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Formação de grãos ferríticos ultrafinos através de transformação de fase induzida por deformação
(Universidade Federal de São Carlos, 2007-10-26) Ferracini Junior, Elcio Geraldo; Balancin, Oscar; https://lattes.cnpq.br/8379205949387493; https://lattes.cnpq.br/3886813925202748
One of the key points in steel development has been the refinement of the microstructure, however without change the chemical composition with addition of alloy elements. The refinement of the ferrite grain size leads simultaneously to an increase in strength and toughness. Ultrafine grains can be produced through thermomechanical controlled treatments, generated by dynamic strain-induced phase transformation (g®a), which also can be associated with others dynamic phenomena, such as dynamic recrystallization. In this work a low and a middle carbon steel were previously austenitized at 900ºC for 180 s and cooled at 1ºC/s to a given deformation temperature established in relation to their critical temperatures. The deformation were applied with a strain of 2,5 at a strain rate of 1 s-1. The behavior of the materials during the deformation was analyzed using the stress-strain curves obtained from torsion experiments. After deformation, the samples were air cooled and the final microstructure characterized by scanning electron microscopy. It was determined with success a route capable to produce ultrafine ferrite grains, where grain size of 1,6 μm were produced for the Cos Ar 60 steel and 1,3 μm for the SAE 1548 steel.
Desenvolvimento do sensor baseado em eletrólito sólido de β-alumina para monitoramento de enxofre na indústria siderúrgica
(Universidade Federal de São Carlos, 2007-10-26) Hasegawa, Haroldo Lhou; Morelli, Márcio Raymundo; https://lattes.cnpq.br/0172837599844991
Electrochemical sensors provide real time information of chemical compositions of molten metal. They can be used to improve the control of various metallurgical processes. One of the most successful and widely used electrochemical sensors is the oxygen sensor, based on zircônia solid electrolyte, usually used in steel making. Sensors are being developed for measurement of other chemical elements, but it is very costly and complicated to be produced. In order to solve this problem, in this work synthesis and assembly of β-alumina and β-alumina based on solid electrolyte sensors were studied. For this, the phase of interest was prepared by the mixing of oxides, and characterized. Traditional ceramic forming processes, isostatic and slip casting, were used to produce the prototypes and their ceramic characteristics were evaluated. Both compositions did not present high density after sintering at 1600°C, reaching 90% theoretical density. This fact could be responsible for the break down during the application of the sensors. The Na-β- alumina sensor produced did not present a satisfactory performance for measuring the dissolved sulphur in liquid pig iron. On the other hand, the β-alumina sensor, despite of the secondary phase, showed good behavior in terms of response time (between 5 and 8 seconds) for measuring the dissolved sulphur in liquid pig iron at temperatures from 1440°C to 1460°C, with La2O2SO4 auxiliary electrode and three different reference electrodes. The signal response of EMF between 54 mV and 174 mV was measured in a measuring level from 32 ppm (weight) to 432 ppm (weight) of sulphur dissolved on the metal bath
Desenvolvimento de banhos alcalinos para eletrodeposição de Pb-Sn e Pb-Cu, na presença de aditivo orgânico. Caracterização do processo de eletrodeposição e dos filmes
(Universidade Federal de São Carlos, 2007-10-26) Siqueira, Joana Luiza Pires; Carlos, Ivani Aparecida; https://lattes.cnpq.br/1666217445807782; https://lattes.cnpq.br/4650162959340860
Alkaline baths containing sorbitol, tartrate or EDTA were developed in this work for Pb-Sn and Pb-Cu electrodeposition on platinum substrate. The characterization of Pb-Sn and Pb-Cu plating baths by potentiometric titration showed the pH when the species of metallic ions were soluble and stable. The voltammetric curves obtained from these baths indicated that the complexation of metallic ions by sorbitol, tartrate or EDTA, had a beneficial effect, since closed the deposition potential these metallic ions, leading to codeposition of Pb-Sn and Pb-Cu. The analysis of the Pb-Sn and Pb-Cu deposits by x-ray dispersive spectroscopy showed that codeposition of Pb-Sn or Pb-Cu occurred. The codeposition type of Pb-Sn was normal irrespective the additive in the plating bath; the coloration of the films was bright gray and the morphology was formed of refined crystallites. For Pb-Cu alloy the codeposition type was anomalous to the deposits obtained from baths containing sorbitol or tartrate and normal in the presence EDTA. The Pb-Cu deposits obtained in the presence of sorbitol, EDTA or tartrate showed black coloration; or coloration varying of brown to redish or golden to dark redish, respectively. X ray diffraction spectroscopy of the Pb-Sn and Pb-Cu codeposits indicated that these were to constitute a mixture of compounds.
Análise química de materiais cerâmicos : digestão por fusão e medidas por ICP OES com configuração axial
(Universidade Federal de São Carlos, 2007-10-26) Matias, Telma Blanco; Nóbrega, Joaquim de Araújo; https://lattes.cnpq.br/8833989058164529; https://lattes.cnpq.br/4705647158043150
Ceramic samples are efficiently digested using fusion procedures. However the elevated amounts of dissolved solids in the resulting solutions may cause spectral and transport interferences, affect the analytical blanks and background signals and consequently the limits of detection. These effects can be even worst when measurements are performed using ICP OES with axial view configuration. Therefore, the goal of this thesis was an evaluation of the feasibility of application of an ICP OES with axial view configuration for determination of analytes in complex inorganic samples digested by fusion. The proposal was based on the suitability of fusion procedures for fusion of refractory samples and, on the other hand, the susceptibility of the axial configuration to spectral interferences and effects caused by high concentrations of dissolved solids. The study was carried out using standard reference materials of bauxite, refractory, silicon carbide and glass that were fused using Na+ and Li+ fluxes. All analytes were determined using selected ionic and atomic emissions lines in solutions containing 0.1, 1.1 and 2.2 % m/v of dissolved solids. The instrument was calibrated using analytical solutions prepared in acid or in the reagents media. The ICP OES parameters were optimized in order to obtain robust and non robust conditions according to the Mg II / Mg I ratio. The limits of detection, dynamic linear range, and sensitivity were established. Despite the complexity of the samples, suitable results were obtained for all of them. The most critical aspect was related to the quartz torch lifetime and it was not possible to introduce solutions containing 2.2. m/v of dissolved solids. The deposition of solids in the quartz torch was minimized by increasing the flow-rate of the auxiliary gas to 2.25 L min-1. Severe matrix effects were not observed in robust and non robust operating conditions (recoveries were around 100 + 20 % for minor elements and 100 ± 10 % for major elements). Finally, this research led to the establishment of analytical procedures for each sample material. The best experimental conditions were those that allowed the determination of most analytes in the same sample solution taking into account the multielement capacity of the ICP OES.
Caracterização eletroquímica de eletrodos de diamante dopado com boro em função de seu pré-tratamento
(Universidade Federal de São Carlos, 2007-10-26) Carvalho, Adriana Evaristo de; Rocha Filho, Romeu Cardozo; https://lattes.cnpq.br/5200717413563550; https://lattes.cnpq.br/6039969237116219
The effect of galvanostatic electrochemical pre-treatments on the surface composition and wettability of boron-doped diamond (BDD) electrodes was characterized by X-ray photoelectron spectroscopy (XPS) analyses and contact angle measurements, respectively. The smallest wettability was presented by the least doped as-received BDD electrode; however, the wettability of all the BDD electrodes increased after the cathodic and anodic pre-treatments. From the XPS analyses, an increase in the surface O/C ratio after the anodic pre-treatment was observed, which was attributed to the introduction of carbon-oxygen functionalities on the surface of the BDD electrodes. The effects of the current and charge densities applied on the BDD electrodes, during the cathodic and anodic pre-treatments, were evaluated through the redox reactions of the Fe(CN)6 3-/4- couple by cyclic voltammetry and by electrochemical impedance spectroscopy. The high sensitivity of the electrochemical and electrical properties of this redox couple to the surface terminations of the BDD electrodes was confirmed; the redox reaction kinetics are much faster after cathodic pre-treatments. The electrical properties presented by the BDD electrodes after anodic pre-treatmens, characterized by a resistive response in intermediate frequencies, have been explained as due to a possible partial blocking of the surface, which would be associated to the presence of carbon-oxygen functionalities on the electrodes surface. On the other hand, the electrochemical and electrical properties were shown to be controllably modulated through the galvanostatic electrochemical pretreatments. Studies on these properties were also carried out for the Fe3+/2+ and Ru(NH3)6 3+/2+ redox couples. For the former, contrary to that for the xxiv Fe(CN)6 3-/4- couple, the charge transfer kinetics (slow) become faster after anodic pre-treatments, instead of after cathodic pre-treatments. In the case of the Ru(NH3)6 3+/2+ redox couple, the electrochemical behavior is independent of the electrode surface state, the same being true for the electrical properties, whose use to evaluate the quality of BDD electrodes is proposed. Finally, studies on the ferrocenecarboxylic acid redox species in non-aqueous medium (acetonitrile), in the absence and after additions of water (or glycerol), were carried out in order to investigate the nature of the surface partial blocking of anodically pre-treated electrodes, in the presence of redox couples such as Fe(CN)6 3-/4- or ferrocene. The obtained results indicate that such partial blocking is due to the adsorption of water molecules, by hydrogen bonding with the carbon-oxygen functionalities. This partially prevents the access of the redox reaction to electrochemically active sites, thus explaining why much smaller charge transfer reaction rates are attained when anodically pre-treated electrodes are used.