以天然沥青岩为原料制备高压缩强度的泡沫炭(英文)

以安纳托利亚东南部的天然沥青岩为原料制备泡沫炭。所制泡沫炭的平均孔径和密度分别为150μm和800 kg/m3。主要研究了压力、温度、泄压时间及在最高温度时的停留时间对泡沫形成的影响,同时还评价了炭化过程对泡沫结构的影响。主要研究了压力、温度、泄压时间及在最高温度时的停留时间对泡沫炭进行了表征,并进行了密度及抗压强度分析。结果表明,1 323 K炭化后,泡沫炭压缩强度由10 MPa增加到18.7 MPa。沥青的灰分含量(41.76%)对泡沫炭的密度和压缩强度起重要作用。     

乙炔黑改性薄壁泡沫炭复合材料的性能研究

以童亭原煤经全组分分离所得的疏中质组为原料,乙炔黑为添加剂,通过简单的炭化过程制备了乙炔黑/泡沫炭复合材料.研究乙炔黑添加量对泡沫炭复合材料的微观结构、抗压强度和隔热性能的影响.结果表明添加乙炔黑后,泡沫炭复合材料的孔隙率降低,体积密度增加,抗压强度显著提升,导热率下降,200℃下导热率仅为0.057 W/(m·k),...     

酚醛树脂为前驱体制备多孔碳泡沫材料

以液态酚醛树脂为前驱体,正戊烷为发泡剂,吐温80为匀泡剂,在高压釜中通过卸压发泡的方法制备了酚醛树脂泡沫,然后将其经1000℃碳化后得到碳泡沫.研究结果表明,所得的典型碳泡沫样品是一种以无定形碳结构为主的轻质多孔碳材料,密度约为0.15g/cm3.碳泡沫的微结构可以通过调节卸压速率而得到有效控制,当卸压速率为0.05MPa/min时,可以得到孔洞相互贯穿、平均孔径约为300μm且分布较为均匀、接点完好,韧带光滑的多孔碳泡沫.     

前驱体对炭泡沫孔结构的影响

分别以煤沥青、石油中间相沥青和AR沥青为前驱体制备炭泡沫材料。采用GPC测定前驱体分子量,SEM观察所制炭泡沫的孔结构,光学显微镜测量所制炭泡沫的孔径及其分布。结果发现,由于煤焦油沥青不含中间相,且QI含量较高,导致在实验条件下不能直接制备出合格的炭泡沫。以石油中间相沥青和AR沥青为原料均能制备出具有分布均匀开孔结构,且微观各向异性的炭泡沫。由AR沥青制备的炭泡沫呈现平均孔径较小(212μm)、孔壁较薄、孔径分布较窄(180μm~300μm)、开孔率较高、以及韧带排列较规整等特点,表明低QI含量、低分子量且分布较窄的前驱体有利于发泡。     

蒙脱土改性炭泡沫复合材料

以酚醛树脂、BJO-0930酚醛微球为原材料,与适量蒙脱土混合,采用模压成型法制备出酚醛泡沫前驱体,在Ar气保护下进行800℃炭化处理,得到蒙脱土改性闭孔微球型炭泡沫复合材料。探讨蒙脱土对炭泡沫微观结构、压缩强度和热导率的影响。结果表明,蒙脱土改性炭泡沫复合材料的基体相与微球相结合更紧密,孔隙率降低;压缩强度提高到25.54MPa;热导率也明显降低,800℃下的热导率降为0.588W/(m·K)。     

碳热还原氮化法结合泡沫前驱体制备超细氮化铝粉体

本研究使用改良的碳热还原氮化法合成超细氮化铝粉体。以γ氧化铝和蔗糖作为铝源和碳源, 先预处理制备成多孔泡沫, 再通过碳热还原氮化法合成氮化铝粉体。反应过程和产物通过X射线衍射分析、SEM和TEM确定。X射线衍射分析表明整个反应过程不存在氧化铝的相转变。高分辨透射电子显微镜显示γ-Al₂O₃颗粒被无定型碳包裹, 从而抑制了γ-Al₂O₃到α-Al₂O₃的相转变。泡沫的多孔结构促进了氮气的扩散和反应副产物的释放, 使得最低反应温度降低至1450 ℃。SEM结果表明得到的氮化铝颗粒粒径大约为50 nm。本研究合成的氮化铝粉体可用于制备高热导氮化铝陶瓷。     

作为炭材料前驱体的离子液聚合物的简易合成(英文)

采用一步法合成新型离子液聚合物,并以聚合物作为炭材料的前驱体。这种新型离子液聚合物的特征包括:聚合无需添加引发剂,聚合引入的阴离子能够控制材料的微孔大小。以含Cl-的离子液聚合物为前驱体合成的炭材料具有较小的比表面积(47m2/g),而以含较大(三氟甲基磺酰基)亚胺基阴离子的离子液聚合物为前驱体合成的炭材料具有较大的比表面积(595m2/g)。含二氰胺阴离子的离子液聚合物为前驱体合成的炭材料的比表面积为30m2/g。     

酚醛树脂基泡沫炭前驱体热处理过程的研究

酚醛树脂基泡沫炭是一种高性能的高强轻质隔热材料,酚醛泡沫的炭化热处理是制备酚醛树脂基泡沫炭倒丶工艺.本文以热塑性酚醛树脂为原料,采用液相低压发泡方法制备得可进一步炭化制得高性能的泡沫炭的酚醛树脂基泡沫前驱体.通过热分析仪、元素分析仪测试和分析酚醛泡沫体在炭化热处理过程中的重量和元素含量的变化及规律,并研究泡沫体在热处理过程中的径向和轴向尺寸、重量、体积和表观体积密度的变化和规律.结果表明:350～700℃,酚醛树脂泡沫体热失重较剧烈,热解速度最快,失重率约为40%,相应的热解温度会比纯树脂延缓和滞后;在热处理过程中,泡沫体在径向和轴向的收缩是不同步的:随热处理温度的提高,泡沫体的重量和体积不断减小,密度却呈现波折形变化:炭化产物中碳元素的含量随温度的升高而不断增加,各元素含量变化最明显的温度区是350～600℃.     

以酚醛包覆玻璃纤维为前驱体制备廉价活性炭纤维（英文）

以酚醛树脂、聚乙烯醇和糠醛的混合物包覆玻璃纤维,经炭化和氯化锌活化制备出一种廉价的纤维状活性炭材料。表征了这种纤维状活性炭材料的表面形态、微晶结构、孔结构、表面化学特征和机械强度,评价了该材料的吸附性能。结果表明,在炭前驱体中加入聚乙烯醇和糠醛可以有效促进孔隙的发育,提升所制备多孔炭材料的孔隙率。当在前驱体中加入聚乙烯醇和糠醛时,所制多孔炭材料的比表面积可达2 023 m~2/g,否则其比表面积则仅为404 m~2/g。聚乙烯醇的加入提高了氯化锌的溶解性,促进了炭前驱体的活化;而糠醛与酚醛交联结构的形成则提高了炭前驱体的热稳定性,提高了炭得率。这两方面的措施均有利于提高样品的比表面积并降低其制备成本。该纤维状活性炭材料具有与传统活性炭纤维相似的微晶结构和吸附性能。     

Through-thickness compressive strength of a carbon/epoxy composite laminate

As carbon-fiber-reinforced composite materials are increasingly used for heavy-duty self-lubricating bearings, their through-thickness compressive strength (TTCS) has become an important parameter because the TTCS depends on the weave type and stacking sequence of laminates regardless of their tribological properties.In this work, the TTCS of a carbon/epoxy composite bearing material was measured with respect to weave type, stacking sequence, and direction of cut from the laminate. The tests showed that, for unidirectional laminate, cylindrical specimens resulted in the most reliable data of TTCS. However, for woven fabric laminate, cubic specimens with the edge length greater than twice the repeating unit gave reliable results.     

On the compressive strength of glass microballoons-based syntactic foams

This work is concerned with particulate composites filled with hollow spherical inclusions, i.e., syntactic foams. We aim at the micromechanical evaluation of the effective uniaxial compressive strength for the most relevant case of glass inclusions of wall thickness of few micrometers (microballoons) filling a thermoset matrix. We develop a three-dimensional Finite Element (FE) modelling which extends and improves that recently proposed by our group. Different microstructures are described by cubic unit cells containing fifty hollow spheres accounting for different filler polydispersions and filler volume fraction f up to 60%. Each microballoon is assumed to undergo brittle failure according to a structural criterion. Here, we account for the matrix nonlinear behaviour and, in a phenomenological way, for the detriment of its mechanical properties, proportional to its defectiveness, which increases with the filler content and becomes extremely relevant at f larger than 50%. Our findings agree with experimental observations from the literature and reveal room for improvement in the effective mechanical properties by acting on the manufacturing process.     

The effect of polyvinyl alcohol functionalized multiwall carbon nanotubes on the improvement of the compressive strength of concrete

Abstract

Multiwalled carbon nanotubes were functionalized by polyvinyl alcohol in order to synthesize potential additive for concrete to improve mechanical properties. The obtained nanostructure was characterized structurally and surface morphologically by various techniques. These techniques revealed the success of the functionalization process in preparation of the strengthening additive. The mechanical characterization of the concrete composite obtained by the addition of the strengthening additive was performed by the compressive strength method. The results show significant positive effects of the synthesized additive material on the mechanical properties of the prepared concrete composite over the reference material. The novelty of this work is the use of the Fischer esterification reaction for the preparation of the strengthening additives for concrete using polyvinyl alcohol and multiwalled carbon nanotubes.     

Hygrothermal studies on syntactic foams and compressive strength determination

Syntactic foams are commonly used as core materials in composite sandwich structures for weight sensitive applications such as aircraft and spacecraft structures and boat hulls. Moisture absorption is highly undesirable in these applications. The present study evaluates the hygrothermal properties of two types of syntactic foams. Distribution of outer diameter of cenospheres (hollow particles) incorporated in both types of syntactic foams is the same but there is variation in the internal diameter causing difference in the density of syntactic foams. Epoxy resin is used as matrix material and the volume fractions of matrix and cenospheres are kept at 0.35 and 0.65 by volume, respectively. Moisture absorption experiments are conducted at two different temperatures, 25 and 70 °C and in deionized and salt waters. Non-destructive ultrasonic imaging technique is used to find the extent of moisture penetration and damage to the specimens. Syntactic foam samples are tested for compressive strength after moisture absorption and the results are compared with the compression test results of dry syntactic foam samples.     

不同分子量的大豆油基多元醇的制备及其在聚氨酯泡沫塑料制备中的应用

通过热聚合法制备了3种不同分子量、羟值和分子结构的大豆油多元醇(Polyols1,Polyols2和Polyols3)。将它们与多亚甲基多苯基多异氰酸酯(PAPI27)反应制备了3种聚氨酯泡沫塑料(PU1,PU2和PU3)。通过压缩试验、拉伸试验和动态热机械分析(DMA)研究了3种聚氨酯泡沫的机械性能。测试结果表明,由高分子量和具有网状结构的多元醇(Polyols3)制备的聚氨酯泡沫(PU3)具有较高的压缩强度,拉伸强度和玻璃化转变温度。     

Through-thickness compressive strength of carbon–phenolic woven composites

Carbon–phenolic woven composites are increasingly employed as the material for the heavy-duty journal bearings. Since the through thickness compressive strength (TTCS) is important for the heavy-duty bearing, in this paper, the effects of lay-up angles and specimen thickness of woven composites on TTCS were investigated for the efficient design of carbon–phenolic woven composite bearings. From the experiments and FEM analysis, it was found that the TTCS of the carbon–phenolic woven composite is much dependent on the stacking sequence rather than composite thickness because different stacking sequence produced much different interlaminar stresses.     

碳纤维复合材料层合板压缩性能的相关影响因素

碳纤维作为一种新型的增强材料,具有优良的理化性能,已在多个领域广泛应用.由于单向碳纤维复合材料层合板的压缩强度较低,其在结构复合材料方面的应用受到限制,提高其压缩性能成为关键.本文综述了影响碳纤维复合材料层合板压缩性能的相关因素,详细介绍了纤维弯曲、孔隙率、纤维体积分数、树脂性能等影响因素对碳纤维复合材料层合板的重要性,以及各影响因素之间的关系等,为提高碳纤维复合材料层合板压缩性能的研究提供了参考.     

Analysis of compressive strength and subsidence of a vertebral body cage with Taguchi methods

Abstract

A titanium mesh cage (TMC) might develop subsidence and cause local kyphotic deformity of the spine. For prevention of this complication, this study was designed to find the most appropriate spike design for a vertebral body cage (VBC). In order to investigate the subsidence of a VBC, three‐dimensional finite element models of the L₅ spinal model with a nonlinear contact analysis have been developed. Then, the Taguchi robust design method was used to evaluate spike designs. Finally, the mechanical experiment was developed to obtain the compressive strength of the VBC. For the results of the FEM‐based Taguchi method, the spike row, the spike obliquity, and the spike height were especially important factors for preventing the subsidence. The optimum combinations were pyramidal spike type, a spike height of 2 mm, a spike diameter of 1.4 mm, an oblique geometry, 11 rows per 28 mm, and an inner diameter of 10 mm. For the results of the experiment, the good relationship between finite element simulation and mechanical testing was found with a correlation coefficient of 0.847. The FEM‐based Taguchi method could decrease the effort and time for analyzing the spike factors of the VBC and the mechanical tests might provide the useful evidence to prove the applicability of the finite element models.     

高比强多孔铝合金的压缩变形性能

采用渗流法制备了新型多组元、高比强多孔铝合金，研究了合金的单向压缩变形特征和能量吸收性能，讨论了孔壁厚度均匀性、孔隙率和强化热处理对性能的影响．结果表明：提高多孔铝合金的孔壁厚度的均匀度和强化热处理都显著提高多孔铝合金的压缩吸能性能；随着孔隙率的降低多孔铝合金的压缩强度增加。     

三维网络结构增强金属基复合材料的抗压强度模型

利用混合定则和参照Zum-Gahr 模型、Khruschov 模型, 建立了一种连续网络结构增强金属基复合材料的抗压强度模型, 并进一步对模型进行了修正。通过压力和负压浸渗技术制备了不同增强相体积分数的复合材料, 测试了其抗压强度值, 将试验数据与模型进行了拟合, 数据基本在模型限定范围内。形成的相互贯穿、相互缠绕的网络结构增强复合材料的抗压强度与增强相的体积分数在上限时呈线性关系, 且随体积分数的增加而增加; 在下限时呈非线性关系, 当增强相体积分数超过80 %以上时, 抗压强度明显增加。与基体相比, 复合材料的抗压强度有明显提高。