铈对纯铁中锑的晶界平衡偏聚及晶界迁移的影响

本文研究了铈对纯铁的再结晶温度和晶界迁移以及锑的晶界平衡偏聚的影响,并测定了两种合金在不同温度下达到晶界平衡偏聚后的脆性转变温度。     

稀土元素在高速钢晶界偏聚的研究

材料的晶界状态对材料的性能有很大的影响,元素在晶界偏聚对材料性质的影响是冶金和材料科学的重要课题。合金元素和杂质元素在晶界偏聚,使晶界的化学成分发生变化,影响晶界移动、晶粒长大、元素沿晶界扩散、沿晶界的破断等现象,从而影响材料的机械性质、化学性质以及电学性质等。溶解在铁中的铈因原子半径远大于铁而产生较大的点阵畸变能,这将促使它们偏聚在晶界上。我们曾指出,铈和镧能够使硫的偏聚减     

立体化学的某些新概念

1848年Pasture对酒石酸钠铵首次完成了人工拆分工作,从而提出了物质的旋光性与结构的关系问题。1874年Van’t Hoff和Le.Bel分别提出碳原子的正四面体学说,初步解决了物质的旋光性与结构的关系。     

特高综合磁性能晶界扩散磁体的研究

采用Tb4O7,TbHx和Nd2O3+Tb4O7三种扩散源,通过晶界扩散技术制备出特高综合磁性能的钕铁硼磁体,对不同扩散源的扩散效果及扩散机制进行研究.采用TbHx进行晶界扩散,获得综合磁性能(BH)max+Hcj=84.26,矫顽力温度系数为-0.361％·℃-1的最佳钕铁硼磁体,SEM微观结构分析表明TbHx扩散源...     

液相烧结碳化硅晶界内氮化反应的研究

碳化硅 ( Si C)由于其高度的共价键结合特性而具有高硬度、耐磨性和高化学稳定性等优异性能而成为热机、高温环境和化学化工等领域的研究应用对象 .碳化硅材料的无压烧结最早是由 Prochazka[1] 实现的 .2 0世纪 80年代初期 ,Omori[2 ] 通过采用氧化物 ( Al2 O3,Y2 O3和稀土氧化物等 )添加剂的手段大大降低了无压烧结的温度 .这些氧化物具有较低的共熔点 ,在高温下易形成液相 ,从而促进了碳化硅的晶粒重排和晶体生长 .2 0世纪 90年代以来 ,氮化物和氧化物的混合添加剂 (如 Al N- Y2 O3) [3]被广泛应用于碳化硅的液相烧结 .这是因为氮在…     

氧含量对烧结NdFeB磁体晶界调控的影响

晶界扩散技术经过近些年的发展,研究人员对晶界扩散技术的涂覆化合物种类、涂覆方式、热处理工艺等进行了系统的研究。O元素是烧结NdFeB磁体生产环节中重要的影响因素,但对晶界扩散的影响却很少被研究。通过调节磁体制备工艺,获得不同O含量的NdFeB磁体,并对磁体分别进行Tb_4O_7和TbH_x晶界扩散。得出当涂覆增重小于7 mg·cm~(-2)时,两种化合物对磁体矫顽力的提升幅度基本一致。当涂覆增重为11 mg·cm~(-2)时,随着基体中O含量的增加,两种化合物对矫顽力的提升都有不同程度的减弱。EPMA结果显示:Tb_4O_7晶界扩散后O, Tb元素主要分布于三角晶界处,呈团聚状态。TbH_x晶界扩散后Tb元素分布相对弥散,浓度梯度不明显。在高O基体中,相同涂覆量条件下, TbH_x晶界扩散后对矫顽力提升幅度比Tb_4O_7晶界扩散后高1.6 kOe。     

钕铁硼电泳法晶界扩散渗镝研究

采用电泳法在钕铁硼磁体表面形成富含重稀土元素Dy附着层,高温扩散处理后磁体性能提高。XRD和DSC测试结果表明:在磁体表面附着层内富含重稀土元素Dy,SEM和EPMA分析测试结果说明高温处理后,表面电泳附着层转化为Dy2O3,并与磁体内Nd元素发生取代反应;取代生成的重稀土元素Dy沿晶界扩散致使磁性能提高。这种方法简单可行,为晶界扩散渗Dy工程应用提供了新的途径。     

晶界扩散铈磁体的组织结构与磁性能

采用涂覆重稀土氢化物为扩散源,制备晶界扩散铈磁体,研究了磁性能和组织结构特点,并对其温度稳定性进行了分析评价。晶界扩散铈磁体的矫顽力从12.07 kOe提高至18.49 kOe,矫顽力和剩磁温度系数分别优化到-0.502%·℃~(-1)和-0.184%·℃~(-1)。采用EPMA和WDS成分分析表明,在磁体表层附近,大量Tb元素扩散到主相晶粒内部;扩散深度大于60μm时, Tb元素主要分布在晶界,并且在主相晶粒边缘形成(RE,Tb)_2Fe_(14)B壳层。由于Tb_2Fe_(14)B相和Ce_2Fe_(14)B相的各向异性场均具有较好的温度稳定性,因此,晶界扩散铈磁体可以获得与烧结钕铁硼磁体相当的矫顽力温度系数。     

放射化学分析的某些特点

随着原子核物理学和原子能科学的迅速发展,出现了新的研究对象——核反应的放射性产物。这些产物的分析被称为放射化学分析,它具有一系列的特点。首先是被照射的元素和它形成的放射性同位素的浓度差别很大。通常浓度相差10~(10)—10~(15)倍。另外必須顾及到的是放射化学分析的时間因素,特别是对于短寿命的放射性同位素的分离具有特别重要的意义。因此,放射化学方法应当是快速的,不应当有冗长的操作手续。     

反应平衡常数的某些应用

欲对许多较复杂的化学反应的反应倾向作出判断,常常把复杂反应看成是几个简单反应的组合。如把氯化银溶于氨水的反应看成是由氯化银的电离平衡和银氨络离子的生成平衡的组合。     

Mo掺杂对高纯Ce1-xNdxO2-x/2(x=0.10, 0.15)体系烧结温度及晶界电性能的影响

用柠檬酸硝酸盐法制备高纯Ce1-xNdxO2-x/2(x=0.10, 0.15)固溶体, 加入摩尔分数为5%的Mo, 研究了Mo掺杂对烧结温度、结构及电性能的影响. 通过X射线衍射、电感偶合等离子体和场发射扫描电镜等手段对氧化物进行了结构表征, 采用交流阻抗谱测试其电性能. 柠檬酸硝酸盐法制备的前驱体经1450 ℃烧结24 h得到致密度大于96%的陶瓷材料; 加入5%Mo, 在1250 ℃下烧结8 h即可达到理想的致密度(>95%). 加入Mo在烧结过程中可加快晶界迁移, 促进晶粒生长, 显著提高了晶界电导率. 在600 ℃时Ce0.85Nd0.15O1.925的晶界电导率为2.56 S/m, 加入Mo后材料的电导率增加到5.62 S/m.     

Grain Boundary Electronic Insulation for High-Performance All-Solid-State Lithium Batteries

Sulfide electrolytes with high ionic conductivities are one of the most highly sought for all-solid-state lithium batteries (ASSLBs). However, the non-negligible electronic conductivities of sulfide electrolytes (≈10⁻⁸ S cm⁻¹) lead to electron smooth transport through the sulfide electrolyte pellets, resulting in Li dendrite directly depositing at the grain boundaries (GBs) and serious self-discharge. Here, a grain-boundary electronic insulation (GBEI) strategy is proposed to block electron transport across the GBs, enabling Li−Li symmetric cells with 30 times longer cycling life and Li−LiCoO₂ full cells with three times lower self-discharging rate than pristine sulfide electrolytes. The Li−LiCoO₂ ASSLBs deliver high capacity retention of 80 % at 650 cycles and stable cycling performance for over 2600 cycles at 0.5 mA cm⁻². The innovation of the GBEI strategy provides a new direction to pursue high-performance ASSLBs via tailoring the electronic conductivity.     

Twist Grain Boundary Liquid‐Crystalline Phases under the Effect of the Magnetic Field: A Complete 2H and 13C NMR Study

A liquid crystal ( HZL 7/* ) containing an (S)‐2‐methylbutyl‐(S)‐lactate unit in the chiral chain, is investigated by means of ²H and ¹³C NMR spectroscopy in order to obtain information on its orientational order, its molecular structure and the effect of external magnetic fields on the supramolecular structure of its phases. This mesogen presents very peculiar mesomorphic properties and exhibits frustrated TGBA* and TGBC* phases in a wide temperature range up to 60 °C, as well as an additional phase transition from TGBC₁* to TGBC₂*. ²H NMR measurements show, for the first time, a peculiar magnetic field effect in unwinding the supramolecular structure of both the TGBA* and TGBC* phases. This effect is particularly evident at higher magnetic fields, while different behaviour is observed at lower magnetic fields. This indicates that the supramolecular structure is very sensitive to magnetic fields of the order of 1 Tesla. Moreover, the analysis of the ²H and ¹³C NMR spectra of HZL 7/* allow us to obtain several structural properties, such as the tilt angle of the TGBC* phases and the local orientational order parameters referred to the phenyl and biphenyl fragments. This is the first structural characterization of the frustrated phases of these complexes by means of NMR.     

二组分体系的相图及其相图边界理论

主要探讨了二组分体系的相图,如气-液相图和液-固相图,总结了二组分相图的分类、绘制及相图分析,这有利于理解和掌握二组分相图的基本规律。并简单介绍了相图边界理论,扩展了相图的热力学研究。     

Y2O3,CeO2掺杂的Mg-PSZ陶瓷材料研究

采用传统的陶瓷工艺制备少量掺杂Ｙ２Ｏ３,ＣｅＯ２的Ｍｇ－ＰＳＺ陶瓷,材料在较低的温度下烧结致密并实现了微晶化,探讨了Ｙ２Ｏ３,ＣｅＯ２的复合稳定作用和１１００℃热处理过程对材料相组成、显微结构和力学性能的影响。经１１００℃适当时间热处理,Ｙ２Ｏ３,ＣｅＯ２的复合稳定作用有效报制亚共析分解反应发生,优化调整ｃ－ＺｒＯ２晶粒中的ｔ－ＺｒＯ２析出体成核长大过程。断裂特征为穿晶、沿晶兼有,相变增韧和微裂纹     

Studies on the Structure and Properties of Multiphase Al_2O_3 Abrasion-resistant Ceramics

1 INTRODUCTION Due to its high intensity, high hardness, high tem- perature resistance, corrosion resistance and abra- sion resistance, Al2O3 abrasion-resistant ceramic is widely applied in many fields, such as metallurgy, minerals, electric power, building materials and che- mical engineering as grinding medium in the ball grinder. The properties of Al2O3 ceramic are positi- vely correlated to its purity: the higher the purity is, the better the properties of the product are, but cor- r…     

Morphotropic Phase Boundary Enhanced Photocatalysis in Sm Doped BiFeO3

This paper presents the results of the synthesis of samarium-doped bismuth ferrite (BFO) nanoparticles by the solution combustion method. The dependence of BFO properties on the amount of the samarium (Sm) in the composition was studied. The synthesized nanocomposites were characterized by scanning electron microscopy SEM), X-ray diffractometry (XRD), Raman, Electron Diffuse Reflectance Spectroscopy (EDRS) and Electron Magnetic Resonance (EMR). The photocatalytic (PC) measurements showed the absence of a strict correlation between the PC activity and the crystallite size and band gap. An increase in the PC activity of BFO samples with 10 and 15% doping was observed and it was concluded that in controlling the PC properties in doped BFO, the processes of interfacial polarization at the boundaries of the morphotropic phase transition are of decisive importance. It was supposed that the internal electric field formed at these boundaries contributes to the efficient separation of photogenerated charge carriers.     

Grain boundary resistance of fast lithium ion conductors: Comparison between a lithium-ion conductive Li-Al-Ti-P-O-type glass ceramic and a Li1.5Al0.5Ge1.5P3O12 ceramic

The structure and ionic conductivity of a lithium-ion conductive Li-Al-Ti-P-O-type glass ceramic (LATP) was studied by means of powder X-ray diffraction, transmission electron microscopy, and broadband impedance spectroscopy. The results were compared to a Li_1.5Al_0.5Ge_1.5P₃O₁₂ (LAGP) ceramic. While the grain conductivity of LATP is higher than that of LAGP, the total conductivity of LATP is lower due to a large grain boundary resistance. The grain boundary resistance of LATP is characterized by a slightly higher activation energy and a slightly higher pre-exponential factor than the grain resistance. Our results indicate that the origin of the grain boundary resistance in these fast lithium ion conductors is clearly distinct from oxide ion conductors.     

Pr掺杂对Ce5.2Sm0.8MoO15－δ晶界及电性能的影响

在Ce_5.2Sm_0.8－xPr_xMoO_15－δ体系中引入少量Pr得新氧化物Ce_5.2Sm_0.72Pr_0.08MoO_15－δ, 通过X射线衍射(XRD), 拉曼光谱(Raman), X射线光电子能谱(XPS), 场发射扫描电镜(FE-SEM)等手段对氧化物结构进行分析, 交流阻抗谱测试电性能; 讨论掺杂少量Pr对Ce_5.2Sm_0.8MoO_15－δ微观结构和电性能的影响. 结果表明, 少量Pr^3＋的掺杂可降低晶界电阻, 增加离子扩散通道, 降低体系的总电导激活能和晶界电导激活能, 提高氧化物的总电导率和晶界电导率; 500 ℃时掺Pr材料的晶界电导率为6.79×10^－3 S•cm^－1, 比未掺Pr材料的晶界电导率(5.61×10^－5 S•cm^－1)提高约2个数量级.     

The morphology of gel-spun polyethylene fibers,investigated by solid-state 13C NMR

Gel-spun polyethylene fibers were analyzed at room temperature with ¹³C NMR, using both, CP-MAS and BILEV (Bloch-decay with two-level decoupling). The analysis shows the existence of three different components in the fiber sample—a crystal component, an amorphous component and a third component, named the oriented, mobile component. This latter component has a ¹³ C chemical shift that is similar to the crystalline chemical shift, but with a mobility, expressed by T₁, that is closer to the amorphous component. The chemical shift and T₁ are as follows: 34.06 ppm and 28.1 s for the crystalline part; 31.70 ppm and 0.3 s for the amorphous part; and 34.06 ppm and 1.8 s for the oriented mobile component. The percentages are 63.2% crystalline; 34.0% oriented mobile, 2.8% amorphous component. Using proton spin-diffusion measurements, it was possible to estimate the domain size of the crystalline and oriented mobile components to be 62.8 and 13.2 nm, respectively, in agreement with the results of a full-pattern x-ray study on the same sample. After melting of the fiber at 450 K and recrystallinzation on cooling, the oriented, mobile component is dramatically reduced. © 1994 John Wiley & Sons, Inc.