1,721,083 research outputs found
Structural analysis of the solid amorphous binuclear complexes of iron(III) and aluminum(III) with chromium(III)-DTPA chelator using Energy Dispersive X-ray Diffraction
No full textPrepn. and structural data are presented for two amorphous binuclear complexes of Fe(III) and Al(III) with Cr(III)-diethylentriaminepentaacetic acid (Cr(III)-DTPA, CrL2-) using the energy-dispersive x-ray diffraction technique. Fe(OH)CrL(H2O)6 and Al(OH)CrL(H2O)6 are binuclear complexes with the metals ions bridged via O atoms. The metal ions are all octahedrally coordinated
Thermal-Analysis of Thione Compounds. 1. The Thermal-Behavior of Thiourea and N-Methylthioureas
No full textAbstract: The thermal behavior of thiourea (Tu), N-methylthiourea (MeTu), N, N'-dimethylthiourea (Me2Tu) and N, N, N', N'-tetramethylthiourea (Me4Tu) was investigated by means of conventional thermal analysis in O2 and N2 and IR spectroscopy of the residues on heating in air at various temperatures.
At ordinary pressure, the compounds are thermally stable up to the melting points. After melting, they show high vapor pressure, combustion in O2 atmosphere and isomerization to ammonium thiocyanate, with the exception of Me4Tu
Using thermoanalytical data: Part 6. Heat transfer contribution in TG/DTA/DSC data processing: non-isothermal kinetics — do they become “applied science” by exiting the “dichotomy”?
No full textAbstract
After a brief overview of the state of the art of kinetic study of solid state reactions, a new promising approach is described. Whilst details of such an approach have been previously reported, the model and its performances are presented here as an overall picture, including the evaluation of the heat transfer perturbations induced in both TG and DTA/DSC. A summary of the results obtained with CaC2O4·H2O is also reported, and a strategy is suggested, which should be used when facing the problem of such a kinetic evaluation or, in general, when processing data according to an assumed model
Multilayer feed-forward artificial neural networks for class-modeling
No full textA class-modeling algorithm based on multilayer feed-forward artificial neural networks is proposed. According to this method, each category model is described by an auto-associator network, so the class space is defined on the basis of a distance to the model criterion which takes into account the residual standard deviation of the reconstructed input vectors. The details of the method are discussed and examples of its application to a simulated ("exclusive-OR") and a real-world (classification of wines) problem are presented. As far as the simulated highly non-linear example is concerned, NN-based class modeling outperforms SIMCA and UNEQ both in terms of classification rate and specificity. On the other hand, when dealing with the wine data set, which has a less non-linear structure, our proposed method still provides comparable and, in some cases, better results than the other two techniques
Using thermoanalytical data. Part 2. The dependence of kinetic data available from thermogravimetry on sample and instrument parameters: a method for calculating ‘true’ kinetic parameters
No full textAbstract Kinetic data available from TG measurements are discussed with respect to thermal coefficients such as sample specific heat, reaction enthalpy, instrument heat-transfer coefficient and heat capacity. The dependence of the available kinetic parameters Z, E and N on these thermal coefficients is examined using a numerical model. A relationship is also derived for calculating the kinetic parameters from experimental TG curves whilst taking into account the perturbation induced by the above-cited thermal coefficients. The dehydration of calcium oxalate is used to evaluate experimentally the predictive power of the kinetic parameters obtained in this way, i.e. their ability to describe the sample behaviour under a wide range of operational conditions (different masses and heating rates), including isothermal reactions
DSC in the chemical analysis of drugs. Determination of diclofenac in pharmaceutical formulations
No full textDifferential scanning calorimetry was applied to the determination of diclofenac in three 'Voltaren' formulas. The pharmaceutical products (soluble tablets, suppositories and vials) were selected in order to show that calorimetric analysis is an easy technique to perform and can be competitive with other conventional methods.
In the tablets diclofenac (DH) was determined, without any pre-treatment, from the area of the endothermic peak which occurs at about 180%C in the DSC curve obtained in N-2 atmosphere. In the analysis of the suppositories and vials, nitrilotriacetic acid (NTA) was added to transform the diclofenac sodium salt (DS) into the thermally active form (DH). In both cases, it was necessary to eliminate the interference of excipient by cyclohexane extraction (suppositories) or by a multistep program for the DSC run (vials).
The accuracy of the results and the simplicity of the procedure justify the important role of DSC in the analysis of these drugs and certainly of several other commercial products
Thermal analysis of thione compounds II. The thermal behaviour of N-ethyl-thiourea,N,N'-diethylthiourea and N-beta-allyl-thiourea
No full textCHROMIUM(III) COMPLEXES WITH DIETHYLENTRIAMINEPENTAACETIC ACID
No full textAbstract Complex formation by chromium(III) with diethylentriaminepentaacetic acid (DTPA) has been studied by potentiometry and spectrophotometry. In equimolar solutions or with a ligand excess, complexation is practically complete at pH > 1 and protonation equilibria have been calculated. Molar absorbtivities of the different species have been evaluated. Equilibrium constants for complex formation have been calculated in 1 mol dm−3 (Na,H)ClO4 at 20°C
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