BiMnO3的高压合成及其磁性研究

具有严重晶格畸变的钙钛矿结构BiMnO3作为可表现出铁磁性和铁电性的多铁材料,在信息存储和传感器等方面具有潜在的应用价值,得到了广泛的关注和研究。利用国产六面顶液压机,以Bi2O3、MnO2和Mn粉末为原料,在高温高压条件下(4 GPa,750~800℃)制备了单斜钙钛矿结构BiMnO3烧结体。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、振动样品磁强计(VSM)对烧结样品进行测试分析,考察了不同含量比(n(MnO2)/n(Mn)=3.5∶0.5、3∶1、2.5∶1.5、2∶2)、烧结时间(10min~2h)对样品结构、组织形貌及磁性的影响。实验结果表明:当n(MnO2)/n(Mn)=3∶1时合成钙钛矿结构BiMnO3的纯度最高;当烧结时间为10min时,即有钙钛矿结构BiMnO3生成,随着烧结时间的延长,BiMnO3的相对含量逐渐增大。800℃、1h合成的钙钛矿结构BiMnO3样品软磁性能最好,其比饱和磁化强度为33emu/g,矫顽力为37.6Oe(测试温度90K)。     

自燃/球磨法制备NiZn系铁氧体

以金属硝酸盐和柠檬酸为原料,用溶胶凝胶自燃烧法制备NiZn系铁氧体前驱体粉末(Ni0.4Zn0.6Fe2O4,Ni0.2Zn0.6Cu0.2Fe2O4,Ni0.33Zn0.59Cu0.11Fe1.97O4(Bi2O3)0.002和Ni0.33Zn0.59Cu0.11 Fe1.97O4(Bi2O3)0.002(MnO2)0.02),然后经30小时高能球磨,从X-ray衍射谱中发现前驱体粉末虽然基本上是尖晶石结构,但是还有一些杂相,经过球磨,杂相明显减少,结构更加完整,颗粒减小.前驱体粉末Ni0.33Zn0.59Cu0.11Fe1.97O4(Bi2O3)0.002经30小时球磨后,在空气中退火,退火温度分别为400℃,600℃,800℃,900℃,1000℃.用X-ray衍射谱分析其物相,发现在800℃退火得到单相的尖晶石结构,无杂相.该样品的最佳退火温度低于1000℃.用振动样品磁强计分别测量制备态和退火态样品粉末的磁性,可以看出,随退火温度的升高,比饱和磁化强度σs逐渐增大,矫顽力Hc逐渐减小,当900℃退火后,比饱和磁化强度已接近块状NiZn系铁氧体.1000℃退火后,上述四种样品中Ni0.4Zn0.6Fe2O4具有最高的比饱和磁化强度σs=65.09emu/g.本文为NiZn铁氧体的低温烧结提供了有用的实验数据.     

单相钡铁氧体磁性材料的制备及磁性能研究

以硝酸钡、硝酸铁和柠檬酸为原料,采用溶胶-凝胶法制备了单相钡铁氧体(BaFe12O19)纳米粉体,并进一步研究了n(Fe)/n(Ba)、热处理温度对产物组成、形貌以及磁性能的影响。用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和振动样品磁强计(VSM)分别对样品的组成、形貌和磁性能进行了表征。实验结果表明,当煅烧温度不变时,样品的晶粒尺寸随着n(Fe)/n(Ba)的增大而变大,磁性能随n(Fe)/n(Ba)的增大而增强;当n(Fe)/n(Ba)不变时,样品的晶粒尺寸随着煅烧温度的升高而变大。当n(Fe)/n(Ba)=12时,在800℃煅烧2h得到单一晶型的钡铁氧体粉体。1000℃时样品的磁性能最佳,饱和磁化强度(Ms)为70.88A.m2/kg,矫顽力(Hc)为372.89kA/m。     

高压下纳米La_(0.8)Sr(0.2)MnO_3块状材料的成型及性能研究

在高压条件下制备出了晶粒尺寸为30nm左右的La0.8Sr0.2MnO3块状材料.采用X射线衍射仪(XRD)和场发射扫描电子显微镜(FESEM)对高压样品的相组成、晶粒尺寸及微观形貌进行了表征;利用显微拉曼光谱仪测量了不同压力下制备出的块状样品在激光功率为400mW时位于100～3000cm-1之内的拉曼光谱.结果表明,高压烧结时样品的晶粒演化受温度和压力的共同影响:300℃以下时,1～3GPa烧结的样品晶粒生长速度随压力的升高而增大,4～5GPa烧结的样品其晶粒生长速度随压力的升高而减小;300℃以上时,其晶粒生长速度随压力和温度的升高而不断增大.测量了高压烧结后纳米La0.8Sr0.2MnO3块状材料的各种物理性能,结果表明,高压烧结后该材料的显微硬度显著提高;当烧结温度为300℃时,不同压力下制得的样品的电阻率随压力的升高呈先减小后增大的趋势;5GPa,300℃时制出的样品在室温下呈典型的铁磁性能.     

热分解法制备磁性介孔铁钴氧化物

通过控制金属草酸盐前驱体的热分解过程,用一步法合成了不同n(Fe)/n(Co)的铁钴尖晶石型介孔氧化物。利用XRD、TEM、BET及振动样品磁强计等研究手段对样品的结构、性能进行了表征。实验表明,所制得的样品具有良好的介孔结构及磁性能。随着n(Fe)/n(Co)的升高,样品的比表面积和最可几孔径增大,饱和磁化强度增加。随着烧结温度增加,饱和磁化强度增加,比表面积降低。     

Sol-gel法制备BaTiO_3、BaTi_2O_5和BaTi_4O_9粉末

采用Sol-gel法合成了BaTiO3、BaTi2O5和BaTi4O9粉末,利用XRD和SEM研究了它们的晶相和微观结构。在较低温度烧结得到的粉末都存在一定量的杂相,随着烧结温度的升高,杂相逐渐消失。在1000℃以上温度烧结,可以得到单相BaTiO3和BaTi2O5粉末,而单相BaTi4O9粉末则在1300℃以上温度烧结得到。随着n(Ba)/n(Ti)减小,所得单相的烧结温度逐渐升高。随着烧结温度的升高,BaTiO3、BaTi2O5和BaTi4O9粉末的晶粒逐渐长大。800℃以上温度烧结得到的四方BaTiO3钙钛矿相粉末主要由方形和圆形的晶粒组成;1100℃烧结得到的单斜BaTi2O5相粉末主要由近似菱形的晶粒组成;在1200℃烧结得到的正交BaTi4O9相粉末基本由长形的晶粒组成。     

Bi2O3掺量对Li0.45Ni0.2Ti0.1Fe2.25O4铁氧体显微结构及磁性能的影响

采用氧化物法陶瓷工艺,在缺铁配方的基础上,制备不同Bi2O3掺量的Li0.45Ni0.2Ti0.1Fe2.25-δO4(δ=0.06)铁氧体样品。结果表明,添加Bi2O3没有在锂铁氧体中形成杂相,烧结后陶瓷样品物相组成单一,结晶状况良好;适量的Bi2O3能有效改善材料微观形貌,促进锂铁氧体的烧结致密化,有助于提高材料的饱和磁化强度4πMs和剩磁比R,降低矫顽力Hc。Bi2O3掺量为1.5%(质量分数)的样品具有较好的综合性能,表观密度d为4.72g/cm3,饱和磁化强度4πMs为2.3T,剩磁比R为0.853,矫顽力Hc为2.3×102 A/m。     

工艺因素对Bi2O3、MnO2掺杂[(Pb,Ca)La](Fe,Nb)O3陶瓷体系微波介质性能的影响

研究了烧结工艺对Bi2O3及MnO2掺杂[(Pb0.5Ca0.5)0.92 La0.08](Fe0.5 Nb0.5)O3陶瓷体系显微结构及介电性能的影响.研究表明Bi2O3及MnO2的加入可降低体系的烧结温度100～140℃,同时提高体密度.XRD图谱、SEM及微波介电性能证明950℃是最佳的煅烧温度.烧结温度对晶粒形貌有显著影响,随烧结温度的增加晶粒尺寸不断增加,但超过一定值后不断减小的气孔率又会增加.当掺杂物的质量比(Bi2O3/MnO2)K=1,掺杂物质量百分含量W=1%,烧结条件为1050℃,保温4h,体系微波介电性能可达εr=91.1,Qf=4870GHz,τf=1.85×10-5/℃.     

Fe77Co2Zr9B10Cu2合金的制备及其磁性能

采用单辊快淬法制备了Fe77Co2Zr9B10Cu2合金,在530～750℃等温退火40 min,利用X射线衍射和振动样品磁强计研究了Fe77 Co2 Zr9 B10 Cu2合金的微观结构和磁性能。结果表明:淬态Fe77Co2Zr9B10Cu2合金为非晶、纳米晶双相结构。随着退火温度的升高,α-Fe晶体相从非晶、基体中析出,晶粒尺寸长大,晶化体积分数增加,矫顽力先减小后增大,比饱和磁化强度逐渐增大。实验结果表明,530℃退火后合金的矫顽力最小,在670℃时迅速增大。样品的磁性与其微观结构、晶粒尺寸、晶化体积分数等因素有关.     

喷射-共沉淀法合成纳米晶CoFe2O4及磁性能

用喷射-共沉淀法成功地制备了纳米晶CoFe2O4铁氧体粉料.研究了不同合成温度对产物晶体结构、微观形貌和磁性能影响.结果表明:喷射-共沉淀法制备的粉料颗粒细小均匀、形状完整.600℃下煅烧1.5h,样品晶粒尺寸为29nm左右,平均颗粒尺寸小于100nm.室温下,样品比饱和磁化强度随煅烧温度增加而增大.850℃煅烧1.5 h时,其比饱和磁化强度Ms为88.6A·m2·kg-1.当晶粒大小为29nm时,纳米晶CoFe2O4铁氧体矫顽力达到最大值64.5kA·m-1,随后又随晶粒尺寸增大而减小.这可能归因于纳米磁性材料存在强烈的晶粒尺寸效应.     

凝固科学技术与材料

从凝固科学与实践发展的角度介绍了当前凝固材料体系的基本框架和凝固科学主要发展阶段的基本理论。作为材料科学与工程的基本组成，凝固科学技术正在现代科学理论的基础上针对传统材料的改性提高和新材料的发展需求，以控形、控构、控性为目标开展优质铸件的定向、晶体生长、快凝、深过冷及各种新型和超常领域凝固过程的研究，并介绍了其中某些方面和展望了可能的发展趋势。     

Development and challenges of planning and scheduling for petroleum and petrochemical production

Production planning and scheduling are becoming the core of production management, which support the decision of a petrochemical company. The optimization of production planning and scheduling is attempted by every refinery because it gains additional profit and stabilizes the daily production. The optimization problem considered in industry and academic research is of different levels of realism and complexity, thus increasing the gap. Operation research with mathematical programming is a conventional approach used to address the planning and scheduling problem. Additionally, modeling the processes, objectives, and constraints and developing the optimization algorithms are significant for industry and research. This paper introduces the perspective of production planning and scheduling from the development viewpoint.     

江澳两地高校文创设计的协同研究与商业实践

目的 探索江门世遗文化的传承、发展和转化的新思路,践行国家在《粤港澳大湾区发展规划》纲要中要求江门承担与港澳地区文化创意合作与开发任务的分工。方法 与澳门高校紧密合作,开展专业培训课程,以开平碉楼为例,从人文视角开展设计研究,梳理开平碉楼的文化脉络,把世遗文化的元素和其背后的文化融入文创产品中,提升文创产品的附加值,推动当地文创产业结构的变革。结果 两地高校构建了稳定的科研团队,开设长期有效的设计培训课程,与景区建立了研究协作关系,帮助景区构建了一套产销研的商业模式。结论 以跨区域高校合作为平台,以文创产品为抓手,依托江澳两地的资源优势,可以构建江门世遗文化全新的品牌形象,最终推动开平世遗文化的活化。     

Creation and motion of dislocations and fracture in metal and silicon crystals

By making a step on one surface ( ) of a rectangular small paralellepiped copper crystal, dislocations could be created by the molecular dynamic method. The dislocation created was not a complete edge dislocation but a pair of Heidenreich-Shockley partial dislocations. Each time a dislocation was created, the stress on the surface was released. Small copper crystals having a notch were pulled (until fracture), compressed and buckled by use of the molecular dynamic method. An embedded atom potential was used to represent the interaction between atoms. Dislocations were created near the tip of the notch. A very sharp yield stress was observed. The results of high speed deformations of pure silicon small crystals using the molecular dynamics are presented. The results suggest that plastic deformation may be possible for the silicon with a high speed deformation even at room temperature. Another small size single crystal, the same size and the same surfaces, was compressed using molecular dynamic method. The surfaces are {110}, {112} and {111}. The compressed direction was [111]. It was found that silicon crystals are possible to be compressed with a high speed deformation. This may suggest that silicon may be plastically deformed with high speed deformation.     

Density and viscosity of tetralin and trans-decalin

New measurements are reported for the density and viscosity of tetralin and trans-decalin. The density was determined from room temperature to 60°C for tetralin and to 95°C for trans-decalin. The kinematic viscosity was measured up to temperatures slightly above 100°C. Our results improve upon the values recommended by the American Petroleum Institute for these liquids.     

Error and uncertainty in modeling and simulation

This article develops a general framework for identifying error and uncertainty in computational simulations that deal with the numerical solution of a set of partial differential equations (PDEs). A comprehensive, new view of the general phases of modeling and simulation is proposed, consisting of the following phases: conceptual modeling of the physical system, mathematical modeling of the conceptual model, discretization and algorithm selection for the mathematical model, computer programming of the discrete model, numerical solution of the computer program model, and representation of the numerical solution. Our view incorporates the modeling and simulation phases that are recognized in the systems engineering and operations research communities, but it adds phases that are specific to the numerical solution of PDEs. In each of these phases, general sources of uncertainty, both aleatory and epistemic, and error are identified. Our general framework is applicable to any numerical discretization procedure for solving ODEs or PDEs. To demonstrate this framework, we describe a system-level example: the flight of an unguided, rocket-boosted, aircraft-launched missile. This example is discussed in detail at each of the six phases of modeling and simulation. Two alternative models of the flight dynamics are considered, along with aleatory uncertainty of the initial mass of the missile and epistemic uncertainty in the thrust of the rocket motor. We also investigate the interaction of modeling uncertainties and numerical integration error in the solution of the ordinary differential equations for the flight dynamics.     

The Candela and Photometric and Radiometric Measurements

The national measurement system for photometric and radiometric quantities is presently based upon techniques that make these quantities traceable to a high-accuracy cryogenic radiometer. The redefinition of the candela in 1979 provided the opportunity for national measurement laboratories to base their photometric measurements on optical detector technology rather than on the emission from high-temperature blackbody optical sources. The ensuing technical developments of the past 20 years, including the significant improvements in cryogenic radiometer performance, have provided the opportunity to place the fundamental maintenance of photometric quantities upon absolute detector based technology as was allowed by the 1979 redefinition. Additionally, the development of improved photodetectors has had a significant impact on the methodology in most of the radiometric measurement areas. This paper will review the status of the NIST implementation of the technical changes mandated by the 1979 redefinition of the candela and its effect upon the maintenance and dissemination of optical radiation measurements.     

SMC／BMC的回收与再利用

SMC／BMC废弃物对工业及环境造成了很大影响，指出了SMC／BMC回收再利用的紧迫性。通过对目前国际上SMC／BMC回收再利用的3种典型途径优缺点的对比，参照国外SMC／BMC回收再利用的先进方法，对我国SMC／BMC回收再利用提供了可行的建议．