LaB3O6-CaB4O7赝二元体系相图的初步研究

本文通过X射线粉末衍射和差热分析等方法研究了LaB3O6-CaB4O7赝二元体系相图.LaB3O6-CaB4O7赝二元体系中除了LaB3O6和CaB4O7外只存在化合物CaLa2B10O19,它是一种非同成分熔融的化合物,转熔温度约1047℃,在此温度下液相、LaB3O6和CaLa2B10O19之间发生包晶反应.在温度967℃左右,存在CaB4O7、CaLa2B10O19和液相之间的共晶反应,共晶点的成分约87mol; CaB4O7.根据所得到的结果,采用高温溶液生长法,选择摩尔比CaB4O7∶CaLa2B10O19分别为1∶1、1.5∶1和2∶1三种不同浓度的熔盐体系来生长CaLa2B10O19,结果都可以长出CaLa2B10O19晶体.     

添加MWCNTs陶瓷拉拔模具材料的摩擦特性研究

通过真空热压烧结方法制备了添加多壁碳纳米管(MWCNTs)的Al2 O3/TiC/MWCNTs陶瓷拉拔模具材料,研究了其摩擦磨损性能、机械性能,并对其磨损机理进行了分析.研究表明:MWCNTs能够减小Al2O3/TiC陶瓷拉拔模具材料的摩擦系数,当MWCNTs含量为5;时,Al2O3/TiC/MWCNTs陶瓷的摩擦系数最小;随着MWCNTs含量的增加,磨损量呈现先下降后上升趋势,当MWCNTs含量为4;时,Al2O3/TiC/MWCNTs陶瓷的磨损量最小.摩擦过程中,MWCNTs被拖覆到摩擦表面,具有自润滑效果,起到减摩抗磨作用.     

Y2O3-SiO2助剂对常压烧结SiC-AlN复相材料烧结性能的影响

SiC∶AlN以质量比1∶1,添加不同质量分数Y2O3-SiO2(摩尔比为2.9∶7.1)复合烧结助剂,分别在氢气和氩气气氛下常压烧结制备SiC-A1N复相材料.研究烧结气氛、烧成温度和Y2O3-SiO2含量对该复相材料烧结性能的影响.结果表明,与氢气气氛相比,氩气气氛下烧结体更易致密;1650 ～1850℃,随着烧结温度升高,烧结致密性明显提高.氩气气氛1850C下保温1h,Y2O3-SiO2复合助剂含量为9.09wt;,烧结体的显气孔率可低于0.15;,晶粒尺寸均匀且连接紧密.烧结过程中,Y2O3、SiO2烧结助剂与AlN表面的Al2O3在一定温度下形成液相有助于样品致密化.Y2O3与AlN表面的Al2O3反应生成钇铝石榴石(Y3Al5O12),SiO2高温下主要形成玻璃相.SiC-AlN复相材料是由主晶相6H-SiC和AlN,次晶相Y3Al5O12组成.     

La-Mn共掺杂的钛酸钡陶瓷还原再氧化研究

以MnO2为受主,La2O3为施主,采用传统高温固相法对钛酸钡陶瓷进行掺杂,并对还原气氛下烧结的样品分别在900 ℃和1000 ℃的温度下进行再氧化处理.采用XRD和电性能测试研究了镧锰共掺杂和再氧化工艺对于钛酸钡陶瓷阻温特性及微观结构的影响.结果表明:钛酸钡陶瓷的阻温特性与施主、受主的掺杂比例和烧结气氛有关;与在空气下烧结相比,在还原气氛下烧结能明显的提高施主掺杂的临界浓度,同时随着再氧化温度从900 ℃提高到1000 ℃,PTC效应明显增强.BaTiO3晶粒尺寸随着施主掺杂浓度的提高而变小.Mn离子的掺入使钛酸钡晶格结构更为紧密,阻碍了晶格内部氧离子向外部的扩散,导致了明显的PTC效应.     

Al2O3陶瓷非等温烧结研究

以高纯α-Al2O3粉体为原料,采用非等温烧结法制备了纯Al2O3陶瓷(AL)及掺杂MgO-Y2O3复合助剂的AJ2O3陶瓷(ALMY).研究了AL和ALMY在不同烧结温度下的相对密度、显微结构及硬度.结果表明,在非等温烧结中,纯Al2O3致密化的烧结温度范围较窄,烧结温度为1500℃时,其相对密度及硬度分别为98.1;和18.1GPa,当烧结温度为1600℃时,AL由于晶粒显著粗化,且产生了晶内气孔,相对密度及硬度分别显著下降到94.6;和12.5 GPa.MgO-Y2O3复合助剂的引入拓宽了Al2O3致密化的烧结温度范围,细化了显微结构,烧结温度在1500℃和1600℃时,ALMY的相对密度均在98;以上,硬度分别为19.2 GPa和17.6 GPa.     

AlN-Y2O3配比对SiC耐磨材料结构和性能的影响

在AlN-Y2O3添加量为6wt;的前提下,将摩尔比分别为10∶90、20∶80、30∶70和40∶60的AlN、Y2O3引入SiC耐磨材料中,于氧化气氛下经1600℃保温3h烧成,研究了AlN、Y2O3配比对SiC耐磨材料结构和性能的影响.结果表明:AlN、Y2O3配比对SiC耐磨材料的性能影响较大,当其为30∶70时,SiC耐磨材料的性能较优,其体积密度和显气孔率分别为2.66 g/cm3和3.95;,磨损量为0.11 g/min,硬度和抗折强度分别为2774 HV和185 MPa.SiC耐磨材料较优异的烧结性能和力学性能可归因于新生成的Y2Si2O7和3Al2O3·2SiO2充填于SiC颗粒间所起的强化作用.     

热压烧结制备BN-MgAlON复合材料及其力学性能研究

以BN-MgAlON复合粉体为原料,Y2O3为烧结助剂,在N2气氛下热压烧结制备了BN-MgAlON复合材料,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,研究了烧结温度对材料的物相组成、烧结性能和力学性能的影响.结果表明,在1650～1750℃可制备出致密的BN-MgAlON复合材料.材料主要成分为MgAlON、Sialon、BN和CaYAl3O7,随烧结温度的提高,MgAlON的衍射峰逐渐增强.1750℃下所得材料结构均匀致密,材料中Al、Mg、O、N分布比较均匀.材料的抗弯强度、断裂韧性和显微硬度均随着烧结温度的升高而提高.1750℃下的材料性能最好,其体积密度为2.79 g·cm-3,显气孔率为0.3;,抗弯强度为283 MPa,断裂韧性为3.85 MPa·m1/2,硬度为15.33 GPa.并且1750cc,恒温1h条件下烧结的得到的BN-MgAlON复合材料的抗冲刷性和耐磨性均远远优于耐磨钢B-hard-450.     

退火工艺对0.9Al2O3-0.1TiO2微波介质陶瓷性能与结构的影响

采用反应烧结法制备0.9Al2O3-0.1Ti O2微波介质陶瓷,研究了退火时间,退火气氛对其物相组成、显微结构、微波介电性能的影响。结果表明:经过退火后,第二相Al2Ti O5分解,陶瓷的表面规整,致密度高;延长退火时间以及合适的退火气氛可以有效地提高0.9Al2O3-0.1Ti O2陶瓷的Q×f值。在空气气氛下,1350℃烧结4 h,氧气气氛下1100℃退火20 h的0.9Al2O3-0.1Ti O2微波介质陶瓷具备优异的介电性能:εr=12.50,Q×f=79812 GHz,τf=0.13 ppm/℃。     

Al2TiO5/Al2O3陶瓷复合材料的晶粒异向生长

通过机械激活法制备了Al2TiO5/Al2O3(nAl2TiO5: nAl2O3=1: 4)的陶瓷复合材料.利用X射线衍射(XRD)、扫描电镜(SEM)以及能谱(EDS)分析了不同的温度制度下Al2TiO5/Al2O3陶瓷复合材料的晶粒生长特性.X射线衍射谱图(XRD)显示烧结样品的主晶相为α-Al2O3和Al2TiO5.SEM和EDS分析显示,较低温度下烧结(1350 ℃)时Al2TiO5晶粒为等轴状.当温度升高到1450 ℃时,Al2TiO5开始异向长大,形成棒状晶粒.随着温度的升高(1500 ℃),棒状Al2TiO5的长径比继续增加.而Al2O3则始终为片状和等轴晶粒,且异向生长的Al2TiO5晶粒填充于Al2O3三角晶界处.研究表明,烧结温度的升高会促进晶体异向生长并增加其体积分数.Al2TiO5会阻碍Al2O3基体颗粒进一步生长,所以当Al2TiO5颗粒平均尺寸随着烧结温度增加而增大,Al2O3基体晶粒生长几乎停滞.     

机械合金化-放电等离子烧结制备Ti_2SnC导电陶瓷

采用放电等离子烧结(SPS)技术对机械合金化合成的Ti2SnC粉体进行烧结,研究了烧结温度对机械合金化和SPS烧结Ti2SnC导电陶瓷块体相组成、显微组织及微结构的影响。结果表明:机械合金化合成Ti2SnC粉体在800~1000℃之间进行SPS烧结可以获得纯度较高的致密块体,在1000℃进行烧结时,孔隙率低于2%。在600~1000℃范围内,烧结块体中Ti2SnC的含量随烧结温度的提高逐渐增加;Ti2SnC的晶粒大小随温度升高逐渐长大。     

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。     

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.     

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.     

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)     

Solubility of Ag2O into the Na2O–B2O3–Al2O3 system

The solubility of Ag₂O was measured for the Na₂O–B₂O₃ and Na₂O–B₂O₃–Al₂O₃ system with the rotating crucible method and static method, respectively, under air atmosphere at temperatures ranging from 1273 to 1423 K. The contamination of melts from crucibles could be avoided by the rotating crucible method, with which it became possible to measure the solubility of Ag₂O for the Na₂O–B₂O₃ system above the melting point of Ag for the first time. It was found that the addition of Na₂O decreases the solubility of Ag₂O while the addition of Al₂O₃ had little effect on the solubility. The effect of Na₂O and Al₂O₃ on the solubility of Ag₂O is expressed by interaction coefficients and is analyzed in terms of the basicity of melts. The solubility of Ag₂O in Na₂O–B₂O₃–Al₂O₃ melts increased with increased temperature. This phenomena was explained by a small enthalpy change in oxidation of silver.     

Selinidin: Crystal structure generated by C–H···O, C–H···π and π-π interactions

The title compound, 9,10-dihydro-8,8-dimethyl-2-oxo-2H,8H-benzo[1,2-b:3,4-b']dipyran-9-yl-2-methyl-2-butenoate, C₁₉H₂₀O₅, was isolated from the roots of Selinum vaginatum. The compound crystallizes into monoclinic space group P2 ₁ with unit cell parameters: a = 12.830(2) Å, b = 9.041(1) Å, c = 14.983(1) Å, β = 95.09(1)°, Z = 4. The crystal structure has been determined using direct methods and refined by full-matrix least-squares to a final R value of 0.0529 for 3142 observed reflections. There are two independent molecules, A and B, per asymmetric unit. In both the molecules, the coumarin nucleus is planar. However pronounced differences are observed in the conformation of dihydropyran ring which has a half-chair conformation with an 8β-9α orientation in molecule A and is intermediate between half-chair and sofa in molecule B. Differences also occur in the conformation of the 2-methylbutenoyloxy side chain at C9 due to the different geometry of C–H···π interactions in molecules A and B. Molecules A and B are connected by π–π interactions between their coumarin fragments forming dimers. The dimers interact through C–H···O and C–H···πhydrogen bonds.     

Chromene and Imidazole Based D-π-A Chemosensor Preparation and Its Anion Responsive Effects

We have designed and synthesized the colorimetric chemosensor through the reactions of 2-(4H-chromen-4-yildene)malonitrile and 4-imidazolecarboxaldehyde. Due to its well conjugated D-π-A system and the existence of NH- fragment in structure, we expected that the chemosensor can detect anion using NH- fragment in the imidazole moiety of the structure. In this regard, UV-Vis absorption spectra were measured to investigate sensing properties of the probe toward different anions in DMSO. This chemosensor can detect both fluoride and cyanide ion with absorption change in intensity. In addition, pH sensing property was also investigated upon the addition of hydroxide ion. These properties are related to the deprotonation effect. The ICT system in this molecule was also observed by the computational approach using Material Studio 4.3 package.     

电子显微分析在表征纳米晶体化学组分中的应用

纳米材料的化学组分及含量影响其光、电、声、热、磁等物理性能,电子显微分析是表征纳米晶体化学组分的重要方法之一.本文综述了X-射线能谱(EDS)、X-射线波谱(WDS)、电子能量损失谱(EELS)和选区电子衍射(SAED)等现代电子显微分析技术在表征纳米晶体化学组分、形貌、尺寸和结构等方面的应用及其研究进展,并比较了这些分析方法存在的差异,提出了其应用中存在的不足及今后的研发方向.     

Considerations on the structure and physical properties of B2O3-SiO2 and GeO2-SiO2 glasses

Data of density, refractive index and thermal expansion coefficient for B₂O₃-SiO₂ and GeO_2-SiO₂ glasses have been analyzed. The volumes of the structural units are the same found for the vitreous B₂O₃, GeO₂ and SiO₂. The volume of any structural unit is constant over the entire composition region of the glass system. The same has been found for the differential refraction and unit refraction of the structural units in these glasses. Different features are observed for the differential expansion of the structural units. There is a considerable change with composition in the differential expansion of BO₃, GeO₄ and SiO₄ units. The effect is attributed to a change in the asymmetry of vibrations with the number of Si-O-B or Si-O-Ge linkages in the matrix. The thermal expansion coefficient is mainly determined by the contribution of B₂O₃ or GeO₂ in the concerned glasses.