类金字塔状GaN微米结构的生长及其形貌表征

采用金属有机化学气相沉积(MOCVD)技术,在非掺杂GaN层上原位生长SiNx掩模层,制备了形貌可控的类金字塔状GaN微米结构,并系统研究了生长温度、生长时间、反应压力和Ⅴ/Ⅲ比等不同生长参数对其形貌的影响。研究结果表明,在生长温度为1 075℃时,所生长的GaN呈现出类金字塔状微米锥结构;当生长时间由3 min延长至20 min时,微米锥的底面直径由3.6μm增大到19.8μm,密度由3.8×10~3cm~(-2)降低至0.8×10~3cm~(-2);压力及Ⅴ/Ⅲ比共同决定该结构顶部的微观形貌(锥状或截顶锥状)。本工作的研究结果为GaN微钠米结构的原位可控生长奠定了一定基础,并有助于三维GaN基LED器件的进一步发展。     

螺旋炭纤维的微观结构与储能特性

采用扫描电镜、激光Raman光谱、X射线衍射(XRD)、热失重分析(TG)、低温氮吸附等研究手段,以平直炭纤维为参照,对比研究了碳氢化合物催化分解法制备的螺旋型炭纤维的微观结构特征。实验结果表明：整体上,螺旋炭纤维的微观结构要比平直炭纤维的结构更加无序;但螺旋炭纤维的外层结构较为有序与中孔分布广、孔容低的平直炭纤维不同,螺旋炭纤维的中孔主要分布在3nm～4nm范围内．且有着较高的孔容,其比表面积几乎足平直碳纤维的10倍。这些结构特性使得螺旋炭纤维在抗氧化性、储氨、电化学电容等方面都体现出超越平直炭纤维的优势和应用潜力。     

甲烷催化裂解制备毛线状炭纤维及其微观结构

以甲烷为碳源，硫酸亚铁为催化剂前驱体，通过化学气相沉积在石墨基板上制得毛线状炭纤维。扫描电子显微镜观察得知所制炭纤维具有毛线状结构，由许多直径更小的子纤维交叉合并而成。单束毛线状炭纤维的直径为4μm-8μm。高分辨透射电子显微镜显示构成纤维的碳层排列不平直，存在偏转角，有序排列的碳层被分割成许多有序微晶区域。进一步采用X射线衍射和激光拉曼光谱等分析手段对其微观结构进行表征，表明毛线状炭纤维中碳层排列有序度较高，石墨微晶尺寸较大（La≈5nm），层间距较小（d002=0．340nm）。推测毛线状炭纤维生长机理符合“吸附-扩散-析出”过程，形成毛线状结构主要由催化剂颗粒直径决定。     

气相催化裂解法制备微米级螺旋形炭纤维的研究

以商用乙炔为碳源，镍板为催化剂，含硫化合物为助催化剂，通过气相催化裂解法（VCC）制得了微米级螺旋形炭纤维。通过对影响微螺旋形炭纤维生长因素研究。发现将镍板直立放置于石英管中，可以提高螺旋形炭纤维的收率。同时发现反应温度为710℃～800℃，C2H2/H2=1：3。含硫化合物的流量为1.0mL/min～1.2mL/min时，有利于规整螺旋纤维的生成，通过调节N2的流量，可以获得螺径不同的炭纤维。气体总流量约200mL/min时可制得螺径约4μm的规整炭纤维；气体总流量约150mL/min时可获得螺径约20μm的炭纤维。利用扫描电子显微镜（SEM）考察了螺旋纤维的微观形貌，发现所得的纤维几乎为双螺旋，同时在螺旋纤维生长的先端常观察到由弯曲纳米级纤维形成的绒状物。     

FeCl3催化生长脱油沥青基气相生长炭纤维

以脱油沥青（DOA）为碳源,氯化铁为催化剂,在氩气和氢气的混合气氛下利用化学气相沉积法（CVD）制备了不同形貌的气相生长炭纤维（VGCFs）。讨论了在温度为1100℃时,不同的反应时间（分别为10min,20min,25min,30min和40min）对产物形貌和结构的影响。利用场发射扫描电镜（FE-SEM）、高分辨透射电镜（HRTEM）、X-射线衍射（XRD）和拉曼（Raman）光谱,对不同工艺参数下合成的产物进行了结构表征。结果表明：随着反应时间的增加,气相生长炭纤维的形貌由弯曲变得相对平直,进而相互贯穿;当反应时间为10min和20min时,气相生长炭纤维的直径分布在1.0μm～1.2μm之间;当反应时间为25min,30min和40min时,气相生长炭纤维的直径分布范围分别为250nm～300nm,350nm～400nm,700nm～800nm。另外,还观察到了V型的气相生长炭纤维。     

基于硅与非硅复合方法的异平面空心微针制作

为了解决制备空心微针工艺复杂且成本高的问题,本文提出了采用湿法刻蚀、光刻和电镀结合的方法制备低成本空心金属微针.首先采用湿法刻蚀硅,得到280μm深的倒四棱锥锥坑;然后在锥坑上甩200μm厚的负胶SU-8填充锥坑,并通过曝光显影负胶形成微针的形貌;最后在曝光显影后的负胶上电镀50μm厚的镍得到所需形状的空心金属微针.用此方法制备的空心微针高度为350μm、壁厚为50μm,其针尖形状为三棱锥和四棱锥.通过有限元仿真分析微针强度与微针结构尺寸的关系.用此方法加工出的微针具有锥形尖,改善了刺入皮肤的效果.     

纤维种类对炭/炭复合材料微观结构和力学性能的影响(英文)

采用6 K的预氧丝和炭纤维制备预制体,通过化学气相渗积制备炭/炭复合材料。通过偏光显微镜、拉曼光谱、纳米硬度和三点弯曲等手段研究其微观结构和力学性能。结果表明,预氧丝复合材料的基体为暗层和粗糙层炭,厚度分别为1.4-2.6μm和10.2-11.6μm;而炭纤维复合材料的基体为光滑层和粗糙层炭,厚度分别为8μm和4.4μm;预氧丝纤维的模量和硬度明显小于炭纤维,同时基体的模量和硬度随消光角的增加而降低;低模量的基体和纤维导致预氧丝复合材料的拉伸强度、拉伸模量、弯曲强度和模量分别降低了14.5%-24.2%、9.7%-19.8%、7.3%-15.4%和15.1%-18.6%;但其韧性指数却提高了224%-235%,这是高含量的粗糙层炭和纤维的石墨化收缩所致;同时提出了一个三单元复合模型用来模拟复合材料的拉伸模量,模拟误差小于9.9%。     

高温处理对螺旋炭纤维微观拓扑结构的影响

对高温处理前后螺旋炭纤维的微观拓扑结构进行了探究与表征,结果表明,制备态螺旋炭纤维具有类似年轮状结构的近圆形横截面,在纵截面上体现为近似鲱鱼骨结构,其石墨微晶尺寸小、取向度差;高温处理后,其三维结构可理想地看作是由石墨微晶以具有锥角的多面柱体形式沿螺旋方向堆叠而成,表观上炭纤维显示为尺寸均匀的多面柱体形貌。X射线衍射和Raman散射结果从宏观量级上证明了样品微观尺度有序度得到提高。为基于结构的性能预测和应用设计提供了可靠的参考。     

螺旋炭纤维的结构分析

分析了螺旋炭纤维的微观结构,发现其主要由纳米级石墨片层(nano graphite structurecell,NGSC,约为5 nm×5 nm)构成,其间夹杂着无定形碳和多层富勒烯等无序结构.由于螺旋炭纤维具有螺旋结构,其中的NGSC发生了一定的弯曲.在宏观尺度上,螺旋炭纤维表现出无序碳结构的特征.根据结构分析的结果提出了表征螺旋炭纤维的几何参数,并对不同螺旋炭纤维的螺旋角进行了比较分析.结果表明,虽然螺旋炭纤维的直径和螺距各不相同,但是其螺旋角具有一定的规律.在微观结构观察和几何构形分析的基础上提出了螺旋炭纤维的生长机理.     

微螺旋炭纤维的制备与表征

采用溶剂热法合成出硫化镍, 并将其作为催化剂, 催化热解乙炔制备出微螺旋炭纤维. 通过SEM、FT-IR和XRD分析了催化剂和微螺旋炭纤维的形貌和微观结构. 结果表明: 硫化镍催化颗粒表面光滑、为规则的六方相结构, 直径为1~2 μm; 微螺旋炭纤维具有双螺旋结构, 截面为矩形, 具有相同的螺径. 微螺旋炭纤维分子结构中既含有不饱和的C=C双键, 又含有饱和的-CH₂-和-CH₃基团, 其微观结构整体有序度较差, 存在一定量的无定型炭和晶体缺陷, 石墨化度低.     

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...     

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.     

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.     

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.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.