Pr_(6)O_(11)对合成金刚石单晶各向异性的刻蚀EI北大核心CSCD

为了探究稀土氧化物对合成金刚石单晶的各向异性刻蚀,在氮气保护下,在750~950℃内用Pr_(6)O_(11)对合成金刚石单晶进行刻蚀。采用扫描电子显微分析、热重分析、X射线衍射和拉曼光谱等技术对刻蚀后金刚石单晶不同晶面的表面形貌、物相组成和刻蚀机理进行表征与分析。采用最大刻蚀深度、单颗粒抗压强度和冲击韧性来表征刻蚀前后金刚石性能的变化。结果表明:Pr_(6)O_(11)对金刚石{100}面和{111}面的刻蚀程度和形貌均不同;当温度为750℃时,Pr_(6)O_(11)对金刚石单晶已有一定程度的刻蚀,随刻蚀温度的增加,刻蚀加剧,且金刚石{111}面的刻蚀程度比{100}面严重;{111}面刻蚀坑形貌从三角形变为层状结构三角形,{100}面由轻微的四边形变为类蜂窝状刻蚀坑;{111}面最大刻蚀深度从1.12μm增加到12.54μm,而{100}面只从0.30μm增加到2.11μm;金刚石单颗粒的抗压强度由未刻蚀金刚石的576.25 N降低到最小530.06 N,冲击韧性由92.94 J/cm^(2)减小到88.53 J/cm^(2);Pr_(6)O_(11)对金刚石单晶的刻蚀机理在885℃前为催化石墨化,885℃后为催化石墨化和氧化。     

(111)晶面同质外延生长单晶金刚石的研究

利用微波等离子体化学气相沉积(MPCVD)法,在天然金刚石衬底的(111)晶面上同质外延生长单晶金刚石,研究了沉积温度、CH_4浓度以及小角度偏离(111)晶面的衬底对金刚石生长的影响。采用SEM和Raman对外延生长的金刚石进行表征,结果表明:高沉积温度、高CH_4浓度条件下,金刚石呈现出无序的多晶生长现象,随着沉积温度的降低,形貌和质量明显提高,在低沉积温度条件下金刚石表现出一致的单晶生长,但是表面形貌较为粗糙。进一步降低CH_4浓度可外延生长质量高、表面平整的单晶金刚石,速率达4.7μm/h.使用倾斜抛光方法将部分衬底面偏离(111)晶面约6°,对比实验发现,微小偏离(111)晶面的斜面衬底在高沉积温度、高CH_4浓度条件下也能生长出质量较好的单晶金刚石,生长速率明显提高,达到了9μm/h。     

直流热阴极PCVD法间歇生长模式制备透明金刚石膜

采用直流热阴极等离子体化学气相沉积(直流热阴极PCVD)方法,通过金刚石膜的间歇生长过程,引入氮原子的作用,实现对非金刚石成份的刻蚀和金刚石膜的择优取向生长,在CH4:N2:H2气氛下制备透明金刚石膜。金刚石膜的间歇式生长分为沉积阶段和刻蚀两个阶段,沉积阶段为20 min,刻蚀阶段为1 min,沉积和刻蚀通过温度的调节来实现,总的生长时间10 h;实验中主要改变的参数是N2气比例,将N2气流量与总气体流量的比例分为高、中、低三档分别进行实验。结果在CH4:N2:H2比例为2:20:180时获得了透明金刚石膜。金刚石膜样品用Raman光谱仪、SEM和XRD进行了表征,研究表明,直流热阴极PCVD间歇生长模式下,通过引入氮原子的作用,可以制备出(111)面取向的透明金刚石膜。     

氧化铁刻蚀金刚石表面形貌的表征及形成机理

为了系统研究不同温度下氧化铁刻蚀金刚石表面的形貌及形成机理,以人造金刚石为刻蚀材料,以氧化铁作为刻蚀剂,先将金刚石洗净,然后将金刚石与氧化铁以质量比为1∶5混合均匀、压实,用氮气作为保护气氛,在650～850℃下用氧化铁刻蚀金刚石单晶表面。再用扫描电子显微镜及其3D重建技术、热重分析、X射线衍射和拉曼光谱等方法对刻蚀后金刚石单晶不同晶面的表面形貌、表面粗糙度、物相组成和刻蚀机理进行了表征与分析。首次用3D重建技术对刻蚀后金刚石不同晶面的形貌进行了立体观测,用铜基结合剂金刚石试样的抗弯强度来评估刻蚀对金刚石与结合剂间结合力的影响。结果表明:氧化铁在不同温度下均能有效刻蚀金刚石单晶,且对不同晶面的刻蚀程度和形貌是各向异性的;当刻蚀温度为650℃时,氧化铁对金刚石单晶已有一定的刻蚀;随温度的升高,刻蚀加剧;在相同条件下,金刚石单晶的{100}面刻蚀程度比{111}面严重,{100}面表面粗糙度S_a从0.84μm升至3.73μm,{111}面表面粗糙度S_a从0.77μm升高至2.01μm。刻蚀后,金刚石单晶的不同晶面形貌由金刚石本身的原子排列决定,随着刻蚀温度从650℃升至850℃,金刚石{100}面刻蚀坑从四边形变为八边形,{111}面由轻微的点状变为三棱锥形凸起。氧化铁对金刚石单晶的刻蚀机理是金刚石的氧化过程。刻蚀后,铜基结合剂金刚石试样的抗弯强度有较大的提高。     

CVD金刚石薄膜(111)与(100)取向生长的热力学分析

用非平衡热力学耦合模型计算了CVD金刚石薄膜生长过程中C2H2与CH3浓度之比[C2H2]/[CH3]随衬底温度和CH4浓度的变化关系,从理论上探讨了金刚石薄膜（111）面和（100）面取向生长与淀积条件的关系。在衬底温度和CH4浓度由低到高的变化过程中,[C2H2]/[CH3]逐渐升高,导致金刚石薄膜的形貌从（111）晶面转为（100）晶面。添加氧后C2H2与CH3浓度都将下降,但C2H2下降得更多,因而添加氧也使[C2H2]/[CH3]下降,从而有利于生长（111）晶面的金刚石薄膜。     

低偏压下化学气相沉积金刚石薄膜的生长形貌研究

在微波等离子体化学气相沉积装置中，研究了偏压电压、甲烷浓度及沉积气压对金刚石晶形显露的影响。实验结果表明，生长时施加低的衬底偏压对金刚石的晶形显露有较大的影响，正的偏压有利于(111)面显露，负偏压有利于(100)面显露。在低偏压条件下生长时，低的沉积气压和甲烷浓度有利于(111)面显露；而高的气压和甲烷浓度有利于(100)面显露。过高的甲烷浓度将恶化金刚石质量，出现菜花状组织，无明显的晶面显露。     

低压气相合成金刚石的机理研究新进展

本文第1部分评述了低压气相合成金刚石的进展。第2部分介绍了用表面分析方法和HREM对金刚石(111)和(100)面的生长机理,原子氢和氧对金刚石生长本身的影响,亚稳态条件下金刚石的晶形显露规律,硅衬底上的形核机理和初期生长规律进行研究所取得的重要进展。     

大气下火焰法合成金刚石薄膜

本文介绍了用氧-乙炔火焰法在大气下合成金刚石薄膜的实验结果,初步研究了基板温度对金刚石晶体生长速度、结晶习性的影响,指出了在金刚石(111)及(100)晶面上外延单晶金刚石膜的温度范围,还探讨了氧对薄膜的质量均匀性的影响。     

碳氧比对金刚石薄膜生长的影响

采用微波等离子体化学气相沉积法,以H_2/CH_4/CO_2为混合气源,通过改变气源碳氧比,探讨了碳氧比对金刚石薄膜生长的影响。利用扫描电子显微镜(SEM)、X射线衍射(XRD)和Raman光谱表征金刚石薄膜的表面形貌、晶粒取向和结晶质量。结果表明,随着C/O比的降低,金刚石膜表面形貌由原来的(100)面为主转向(111)面为主的金字塔形,薄膜质量有所提高,内应力降低。     

C-H-O和C-H-N体系生长金刚石膜的气相化学模拟

数值模拟了C-H-O和C-H-N体系的气相化学,构建了含氧和含氮气源化学气相沉积金刚石膜的三元相图,探讨了加氧和加氮影响金刚石膜生长的途径.结果表明,甲基是金刚石生长主要的前驱基团,乙炔导致非金刚石碳沉积,原子氢刻蚀非金刚石碳.通过气相反应改变这些基团的浓度是加氧的一个重要作用途径,而加氮在改变这些基团浓度的同时,CN等含氮基团还强烈地参与了金刚石膜成核和生长的表面过程.     

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 ...