Thermally Stimulated Creepe and Current (TSCr and TSC) have been used for investigating the interface/interphase in DGEBA-DDA matrix and glass beads composites. In all samples, a complex α retardation/relaxation mode is observed near the glass transition of the matrix. A study of the fine structure has shown that, for the elastic processes, the activation enthalpies are ranging from 2 and 8 eV, while for the dielectric ones, they are restricted between 0.5 and 1.5 eV. Moreover, for a given activation enthalpy, the preexponential factor τo and the activation entropy ΔS are characteristic of matrix filler interface. 相似文献
All kinetic analyses aim to determine a sufficient number of kinetic parameters, usually at least an apparent Arrhenius activation energy and pre-exponential factor, and a conversion function or kinetic model (making up a ‘kinetic triplet’), so that accurate extrapolations of kinetic behaviour can be made. “Model-free” methods of kinetic analysis postpone the problem of identifying a suitable kinetic model until an estimate of the activation energy has been made. A major reason for doing this is that misidentification of the kinetic model has a marked effect on the values obtained for the Arrhenius parameters in both isothermal and non-isothermal kinetic analyses. Some aspects of this problem are discussed.
The non-parametric kinetics (NPK) method [1 and 2] is a “model-free” method of kinetic analysis that does not seem to have received the attention that it deserves. This is probably because of its mathematical sophistication and the fact that the matrix and non-linear regression calculations involved are not readily automated. The principle of the method appears to be that of “forcing” a set of non-isothermal data into the set which should have been obtained if the experiments had been carried out isothermally. The method deserves wider testing and also raises some interesting aspects of the philosophy behind non-isothermal kinetic analysis. 相似文献
Glassy residues of the complex bis(N,N-disalicylidene-1,2-phenylenediamino)zirconium(IV), Zr(dsp)2, on glass slides were exposed to atomic oxygen in a plasma asher or an atomic beam facility for various amounts of lime in order to study the erosion process, determine the rate of erosion, and learn the chemical identity of the residue. The exposed films were characterized by weight loss, optical photography, profilometry, diffuse reflectance and total transmittance spectroscopy, scanning electron microscopy (SEM) with wavelength dispersive X-ray spectrometry (WDS), X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). Results indicate that these films erode much more slowly polyimide (Kapton) film under identical conditions, that the erosion is very nonuniform, and that zirconium dioxide is the predominant product after extended exposure. This complex is currently being evaluated as a polymer additive. 相似文献
A conductance study of the interaction between cobalt, nickel, copper, zinc, cadmium, and lead ions with 1,10-diaza-18-crown-6 in different acetonitrile-dimethylsulfoxide mixtures has been carried out at various temperatures. The formation constants of the resulting 11 complexes were determined from the molar conductance-mole ratio data and found to vary in the order Zn2+2+2+2+2+2+. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. A linear relationship is observed between the log Kf of different complexes and mole fraction of acetonitrile in the solvent mixtures. The TS vs. H plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of an enthalpy-entropy compensation in the complexation reactions. 相似文献
The CLST/PTFE/5%GF composite sharply decreases the CTE in both X&Y and Z directions, obtained a promising microwave dielectric material for microwave communication. 相似文献
In vitro degradation of porous 50/50, 70/30 and 90/10 PLGA (poly(dl-lactide-co-glycolide)) foams and PLGA/bioactive glass (20 wt%) composite foams was studied up to 16 weeks in TRIS (pH 7.4; 37 °C). Polar PLGA/bioactive glass composite films were prepared by applying the bioactive glass (S53P4) on one side of the composite. Porous foams were made by solvent casting and pressure quenching with CO2. The fabricated foams had an initial pore size of 50-500 μm and thickness of 2-2.5 mm. In vitro degradation of the prepared foams was evaluated after 1, 2, 4, 6, 8, 12 and 16 weeks. Weight loss, water uptake, molecular mass and the amount of dissolved bioactive glass were measured after each time period. Changes in pore morphology were analysed with SEM. The present in vitro results will be evaluated and compared with the results from ongoing animal studies where comparable implants are used for bone defect treatment under non-load-bearing conditions. 相似文献
A number of 7 complexes of the [Co(DH)2(amine)2)]I type (DH2 stands for dimethyloxime) have been studied by means of thermogravimetry and differential scanning calorimetry in nitrogen atmosphere, by using heating rates of 2.5, 5 and 10 K min–1. In all cases an endothermal deamination reaction occurs leading to the relatively stable [Co(DH)2I(amine)] intermediate. For this reaction apparent kinetic parameters have been derived. The influence of heating rate is discussed. The validity of a linear and a non-linear kinetic compensation law was verified.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献