生物医用微晶陶瓷的研究进展

综述了生物医用微晶陶瓷的研究进展以及生物医用微晶陶瓷在人体生理环境中的反应机理和补强增韧方法的现状研究.     

Ba2ZnZCo2-ZFe12O22-SiO_2微晶玻璃陶瓷的sol-gel合成及性能研究

采用柠檬酸so1-gel工艺合成了Ba2ZnzC02-zFel2O22-SiO2微晶玻璃陶瓷；采用XRD、SEM对其相成分、显微结构进行了分析，结果表明，1200℃／5h得到的BBa2ZnzC02-zFel2O22-SiO2微晶玻璃陶瓷的平均晶粒尺寸在0．3μm左右；采用HP8753E网络分析仪测定了微晶玻璃陶瓷在100MHz～6GHz范围内的介电常数及其磁导率，其复介电常数值、磁导率实部都随测试频率的增加而减小，其磁导率虚部～f曲线上显示出明显的自然共振峰。     

Ba2ZnZCo2-ZFe12O22-SiO_2微晶玻璃陶瓷的sol-gel合成及性能研究

采用柠檬酸sol-gel工艺合成了Ba₂Zn_ZCo_2-zFe₁₂O₂₂-SiO₂微晶玻璃陶瓷;采用XRD、SEM对其相成分、显微结构进行了分析,结果表明,1200°C/5h得到的Ba₂Zn_ZCo_2-zFe₁₂O₂₂-SiO₂微晶玻璃陶瓷的平均晶粒尺寸在0.3μm左右;采用HP8753E网络分析仪测定了微晶玻璃陶瓷在100MHz～6GHz范围内的介电常数及其磁导率,其复介电常数值、磁导率实部都随测试频率的增加而减小,其磁导率虚部～f曲线上显示出明显的自然共振峰。     

PbTiO3微晶玻璃陶瓷的结构和热释电性能研究

采用溶胶－凝胶方法在ＰbTiO3微晶玻璃体系中,析出了ＰbTiO3微晶。ＤＴＡ和Ｘr-ary衍射分析表明,随玻璃含量的增加,析晶温度升高,热释电测试结果表明,随着玻璃含量的增加,热释电系数增大,随烧结温度的升高,ＰbTiO3微晶玻璃陶瓷的热释系数也随之增大,介电温谱的测量则显示,ＰbTiO3陶瓷与ＰbTiO3微晶玻璃陶瓷具有明显的差异。     

BaFe12O19/SiO2微晶玻璃陶瓷的柠檬酸盐Sol-Gel合成及其微波性能的研究

采用柠檬酸sol-gel工艺合成了BaFe12O19/SiO2微晶玻璃陶瓷,并对其介电常数及其磁导率在100MHz-6GHz下的变化规律进行了研究。结果表明,BaFe12O19/SiO2微晶玻璃陶瓷的合成与体系中Fe/Ba,烧结温度密切相关;其介电常数、磁导率基本都随测试频率的增加而下降,介电损耗值最大达到0．40,磁损耗值较小。     

Na2CO3助熔剂与基于石棉尾矿微晶陶瓷晶相转变和理化性能的关联规律探索

以石棉尾矿为主要原料,Na2 CO3作为助熔剂,采用一次烧结法制备出以镁橄榄石为主晶相的微晶陶瓷.采用X射线衍射分析、场发射扫描电子显微镜等测试手段对不同条件制备的微晶陶瓷样品进行表征,研究了烧结温度、Na2 CO3添加量对微晶陶瓷晶相转变、显微结构和理化性能的影响.结果表明:未添加Na2 CO3时,提高烧结温度仅使赤铁矿消失;当Na2 CO3添加量为4％(质量分数,下同)时,赤铁矿与顽火辉石消失.高温烧结过程中赤铁矿与顽火辉石逐渐转化为镁铁尖晶石和镁橄榄石.Na2 CO3添加量为4％(质量分数)时,在烧结温度1150℃条件下制备的微晶陶瓷的理化性能达到最佳,其体积密度、线性收缩率、抗折强度分别为2.85 g/cm3、11.4％、65.4 MPa.添加Na2 CO3对石棉尾矿微晶陶瓷晶相转变及理化性能具有重要的影响.     

BaFe12O19/A12O3-SiO2-K2O微晶玻璃陶瓷的柠檬酸SOl-Gel合成及其微波性能的研究

采用柠檬酸sol-gel工艺合成了BaFe12O19/A12O3-SiO2-K2O微晶玻璃陶瓷,并对其介电常数及其磁导率在1MH2～6GHz下的变化规律进行了研究.结果表明,BaFe12O19/Al2O3-SiO2-K2O微晶玻璃陶瓷的合成与体系中Fe/Ba、烧结温度密切相关;其介电常数、磁导率基本都随测试频率的增加而下降;介电损耗值最大可达到0.30磁损耗值较小.     

PbTiO_3微晶玻璃陶瓷的结构和热释电性能研究

采用溶胶－凝胶方法在Ｐｂ－Ｔｉ－Ｂ－Ｓｉ－Ｏ凝胶玻璃体系中,析出了ＰｂＴｉＯ３微晶．ＤＴＡ和Ｘ－ｒａｙ衍射分析表明,随玻璃含量的增加,析晶温度升高．热释电测试结果说明,随着玻璃含量的增加,热释电系数增大;随烧结温度的升高,ＰｂＴｉＯ３微晶玻璃陶瓷的热释电系数也随之增大．介电温谱的测量则显示,ＰｂＴｉＯ３陶瓷与ＰｂＴｉＯ３微晶玻璃陶瓷具有明显的差异．     

BaFe_(12)O_(19)/SiO_2微晶玻璃陶瓷的柠檬酸盐Sol-Gel合成及其微波性能的研究

采用柠檬酸 Ｓoｌ－ｇｅｌ工艺合成了 ＢａＦｅ12Ｏ１９／ＳｉＯ２微晶玻璃陶瓷,并对其介电常数及其磁导率在１００ＭＨｚ～６ＧＨｚ下的变化规律进行了研究.结果表明,ＢａＦｅ１２Ｏ１９／ＳｉＯ２微晶玻璃陶瓷的合成与体系中 Ｆｅ／Ｂａ、烧结温度密切相关;其介电常数、磁导率基本都随测试频率的增加而下降;介电损耗值最大达到０．４０,磁损耗值较小．     

非铁电压电极性微晶一维生长驱动力分析

利用熔融法制备了BaO-SrO-TiO₂-SiO₂玻璃,并在温度梯度条件下制备了极性微晶Ba_2-xSr_xTiSi₂O₈沿c轴一维取向的压电玻璃陶瓷.用X-ray衍射分析和扫描电镜对极性微晶的取向生长结构进行了分析.建立了极性微晶沿c轴取向生长的模型,其结果与实验结果相一致.结果表明在光滑的表面,温度梯度方向和偶极子电场方向都是沿c轴晶格能大的方向,其共同作用的结果使极性微晶沿c轴一维取向生长.     

Impedance spectroscopy study of polycrystalline Bi6Fe2Ti3O18

The electrical properties of polycrystalline Bi₆Fe₂Ti₃O₁₈ are investigated by impedance spectroscopy in the temperature range 30–550°C. The imaginary part of impedance as a function of frequency shows Debye like relaxation. Impedance data are presented in the Nyquist plot which is used to identify an equivalent circuit and the fundamental circuit parameters are determined at different temperatures. The grain and grain-boundary contributions are estimated. The results of bulk a.c. conductivity as a function of temperature and frequency are presented. The activation energies for the a.c. conductivity are calculated. The polaron hopping frequencies are estimated from the a.c. conductivity data.     

Experimental investigations on buckling of cylindrical shells under axial compression and transverse shear

This paper presents experimental studies on buckling of cylindrical shell models under axial and transverse shear loads. Tests are carried out using an experimental facility specially designed, fabricated and installed, with provision forin-situ measurement of the initial geometric imperfections. The shell models are made by rolling and seam welding process and hence are expected to have imperfections more or less of a kind similar to that of real shell structures. The present work thus differs from most of the earlier investigations. The measured maximum imperfections δ_max are of the order of ±3t (t = thickness). The buckling loads obtained experimentally are compared with the numerical buckling values obtained through finite element method (FEM). In the case of axial buckling, the imperfect geometry is obtained in four ways and in the case of transverse shear buckling, the FE modelling of imperfect geometry is done in two ways. The initial geometric imperfections affect the load carrying capacity. The load reduction is considerable in the case of axial compression and is marginal in the case of transverse shear buckling. Comparisons between experimental buckling loads under axial compression, reveal that the extent of imperfection, rather than its maximum value, in a specimen influences the failure load. Buckling tests under transverse shear are conducted with and without axial constraints. While differences in experimental loads are seen to exist between the two conditions, the numerical values are almost equal. The buckling modes are different, and the experimentally observed and numerically predicted values are in complete disagreement.     

Optical and dielectric properties of lanthanide titanium tantalate and niobate ceramic composites

The xPrTiTaO₆ (1 − x) YTiNbO₆ dielectric ceramic composites are fabricated through the solid state ceramic route. The compositions are calcined in the temperature range 1,200–1,260 °C and sintered in the range 1,350–1,410 °C. Structural analysis of the materials is done using X-ray Diffraction analysis. The composites contain both aeschynite and euxenite orthorhombic phases. The surface morphology of the sintered pellets is examined by scanning electron microscopy. The dielectric constant, conductance and loss factor are measured in the radio frequency region. The UV–visible spectra are recorded and the band gap is calculated. The photoluminescence spectra of the compositions are recorded and the transitions causing emission are identified. The elemental composition of the composites is confirmed using energy dispersive spectroscopy. The materials are suitable for substrate and optoelectronic applications.     

Heat transfer and flow pattern during two-phase flow boiling of R-134a in horizontal smooth and microfin tubes

Flow pattern and heat transfer during evaporation in a 10.7 mm diameter smooth tube and a micro-fin tube are presented. The tubes were tested in the ranges of mass flux between 163 and 408 kg m⁻² s⁻¹, and heat flux between 2200 and 56 000 W m⁻². The evaporation temperature was 6 °C. Flow maps for both the tubes are plotted in the coordinates of mass flux and vapor quality. The relations of flow pattern and local heat transfer coefficient are discussed. The heat transfer coefficients for intermittent and annular flows in both the smooth tube and the micro-fin tube are shown to agree well with Gungor and Winterton's correlation with modified constants.     

Cation-cation interactions between uranyl(VI) ions

Data on crystalline U(VI) compounds with mutual coordination of uranyl ions in their structure (cation-cation interactions, CCIs) are summarized. The topology and geometry of CCIs, including the characteristics of Voronoi-Dirichlet polyhedra of uranium atoms, are analyzed. 15 types of complexes [UO ₂ ²⁺ ] _n formed by CCIs are revealed. The influence of CCIs on the stereochemical features of U(VI) are considered, and common and distinctive features of CCIs in uranyl(VI) and neptunyl(V) compounds are discussed. Factors favoring the occurrence of CCIs in uranyl compounds are analyzed. The spectroscopic manifestations of CCIs are considered. Data on CCIs in some noncrystalline media are presented. The strength of cation-cation bonds in uranyl complexes is analyzed.     

Oscillatory flow of a micropolar fluid generated by the rotary oscillations of two concentric spheres

In this paper we examine the flow of an incompressible micropolar fluid between two concentric spheres, generated by their rotary oscillations about a common diameter. The spheres are assumed to be oscillating with the same amplitude but with different angular speeds. The speeds of oscillation are assumed to be small so that the nonlinear terms in the equations of motion can be neglected under the usual Stokesian assumption. The analytical expressions for velocity and microrotation components are determined in terms of modified Bessel functions of first and second kind. The couples experienced by the inner and outer spheres are calculated and are expressed in terms of two real parameters K and K^′ whose variation is studied numerically. The variations of K and K^′ with respect to micropolarity parameter and frequency parameter are displayed graphically.     

Computer Simulation of Liquid Copper Tellurides and Silver Selenide from Diffraction Data

The structural models of liquid Ag₂Se, CuTe, and Cu₂Te are constructed from available diffraction data using molecular dynamics simulations with the BELION algorithm. The structural characteristics of the models are in good agreement with the diffraction data, and the calculated atomization energies agree with thermodynamic estimates. The charge state of the Ag ion is close to 1+, and those of the Cu ions in both tellurides are close to 0.3+. The structures of the three chalcogenides, particularly that of Cu₂Te, are rather loose. The simulation results on the distribution of Voronoi polyhedra and pore size attest to significant local structural inhomogeneity, particularly pronounced in Cu₂Te. The self-diffusion coefficients of the constituent components in the melts are evaluated.     

Thermal and nonequilibrium responses of superconductors for radiation detectors

This work summarizes the progress in the study of the superconductor response to optical radiation and in the development of infrared detectors. The recent advances in the design of high-T _c superconducting radiation detectors using silicon microfabrication technology are emphasized. Thermal and optical properties important for the detector performance are discussed. The mechanism of the nonequilibrium optical response and its potential use to build fast and sensitive radiation detectors are described. Future challenges and opportunities in the development of high-T _c superconducting radiation detectors are highlighted.     

Rare earth elements in α-Ti: A first-principles investigation

The interaction energies between substitutional rare earth (RE) atoms, between RE and interstitial C, N, O, H atoms, as well as between RE and vacancies in α-Ti are calculated via first-principles density-functional theory with projector augmented-wave (PAW) pseudopotentials. The results show that the RE–vacancy and RE–RE interactions are attractive due to the weaker RE–Ti bond than the host Ti–Ti bond. All of the RE atoms investigated in this paper are repulsive to C and N, but attractive to H. RE–O interactions are repulsive for the light RE atoms, though the interactions are very weak for the heavy RE atoms. The mechanism underlying the interactions and their possible influence on the properties of Ti alloys are discussed.     

Stability,thermal and mechanical properties of PtxAly compounds

The stability, thermal and mechanical properties of Pt_xAl_y intermetallic compounds are investigated by density functional theory (DFT). The cohesive energy and formation enthalpy of Pt_xAl_y phases show that they are thermodynamically stable structures and these are in good agreement with the experiments. The heat capacity of the compounds is calculated by quasi-harmonic approximation (QHA) method. The thermal expansion coefficient as a function of temperature for each compound is also discussed. The elastic properties such as bulk modulus, Young’s modulus are evaluated by Viogt–Reuss–Hill approximation. The anisotropic properties of sound velocities for the Pt_xAl_y compounds are explored. The calculated Poisson’s ratio varies from 0.26 to 0.39 for Pt_xAl_y phases and the bonds in the compounds are mainly metallic and covalent types.