连续制备柔性导热的氮化铝/芳纶纳米纤维复合薄膜

设计制备柔性导热材料对柔性电子器件的热管理具有重要意义。本文基于溶剂剥离的芳纶纳米纤维和氮化铝(AlN)纳米颗粒,采用溶胶-凝胶-薄膜转换方法,连续制备了柔性导热的AlN/芳纶纳米纤维复合薄膜材料。其中,芳纶纳米纤维形成了三维连通的网络结构,提供力学支撑作用;AlN颗粒填充在该网络结构中,赋予复合材料良好的导热性能。结果显示,该复合材料的拉伸强度为65.5 MPa,断裂应变为12%,反复折叠300次后其拉伸强度和断裂应变保持率在90%以上,导热率为13.98 W·(m·K)?1。此外,该复合薄膜显示出良好的绝缘性能和耐热性能,体积电阻率为1.85×1015 Ω·cm、起始热分解温度为524℃。最后,演示该高性能的AlN/芳纶纳米纤维复合薄膜作为柔性基底材料,可用于冷却电子器件。      

纳米金属粒子强化正十八烷相变传热性能的实验研究

对正十八烷中分别添加纳米Cu粒子、纳米Al粒子及纳米Fe2O3粒子的复合相变材料的传热性能进行了实验研究。采用热针法分别对正十八烷及其与纳米金属粒子的复合相变材料的固态体系、液态体系的导热系数进行了实验研究,结果表明:在正十八烷中添加纳米金属粒子后,纳米金属粒子/正十八烷复合相变材料固、液态体系的导热系数随着纳米金属粒子质量分数的增加而显著提高,且纳米Al粒子/正十八烷复合相变材料导热系数的提高较其他两者更为明显。采用DSC对正十八烷及添加了不同质量分数的纳米金属粒子/正十八烷复合相变材料的相变潜热及相变温度进行了实验研究,结果表明:纳米金属粒子/正十八烷复合相变材料的相变潜热比纯正十八烷材料略低,且随纳米金属粒子质量分数的增大逐渐减小,但其相变温度变化不大。     

细菌纤维素/氧化铝/二氧化硅改性石墨烯复合导热膜的结构与性能

采用真空辅助抽滤方法制备了细菌纤维素(BC)/球形氧化铝粒子/改性石墨烯纳米片(SiO_2@GNPs)薄膜热界面材料,研究了球形氧化铝粒子粒径对热界面材料形态结构和导热性能的影响。结果表明,球形粒子与二维片状导热粒子复配时,可有效构筑面外方向导热通路。调节氧化铝粒子和改性石墨烯纳米片的直径比可有效调整改性石墨烯纳米片在复合薄膜中在面外方向的取向程度,从而提高复合材料的面外导热系数。随着球形氧化铝的直径从2μm增加到60μm,导热薄膜的面外导热系数从0.5 W/(m·K)提高到4.2 W/(m·K),导热系数提高了7.4倍。     

导热型高性能树脂微电子封装材料之二:封装材料的导热和热膨胀性能

微电子行业迫切需要新一代优异性能的封装材料。采用聚酰亚胺/氮化铝复合材料作为封装材料，可以组合聚酰亚胺和氮化铝的优点，具有高导热、低热胀、低介电、电绝缘等优异的性能，应用于现代微电子领域前景良好。文章讨论了这种封装材料的导热性能和热膨胀性能。PMR聚酰亚胺/氮化铝复合封装材料导热系数随氧化铝的加入量而显著提高，Bruggeman方程最适合于描述该封装材料的导热系数。PMR聚酰亚胺与氮化铝复合后热膨胀系数显著减小。     

铜纳米粒子强化正十八烷相变传热性能的实验研究

针对纯石蜡(正十八烷)作为固-液相变储能材料存在导热系数小、传热性能差的缺点,采用两步法制备了铜纳米粒子质量分数分别为0%、0.1%、0.2%、0.5%、1%、2%的铜纳米粒子/正十八烷复合相变材料,并对其热物性进行了实验研究。采用瞬态热针法测量复合相变材料的导热系数。实验结果表明,铜纳米粒子可有效提高正十八烷的导热系数。利用DSC对铜纳米粒子/正十八烷复合相变材料进行热分析,结果表明,体系中添加铜纳米粒子后正十八烷的相变温度变化很小,而体系的相变潜热随铜纳米粒子质量分数的增加而逐渐减小,但减小幅度不大,因此铜纳米粒子的加入对正十八烷的蓄热能力影响较小。另外,对铜纳米粒子质量分数为1%的铜纳米粒子/正十八烷复合相变材料的热稳定性进行研究,结果表明其具有良好的热稳定性。     

有机硅基导热硅脂的改性及渗油机理研究

针对目前传统导热硅脂渗油现象严重的问题,以铝粉和银粉为填料制备有机硅基导热硅脂,采用硅烷偶联剂改性粉体、添加聚硅氮烷改性硅油、添加纳米氮化铝粒子3种方法改善导热硅脂的渗油性能,分别测试其在高温加热和热循环实验后的渗油性能。结果表明,3种改性导热硅脂的渗油抑制性能相较市售导热硅脂明显改善,其中添加纳米氮化铝粒子的导热硅脂渗油抑制效果最佳,其分油量为0. 049%(质量分数)。改性导热硅脂经过热循环后,渗油性未发生明显变化。     

SiO_2表面包覆改性钛酸钡/聚酰亚胺复合薄膜的制备与性能

以聚酰亚胺(PI)为基体,将聚酰亚胺与钛酸钡(BaTiO3)纳米粒子进行复合,采用原位聚合法制备BaTiO3/PI复合薄膜。为提高BaTiO3纳米粒子的分散性和表面性能,采用SiO2对BaTiO3纳米粒子进行表面包覆改性,并制备改性BaTiO3/PI复合薄膜。采用红外光谱、X射线衍射、扫描电镜等对制备得到的改性BaTiO3进行了表征,测试了复合薄膜的介电性能。结果发现,SiO2与BaTiO3粒子间仅是物理包覆,没有新物质形成。测试频率为103 Hz时,质量分数为5%的SiO2包覆改性使复合薄膜的介电常数增大到21.8,介电损耗为0.00521,击穿强度为76 MV/m,储能密度为0.56J/cm3。研究表明,采用SiO2对BaTiO3改性使得复合薄膜的介电性能有所提高。     

导热聚对苯二甲酸丁二醇酯的制备及不同成核剂对其结晶性能的影响

为提高聚对苯二甲酸丁二醇酯(PBT)的导热系数,在PBT基体中添加导热填料氮化铝(AlN)、氮化硼(BN)制备复合导热PBT材料。导热填料的加入使树脂的物理机械性能下降,采用差示量热、X射线衍射等方法研究了不同成核剂对导热PBT结晶性能的影响。结果表明:成核剂的加入改善了导热PBT的结晶性能,同时恢复了其物理机械性能。其中氧化镁起到了明显的成核作用,提高了导热PBT的结晶度、结晶峰峰值温度和熔融焓。     

高效热管理用金属基复合材料研究进展

从高导热复合构型、高导热复合界面及新型高导热纳米碳增强体3个方面,综述了热管理用铜基和铝基功能复合材料的研究进展,并对高导热金属基复合材料的未来发展方向进行了预测与展望.在材料组分相同的情况下,基于金属基体与导热增强体之间复合构型和复合界面的差异,制备的金属基复合材料的导热与热膨胀性能会发生显著变化.此外,由于纳米增强体与基体在形貌、尺寸及表面化学性质等方面的不相容性,在新型高导热金属基纳米复合材料的研发过程中,更需要兼顾高导热复合构型与复合界面的优化设计.可以预言,采用碳纳米管、石墨烯纳米片等新型纳米碳增强体,设计与制备具有微/纳米跨尺度分级复合构型的金属基复合材料将成为未来的研究热点.     

导热型高性能树脂微电子封装材料之一:封装材料的制备

微电子行业迫切需要新一代优异性能的封装材料。采用聚酰亚胺／氮化铝复合材料作为封装材料，可以组合聚酰亚胺和氮化铝的优点，具有高导热、低热胀、低介电、电绝缘等优异的性能，应用于现代微电子领域前景良好。文章讨论了这种封装材料的制各，首先将单体反应物反应得到聚酰亚胺预聚体，然后将预聚体与氮化铝高能球磨混合，最后热压成型。成功制各出一系列聚酰亚胺／氮化铝复合导热型高性能塑料微电子封装材料。     

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 ...