Chromium at concentrations of parts per billion in water, may be determined by activation analysis using an instrumental method
preceded by concentration on anion exchange resins. Blank runs, using deionized water, are carried through the steps of preconcentration.
The blank-resin and sample-resin are irradiated together with thermal neutrons, and the gamma spectrum of each is stored in
half of the memory unit of a multichannel analyzer. Subtraction of the blank-resin spectrum from the sample-resin spectrum
gives the51Cr peak free from interfering activities.
The determination of arsenic by activation analysis in germanium may be disturbed by arsenic isotopes formed in the irradiation
of the germanium matrix itself. The isotopic dilution technique will eliminate such interferences, but it requires weighing
of very small masses of arsenic, after appropriate chemical separation. This weighing procedure can be avoided if the mass
of the recovered arsenic is determined by activation analysis. In order to apply such a procedure, a known amount of arsenic
labelled with76As, whose specific activity is also known, is added to the germanium sample to be analysed. The sample is processed, the arsenic
separated, and the chemical yield established. The recovered mass of arsenic is then determined by activation analysis applying
the classical isotopic dilution analysis formula. The accuracy precision and linearity of the method are discussed.
In this paper it is presented a case of falsification of whisky in which empty bottles of genuine spirit were re-used as containment
for low price whisky. Activation analysis was made of bottle-caps (a lead and tin alloy) of counterfeited bottles and of genuine
imported ones as well as of a stock of bottle-caps found at the place where the material was apprehended. Results for trace
and main elements indicated common origin for the bottle-caps in the counterfeited bottles and the ones found at the place
where the material was apprehended and different origin for the bottle-caps in the imported bottles, indicating re-use of
the imported bottles.
Porous ceramic materials based on calcium phosphate compounds (CFC) have been studied and developed for several biomedical
applications such as implants, controlled drug delivery, and radioactive sources for brachytherapy. Two kinds of hydroxyapatite
(HAp) powders and their ceramic bodies were characterized. In this study, non-radioactive iodine was incorporated in two types
of biodegradable hydroxyapatite-based porous matrices (HA and HACL). The results reveal that both systems present a high capacity
of incorporating iodine. The quantity of incorporated iodine was measured by neutron activation analysis (NAA). The porous
ceramic matrices based on hydroxyapatite demonstrated a great potential for uses in low dose rate (LDR) brachytherapy.
Authors:J. Dweck, P. Ferreira da Silva1, R. Silva Aderne, P. Büchler, and F. Cartledge
This paper presents a method to study cement hydration at ambient temperatures by using a micro processed non-conventional
differential thermal analysis (DTA) system, which was used to evaluate the solidification/stabilization process of tannery
wastes produced in the leather industry. The DTA curves of pastes composed by slag cement, Wyoming bentonite and waste are
obtained in real time and used to analyze the heat effects of the reactions during the first 24 h of hydration. By applying
a deconvolution method to separate the overlapped DTA peaks, the energy released in the several hydration stages may be estimated
and consequently, the effects of each component on the solidification process. The highest separated DTA peak occurs during
the several early stages of cement hydration and is due mainly to tricalcium silicate hydration. Very good correlation shows
that the greater is the waste content in the paste composition, the higher is its effect on the rates of reactions occurring
during the induction (dormant) period of cement hydration. The presence of bentonite used as a solidification additive in
the stabilization process has a similar but less dramatic effect on the dormant period.
Authors:S. Silva, M. Conceiçăo, A. Souza, S. Prasad, M. Silva, V. Fernandes, A. Araújo, and F. Sinfrônio
The powder and the bran of algaroba pods, submitted to drying temperatures of 55, 65, 75, 85, 95 and 105C, were studied by
conventional and thermogravimetric methods. The dynamic thermogravimetric curves of the samples indicated the following thermal
stability order: 105>55>65>95>85>75C. The powder and the bran of algaroba pods, dried at 55C, presented protein content
higher and isothermal thermogravimetric profiles comparable. The calorimetric curves of samples, dried at 55C, indicated
the gelatinization of starch.
Authors:Marta Conceição, V. Fernandes Jr, A. Bezerra, M. Silva, Iêda Santos, F. Silva, and A. Souza
Diesel oil has an important role in the field
of urban traffic as well as in the transportation of products. However, the
amount of the non-renewable sources is continuously decreasing. This fact
and the environmental requirements brought the necessity to search for other,
renewable sources. This paper aimed the dynamic kinetic calculation of thermal
decomposition of castor oil, methanol biodiesel and ethanol biodiesel using
Coats–Redfern, Madhusudanan and Ozawa methods. On the base of the thermogravimetric
curves the following thermal stability order could be established: castor
oil>ethanol biodiesel>methanol biodiesel. Kinetic data presented coherent
results. Methanol biodiesel presented lower activation energy than ethanol
biodiesel, suggesting that methanol biodiesel has a better quality for combustion.
Authors:C. Bertol, A. Cruz, H. Stulzer, F. Murakami, and M. Silva
Primaquine (PQ) is the drug of choice for the radical cure of Plasmodium vivax malaria, and currently being administered in solid dosage form. In this study, the compatibility studies were carried out
using differential scanning calorimetry (DSC), thermogravimetry (TG), and fourier transformed infrared (FT-IR). Non-isothermal
and isothermal methods were employed to investigate kinetic parameters under nitrogen and air atmospheres using TG. The DSC
investigations obtained by physical mixtures showed slight alterations in the melting temperatures of PQ with some excipients.
The FT-IR confirmed the possible interactions obtained by DSC for the physical mixtures with PQ and lactose, magnesium stearate
and mannitol. The results showed that the thermal decomposition followed a zero order kinetic in both atmospheres in non-isothermal
method. The activation energy in both methods using nitrogen atmosphere was similar, and in air atmosphere the activation
Authors:M. D. Fonseca, F. T. Silva, and T. Ogasawara
Feldspathic glass–ceramics reinforced with leucite are usually used in dental prosthesis. This study focused on leucite crystallization kinetics due to its importance to the end product of a dental crown processing. Leucite grains were nucleated and grown from feldspathic glass frit powders with particle size smaller than 45 μm. The nucleation and crystallization kinetics of leucite crystals in the glass matrix was investigated under isothermal and non-isothermal conditions through differential thermal analysis. The samples were also characterized by X-ray diffraction and scanning electron microscopy. The temperature of maximum nucleation rate was determined from the DTA curves of samples heat treated at different temperatures. The activation energy (E) of leucite crystallization was determined by the Kissinger method and the Avrami parameter (n) indicated that surface crystallization is the dominant mechanism in the glass.
Authors:P. Oliveira, L. Bernardi, F. Murakami, C. Mendes, and M. Silva
Norfloxacin (NFX) is a synthetic antibacterial drug. The development of extended release tablets improves the patients’ comfort
and compliance, resulting in lower discontinuation of the therapy; with consequently decrease in bacterial resistance. In
the present work, the thermal behavior of NFX was investigated using TG and DSC techniques. Isothermal and non-isothermal
methods were employed to determine kinetic data of decomposition process. Compatibility studies between NFX and pharmaceutical
excipients, including three hydrophilic polymers were carried out in order to develop a new formulation of NFX to obtain extended
release tablets with an approved quality.