石墨烯纳米片/环氧树脂复合材料的制备与介电性能研究

以天然鳞片石墨为原料,通过Hummers法制备氧化石墨,微波热解剥离制备出少层数的石墨烯纳米片。以硅烷偶联剂KH-560为改性剂,超声共混制备石墨烯纳米片/环氧树脂复合材料。采用FT-IR和SEM分析样品的微观结构和形貌,测试其介电性能。结果表明,随着石墨烯纳米片添加量的增加,复合材料介电常数呈现先增大后减小的趋势,当石墨烯纳米片含量为0.3%(质量分数)时,介电常数达到最大;石墨烯纳米片对复合材料介电损耗的影响与之相反;偶联改性使复合材料的介电常数增大,介电损耗减小。     

氧化石墨烯纳米片/环氧树脂复合材料的制备与性能

氧化石墨烯(GO)是石墨烯重要的衍生物之一,通过氧化和超声波分散制备了GO纳米片/环氧树脂复合材料。采用XRD、拉曼光谱、FTIR和TEM表征了GO纳米片的结构与形貌,研究了GO纳米片用量对GO纳米片/环氧树脂复合材料热稳定性、力学性能及介电性能的影响。结果表明:GO纳米片的加入提高了GO纳米片/环氧树脂复合材料失热稳定性;随着GO纳米片填充量的增加,GO纳米片/环氧树脂复合材料的冲击强度和抗弯性能先提高后降低,其介电常数和介电损耗则先减小后增加。GO纳米片填充量为0.3wt%的GO纳米片/环氧树脂复合材料的失重5%时的热分解温度由纯环氧树脂的400.2℃提高到424.5℃,而冲击强度和弯曲强度分别在GO纳米片填充量为0.2wt%和0.3wt%时达到最大,冲击强度由纯环氧树脂的10.5kJ/m2提高到19.7kJ/m2,弯曲强度由80.5 MPa提高到104.0 MPa。     

热塑性聚氨酯/石墨烯纳米复合材料的制备及性能研究

采用热剥离法和甲苯二异氰酸酯(TDI)改性制备了功能化氧化石墨烯(iGO),并以iGO作为填料制备了热塑性聚氨酯/石墨烯(TPU/iGO)纳米复合材料。采用扫描电镜(SEM)对GO和iGO进行了微观形貌研究;采用XRD衍射仪、拉曼光谱仪和傅里叶红外光谱仪等对复合材料的结构进行了研究;采用精密介电频潜仪测定了复合材料的介电常数和介质损耗因数。结果表明,TDI对iGO材料的插层改性,增大了石墨烯的层间距;TPU-2.0%iGO纳米复合材料的拉曼光谱与纯iGO材料更加相似,而其红外光谱与纯TPU材料更加相似;iGO的掺入,有效提高了复合材料的抗拉强度,当iGO添加量为0.5%(体积分数)时,TPU/iGO纳米复合材料的抗拉强度达到最大,为54.6MPa,比纯TPU基体材料提高了20.5%;在频率为1 000 Hz时,TPU-2.0%iGO纳米复合材料薄膜的介电常数最高可以达到308.2,同时介电损耗却很低,在频率1 000 Hz时,其介电损耗在0.2以下。因此,TPU/iGO纳米复合材料可作为有效的EMI屏蔽和ESD材料。     

石墨烯纳米片/聚四氟乙烯复合材料的制备及磨损性能研究

以石墨烯纳米片、聚四氟乙烯(PTFE)为原料,制备了石墨烯纳米片/聚四氟乙烯复合材料。研究了不同石墨烯纳米片含量(0,0.25%,0.50%,0.75%,1.00%,1.25%(质量分数))对复合材料导热性能、力学性能、摩擦磨损性能的影响。结果表明,随着聚四氟乙烯中石墨烯纳米片含量的增加,复合材料的微观结构趋于无序,其导热系数逐渐增大,导热性能逐步增强;当石墨烯纳米片含量为0.75%(质量分数)时,复合材料的抗拉强度和断裂伸长率最佳;当石墨烯纳米片含量为1.25%(质量分数)时,复合材料的摩擦系数最小,为0.195,磨损量最低,仅37 mg。磨损实验前后复合材料的碳结构发生了变化,磨损后复合材料的缺陷增大,石墨化程度大大降低,石墨烯纳米片/聚四氟乙烯复合材料具有良好的耐磨损性能。     

苎麻/纳米颗粒增强环氧封装材料的介电性能

以苎麻原麻和苎麻布为增强体,加入不同含量的纳米Sn(OH)4和Al(OH)3,采用模压成型法制备了苎麻/纳米颗粒增强环氧封装材料,探讨了不同纳米颗粒含量及不同比例对封装材料介电性能的影响。结果表明:纳米氢氧化物比表面积越大,封装材料的介电常数和介电损耗略大;加入单一颗粒时,封装材料的介电常数和介电损耗随着粒子含量的增加而增大;加入混合颗粒时,封装材料的介电常数和介电损耗随着Sn(OH)4比例的下降而减小。     

CoFe_2O_4/PVDF复合材料介电和磁性能研究

为增强聚偏氟乙烯(PVDF)的介电性能和磁性能,以湿法化学法合成的纳米铁酸钴(CoFe_2O_4)和PVDF为原料,通过粉末热压法制备了CoFe_2O_4/PVDF复合材料,并对其介电性能和磁性能进行了研究。结果表明,成功合成了纳米CoFe_2O_4,CoFe_2O_4在PVDF基体中分散均匀;与纯PVDF相比,随CoFe_2O_4掺杂量的增加,复合材料的介电常数、电导率、损耗因子均逐步增大;12%(wt,质量分数)CoFe_2O_4掺杂量时,复合材料的介电常数达18.7,介电损耗仅为0.11;复合材料为硬磁材料;复合材料的击穿电压与击穿场强随CoFe_2O_4掺杂量的增加先增大后减小。     

CB/CNTs/PP导电高聚物力/温度作用下介电性能的研究

以聚丙烯(PP)为基体,炭黑(CB)和碳纳米管(CNTs)为填料,通过熔融共混、注塑成型制备导电复合材料,测定电场频率、填料种类、填料含量以及温度、载荷等因素对其介电性能的影响。结果表明,室温下,随着填料含量的增加,材料介电常数和介电损耗均呈增大趋势;随着频率的增加(100 Hz～10MHz),介电常数和介电损耗首先迅速降低,然后逐渐趋于稳定;随着CNTs的加入,CB/CNTs/PP导电复合材料的介电常数明显增大,但是当填料含量达到某一定值时,继续增大CNTs的含量,介电常数反而下降;同一频率下,随着温度的升高(30～100℃),由热膨胀引起炭黑粒子间距的变化会导致介电常数减小。复合材料压缩实验表明:压缩载荷作用下,材料发生形变,基体中的CB粒子间相对位置改变,引起介电常数减小。     

脱掺杂聚苯胺纳米纤维/低密度聚乙烯复合材料的制备及介电性能EI北大核心CSCD

采用苯胺单体与氧化剂"迅速混合"的聚合方法制备了盐酸掺杂的聚苯胺(PANI)纳米纤维,后经氨水脱掺杂得到脱掺杂聚苯胺纳米纤维,利用扫描电子显微镜观察了脱掺杂PANI纳米纤维的形貌。通过熔融共混的方式配制出不同PANI用量的脱掺杂PANI纳米纤维/低密度聚乙烯(LDPE)复合材料,采用傅里叶变换红外光谱研究了纳米复合材料的结构,并测量了不同温度、不同PANI用量的脱掺杂PANI纳米纤维/LDPE复合材料的电导率、击穿强度和不同频率下相对介电常数及介电损耗。研究结果表明,实验得到了直径均一的脱掺杂PANI纳米纤维;添加适量的脱掺杂PANI纳米纤维的LDPE复合材料电导率降低;添加少量脱掺杂PANI纳米纤维复合材料的击穿强度没有降低;复合材料的相对介电常数先降低后增大,但介电损耗一直在增大。     

脱掺杂聚苯胺纳米纤维/低密度聚乙烯复合材料的制备及介电性能

采用苯胺单体与氧化剂"迅速混合"的聚合方法制备了盐酸掺杂的聚苯胺(PANI)纳米纤维,后经氨水脱掺杂得到脱掺杂聚苯胺纳米纤维,利用扫描电子显微镜观察了脱掺杂PANI纳米纤维的形貌。通过熔融共混的方式配制出不同PANI用量的脱掺杂PANI纳米纤维/低密度聚乙烯(LDPE)复合材料,采用傅里叶变换红外光谱研究了纳米复合材料的结构,并测量了不同温度、不同PANI用量的脱掺杂PANI纳米纤维/LDPE复合材料的电导率、击穿强度和不同频率下相对介电常数及介电损耗。研究结果表明,实验得到了直径均一的脱掺杂PANI纳米纤维;添加适量的脱掺杂PANI纳米纤维的LDPE复合材料电导率降低;添加少量脱掺杂PANI纳米纤维复合材料的击穿强度没有降低;复合材料的相对介电常数先降低后增大,但介电损耗一直在增大。     

纳米BaTiO3/聚醚砜复合材料的制备和性能研究

为了改善有机介质材料的介电性能,采用溶液共混和水沉淀工艺,以聚乙二醇为分散剂,并辅以超声振荡制备了钛酸钡/聚醚砜复合材料。用透射电子显微镜和扫描电子显微镜观察复合材料的微观形态,观察到纳米钛酸钡在复合材料中均匀分散。用Q表测定复合材料的介电常数和介电损耗正切值,发现复合材料的介电常数和介电损耗正切值随着钛酸钡体积分数增加而增加,得到了复合材料的介电常数、介电损耗与钛酸钡体积分数的关系式。在兼顾可加工性能的前提下,复合材料的介电常数可达到8.2,比纯聚醚砜提高了2倍多。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...