基于共凝聚PTFE/炭黑粒子复合材料的制备和性能

在不使用凝聚剂的情况下采用下压式机械搅拌方式使聚四氟乙烯(PTFE)乳液和炭黑(CB)共凝聚,得到颗粒大小均匀的PTFE/CB粒子,然后用冷压成型和高温烧结工艺制备PTFE/CB复合材料,研究了烧结温度和CB含量对PTFE/CB复合材料的力学性能、导电性能和结晶度的影响。结果表明,烧结温度为390oC时复合材料中形成了均匀分布的微纤结构,力学性能最好;CB的填充明显提高了PTFE的力学性能和导电性能,当CB含量(质量分数)为2%时复合材料的力学性能最佳,拉伸强度从19.1 MPa增加至27.3 MPa,断裂伸长率从420%增加到525%。CB含量提高到3%的PTFE/CB复合材料结晶度最大,且CB在PTFE基体中形成了导电网络,电导率出现"逾渗",PTFE/CB复合材料具有抗静电性能。     

莫来石填充的聚四氟乙烯复合材料及其摩擦学性能

采用机械混匀、带温预压、烧结等工艺制备了莫来石填充的聚四氟乙烯(PTFE)复合材料,通过万能材料试验机、X射线衍射仪(XRD)、静态热机械分析仪(TMA)分别表征了复合材料的力学性能、物相和热学性质;研究使用MRH-3型高速环块磨损试验机来测试复合材料的耐摩擦磨损性能,借助场发射扫描电子显微镜研究了复合材料摩擦面形貌并分析摩擦磨损机理。结果表明:莫来石在PTFE体系中起填充增强作用,改性聚四氟乙烯复合材料的弹性模量显著增加;莫来石的填充提高了聚四氟乙烯的玻璃化转变温度,其平均线膨胀系数也呈下降趋势;当莫来石的质量分数由0增加至50%时,复合材料的摩擦系数呈先降低、后升高的趋势,复合材料的耐磨损性能显著改善;当莫来石的质量分数为40%时,其磨损率降低至纯聚四氟乙烯的1/530。     

埃洛石-玻纤/聚四氟乙烯复合材料的摩擦磨损热膨胀及力学性能

采用冷压成型烧结工艺制备出玻璃纤维（GF）和埃洛石（HNTs）填充的聚四氟乙烯（PTFE）复合材料。研究了填料类型及不同配比的填料对PTFE复合材料的界面、摩擦学性能、线膨胀系数及力学性能的影响。结果表明:适量填充HNTs可以提升GF/PTFE复合材料的摩擦磨损、热膨胀及力学性能。填充2.0%HNTs时的HNTs-GF/PTFE复合材料比GF/PTFE复合材料的磨损率降低32.7%,高温时HNTs-GF/PTFE复合材料的线膨胀系数（CTE）比纯PTFE降低近2个数量级,断裂伸长率、拉伸强度和弯曲强度分别提高40.0%、2.3%和7.1%。      

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。     

复配稀土改性剂对MGF/PTFE复合材料性能的影响

采用稀土改性剂(RES)与硅烷偶联剂(PTMS)按不同组分配比对磨碎玻璃纤维(MGF)表面进行改性处理,将改性后的磨碎玻璃纤维粉末与聚四氟乙烯分散液机械混合,然后热压制得复合材料。探讨了复配稀土改性剂对MGF/PTFE复合材料介电性能、热膨胀系数(CTE)、热导率的影响。采用FTIR手段对稀土改性剂未改性的磨碎玻璃纤维和改性后的磨碎玻璃纤维的结构进行了测试,并用扫描电子显微镜(SEM)对复合材料的断口形貌进行分析。结果表明,复配改性剂能很好地促进MGF与PTFE之间的界面粘结,提高MGF/PTFE复合材料的性能。当RES、PTMS的含量分别为0.3%(质量分数)、1.7%(质量分数)时,MGF/PTFE复合材料的性能最好。     

纳米金刚石与聚醚醚酮填充改性聚四氟乙烯复合材料的摩擦学性能

采用模压-烧结方法制备了纳米金刚石(ND)与聚醚醚酮(PEEK)填充改性的聚四氟乙烯(PTFE)复合材料,并研究了复合材料的摩擦磨损性能及其微观结构。结果表明,随着PEEK含量增加到20%(质量分数),复合材料的耐磨性显著提高;而较低填充量的ND可以在降低复合材料摩擦系数的情况下提高其耐磨性能。1.0%ND/20%(质量分数)PEEK/PTFE复合材料的减摩耐磨性能优良,与纯PTFE相比,该复合材料的摩擦系数下降约20%,耐磨性能提高120倍,原子力显微分析表明该复合材料中ND分布均匀。     

炭纤维/聚四氟乙烯复合材料的摩擦磨损性能

分别采用热空气氧化后经钛酸酯偶联剂处理炭纤维(CF)和氩等离子体处理聚四氟乙烯(PTFE)分散液包覆炭纤维制备CF/PTFE复合材料,研究这两种CF表面改性方法对复合材料拉伸性能及摩擦磨损性能的影响,并采用扫描电子显微镜对试样拉伸断面与磨损表面进行观察和分析。结果表明,热空气氧化后经偶联剂处理炭纤维可使CF/PTFE复合材料的拉伸强度与断裂伸长率分别提高33%和82%、磨损率下降44%,氩等离子体处理PTFE分散液包覆炭纤维可使复合材料的拉伸强度与断裂伸长率分别提高49%和100%、磨损率下降56%。     

聚丙烯/改性煤系高岭土复合材料的制备与性能

煤系高岭土经过硅烷偶联剂表面改性后,与聚丙烯(PP)树脂熔融共混制备出聚丙烯/改性煤系高岭土复合材料。通过X射线衍射、红外光谱、力学性能和扫描电镜分析,研究了改性煤系高岭土的填充量对复合材料力学性能的影响。结果表明,利用硅烷偶联剂可以实现煤系高岭土的表面改性。改性煤系高岭土填充量为3%时,复合材料具有最佳的冲击韧性。填充量为5%时,复合材料的断裂伸长率达到最大值。随着改性煤系高岭土填充量的增加,复合材料的弯曲强度和弯曲模量逐渐增大,填充量为10%时,二者比纯PP分别提高14.5%和27.5%。     

白炭黑的功能化改性及其改性橡胶基复合材料的制备与表征

利用沉淀法白炭黑生产工艺,在相同的条件下,选用不同质量分数的羟基羧酸酯作为改性剂进行湿法改性,研究了白炭黑/天然橡胶(NR)复合橡胶的力学性能、动态性能以及动态生热性能。结果表明:制备的白炭黑均为非晶态白炭黑,采用质量分数为6%的羟基羧酸酯改性的白炭黑,其分散性好,颗粒分布均匀,呈近球状,经羟基羧酸酯改性后的白炭黑有效的去除了部分亲水基团,改善了其在NR中的分散性。随着白炭黑用量的增加,分散性变差,损耗因子和动态温升均有所提高,Payne效应增大。当白炭黑用量达到临界值(白炭黑与NR质量比为40∶100)时,白炭黑/NR复合材料表现出较好的性能,改性白炭黑/NR复合材料比未改性白炭黑/NR复合材料的硬度、拉伸强度、断裂伸长率有所提高,而磨耗体积和动态生热则有所下降。动态力学性能测试结果表明,改性白炭黑与天然橡胶的质量比为40∶100时,改性白炭黑/NR复合材料的60℃滚动阻力损耗因子由0.123降到0.104。SEM结果表明,改性白炭黑在橡胶基体中的分散性优于未改性白炭黑,与NR基体界面结合的更加紧密。     

PTFE-PDMS/PET复合膜制备及其渗透汽化性能

以聚四氟乙烯(PTFE)微粉填充聚二甲基硅氧烷(PDMS)硅橡胶膜为活性皮层和PET无纺布为底膜,制备了PTFE-PDMS/PET渗透汽化复合膜并用于分离乙醇水溶液,分析了复合膜结构、疏水性、力学性能及溶胀性能.研究表明,随着PDMS复合膜中PTFE含量(质量分数,下同)增加,复合膜结晶度及水接触角增加;断裂伸长率和拉伸强度均呈现先增加后减小的趋势;膜溶胀度呈线性减少.复合膜渗透汽化选择性α和乙醇渗透系数J_E随PTFE含量的增加先增加后减少,而水渗透系数J_W呈逐渐减小的趋势,当PTFE填充量为10%时,乙醇渗透系数J_E最大.     

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 ...