纳米晶钛酸钡的介电性能

采用硬脂酸凝胶法制备了纳米晶BaTiO3,用差热热重分析、红外光谱分析、X射线衍射分析等手段对产物的形成过程、晶型、粒径进行了分析.通过对材料介电性能的研究发现,纳米材料的静态介电常数远大于常规材料的介电常数,随着粒径的减小,纳米材料的介电常数先增大而后有所降低.随着环境湿度的升高,纳米晶材料的介电常数逐渐增大,在高湿度条件下,其介电常数与湿度成线性关系.     

Sol‐Gel Preparation and Characterization of Codoped Yttrium Aluminium Garnet Powders

A sol‐gel method has been developed to prepare lanthanide‐codoped yttrium aluminium garnet (Y₃Al₅O₁₂, YAG) ceramic samples. The XRD patterns of the polycrystalline Y₃Al₅O₁₂:Nd,Ho and Y₃Al₅O₁₂:Nd,Er powders sintered at 1000 °C showed the formation of monophasic garnet materials. A homogeneous distribution of rare‐earth dopants in the YAG lattice was achieved in both cases. The morphological characterization of lanthanide‐codoped YAG by scanning electron microscopy (SEM) showed the formation of highly agglomerated nanocrystalline samples. The luminescence properties of sol‐gel derived doubly activated yttrium aluminium garnet samples were also investigated in the present study.     

YAG:Eu3+、Bi3+的溶胶-凝胶法合成及其结构和发光性能

溶胶-凝胶法以其各组分混合均匀性好、反应温度低、节省能源等诸多优点而引起了人们极大兴趣[1,2].近年来,利用该法研制玻璃和陶瓷等无机材料的报道越来越多[3,4].     

溶胶—凝胶法合成LaCr1—xFexO3超细粉末

以无机盐为原料，用溶胶－凝胶法合成了ＬａＣｒ１－ｘＦｅｘＯ３超细粉末，其平均粒径〈１３０ｎｍ。研究表明，随着焙烧温度的升高或时间的增加，粉末的粒径随之增大，比表面积则随之减小；ＬａＣｒ１－ｘＦｅｘＯ３粉末为钙钛矿型结构，其晶胞参数随着Ｆｅ含量的增加而增大。     

Dielectric Properties of Nanocrystalline TiO2 Prepared by the Stearic Acid Gel Method

Nanocrystalline TiO2 was prepared by means of a stearic acid gel method. The product was investigated by differential thermal analysis, thermogravimetric analysis, X-ray powder diffraction and transmission electronic microscopy (TEM ). The results of the dielectric properties tested indicate that the dielectric constant of anatase-form nanocrystalline TiO2 is much higher than that of the coarse crystal. The dielectric constant of the nanocrystalline material is not related with the amplitude of an external AC field in a certain range.     

Electrochemical Sensor for Sulfite and Sulfur Dioxide Based on 3‐Aminopropyltrimethoxysilane Derived Sol‐Gel Composite Electrode

A new sol‐gel derived composite sensor has been developed for the determination of sulfite and sulfur dioxide using 3‐aminopropyltrimethoxysilane, ferrous sulfate and graphite powder by sol‐gel process. Cyclic voltammetry and amperometry studies revealed that the modified iron dispersed sol‐gel derived ceramic composite electrode exhibited excellent characteristics for the electrocatalytic oxidation of sulfite at a reduced potential of +0.35 V with good sensitivity and selectivity. The pH and the potential for sulfite estimation have been optimized. The sensor exhibited rapid and linear response to sulfite in the concentration range from 0.73 mg/L to 95.42 mg/L with a correlation coefficient of 0.997. The proposed sensor can be utilized for the determination sulfur dioxide after absorbing in a suitable medium and has promising characteristics such as, rapid response, good reproducibility and remarkable stability.     

Preparation of GOD/Sol‐Gel Silica Film on Prussian Blue Modified Electrode for Glucose Biosensor Application

A novel amperometric glucose biosensor was fabricated by in situ incorporating glucose oxidase (GOD) within the sol‐gel silica film on a Prussian blue (PB) modified electrode. The method is simple and controllable, which combined the merits of in situ immobilizing biomolecules in sol‐gel silica film by electrochemical method and the synergic catalysis effects of PB and GOD molecules. Scanning electron microscopy (SEM) showed that the GOD/sol‐gel silica film was homogeneous with a large number of three‐dimensional nanopores, which not only enhanced mass transport, but also maintained the active configuration of the enzyme molecule and prevented the leakage of enzyme, therefore improved the stability and sensitivity of the biosensor. The fabricated biosensor showed fast response time (10 s), high sensitivity (26.6 mA cm^?2 M^?1), long‐term stability, good suppression of interference, and linear range of 0.01 mM–5.8 mM with a low detection limit of 0.94 μM for the detection of glucose. In addition, the biosensor was successfully applied to determine glucose in human serum samples.     

Synthesis of Pure Cementitious Phases by Sol‐Gel Process as Precursor

Calcium silicates and aluminates are the main constituents of ordinary Portland cement (OPC) and calcium aluminate cements (CAC) and therefore the pure phases are of great importance for the investigation of interactions between binder and additives or admixtures. Additionally, investigations on clinker phases doped with foreign ions enable the improvement of the performance of cements. For this purpose great amounts of pure phases are needed. These phases are hard to synthesize via a solid state reaction of solid educts. Thus there is a need for a new, more efficient route to synthesize these phases. The sol‐gel process as precursor provides an alternative to the conventional method. In this paper experimental evidence is presented for an improved synthesis of calcium silicates and aluminates via sol‐gel processes, the characterisation of these clinker phases and their hydration behaviour.     

Synthesis and Characterization of High Surface Area Tin Oxide Nanoparticles via the Sol‐Gel Method as a Catalyst for the Hydrogenation of Styrene

A systematic study on the preparation of SnO₂ nanoparticles using a simple sol‐gel technique has been conducted by varying reaction parameters such as concentration of ammonia, ammonia feed rate and reaction temperature. The tin oxide obtained was characterized by using FTIR, BET, XRD and TEM. Particles size was obtained in the range of 4 to 5.6 nm and the surface area was found to be between 76 to 114 m² g^?1 depending on the reaction parameters. Meanwhile, the catalytic activity of SnO2 was first time investigated for the hydrogenation reaction of styrene using ethanol as the solvent at 70 °C and 1 atmospheric pressure. It is found that SnO2 acts as a good catalyst in this hydrogenation process. The product conversions in the presence of catalysts prepared at different conditions were between 37 to 72%.     

Structural and Electrical Properties of Sol–Gel-processed CdTiO3 Powders and Films

Cadmium titanate, CdTiO₃, was prepared by the sol–gel technique in bulk and in thin film form. The thermal evolution of the gels and the phase changes were studied by thermo- gravimetric analysis (TGA), X-ray diffractometry (XRD) and Raman and energy-dispersive (EDS) spectroscopies. The morphology of the samples was observed using scanning electron microscopy (SEM). Gels heated to 800 °C gave rise to powders with only the ilmenite-like phase. The orthorhombic perovskite phase is the only crystalline phase observed after a 4 h heat-treatment at 1100 °C. With respect to the conventional preparation method by solid-state reaction, by the sol–gel method it is possible to prepare the ilmenite phase at lower temperatures and the perovskite phase in a shorter time. Clear, homogeneous thin films were obtained by the dip-coating method. The refraction index and the thickness of the films were measured using ellipsometry. The humidity-sensitive electrical properties were measured for thin films deposited on alumina substrates with comb-type gold electrodes, heated to 200 °C and 450 °C. The films heated to 200 °C, which still contained organics, showed a variation of the resistance of six orders of magnitude in the relative humidity (RH) range tested (4–87% RH). The films heated to 450 °C, made of ilmenite-type CdTiO₃, were nearly insensitive to RH. © 1997 by John Wiley & Sons, Ltd.     

Beiträge zu den Eigenschaften von Titanaten mit Ilmenitstruktur. I. Aspekte eines Hochtemperaturphasenübergangs in NiTiO3

Contributions to the Properties of Titanates with Ilmenite Structure. I. Aspects of a High Temperature Phase Transition in NiTiO₃ NiTiO₃ (Ilmenite structure) shows an anomalous increase of the electrical conductivity in the temperature range between 1 250°C and 1 290°C. The temperature dependence of the Seebeck coefficient is also found to be anomalous in this region. DTA experiments are consistent with a phase transition; the transition enthalpy was estimated to Δ_uH_m = 17 ± 3 kJmol^?1. NiTiO₃ powders and single crystals were quenched from 1 350°C and 1 200°C to room temperature; in principle no differences of the lattice parameters or atomic positions could be detected. The determination of the distribution of cations using x-ray powder methods failt because of strong texture effects. Structure refinements with single crystal methods suggest an ordered Ilmenite structure independent of the quenching temperature. The results are in agreement with a reversible order-disorder transition of higher order. It seems to be impossible to quench the high temperature phase by conventional methods.     

Photoluminescence Properties of Quinidine and Quinidine Sulfate in the Sol‐gel System

The emission spectra of quinidine and quinidine sulfate doped in sol‐gels (tetraethoxysiliane system) have been measured during the sol‐gel transformation. Shifts in the emission spectra from 370 nm to 435 nm were observed in both molecules as the system changed from sol stage to dried glass over a period of two weeks. These shifts are attributed to the conformational changes of the doped molecules. In addition, the process of the signal changes was observed by an emerging new band at ?435 nm with a concomitant decline of the original band at 370 nm during the sol‐gel transformation. These results indicate that the conformational changes induced by the sol‐gel transformation are accomplished in one step instead of several intermediate states.     

Electrocatalytic Reduction of Nitrite Ion on a Toluidine Blue Sol‐Gel Thin Film Electrode Derived from 3‐Aminopropyl Trimethoxy Silane

An organically modified sol‐gel electrode using 3‐aminopropyltrimethoxy silane for covalent immobilization of a redox mediator namely toluidine blue has been reported. Cyclic voltammetric characterization of the modified electrode in the potential range of 0.2 V to ?0.6 V exhibited stable voltammetric behavior in aqueous supporting electrolyte with a formal potential of ?0.265 V vs. SCE, corresponding to immobilized toluidine blue. The electrocatalytic activity of the modified electrode when tested towards nitrite ion exhibited a favorable response with the electrocatalytic reduction of nitrite occurring at a reduced potential of ?0.34 V. A good linear working range from 2.94×10^?6 M to 2.11×10^?3 M with a detection limit of 1.76×10^?6 M and quantification limit of 5.87×10^?6 M was obtained for nitrite determination. The stable and quick response (4 s) of the modified electrode towards nitrite under hydrodynamic conditions shows the feasibility of using the present sensor in flow systems. Significant improvements in the operational stability by overcoming the leachability problem and repeatability with a relative standard deviation of 1.8% of the TB thin film sensor have been obtained by the strategy of immobilization of the mediator in the sol‐gel matrix.     

Antibacterial and Chemical Characterization of Silica-Quercetin-PEG Hybrid Materials Synthesized by Sol–Gel Route

This paper aims to synthesize, via the sol–gel method, a biomaterial usable in the medical field. Here, the silica-PEG-quercetin system was evaluated in relation to the different concentrations of PEG (0, 6, 12, 24, 50 wt%) and quercetin (0, 5, 10, 15 wt%), respectively. In addition, Fourier Transform-Infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and Kirby–Bauer analyses were performed. FT-IR was used to evaluate the hybrid formation and the influence of both PEG and Quercetin in the hybrid synthesized materials, SEM was used to evaluate the morphological properties, while the Kirby–Bauer test was used to understand the ability of the materials to inhibit the growth of the assayed bacterial strains (Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, and Staphylococcus aureus).     

Hydrogen Peroxide Detection at Electrochemically and Sol‐Gel Derived Ir Oxide Films

Ir oxide (IrOx) films, formed electrochemically on bulk Ir metal (Ir/IrOx) and also on sol‐gel (SG) derived non‐silica based nanoparticulate Ir, have been studied as material useful for the detection of hydrogen peroxide, with possible application as a glucose biosensor. H₂O₂ reduction and oxidation on Ir/IrOx and SG‐derived IrOx films, deposited on various substrates such as Pt, Ir and GC, have been compared to the H₂O₂ behavior at the bare substrate. It was found that H₂O₂ reduction proceeds on the underlying electrode substrate, while H₂O₂ oxidation is independent of the nature of the substrate, therefore occurring via the IrOx film. The reactivity of IrOx towards H₂O₂ oxidation is similar to that seen at Pt, although IrOx has the additional advantages of excellent stability, insensitivity to common interfering substances, biocompatibility and a linear range of detection, up to at least 12 mM H₂O_2. At micromolar concentrations of H₂O₂, a second mode of detection, involving the catalyzed growth of IrOx films at Ir substrates, can be employed. These two methods of H₂O₂ analysis (oxidation/reduction and enhanced IrOx growth) can also be employed for glucose detection using IrOx‐based glucose biosensors.     

A Cholesterol Biosensor Based on Entrapment of Cholesterol Oxidase in a Silicic Sol‐Gel Matrix at a Prussian Blue Modified Electrode

A cholesterol biosensors fabricated by immobilization of cholesterol oxidase (ChOx) in a layer of silicic sol‐gel matrix on the top of a Prussian Blue‐modified glassy carbon electrode was prepared. It is based on the detection of hydrogen peroxide produced by ChOx at ?0.05 V. The half‐lifetime of the biosensor is about 35 days. Cholesterol can be determined in the concentration range of 1×10^?6?8×10^?5 mol/L with a detection limit of 1.2×10^?7 mol/L. Normal interfering compounds, such as ascorbic acid and uric acid do not affect the determination. The high sensitivity and outstanding selectivity are attributed to the Prussian Blue film modified on the sensor.     

Ca改性钛酸铅纳米晶的制备及结构研究

用溶胶-凝胶工艺制备了Pb_1-xCa_xTiO₃(0≤x≤0.3)纳米晶,在不同焙烧条件下研究其粉体晶相结构的变化.研究结果表明,升温速度和焙烧温度对纳米粉的晶相、晶胞参数和晶粒尺寸有显著影响.讨论了晶胞参数、四方畸变度和晶胞体积与Ca含量的关系.