铁氧体Ba(Zn_(1-x)Co_x)_2Fe_(16)O_(27)/环氧树脂复合材料吸波性能

采用化学共沉+高温助熔工艺制备了铁氧体Ba(Zn(1-x)Cox)2Fe16O27粉体,然后用模压法制备了铁氧体粉体/环氧树脂复合材料板,采用同轴电缆法测定了复合材料的电磁参数。研究表明,随着铁氧体中Co含量增加,铁氧体主相由BaZn2Fe16O27转变成Ba-Co2Fe16O27,材料磁损耗逐渐加强,复合材料与空气的电磁匹配特性在频率低于12GHz时较好。然后将M-玻璃纤维/环氧树脂复合材料置于铁氧体粉体/环氧树脂复合材料前端组合成多层复合材料结构,复合材料板与空气的电磁匹配性能和吸波性能都有很大提高。数据如下:当复合材料结构中x=0.75铁氧体吸波层厚度为2.0mm,结构总厚度5.3mm时,复合结构反射系数R的绝对值在2～8GHz时4dB、在8～18GHz时10dB的吸波性能。     

空心微珠铁氧体复合粉体的改性与吸波性能

研究了柠檬酸盐溶胶-凝胶方法制备空心微珠-钡、锶、钴镍钡铁氧体复合粉体的微观形貌, 采用化学添加剂改善铁氧体的包覆性能. SEM、EDS分析表明铁氧体在空心微珠表面的包覆状态与铁氧体种类无关; 在前驱体中加入乙二醇或聚乙二醇可以使铁氧体对空心微珠的包覆更加完整、牢固致密. 用网络分析仪测试了C波段5.0～6.5GHz、X波段8.2～12.4GHz、Ku波段12.5～18.0GHz内1.8mm厚铁氧体空心微珠复合粉体制备的吸波涂层的微波损耗. 试验表明：铁氧体空心微珠复合粉体具有良好的电磁吸波性能, 吸波涂层在5～18GHz内微波反射损失总体上大于单纯铁氧体涂层; 加入乙二醇或聚乙二醇有助于提高涂层的吸波效果.     

铁氧体/石墨复合吸波涂层的微波吸收性能

本文将固相法制备的磁损耗型Ba0.9Sm0.1Co2Fe16O27铁氧体与电损耗型石墨相结合,通过测试两者的电磁参数,采用YRcomputor软件模拟计算了双层复合吸波涂层的反射率。结果表明：铁氧体/石墨复合吸波涂层在2～8 GHz频段有较好的吸波性能;其中,下层为含量80 wt%的Ba0.9Sm0.1Co2Fe16O27,厚度1.5 mm,上层为10 wt%的石墨,厚度1.5 mm时,该复合涂层表现出优良的微波吸收特性,反射率损耗RL〈-10 dB时,带宽约为3 GHz（3.5～6.5 GHz）,最大吸收值约为-27 dB。     

磁性聚膦腈纳米管碳化材料的微波吸收性能研究

在惰性气氛下对磁性聚膦腈纳米管进行高温碳化,制备了新型的电磁损耗型碳基复合吸波材料。在磁场中检验了磁性聚膦腈纳米管碳化材料的磁响应性,通过四探针法测量了其电阻率,采用同轴传输反射法测定了电磁参数,并研究了该复合材料的微波吸收性能。研究结果表明,合成的磁性聚膦腈纳米管碳化材料在磁场中沿磁场方向作规则的定向排列,具有很好的磁响应性;电阻率为7.88(Ω·cm),是一种半导体材料;在测试频率范围2~18GHz内,磁性聚膦腈纳米管碳化材料同时存在一定的介电损耗和磁损耗,是一种磁损耗型和介电损耗型相结合的复合吸波材料;在14GHz附近存在最大反射损耗-14dB,并且显示了一定的宽频吸收特性。     

漂珠/钡铁氧体复合材料的制备和吸波性能

采用溶胶-凝胶自蔓延燃烧法制备出漂珠/钡铁氧体低密度磁性复合材料,用扫描电镜、热重-差热分析仪、X射线衍射仪、振动样品磁强计和矢量网络分析仪表征了样品的形貌、结构、电磁性能和吸波性能。结果表明:在漂珠表面形成的钡铁氧体包覆层厚度为5-15 nm,颗粒粒径均小于60 nm。复合材料由六角晶钡铁氧体、α-氧化铁及少量莫来石和石英组成,其磁性能随钡铁氧体与漂珠质量比的增大而增强。复合材料在2-18 GHz频段具有较好的介电损耗和磁损耗性能,当吸波材料厚度为1.5 mm、在14.2 GHz处反射损耗峰值为-29.2 d B,反射损耗小于-10 dB的带宽为4.5 GHz。     

W型钡锌铁氧体相形成过程及其电磁特性

采用固相球磨法制备了W型钡锌铁氧体粉体,使用X射线衍射仪、扫描电子显微镜和微波网络分析仪分别对其相组成、颗粒形貌和不同煅烧温度下铁氧体粉体的电磁特性进行测试分析。结果发现:煅烧温度为1300℃时生成了较纯的W型钡锌铁氧体相,形成了较为完整的六角片状结构。在6~12GHz频段,随着煅烧温度的增加,μ′、tanμ的值随之增大,并且当煅烧温度达1300℃时,其磁损耗达到最大。     

羰基铁/ 导电聚苯胺微管复合材料的电磁性能

采用原位掺杂的方法合成了聚苯胺微管, 将具有介电损耗性能的高分子材料聚苯胺微管与具有磁损耗性能的无机材料羰基铁复合, 并采用波导法研究了复合材料在8.2～12.4 GHz 频段内的电磁参数。结果表明, 在羰基铁/ 聚苯胺复合材料与石蜡的质量比为1 ∶1 的情况下, 通过复合, 可以调节电磁参数, 提高材料的吸波性能。      

磁功能化多孔生物质炭复合材料的制备及吸波性能

采用高温炭化和水热法制备了兼具介电损耗和磁损耗特性的磁功能化生物质炭(Fe_3O_4/多孔生物质炭)吸波材料。在200℃水热条件下,随着FeCl_3浓度的增加,PLSC表面生成的聚集态Fe_3O_4纳米晶粒有所增加,颗粒大小规整,平均粒径约为200 nm。通过矢量网络分析仪探讨了磁材料含量、复合材料的形貌结构对吸波性能的影响,并分析了多重损耗吸波机理。结果表明,在2～18 GHz范围内,当FeCl_3浓度为4 mmol时制备的磁功能化生物质炭复合吸波材料具有最佳的吸波性能,在厚度为2 mm时,其在11.42 GHz处的最大反射损耗值可达-42.2 dB,有效频宽达3.14 GHz (反射损耗小于-10 dB)。     

离子掺杂对W型钡铁氧体电磁特性的影响

研究了六角晶系W型铁氧体Ba(Zn1-x Cox)2Fe16O27中Co2+离子掺杂量对产物电磁参数的影响。采用溶胶—凝胶自蔓延燃烧法制备了不同Co2+离子掺杂量的铁氧体产物,利用微波网络矢量分析仪在X波段范围内选取8.2GHz、10.0GHz和12.4GHz三个典型频率对不同产物的动态电磁参数进行了测量和分析。研究表明:铁氧体在各频率下的介电损耗变化是由于随着Co2+离子含量的增加带来的电偶极子极化和界面极化造成的;铁氧体的磁损耗是由于Co2+离子含量的增加,W型铁氧体的磁矩从优方向由单轴过渡到平面,磁晶各向异性场的变化导致了其共振频率的变化,从而证明了调整Co2+离子的含量可以对铁氧体的工作频段加以控制。同时确定了在X波段,当x=0.6~0.8时,Ba(Znx Co2-x)2Fe16O27具有最佳的吸波性能。     

无定形炭/磁性粒子复合吸波材料的制备和电磁性能研究

以二甲基亚砜(DMSO)为溶剂进行溶液聚合制得聚丙烯腈(PAN)溶液,在此溶液中混入了微米级铁粉后将其压成薄膜,将烘干后的薄膜高温碳化处理制得一种碳基吸波材料。采用X射线衍射(XRD)、扫描电镜(SEM)等手段对材料的成分、形貌、结构进行了表征。采用矢量网络分析仪对该复合材料在2～18GHz频段内的电磁参数进行了测试,并作了微波反射率的数值模拟。研究了碳化温度对材料物相组成和电磁性能的影响以及碳化温度和涂层厚度对材料吸波性能的影响。此种吸波材料是无定形炭和铁的氧化物、铁的氮化物等磁性物质的复合材料,兼有电损耗和磁损耗,具有较好的吸波性能。     

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 ...