La_(0.7)Ca_(0.3)MnO_3与Al复合体系电磁输运性质的研究

研究了具有庞磁电阻(CMR)效应的锰基钙钛矿氧化物La0.7Ca0.3MnO3(LCMO)与Al复合体系的电磁输运性质.根据X射线衍射分析及电阻率与温度的关系可知,在(1-x)LCMO+xAl(x代表物质的量)复合样品中,发现了新相Al2O3,且LCMO晶格常数和晶胞体积随Al掺量的增加而减小,同时在复合样品中出现了除对应LCMO本征金属-绝缘体转变峰TP1之外,在较低温度区域出现了另外一个转变峰TP2的现象,且复合样品转变峰TP2比LCMO本征金属-绝缘体转变峰TP1处于较宽的温度区域.经研究认为,在合成复合样品的实验过程中,既有Al被氧化为Al3+替代Mn3+的替代反应,也有Al经过高温与空气发生反应生成Al2O3,进而填隙在LCMO晶界处影响母体的电磁输运性质.本系列复合物中较宽温度区域CMR的发现为今后同类问题的研究提供了很好的实验基础.     

Cr_2O_3在一维TiO_2中的掺杂行为

以硝酸铬和四氯化钛为前驱体,采用化学共沉淀法制得TiO2和Cr2O3的复合粉体。将复合粉体进行水热处理,用透射电子显微镜、场发射扫描电子显微镜、电子衍射、X射线衍射以及紫外-可见光谱吸收仪等测试手段对样品的形貌和成份以及光吸收性进行了分析。结果表明,水热处理后得到一维管状结构,其管长500~600 nm,直径10~20nm,壁厚4~6 nm。研究还发现,与纯的TiO2相比,Cr2O3/TiO2复合粉体的紫外-可见光吸收光谱显著红移。     

Effect of Al_2O_(3np) on the Properties and Microstructure of B_4C_p/Al Composites

Aluminum-matrix boron carbide (B_4C_p/Al) is a kind of neutron absorbing material widely used in nuclear spent fuel storage.In order to improve the tensile property of B_4C_p/Al composites,a new type of nano-Al_2O_3 particle (Al_2O_(3np)) reinforced B_4C_p/Al + Al_2O_(3np) composites were prepared by powder metallurgy method.The Monte Carlo particle transport program (MCNP) was used to determine the influence of Al_2O_(3np )on the thermal neutron absorptivity of composites.The universal material testing machine and scanning electron microscope (SEM) were used to study the mechanical properties,microstructure and fracture morphology of B_4C_p/Al composites.The results indicated that the neutron absorption properties of B_4C_p/Al composites were not affected by the addition of nano-Al_2O_3 particles in the range of 1 wt%-15 wt%.The addition of Al_2O_(3np) can obviously reduce the grain size of B_4C_p/Al matrix metals thus improve the tensile strength of the composites.The addition threshold of Al_2O_(3np) is about 2.5 wt%.Both B_4C_p and Al_2O_(3np) change the fracture characteristics of the composites from toughness to brittleness,and the latter is more important.     

Al_2O_3对中温变换催化剂活性的影响

氧化铬属剧毒物质,至今仍是一氧化碳变换催化剂的重要助剂。本研究致力于以无毒三氧化二铝代替氧化铬,为此对三氧化铝为助剂的新型中变催化剂的反应活性进行了系列测试。结果认为,三氧化二铝虽对活性不利,但可起良好结构助催化剂作用,如和其它填加物恰当配合,则新型无毒中变催化剂将有希望成功。     

多晶钠离子导体Na_5Y_(1-x)Cr_xSi_4O_(12)的正电子湮没一维角关联辐射研究

本文用正电子湮没辐射一维角关联实验装置,测量了多晶钠离子导体Na_5Y_1—xCr_xSi_4O_(12)(简称NYCS)系列各组分的正电子湮没辐射的一维角关联曲线,对测得的电子动量分布曲线归一化后,计算了线形参数,从H、W和S参数反映出NYCS系列样品中Na~+离子空位浓度的变化。测试结果表明,Cr_2O_3的含量不同,对多晶NYCS样品的一维角关联曲线的H、W和S参数均有很大影响,随Cr_2O_3的加入,H和S参数提高,W参数下降,当x=0.05时,两者均达到极值;继续加入Cr_2O_3,则H和S参数下降,W参数提高。这些结果说明,加入Cr_2O_3后,电导率的变化和Na~+离子空位浓度的变化密切相关,Na~+离子空位浓度增加,电导率提高,反之则降低。     

Flexural Stress Homogenization Effects of Interfacial Transition Layers in Modified ZrB_2-Al_2O_3/Epoxy Composites

The effect of interfacial modification on flexural strength of epoxy composites filled with modified ZrB_2-Al_2O_3 composite fillers was investigated in order to explore the stress distribution of modified composites under external load. The mechanical performance of epoxy composites filled with 0 vol%, 1 vol%, 3 vol% and 5 vol% unmodified and modified ZrB_2-Al_2O_3 fillers was characterized by three point bending(TPB) tests. The fracture surfaces of epoxy composites were observed by scanning electronic microscope(SEM). The results showed that the epoxy composite reinforced by 1 vol%modified fillers exhibited the optimal mechanical performance. According to the Von Mises stress contours simulated by finite element models(FEM) and the SEM images, it was shown that the modified ZrB_2-Al_2O_3 multiphase fillers could homogenize the stress in the epoxy composites due to the transition effect resulted from the interfacial modification layers on the surfaces of multiphase fillers. It contributed to the improvement of mechanical performance of epoxy composites further.     

高能振动球磨作用对纳米Al2O3相变温度的影响

为了探讨球磨作用对纳米A l2O3颗粒相变温度的影响,利用高能振动球磨机分别对纳米A l2O3进行不同时间的球磨,并将球磨作用后的A l2O3粉末在不同温度下进行退火处理。采用XRD、TEM、FT-IR及DTA等方法测定处理前后A l2O3粉末的结构、物相组成及相变温度。结果表明:随着球磨时间的增长,A l2O3的相变温度降低,当球磨时间达50 h时,-γA l2O3到θ-A l2O3相变以及-θA l2O3到-αA l2O3相变的温度均降低了100℃左右;球磨作用促进了A l2O3的晶化,同时可以造成纳米氧化铝的晶格缺陷,是导致相变温度降低的主要原因。     

重铬酸钾用于碳纳米管开口及表面处理的研究

用重铬酸钾作为氧化剂对碳纳米管进行开口及表面的氧化处理,采用失重率显示氧化效果并通过TEM观察碳纳米管.结果显示:重铬酸钾的浓度、氧化温度、氧化时间对碳纳米管的氧化效果均产生影响,其中以氧化温度的影响最大;重铬酸钾氧化碳纳米管时先是浸蚀碳纳米管表面,使碳纳米管管壁     

Hierarchical Co_3O_4 Microstructures Decorated with Ag and Cu Oxides: Study of Photocatalytic and Electrochemical Properties

Three-dimensional hierarchical Co_3O_4 microstructures decorated with Ag and Cu oxides were prepared via displacement reaction and subsequent annealing treatment.Photocatalytic properties measurements revealed that the photocatalystic activities of Cu O/Co_3O_4 composites(Co_3O_4 microstructures decorated with Cu O)were enhanced while those of Ag_2O/Co_3O_4 composites(Co_3O_4 microstructures decorated with Ag_2O)were reduced,when compared with those of pure hierarchical Co_3O_4 microstructures toward the degradation of methyl orange.In addition,Cu O/Co_3O_4 composites exhibited an excellent recyclability ability of photodegradation.The electrochemical properties test indicated that both of the composite oxide electrodes exhibited excellent pseudocapacitive performance with relatively high specific capacitance and good long-term cycling stability.With the increase of the loaded Ag_2O and Cu O dosages deposited on the Co_3O_4 microstructures surface,the specific capacitance values of the composites were increased.Ag_2O/Co_3O_4 composite electrodes showed higher specific capacitance values and better cycling stability than Cu O/Co_3O_4 composite ones.     

Synthesis and characterization of spinel Li_(1.05)Cr_(0.1)Mn_(1.9)O_(4-z)F_z as cathode materials for lithium-ion batteries

Samples with the nominal stoichiometry Li_(1.05)Cr_(0.1)Mn_(1.9)O_(4-z)F_z(z=0,0.05,0.1,0.15,and 0.2) were synthesized via the solid-state reaction method and characterized by X-ray powder diffraction(XRD),scanning electron microscopy(SEM),galvanostatic charge/discharge, and slow rate cyclic voltammetry(SSCV) techniques.The results show that the pure spinel phase indexed to Fd3m can be obtained when z=0, 0.05,and 0.1.The substitution of F for O with z≤0.1 contributes to the increase of initial capacity c...     

La1-xZnxMnO3和La2/3Sr_((1-x)/3)Znx/3MnO3的磁电输运特性

用固相反应方法制备La1-xZnxMnO3和La2/3Sr(1-x)/3Znx/3MnO3化合物。La1-xZnxMnO3在不同掺杂浓度x的研究表明:Zn2+在一定浓度范围内掺杂,具有钙钛矿结构,但掺杂浓度在50%~70%时有ZnO衍射峰,其电阻率在100 K以上随温度而下降,当掺杂浓度为x=0.3时电阻率最低。当Zn2+和Sr2+共掺而     

Structure of Bi2O3-ZnO-B2O3 system low-melting sealing glass

Bi_2O_3-ZnO-B_2O_3 system glass is a kind of lead-free low melting sealing glasses. The structure of Bi_2O_3-ZnO-B_2O_3 system low-melting sealing glass was investigated by DSC, FT-IR, XRD and SEM. The results show that with the increase of B_2O_3 content, the transition temperature Tg and softening temperature T_f of Bi_2O_3-ZnO-B_2O_3 system low-melting sealing glasses increase, which leads to the liquid phase precipitation temperature increasing and promotes the structure stability in the glass. With increasing the heat treatment temperature, a large number of liquid phases appear in samples and the sinter efficiency of the samples increases. The FT-IR spectra of the glasses show the presence of some bands that are assigned to vibrations of Bi-O bond from [BO_3] pyramidal and [BiO_6] octahedral units and B-O from [BO_3] and [BO_4] units. With the decrease of B_2O_3 content, the crystallization tendency of the glass increases. In glass samples B_1 and B_2, crystallization starts at 460 ℃ and 540 ℃, respectively. Both of them precipitate Bi-(24)B_2O_(39) phases.     

添加物对合成堇青石性能的影响

本文探讨了碱金属氧化物、碱土金属氧化物、过渡金属氧化物及稀土金属氧化物对合成堇青石烧结性能及热膨胀性能的影响,结果表明,碱金属氧化物K_2O和碱土金属氧化物CaO均能降低堇青石的热膨胀和烧结温度,扩大了烧结范围。过渡金属氧化物Cr_2O_3增大了堇青石的热膨胀系数,对烧结有一定的促进作用,而稀土金属氧化物Y_2O_3对堇青石的烧结性能影响较小。     

Al2O3/Ti-Al复合材料的抗高温氧化性研究

利用氧对金属Ti、Al粉的部分氧化，原位合成了Ti—Al金属间化合物和氧化铝，从而制备出了Al2O3／Ti—Al复合材料，通过氧化增重实验研究了材料的抗高温氧化性能，发现随着原始配比中Al含量和烧成温度的增加，复合材料的抗高温氧化性能逐渐提高，并借助X衍射和SEM手段对复合材料的组成和显微结构进行了分析，讨论了工艺因素对材料氧化性能产生影响的机理。     

人工合成Al2OTiO5稳定性的初步研究：添加剂对AT的稳定作用

本文探讨了单独加入 MgO、SiO_2和 Cr_2O_3对 AT 的稳定作用,实验结果表明,单独引入 MgO 或 SiO_2时能改善 AT 的烧结性能和力学性能,在不明显提高热膨胀系数的情况下稳定了 AT。而 Cr_2O_3没有起到稳定 AT 的作用。利用 XRD、SEM、EPMA 等手段测试分析了物相组成、晶格常数和显微结构形貌等。     

Micro-analysis of high-temperature oxidation-resistance of a new kind of heat-resistant grid plate in grate-kiln

To further improve the oxidation-resistance of materials and reduce the cost of grid plates in grate-kiln, a new kind of heat-resistant grid plate was developed. The microstructure of this grid plate with a life more than 18 months was studied by XRD, SEM and EDS techniques. The results show that high hardness, high intensity and good impact property make the new kind of heat-resistant grid plate and its oxide film have a higher resistance to deformation and abrasion at 900-1000°C. Besides, small grain size...     

混杂增强AZ91复合材料的制备及其显微组织和性能

采用挤压铸造方法制备了以AZ91镁合金为基体、Al2O3短纤维(Al2O3f)和石墨颗粒(Grp)混杂为增强体的复合材料。观察了不同复合材料的显微组织,测试了其力学性能,并对其摩擦磨损性能进行了研究。结果表明:用此法制备的镁基复合材料增强相分布均匀,与基体结合紧密。硬度随Grp体积分数的增加而降低,Al2O3f的加入能提高复合材料的硬度。抗拉强度和伸长率都随Grp体积分数的增加而减小。Grp体积分数增加,磨损质量损失和摩擦系数都降低。随着摩擦过程的进行,在试样表面逐渐形成一层黑色连续的润滑膜。     

SiO2氧化层在DIMOX法制备SiCp/Al2O3-Al复合材料中的作用机制

利用直接金属氧化法制备了SiC颗粒增强Al2O3-Al基复合材料，借助于XRD、光学金相显微镜（OM）和扫描电镜（SEM）对该复合材料的微观结构进行了观测，分析了SiO2氧化层的形成在复合材料制备过程中的作用。结果表明，SiO2层可以防止材料粉化现象的发生。缩短反应的孕育期，并可避免材料的胞状生长，促进材料的致密化。     

水溶液中重铬酸钾与硝酸银反应产物的研究

本文研究了水溶液中重铬酸钾与硝酸银反应生成的沉淀产物的组成,以及反应物浓度和溶液体积对沉淀产物组成的影响。实验证明,K_2Cr_2O_7与AgNO_3反应生成的沉淀通常是Ag_2CrO_4和Ag_2Cr_2O_7的混合物。但在特定操作条件下可获得单一的Ag_2CrO_4沉淀。     

电镀废水中铬的回收及利用

以电镀废水为研究对象，采用几种絮凝剂对其中的铬进行了回收处理，对几种絮凝剂的回收结果进行了比较，筛选出最佳的絮凝剂，用选出的最佳絮凝剂即复合絮凝剂——聚合氯化铝、聚合硫酸铁和阳离子聚丙烯酰胺将铬回收为Cr2O3，配制成抛光膏，将其用于金属机件表面的抛光，使电镀废水实现了达标排放，并使铬得到回收利用。