直流碳弧法制备碳包覆铁纳米颗粒机理研究

采用直流碳弧等离子体法成功制备了碳包覆铁纳米颗粒,利用透射电子显微镜和高分辨透射电子显微镜、X射线衍射、X射线能谱仪对样品的形貌、物相结构、化学成分和粒度进行表征分析,并对碳包覆纳米金属颗粒的形成机理进行初步探讨。结果表明:直流碳弧等离子体技术制备的碳包覆纳米金属颗粒具有明显的铁核(bcc-Fe)/碳壳(石墨层片)包覆结构,颗粒大多呈球形和椭球形,粒径分布在20~60nm范围,平均粒径为44nm,铁粒子外碳层的厚度为5~8nm。碳包覆铁纳米铁颗粒是通过颗粒内部固态形式的碳自行扩散至颗粒表面和颗粒外部气态形式的碳沉积到颗粒表面形成的。     

直流碳弧等离子体法制备碳包覆铁纳米颗粒研究

在惰性保护气氛下,采用直流碳弧等离子体法成功制备了碳包覆铁纳米颗粒,并利用x射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、X射线能谱仪(EDS)、透射电子显微镜(TEM)和相应选区电子衍射(ED)等测试手段,对样品的化学成分、形貌、物相结构、粒度等特征进行表征分析.实验结果表明:直流碳弧等离子体技术制备的碳包覆纳米金属颗粒具有明显的核-壳结构,内核金属结晶度较高,外壳碳为类石墨层结构,颗粒大多呈球形和椭球形,粒径分布在20nm～60nm范围,平均粒径为44nm.     

纳米铜粉与碳包覆铜纳米粉的分散性能比较

采用直流碳弧法制备平均粒径为25 nm的碳包覆铜纳米粉,应用X射线衍射(XRD)、透射电镜(TEM)等分析手段对所制备的纳米颗粒物相、形貌等进行表征。采用超声波分散法对所制备的碳包覆铜纳米粉和市售的纳米铜粉进行分散,并通过分光光度法和沉降实验对两者的分散性能进行比较。结果表明:铜纳米颗粒具有很高的表面自由能,容易被氧化,在水性液相介质中分散时容易产生氢氧化铜絮状沉淀。碳包覆铜纳米颗粒表面有碳层的保护,且密度小、表面吸附性能好,分散性能明显优于铜纳米颗粒。     

纳米碳酸钙表面原位聚合包覆

通过超重力场制备了纳米碳酸钙,对纳米碳酸钙进行超声波分散,然后进行原位乳液聚合,采用分步聚合的方式,在纳米碳酸钙表面包覆了丙烯酸酯类共聚物,制得了纳米碳酸钙表面原位聚合包覆产物.采用TEM、DSC、TGA和表面电子能谱(ESCA)对纳米碳酸钙表面原位聚合包覆产物进行了表征.结果表明:制备的纳米碳酸钙粒子粒径在20nm左右,通过原位乳液聚合包覆后,粒径在40～80nm,包覆后的纳米碳酸钙复合粒子表面几乎不含Ca元素,表明纳米碳酸钙被良好包覆,并形成了以纳米碳酸钙为核、PBA为中间层、MMA和EA,St共聚物为壳的三层结构有机-无机纳米复合粒子.     

快速热解法制备炭包覆纳米金属磁性颗粒(英文)

以简单金属前躯体为原料通过快速热解法制备炭包覆纳米金属磁性颗粒,通过透射电镜、X-射线衍射、热重-示差扫描同步热分析及振动样品磁强计等对产物形貌、结构、成分与磁性能进行表征。结果表明:采用该方法制备的炭包覆纳米金属磁性颗粒形状为近球形颗粒,粒径均一,其中炭包覆镍纳米磁性颗粒的粒径集中在10nm～30nm范围,炭包覆铁纳米磁性颗粒粒径则在50nm～60nm范围;所制炭包覆纳米金属磁性颗粒在室温下具有顺磁性,其磁性能随金属颗粒含量的变化而改变。该方法有望发展成一种工艺简单,可进行连续工业化生产炭包覆纳米金属磁性颗粒的方法。     

碳包覆NiO纳米颗粒的制备与性能

采用直流电弧放电等离子体技术成功制备了碳包覆NiO(NiO@C)纳米颗粒,并对样品的形貌、晶体结构、粒度、比表面积和孔结构采用高分辨透射电子显微镜、X射线衍射、X射线能量色散分析谱仪、拉曼散射光谱和N_2吸-脱附等测试手段进行了分析。实验结果表明:直流电弧等离子体技术制备的NiO@C纳米颗粒具有典型的核壳结构,内核为面心立方结构的NiO纳米颗粒,外壳为碳层。颗粒形貌主要为立方体结构,粒度均匀,分散性良好,粒径分布在30~70nm范围,平均粒径为50nm,外壳碳层的厚度为5nm。NiO@C纳米颗粒BET比表面积为28m~2/g,等效直径为46nm,与TEM和XRD测得的结果基本一致。Raman光谱说明样品中碳包覆层的石墨化程度较低,发生了红移现象。     

碳包覆氧化亚钴纳米颗粒的制备与性能研究

采用直流电弧放电等离子体技术成功制备了碳包覆氧化亚钴纳米颗粒,并对样品的形貌、晶体结构、粒度、比表面积和孔结构采用高分辨透射电子显微镜(HRTEM)、X射线衍射(XRD)、X射线能量色散光谱(XEDS)、拉曼散射光谱(Raman)和N_2吸-脱附等测试手段进行了分析。HRTEM表明该方法制备的碳包覆氧化亚钴纳米颗粒具有典型的核壳结构,颗粒形貌主要为球形或椭球结构,粒度均匀,分散性良好,粒径分布在20~60nm,平均粒径为40nm,外壳碳层的厚度为5nm。XRD证明样品的内核为面心立方结构的氧化亚钴纳米颗粒,外壳为碳层。XEDS图谱表明样品中主要存在Co、O和C元素的特征峰。Raman光谱说明样品中碳外包覆层的石墨化程度较低,发生了红移现象。样品的N_2吸附-脱附等温曲线属Ⅳ型,BET比表面积为33m~2/g,BJH脱附累积总孔孔容和脱附平均孔径分别为0.078cm~3/g和11nm。当量粒径为43nm,与TEM和XRD测得的结果基本一致。     

化学镀法制备纳米Cu/Al复合粉末

为了改善超细铝粉的表面易氧化问题和微米级铝粉对推进剂的热分解催化作用不明显现象,以对推进剂具有良好催化作用的纳米Cu包覆金属Al表面.采用化学镀铜法对微米级铝粉表面进行镀覆,制备出纳米Cu粒子在超细Al颗粒表面包覆完整的Al-Cu核壳式复合粉末,并利用正交实验优化镀液组分及镀覆工艺条件.利用XRD、SEM、EDX等仪器,对复合粉末的形貌、物相结构及表面成分进行分析,结果表明铝粉表面包覆一层致密的纳米铜层,这种纳米层是由粒度约为18.83nm的晶态析出的纳米铜组成.     

催化剂结构与形态对碳纳米管生长的影响

采用溶胶-凝胶超临界流体干燥技术制备了含铁、钴的纳米SiO2复合气凝胶催化剂,用于碳纳米管和纳米碳包覆磁性纳米粒子的合成。利用N2物理吸附、XRD、TEM、HRTEM、EDS、SAED等手段对催化剂在不同温度下处理后晶型的转变、形态的变化进行了分析,并考察了催化剂对碳纳米管形貌、结构和碳增重率的变化。结果表明:随着处理温度从600℃升高到1000℃,催化剂比表面积从312.4m2 g降低到79.6m2 g,催化剂粒子从非晶态向晶态转变,粒径从5nm增大至60nm左右,碳的增重率从254.8%下降41.5%。采用低温处理的催化剂,碳产物中以碳纳米管为主,而采用较高温度处理后的催化剂,碳产物中则以碳包覆粒子为主,且随处理温度的升高碳包覆粒子的含量逐渐增加。     

H_2O_2处理碳包覆铁纳米颗粒的表面特性及分散行为

采用体积分数30%的H2O2处理碳包覆铁纳米粒子外层的非晶态类石墨碳层,并将其超声分散于水介质中,通过改变pH值分析测定碳包覆铁纳米粒子表面zeta电位和粒径。结果表明:碳包覆铁纳米粒子非晶碳层的特殊结构可通过双氧水化学处理使其表面产生羧基和羟基;在强碱性介质下,羟基和羧基可强化颗粒间的静电斥力,提高碳包覆铁纳米粒子在水介质中的分散性能。当pH值约为11.5时,碳包覆铁纳米粒子表面zeta电位为48 mV,水合粒子粒径可达到110 nm。     

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 ...