Search Results

You are looking at 1 - 10 of 52 items for

  • Author or Editor: J. Matos x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

Evidence for the cathodic deposition of222Rn was given in experiments involving the electrodeposition of226Ra and its daughters from an ethanolic solution slightly acidified with hydrogen fluoride. The presence of silicate ions was found to be essential for the radon deposition to take place.

Restricted access

Abstract  

Some synergistic effects of antioxidants in natural rubber were investigated considering results obtained by differencial scanning calorimetry (DSC). Rubber formulations were obtained with mixtures of diaminic(DPPD, IPPD, HPPD) and monoaminic (ADPA, PBN) stabilizers and evaluated. The samples containing the mixture diamine/ADPA stabilizers showed synergistic effects while, for those containing diamine/PBN, no effect was observed. Additionally, the diffusion constants determined by use of vulcanized rubber disks confirmed the molar mass dependence of the stabilizer.

Restricted access

Abstract  

Differential Scanning Calorimetry (DSC), thermogravimetry/derivative thermogravimetry (TG/DTG) and infrared spectroscopy (IR) techniques were used to investigate the compatibility between prednicarbate and several excipients commonly used in semi solid pharmaceutical form. The thermoanalytical studies of 1:1 (m/m) drug/excipient physical mixtures showed that the beginning of the first thermal decomposition stage of the prednicarbate (T onset value) was decreased in the presence of stearyl alcohol and glyceryl stearate compared to the drug alone. For the binary mixture of drug/sodium pirrolidone carboxilate the first thermal decomposition stage was not changed, however the DTG peak temperature (T peak DTG) decreased. The comparison of the IR spectra of the drug, the physical mixtures and of the thermally treated samples confirmed the thermal decomposition of prednicarbate. By the comparison of the thermal profiles of 1:1 prednicarbate:excipients mixtures (methylparaben, propylparaben, carbomer 940, acrylate crosspolymer, lactic acid, light liquid paraffin, isopropyl palmitate, myristyl lactate and cetyl alcohol) no interaction was observed.

Restricted access

Abstract  

This paper demonstrates the application of thermal analysis in compatibility and stability studies between an ACE inhibitor (enalapril maleate) and excipients. The results have helped to elucidate the reason of a stability problem observed during the storage of enalapril maleate tablets. Incompatibility between enalapril maleate and colloidal silicon dioxide was detected. Besides, it was confirmed that the reaction between enalapril maleate and NaHCO3 increases the thermal stability of the drug. This study supports the importance of using thermoanalytical methods in the development of pharmaceuticals.

Restricted access

Abstract  

The synthesis and characterization of lanthanide(III) citrates with stoichiometries 1:1 and 2:3; [LnL·xH2O] and [Ln2(LH)3·2H2O], Ln=La, Ce, Pr, Nd, Sm and Eu are reported. L stands for (C6O7H5)3− and LH for (C6O7H6)2−. Infrared absorption spectra of both series evidence coordination of carboxylate groups through symmetric bridges or chelation. X-ray powder patterns show the amorphous character of [LnL·xH2O]. The compounds [Ln2LH3·2H2O] are crystalline and isomorphous. Emission spectra of Eu compounds suggest C 2v symmetry for the coordination polyhedron of [LnL·xH2O] and C 4v for [Ln2(LH)3·2H2O]. Thermal analyses (TG-DTG-DTA) were carried out for both series. The thermal analysis patterns of the two series are quite different and both fit in a 4-step model of thermal decomposition, with lanthanide oxides as final products.

Restricted access

Abstract  

The title polymer was obtained electrochemically by the reduction of 4,4'-bis(dibromomethyl)-2,2'-dimethoxybiphenyl under very smooth conditions. The DSC and TG/DTG curves registered at four different heating rates showed that the polymer is stable in air up to 150C, where smooth degradation starts. Above 300C, decomposition is fast and exothermic (ΔH= –323 J g–1) . The activation energy (1164 kJ mol–1 ) was determined by Ozawa's method.

Restricted access

Excess molar enthalpies of dichloropropane + n-alkane mixtures

Study on the effect of increasing the chain length of the n-alkane and the influence of the chlorine position

Journal of Thermal Analysis and Calorimetry
Authors: M. Mato, J. Fernández, J. Legido, and M. Paz Andrade

Abstract  

We have determined the excess molar enthalpies
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$H_{\text{m}}^{\text{E}}$$ \end{document}
at 298.15 K and normal atmospheric pressure for the binary mixtures containing dichloropropane and n-alkane [{xCH2ClCHClCH3 + (1−x) CnH2n+2 (n = 6, 8, 10, 12)} and {xCH2ClCH2CH2Cl + (1−x) CnH2n+2 (n = 8, 10)}] using a Calvet microcalorimeter. The
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$H_{\text{m}}^{\text{E}}$$ \end{document}
values for all the mixtures show endothermic behaviour for the whole composition range. The Redlich–Kister equation was used to correlated the experimental values. The experimental excess molar enthalpies were examined on basis of the DISQUAC group-contribution model and the UNIFAC group-contribution method using the version considered by Larsen et al. The experimental and calculated results are discussed in terms of molecular interactions and the proximity effect.
Restricted access

Abstract  

Lanthanide picrates with 1,3-dithiane-1,3-dioxide ligand were synthesized and characterized. Thermal decomposition of these compounds by TG/DTG and DSC and structural studies were performed. It was found that the compounds are comprised in a single isomorphous series and their thermal decomposition occurs as exothermic events. The final products were found to be lanthanide dioxysulfates.

Restricted access

Abstract  

A porous nickel–8 mol% yttria stabilized zirconia (Ni–8YSZ) composite, used as anode for solid oxide fuel cell, was obtained by reduction of NiO–8YSZ cermet. The first goal was the evaluation of the temperature effect of powder processing by thermogravimetry. In addition, the influence of porosity in the reduction kinetic of the sample sintered at 1450 °C was evaluated. The final porosity produced in NiO–8YSZ composite by pore former was 30.4 and 37.9 vol.%, respectively, for 10 and 15 mass% of corn starch. The sample with 15 mass% of corn starch promotes a reduction rate almost twice higher than sample with 10 mass% of corn starch. The porosity introduced by the reduction of NiO was 23 vol.%.

Restricted access

Abstract  

Osmotically controlled and oral drug delivery systems utilize osmotic pressure for controlled delivery of active agent(s). Drug delivery from these systems, to a large extent, is independent of the physiological factors of the gastrointestinal tract and these systems can be utilized for systemic as well as targeted delivery of drugs. We apply the thermal methods and IR spectroscopy to study compatibility between atenolol and several excipients usually found in the osmotic systems formulations (Polyethylene oxide, MW 3350, 100000, 200000 and 5000000; HPMC K4000, magnesium stearate and cellulose acetate. Cellulose acetate, HPMC K4000 and magnesium stearate have essentially no interaction with atenolol otherwise all Polyethylene oxide excipients modifies significantly the drug melting point indicating some extend of interaction.

Restricted access