聚硅氧烷的交联与裂解陶瓷化研究

研究了含氢聚硅氧烷(HPSO)与二乙烯基苯(DVB)的交联与裂解行为。结果表明,氯铂酸能有效催化两者之间的交联反应。DVB/HPSO质量比例对交联程度和陶瓷产率有明显影响。催化剂的含量为11.31×10-6、m(DVB)/m(HPSO)=0.5∶1的体系在120℃交联6h后达到完全交联状态。1000℃时裂解完全,陶瓷产率76%,产物组成为38.33%Si、27.33%O、34.34%C。DVB/HPSO的裂解陶瓷化主要发生在370℃～800℃范围内,分为两个阶段。第一阶段在420℃～610℃区间,裂解活化能为208.38kJ/mol,由随机成核步骤控制裂解反应。第二阶段在620℃～800℃区间内,裂解活化能为339.89kJ/mol,由一维扩散步骤控制裂解反应。     

采用聚硅氧烷(HPSO VPSO)和Al-Si粉连接无压烧结SiC陶瓷

采用含氢聚硅氧烷(HPSO)和含乙烯基聚硅氧烷(VPSO)2种陶瓷先驱体作为连接剂的主要组分, 以Al-Si粉为填料, 通过反应成形连接工艺连接无压烧结碳化硅。采用热重法、 差示扫描量热法和X射线衍射法研究了Al-Si粉对HPSO和VPSO的混合物(HPSO-VPSO)的裂解过程和陶瓷产率的影响, 同时也研究了Al-Si粉含量、 升温速率及连接温度对连接强度的影响。并采用扫描电镜和能谱仪对连接件界面区域的微观结构和成分进行了分析。Al-Si粉的加入促进了HPSO-VPSO的裂解, 提高了陶瓷产率。当HPSO-VPSO与Al-Si粉质量比为1∶1, 连接压力为50kPa, 连接温度为900℃, 高温保温时间为30min, 升温速率为4℃/min时, 所得连接件的连接强度(剪切强度)达到最大值93MPa。连接层厚度约为75μm, 结构均匀致密, 连接层与母材结合良好, 在界面处没有明显的裂纹、 孔洞等缺陷。Al、 Si元素在连接层与无压烧结碳化硅的界面处发生了扩散, 促进了界面结合, 从而提高了连接强度。      

聚硅氧烷先驱体转化制备三维Cf/Si-O-C复合材料的研究

研究了含氢聚硅氧烷(PSO)与二乙烯基苯(DVB)的交联与裂解。结果表明:只有在氯铂酸的催化作用下,PSO与DVB才能完全交联。DVB/PSO质量比对陶瓷产率的影响较大,DVB/PSO＝0.5时陶瓷产率最高,达到76%。裂解产物中Si,C,O的含量分别为38.3wt%,34.3wt%,27.4wt%。以质量比为0.5的DVB/PSO体系为先驱体,采用先驱体转化法制备出三维C_f/Si-O-C复合材料。研究发现:第一次裂解时采用热压辅助可以明显提高材料的力学性能。第一次在1600℃,10MPa的条件下热压裂解5min,后续真空浸渍-常压裂解处理六个周期所制得的材料具有较高的力学性能,其弯曲强度和断裂韧性分别为502MPa,23.7MPa·m 1/2。理想的界面结合状态是其具有高性能的主要原因。     

硅树脂249的交联与裂解陶瓷化研究

研究了硅树脂249(SR 249)的交联与裂解行为。结果表明,SR 249在250℃能自交联,其机理主要通过硅羟基脱水缩合实现。裂解产物组成为34.69%S i,37.99%C,27.32%O。SR 249的裂解陶瓷化主要在470℃~1150℃范围,分为三个阶段。第一阶段在470℃~600℃区间,裂解活化能为23.32 kJ/m o l,由随机成核步骤控制裂解反应。第二阶段在720℃~800℃区间内,裂解活化能为196.95 kJ/m o l,由三维扩散步骤控制裂解反应。第三阶段在1000℃~1150℃区间内,裂解活化能为135.87 kJ/m o l,由随机成核步骤控制裂解反应。引入纳米级活性填料A l、S i进行裂解,可以减少裂解产物中的自由炭,形成S i-A l-O-C陶瓷。     

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 ,并以其为先驱体制备出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 6 0 5 2 %。经 6次浸渍 交联 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 5 9g cm3 ,弯曲强度达到 32 1MPa ,断裂韧性达到 9 38MPa·m1 2 。     

含铁碳化硅复合材料的制备

以聚碳硅烷(PCS)、羰基铁(Fe(CO)_5)、二乙烯基苯(DVB)和碳化硅(SiC)纤维为原料,采用先驱浸渍裂解工艺制备含铁碳化硅纤维增强碳化硅基(SiC_f/SiC)复合材料,研究了原料配比对交联反应的影响,以及浸渍次数对复合材料致密度及陶瓷产率的影响。研究表明:当羰基铁添加量为20%(质量分数),二乙烯基苯为5%(质量分数)时有利于基体交联的进行;经1100℃裂解后基体中可明显观察到β-SiC晶体的生成;经5次浸渍裂解,制得的复合材料密度为1.72g/cm~3,孔隙率为20.43%,陶瓷产率得到提高,达到82.67%。     

不同陶瓷先驱体的裂解过程及粘接性能

研究了三种陶瓷先驱体聚硅氮烷（PSZ）、聚硅氧烷（PSO）、聚碳硅烷（PCS）的裂解过程,并对其裂解产物进行了物相分析,在此基础上分别采用这三种先驱体为粘接剂连接碳化硅陶瓷。结果表明,PSZ、PSO在裂解过程中发生了交联反应,获得了较高的陶瓷产率;PCS交联性能较差,陶瓷产率较低;由XRD分析得出,在1200℃～1400℃温度范围内,随着温度的升高,三种先驱体的裂解产物均发生了由非晶态向晶态的转变。连接实验表明,采用PSZ、PSO为粘接材料均能获得较好的连接效果,连接件剪切强度分别达38．6MPa和33．2MPa,连接层厚度小于5μm,其结构较为均匀致密,与基体间界面接合良好;采用PCS为粘接材料时,不能获得有效的连接强度。     

硅硼复配对木塑复合材料阻燃协效作用的研究

木塑复合材料(WPC)的阻燃研究近年来得到了广泛关注,硅系与硼系阻燃剂作为环境友好型阻燃剂成为了研究热点。将纳米SiO_2、聚硅氧烷分别与硼酸锌复配,应用在杨木粉-聚丙烯复合材料中测试其燃烧性能及力学性能,以判断是否具有阻燃协效作用及其对材料力学性能的影响。结果表明:纳米SiO_2、聚硅氧烷与硼酸锌之间存在阻燃协效作用,当m(纳米SiO_2)∶m(聚硅氧烷)∶m(硼酸锌)=4∶2∶4时,加入20%(wt,质量分数)的阻燃剂,阻燃型复合材料的燃烧性能达到最佳,极限氧指数为32.6%,UL-94达到V-0级,800℃时材料的残炭量达到37.2%。     

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.     

过氧化苯甲酰在液态聚碳硅烷交联中的应用

聚碳硅烷热解前的交联对于提高其最终陶瓷产率至关重要.研究了过氧化苯甲酰(BPO)引发液态超支化聚碳硅烷(HBPCS)的交联反应对于陶瓷产率的影响.FT-IR和GPC证实,添加为0.5%～2.0%(质量分数,下同)的BPO,即可在80～140℃下引发HBPCS交联;在考察的实验条件下,提高交联温度、延长反应时间或增加BPO用量,均可提高HBPCS交联程度.BPO用量为2.0%时,HBPCS交联样品在1000℃下的陶瓷产率高达65%,比未加BPO的提高25%.     

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 ...