Multivariate curve resolution analysis applied to time-resolved synchrotron X-ray Absorption Spectroscopy monitoring of the activation of copper alumina catalyst

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Evaluation of the electrochemical behavior of carbon paste electrode (CPE) with chalcopyrite (CuFeS2) in the presence of ferrous ions

In this work we present an electrochemical study using carbon paste electrode (CPE) with CuFeS2 in solutions with different concentrations of Fe2+ ions in order to evaluate the possible interaction between these ions and mineral sulfide in the absence and presence of the bacteria Acidithiobacillus ferroxidans.

Textured macro- and mesoporous alumina samples designed in the presence of different surfactant types

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A new and practical carbon paste electrode for insoluble and ground samples

This work presents a new and simple electrode, which may be used to achieve the electrochemical response of ground solids or insoluble samples. Ore samples from Morro Velho Mine (Brazil) were employed to exemplify the use of such electrodes. The new electrode avoids the use of binders or other agents overcoming major deterioration problems. (C) 2002 Published by Elsevier Science B.V.

Caracterização geológica do perfil laterítico no município de Rondon do Pará, bloco sul do projeto Alumina Rondon

This completion of course work has as its object of study the Bauxite Province of Paragominas regarded as the richest Amazon bauxite province and whose genesis is related to laterization processes responsible for the formation of mineral deposits of the Rondon Alumina Project, designed to assess areas in the southeast of Pará State, for mineral resources exploration of bauxite, which is the main source of aluminum in the country. Located in the region of Rondon do Pará - PA, the study area is geologically inserted in Lithostratigraphic Unit called Cobertura Laterítica Matura (Mature Lateritic Cover), formed by alteration of paleotropics Cretaceous siliciclastic rocks, and its geomorphology corresponds to a broad plateau with displays of representative profiles of the processes that acted in the region. In this context, the present research aims to characterize the geological evolution of the laterite profile, with detailed studies in the area, geological description of the formations from the bauxite surfaces, and mineralogical composition litochemical of different horizons that were correlated and deployed in an evolutionary model compatible with its traits. The data collected during the analysis subsidized metalogenetic understanding of the processes that acted in the enrichment of aluminum and iron as well as the redistribution of the latter modified profile. The results and information were embodied in the form of geological characterization of the different constituents of mineral associations of bauxite horizons, similarities or differences in both textural and structural aspects, in order to propose a evolutionary model with retaken of gibbsitization processes

Estudo do comportamento térmico e reológico de amidos na conformação cerâmica de compostos multicamada com alumina, titanato de alumínio e dióxido de titânio

The project aims to develop ceramic compounds with gradients of the mechanical properties, using the molding technique with commercial starches. To understand the process of interaction between starch and ceramic powders, the proposed methodology involves viscometry tests (up to 200 °C). Viscometric assays were carried out with slurries of alumina, titania and aluminum titanate with potato starch, cassava and corn. The specimens were tested for dilatometry, thermomechanical, thermal shock, mechanical and characterization by SEM. The ceramic powders and starches were analyzed using the optical microscope to measure the size of these. It was made of th kinetics of starch gelatinization and titania with the cornstarch in theoptical microscope to observe how the grains of starch behaved in welling

Oxide surface modification: Synthesis and characterization of zirconia-coated alumina

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Bonding ability of paste-paste glass ionomer systems to tooth structure: in vitro studies

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise do acabamento superficial e força de corte no torneamento de alumina a verde

In experimental conditions, cutting forces were studied during turning of green alumina billets, including their correlation with surface aspects of the workpiece. The correlation between cutting power and the removal rate are important parameters for defining the design of ceramic products, since inadequate parameters can produce excessive surface damage to the workpiece. This study examined the forces obtained during turning of alumina workpieces with 99.8% purity in their green state, by means of a three-point dynamometer, evaluating the cutting, feed and depth forces, using a cermet tool under constant machining conditions. Variables were compared with the forces, including surface finish, tool wear and temperature during machining. In the study, it was found that the depth of cut had no significant effect on the surface quality, and the cutting speed and feed influencing the finish. However, preliminary tests for selecting the cutting conditions showed that unsuitables cutting speeds and feeds generate severe damage to the workpiece surface. The best condition was 1.00 mm depth of cut, and the forces increasedfor with each pass performed, with the feed force the variable with greatest increases in relation to the cutting and depth forces, and wear of the cutting tool directly influenced the surface finish, generated by the highly abrasive nature of the alumina particles of the green compact. It is emphasized that the alumina in its green state showed high abrasive effect on the cutting tool during the turning process and the surface finishing of the green workpiece had a direct influence on the sintered workpiece.

Surface analysis of alumina ceramic exposed to shock waves produced by plasma expander

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Correlation between structural and catalytic properties of copper supported on porous alumina for the ethanol dehydrogenation reaction

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Innovative low temperature plasma approach for deposition of alumina films

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of home-bleaching gels modified by calcium and/or fluoride and the application of nano-hydroxyapatite paste on in vitro enamel erosion susceptibility

This in vitro study compared the effect of bleaching agents modified by the addition of calcium and/or fluoride and the application of a nano-hydroxyapatite paste after bleaching, on the susceptibility of enamel to erosion. Bovine enamel cylindrical samples (3 mm diameter) were assigned to six groups (n = 20 specimens/group) according to the bleaching agent: no bleaching (C-control), 7.5% hydrogen peroxide gel (HP), HP with 0.5% calcium gluconate (HP+Ca), HP with 0.2% sodium fluoride (HP+F), HP with calcium and fluoride (HP+Ca+F) and HP followed by the application of a nano-hydroxyapatite agent (HP+NanoP). The gels were applied on the enamel surface (1 h) followed by cyclic erosive challenges (Sprite Zero®-2 min), for 14 days. The paste was applied after bleaching for 5 min (HP+NanoP). The enamel surface alteration was measured by contact profilometry (µm) (after 7 and 14 days). C-control (mean ± SD: 2.29 ± 0.37 at 7 days/4.86 ± 0.72 at 14 days) showed significantly lower loss compared to the experimental groups. HP+Ca (3.34 ± 0.37/6.75 ± 1.09) and HP+F (4.49 ± 0.92/7.61 ± 0.90) presented significantly lower enamel loss than HP (4.18 ± 0.50/10.30 ± 1.58) only for 14 days and HP+Ca+F (4.92 ± 1.03/8.12 ± 1.52) showed values similar to the HP+F group. The HP+NanoP (5.51 ± 1.04/9.61 ± 1.21) resulted in enamel loss similar to the HP after 14 days. It was found that 7.5% hydrogen peroxide increased the susceptibility of enamel to erosion. The addition of calcium or fluoride to the bleaching gel reduced the erosion effect, while the nano-hydroxyapatite agent did not provide any protective effect.

Preparation of a clay-modified carbon paste electrode based on 2-thiazoline-2-thiol-hexadecylammonium sorption for the sensitive determination of mercury

A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg 2+, Pb 2+, Cd 2+, Cu 2+, and Zn 2+ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0.25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO 3 vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 μg L -1. The precision of determination was satisfactory for the respective concentration level. 2005 © The Japan Society for Analytical Chemistry.