静电纺工艺参数对含银PA6纳米纤维直径的影响

为了研究静电纺工艺参数对含银PA6纳米纤维直径分布的影响,采用静电纺丝技术,在不同含银量、纺丝液质量分数、纺丝电压、接收距离(C-SD)、喷嘴直径条件下制备出含银PA6纳米纤维膜.利用扫描电镜(SEM)及相关软件分析纳米纤维直径分布及形态,在银溶胶质量分数0.2%～0.4%、纺丝液质量分数10%～16%、纺丝电压12～21kV、接收距离9～18cm、喷嘴直径0.5～1.2mm的实验范围内,纳米纤维的平均直径为70～90nm;纳米纤维直径随银溶胶质量分数的增加而减小,随纺丝液质量分数的增加而增大,随喷嘴直径的增大而增大;电压和接收距离对纳米纤维直径的影响较小.     

溶液静电纺丝制备热塑性聚酰亚胺超细纤维无纺布

为实现热塑性聚酰亚胺(LPI)无纺布的宏量制备奠定基础,以N-N-二甲基乙酰胺(DMAc)为溶剂,采用静电纺丝技术成功制备了平均直径范围为0.36~1.47μm的LPI超细纤维,系统探讨了纺丝液浓度、流速以及纺丝电压等工艺条件对LPI纤维形貌和直径的影响。结果表明:随着浓度从22%(质量分数,下同)增加到30%,LPI纤维的平均直径显著增大,同时直径分布逐渐变宽,并且在纺丝溶液浓度较低时,有纺锤状纤维存在,随着溶液浓度上升,纺锤状纤维消失,随浓度继续上升,纤维开始产生粘连。纺丝电压的改变对纤维的形貌和平均直径变化不显著;随着流速增加,纤维平均直径随之增大,当流速大于1.5mL/h时,开始出现纤维粘连,大于1.8mL/h时,出现纺锤状纤维。通过优化工艺条件,在LPI浓度28%,电压15kV,流速1.2mL/h,温度30℃,接收距离25cm条件下,制备了平均直径为1.18μm的纤维。     

静电纺丝制备聚合物超细纤维的研究及应用

静电纺丝是一种制备聚合物超细纤维的有效方法,并可直接获得直径达5～500nm的超细纤维膜.综述了静电纺丝的发展过程、基本原理和研究现状,介绍了静电纺丝超细纤维膜微观形貌的影响因素及其应用前景.     

静电纺丝制备竹纤维素/PAN超细纤维及应用EI北大核心CSCD

利用氯化锂/N,N-二甲基乙酰胺(LiCl/DMAc)溶剂体系先后溶解竹纤维素和聚丙烯腈(PAN),配成纺丝液,采用静电纺丝技术成功制备出直径为130 nm^450 nm的竹纤维素/PAN超细纤维。通过研究竹纤维素/PAN超细纤维平均直径与纺丝参数关系发现,该超细纤维的平均直径随着竹纤维素浓度的增大而增大,随纺丝电压的增大而减小,随纺丝距离的增大而减小,且最佳纺丝参数是竹纤维素质量分数为0.8%,纺丝电压为16 kV,接收距离为14 cm。采用该复合纤维制成夹心净化材料并做过滤测试发现,其过滤效率随着夹心层中超细纤维的膜密度和浊液的起始浊度值增加而增大,最大过滤效率可达99.5%。     

静电纺丝制备竹纤维素/PAN超细纤维及应用

利用氯化锂/N,N-二甲基乙酰胺(LiCl/DMAc)溶剂体系先后溶解竹纤维素和聚丙烯腈(PAN),配成纺丝液,采用静电纺丝技术成功制备出直径为130 nm~450 nm的竹纤维素/PAN超细纤维。通过研究竹纤维素/PAN超细纤维平均直径与纺丝参数关系发现,该超细纤维的平均直径随着竹纤维素浓度的增大而增大,随纺丝电压的增大而减小,随纺丝距离的增大而减小,且最佳纺丝参数是竹纤维素质量分数为0.8%,纺丝电压为16 kV,接收距离为14 cm。采用该复合纤维制成夹心净化材料并做过滤测试发现,其过滤效率随着夹心层中超细纤维的膜密度和浊液的起始浊度值增加而增大,最大过滤效率可达99.5%。     

电纺聚丙烯腈纤维毡的制备与性能表征

以聚丙烯腈为原料,N,N-二甲基甲酰胺为有机溶剂,用静电纺丝方法纺制聚丙烯腈纤维毡,并测试了纤维毡的平均孔径和直径,研究了纺丝液浓度、施加电压、接收距离对孔径和纤维直径的影响,实验表明:施加电压、接收距离对平均孔径影响较大,纺丝液浓度对其的影响次之;纺丝液浓度是影响纤维直径的一个重要参数。正交试验得出的最佳工艺:纺丝液浓度12%(wt,质量分数)、施加电压15kV、接收距离165mm;此工艺下纺制的纤维毡中,孔径和纤维直径小且集中,纤维毡均匀度好。     

静电纺多孔/无孔二醋纤复合膜的制备及过滤性能研究

采用静电纺丝技术,借助高挥发溶剂的制孔性,制备了多孔超细二醋酸纤维。通过调控纺丝过程中多孔超细二醋酸纤维和无孔纳米二醋酸纤维的比例,制备了不同交叉结构的多孔超细/无孔纳米二醋纤复合膜。通过扫描电镜观察纤维膜的形貌,利用电导率仪测试纺丝液电导率,运用黏度计测试纺丝液的黏度,利用多孔材料孔径分析仪测试复合膜的孔径分布,通过滤料综合性能测试台测试不同空气流量下复合膜的过滤性能。结果表明:随着无孔纳米纤维在复合膜中比例的增加,复合膜的孔径分布范围变窄,孔径减小,堆积密度增加;过滤效率和过滤阻力都呈增大的趋势;当纺丝过程中,多孔超细纤维与无孔纳米纤维纺丝针管数目比例为1∶2时,所制备的复合膜具有最好的品质因数,在空气流量为80L/min时,其过滤阻力仅为280Pa,过滤效率可达99.472%。     

二醋酸(SCA)纳米纤维的制备与性能表征

为了研究二醋酸纳米纤维的制备方法和性能,采用静电纺丝技术,选择丙酮和二甲基乙酰胺为溶剂,制备出直径分布均匀的SCA纳米纤维膜.利用原子力显微镜(AFM)和扫描电镜(SEM)及相关软件,分析纳米纤维直径分布及形态;在静电纺电压为16kV、纺丝液质量分数为11%、接收距离(C-SD)为12cm的条件下,纺出连续均匀的纳米纤维,其直径分布在200～300nm之间;对二醋酸纳米纤维膜进行透气性测试发现,纳米纤维膜的透气性与中性定性滤纸的透气性相当.     

静电纺聚醚砜纳米纤维膜的制备及性能研究

配制不同浓度的聚醚砜(PES)纺丝液,在不同纺丝温度和进液速度下,采用静电纺丝技术制备PES纳米纤维膜,并通过扫描电子显微镜观察膜表面的微观形貌,探究纺丝液浓度、进液速度和纺丝温度等条件对纤维的形貌、直径和孔径分布等的影响。结果表明:当纺丝液浓度为28%(质量分数),推进速度为1mL/h,纺丝温度为45℃时,纺丝效果最佳。分别采用电子万能试验机和泡压法滤膜孔径分析仪对优化条件下制得的PES纳米纤维膜的力学性能、通孔孔径及孔径分布进行测试,发现该条件下所得PES纳米纤维膜的弹性模量为33.4MPa,断裂伸长率为38.63%,拉伸屈服应力为3.47MPa;纤维平均直径为0.723μm,平均孔径为3.5689μm,最可几孔径为3.5655μm。静电纺PES纳米纤维膜有望作为高精度滤膜材料使用。     

电纺丝技术制备纳米/亚微米级取向纤维

静电纺丝是一种制备直径在纳米级到微米级超细纤维的新技术。普通的静电纺丝装置制备出的是无纺布状超细纤维,但有些场合需要使用取向纤维,因此文中介绍了制备取向纤维的方法,并成功地采用自制装置制备出取向的纳米/亚微米纤维,研究了电纺丝参数,如纺丝电压、溶液浓度、接收距离等对纤维取向的影响,最后对取向原理进行了简单分析。     

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.……     

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.     

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...     

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 ...