冷冻干燥法制备纳米Al_2O_3包覆W复合粉体

用冷冻干燥法合成了包覆型粉体,与传统方法相比,无需以纳米或微米级核颗粒为前提,过程简单,成本低。以偏钨酸铵和硫酸铝为原料,经喷雾预冻、真空冷冻干燥获得W/Al混合盐冻干前驱体,分段还原得到纳米Al2O3包覆W的复合粉体。采用XRD、IR、SEM等测试技术分析了样品的物相组成、结构、形貌,探讨了包覆结构的形成机理。结果表明:合成的包覆粉体是由40nm左右Al2O3颗粒均匀的包覆在1μm左右W颗粒表面。包覆结构的形成过程分为三个阶段:W晶粒的形核生长,非晶铝氧化合物包覆层的形成,Al2O3的非均匀形核生长。     

Fe2O3粉末表面非均匀成核法包覆

为解决氧化铁红在高温下呈现不稳定性的问题, 采用非均匀成核法使Si（OH）4和Al（OH）3均匀包覆在氧化铁红粉末颗粒表面, 用X射线衍射仪、透射电镜、 Zeta电位测定仪对包覆前后的Fe2O3粉末颗粒进行分析. 结果表明, 通过非均匀成核法可以制备出被SiO2和Al2O3包覆的Fe2O3复合粒子, 其技术的关键是如何控制反应溶液pH值和涂层物质沉淀的反应浓度, 以保持被覆颗粒稳定的悬浮特性.     

共沉淀法制备Al/Cr_2O_3复合粒子及其性能研究

采用共沉淀法将Cr2O3复合于片状金属铝粉表面获得了包覆效果好的Al/Cr2O3复合粒子。为了保证复合粒子的红外隐身性能,对前躯体粒子Al/Cr(OH)3进行了TG-DSC测试,确定了对前躯体的热处理温度;同时借助于XRD,SEM测试对制得的Al/Cr2O3粉末的相组成和形貌进行了表征,此外,将Al/Cr2O3粉末制成红外隐身涂层进行红外辐射率性能测试。结果表明,当铝粉含量为50%(质量分数)时制得的Al/Cr2O3复合粒子包覆较为完整,红外辐射率值最低为0.77。Cr2O3对片状Al粉的包覆在降低红外辐射率的同时不仅避免了Al粉的"显形"和氧化,其本身的绿色还可以起到可见光隐身的效果,在林地的迷彩隐身中具有重要的应用价值。     

尖晶石LiMn2O4的表面修饰改性

尖晶石LiMn2O4是很有发展前途的锂离子电池正极材料,但它在循环过程中存在着容量衰减的问题。介绍了几种容量衰减机理:Mn的溶解,Jahn Teller效应以及氧的缺陷。表面修饰是1种抑制尖晶石LiMn2O4容量衰减的有效方法。还介绍了几种表面修饰尖晶石LiMn2O4的方法:锂硼氧化物玻璃(LBO)包覆,碳酸盐包覆,乙酰丙酮包覆,LiCoO2包覆,金属氧化物包覆。其中用Li CoO2包覆的方法具有优异的效果。     

超声辅助TiO2包覆尖晶石LiMn2O4及电化学性能研究

采用超声辅助溶液法在尖晶石LiMn2O4表面包覆TiO2.通过X射线衍射、扫描电子显微镜、恒电流充放电、交流阻抗技术分析合成材料的结构、形貌及电化学性能.结果表明:TiO2包覆LiMn2O4与LiMn2O4具有相似的X射线衍射结果,衍射峰尖锐,样品颗粒大小均匀,无明显团聚.室温下0.2C充放电时,表面包覆1％TiO2的LiMn2O4首次放电比容量为123.51 mAh·g-1,略低于未包覆LiMn2O4的124.02 mAh·g-1,但在2C和4C高倍率时,表面包覆1％TiO2的LiMn2O4比容量分别为105.54和80.73 mAh·g-1,远高于未包覆的79.76和66.37 mAh·g -1.室温及55℃下以0.2C倍率循环50后,表面包覆1％ TiO2的LiMn2O4容量保持率分别为91.69％和87.36％,远高于未包覆LiMn2O4的86.58％和78.02％.室温下以1C倍率循环100次后,表面包覆1％ TiO2的容量保持率比未包覆LiMn2O4高出3.75％.表面包覆TiO2后LiMn2O4的循环性能得到了大大的提高,尤其是高温循环性能.     

锂离子电池正极材料锰酸锂的钴酸锂包覆研究

介绍了一种用溶胶-凝胶法制备包覆LiCoO2的LiMn2O4的方法。以乙二醇为螯合剂,将商业化的LiMn2O4加入到醋酸钴和醋酸锂的混合溶液中,调节pH值,在水浴中搅拌后离心分离,并在高温条件下煅烧即得到产品。利用X-射线衍射、差热—热重分析、透射电子显微镜以及充放电性能测试等分析方法来考察包覆LiCoO2的质量、煅烧温度和煅烧时间对晶体结构和电化学性能的影响。通过电化学性能测试表明,在最佳工艺条件下制备的LiCoO2包覆LiMn2O4材料的电化学比容量(115mAh/g)明显高于未包覆的LiMn2O4材料(110mAh/g),充放电循环次数明显高于其它合成条件下的样品,在20℃下的循环电化学比容量持有率大于85%。     

锂离子电池正极材料锰酸锂的钻酸锂包覆研究

介绍了一种用溶胶-凝胶法制备包覆LiCoO2的LiMn2O4的方法.以乙二醇为螯合剂,将商业化的LiMn2O4加入到醋酸钴和醋酸锂的混合溶液中,调节pH值,在水浴中搅拌后离心分离,并在高温条件下煅烧即得到产品.利用X-射线衍射、差热-热重分析、透射电子显微镜以及充放电性能测试等分析方法来考察包覆LiCoO2的质量、煅烧温度和煅烧时间对晶体结构和电化学性能的影响.通过电化学性能测试表明,在最佳工艺条件下制备的LiCoO2包覆LiMn2O4材料的电化学比容量(115 mAh/g)明显高于未包覆的LiMn2O4材料(110 mAh/g),充放电循环次数明显高于其它合成条件下的样品,在20℃下的循环电化学比容量持有率大于85%.     

异丙醇协助Al_2O_3包覆LiMn_2O_4合成及高温电化学性能研究

采用溶胶凝胶法,以硫酸铝、异丙醇(IPA)为原料对Li Mn2O4进行包覆。合成了含2%(质量分数)Al2O3表面包覆的Li Mn2O4电极材料。利用场发射扫描电镜(FESEM)对制备材料的形貌进行表征。结果显示,异丙醇协助包覆后材料表面呈现均匀分布的Al2O3颗粒。在55℃,3.0~4.5 V,1C充放电测试表明,IPA协助包覆可以显著提高Li Mn2O4正极材料高温下的循环稳定性。以异丙醇协助的Al2O3包覆Li Mn2O4材料作为正极,100次循环容量保持率为87.3%,而未加异丙醇包覆后的Li Mn2O4材料100次循环容量保持率为82.2%,未经过包覆的材料只有74.1%。不同倍率恒流充放电测试结果表明,异丙醇协助包覆能够改善Li Mn2O4的倍率性能,在5C和10C的放电倍率下的放电比容量分别达到了102.1和91.0 m Ah·g-1。通过电感耦合等离子体质谱仪(ICP)测试样品在电解液中Mn的溶解浓度。结果显示,高温(55℃)储存20 d后,异丙醇协助包覆的Li Mn2O4材料中Mn在电解液中的浓度仅为58.7×10-6,远远低于未加异丙醇包覆的和未经过包覆的。     

共沸蒸馏法制备W-ZrO_2复合粉末的相变过程及微观结构表征

以(NH4)6H2W12O40·xH2O(偏钨酸铵)和Zr(NO3)4·3H2O(硝酸锆)为原料,并以CH_3CH_2OH(乙醇)和CH_3CH_2CH_2CH_2OH(正丁醇)为分散剂,采用共沸蒸馏法制备出W-2%ZrO_2复合粉末,利用XRD、SEM、EDS、TEM等检测手段对粉末制备过程中不同阶段产物的物相、形貌及微观结构进行了分析与表征。结果表明:在共沸蒸馏过程中,(NH4)6H2W12O40·xH_2O与Zr(NO3)4·3H2O发生共沉淀反应,生成WO3·mH2O和Zr(WO4)2·nH_2O复合络合物。这种复合络合物较蒸发结晶法所制备的前驱体粉末具有更好的分散性且无硬团聚,经750℃煅烧后转变为由m-ZrO_2和WO_3组成的复合氧化物粉末;再经两段还原(一段还原温度750℃,二段还原温度800℃,还原时间均为2h)后,复合粉末中仍存在WO_2包覆ZrO_2的颗粒,其结构为椭圆形蠕虫状,粒径为15~20nm。当二段还原温度提高到900℃后,复合氧化物粉末完全转化为具有多面体球形和方形结构的W-ZrO_2复合粉末。     

化学共沉淀法制备FeSi@SiO_2@CoFe_2O_4复合粉末的吸波性能

以FeSi合金粉、TEOS、CoCl_2·6H_2O和FeCl_3·6H_2O为原料,对FeSi粉末进行包覆改性,采用化学共沉淀法制备FeSi@SiO_2@Co Fe_2O_4复合粉末,研究煅烧温度对包覆层结构、复合粉末磁性能与吸波性能的影响。结果表明,随煅烧温度从500℃升到800℃,均匀覆盖于FeSi粉末表面的CoFe_2O_4@SiO_2包覆层粒子逐渐聚集长大,导致包覆层局部结构被破坏。600℃煅烧的复合粉末具有均匀致密的包覆层结构,并具有较高的饱和磁化强度(173.2 (A·m~2)/kg、高矫顽力(3 047.8 A/m)和优良的电磁波吸收性能。FeSi@SiO_2@Co Fe_2O_4复合粉末的最大反射损耗(maximum reflection loss,RL_(max))达-53.5～-56.5 dB,有效带宽(反射损耗RL≤-10 dB,下同)为4.64～5.68 GHz。其中600℃煅烧的粉末可在薄厚度下实现对电磁波宽频带的有效强吸收。该粉末具有3个强吸收峰,RL_(max)分别为-56.5 dB (电磁波频率8.76 GHz,匹配厚度2.78 mm)、-49.2 dB (14.00 GHz,2.11 mm)和-40.5 dB (15.28 GHz,1.60 mm),3个强吸收峰的有效带宽大,分别为4.80、6.24和3.44 GHz,粉末的电磁波损耗机制为优良的阻抗匹配特性、高电磁波衰减常数、多重介电弛豫过程、多重界面极化以及高磁损耗和高介电损耗能力。     

Phase diagram of the ZrO2-Y2O3-Sm2O3 system in the melting-point region

A polynomial method has been used to construct a model for the liquidus surface in the ZrO₂-Y₂O₃-Sm₂O₃ phase diagram; that surface is made up of four fields of primary crystallization for the following phases: solid solutions based on cubic (C) and hexagonal (H) Y₂O₃, cubic ZrO₂ with a structure of fluorite type F, and high-temperature cubic La₂O₃ (X). The ternary system has two nonvariant four-phase equilibria of incongruent type. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 60–67, July–August, 2006.     

Phase diagram of the Al2O3-ZrO2-Sm2O3 system. II. Liquidus surface

A projection has been constructed for the liquidus surface on the plane of the concentration triangle for the Al₂O₃-ZrO₂-Sm₂O₃ phase diagram. There are no ternary compounds, or appreciable regions of solid solutions based on the components and the binary compounds. The liquidus surface is formed by nine fields of primary phase crystallization. There are five four-phase nonvariant peritectic equilibria, as well as two four-phase nonvariant eutectic equilibria, and one three-phase nonvariant eutectic equilibrium. As the ZrO₂ and SmAlO₃ phases interact with other phases by a eutectic mechanism, it is possible to combine the unique properties of the T and F solid solutions based on ZrO₂ with the properties of the other phases in the form of composites. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 28–35, March–April, 2006.     

Catalytic Synthesis of Tert-Butyl Acetate by Nd2O3/Al2O3-Nd2O3/ZnO

Nd2O3 was used to support Al2O3 and ZnO to prepare a supported solid base catalyst and investigate the effect of catalyst and reaction conditions on the synthesis of tert-butyl acetate. The composited oxide of Nd2O3/Al2O3-Nd2O3/ZnO exhibited excellent catalytic activity for the synthsis of tert-butyl acetate. The molar ratio of tert-butanol to acetic anhydride is 31, the catalyst in total amount of reactant nearly 0.5%, and reaction time 6 h. With the above conditions, yield of the reaction could reach to 65%. The structure of product were verified by the FT-IR, Element analysis, and MS, which proved that the product was tert-butyl acetate.     

Wettability of silicon carbide ceramic by Al2O3/Dy2O3 and Al2O3/Yb2O3 systems

Wettability is an important phenomenon in the liquid phase sintering of silicon carbide (SiC) ceramics. This work involved a study of the wetting of SiC ceramics by two oxide systems, Al₂O₃ /Dy₂O₃ and Al₂O₃ /Yb₂O₃, which have so far not been studied for application in the sintering of SiC ceramics. Five mixtures of each system were prepared, with different compositions close to their respective eutectic ones. Samples of the mixtures were pressed into cylindrical specimens, which were placed on a SiC plate and subjected to temperatures above their melting points using a graphite resistance furnace. The behavior of the melted mixtures on the SiC plate was observed by means of an imaging system using a CCD camera and the sessile drop method was employed to determine the contact angle, the parameter that measures the degree of wettability. The results of variation in the contact angle as a function of temperature were plotted in graphic form which showed that the curves displayed a fast decline and good spreading. All the samples of the two systems presented final contact angles of 40° to 10° indicating their good wetting on SiC in the argon atmosphere. The melted/solidified area and interface between SiC and melted/solidified phase were evaluated by scanning electron microscopy (SEM) and their crystalline phases were identified by X-ray diffraction (DRX). The DRX analysis showed that Al₂O₃ and RE₂O₃ reacted and formed the Dy₃Al₅O₁₂ (DyAg) and Yb₃Al₅O₁₂ (YbAg) phases. The results indicated that the two systems had a promising potential as additives for the sintering of SiC ceramics.     

Phase equilibria in the system HfO2-Y2O3-La2O3 AT 1900°C

We have used x-ray phase analysis, electron-probe microanalysis, petrography, and electron microscopy on annealed specimens to study phase equilibria in the ternary system HfO₂-Y₂O₃-La₂O₃ at 1900 °C over the entire concentration range. We have plotted the isothermal cross section of the phase diagram for this system at the indicated temperature. We found 23 phase regions. A typical feature of the system is formation of solid solutions based on different crystal modifications of the starting components (A-and H-La₂O₃, C-Y₂O₃, T-and F-HfO₂) and also the compounds La₂Hf₂O₇, LaYO₃. We did not observe new phases in the system. The nature of the phase equilibria in the system is consistent with the high relative thermodynamic stability of lanthanum hafnate (ΔH °La₂Hf₂O₇ ≈ 100 kJ/mole) compared with LaYO₃. We established that adding a third component extends the thermal stability region for the ordered phase of LaYO₃ toward higher temperatures. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 73–87, January–February, 2006.     

火焰原子吸收光谱法测定玻璃产品中Co_2O_3,CuO和NiO

采用HF分解玻璃基体硅酸盐,在稀盐酸、高氯酸介质中以空气-乙炔火焰原子吸收法直接连续测定玻璃产品中Co2O3,CuO和NiO,样品的加标回收率为96.4%～106%,RSD在1.18%～5.18%范围。     

Research on Glass Forming Ability of Er2O3 -Al2O3 -B2O3 -SiO2 System

The glass forming range of Er2O3-Al2O3-B2O3-SiO2 system was explored, and the effect of the content of Al2 O3 and Er2 O3 on glass-forming region was experimentally examined. It is shown that the region of glass formation range expends when the content of Al2O3 is changed from 15% to 20%, while it shrinks when the content of Er2O3 is changed from 20% to 30%. At the same time, the glass forming ability of Er2O3-Al2O3-B2O3-SiO2 system was also discussed using a value of β, which is an indication of crystallization tendency of glasses, calculated from thermo-analysis data. It is found that the glass forming ability of Er2O3-Al2O3-B2O3- SiO2 glasses is poor, while the glasses network may be enhanced when Al2O3 is added to the system, the glass forming ability being heightened. In addition, the crystallization temperatures of the rare earth glasses were determined using differential thermal analysis technique. The Er2O3-Al2O;-B2O3-SiO2 glass samples were heat treated at 1000,1100 and 1260℃ respectively. The results show that it is the Er2O3 phase that separates out from the glasses after crystaline heat treatment, and it is tiered up in glasses, as detected through XRD and SEM. This indicates that the phase separation occurs when the glasses are heated, Er3 being mainly distributed in the boron rich phase, then separated out from glasses, while the silicate rich phase remaining glassy state.