Shear and NMR experiments of materials with flow behaviour depending on the deformation history

Oxide ceramic masses react to simple shearing with hardening (peptisation: increase in the shear stress with the shear deformation). In the present study the correlation between the increase in the shear stress and the porosity, agglomeration processes and the type of flow are analysed. For this purpose oxide ceramic masses are tested in a shear device especially developed for pastes and analysed by rheometric experiments, NMR methods and particle size analysis. The results support the hypothesis that structural changes (hardening, increase in the mean porosity) of the material during the peptisation mainly depend on the magnitude and not on the kind of the energy input and thus of the type of flow. The fraction of bound (more generally, the immobilised) water increases with the shear displacement. Also crushing of primary particles could be observed. Both the crushing of solid particles causing an increased solid surface and the formation of a three-dimensional gel structure are microscopic effects capable of resulting in the binding or retaining water. On a macroscopic scale these phenomena cause hardening. Magnetic resonance imaging visualises flow-induced agglomerates, which form owing to the shear flow and increase the porosity averaged over the whole sample. After the shear experiment rolls of paste can be seen which indicate that the general assumption of a plane shear flow in the shear device is not warrantable. Received: 19 July 2001 Accepted: 25 October 2001     

Templated ceramic microstructures by using the breath-figure method

We describe the synthesis of two cyclobutadiene(cyclopentadienyl)cobalt-containing poly(p-phenylene ethynylene)s (PPEs) and their use as precursors for stable ceramic surface coatings. Organometallic PPEs were shaped into hexagonally ordered assemblies by using the breath-figure method. Such breath figures can be washed away with an appropriate solvent. Upon pyrolysis at 500 degrees C under either nitrogen or air, the bubble arrays persist as ceramics and are insoluble in organic solvents or water. The formed pyrolyzed bubble arrays were analyzed by optical and scanning electron microscopy, as well as energy dispersive X-ray microanalysis (EDX). The composition of the ceramic materials is discussed based on EDX and IR data.     

An investigation into the self-propagating high temperature synthesis (SHS) of superconducting ceramics by thermal methods

The SHS route is based on the well-known thermite reaction, in which a strongly exothermic reaction can sustain itself and propagate in the form of a combustion wave until the reactants have been completely consumed. The successful application of the method to the synthesis of superconducting ceramics of stoichiometry RBa₂Cu₃O_y (R=Y, Er, Yb) is reported. The 123 phase was obtained when pellets of R₂O₃, BaO₂ and Cu metal in the correct proportions were dropped into a heater held at 800°C in an oxygen atmosphere and left there for only 10 minutes. Thermal methods (DSC and DTA) are excellent techniques with which to investigate the dependence of the reaction on heating rate, atmosphere and starting composition.     

碳酸盐前驱物制备Y2O3超细粉及透明陶瓷

以Y(NO3)3和NH4HCO3为原料,通过向Y(NO3)3溶液中滴加NH4HCO3的方式制备了化学组成为Y2(CO3)3·2H2O的先驱沉淀物。研究了先驱沉淀物煅烧过程中的物相变化。先驱沉淀物1100℃煅烧4h后得到了平均粒径为60nm的无团聚Y2O3超细粉体。所得粉体不添加任何添加剂,在1700℃下真空烧结4h得到了透明Y2O3陶瓷。     

碳纳米管/高分子复合导电材料的研究进展

从碳纳米管的电性质出发,对以它为填料的导电性复合材料的制备方法和研究进展进行了综述,同时简单介绍了导电性复合材料电性质转变现象的理论分析模型,最后对碳纳米管/高分子复合导电材料的研究前景作了一定探讨。     

The investigation of ancient pottery

Summary Ancient ceramic samples (single fragments and different parts of pots, unbroken and repaired; total about 180 samples) dated from the transitional period of late Bronze to early Iron Age (VIII-VI centuries BC) and early Iron Age (VII-IV centuries BC) were investigated by thermal analysis, X-ray powder diffraction, petrography, and scanning electron microscopy equipped with the energy-dispersive X-ray analyzer. In addition to that, to identify the clay sources for the ceramic manufacturing, about 15 samples of clays and soils found near archeological digs and taken from the mineralogical museum were investigated. We found out that the calcite content of ceramics is a very informative parameter for the identification of the clay source for the pottery manufactured at low technological level (low-temperature firing).     

聚苯胺复合材料研究进展

综述了聚苯胺/无机物复合材料和聚苯胺/有机高聚物复合材料的合成方法，性能特征，并展望了聚苯胺复合材料的研究，应用前景。     

Electrocatalytic Properties of a Novel Poly‐1‐Naphthylamine‐Modified Electrode Using Ascorbic Acid as Molecule Probe

A glassy carbon electrode was modified with an electropolymerized film of 1‐naphthylamine in aqueous solution. The electrocatalytic properties of this modified electrode (ME) were investigated using ascorbic acid (AA) as probe molecule. The electrochemical behavior of AA in buffer solution was examined by voltammetry and amperometry. The results showed that the ME exhibited good electrocatalytic activity towards the oxidation of AA, as a consequence, it can be used as amperometric sensor of this analyte in a flow injection system with good sensitivity. Calibration curves were linear over the concentration range 0.05–1.50 mM with a phosphate buffer solution pH 3 as the carrier, the detection limit was 1 ppm (S/N=3). The methods were applied to the determination of AA in beverages and pharmaceutical products. A good correlation with a reference method was attained.     

聚丙烯腈表面金属化新方法的研究

以硼氢化钠（ＮａＢＨ４）水溶液还原聚丙烯腈（ＰＡＮ）／金属盐络合膜后，就可得到一种新的高分子表面金属化材料．其导电性能较好，表面电阻约为１０－１～１０Ω／□通过ＵＶ、ＩＲ等分析手段证实了在高聚物和金属离子之间存在络合作用。研究了影响表面电阻的因素。通过电镜和测量还原率、电子探针微区分析，证实了还原过程中存在离子迁移     

Microfabricated ISEs: critical comparison of inherently conducting polymer and hydrogel based inner contacts

A rigorous side by side comparison of miniature planar potassium-selective electrodes with hydrogel and potassium hexacyanoferrate(II)/(III) doped polypyrrole (PPy/FeCN) based inner contacts is presented. The planar electrodes were manufactured by screen printing as four- and five-site arrays on ceramic substrates. These electrode arrays were incorporated into a flow-through cell, which could accommodate nine electrode sites. Two identical flow cells were connected in series and the effect of the inner contacts on the analytical performance of the respective electrodes has been critically evaluated. The time necessary to reach steady state conditions has been determined and the effect of experimental parameters (temperature, ambient light intensity, CO₂, and O₂ concentration of the sample) on the potential stability of the electrodes was analyzed. At controlled temperature, the drift of the planar potassium electrodes with hydrogel and PPy/FeCN solid contact were 0.11±0.02 mV h⁻¹ and 0.03±0.007 mV h⁻¹, respectively. The experimental data proved that there is no aqueous film formation between the PPy/FeCN film and the potassium-selective solvent polymeric membrane.