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。     

2D-C/C复合材料氧化动力学模型及其氧化机理

用热重法研究了二维炭/炭(2D-C/C)复合材料的等温氧化, 提出了氧化动力学模型, 用SEM观察了样品不同氧化程度的微观形貌, 并探讨了材料的等温氧化机理。氧化分2个阶段: 线性氧化阶段, 氧化失重率小于约65%, 氧化速率处于稳定状态; 非线性氧化阶段, 氧化失重率约大于65%, 氧化速率急剧减小。Arrhenius曲线由折点在800~850℃之间的2条直线组成。线性氧化阶段, 活化能分别为217.2kJ/mol和157.0kJ/mol; 非线性氧化阶段, 反应级数分别为0.55和0.65, 活化能分别为219.3kJ/mol和182.0kJ/mol。通过实验验证, 氧化动力学模型可以较好地预测材料的恒温氧化。氧化从炭纤维与基体炭的界面开始, 基体氧化快于纤维, 氧化后期主要是纤维的氧化。在750~800℃, 氧化为化学反应控制; 在850~905℃, 氧化由化学反应和气体扩散共同控制, 但非线性氧化阶段气体扩散对氧化的贡献小于线性氧化阶段。      

丙烯热解炭过程的气相产物分析和动力学研究(英文)

以丙烯为碳源,在700℃～1200℃进行化学气相沉积热解炭。采用气相色谱和质谱联用对反应过程中的气体产物进行定性和半定量分析,采用磁悬浮天平实时称量反应过程中的固相产物进行动力学研究,在此基础上提出丙烯分解形成热解炭的机理。气相产物的分析结果表明:丙烯热解过程产生30多种芳香化合物,随着温度的升高,主要反应生成物由萘转变为苯;动力学研究结果表明,800℃～1000℃的活化能为137±25kJ/mol,生成乙炔的基元反应控制固相产物的形成。当温度高于1000℃时,沉积行为由气相分子通过边界向固相表面扩散和气相成核共同控制,形成热解炭的主要物质逐渐由苯转变为不饱和碳氢化合物如乙烃,乙烯等。     

丙烯化学气相沉积热解碳的原位动力学

以丙烯为气源,在800℃～1200℃进行化学气相沉积热解碳。研究了温度、压力和滞留时间对沉积速率和气相产物的影响。采用磁悬浮天平原位实时称量反应过程中的固相产物进行动力学研究;采用气相色谱和质谱联用半定量分析了反应过程中的气体产物。动力学研究结果表明, 800℃～1000℃内活化能为137 kJ/mol±25 kJ/mol,沉积过程为化学动力学控制;高于1000℃时,沉积行为由气相分子的传质和气相成核控制。压力和滞留时间对沉积速率的影响说明,热解碳是经过一系列气相反应和固体表面反应后获得。气相产物分析说明,不同控制机制时形成热解碳的主要物质不同。在此基础上提出了丙烯分解形成热解碳的机制。      

聚硅氧烷制备高比表面积微介孔炭材料(英文)

通过对聚甲基(苯基)硅树脂(SR249)在1250～1350℃、真空气氛下裂解以及氢氟酸酸洗处理制备得到具有高比表面积的纳米多孔炭材料。采用X-ray衍射光谱、拉曼光谱、元素分析、透射电镜及氮气吸附法对不同温度所制样品进行元素组成及结构研究。裂解产物中的SiO2相作为一种天然模板经腐蚀处理除去。裂解温度和酸洗处理对多孔炭材料的成分和结构变化影响较大。HF酸处理前,裂解产物的比表面积小于55m2/g;而酸洗后产物比表面积和总孔容量显著增加,而最高值是裂解温度为1300℃时获得,分别为1148m2/g、0.608 cm3/g。经酸洗处理得到的多孔炭,孔径分布均相对较窄,在1～4 nm。透射电镜结果显示炭材料中的自由碳相和少量的SiC纳米晶及SiOC陶瓷彼此相互包裹。     

3221中温固化环氧树脂体系的固化反应

采用DSC方法研究了不同固化体系对3221环氧树脂固化体系固化反应的影响,探讨了反应机理,分析了双氰胺及双氰胺 取代脲作为固化剂的反应动力学,预测了氰胺 取代脲固化体系的固化工艺参数,并加以验证。结果表明,采用双氰胺 取代脲的复合固化体系能使3221体系的表观活化能Ea比单独使用双氰胺时降低58 kJ/m o l,前者固化温度比后者降低50℃左右,并能使反应缓和。     

真空碳热还原钛精矿中铁的等温动力学北大核心CSCD

采用等温动力学研究的方法在1100~1300℃下对攀枝花钛精矿真空碳热还原中铁的动力学进行了研究。研究结果表明:还原温度的升高和保温时间的延长,能促进钛精矿中Fe3O4的还原以及铁的聚集长大;钛精矿中的铁在1100~1250℃保温的前期即0~30 min时,还原反应受界面化学反应控制,反应的表观活化能为207.92 kJ/mol;在1100~1200℃保温的后期即30~90min时,还原反应受内扩散控制,反应的表观活化能为521.47 kJ/mol。     

温度对CVD法在纤维表面制备BN涂层的影响

采用BCl_3-NH_3-H_2体系,在不同温度下通过化学气相沉积法在SiC纤维表面沉积BN涂层。研究温度对BN涂层的沉积速率、形貌、组成以及结构的影响。结果表明:在低温阶段(700~900℃),生长速率随着温度的增加而增大,该结果与阿仑尼乌斯定律相一致,计算得出该反应表观活化能为57.2kJ/mol。涂层表面光滑致密,沉积均匀,沉积速率受表面反应控制。在900℃时,反应速率达到最大值(174nm/h),此时,反应速率由表面反应控制转变为物质运输控制。在高于900℃时,由于气相成核的缘故,沉积速率随着温度的增加而减小,涂层变得疏松粗糙。BN涂层为化学计量比1∶1的乱层结构,有序度随着制备温度的升高而增大。     

非等温动力学积分-微分法研究聚苯乙烯热解反应机理及动力学参数

首次采用积分-微分相结合的方法研究了聚苯乙烯非等温热解动力学,通过比较同一机理函数的微分和积分法结果,推测了聚苯乙烯热解所遵循的机理及动力学参数。实验结果显示,在氮气中聚苯乙烯有一个失重阶段,温度范围282.9℃~398.2℃,在此范围内约有96%聚苯乙烯发生了分解,其最大失重速率发生在372.4℃。积分-微分法拟合结果表明,聚苯乙烯在氮气中的热解符合一级化学反应,其动力学模型方程式为:dα/dt=A exp(-E/RT)(1-α)。平均表观活化能E为199.2 kJ/m o l,lnA为36.56。     

低温化学气相沉积SiC涂层沉积机理及微观结构

由MTS-H2体系在1000～1300℃沉积了SiC涂层,研究了SiC涂层沉积速率和温度之间的关系,MTS-H2体系沉积反应的平均活化能为114kJ/mol,用理论模型证明了低温化学气相沉积SiC为动力学控制过程.SiC涂层表面的显微结构随沉积温度变化而呈现规律的变化:沉积温度T<1150℃时,CVD SiC涂层表面致密、光滑;T≥1150℃时,CVD SiC涂层表面变得疏松、粗糙.随着沉积温度的升高,CVD SiC涂层的结晶由不完整趋向于完整;当沉积温度T≥1150℃,CVD SiC涂层的XRD谱图中除了β-SiC占主体外还出现了少量α-SiC.     

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 ...