无压烧结制备透辉石/AlTiB增韧补强氧化铝基结构陶瓷材料

采用温度梯度无压烧结工艺制备了透辉石/AlTiB增韧补强Al2O3基结构陶瓷材料,探讨了其致密化烧结特性,并对其力学性能进行了测试和分析.研究了透辉石/AlTiB增韧补强Al2O3基结构陶瓷材料的微观结构,并分析了其力学性能和微观结构与透辉石含量的关系.结果表明:与纯Al2O3相比,透辉石/AlTiB增韧补强Al2O3基结构陶瓷材料的力学性能得到明显提高,其中添加6;(体积百分含量,下同)透辉石和4;AlTiB的Al2O3基结构陶瓷材料获得较好的综合力学性能,其硬度、抗弯强度和断裂韧性分别达到16.02 GPa、370 MPa和5.11 MPa·m1/2.力学性能提高的主要原因为:添加相与Al2O3基体之间界面反应的发生以及透辉石和AlTiB对复合材料的协同晶粒细化效应.     

烧结工艺对原位合成ZrO2/TiB2复合陶瓷材料的力学性能影响

以TiC和B4C为原料反应生成TiB2,原位合成了TiB2含量为20％的ZrO2/TiB2复合陶瓷材料.分析了烧结工艺中烧结温度、保温时间和烧结压力对力学性能的影响.结果表明:当烧结温度由1650℃提高到1750℃时,复合陶瓷材料的抗弯强度由820 MPa增加到980 MPa,断裂韧性从7.2 MPa·m1/2提高到9.4 MPa·m12;当烧结温度升至1850℃时,抗弯强度和断裂韧性下降;显微硬度随烧结温度的升高而提高.在烧结温度1750℃压力为30MPa保温时间由30 min提高到45 min时,断裂韧性从8.6 MPa·m1/2提高到9.4 MPa·m1/2;保温时间增加至60 min时,断裂韧性下降;保温时间的变化对材料的抗弯强度、硬度影响不大.烧结压力对复合陶瓷材料的力学性能的影响较小.当烧结参数为1750℃、45 min、30MPa,ZrO2/TiB2复合陶瓷材料的抗弯强度、显微硬度、断裂韧性分别达到980 MPa、13.6 GPa、9.4 MPa·m1/2.     

水基流延成型和热压烧结制备碳化硼陶瓷及性能研究

以工业碳化硼粉末为原料、采用Si3N4磨球磨损法引入Si3N4烧结助剂,采用水基流延成型和热压烧结方法制备了碳化硼陶瓷.研究了氧含量、分散剂、pH值等因素对B4C陶瓷浆料分散性能的影响,采用XRD、SEM等对碳化硼陶瓷的物相、显微结构和第二相分布进行了表征,并测试了样品的维氏硬度、断裂韧性、抗弯强度和弹性模量.结果表明:经醇洗后的碳化硼粉末中氧化硼含量降低,有利于B4C陶瓷浆料的分散稳定.采用球磨磨损引入了Si3N4粉,在B4C基体中通过原位反应形成第二相SiC和BN,SiC和BN第二相颗粒在B4C基体中弥散分布均匀.在2100 ℃热压烧结样品的维氏硬度、抗弯强度、断裂韧性和弹性模量分别达到30.2 GPa、596.5 MPa、3.36 MPa·m1/2和362.3 GPa.     

工业级氢氧化铝制备高韧性氧化铝陶瓷及机理分析

采用价格低廉的工业氢氧化铝粉为初始原料,通过球磨介质磨耗向氢氧化铝中引入高纯α-Al2O3作为晶种,通过热压烧结,氧化铝晶粒原位异向生长成长柱状和板状的晶粒,从而在瓷体的断裂过程中产生裂纹桥接、偏转和晶粒拔出的增韧机制,使制备出的氧化铝陶瓷断裂韧性得到了显著的提高.在热压烧结压力为30 MPa、1600 ℃烧结2 h制备的氧化铝烧结体,其抗弯强度和断裂韧性分别为550 MPa、6.08 MPa·m1/2.     

LaMgAl11O19-Al2O3复相陶瓷的制备及其力学性能的研究

以板片状结构的LaMgAl11O19作为第二相来对Al2O3陶瓷进行增韧补强,采用无压烧结工艺在1650℃下保温4 h制备了LaMgAl11O19-Al2O3复相陶瓷,研究了LaMgAl11O19的添加量对LaMgAl11O19-Al2O3复相陶瓷的物相组成、体积密度和力学性能的影响,并结合复相陶瓷试样断面的SEM照片分析了其强韧化机理。研究表明,添加一定量的LaMgAl11O19后,LaMgAl11O19-Al2O3复相陶瓷材料的抗弯强度和断裂韧性均有明显提高,当添加LaMgAl11O19的质量分数为10%时,LaMgAl11O19-Al2O3复相陶瓷的抗弯强度和断裂韧性分别为321 MPa和5.03 MPa.m1/2,其中片状晶的拔出效应、裂纹偏转作用以及裂纹分支等增韧机制发挥了主导作用。     

热压烧结制备AlN/BN复相陶瓷及其性能研究

以氮化铝(AlN)粉和高活性六方氮化硼(h-BN)粉为原料,不添加烧结助剂,采用热压烧结法制备了AlN/BN(20vol;)复相陶瓷.研究了烧结温度(1750～1900℃)对复相陶瓷相对密度、物相组成、显微结构、力学性能、热导率及介电性能的影响.结果表明,在1850℃以上可以制备出相对密度大于98.6;的致密AlN/BN复相陶瓷.试样显微结构均匀,晶粒细小,晶界干净,无明显杂质相,h-BN未形成明显的卡片房式结构.随着烧结温度的提高,试样的相对密度、力学性能、热导率及介电性能(1 MHz)均显著提高.1900℃烧结的试样性能最优,相对密度99.3;,抗弯强度482±42 MPa、断裂韧性4.4±0.4 MPa·m1/2、维氏硬度8.56±0.33GPa、热导率47.2 W·m-1·K-1、介电常数7.64,介电损耗4.62×10-4.     

烧结制度对AlON-AlN复相陶瓷的结构及性能影响

分别采用无压及热压反应烧结方式,在氮气条件下制备了AlON-AlN复相陶瓷,研究了烧结温度和保温时间对AlON-AlN复相陶瓷的显微结构、气孔率、抗弯强度及热导率的影响规律.结果表明:相同烧结条件下,热压烧结比无压烧结更易获得气孔率低、抗弯强度高、热导率大的AlON-AlN复相陶瓷.无压烧结复合陶瓷的断裂为沿晶断裂和穿晶断裂的混合模式,而热压烧结复合陶瓷的断裂方式主要为穿晶断裂.     

原位热压烧结制备NbC增强Nb4AlC3复合材料及其力学性能研究

以Nb、Al、石墨粉为原料,采用原位反应热压烧结在1700℃下制备出了致密的NbC增强Nb4AlC3复合材料,采用X射线衍射和扫描电镜对材料的物相组成和显微结构进行了表征,研究了NbC含量对材料的物相组成、烧结性能、显微结构与力学性能的影响.结果表明:NbC的原位引入促进了材料的烧结,并对Nb4AlC3基体起到了显著的强韧化效果.随着NbC含量从0增加至15vol;,材料的抗弯强度和断裂韧性先增大后减小.当NbC含量为8vol;时,强度和断裂韧性达到最大值494 MPa和8.4 MPa·m1/2.材料的显微硬度则由2.6 GPa提高至4.4 GPa.     

Al2O3/TiB2/AlN/TiN复合陶瓷材料的力学性能及显微结构

将金属Al、Al3Ti和TiB2以AlTiB中间合金的形式引入Al2O3基体材料中,采用热压原位反应生成法制备了Al2O3/TiB2/AlN/TiN复合陶瓷材料.复合材料在烧结过程处于过渡液相烧结,并有新相AlN和TiN生成;对热压烧结后材料的硬度、断裂韧性和抗弯强度进行了测试和分析;分析了复合材料力学性能随AlTiB体积百分含量的变化规律;探讨了复合材料断面断裂方式的变化对其力学性能的影响;并对AlTiB中间合金的细化特性进行了分析.     

原位合成ZrO2/TiB2复相陶瓷材料的制备及性能

以3Y-ZrO2为基体,用TiC和B4C为原料反应生成TiB2,原位合成了ZrO2/TiB2复相陶瓷材料,测试和分析了复合材料的抗弯强度、维氏显微硬度和断裂韧性。结果表明:原位生成的TiB2对基体起到较好的增韧补强作用。当TiB2的质量分数为30%时,复合陶瓷的综合力学性能最好,其抗弯强度、维氏显微硬度及断裂韧性分别达到1060 MPa、14.5 GPa和11.2 MPa.m1/2。     

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).     

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.     

Crystal structures of the cis and trans isomers of a tetrathia[3.3.3.3]cyclophane

Both the cis and trans isomers of 3,11,18,26-tetrathiatricyclo[26.2.2.1^5,9.2^13,16.1^20,24] hexatriaconta-5,7,9,20,22,24-hexene have been prepared and structurally characterized. Each of these centrosymmetric tetrathia dimers includes two cyclohexane rings in chair conformations with either 1,4-cis or 1,4-trans bonding and two meta-substituted benzene rings. The cis isomer packs into the monoclinic space group P2₁/a with a = 10.485(3)Å, b = 10.3956(18)Å, c = 14.1343(10)Å, = 105.200(13)°, Z = 2 and refined to an R factor of 0.046. The trans isomer crystallizes in the monoclinic space group P2₁/c with a = 10.7217(12)Å, b = 5.6797(7)Å, c = 25.415(5)Å, = 96.001(12)°, Z = 2 and refined to an R factor of 0.043. In the cis structure each benzene ring faces a cyclohexane ring while in the trans structure the cyclohexane rings face one another.     

Crystal structure of Zn4Na(OH)6SO4Cl·6H2O

The structure of Zn₄Na(OH)₆SO₄Cl·6H₂O, a secondary mineral from Hettstedt, Germany, was determined by single-crystal X-ray diffraction. The crystals are hexagonal,a=8.413(8),c=13.095(24) Å, space group $P\bar 3$ , Z=2. The structure was refined to R=0.0554 and R_w=0.0903 for 970 reflections with I≥3σ(I). The structure can be described as zinc hydroxide layers perpendicular toc, from which sulfates and chlorides extend. The layers are held together by a system of hydrogen bonds involving hexaaquo Na⁺ ions which occupy the interlayer space.     

Synthesis and Crystal Structure of 5-[2-(6-bromonaphthalenyloxymethyl)]-3-(4-morpholinomethyl)-1,3,4-oxadiazole-2(3<Emphasis Type="Italic">H</Emphasis>)-thione

Abstract  The title compound, C₁₈H₁₈BrN₃O₃S, a derivative of 1,3,4-oxadiazole, crystallizes in the triclinic space group P-1 with unit cell parameters a = 6.8731(3), b = 8.9994(4), c = 15.7099(6) ?, α = 92.779(3)°, β = 130.575(3)°, γ = 107.868(4)°, Z = 2. The dihedral angle between the mean planes of the planar naphthyl and morpholine (chair) rings with the planar oxadiazol ring is 50.1(8) and 76.8(6)°, respectively. The planar naphthyl ring is twisted 52.2(5)° with the mean plane of the morpholine ring. A group of four intermolecular close contacts are observed between a bromine atom and hydrogen atoms from the closely packed naphthyl, morpholine and oxy–methyl groups in the unit cell. These molecular interactions in concert with an additional series of π–π stacking interactions that occur between the center of gravity of the two 6-membered rings of the naphthalene group influence the twist angles of each of these three groups. A MOPAC AM1 calculation of the conformation energy of the crystal structure [226.0128(9) kcal] compared to that of the minimum energy structure after geometry optimization [29.9744(1) kcal] reveals a significantly reduced value. The twist angles of the three groups above also change after the AM1 calculation giving support to the influence of both intermolecular C–H···Br short-range interactions and Cg π–π stacking interactions on these angles which therefore play a role in stabilizing crystal packing. Graphical Abstract  Crystal structure of 5-{[(6-bromonaphthalen-2-yl)oxy]methyl}-3-(morpholin-4-ylmethyl)-1,3,4-oxadiazole-2(3H)-thione, C₁₈H₁₈BrN₃O₃S, is reported and its geometric and packing parameters described and compared to a MOPAC computational calculation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

电沉积法制备ZnO纳米棒阵列及其发光特性

本文以掺F的SnO2导电玻璃为基板,以硝酸锌水溶液为电解液,采用三电极恒电位体系电沉积制备ZnO纳米棒阵列,系统考察了硝酸锌浓度和沉积电位等工艺参数对ZnO纳米棒阵列的微观形貌及其发光性能的影响规律.结果表明,硝酸锌浓度和沉积电位对纳米棒阵列的形貌有显著影响,控制适宜的工艺条件可以制备出直径分布均匀、结晶性好且纯度高的六方纤锌矿ZnO纳米棒阵列.荧光光谱分析表明,电沉积制备出的ZnO纳米棒阵列在385 nm附近有一个强荧光发射峰,且发光性能稳定、对纳米棒阵列微观形貌的细微变化不敏感,使其在发光二极管和激光器等领域具有广阔的应用前景.     

Crystal structure of irisolidone from the flowers of Pueraia lobata

Irisolidone (5,7-dihydroxy-6,4′-dimethoxyisoflavone) was isolated from the flowers of Pueraia lobata and its crystal structure was examined by X-ray single crystal diffraction. The crystal structure of irisolidone is monoclinic, space group P2₁/c with a = 15.491(9) ?, b = 7.895(4) ?, c = 13.321(7) ?, β = 110.546(9)° and Z = 4. Hydrogen bonding and aromatic π–π stacking assemble the title compound into a three-dimensional networking structure.