铝掺杂超细氧化锌粉体的制备与性能研究

本文以Zn(NO3)2·6H2O和Al(NO3)3·9H2O为原料采用均匀沉淀法制备了Al掺杂ZnO(ZAO)超细粉体,用XRD、SEM、纳米粒度分析仪及四探针电阻仪等对ZAO超细粉体进行了测试表征.研究了反应温度、煅烧温度、反应物浓度、Al掺杂量及分散剂添加量对ZAO超细粉体形貌、尺寸及电阻率的影响.研究结果表明:制备的ZAO粉体为纤锌矿结构;煅烧温度为550℃时,ZAO晶相形成很好;随着Al掺杂量的增加,ZAO粉体电阻率降低,晶格常数减小,但当Al掺杂量大于2.0 mol;时,生成尖晶石相,其电阻率反而上升.     

纳米高近红外反射颜料制备工艺研究

采用柠檬酸溶胶-凝胶法制备了纳米高近红外反射颜料,研究了Fe/Cr摩尔比、水解温度、溶液金属离子浓度、pH值、煅烧温度等因素对凝胶时间及试样性能的影响.结果表明,在Fe/Cr摩尔比为0.50,水解温度70℃,溶液金属离子浓度为2.5～3.5 mol/L,pH =3 ～4,煅烧温度为900℃保温60 min的条件下,制备颜料的主晶相为Cr1.3Fe0.7O3,近红外波段范围内(700～2500 nm)其平均反射率可达到77.58;,晶粒尺寸在50～ 200 nm之间.     

溶胶-凝胶法制备Y_(3-x)Ce_xAl_5O_(12)纳米粉体的研究

以Y(NO3)3.6H2O、Ce(NO3)3.6H2O、Al(NO3)3.9H2O、柠檬酸为主要原料,以聚乙二醇作为分散剂,采用溶胶-凝胶法合成了纳米级YAG∶Ce3+粉体。研究了煅烧温度、溶液中金属离子浓度、溶液pH值及Ce3+掺杂量等因素对制备纳米YAG∶Ce3+粉体的颗粒尺寸、颗粒形貌、物相的影响。结果表明:当溶液pH为=4.0、金属离子浓度为0.50 mol/L、煅烧温度为1000℃时,可以制备出具有良好的分散性,平均粒径在30 nm的粉体。     

Nd∶Lu2O3纳米陶瓷的制备和EXAFS研究

通过氨水加碳酸氢铵复合沉淀剂合成了Nd3+掺杂的氧化镥纳米晶粉体。经马弗炉900℃煅烧2 h,获得了分散性好、晶粒尺寸约为40 nm的高质量的Nd∶Lu2O3纳米晶粉体。采用无压流动H2气氛对所得素坯进行两步烧结致密化(T1=1720℃,T2=1620℃)获得了半透明的纳米Lu2O3陶瓷。荧光光谱表明在808 nm波长激发下,纳米陶瓷发光强度明显超过微米级陶瓷。同步辐射研究表明,随着晶粒尺寸减小,纳米陶瓷中Nd原子的局域环境混乱度增大,无序度相对变大。在Nd掺杂浓度相同情况下,对同一光子能量的X射线吸收系数纳米陶瓷小于微米级陶瓷。     

纳米铝粉的性质及其对沉淀法制备纳米氧化铝粉体的作用

研究了纳米铝粉的氧化性质,并利用Al(NO3)3*9H2O、氨水和纳米铝粉为原料,采用液相沉淀法制备出Al(OH)3溶胶,经过真空抽滤和高温煅烧获得了纳米α-Al2O3粉体. 利用DSC/TG曲线分析了纳米铝粉和复合粉体不同温度下晶型和重量的变化,利用XRD分析了不同煅烧温度下复合粉体的成份变化、利用SEM观测了获得的α-Al2O3粉体形貌.研究表明纳米铝粉在相对较低的温度下氧化,这种氧化物籽晶的存在有利于α-Al2O3晶型的低温转化.     

LiNO3熔盐辅助煅烧制备高分散纳米ZrO2粉体

以可溶性锆盐溶液反向滴定氨水溶液成功地制备了纳米ZrO2粉体,系统研究了反应物浓度与煅烧温度对产物粒径和形貌的影响;在反应过程中加入表面活性剂,并采用正丁醇共沸蒸馏干燥和LiNO3熔盐辅助煅烧等方法,以控制粒径、减少团聚.通过热重-差热分析(TG-DTA)、透射电镜(TEM)、X射线衍射(XRD)、比表面积分析(BET)等对样品进行了形貌表征、晶型及粒径分析.结果表明:上述多种方法联合使用能够有效控制粒径、减少团聚,制备出的纳米ZrO2粉体分散性优异,为立方晶相结构,粒径15 nm左右.     

可控溶胶-凝胶法制备纳米ZrO2

以ZrOCl2 · 8H2O和六次甲基四胺(C6H12N4)为原料,三嵌段聚合物Pluronic P123为分散剂,采用可控溶胶-凝胶法制备了纳米ZrO2粉体.采用XRD、TEM和SEM表征所得粉体.结果表明:反应物配比和水浴温度决定了溶胶的凝胶化所需时间,凝胶化时间在5~1290 min内可调;热处理温度越高,纳米ZrO2粉体的粒径越大.热处理温度在450～800 ℃区间内,ZrO2粉体粒径变化范围为10~100 nm;分散剂P123能明显降低粉体的硬团聚程度.当c(ZrOCl2)=0.3 mol/L、n(ZrOCl2): n(C6H12N4)=1: 0.8、n(ZrOCl2): n(P123)=1: 0.714,水浴温度为40 ℃,热处理温度为550 ℃时,制得平均粒径为20 nm的纳米ZrO2粉体.所得纳米粉体具有良好的烧结活性.该方法在调整纳米ZrO2的凝胶化时间和粉体粒径方面具有可控性.     

NH4F含量及煅烧工艺对氧化铝相变及α-Al2O3微观形貌的影响

为研究NH4F含量及煅烧工艺对氧化铝相变及α-Al2O3微观形貌的影响,向Al(OH)3粉体中引入不同质量分数的NH4F,经不同条件煅烧后获得Al2 O3粉体样品.采用X射线衍射仪和扫描电子显微镜进行物相分析和晶相形貌观察.结果表明,NH4F的引入可以显著降低Al2 O3的相变温度,含量5.0; NH4F的Al(OH)3在900℃保温2.5h全部转变为α-Al2O3,这比传统的转变温度低200～ 250℃.同时,随着NH4F含量的增加,α-Al2O3晶粒形貌由颗粒状变为平面六角片状.但是平面六角片状α-Al2 O3在1200℃是不稳定的,长时间煅烧时,α-Al2O3晶体又"熔解"为小颗粒晶粒.     

微波水热法制备ZnO纳米晶

采用微波水热(microwave hydrothermal,M-H)法在MDS-6型温压双控微波水热反应仪中成功地制备出平均晶粒尺寸为30 nm且呈现棒状形貌的ZnO纳米晶.并在一定的水热温度和反应时间下系统研究了微波水热反应过程中[Zn2+]离子浓度、反应釜填充比、反应物浓度比[Zn2+]/[OH]等工艺因素对ZnO纳米晶的晶粒尺寸及形貌的影响.采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)和透射电子显微镜(TEM)对所制备的ZnO纳米晶进行表征.结果表明:所制备ZnO的平均晶粒尺寸约为30 nm,ZnO纳米晶呈现棒状形貌.随着[Zn2+]离子浓度的增加,ZnO纳米晶的晶粒尺寸先减小后增大;随着反应釜填充比和反应物浓度比[Zn2+]/[OH]的增大,ZnO纳米晶的晶粒尺寸先减小后增大,并逐渐趋于稳定.制备ZnO纳米晶的最佳反应条件为:[Zn2+]=1.6 mol·L-1;反应釜填充比=70;;[Zn2+]/[OH]=1/2.     

超声波辅助固液反应球磨制备ZnFe2O4纳米晶的研究

以α-Fe2O3和ZnO粉体为原料,在超声波辅助高能球磨作用下通过诱发固液相反应,并在低温下烧结合成了ZnFe2O4纳米晶粉末.采用X射线、透射电镜(TEM)对前驱体和烧结产物进行了表征,分析了球磨过程对粉体晶粒尺寸的影响和znFe2O4的形成过程.实验结果表明:超声波辅助固液球磨能在低温下烧结合成ZnFe2O4纳米晶,纳米晶的晶粒尺寸为15～25 nm;相比无超声波辅助下的固液球磨,超声波球磨降低znFe2O4烧结温度约50℃;同一烧结温度下,球磨时间越长,ZnFe2O4转化率越高,晶粒尺寸越小.     

CsI-LiCl共晶材料的坩埚下降法生长与闪烁性能研究

本文采用坩埚下降法,在真空密封的石英坩埚中成功生长出CsI-LiCl与CsI-LiCl:Na共晶闪烁体。通过扫描电子显微镜(SEM)观察晶体微结构表明该共晶中LiCl相与CsI相存在周期性的层状排列,CsI相的厚度在5 μm左右。共晶样品的X射线激发发射谱显示在CsI-LiCl和CsI-LiCl:Na共晶样品存在缺陷发光,在CsI-LiCl样品中还观察到了纯CsI的自陷激子(STE)发光。CsI-LiCl样品在α粒子激发下的多道能谱中观察到明显的全能峰,这一结果证明CsI-LiCl共晶可用于热中子探测的潜力。     

静电纺丝法制备CeO2微纳米纤维及其除氟性能

以聚丙烯腈(PAN)为载体,六水合硝酸铈[Ce(NO₃)₃·6H₂O]为原料,采用静电纺丝法制备了Ce(NO₃)₃/PAN纤维,在空气中热处理得到CeO₂微纳米纤维,通过XRD、BET和SEM对CeO₂微纳米纤维进行表征。采用静态吸附实验探讨了CeO₂微纳米纤维去除水溶液中氟离子的性能,考察了溶液pH值、初始氟离子浓度及共存阴离子等对吸附性能的影响。结果表明,pH=3时,CeO₂微纳米纤维对F^-的吸附性能最佳,CeO₂吸附量随着F^-浓度的增大呈上升趋势。CeO₂微纳米纤维对F^-的吸附等温线遵循Langmuir模型,二级动力学模型能很好地描述CeO₂微纳米纤维对F^-的吸附过程。CeO₂微纳米纤维的除氟性能优良,可为其实际应用提供理论参考。     

First-principles coexistence simulations of supercooled liquid silicon

We perform first-principles coexistence simulations of the low-density and the high-density phases of supercooled liquid silicon and find a negative slope for the coexisting line in the temperature-pressure plane. Electron density maps and electron-localization function plots of the two phases of silicon show marked differences. The calculated differences suggest more localized electrons in the low-density liquid compared to the high-density liquid, coming from an increased population of covalent bonds, which further explain the calculated negative slope in the two phase coexistence regime. This is consistent with the presence of a pseudo-gap in low-density liquid silicon, absent in the high-density liquid which shows a metallic behavior.     

Crystal structures of thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane

Structures of both thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane, ?C₆H₄?CH₂SCH₂?C₆H₁₀?CH₂SCH₂?, have been determined, wherecis andtrans refer to the attachments to the cyclohexane ring. Thecis form crystallizes in the monoclinic space groupP2₁/c witha=8.4299(11)Å,b=21.772(2)Å,c=8.9724(13)Å, β=116.574(11)^o, andZ=4. Thetrans isomer packs into the monoclinic space groupP2₁ witha=8.159(16)Å,b=10.185(5)Å,c=9.558(2)Å, β=112.435(18)^o, andZ=2. The cyclohexane ring of thecis isomer is in the chair conformation, while the cyclohexane of thetrans isomer is found in a twisted boat conformation.     

CTAB与SDBS对碳酸锶粒子生长形态调控及机理研究

以表面活性剂CTAB和SDBS为化学添加剂,采用化学共沉淀法对碳酸锶晶体的生长形态进行调控,成功地制备出了实心的树枝状和花瓣为空心的花状碳酸锶粉体,并用X射线衍射(XRD)、扫描电子显微镜(SEM)和傅里叶变换红外光谱(FT-IR)等分析手段对样品进行了表征;最后重点对化学添加剂可能产生的影响机理进行了初步的探讨.结果表明,CTAB和SDBS在晶体生长的过程中能起到显著的影响作用,两者对粒子分散性能的作用效果相反,而且后者对晶体(013)和(213)晶面表面能降低的贡献明显大于前者.     

Triethyl ammonium salt of O,O′-bis(p-tolyl)dithiophosphate, [Et3NH]+[(4-MeC6H4O)2PS2]−

Triethyl ammonium Salt of O,O′-bis(p-tolyl)dithiophosphate and O,O′-bis(m-tolyl)dithiophosphate have been obtained by reaction of p- and m-cresol, respectively with P₂S₅ in toluene and have been characterized by elemental analysis, IR, ¹H and ³¹P NMR spectroscopy. The molecular structure of O,O′-bis(p-tolyl)dithiophosphate has been determined. Crystal data: [Et₃NH]⁺[(4-MeC₆H₄O)₂PS₂]⁻: Monoclinic, P2₁/c, a=15.2441(9) ?, b=10.415(2) ?, c=3.9726(9) ?, β=91.709(7)°, V=2217.5(1) ?⁻³, Z=4.Supplementary materials Additional material available from the Cambridge Crystallographic Data Centre (CCDC no. 600927 for [Et₃NH]⁺[(4-MeC₆H₄O)₂PS₂]⁻ comprises the final atomic coordinates for all atoms, thermal parameters, and a complete listing of bond distances and angles. Copies of this information may be obtained free of charge on application to The Director, 12 Union Road, Cambridge CB2 2EZ, UK (fax: +44-1223-336033; email: deposit@ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk).     

X-ray analysis of sideroxol from <Emphasis Type="Italic">Sideritis leptoclada</Emphasis>

Sideroxol (1), a kaurane diterpene which has the ent-7α,18-dihydroxy-15β,16β-epoxykaurane structure (MW = 320.47, C₂₀H₃₂O₃) was obtained from the acetone extract of Sideritis leptoclada plant as well as from some other Sideritis species. It crystallizes in the orthorhombic space group P2₁, 2₁, 2₁ with a = 10.967(3), b = 24.555(5), c = 6.372(4) Å, Dc = 1.240 g cm⁻³, Z = 4, and refines to R = 0.065 for 721 independent reflections. The skeleton consists of three fused six-membered rings and a five-membered ring with fused epoxide. The six membered rings exhibited slightly distorted chair conformation. In addition to sideroxol, two kaurane and five kaurene diterpenes were isolated from the hexane and acetone extracts of the studied plant.     

New zeotype borophosphates with chiral tetrahedral topology: (H)0.5M1.25(H2O)1.5[BP2O8]·H2O (M = Co(II) and Mn(II))

Two new isostructural open‐framework zeotype transition metal borophosphate compounds, (H)_0.5M_1.25(H₂O)_1.5[BP₂O₈]·H₂O (M = Co(II) and Mn(II)) were synthesized by mild hydrothermal method. The structure of compounds were characterized by single‐crystal X‐ray diffraction which have ordered, alternating, vertex‐sharing BO₄, PO₄, and (MO₄)OM(H₂O)₂ groups with hexagonal, P 6₁ 2 2 (No 178) space group and unit cell parameters for Co a = 9.4960(6) Å, c = 15.6230(13) Å, for Mn a = 9.6547(12) Å, c = 15.791(3) Å, Z = 1 for both of them. TGA/DTA analysis, IR spectroscopy were used for characterization. Magnetic susceptibility measurements for both of the compound indicate strong antiferromagnetic interaction between metal centers. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoluminescence characteristics of Mg- and Si-doped GaN thin films grown by MOCVD technique

We have studied the optical, structural and surface morphology of doped and undoped GaN thin films. The p- and n-type thin films have been successfully prepared by low-pressure MOCVD technique by doping with Mg and Si, respectively. The different carrier concentrations were obtained in the GaN thin films by varying dopant concentrations. Photoluminescence (PL) studies were carried to find the defect levels in the doped and undoped GaN thin films at low temperature. In the undoped GaN thin films, a low intensity and broad yellow band peak was observed. The donor–acceptor pair (DAP) emission and its phonon replicas were observed in both the Si or Mg lightly doped GaN thin films. The dominance of the blue and the yellow emissions increased in the PL spectra, as the carrier concentration was increased. The XRD and SEM analyses were employed to study the structural and surface morphology of the films, respectively. Both the doped and the undoped films exhibited hexagonal structure and polycrystalline nature. Mg-doped GaN thin films showed columnar structure whereas Si-doped films exhibited spherical shape grains.