聚乙烯醇基相变复合材料研究进展

亲水性聚乙烯醇(PVA)具有相对较好的可加工性、安全性及生物可降解性,被广泛用作支撑材料,可将相变材料封装在其三维网状结构中以解决相变组分泄露的问题并使复合材料获得良好的导热性。基于此,综述了分别利用分子间作用力、共价键将PVA基体与相变材料复合的物理共混法及化学接枝法,对比了两种方法用于封装相变材料的优缺点;总结了目前PVA基相变复合材料的类型、成型方法及性能,包括经湿法纺丝、干法纺丝及静电纺丝等方法制备的相变复合纤维,经物理共混法制备的相变复合膜以及经一步法原位复合制备的相变复合多孔材料;分析了复合材料中相变组分及成型工艺等对材料结构及相变蓄热、力学及热稳定性等性能的影响;同时展望了功能化PVA基相变复合材料的研究方向及发展前景。     

有机/无机复合相变储能材料的长期化学稳定性研究

根据傅立叶变换红外光谱图,对用真空浸渗法制备的多孔介质基复合相变储能材料的相变循环稳定性进行了研究。对其中的有机相变材料月桂酸的结构进行了分析,并与未经相变循环的纯月桂酸及月桂酸盐的红外谱图进行了对比。结果表明,月桂酸相变材料的各个基团和化学键的振动吸收峰仍然存在,与基体材料的化学相容性非常好。     

吸热型隔热材料在冲压发动机热防护中的应用

首先介绍了相变吸热材料的概念、分类及部分相变材料的热物性,并探讨了其在冲压发动机热防护中的应用价值.无机熔融盐具有较高的相变温度和较大的相变焓,适于作为冲压发动机热防护热端相变材料;热防护层冷端选择多元醇作为相变材料,可通过相变吸热有效减缓冷端升温速率.以纤维多孔陶瓷作为基体制备复合相变材料可解决无机熔融盐的液相流动渗透问题,并讨论了复合材料的制备工艺.     

基于溶-凝胶制备工艺的SiO_2基复合相变材料研究综述

相变材料可吸收或释放潜热,从而拥有储能调温潜力。溶-凝胶工艺制备的SiO_2基体可为相变材料提供优良的骨架结构,改善相变材料的泄露问题。总结国内外相关文献,介绍了溶-凝胶制备工艺及SiO_2基复合相变材料的形貌。阐述了SiO_2基体与相变材料间的化学相容性、SiO_2基体对相变材料结晶性能的影响以及SiO_2基复合相变材料的热物性、热循环稳定性和储/放热性能。最后对引入碳纤维/碳纳米管和金属/金属氧化物粒子等功能型材料,以增强其导热性能及光热转化能力的两类增强型SiO_2基复合相变材料进行了概述。     

生物质多孔高导热碳基复合相变材料热性能的研究进展

通过现有文献的研究总结了生物质基的制备方法，主要通过物理改性方法制备出生物质基三维多孔碳载体、生物质气凝胶等封装相变材料防止泄露；通过高分子聚合、静电纺丝等化学制备法实现对相变材料的封装。针对复合相变材料导热性能差提出多孔材料吸附、微胶囊化、添加导热材料等方法以提高导热性能。对比了以无机多孔材料为载体和以生物质多孔基为载体的不同复合材料的导热系数，分析两种载体的优缺点。同时指出多元混合相变材料与生物质微胶囊化的研究方向，且目前在生物质基的基础上添加高导热材料的研究相对较少，对此不足之处进行探究，在未来可以制备出性能更佳的复合材料应用于更多领域。     

生物质多孔相变材料的制备及调温调湿性能研究

以废弃核桃壳为原料,采用磨细、化学-物理耦合活化、微波加热法,制备出生物质多孔材料。采用压汞法、扫描电镜分别测试了生物质多孔材料的孔径分布和孔隙特征。试验表明:制备生物质多孔材料的最佳工艺条件为:微波功率640W,活化时间6min,磷酸质量分数85%。采用真空浸入法,将有机相变材料渗入生物质多孔材料中,试验得出:生物质多孔材料与相变材料质量比为4∶6时,其吸附量可达34.7%。将多孔复合基体为调节剂,以不同比例掺入建筑石膏内。采用DSC对其热储存能力进行测试,采用饱和盐溶液方法对其湿性能进行试验。结果表明:改性剂的加入赋予建筑石膏具有较好的储热储湿能力。     

石蜡/多孔火山岩复合相变材料的制备及性能表征

基于相变理论,以石蜡为相变材料、毫米孔径的多孔火山岩为吸附基体,通过真空吸附及环氧包封制备出石蜡/多孔火山岩复合相变材料。对复合相变材料吸附性能、储热性能、导热性能和结晶性能进行表征,并分析多孔火山岩中与石蜡的作用机理。结果表明:多孔火山岩对石蜡的平均吸附率为15.3%;红外光谱分析结果显示二者之间的吸附仅为物理吸附;复合相变材料的相变起始温度为34.2℃,相变焓为35.32J/g,导热系数为0.6972W/(m·K);XRD分析结果表明,石蜡在复合相变材料中仍具有良好的结晶性能。     

有机/复合相变储能材料研究进展

相变储能材料在相变过程中实现能量的储存或释放,这种材料因具有优良的性能而成为近年来研究的热点.主要介绍了相变材料的分类、性质以及评价标准,着重讨论了有机/复合相变材料的一些常见的制备方法,如原位聚合法、界面聚合法、喷雾干燥法、多孔材料吸附法和溶胶-凝胶法等.概括了相变材料在太阳能利用、建筑材料、空调蓄冷、工业余热回收和军事伪装隐身等方面的应用研究,并提出了相变材料研究的未来发展趋势.     

聚乙烯醇/相变微胶囊多孔定形复合相变材料的制备及性能

实验中将相变微胶囊乳液与聚乙烯醇(PVA)溶液复合,通过物理发泡法制得具有形状记忆性能的多孔定形复合相变材料,研究了相变微胶囊对多孔定形复合相变材料孔结构及吸水保水性、相变性能、形状记忆性能等的影响。结果表明,所制备多孔定形复合相变材料的孔结构随着微胶囊乳液用量的增大出现并泡现象,孔径与开孔率增大;吸水率与保水率明显提高,吸水率最大可达1025%;相变焓值随相变微胶囊乳液用量的增大而增大,可达10.85 J/g,具有良好的相变储热性能;多孔定形复合相变材料经弯折形变固定后,热致形变回复率5 min内可达77.8%,湿致形状回复率在1 min内可达到83.3%,具有较好的形状记忆特性。     

聚乙二醇/二氧化硅复合相变蓄热材料的性能研究

以二氧化硅(SiO2)为载体、聚乙二醇(PEG)为相变蓄热材料,利用多孔的二氧化硅良好的吸附性能,制备出聚乙二醇/二氧化硅复合相变材料.由于二氧化硅的多孔网络结构,其毛细作用力和表面张力使得聚乙二醇在发生固液相变的过程中,失去了流动性.实验结果证明,聚乙二醇/二氧化硅复合相变材料仍具有较高的蓄热能力.同时二氧化硅作为基体材料形成空间传热网格,较大的提高了相变材料的导热率.     

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.     

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...     

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.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

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.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

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.……     

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles.