裂解升温速率对聚碳硅烷先驱体转化制备Cf/SiC材料弯曲性能的影响

以聚碳硅烷(PCS)／二乙烯基苯(DVB)为先驱体制备了3D-B Cf／SiC复合材料，研究先驱体转化过程中不同裂解升温速率对材料力学性能的影响。结果表明：随着裂解升温速率的提高，材料致密度增加，界面结合变弱，从而陶瓷基复合材料的力学性能明显提高。以15℃／min裂解升温速率制得的陶瓷基复合材料的室温弯曲强度达到556．7MPa，1300℃真空下测试，材料的弯曲强度达到680．3MPa。     

活性填料在先驱体转化法纤维增强陶瓷基复合材料中的应用 Ⅰ.复合材料的致密化模型

在先驱体转化陶瓷基复合材料的制备中,坯体在裂解前后的体积发生变化。引入体系体积收缩率参数,对单一先驱体转化纤维增强陶瓷基复合材料致密化模型进行了修正。同时,分别对含惰性填料和/或活性填料的先驱体浆料浸渍-裂解纤维增强陶瓷基复合材料致密化进行了模型分析。从理论上揭示了复合材料的浸渍-裂解周期与材料的理论密度和理论孔隙率之间的关系。当先驱体浆料中含有活性填料时,复合材料的理论密度和理论孔隙率与活性填料的反应陶瓷产率、反应密度比、体积收缩率有密切的数学关系。在先驱体中引入活性填料比引入惰性填料能更为有效地提高材料的密度,降低材料的孔隙率。     

热模压辅助先驱体浸渍裂解制备Cf/SiC复合材料研究

以聚碳硅烷为先驱体,采用热模压辅助先驱体浸渍裂解工艺制备3D-B C_f/SiC复合材料,研究了热模压辅助对3D-B C_f/SiC复合材料致密度和力学性能的影响。结果表明:先驱体浸渍裂解制备陶瓷基复合材料第一次浸渍后引入高温热模压工艺可以改善材料微观结构,显著提高材料的致密度和力学性能。其中1600℃,10MPa,1h下热模压辅助先驱体浸渍裂解6次制备的3D-B C_f/SiC复合材料的密度为1.79g/cm3,弯曲强度高达672MPa,断裂韧性达18.9MPa·m1/2,剪切强度接近50MPa,且具有较好的抗热震性和高温抗氧化性。     

低分子量聚碳硅烷制备3D-Cf/SiC复合材料

研究了低分子量聚碳硅烷 (PCS) 通过先驱体浸渍裂解 (PIP) 工艺制备C_f/SiC复合材料。分析表明:PCS的数均分子量为400,活性较强,陶瓷化产率为70％左右,在1200℃基本转化为微晶态的β-SiC。分别通过3种不同升温速率制备了3D-C_f/SiC复合材料试样,其弯曲强度分别为745.2MPa、686.7MPa和762.5MPa,明显高于文献报道3D-C_f/SiC复合材料弯曲强度300~500MPa的水平。试样断口的SEM照片均显示长的纤维拔出,有良好的增韧效果,低分子量PCS裂解得到的基体比较致密。实验结果说明,低分子量PCS适合于制备3D-C_f/SiC复合材料,并且提高升温裂解速率对材料性能影响很小。      

先驱体陶瓷

综述了用先驱体法制备陶瓷纤维、陶瓷基复合材料等的特点及其研究进展,针对制备陶瓷基复合材料基体的有机聚合物先驱体,提出了先驱体必须满足的理化特性和结构特征,同时还针对先驱体法高气孔率及高收缩率的不足,提出了３个解决办法,并着重讨论了活性填料在先驱体裂解制备陶瓷基复合材料中的特点与应用。     

裂解工艺对先驱体转化制备Cf/SiC材料结构与性能的影响

以聚碳硅烷(PCS)/二乙烯基苯(DVB)为先驱体,经8个周期的反复真空浸渍-交联-裂解处理制备出三维编织碳纤维增强碳化硅(3D-B C_f/SiC)复合材料,考察了裂解工艺对材料结构与性能的影响。结果表明:提高裂解升温速率可以提高材料密度,形成较理想的界面结合,从而提高材料的力学性能。裂解温度对材料性能也有较大的影响,C_f/SiC复合材料在第6个周期采用1600℃ 裂解可以弱化纤维与基体之间的界面,提高材料致密度,材料的力学性能也得到较大改善。裂解升温速率为15℃/min,第6个周期采用1600℃裂解制备的C_f/SiC材料性能较好,弯曲强度达到556.7 MPa。      

聚硅氧烷先驱体转化制备低成本Si—O—C陶瓷基复合材料

研究了廉价聚硅氧烷的交联与裂解情况，并以其为先驱体转化制备Si-O-C陶瓷基复合材料，结果表明，在氯铂酸的催化下，聚硅氧烷与二乙烯基苯可以交联固化，当聚硅氧烷／二乙烯基苯摩尔比为1：0．5时，陶瓷产率达60．52％，经6次浸渍－交－裂解过程制备出碳纤维三维编织物增强陶瓷基复合材料，其密度达到1.59g/cm^3，弯曲强度达到321MPa，断裂韧性达到9.38MPa.m^1/2.     

先驱体浸渍-裂解法制备SiBN纤维增强SiBN陶瓷基复合材料

连续纤维增强氮化物陶瓷基复合材料是耐高温透波材料的主要发展方向,纤维是目前制约耐高温透波复合材料发展的关键,而SiBN陶瓷纤维是一种兼具耐高温、透波、承载的新型陶瓷纤维。以聚硅氮烷为陶瓷先驱体,以SiBN连续陶瓷纤维为增强体,采用先驱体浸渍-裂解法制备了SiBN陶瓷纤维增强SiBN陶瓷基复合材料,研究了复合材料的热膨胀特性、力学性能、断裂模式以及微观结构。结果表明:SiBN陶瓷纤维增强SiBN陶瓷基复合材料呈现明显的脆性断裂特征,复合材料的弯曲强度和拉伸强度分别为88.52 MPa和6.6 MPa,纤维的力学性能仍有待于提高。     

活性填料在先驱体转化陶瓷基复合材料及其构件中有应用

有机聚合物先驱体由于其分子可设计性好、成型方便、低温裂解转化为陶瓷的特点,在陶瓷纤维和纤维增韧陶瓷基复合材料的制备中表现出极大的优势。针对先驱体转化法体积收缩大、孔隙率高的不足,在先驱体中引入适当的活性填料是解决其不足的有效方法。以聚碳硅烷(PCS)为 SiC 陶瓷的先驱体,以金属(Al、Cr、Mo、Ta、Ti、W、Zr)、非金属(B、Si)及其化合物(CrSi_2、TiH_2、TiB_2)微粉为活性填料,对活性填料控制的 PCS 裂解陶瓷的陶瓷产率、线收缩率、密度、力学性能、产物结构等进行了系统的研究。对活性填料控制的 PCS 先驱体裂解陶瓷的尺寸变化进行了模型分析。从理论上揭示了活性填料的临界体积分数与活性填料反应的产率、反应前后的密度比之间的相关性。通过对 PCS/Al/SiC/N_2裂解体系反应热力学参数的计算,从理论上预测可能发生的反应与不可能发生反应。将热分析反应动力学方法应用到活性填料 Al 控制的 PCS 先驱体的裂解中。分别研究了 N_2中纯 PCS、纯 Al、Al/SiC、PCS/Al/SiC 体系各阶段的表观活化能及其裂解-反应机理函数以 X 射线衍射,电子显微镜元素线扫描等方法对 PCS/Al/SiCN_2体系的裂解-反应机理进行研究。在含活性填料的先驱体转化法制备纤维复合材料的致密化-密度增长模型中,引入体积收缩率的参数,对先驱体转化法纤维复合材料的密度增长模型进行了修正。将活性填料 Al 应用到单向 M40JB 纤维和吉林碳纤维增强 SiC 陶瓷基复合材料及反坦克导弹陶瓷喷管的制备工艺中,并对裂解产物进行了表征,获得很好的效果。这一结果对促进先驱体转化法陶瓷构件在武器装备中的应用具有重要意义。     

热压浸渍裂解法制备3D—B Cf／SiC复合材料性能的研究

本文通过先热压后先驱体浸渍裂解工艺制备3D-B Cf/SiC陶瓷基复合材料，以期达到缩短材料制备周期的目的。着重对热压温度、压力、时间等因素进行了研究，得到了可优化材料性能的工艺参数。     

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 ...