La改性 BaTiO3陶瓷的结构与电性能

采用气相扩渗和液相掺杂两种方法制备了 La改性的 BaTiO3陶瓷,并对其组成、结构、形貌以 及电性能的变化进行了研究. La的液相掺杂可使纯 BaTiO3陶瓷的电阻率从 4.0× 1012Ω· m下降 为 3.0× 106Ω· m; 而 La的气相扩渗使其电阻率下降更为明显, 变为 8.2× 104Ω· m. La掺杂 BaTiO3陶瓷的晶粒电阻随温度的变化,呈现出明显的 NTC效应,而晶界电阻则呈现 PTC效应. La 扩渗 BaTiO3陶瓷的晶粒电阻随温度的变化,呈现出明显的 PTC效应;晶界电阻随着温度的升高急 剧连续降低 ,样品总电阻的 PTC效应已不存在. XRD分析表明, La掺杂的 BaTiO3陶瓷并没有形成 新相,而扩渗的 La元素已经与陶瓷组元发生了复杂反应,生成了 La2C2O2 、 Ba5La4Ti8O27一些新的 化合物,从而导致了导电性的显著变化. SEM分析表明, La扩渗的 BaTiO3陶瓷,因形成新相,从而 使形核数量增多,形成了均匀、细小、弥散的形貌特征.     

Sm对BaTiO3陶瓷的气相扩渗及其电性能

为了改善BaTiO3陶瓷的电性能,采用气相法对BaTiO3陶瓷扩渗了Sm元素,探讨了Sm扩渗对BaTiO3陶瓷导电性能和介电性能的影响.研究表明:经Sm扩渗后,BaTiO3陶瓷的室温电阻率从4.3×109 Ω·m下降到2.1×102 Ω·m,而且随着频率增大和温度升高,交流电导逐渐增大,BaTiO3陶瓷的导电性更强;经Sm扩渗的BaTiO3陶瓷的晶粒电阻随着温度的变化,呈现PTC效应,而晶界电阻随着温度的升高,呈急剧连续降低状态,总电阻的变化规律与晶界电阻的变化相一致,试样总电阻的PTC效应已不存在,有向导电体过渡的趋势;Sm扩渗使BaTiO3陶瓷的介电常数在低频下显著增加,介电常数随温度的变化呈明显的PTC效应,并使BaTiO3陶瓷的居里温度升高到128.9℃.     

Pr, Mn多元渗对 BaTiO3陶瓷结构与电性能的影响

采用溶胶-凝胶法制备了纯BaTiO3、Pr,Mn液相掺杂及气相多元扩渗改性的BaTiO3陶瓷.研究结果表明,Pr掺杂能使纯BaTiO3陶瓷的室温电阻率下降为1.01×10^5Ω·m;而Mn掺杂使室温电阻率升高为1.50×10^13Ω·m.但Pr和Mn的气相扩渗都能降低BaTiO3陶瓷的室温电阻率至1.08×10^3Ω·m和1.29×10^5Ω·m.Pr-Mn共渗BaTiO3陶瓷出现了典型的NTC效应.XRD分析表明,Pr或Mn掺杂并不能改变BaTiOa陶瓷的物相结构,但经Pr-Mn共渗后,出现了新化合物BaMn0.12Al1.88O4和Al8Mn4Pr的特征峰.XPS分析表明,气相多元渗使Pr,Mn,C元素都扩渗到陶瓷体内,并使各化学元素之间的结合更加牢固.SEM测试结果表明,Pr,Mn气相扩渗使陶瓷表面明显改观,晶粒生长完整,粒度分布均匀,气孔率下降.     

BaTiO3—R2O3—MgO系介质的稀土掺杂效应

研究了BaTiO03-R2O3-MgO(R=La,Ce,Pr,Nd,Sm,Gd,Dy,Ho,Y,Er,Yb)系介质的稀土掺杂效应.结果表明,大半径稀土离子在BaTiO3中形成元素均匀性分布,并促进晶粒的长大;而小半径稀土离子能产生明显的细晶效应,在晶界局部富集而偏析出现焦绿石型第二相晶粒R2Ti2O7.随着镧系收缩,稀土掺杂BaTiO3陶瓷的绝缘电阻率明显提高,而稀土离子在BaTiO3中的固溶度大致呈降低趋势.大半径稀土掺杂材料的ε-T曲线呈现单峰效应且居里点下移,而小半径稀土掺杂材料为双峰效应且居里点上升,△C/C-T稳定性显著提高达到X8R.     

Sb掺杂BaPbO3系导电陶瓷的制备及电性能

以可溶性无机盐为原料,柠檬酸和乙二胺四乙酸(EDTA)为复合螯合剂,采用sol-gel工艺制备了Sb掺杂BaPbO3(BPO)陶瓷,讨论了不同的Sb施主掺杂浓度对BPO陶瓷的电导率和阻温特性的影响.实验结果表明:采用sol-gel法获得了均一相、化学计量比的Sb掺杂BPO陶瓷;当施主掺杂量≤1 mol%,Sb-BPO陶瓷的室温电阻率随Sb掺杂量的增加而升高,当施主掺杂量≥1mol%,室温电阻率随Sb掺杂量呈"U"形变化,掺杂量为12 mol%～13 mol%时室温电阻率最低,约为2.69×10-4 Ω·cm;BPO陶瓷引入施主杂质Sb后,不但可以降低材料的室温电阻率,而且可以使材料呈现出高温PTC效应,当掺杂量为5 mol%时,材料的升阻比最高,其居里温度Tc约为850 ℃.     

Sm2O3掺杂BaTiO3陶瓷的结构与电性能研究

采用溶胶-凝胶法制备了掺杂不同浓度Sm2O3(分别为0.001,0.002,0.003,0.005,0.007mol)的BaTiO3陶瓷,并对其结构与电性能进行了研究.结果表明:Sm2O3掺杂BaTiO3陶瓷的晶型在室温下为四方相,而且随着Sm2O3掺杂浓度的增加,BaTiO3陶瓷的晶粒尺寸变小,说明Sm2O3掺杂对BaTiO3陶瓷晶粒的生长有一定的抑制作用;Sm2O3掺杂BaTiO3陶瓷的电阻率比纯BaTiO3陶瓷明显下降,当添加量为0.001mol时,电阻率最小,.从4.3×109Ω·m下降为6.536×103Ω·m;Sm2O3掺杂BaTiO3陶瓷的晶粒电阻随着温度的变化,呈现NTC效应,而晶界电阻随着温度的变化,呈现PTC效应,且晶界电阻远远大于晶粒电阻,说明该材料的PTC效应是由晶界效应引起的.     

YCl3取代Y2O3降低BaTiO3基PTCR陶瓷电阻率机理研究

采用YCl3溶液作为施主掺杂剂,在空气中烧结制备一系列BaTiO3陶瓷样品,对其室温电阻率及PTC效应进行研究.同时与Y2O3和YNO3溶液掺杂的样品对比,借助XRD、XRF等分析手段,研究了YCl3溶液掺杂降低BaTiO3基PTCR陶瓷室温电阻率的机理.研究结果表明,经空气中高温烧结后,样品中仍残留部分Cl元素,能取代O位起施主作用,烧结时Cl的挥发过程也能导致样品室温电阻率的降低,最后,施主掺杂剂以溶液的形式加入,能使其在粉料中分布均匀,有助于半导化.     

Ni/PTC陶瓷复合材料的制备和性能

采用液相包裹法由NiC2O4·2H2O/BaTiO3前躯体热分解制得Ni/PTC陶瓷复合材料,并对其结构和性能进行了表征.Ni/PTC陶瓷复合材料具有多孔性结构和较好的分散性,Ni主要以微细金属颗粒的形式分布于晶界和孔隙中;在Ni/PTC陶瓷复合材料中氧化Ni导致室温电阻率增大,对PTC效应产生消极影响;采用石墨扣烧的方法能避免金属Ni氧化,制得的Ni/PTC陶瓷复合材料具有非常低的室温电阻率,但几乎失去了PTC效应,在烧成后热处理过程中晶界氧的吸附可使其恢复PTC效应;Ni/PTC陶瓷复合材料结构的多孔性和金属Ni的充分分散有利于PTC效应的恢复.     

BaTiO3陶瓷中Gd、Ce的掺杂效应研究

在BaTiO3(BT)-Nb2O5-ZnO系统中引入硼硅酸盐助烧剂,加入Gd、Ce稀土氧化物以期获得中温烧结X7R陶瓷材料.研究发现,随着Gd用量的增加,单独掺杂时陶瓷室温介电常数先减小后增大,而与Ce复合掺杂时室温介电常数单调递增,分析认为,这是由于Gd在BT晶粒中对A位和B位的不同取代造成;随着Ce掺杂量的增大,室温介电常数减小,这与壳芯结构理论吻合.SEM图分析发现,Gd、Ce共掺杂BT陶瓷晶粒生长明显大于单独掺Gd或Ce的BT陶瓷,且陶瓷气孔率低,致密化程度高.     

Sm2O3掺杂BaTiO3陶瓷的结构与电性能研究

采用溶胶-凝胶法制备了掺杂不同浓度Sm₂O₃(分别为0.001,0.002,0.003,0.005,0.007mol)的BaTiO₃陶瓷,并对其结构与电性能进行了研究.结果表明:Sm₂O₃掺杂BaTiO₃陶瓷的晶型在室温下为四方相,而且随着Sm₂O₃掺杂浓度的增加,BaTiO₃陶瓷的晶粒尺寸变小,说明Sm₂O₃掺杂对BaTiO₃陶瓷晶粒的生长有一定的抑制作用;Sm₂O₃掺杂BaTiO₃陶瓷的电阻率比纯BaTiO₃陶瓷明显下降,当添加量为0.001mol时,电阻率最小,.从4.3×109Ω·m下降为6.536×103Ω·m;Sm₂O₃掺杂BaTiO₃陶瓷的晶粒电阻随着温度的变化,呈现NTC效应,而晶界电阻随着温度的变化,呈现PTC效应,且晶界电阻远远大于晶粒电阻,说明该材料的PTC效应是由晶界效应引起的.     

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.……     

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 ...