌｐｉｎａｎｄＭ．Ｈｅｕｃｈｅｌ引言在各种多孔性固体中，具有微孔的炭材料如活性炭和活性炭纤维在工业领域、科研及日常生活中都有着广泛的用途（１）。这些材料具有明显的多相性。这是因为它们含有...     

一种非均匀采样系统采样均匀性的评价新方法

提出了在多A/D合成采样系统中采样均匀性的评价方法;通过使用正弦波激励系统,将各个子A/D的数据分别抽取形成子抽样序列,使用最小二乘正弦波曲线拟合法,获得各个子抽样序列初始相位间的差异,该差异对应的时间差即为各个子A/D间的采样延迟时间,它们的一致性就是系统的采样均匀性。在一组仿真数据上验证了方法的正确性。在数字存储示波器的实测数据上进行了实验验证,获得了有效的测量结果,验证了方法的可行性。该方法可以用来评价非均匀采样系统的采样均匀性。     

可发性聚苯乙烯泡沫材料密度与压缩强度的关系及其应用

介绍我国现阶段普遍采用的螺旋传动，蒸汽加热发泡工艺生产的可发性聚苯乙烯泡沫材料密度与压缩强度（压缩５０％时）的关系，分析成果应用的可行性和给工厂带来的经济效益。     

Preparation and characterization of ultra-low density porous gold foams

We present a simple approach to generate ultra-low density porous gold foams with the density as low as 0.519 gcm^-3. In our work, gold nanoparticles with small grain sizes and good solubility were prepared and used as starting building blocks; afterwards, the freeze-dry technique was employed to prepare gold compound foams. Finally the gold compound foams were sintered to obtain porous gold foams with ultra-low density. The results show that the content of gold element in the foams is close to 99.2%. Even though the density is as low as 0.519 gcm^-3 the foams still have good intensity and can be machined to simple regular shapes. The microstructure analysis results indicate that the gold foams have continuous open structure, the average pores size is about 1-2 μm, and the framework of the gold foams is piled up with gold particles of different sizes. Our approach might give a way to produce low-density gold foams with simple fabrication procedures.     

海水槽控温波动性及均匀性的概率密度分布分析

针对海水槽控温波动性和均匀性所满足概率分布的推断问题,提出一种基于卡方检验的概率密度函数统计推断方法。该方法由波动性和均匀性测量数据的直方图获取其概率分布的直观印象,进而确定概率分布函数的数学形式。采用最大似然法对函数未知参数进行估计;由卡方检验法实现对其概率分布的严格统计推断。通过测量数据的分析,得到海水槽控温波动性和均匀性的概率密度分布函数,避免在海水槽测量不确定度评定中主观确定概率分布函数等问题。     

Processing of sucrose to low density carbon foams

A novel process for preparation low density carbon foams from sucrose has been demonstrated. A resin prepared by heating aqueous acidic sucrose solution when heated in an open Teflon mould at 120 °C undergoes foaming and then setting in to a solid organic foam. The solid organic foam undergoes carbonization in air by dehydration at 250 °C under isothermal condition. Carbon foams thus obtained sintered at temperature in the range 600–1,400 °C showed density in the range 115–145 mg/cc and electrical conductivity in the range 1.5 × 10⁻⁵ to 0.2 ohm⁻¹ cm⁻¹, respectively. The carbon foams contain spherical cells of size in the range 450–850 μm and the cells are interconnected through circular or oval shape windows of size in the range 80–300 μm. The carbon foam samples sintered at 1,400 °C showed compressive strength of 0.89 MPa.     

Effects of density and strain rate on properties of syntactic foams

Syntactic foams are characterized for high strain rate compressive properties using Split-Hopkinson Pressure Bar (SHPB) technique in this study. The results at high strain rates are compared to quasi-static strain rate compressive properties of the same material. Four different types of syntactic foams are fabricated with the same matrix resin system but different size microballoons for testing purpose. The microballoons have the same outer radius. However, their internal radius is different leading to a difference in their density and strength. The volume fraction of the microballoons in syntactic foams is maintained at 0.65. Such an approach is helpful in isolating and identifying the contribution of matrix and microballoons to the dynamic compressive properties of syntactic foams. Results demonstrate considerable increase in peak strength of syntactic foams for higher strain rates and increasing density. It is also observed that the elastic modulus increases with increasing strain rate and density. Scanning electron microscopy is carried out to understand the fracture modes of these materials and the density effect on high strain rate properties of syntactic foam.     

Tailoring properties of reticulated vitreous carbon foams with tunable density

Reticulated vitreous carbon (RVC) foams were manufactured by multiple replications of a polyurethane foam template structure using ethanolic solutions of phenolic resin. The aims were to create an algorithm of fine tuning the precursor foam density and ensure an open-cell reticulated porous structure in a wide density range. The precursor foams were pyrolyzed in inert atmospheres at 700°C, 1100°C and 2000°C, and RVC foams with fully open cells and tunable bulk densities within 0.09–0.42 g/cm³ were synthesized. The foams were characterized in terms of porous structure, carbon lattice parameters, mechanical properties, thermal conductivity, electric conductivity, and corrosive resistance. The reported manufacturing approach is suitable for designing the foam microstructure, including the strut design with a graded microstructure.     

Morphological and biological characterization of density engineered foams fabricated by ultrasonic sonication

The successful manufacture of functionally tailored materials (e.g., density engineered foams) for advanced applications (e.g., structures or in bioengineering) requires an effective control over the process variables. In order to achieve this, density gradation needs to be represented and quantified. Current density measurement techniques offer information on bulk values, but neglect local position as valuable information (i.e., do not associate density scalar values with specific location, which is frequently critical when mechanical properties or functionalities have to be engineered). In this article, we present a method that characterizes the density gradation of engineered foams manufactured by the sonication technique, which allows the generation of sophisticated porous architectures beyond a simple linear gradient. A 3D data capture (μCT) and a flexible analysis software program (ImageJ) are used to obtain “global” density gradation values that can, ultimately, inform, control, and optimize the manufacture process. Polymeric foams, i.e., polyurethane (PU) foams, were used in this study as proof of concept. The measurements performed on the PU foams were validated by checking consistency in the results for both horizontal and vertical image slices. Biological characterization was done to assess the samples’ tailored structure viability as scaffolds for tissue engineering. The comparison between untreated and sonicated samples yielded a 12.7% of increment in living cell count adhered to the walls after treatment. The conclusions drawn from this study may inform the design and manufacture of density-engineered materials used in other fields (e.g., structural materials, optoelectronics, food technology, etc.)     

相对密度对泡沫铝力学性能和能量吸收性能的影响

对不同相对密度的两种胞孔结构--开孔和闭孔泡沫铝进行了单轴压缩试验,研究了相对密度对泡沫铝力学性能和能量吸收性能的影响.结果表明:随着相对密度的增大,泡沫铝的屈服强度与流动应力也相应增加,通过对本实验结果进行拟合,得出泡沫铝的屈服强度与相对密度的关系式.泡沫铝材料吸收的能量随着应变量的增大而增加,在相同应变量下,高密度开孔泡沫铝的吸收能比低密度闭孔材料多.吸能效率反映材料本身的一种属性,高的理想吸能效率表明泡沫铝是一种优良的吸能材料.     

Elastic modulus dependence on density for polymeric foams with systematically changing microstructures

Several series of foams were prepared by filling an open-cellular foam preform with varying amounts of polymer. The foams had systematically changing cellular structures and their compressive moduli were found to vary as the square of the density. A change from plastic to elastic-plastic behaviour occurred as the density increased. Current mathematical models did not adequately handle the observed relationship between yield strength and density.