Y2O3添加对Nb2O5低膨胀陶瓷结构与性能的影响

采用高温固相烧结法制备了Y2O3改性Nb2O5低膨胀陶瓷材料.研究了Y2O3添加量对Nb2O5陶瓷的物相组成、微观结构、气孔率、热膨胀性能、抗弯强度和抗热震性能等的影响.结果表明,经1390℃保温2h烧成,纯Nb2O5陶瓷样品存在开裂现象,表现出低的抗弯强度和差的抗热震性能.添加2～ 10;Y2O3后,样品主晶相为单斜相Nb2O5,还生成了YNbO4晶相.通过添加适量Y2O3改性,可抑制Nb2O5陶瓷烧成过程中的晶粒增长和避免开裂现象,形成致密的微观结构,样品的抗弯强度和抗热震性能显著提高.Nb2O5陶瓷的热膨胀系数随Y2O3添加量的增加而逐渐增大.Y2O3添加量为6;时,样品的热膨胀系数和抗弯强度分别为1.9×10-6/℃和103.4 MPa,表现出良好的抗热震性能.     

TiO2对Nb2O5低膨胀陶瓷的烧结性、力学强度和抗热震性能的影响

以TiO2和Nb2O5微粉为主要原料,通过高温固相反应烧结制备了TiO2掺杂改性的Nb2O5陶瓷,研究了TiO2含量对Nb2O5陶瓷的晶相组成、烧结性能、热膨胀性能、抗弯强度和抗热震性能的影响.研究表明,2; ～ 8; TiO2掺杂未改变Nb2O5陶瓷的单斜晶系结构,而TiO2含量为12;时,除Nb2O5主晶相外,还生成了少量Ti2Nb10O29晶相.通过加入适量TiO2改性,可明显抑制Nb2O5陶瓷烧成过程晶粒异常生长,改善烧结性能,避免开裂现象,获得较为均匀致密的显微结构,有效提高样品的抗弯强度.Nb2O5陶瓷的热膨胀系数和抗弯强度都随着TiO2含量增加而表现出先增大后减小的变化趋势,其中TiO2含量为4;时,样品具有最高的抗弯强度(75.6 MPa)和低的热膨胀系数(1.42×10-6/℃).添加4; ～12;的TiO2都可明显改善Nb2O5陶瓷的抗热震性能.     

耐高温氧化锆-刚玉-莫来石复相陶瓷的制备及其抗热震性

以煤系高岭土、α-Al2O3和部分稳定氧化锆(PSZ, 3;molY2O3)为原料,制备了耐高温氧化锆-刚玉-莫来石复相陶瓷.采用XRD、SEM等测试技术对样品的物相组成及显微结构进行了表征,研究了PSZ添加量(分别为5wt;、10wt;、15wt;、20wt;、25wt;、30wt;)对样品物理性能、高温塑性变形及抗热震性的影响.结果表明:由于采用含3;molY2O3的PSZ,Y2O3在高温下起到了烧结助剂的作用,致使样品的烧成温度显著降低;同时随着PSZ添加量的增加,样品的抗折强度增加.经最佳烧成温度烧成的各样品的抗折强度分别达到147.4 MPa、161.3 MPa、205.9 MPa、234.4 MPa、294.0 MPa、385.0 MPa.当PSZ的最佳添加量为10wt;时,样品具有较低的高温塑性变形及良好的抗热震性;当PSZ添加量继续增加,样品在高温易产生液相,抗蠕变及抗热震性降低.SEM显微结构研究表明,随着氧化锆添加量增加,样品结构越致密,增强效果越显著.XRD分析结果表明,复相陶瓷具有良好的耐高温性能,热震前后样品的物相组成不变,均为莫来石、刚玉、m-ZrO2和t-ZrO2.     

铝纤维对Al2O3-Al-C材料高温机械性能和显微结构的影响

分别以板状刚玉、α-Al2O3微粉、金属铝(铝纤维和铝粉)、石墨为原料,以酚醛树脂为结合剂,制得Al2 O3-Al-C材料.借助XRD和SEM分析了试样的物相组成和显微结构,研究了铝纤维加入量对材料抗热震性、高温抗折强度的影响,结果表明:用铝纤维代替铝粉可提高材料的高温抗折强度和抗热震稳定性.保持金属铝的总加入量为6;,当铝纤维加量由0;增加到1;时,1400℃的高温抗折强度由26.5 MPa提高到34.7 MPa,热震后的残余强度保持率由62;增加到69;.高温时铝纤维转变为非氧化物晶须编织体或纤维束,与基质紧密结合,起桥接和强化作用,可改善材料的抗热震性并显著提高其高温抗折强度.     

La2O3对氧化镁陶瓷烧结性能与抗热震性能的影响

本文以纳米氧化镁为主要原料,La2O3为添加剂,聚乙烯醇为结合剂,制备烧结性能良好和抗热震性能优异的氧化镁陶瓷.通过常温力学性能、抗热震性能、XRD和SEM等手段对试样进行分析和表征,重点研究La2O3对氧化镁陶瓷烧结性能及抗热震性能的影响.结果表明:La2O3的加入能够促进氧化镁陶瓷的烧结.从微观结构看出La2 O3加入后可与氧化镁形成固溶体及一些不定形态物质,均匀分布在晶界处,减缓试样在热震时裂纹的尖端应力,阻碍裂纹延伸,有效提高氧化镁陶瓷的抗热震稳定性.经1640℃烧结La2O3的加入量为1;的试样相对密度最高,为99.72;;热震后经1560℃烧结La2O3的加入量为2;的试样常温耐压强度达到最大值,58 MPa.     

退火对TiO2-Ta2 O5-CaCO3陶瓷结构及压敏性能的影响

本文研究了退火对TiO2-Ta2 O5-CaCO3压敏陶瓷的压敏性能的影响,采用球磨-成型-烧结的传统方法制备TiO2-Ta2 O5-CaCO3压敏陶瓷,并将TiO2-Ta2 O5-CaCO3压敏陶瓷在不同温度下退火,用压敏直流参数仪测试样品的非线性系数α、压敏电压EB,采用XRD、SEM和STEM分析微观结构.结果表明,适宜温度下退火适当时间,可使晶粒适当长大,并使晶粒粒度分布均匀,减少气孔和提高致密度.退火过程中,半径较大的受主离子获得动能进一步向晶界偏析,增大晶界受主态密度,从而提高非线性系数α.晶粒适当长大,晶界数量和晶界总面积减小,有助于减小压敏电压;提高致密度可减小电阻率,从而进一步减小压敏电压.当掺杂浓度为0.20mol;,烧结温度为1350℃,700℃退火3 h的TiO2-Ta2O5-CaCO3压敏陶瓷获得最高的非线性系数和较低的压敏电压(α=8.6,EB=22.5 V·mm-1),优于没有退火样品.     

Co包覆Al2O3/TiC复相陶瓷的力学性能与抗热震性能

不同Co含量Al2O3/TiC复相陶瓷的力学性能测试结果表明,综合力学性能最佳的复合材料含Co量为8;质量分数.采用急冷-强度法表征了单相Al2O3、Al2O3/TiC及Co包覆Al2O3/TiC三种材料的抗热震性能.单次热震结果表明,Co包覆Al2O3/TiC的抗热震性能是最佳的.SEM观察发现,随着热震温度的升高,材料的致密度越来越低,力学性能大幅下降,从而导致了抗热震性能的降低.循环热震结果表明,随循环次数的增加,ATC复合材料的抗热震性越来越差.Co的少量添加,虽然对复合材料的热物理性能改变较小,但却较大幅度地提高了ATC复合材料的力学性能,有效缓解了热应力,从而提高了ATC复合材料的抗热震能力.     

ZrN-Sialon复相粉体对Al2O3-C耐火材料性能的影响

采用酚醛树脂为结合剂,板状刚玉、石墨为主要原料,ZrN-Sialon复相粉体为添加剂,制备Al2O3-C耐火材料.研究了ZrN-Sialon复相粉体对Al2O3-C耐火材料常温物理性能、抗热震性能以及抗氧化性能的影响.结果表明:ZrN-Sialon复相粉体加入量为9;时,材料的常温耐压强度、常温抗折强度最高,分别为59.93 MPa、18.75 MPa;此时材料的抗热震性能最佳,三次热震试验后强度保持率为79.60;;加入适量的ZrN-Sialon复相粉体可以明显提高材料的抗氧化性能,但加入量过多不利于抗氧化能力提高,ZrN-Sialon的加入量为9;时材料表现出较好的抗氧化能力.     

Ce掺杂对0.9Na0.5Bi2.5Nb2O9-0.1LiNbO3高温无铅压电陶瓷性能的影响

本文采用固相法制备了Ce掺杂的0.9Na0.5Bi2.5Nb2O9-0.1LiNbO3(NBN-LN+ xwt; CeO2)层状高温无铅压电陶瓷;系统地研究了CeO2掺杂对NBN-LN陶瓷的物相、显微结构及电性能的影响;获得的样品均为居里点高于780℃的单一铋层状结构相陶瓷;当CeO2掺杂量x=0.75时,样品具有最佳电性能:d33=28 pC/N,kp=12.11;,tan δ=0.10;,Pr=9.50 μC/cm2;且该组分陶瓷样品在700℃经退极化处理后,其d33仍保持在22 pC/N以上,表明该材料在高温领域下具有良好的应用前景.     

CeO2对β-Sialon-cBN复合材料显微结构和力学性能的影响

以CeO2作为烧结助剂,采用高温(1700℃)、高压(5 GPa)烧结,制备出β-Sialon-cBN陶瓷基复合材料,观察了样品的断面微观形貌,并测试了样品的气孔率、密度,抗弯强度和硬度.研究了不同百分含量的CeO2对β-Sialon-cBN复合材料的显微结构和相关力学性能的影响.结果表明:随着烧结助剂CeO2的加入,促进了β-Sialon与cBN之间的界面结合,β-Sialon长径比提高.结果增强了β-Sialon-cBN复合材料的致密性,使复合材料的抗弯强度和硬度增大.     

Ultraviolet Absorption of Hg2Cl2-and Hg2Br2 Single Crystals

The optical unpolarized absorption spectra of Hg₂Cl₂ and Hg₂Br₂ single crystals were measured in the spectral range 230–400 nm. A sharp exciton peak and other absorption bands of both halides were observed near the fundamental absorption edge. The absorption peaks due to the splitting of the halogen doublet were also observed. Positions of the exciton peaks are characteristic for the Frenkel (localized) type of excitons. Possible interpretations of the other observed bands are discussed.     

Crystal structure of Rb2[GeO2(OH)2]·2H2O

Single crystals of Rb₂[GeO₂(OH)₂] · 2H₂O are studied by X-ray diffraction. The crystals belong to the orthorhombic system, sp. gr. Pna2₁, a = 13.523(6) Å, b = 8.143(4) Å, c = 13.407(6) Å, Z = 8, R ₁ = 0.0506. In [GeO₂(OH)₂]^2? anions, the Ge-O distances (1.71–1.73(1) Å) are shorter than the Ge-OH distances (1.76–1.80(1) Å). Anions are linked to each other by pairs of hydrogen bonds to form infinite chains. The chains are linked by hydrogen bonds involving water molecules to form a 3D structure. The assignment of the bands in the IR spectrum of the compound under study is performed.     

Optical Properties of MnIn2S2Se2 Single Crystals

Optical transmittance and reflectance spectra of MnIn₂S₂Se₂ single crystals are measured in the wavelength range from 0.5 to 30 μm. The interference method is used to determine the refractive index of the compound for wavelengths between 0.8 and 12 μm. From an analysis of the absorption spectrum it follows that the fundamental edge is due to forbidden indirect transitions between parabolic bands for the polarization E ⊥ c with a gap energy of 1.50 eV at room temperature.     

Identification of a new family of diphosphate compounds, AI2BII3(P2O7)2: Structures of Ag2Co3(P2O7)2, Ag2Mn3(P2O7)2, and Na2Cd3(P2O7)2

Syntheses and single-crystal X-ray structural results are reported for three new mixed diphosphates of the family A^I ₂B^II ₃(P₂O₇)₂; Ag₂Co₃(P₂O₇)₂ (I), Ag₂Mn₃(P₂O₇)₂ (II), and Na₂Cd₃(P₂O₇)₂ (III). All crystallize in the triclinic system, space group P1 bar: (I) a = 5.351(4), b = 6.375(4), c = 16.532(4) Å, = 80.83(6) = 81.45(4), = 72.87(5)°, V = 528.9(6) ų, Z = 2, D _calc = 4.649 mg/m³, R/Rw = 0.0428/0.0548 for 3949 obs. reflns; (II) a = 5.432(7), b = 6.619(6), c = 16.51(3) Å, = 80.78(8) = 82.43(9), = 72.82(7)°, V = 557.7(13) ų, Z = 2, D _calc = 4.338 mg/m³, R/Rw = 0.0679/0.1303 for 2100 obs. reflns and (III) a = 5.67(3), b = 7.08(4), c = 7.90(4) Å, = 77.0(2), = 82.5(2), = 67.8(2)°, V = 286(3) ų, Z = 2, D _calc = 4.249 mg/m³, R/Rw = 0.0307/0.0342 for 1945 obs. reflns. (I) and (II) are isostructural but (III) is of a different type. All three structures are characterized by layers of P₂O₇ groups alternating with layers of mixed metal atoms. Differences are seen in the conglomerate bonding patterns of B atoms and in the irregular geometry of Ag in (I) and (II) compared to the octahedral bonding seen for Na in (III). The differences in structure may be understood in terms of the ratios of the ionic radii of A and B atoms.     

Dissociation of LiAlO2 and LiGaO2

The thermodynamic calculations of dissociation of LiAlO₂ and LiGaO₂ as function of temperature and oxygen pressure are presented. It has been found that LiGaO₂ evaporates congruently at the melting point under the oxygen pressure equal to 1 · 10^—5 atm. LiAlO₂ evaporates incongruently, the equilibrium oxygen partial pressure at the melting point is equal to 9.6 · 10^—5 atm and the partial pressure of Li and Al oxides decrease with increasing of oxygen pressure.     

The Improvement of Superconductivity in PbxBi2-xSr2CaCu2Oy

In this paper we present the results of recent studies on the improvement of superconductivity in Pb_xBi_2-xSr₂CaCu₂O_y single crystals by preventing impurities incorporation, employing ZrO₂ crucible for crystal growth and post annealing the as-grown crystals in vacuum or argon. It is realized that the superconductivity of as-grown crystals is improved.     

Synthesis and characterization of (NH4)2CuBr2Cl2·2H2O crystals

Single crystals of a new compound, (NH₄)₂CuBr₂Cl₂.2H₂O, were grown from saturated aqueous solution at room temperature by slow evaporation method. The grown crystals were characterized through elemental, powder XRD, thermal and DSC analyses and FTIR and far IR spectra. The elemental analysis and the decomposition pattern formulated using the TG‐DTG studies confirm the stoichiometry of the compound. The crystallinity of the compound is confirmed from the powder XRD pattern. A preliminary single crystal X‐ray diffraction structural analysis reveals that the title compound belongs to the orthorhombic system with a = 7.7466 Å, b = 7.783 Å and c = 8.1211 Å. The low temperature DSC shows thermal anomalies at –161.1, –156.5, –152.4, –145.2, –134, –18.5, and 1.4°C during the heating run and at –4.3, –54.8, –66.1, –90.6, –109.7 and –147.2 °C during the cooling run. The thermal hysterses indicate first order phase transitions in the title compound at these temperatures. The FTIR spectra were used to assign the characteristic vibrational frequencies due to NH₄⁺, CuX₄^2– ions and other chemical bonds. The effect of substitution of two bromine atoms on the phase transitions of a closely related crystal, diammonium tetrachloro cuprate dihydrate is also discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ru掺杂MoS2对SO2F2和H2S气体吸附的第一性原理研究

本文基于第一性原理探讨了Ru掺杂的单层MoS₂(Ru-MoS₂)的结构及其对SF₆绝缘设备中的两种主要分解气体SO₂F₂和H₂S的传感和吸附行为。Ru原子进入硫空位从而产生Ru-MoS₂,结果表明,Ru-MoS₂对SO₂F₂和H₂S气体的吸附能(E_ad)分别为-1.52和-2.11 eV,属于化学吸附。通过能带分析(BS)和态密度(DOS)分析进一步证明了两个体系的吸附性能,并阐述了Ru-MoS₂用于电阻式气体传感器时的气体吸附传感机制。除此之外,本文在理论上探索了不同温度下Ru-MoS₂解吸附SO₂F₂和H₂S的恢复时间,在598 K温度下,SO₂F₂吸附体系的恢复时间为6...     

Optical properties of the germanate melilites Sr2MgGe2O7, Sr2ZnGe2O7 and Ba2ZnGe2O7

Refractive indices and their dispersion in the wavelength range from 365 nm to 2325 nm and transmission ranges of the tetragonal melilite‐type germanates Sr₂MgGe₂O₇, Sr₂ZnGe₂O₇ and Ba₂ZnGe₂O₇ were determined. The uniaxial positive crystals Sr₂MgGe₂O₇ and Ba₂ZnGe₂O₇ both offer the possibility for phase matched second harmonic generation, a detailed analysis of phase matching conditions is given. The refractive indices of Sr₂ZnGe₂O₇ show an isoindex (isotropic) point at 467 nm. The investigation was performed on Czochralski grown large single crystals. The crystal structure of all three germanates were determined by means of X ‐ray diffraction. The results corroborate unmodulated melilite‐type structures at room temperature. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure of {Pb[S2CN(C2H5)2]2(1,10-phenanthroline)}2

Lead (II) nitrate reacts with 1,10-phenanthroline and sodium diethyldithiocarbamate in water to produce yellow bisdiethyldithiocarbamata 1,10-phenanthroline lead(II). Crystals from water are triclinic, space group $P\bar 1$ (#2),a=10.53(2) Å,b=11.050(12)Å,c=24.74 (3) Å, α=94.71 (9)⁰, β=98.15(11)^o, γ=114.11(9)^o,V=2569(6) ų,Z=2. Each lead atom has approximate pentagonal pyramid coordination geometry through the nitrogens of a phenathroline and sulfurs of two dithiocarbamates. Additionally, complexes form loose dimers in which lead atoms are weakly coordinated to a sulfur in an adjacent complex. IR and proton nmr spectrum of the complex are consistent with the solid state structure.