纳米Fe2O3水泥基复合材料制备的响应曲面研究

配制三种常用高效减水剂溶液,观察纳米Fe_2O_3在三种溶液中的分散效果;基于响应曲面正交旋转组合设计,并考虑纳米Fe_2O_3掺量(Nano-Fe_2O_3content,NFC)、聚羧酸减水剂母液掺量(Polycarboxylate superplasticizer content,PSC)、水胶比(Water-binder rational,WBR)三因素,研究水泥硬化浆体的配比参数与强度间的响应曲面,分析各参数对强度的影响规律。结果表明:纳米Fe_2O_3在聚羧酸高性能减水剂母液溶液中分散效果最好;当配比参数NFC=0.027、PSC=0.017 5、WBR=0.28时,水泥硬化浆体具有较高的强度;从统计学与实践角度来看,响应曲面方程具有较高的可靠性和精度;抗压强度随PSC的增大先增大后减小,随WBR的增大而减小,随NFC的增大而增大;最佳数值附近存在最适宜配方和掺量,使水泥基复合材料具有较好的强度和施工性;响应曲面法(Response surface methodology,RSM)可广泛应用于新型水泥基复合材料的研发领域,发展前景广阔。     

矿物掺合料对聚羧酸减水剂与水泥相容性的影响

高性能减水剂与水泥适应性差会导致混凝土流动性和坍落度损失过快,矿物掺合料将影响高性能减水剂与水泥的相容性。对比研究矿物掺合料种类和掺量对水泥净浆、砂浆和混凝土流动性的影响;采用TOC法测试了矿物掺合料对聚羧酸减水剂吸附量的影响;分析了矿物掺合料影响聚羧酸减水剂与水泥相容性的机理。结果表明,粉煤灰和矿渣对提高水泥净浆流动性具有一定的叠加效应,可用胶砂减水率的加权平均值进行量化;硅灰对水泥浆体流动性的不利影响远大于粉煤灰和矿渣的辅助减水分散作用,不利于改善聚羧酸减水剂与水泥的相容性;粉煤灰和矿渣增加聚羧酸减水剂在水泥体系中的吸附量;粉煤灰和矿渣对聚羧酸减水剂在混凝土中的减水分散效果有改善作用但不显著。     

基于数值模拟的碳纳米管水泥基复合材料导电机理分析

通过建立碳纳米管水泥基复合材料的代表性体积单元模型,基于有限元法进行了有效介质方程导电模型的拟合和感知性能的计算,得到碳纳米管水泥基复合材料在荷载作用下的应力与体积电阻率的关系,在此基础上了分析了碳纳米管水泥基复合材料的导电机理。研究结果表明,碳纳米管体积掺量为1.50%时,随碳纳米管直径减小及长径比增大,有限元数值解的有效介质方程拟合值变化不大,这是因为1.5%的掺量已超过渗流阈值且有限元分析只考虑接触导电;当碳纳米管的体积掺量在0.31%~1.33%范围内时,碳纳米管水泥基复合材料的感知性能满足Simmons隧道效应普适方程。     

三种水泥与聚羧酸减水剂相容性初探

聚羧酸减水剂与水泥的相容性是混凝土生产中备受关注的问题。采用净浆流动度法测试水泥净浆初始流动度、饱和掺量点、流动度经时损失三个参数,以此考察某聚羧酸减水剂与乐山地区三种常用水泥(A、B、C)的相容性。分别采用激光粒度仪、Zeta电位仪和X射线衍射仪测试水泥的粒径、Zeta电位和物相组成,探索导致三种水泥与聚羧酸减水剂相容性出现差异的可能因素。研究结果表明三种水泥与聚羧酸减水剂相容性优劣顺序为:A>B>C,这与根据Zeta电位和粒径推测出的相容性顺序不一致,但与根据相成分测试结果推测出的相容性优劣顺序是一致的。由此可以推测Zeta电位与粒径均不是影响三种水泥与聚羧酸减水剂相容性的主要因素,而水泥各相成分的含量可能是影响相容性的一个主要因素。     

氧化石墨烯调控水泥基材料形成大规模规整结构及其性能表征

将制备的GO与减水剂和拌合水超声处理后用于制备水泥基复合材料,研究结果表明,GO纳米片层在水泥基体中达到了均匀分散,水泥水化产物成为了规整形状的多面体状水化晶体,通过其交织交联形成了大规模规整致密的微观结构。当GO掺量为0.03%时,尺寸为30~190nm GO的水泥基复合材料28d时的抗压强度和抗折强度比对照样品分别提高了78.8%和112.7%,尺寸为110~410nm GO的水泥基复合材料的抗压强度和抗折强度分别提高了72.3%和93.9%,水泥基复合材料的耐久性显著提高。同时提出了水泥基复合材料微观结构形成机理。     

固体聚羧酸减水剂制备方法研究现状

随着水泥基材料和石膏基材料对施工性能和力学性能要求的提高，固体聚羧酸减水剂因运输方便、存储时间长、性能稳定等特点，应用越发普遍。固体聚羧酸减水剂制备方法各异，性能也各有不同。概括固体聚羧酸减水剂不同制备方法所使用的生产设备、生产工艺流程及产品性能，总结固体聚羧酸减水剂不同制备方法的优缺点及生产成本范围；详细阐述固体聚羧酸减水剂喷雾干燥法、本体聚合法、沉淀法、吸附法等制备方法的特点及影响因素。基于喷雾干燥法生产工艺成熟，但多级干燥及节能降耗问题导致生产成本较高；本体聚合法存在反应温度不均等工业化技术问题；沉淀法和吸附法存在大量使用有机溶剂、环保和成本等问题，短时间内均较难大规模的推广应用，提出本体聚合法在未来几年将会得到深入研究和快速发展。     

含短侧基低分子量聚羧酸系减水剂的合成与作用机理探讨

利用合成的马来酸酐柠檬酸酯类大单体(MACA)与丙烯酸(AA)、烯丙基磺酸钠(SAS)等进行自由基聚合,制备出一种含短侧基低分子量的新型聚羧酸系减水剂。通过红外光谱、黏度、水泥净浆流动度和ζ电位等方法对共聚物的结构组成和性能进行了表征,并初步探讨了新型聚羧酸系减水剂与水泥的作用机理。研究表明:该减水剂有较好的分散性,且水泥净浆流动度保持性较好,无泌水离析现象;该减水剂与水泥粒子的塑化机理符合静电斥力与空间位阻理论。     

聚羧酸系减水剂的构性关系及其作用机理研究

聚羧酸系减水剂作为一种高性能减水剂,目前已成为国内外研究与发展的热点。概述了近几年国内外高效减水剂的研究与发展现状,阐述了聚羧酸系高效减水剂的分子结构、性能特点及作用机理,分子主链上阴离子基团越多及聚氧乙烯长侧链越长,聚羧酸系减水剂的分散性能和流动保持性能越好。聚羧酸系减水剂主要依靠聚氧乙烯长侧链的位阻效应和羧基及磺酸基的静电斥力来分散水泥颗粒。最后,提出了减水剂在应用中存在的问题并展望了其发展趋势。     

冲击荷载下高韧性水泥基复合材料动态力学特性与微结构演化研究

为提升水泥基材料静态力学性能、抗冲击特性及为减少温室气体排放而降低水泥用量,以硅粉为矿物掺合料(掺量为10%,质量比)、钢纤维为功能组分(掺量为2%,体积比),并匹配高效减水剂(掺量为1.5%～2.0%,质量比)制备高韧性水泥基复合材料,通过准静态抗压/抗折强度、分离式霍普金森压杆试验和采用水化微量热仪、热重分析仪,分别研究了高韧性水泥基复合材料准静态/动态力学特性及其微结构演变特征。结果表明：冲击荷载下(冲击速率为0.5 MPa/s)水泥基材料典型破坏过程分为三阶段,高韧性水泥基复合材料受作用后仅出现局部浆体剥落、飞散现象,而基准组体系均发生显著破坏直至整体破碎;硅粉在10%掺量下有效提升了水泥基复合材料体系早期和后期的准静态力学性能,1 d天龄期下抗压强度和抗折强度最高可达61.4 MPa、23.9 MPa,也显著提升了动态抗压强度至123.3 MPa(28 d天龄期)。微结构演变结果表明：硅粉和减水剂复合作用下浆体水化放热速率主峰提前,且主要水化产物——氢氧化钙含量减少,降低了浆体内部氢氧化钙分布的取向性,有助于改善浆体微结构。     

PCs/GO复合物对水泥基材料微观结构和力学性能的影响

用氧化石墨烯(GO)纳米片层分散液与甲基丙烯酸聚氧乙烯单甲醚(MPE)、甲基丙烯酸(MAA)和丙烯磺酸盐(AA)进行插层聚合反应制备了聚羧酸减水剂(PCs)与GO的插层复合物(PCs/GO),将其应用于水泥基复合材料。结果表明,PCs/GO能够调控水泥基体成为由多面体状产物构成的规整的微观结构,具有显著的增强增韧效果,同时也发现PCs/GO能够在水泥基体的裂缝和孔洞处产生花状和多面体状晶体,具有修复裂缝、孔洞的功效。研究结果对于制备无裂缝及高强度、高韧性和高耐久性水泥基复合材料具有积极的意义。     

Electrical and rheological percolation of polymer nanocomposites prepared with functionalized copper nanowires

The morphological, electrical and rheological characterization of polystyrene nanocomposites containing copper nanowires (CuNWs) functionalized with 1-octanethiol is presented. Characterization by SEM and TEM shows that surface functionalization of the nanowires resulted in significant dispersion of CuNWs in the PS matrix. The electrical characterization of the nanocomposites indicates that functionalized CuNWs start to form electrically conductive networks at lower concentrations (0.25?vol% Cu) than using unfunctionalized CuNWs (0.5?vol% Cu). The organic coating on the nanowires prevents significant changes in the electrical resistivity in the vicinity of the percolation threshold. Percolated nanocomposites showed electrical resistivity in the range of 10(6)-10(7)?Ω?cm. The transition from liquid-like to solid-like behavior (rheological percolation) of the nanocomposites was studied using dynamic rheology at 200?°C. Unfunctionalized CuNWs result in electrical and rheological percolation at similar concentrations. Functionalized CuNWs show rheological percolation at higher concentration (1.0-2.0?vol%) than that required for electrical percolation. This is attributed to the decrease in the interfacial tension between nanowires and polymer chains and its effect on the viscoelastic behavior of the combined polymer-nanowire networks.     

Percolation threshold and morphology of composites of conducting carbon black/polypropylene/EVA

Conducting carbon black (CB), one of the intrinsic semi-conductors, was added into matrix polypropylene (PP) to prepare conducting composites by means of the melt processing method. Another component EVA was mixed into the composites in order to lower the percolation threshold. The percolation threshold of the ternary CB/PP/EVA composites was merely 3.8 vol%, while it was up to 7.8 vol% for the binary CB/PP composites without EVA. The conductivity of the ternary CB/PP/EVA composites was up to 10^–2 S/cm when the CB percentage was 5 vol%, while that of the binary CB/PP was lower than 10^–2 S/cm when the CB percentage was up to 10 vol%. DSC thermograms of the CB/PP/EVA composites showed that the melting peak shifted to low temperature with increasing CB content. The addition of CB and EVA resulted in the decrease of the crystallinity of PP in the ternary composites. The mechanical properties are also discussed. SEM and TEM were employed to study the morphology of the blend system. The results indicated that CB existed in the form of aggregations in the blend system. The smallest unit that formed a percolation network was grape-like aggregates with some small branches, which consisted of some CB particles, rather than the individual particles. This distribution was very valuable for forming conducting paths and for lowering the percolation value.     

Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of self-compacting concrete

This paper presents the results of an experimental investigation carried out to study the effect of granulated blast furnace slag and two types of superplasticizers on the properties of self-compacting concrete (SCC). In control SCC, cement was replaced with 10%, 15%, 20%, and 25% of blast furnace slag. Two types of superplasticizers: polycarboxylate based superplasticizer and naphthalene sulphonate based superplasticizers were used. Tests were conducted for slump flow, the modified slump test, V-Funnel, J-Ring, U-Box, and compressive strength. The results showed that polycarboxylate based superplasticizer concrete mixes give more workability and higher compressive strength, at all ages, than those with naphthalene sulphonate based superplasticizer. Inclusion of blast furnace slag by substitution to cement was found to be very beneficial to fresh self-compacting concrete. An improvement of workability was observed up to 20% of slag content with an optimum content of 15%. Workability retention of about 45 min with 15% and 20% of slag content was obtained using a polycarboxylate based superplasticizer; compressive strength decreased with the increase in slag content, as occurs for vibrated concrete, although at later ages the differences were small.     

Electric conductivity-tunable transparent flexible nanowire-filled polymer composites: orientation control of nanowires in a magnetic field

Cobalt compound nanowires were dispersed in a transparent nonconductive polymer film by merely stirring, and the film's transparency and electrical conductivity were examined. This composite film is a unique system in which the average length of the nanowires exceeds the film's thickness. Even in such a system, a percolation threshold existed for the electric conductivity in the direction of the film thickness, and the value was 0.18 vol%. The electric conductivity value changed from ～1 × 10(-12) S/cm to ～1 × 10(-3) S/cm when the volume fraction exceeded the threshold. The electric conductivity apparently followed the percolation model until the volume fraction of the nanowires was about 0.45 vol %. The visible light transmission and electric conductivity of the composite film of about 1 vol % nanowires were 92% and 5 × 10(-3) S/cm, respectively. Moreover, the electric conductivity in the direction parallel to the film surface did not depend on the amount of the dispersed nanowires, and its value was about 1 × 10(-14) S/cm. Even in a weak magnetic field of about 100 mT, the nanowires were aligned in a vertical and parallel direction to the film surface, and the electric conductivity of each aligned composite film was 2.0 × 10(-2) S/cm and 2.1 × 10(-12) S/cm. The relation between the average wire length and the electric conductivity was examined, and the effect of the magnetic alignment on that relation was also examined.     

Preparation and properties of carbon black/polymer composites with segregated and double-percolated network structures

A carbon black (CB)/low-density polyethylene (LDPE)/ultrahigh-molecular-weight polyethylene (UHMWPE) composite with a segregated and double-percolated structure has been fabricated using the solution mixing and high-speed mechanical mixing method. Structural observations show that the conducting CB/LDPE layers were only dispersed at the interface of UHMWPE granules and formed a well-developed CB conductive network with a percolation threshold of 0.26 vol%. The low percolation threshold in CB/LDPE/UHMWPE composites can be explained by the segregated and double-percolated networks of CB within the polymer matrix. A noticeable double positive temperature coefficient of resistivity can be observed around the melting temperature of LDPE and UHMWPE followed by a negative temperature coefficient of resistivity. The microstructure evolution of CB/LDPE/UHMWPE composites can be observed and explained by in situ optical micrographs.     

具有隔离结构的超高分子量聚乙烯/镍高导电复合材料

采用化学镀手段制备金属镍包覆的超高分子量聚乙烯复合粒子,通过热压成型方法制得具有隔离结构的超高分子量聚乙烯(UHMWPE)/镍(Ni)高导电复合材料。通过调节金属(镍)镀层厚度及加工温度考察不同Ni含量及加工温度对复合材料导电性能的影响。结果表明,复合材料具有明显的导电逾渗行为;通过化学镀工艺可有效提高金属填料与基体的结合力,同时实现金属镍在聚合物基体中的选择性稳定分布,构建具有隔离结构的导电网络,使得复合材料的逾渗值降低至1.02%(体积分数)。基于金属填料优异的导电性能,在Ni体积分数仅为2.53%时,复合材料的电导率达到2648S/m。此外,降低复合材料的加工成型温度有助于减少加工过程对导电网络的破坏作用,从而有效降低复合材料的导电逾渗值,对提高复合材料导电性能具有重要意义。     

Surface modified microcrystalline cellulose from cotton as a potential mineral admixture in cement mortar composite

The objective of the work is to examine the performance of tetraethyl orthosilicate (TEOS) modified microcrystalline cellulose (MCC) fiber, derived from cotton, as a mineral admixture that could be compatible in cement mortar composites. The effectiveness of surface modification of MCC is characterized by powder X-ray diffraction, FTIR, TGA and SEM techniques. The present silane based surface modifier (TEOS) minimizes the water uptake and acts as a pozzolan, that could result in additional calcium silicate hydrates (C-S-H) linkages. This is reflected by the enhancement in the mechanical properties of the cement mortar composite. A dramatic two fold enhancement of flexural strength and almost 45% increase of compressive strength are observed in the case of TEOS-MCC when compared with the cement mortar composites without any mineral admixture there by validating the method chosen. The enhancement of compressive and flexural strength could be due to proper dispersion of smaller size MCC fibers within the pores of the cement mortar composite. When an optimized amount of chemical admixture (polycarboxylate ether (PCE) superplasticizer) is used along with TEOS- MCC a greater enhancement in flexural strength and compressive strength is observed with good workability, at a lower water/cement ratio.     

金属Mo对AlN基复相材料性能的影响

以氮化铝、金属Mo 为原料,Y₂O₃为烧结助剂,氮气氛下、1800～1900℃热压烧结制备Mo/AlN 复相材料。利用 XRD、SEM对材料的相组成、显微结构进行表征,四探针法测试复相材料的电阻率,微带线法测试2～20 GHz频率范围内材料的微波衰减特性,探讨了渗流现象与衰减特性之间的内在联系。结果表明;当 Mo 添加量为4. 56 vol %～15. 03 vol %,材料呈现宽频衰减特性,且随着 Mo 含量和烧结温度的增加衰减量增大;当Mo 添加量为16. 18 vol %～24. 88 vol %,材料仅在 6、10、14、18 GHz? 4个频率点出现了明显的谐振峰。根据渗流模型对电阻率数据进行拟合,得到导电相渗流阈值V_c和相应电阻率分别为14. 87 vol %和11. 59 Ω·m。当Mo 体积分数V >V_c时 , 复相材料的衰减特性由宽频向选频转变。