Search Results

You are looking at 1 - 10 of 20 items for

  • Author or Editor: M. de Oliveira x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

After more than ten years working with multicomparator instrumental neutron activation analysis, mainly applied to the characterization of environmental samples, the Radioisotopes Laboratory (CENA/USP) started changing gradually to the k 0-method in 1997. The main activities developed, as well as some of the results obtained, are presented here. Even though there is much more work to be done, the good quality of the results and the possibility of elemental determinations without the co-irradiation of standards may lead to the definitive adoption of the k 0-method in a near future.

Restricted access

Abstract  

Polyurethane composites with bagasse of sugar cane (BSC) at different proportions: 5, 10 and 20 mass/mass% were prepared by melt mixing method. The thermal behavior of these composites were studied by thermogravimetry (TG/DTG). The influence of fiber concentration on the kinetic parameters of the composites was studied and a better interaction was suggested between PU/BSC with 5mass/mass% of fiber. Scanning electron microscopy was carried out to investigate surface morphology.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Daniela Schlemmer, E. de Oliveira, and M. Araújo Sales

Abstract  

Conventional plastics has a large impact in increasing the environment’s pollution. That’s why the interest has turned towards novel partially and completely biodegradable polymers. In this work, blends of polystyrene and thermoplastic starch with glycerol and Buriti (Mauritia flexuosa L.) oil as plasticizers were prepared. Samples were analyzed using TG/DTG and DSC techniques. The TG results indicated that the blends with Buriti oil are thermally more stable than those with glycerol. The DSC analysis that Buriti oil provides a higher degree of plasticization of PS, compared to the blends plasticized using glycerol under the studied conditions.

Restricted access
Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: L. Pirani, L. De Oliveira, P. Petchevist, M. Moreira, D. Ila, and A. De Almeida

Abstract  

Dosimetric gel is used in several measurements due to its linearity, low cost, and possibility for 3D measurements. This work brings a new possibility to apply the Fricke Xylenol Gel recipe in the diagnostic measurements region. The Fricke Xilenol Gel (FXG) dosimeter is associated with the Fe(II) to Fe(III) oxidation, when irradiated, being the final ion concentration proportional to the absorbed dose. To achieve the scope, the former dosimeter was modified through the benzoic acid addition in the original recipe forming a new dosimeter, the Benzoic Xylenol Gel (BFXG). The results obtained with this new dosimeter demonstrated a higher sensibility for low absorbed dose values, bringing down the absorbed dose inferior limit from 0.1 to 0.006 Gy, that is more adequate for radiodiagnostic absorbed dose measurements. This result shows the possibly of BFXG dosimeter to be used for measurements in the radiodiagnostic region, as for tomography and mammography techniques.

Restricted access

Hydrolytic parameters were tested to prepare casein hydrolysates with high oligopeptide content for dietetic purpose, using papain. Employing a temperature of 37 °C and an E:S ratio of 2% was the most economical condition for large-scale manufacture. The encapsulation in liposomes was used for masking the bitterness, and was also able to reduce the hydrophobicity as well as to keep the chemical stability during 60 days of storage. The UV spectrometry with second derivative transformation was used to measure the encapsulation rate, which changed from 56% to 62%. The size distribution of vesicles was in the range of 500 to 1000 nm.

Restricted access

Abstract  

This study presents preliminary results on mercury distribution, released by gold mining activities, in soils from Vila Nova River region, an area located in Serra do Navio, Amapá, in the Brazilian Amazon. The soil samples were separated in two grain sizes, sand (between 2 and 0.063 mm) and silt+clay (<63 μm), and have been analysed by radiochemical neutron activation analysis. The precision and accuracy of the method were verified by means of the reference material analysis GXR-5 (USGS).

Restricted access
Reaction Kinetics, Mechanisms and Catalysis
Authors: Cleanio L. Lima, Hélvio S. A. de Sousa, Santiago J. S. Vasconcelos, Josué M. Filho, Alcemira C. Oliveira, Francisco F. de Sousa, and Alcineia C. Oliveira

Abstract

Sulfated molecular sieves were synthesized and characterized by XRD, FTIR, chemical analyses, acidity measurements and N2 adsorption–desorption isotherms. Sulfatation led to structural changes in the solid framework by increasing the acidity and accessibility of the acid sites. Br⊘nsted and Lewis acid sites of mild to high strength improved the conversion of alcohols, but the selectivity was modest over sulfated FAU type Y, ZSM-5 and γ-Al2O3 solids at temperatures lower than 200 °C. The characteristics of the sulfated AlSBA-15 molecular sieve in terms of acidity, textural properties and accessibility possibly make this solid useful for catalytic reactions involving bulky organic compounds.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Freitas, M. Reis, A. Marques, S. Almeida, M. Farinha, O. de Oliveira, M. Ventura, A. Pacheco, and L. Barros

Abstract  

Examples of the application of k 0 standardized instrumental neutron activation analysis (k 0 -INAA) to aerosols and biological monitors in the last 10 years at Instituto Tecnológico e Nuclear (ITN) are given. As an analytical technique, INAA, in association with the k 0 method was applied to these materials in four different projects, aiming at monitoring concentrations of heavy metals and others elements in the atmosphere in the Portuguese territory. In these studies we analysed the lichen Parmelia sulcata Taylor and olive tree bark as monitors as well as aerosol samples. For each project some representative results are presented, followed by a discussion of the application of this technique to environmental studies.

Restricted access