Search Results

You are looking at 1 - 10 of 17 items for

  • Author or Editor: L. Machado x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

The mathematical evaluation of the activation energy, E, of non-isothermal degradation reactions is usually made using the Ozawa/Flynn–Wall isoconversion principle and involves the numerical resolution of a set of integrals without closed form solution, which are solved by polynomial approximation or by numeric integration. In the present work, the isoconversion principle, originally described and maintained until now as an algebraic problem, was written as a set of ordinary differential equations (ODEs). The individual ODEs obtained are integrated by numeric methods and are used to estimate the activation energy of simulated examples. A least square error (LSE) objective function using the introduced ODEs was written to deal with multiple heating rate CaCO3 thermal decomposition TG experiments.

Restricted access

Abstract  

A method for the determination of lathanum, praseodymium, neodymium and samarium oxides in cerium dioxide has been developed. The sample in the oxalate form is mixed with the binding material (boric acid) in the ratio 1∶1 pressed to form a double layer pellet over a boric acid backing pellet and irradiated by X-rays from a tungsten tube. The secondary X-rays are dispersed with a LiF (200) crystal in a Philips PW 1220 semiautomatic X-ray fluorescence spectrometer. The intensity of fluorescent X-rays is measured by a flow proportional counter. The minimum determination limit is 0.01% for lanthanum and samarium oxides and 0.02% for praseodymium and neodymium oxides. The precision at each concentration of the standards and theoretical minimum determination limit for each element have been calculated.

Restricted access

Abstract  

A study on the trace elements transfer from tidal water to mangrove sediments from Guanabara Bay (southeastern Brazil) was performed in laboratory microcosms. Sediment cores were covered with tidal water spiked with 137Cs, 54Mn and 57Co during 5-h experiments, and water samples were taken at regular intervals to measure uptake kinetics at the sediment–water interface. At the end of the experiments, the uptake and diffusional penetration into the sediments was evaluated. Half-removal times from water to sediments were slightly higher for 137Cs (3.4 ± 1.7 h) than observed for 54Mn (2.3 ± 0.2 h) and 57Co (2.6 ± 1.1 h). After these experiments, all radioisotopes presented decreasing activities with increasing sediment depth, being the distribution of 137Cs indicative of higher diffusion within the upper 2 cm. This study on the removal of 137Cs, 54Mn and 57Co from tidal water by mangrove sediments suggests that while 57Co and 54Mn presented closer behaviors, there was a slightly higher mobility of 137Cs.

Restricted access

Abstract  

Radiation-curable coatings have acquired importance, because they are environmentally-friendly (no solvent emission)and require low energy for curing, when compared to other conventional heat-curable products. UV-curable coatings performance depends on the cure quality. Suitable methods were evaluated to estimate the degree of cure applying quantitative techniques, such as differential scanning calorimetry (DSC) and differential photocalorimetry (DPC), in order to determine the residual heat of curing in UV-cured films. The results of the DPC technique showed better sensibility than DSC technique, although the use of suitable pans for the case of clear coats must be considered.

Restricted access

Abstract  

Hydrogels, in general, can be used as a compliant surface in prosthesis of human synovial joints due to their biocompatible characteristics. In this work, different hydrogels were prepared from two aqueous solutions of PVAL (15 and 20 mass/mass%) by chemical reactions using citric acid as a cross-linking agent and by electron beam (EB) irradiation with doses from 25 to 100 kGy. The hydrogels were evaluated by their mechanical properties through indentation creep test, thermal properties by differential scanning calorimetry (DSC), and also equilibrium water content (EWC).

Restricted access

Abstract  

Radiation curing is an environmentally-friendly technology. Furthermore, radiation curing is a faster, energy saving and more efficient industrial process than the heat-curable process. One of the most important requirements for the widespread application of UV curable coatings in the coating industry is that they are stable vs. atmospheric degradation. Today's state of the art in oxidative drying and thermosetting coatings is the use of light stabilizers to protect polymers vs. the damage of outdoor exposure. Oxygen has a detrimental effect on the cure response of free radical systems, especially in thin-film coatings. Differential photocalorimetry (photo-DSC) was used to investigate the oxygen effect and the use of light stabilizers on UV curing of photocurable formulations based on acrylate materials. Coating thickness influence was also considered.

Restricted access

Abstract  

The thermal decomposition kinetics of the solid complexes Cd(S2 CNR2 )2 , where R =C2 H5 , n -C3 H7 , n -C4 H9 or iso -C4 H9 , was studied by using isothermal and non-isothermal thermogravimetry. The superimposed TG/DTG/DSC curves revealed that thermal decomposition reactions occur in the liquid phase. The kinetic model that best fitted the experimental isothermal TG data was the one-dimensional phase-boundary reaction-controlled process R1 . The thermal analysis data suggested the thermal stability sequence Cd(S2 CNBun 2 )2 >Cd(S2 CNPrn 2 )2 >Cd(S2 CNBui 2 )2 >Cd(S2 CNEt2 )2 , which accords with the sequence of stability of the apparent activation energies.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
D. Rosa
,
M. Bardi
,
L. Machado
,
D. Dias
,
L. Silva
, and
Y. Kodama

Abstract  

Plastics have been used in short-life products, which have presented harmful consequences for the nature, due to the low degradation rate reached by the most common polyolefins, such as the polypropylene. By this way, the incorporation of pro-oxidants has been shown nice results to the bio-assimilation of the common polymers. The aim of this study is to evaluate the mechanical and thermal properties of pure iPP, plasticized starch (TPS) with biodiesel glycerol (TPSBio) or commercial glycerol (TPSCom), and their blends (iPP/TPSPlas). TPS was plasticized in proportions of 80/20 (wt starch/wt glycerin). Blends of iPP/TPSPlas were obtained by extrusion in the following composition rates: 95/5, 90/10, 80/20, and 70/30 of modified PP/TPSPlas. Mechanical properties, calorimetric analysis, and thermogravimetric data were obtained, and biodegradation under simulated soil was performed. It can be verified that there were no meaningful variation induced by the incorporation of TPSPlas on the melting temperature on the blends, when compared to pure iPP. The addition of TPSPlas caused an increasing on the crystallinity of iPP, mainly for the compositions 90/10 and 80/20 of iPP/TPSPlas, probably due a morphological alteration such as crosslinking, which may have modified the molecular arrangement of the iPP macromolecules by the presence of glycerol, which was also indicated by mechanical evaluations.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
M. Evora
,
L. Machado
,
V. Lourenço
,
O. Gonçalez
,
H. Wiebeck
, and
L. de Andrade e Silva

Abstract  

The aim of this work is to study the ionizing radiation effects on thermal properties of there cycled polyamide-6. This polymer was irradiated with an electron beam of 1.5 MeV with different doses. The thermal properties of the samples were determined by TG, DSC and DMA measurements. It was observed that the irradiated samples of recycled polyamide-6undergo a crosslinking process.

Restricted access

Abstract

Magnetic thermogravimetric analysis (TGM) was used to investigate the influence of the milling time (t mill) in the Curie temperature (T C) of nanocrystalline powders and of a melt-spun amorphous ribbon with composition Fe56Co7Ni7Zr10B20. The TGM analysis was carried in a continuous flow of 99.99% pure argon from room temperature up to 1250 K. A magnetic field of 100 Oe was applied throughout the measurements. Nanopowders of Fe56Co7Ni7Zr10B20 were produced by mechanical alloying the samples in an argon atmosphere for milling times ranging from 1 to 100 h. The samples were characterized by X-ray diffraction and by scanning electron microscopy. The average particle size decreased from 45.4 nm for a powder milled for 1 h to 5 nm after being milled for 100 h. Moreover, T C (=1126.4 ± 4.4 K) was found to be nearly independent of t mill while for the melt-spun amorphous ribbon it was found to be substantially smaller (T C = 482 K). This is a clear indication that T C is quite sensitive to the degree of amorphosity present in the sample. The activation energy associated to the crystallization process was estimated from DSC data by using the Kissinger's method to be 193 kJ/mol.

Restricted access