LLDPE硅烷接枝交联反应的研究

选用线性低密度聚乙烯(LLDPE),接枝单体乙烯基三甲氧基硅烷(VTMOS),以过氧化二异丙苯(DCP)为引发剂,采用熔融挤出法对LLDPE进行硅烷接枝,然后在催化剂二月桂酸二丁基锡(DBTDL)存在下进行水解交联反应.研究了凝胶含量随水解时间的变化关系.通过改变VTMOS、EGP用量,系统地考察了对交联LLDPE的凝胶含量、力学性能以及结晶性能的影响.结果表明:凝胶含量在水解初期随时间的增长而快速增加,10h后凝胶含量趋于平缓.硅烷接枝交联LLDPE,由于其三维网络结构的存在,使得力学性能显著提高,其熔点和结晶度则都有不同程度的降低.     

室温自交联聚丙烯

本文在介绍交联聚丙烯基本原理和工艺的基础上，讨论了以氢氧化铝作为脱水物质，使硅烷交联反应在室温条件下自发进行，硅烷交联聚丙烯所需的水分在聚合物内部解决，省去PP常规交联时的热水交联过程。研究了自交联聚丙烯凝胶率及机械性能随交联时间的变化规律。硅烷接枝PP试样在室温下脱水发生自交联反应，交联PP凝胶含量在室温条件下随时间的变化逐渐升高，在室温下放置40天左右后，凝胶含量基本保持稳定；当Al（OH）3含量逐渐增大时，凝胶含量变得更大，当Al（OH）3含量增大到2％以上时，制品表面出现大量气泡；随时间的变化，交联PP体系的机械性能变得更优异，Al（OH）3含量为1％的新生态PP在室温下放置40天左右后，拉伸强度和断裂伸长率基本保持稳定。     

SiC微粉含量对先驱体转化制备碳纤维布增强碳化硅复合材料性能的影响

以聚碳硅烷(PCS)、二乙烯基苯(DVB)和SiC微粉为原料制备了碳纤维布增强碳化硅复合材料，考察了SiC微粉含量对材料结构与性能的影响。实验表明，SiC微粉含量过低，材料内部存在大的孔洞，容易造成应力集中，导致材料的力学性能较差；而当SiC微粉含量较高时，在制备过程中微粉对碳纤维机械损伤加大，同样导致材料力学性能下降。当SiC微粉含量为30％(质量分数)时，所制备的材料的力学性能较好，其弯曲强度和拉伸强度分别为246．4MPa和72．5MPa。     

光引发交联改性对尼龙6性能的影响

在光交联剂的存在下,研究紫外光辐照交联改性尼龙6。通过凝胶含量测试、衰减全反射红外光谱、热重分析和差示扫描量热法(DSC)考察了紫外光辐照尼龙6的交联特征及相关性能。结果表明,当紫外光辐照5s时,凝胶含量达到99.2%,拉伸强度从60.0MPa增加到73.2MPa。紫外光辐照后,尼龙6的结晶度和熔点下降,热稳定性提高。在光交联同时,尼龙6表面也发生光氧化降解,并随辐照时间的延长而加剧,导致尼龙6的力学性能下降。     

紫外光辐照对超高分子量聚乙烯纤维结构与性能的影响

选用2种紫外光源,以二苯甲酮(BP)为光敏剂进行超高分子量聚乙烯(UHMWPE)纤维的表面光交联反应;采用凝胶含量测定、差示扫描量热仪分析及力学性能测试等方法,研究了辐照时间对UHMWPE纤维结构与性能的影响。结果表明,随辐照时间延长,纤维凝胶含量增加,结晶度和常规力学性能略有下降,低压汞灯和高压汞灯分别辐照20 min和10 min后UHMWPE纤维长期抗蠕变性能得到明显改善。其中,低压汞灯辐照20 min时,纤维恒定蠕变速率和强度分别为原纤维的67%和93%,性能优于相同辐照时间的高压汞灯试样。     

冻胶法制备超高分子量聚乙烯/SiO2杂化微孔膜研究——稀释剂与SiO2对铸膜液熔融结晶性能的影响

根据界面相分离原理,以矿物油为稀释剂,O2为添加剂,采用冻胶法制备了超高分子量聚乙烯(UHMWPE)膜以及UHMWPE/SiO2杂化微孔膜,讨论了稀释剂以及无机粒子含量对膜熔融结晶性能的影响.结果表明,矿物油作为微孔稀释剂,其加入使微孔膜中UHMWPE熔点降低,结晶度减小.当SiO2与UHMWPE质量比低于8/10时,随SiO2含量增加,UHMWPE熔点变化不显著,熔限增加,结晶温度升高,相对结晶度增大,微晶尺寸减小;当SiO2加入量足够大时,相对结晶度反而减小.随SiO2其含量增加,界面孔增多,膜孔隙率提高,水通量增大,泡点孔径先增大后减小.     

HAP／UHMWPE生物复合材料的制备与微观结构

通过化学共沉淀．水热合成法制备纳米级羟基磷灰石（HAP），再用自制模具制备出羟基磷友石／超高分子量聚乙烯（UHMWPE）复合材料．通过SEM观察、X射线分析、DSC测试、热重分析以及力学性能测通过其超长分子链获得网状结构，为材料提供机械强度，HAP在复合材料中试，研究了HAP／／UHMWE复合材料的微观组织和力学性能．结果表明：UHMWPE分布比较均匀，并被包裹在UHMWPE超长细链形成的层层网状结构之中．随着HAP含量的增加，复合材料的熔点下降，熔融热焓有所降低，UHMWPE的结晶度降低了．随着HAP体积含量的增加，复合材料的拉伸强度和抗弯强度均下降，从30．1MPa降到21．5MPa以及从63．1IMPa降到46．7MPa，而弹性模量有所上升，从1．6GPa上升到4．1GPa．     

超高分子量聚乙烯摩擦磨损行为及拉曼成像

以未交联超高分子量聚乙烯(UHMWPE)和交联UHMWPE为研究对象,探讨2种材料在滑动和滚动摩擦条件下的摩擦磨损行为,重点采用拉曼成像的方法分析了磨损表面的结晶度分布和取向分布。结果表明,交联降低了UHMWPE的摩擦系数和磨损率;在滑动摩擦下,交联使UHMWPE的耐磨性提高了96%,在滚动摩擦方式下,交联使UHMWPE的耐磨性提高了41%;拉曼光谱成像表明,UHMWPE和交联UHMWPE磨损区域的表面结晶度都比未摩擦区域高;在滑动摩擦下,纯UHMWPE和交联UHMWPE均发生了取向,而在滚动摩擦下两者都没有发生明显的取向。     

紫外光辐射交联甲基乙烯基硅橡胶/线性低密度聚乙烯热塑弹性体的性能

在光引发剂存在的条件下,利用紫外光对甲基乙烯基硅橡胶/线性低密度聚乙烯(MVQ/LLDPE)热塑弹性体进行辐射交联改性,通过凝胶含量、力学性能和热延伸测试,以及差示扫描量热法(DSC)和扫描电镜(SEM)分析,考察其交联特性及相关力学性能。实验结果表明,凝胶含量随光引发剂用量先增加后减小,在1%时出现极大值88%。凝胶含量随着辐照时间快速增加,当辐照时间为6s时,凝胶含量可以达到89%。随着辐照时间的延长,材料的拉伸强度显著提高,而断裂伸长率和热延伸率逐渐下降。扫描电镜(SEM)照片表明,紫外光交联提高了MVQ和LLDPE两相的相容性。差示扫描量热法(DSC)结果表明,紫外光交联可使材料的熔点从124.6℃下降到112.3℃,熔融焓由39.09 J/g下降到32.22 J/g。     

LDPE交联物结构的研究EI北大核心

通过凝胶含量、平衡溶胀比和高温模量等的测定 ,比较了过氧化物交联 LDPE和硅烷交联 LDPE的结构与性能的差异。根据交联网络方程和 Mooney-Rivlin方程的计算表明 ,当凝胶含量相同时 ,过氧化物交联聚乙烯的交联密度远小于硅烷交联聚乙烯的交联密度。采用苯中的平衡溶胀比或交联密度来表征 LDPE交联物的交联程度比采用凝胶含量来表征更为确切。而 LDPE/沸腾苯体系的 Huggins参数为 0 .3 0。     

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.……     

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.     

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.     

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 ...